Allow multiple projects per issue and pull requests (#36784)

Add ability to add and remove multiple projects per issue
and pull request.

Resolve #12974

---------

Signed-off-by: Icy Avocado <avocado@ovacoda.com>
Co-authored-by: Tyrone Yeh <siryeh@gmail.com>
Co-authored-by: copilot-swe-agent[bot] <198982749+Copilot@users.noreply.github.com>
Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>
Co-authored-by: OpenCode (gpt-5.2-codex) <opencode@openai.com>
Co-authored-by: wxiaoguang <wxiaoguang@gmail.com>
Co-authored-by: silverwind <me@silverwind.io>
Co-authored-by: Claude (Opus 4.7) <noreply@anthropic.com>

.gitignore

@@ -65,6 +65,7 @@ cpu.out
 /indexers
 /log
 /public/assets/img/avatar
+/tests/e2e-output
 /tests/integration/gitea-integration-*
 /tests/integration/indexers-*
 /tests/*.ini

Makefile

@@ -478,7 +478,7 @@ playwright: deps-frontend
 	@pnpm exec playwright install $(if $(GITHUB_ACTIONS),,--with-deps) chromium firefox $(PLAYWRIGHT_FLAGS)
 
 .PHONY: test-e2e
-test-e2e: playwright backend
+test-e2e: playwright frontend backend
 	@EXECUTABLE=$(EXECUTABLE) ./tools/test-e2e.sh $(GITEA_TEST_E2E_FLAGS)
 
 .PHONY: build

models/issues/issue.go

@@ -59,17 +59,18 @@ type Issue struct {
 	PosterID          int64                  `xorm:"INDEX"`
 	Poster            *user_model.User       `xorm:"-"`
 	OriginalAuthor    string
-	OriginalAuthorID  int64                  `xorm:"index"`
-	Title             string                 `xorm:"name"`
-	Content           string                 `xorm:"LONGTEXT"`
-	RenderedContent   template.HTML          `xorm:"-"`
-	ContentVersion    int                    `xorm:"NOT NULL DEFAULT 0"`
-	Labels            []*Label               `xorm:"-"`
-	isLabelsLoaded    bool                   `xorm:"-"`
-	MilestoneID       int64                  `xorm:"INDEX"`
-	Milestone         *Milestone             `xorm:"-"`
-	isMilestoneLoaded bool                   `xorm:"-"`
-	Project           *project_model.Project `xorm:"-"`
+	OriginalAuthorID  int64                    `xorm:"index"`
+	Title             string                   `xorm:"name"`
+	Content           string                   `xorm:"LONGTEXT"`
+	RenderedContent   template.HTML            `xorm:"-"`
+	ContentVersion    int                      `xorm:"NOT NULL DEFAULT 0"`
+	Labels            []*Label                 `xorm:"-"`
+	isLabelsLoaded    bool                     `xorm:"-"`
+	MilestoneID       int64                    `xorm:"INDEX"`
+	Milestone         *Milestone               `xorm:"-"`
+	isMilestoneLoaded bool                     `xorm:"-"`
+	Projects          []*project_model.Project `xorm:"-"`
+	isProjectsLoaded  bool                     `xorm:"-"`
 	Priority          int
 	AssigneeID        int64            `xorm:"-"`
 	Assignee          *user_model.User `xorm:"-"`
@@ -305,7 +306,7 @@ func (issue *Issue) LoadAttributes(ctx context.Context) (err error) {
 		return err
 	}
 
-	if err = issue.LoadProject(ctx); err != nil {
+	if err = issue.LoadProjects(ctx); err != nil {
 		return err
 	}
 
@@ -355,6 +356,7 @@ func (issue *Issue) ResetAttributesLoaded() {
 	issue.isMilestoneLoaded = false
 	issue.isAttachmentsLoaded = false
 	issue.isAssigneeLoaded = false
+	issue.isProjectsLoaded = false
 }
 
 // GetIsRead load the `IsRead` field of the issue

models/issues/issue_list.go

@@ -185,7 +185,7 @@ func (issues IssueList) LoadMilestones(ctx context.Context) error {
 
 func (issues IssueList) LoadProjects(ctx context.Context) error {
 	issueIDs := issues.getIssueIDs()
-	projectMaps := make(map[int64]*project_model.Project, len(issues))
+	issueProjectMaps := make(map[int64][]*project_model.Project, len(issues))
 	left := len(issueIDs)
 
 	type projectWithIssueID struct {
@@ -202,19 +202,21 @@ func (issues IssueList) LoadProjects(ctx context.Context) error {
 			Select("project.*, project_issue.issue_id").
 			Join("INNER", "project_issue", "project.id = project_issue.project_id").
 			In("project_issue.issue_id", issueIDs[:limit]).
+			OrderBy("project_issue.issue_id ASC, project.id ASC").
 			Find(&projects)
 		if err != nil {
 			return err
 		}
 		for _, project := range projects {
-			projectMaps[project.IssueID] = project.Project
+			issueProjectMaps[project.IssueID] = append(issueProjectMaps[project.IssueID], project.Project)
 		}
 		left -= limit
 		issueIDs = issueIDs[limit:]
 	}
 
 	for _, issue := range issues {
-		issue.Project = projectMaps[issue.ID]
+		issue.Projects = issueProjectMaps[issue.ID]
+		issue.isProjectsLoaded = true
 	}
 	return nil
 }

models/issues/issue_list_test.go

@@ -65,10 +65,10 @@ func TestIssueList_LoadAttributes(t *testing.T) {
 		}
 		if issue.ID == int64(1) {
 			assert.Equal(t, int64(400), issue.TotalTrackedTime)
-			assert.NotNil(t, issue.Project)
-			assert.Equal(t, int64(1), issue.Project.ID)
+			assert.NotEmpty(t, issue.Projects)
+			assert.Equal(t, int64(1), issue.Projects[0].ID)
 		} else {
-			assert.Nil(t, issue.Project)
+			assert.Empty(t, issue.Projects)
 		}
 	}
 }

models/issues/issue_project.go

@@ -12,41 +12,38 @@ import (
 	"code.gitea.io/gitea/modules/util"
 )
 
-// LoadProject load the project the issue was assigned to
-func (issue *Issue) LoadProject(ctx context.Context) (err error) {
-	if issue.Project == nil {
-		var p project_model.Project
-		has, err := db.GetEngine(ctx).Table("project").
+// LoadProjects loads all projects the issue is assigned to
+func (issue *Issue) LoadProjects(ctx context.Context) (err error) {
+	if !issue.isProjectsLoaded {
+		err = db.GetEngine(ctx).Table("project").
 			Join("INNER", "project_issue", "project.id=project_issue.project_id").
-			Where("project_issue.issue_id = ?", issue.ID).Get(&p)
-		if err != nil {
-			return err
-		} else if has {
-			issue.Project = &p
+			Where("project_issue.issue_id = ?", issue.ID).
+			OrderBy("project.id ASC").
+			Find(&issue.Projects)
+		if err == nil {
+			issue.isProjectsLoaded = true
 		}
 	}
 	return err
 }
 
-func (issue *Issue) projectID(ctx context.Context) int64 {
-	var ip project_model.ProjectIssue
-	has, err := db.GetEngine(ctx).Where("issue_id=?", issue.ID).Get(&ip)
-	if err != nil || !has {
-		return 0
-	}
-	return ip.ProjectID
+func (issue *Issue) projectIDs(ctx context.Context) (projectIDs []int64, _ error) {
+	err := db.GetEngine(ctx).Table("project_issue").Where("issue_id = ?", issue.ID).Cols("project_id").Find(&projectIDs)
+	return projectIDs, err
 }
 
-// ProjectColumnID return project column id if issue was assigned to one
-func (issue *Issue) ProjectColumnID(ctx context.Context) (int64, error) {
-	var ip project_model.ProjectIssue
-	has, err := db.GetEngine(ctx).Where("issue_id=?", issue.ID).Get(&ip)
-	if err != nil {
-		return 0, err
-	} else if !has {
-		return 0, nil
+// ProjectColumnMap returns a map of project ID to column ID for this issue.
+func (issue *Issue) ProjectColumnMap(ctx context.Context) (map[int64]int64, error) {
+	var projIssues []project_model.ProjectIssue
+	if err := db.GetEngine(ctx).Where("issue_id=?", issue.ID).Find(&projIssues); err != nil {
+		return nil, err
 	}
-	return ip.ProjectColumnID, nil
+
+	result := make(map[int64]int64, len(projIssues))
+	for _, projIssue := range projIssues {
+		result[projIssue.ProjectID] = projIssue.ProjectColumnID
+	}
+	return result, nil
 }
 
 func LoadProjectIssueColumnMap(ctx context.Context, projectID, defaultColumnID int64) (map[int64]int64, error) {
@@ -64,66 +61,91 @@ func LoadProjectIssueColumnMap(ctx context.Context, projectID, defaultColumnID i
 	return result, nil
 }
 
-// IssueAssignOrRemoveProject changes the project associated with an issue
-// If newProjectID is 0, the issue is removed from the project
-func IssueAssignOrRemoveProject(ctx context.Context, issue *Issue, doer *user_model.User, newProjectID, newColumnID int64) error {
+// IssueAssignOrRemoveProject updates the projects associated with an issue.
+// It adds projects that are in newProjectIDs but not currently assigned,
+// and removes projects that are currently assigned but not in newProjectIDs.
+// If newProjectIDs is empty, all projects are removed from the issue.
+// When adding an issue to a project, it is placed in the project's default column.
+func IssueAssignOrRemoveProject(ctx context.Context, issue *Issue, doer *user_model.User, newProjectIDs []int64) error {
 	return db.WithTx(ctx, func(ctx context.Context) error {
-		oldProjectID := issue.projectID(ctx)
-
 		if err := issue.LoadRepo(ctx); err != nil {
 			return err
 		}
 
-		// Only check if we add a new project and not remove it.
-		if newProjectID > 0 {
-			newProject, err := project_model.GetProjectByID(ctx, newProjectID)
-			if err != nil {
-				return err
-			}
-			if !newProject.CanBeAccessedByOwnerRepo(issue.Repo.OwnerID, issue.Repo) {
-				return util.NewPermissionDeniedErrorf("issue %d can't be accessed by project %d", issue.ID, newProject.ID)
-			}
-			if newColumnID == 0 {
-				newDefaultColumn, err := newProject.MustDefaultColumn(ctx)
-				if err != nil {
-					return err
-				}
-				newColumnID = newDefaultColumn.ID
-			}
-		}
-
-		if _, err := db.GetEngine(ctx).Where("project_issue.issue_id=?", issue.ID).Delete(&project_model.ProjectIssue{}); err != nil {
-			return err
-		}
-
-		if oldProjectID > 0 || newProjectID > 0 {
-			if _, err := CreateComment(ctx, &CreateCommentOptions{
-				Type:         CommentTypeProject,
-				Doer:         doer,
-				Repo:         issue.Repo,
-				Issue:        issue,
-				OldProjectID: oldProjectID,
-				ProjectID:    newProjectID,
-			}); err != nil {
-				return err
-			}
-		}
-		if newProjectID == 0 {
-			return nil
-		}
-		if newColumnID == 0 {
-			panic("newColumnID must not be zero") // shouldn't happen
-		}
-
-		newSorting, err := project_model.GetColumnIssueNextSorting(ctx, newProjectID, newColumnID)
+		oldProjectIDs, err := issue.projectIDs(ctx)
 		if err != nil {
 			return err
 		}
-		return db.Insert(ctx, &project_model.ProjectIssue{
-			IssueID:         issue.ID,
-			ProjectID:       newProjectID,
-			ProjectColumnID: newColumnID,
-			Sorting:         newSorting,
-		})
+
+		projectsToAdd, projectsToRemove := util.DiffSlice(oldProjectIDs, newProjectIDs)
+		issue.isProjectsLoaded = false
+		issue.Projects = nil
+
+		if len(projectsToRemove) > 0 {
+			if _, err := db.GetEngine(ctx).Where("issue_id=?", issue.ID).In("project_id", projectsToRemove).Delete(&project_model.ProjectIssue{}); err != nil {
+				return err
+			}
+			for _, projectID := range projectsToRemove {
+				if _, err := CreateComment(ctx, &CreateCommentOptions{
+					Type:         CommentTypeProject,
+					Doer:         doer,
+					Repo:         issue.Repo,
+					Issue:        issue,
+					OldProjectID: projectID,
+					ProjectID:    0,
+				}); err != nil {
+					return err
+				}
+			}
+		}
+
+		if len(projectsToAdd) > 0 {
+			projectMap, err := project_model.GetProjectsMapByIDs(ctx, projectsToAdd)
+			if err != nil {
+				return err
+			}
+
+			for _, projectID := range projectsToAdd {
+				newProject, ok := projectMap[projectID]
+				if !ok {
+					return util.NewNotExistErrorf("project %d not found", projectID)
+				}
+				if !newProject.CanBeAccessedByOwnerRepo(issue.Repo.OwnerID, issue.Repo) {
+					return util.NewPermissionDeniedErrorf("issue %d can't be accessed by project %d", issue.ID, newProject.ID)
+				}
+
+				defaultColumn, err := newProject.MustDefaultColumn(ctx)
+				if err != nil {
+					return err
+				}
+
+				newSorting, err := project_model.GetColumnIssueNextSorting(ctx, projectID, defaultColumn.ID)
+				if err != nil {
+					return err
+				}
+
+				err = db.Insert(ctx, &project_model.ProjectIssue{
+					IssueID:         issue.ID,
+					ProjectID:       projectID,
+					ProjectColumnID: defaultColumn.ID,
+					Sorting:         newSorting,
+				})
+				if err != nil {
+					return err
+				}
+
+				if _, err := CreateComment(ctx, &CreateCommentOptions{
+					Type:         CommentTypeProject,
+					Doer:         doer,
+					Repo:         issue.Repo,
+					Issue:        issue,
+					OldProjectID: 0,
+					ProjectID:    projectID,
+				}); err != nil {
+					return err
+				}
+			}
+		}
+		return nil
 	})
 }

models/issues/issue_project_multi_test.go

@@ -0,0 +1,149 @@
+// Copyright 2026 The Gitea Authors. All rights reserved.
+// SPDX-License-Identifier: MIT
+
+package issues_test
+
+import (
+	"fmt"
+	"testing"
+
+	issues_model "code.gitea.io/gitea/models/issues"
+	project_model "code.gitea.io/gitea/models/project"
+	"code.gitea.io/gitea/models/unittest"
+	user_model "code.gitea.io/gitea/models/user"
+
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+)
+
+func TestIssueMultipleProjects(t *testing.T) {
+	require.NoError(t, unittest.PrepareTestDatabase())
+
+	t.Run("GeneralTest", func(t *testing.T) {
+		// Get test data
+		issue1 := unittest.AssertExistsAndLoadBean(t, &issues_model.Issue{ID: 1})
+		user2 := unittest.AssertExistsAndLoadBean(t, &user_model.User{ID: 2})
+		project1 := unittest.AssertExistsAndLoadBean(t, &project_model.Project{ID: 1})
+
+		// Create a second project for the same repository
+		project2 := &project_model.Project{
+			Title:        "Test Project 2",
+			RepoID:       issue1.RepoID,
+			Type:         project_model.TypeRepository,
+			TemplateType: project_model.TemplateTypeBasicKanban,
+		}
+		require.NoError(t, project_model.NewProject(t.Context(), project2))
+		defer func() {
+			_ = project_model.DeleteProjectByID(t.Context(), project2.ID)
+		}()
+
+		err := issues_model.IssueAssignOrRemoveProject(t.Context(), issue1, user2, []int64{})
+		require.NoError(t, err)
+		err = issue1.LoadProjects(t.Context())
+		require.NoError(t, err)
+		require.Empty(t, issue1.Projects)
+
+		// assign issue to both projects (each project uses its own default column)
+		err = issues_model.IssueAssignOrRemoveProject(t.Context(), issue1, user2, []int64{project1.ID})
+		require.NoError(t, err)
+		assert.Nilf(t, issue1.Projects, "Issue's Projects should be nil after IssueAssignOrRemoveProject to ensure it reloads fresh data")
+		err = issue1.LoadProjects(t.Context())
+		require.NoError(t, err)
+		require.Len(t, issue1.Projects, 1)
+
+		err = issues_model.IssueAssignOrRemoveProject(t.Context(), issue1, user2, []int64{project1.ID, project2.ID})
+		require.NoError(t, err)
+		assert.Nilf(t, issue1.Projects, "Issue's Projects should be nil after IssueAssignOrRemoveProject to ensure it reloads fresh data")
+		err = issue1.LoadProjects(t.Context())
+		require.NoError(t, err)
+		require.Len(t, issue1.Projects, 2)
+		assert.ElementsMatch(t, []int64{project1.ID, project2.ID}, []int64{issue1.Projects[0].ID, issue1.Projects[1].ID}, "Issue should be in both projects")
+
+		// test issue's project column map
+		projectColumnMap, err := issue1.ProjectColumnMap(t.Context())
+		p1Col, _ := project1.MustDefaultColumn(t.Context())
+		p2Col, _ := project2.MustDefaultColumn(t.Context())
+		require.NoError(t, err)
+		assert.Equal(t, p1Col.ID, projectColumnMap[project1.ID])
+		assert.Equal(t, p2Col.ID, projectColumnMap[project2.ID])
+
+		// only keep project2
+		err = issues_model.IssueAssignOrRemoveProject(t.Context(), issue1, user2, []int64{project2.ID})
+		require.NoError(t, err)
+		err = issue1.LoadProjects(t.Context())
+		require.NoError(t, err)
+		require.Len(t, issue1.Projects, 1)
+		assert.Equal(t, project2.ID, issue1.Projects[0].ID)
+
+		// also test ResetAttributesLoaded
+		issue1.Projects = nil
+		issue1.ResetAttributesLoaded()
+		err = issue1.LoadProjects(t.Context())
+		require.NoError(t, err)
+		require.Len(t, issue1.Projects, 1)
+		assert.Equal(t, project2.ID, issue1.Projects[0].ID)
+
+		// remove issue's projects
+		err = issues_model.IssueAssignOrRemoveProject(t.Context(), issue1, user2, []int64{})
+		require.NoError(t, err)
+		err = issue1.LoadProjects(t.Context())
+		require.NoError(t, err)
+		require.Empty(t, issue1.Projects)
+	})
+
+	t.Run("QueryByMultipleProjectIDs", func(t *testing.T) {
+		// Get test data
+		issue1 := unittest.AssertExistsAndLoadBean(t, &issues_model.Issue{ID: 1})
+		issue2 := unittest.AssertExistsAndLoadBean(t, &issues_model.Issue{ID: 2})
+		user2 := unittest.AssertExistsAndLoadBean(t, &user_model.User{ID: 2})
+
+		// Create three projects
+		var projects []*project_model.Project
+		for i := 1; i <= 3; i++ {
+			project := &project_model.Project{
+				Title:        fmt.Sprintf("Query Test Project %d", i),
+				RepoID:       issue1.RepoID,
+				Type:         project_model.TypeRepository,
+				TemplateType: project_model.TemplateTypeBasicKanban,
+			}
+			require.NoError(t, project_model.NewProject(t.Context(), project))
+			projects = append(projects, project)
+			defer func(id int64) {
+				_ = project_model.DeleteProjectByID(t.Context(), id)
+			}(project.ID)
+		}
+
+		// Assign issue1 to projects 1 and 2
+		err := issues_model.IssueAssignOrRemoveProject(t.Context(), issue1, user2, []int64{projects[0].ID, projects[1].ID})
+		require.NoError(t, err)
+
+		// Assign issue2 to project 3
+		err = issues_model.IssueAssignOrRemoveProject(t.Context(), issue2, user2, []int64{projects[2].ID})
+		require.NoError(t, err)
+
+		// Query for issues in project 3 only (should find issue2)
+		issues, err := issues_model.Issues(t.Context(), &issues_model.IssuesOptions{
+			RepoIDs:    []int64{issue1.RepoID},
+			ProjectIDs: []int64{projects[2].ID},
+		})
+		require.NoError(t, err)
+		assert.NotEmpty(t, issues, "Should find issues in project 3")
+
+		// Verify issue2 is in the results
+		foundIssue2 := false
+		for _, issue := range issues {
+			if issue.ID == issue2.ID {
+				foundIssue2 = true
+				break
+			}
+		}
+		assert.True(t, foundIssue2, "Issue 2 should be found when querying project 3")
+
+		// FIXME: ISSUE-MULTIPLE-PROJECTS-FILTER: no multiple project filter support yet. Search logic is wrong. It should use "AND" but not "OR".
+		// Clean up
+		err = issues_model.IssueAssignOrRemoveProject(t.Context(), issue1, user2, []int64{})
+		require.NoError(t, err)
+		err = issues_model.IssueAssignOrRemoveProject(t.Context(), issue2, user2, []int64{})
+		require.NoError(t, err)
+	})
+}

models/issues/issue_search.go

@@ -16,6 +16,7 @@ import (
 	user_model "code.gitea.io/gitea/models/user"
 	"code.gitea.io/gitea/modules/container"
 	"code.gitea.io/gitea/modules/optional"
+	"code.gitea.io/gitea/modules/util"
 
 	"xorm.io/builder"
 	"xorm.io/xorm"
@@ -36,8 +37,7 @@ type IssuesOptions struct { //nolint:revive // export stutter
 	ReviewedID         int64
 	SubscriberID       int64
 	MilestoneIDs       []int64
-	ProjectID          int64
-	ProjectColumnID    int64
+	ProjectIDs         []int64
 	IsClosed           optional.Option[bool]
 	IsPull             optional.Option[bool]
 	LabelIDs           []int64
@@ -198,26 +198,19 @@ func applyMilestoneCondition(sess *xorm.Session, opts *IssuesOptions) {
 }
 
 func applyProjectCondition(sess *xorm.Session, opts *IssuesOptions) {
-	if opts.ProjectID > 0 { // specific project
-		sess.Join("INNER", "project_issue", "issue.id = project_issue.issue_id").
-			And("project_issue.project_id=?", opts.ProjectID)
-	} else if opts.ProjectID == db.NoConditionID { // show those that are in no project
-		sess.And(builder.NotIn("issue.id", builder.Select("issue_id").From("project_issue").And(builder.Neq{"project_id": 0})))
+	projectIDs := util.SliceRemoveAll(opts.ProjectIDs, 0)
+	if len(projectIDs) == 1 && projectIDs[0] == db.NoConditionID { // show those that are in no project
+		sess.And(builder.NotIn("issue.id", builder.Select("issue_id").From("project_issue")))
+	} else if len(projectIDs) == 1 && projectIDs[0] > 0 { // single specific project
+		sess.Join("INNER", "project_issue", "issue.id = project_issue.issue_id AND project_issue.project_id = ?", projectIDs[0])
+	} else if len(projectIDs) > 1 { // multiple projects
+		// FIXME: ISSUE-MULTIPLE-PROJECTS-FILTER: this logic is not right, it should use "AND" but not "OR"
+		sess.And(builder.In("issue.id", builder.Select("issue_id").From("project_issue").Where(builder.In("project_id", projectIDs))))
 	}
-	// opts.ProjectID == 0 means all projects,
+	// empty projectIDs means all projects,
 	// do not need to apply any condition
 }
 
-func applyProjectColumnCondition(sess *xorm.Session, opts *IssuesOptions) {
-	// opts.ProjectColumnID == 0 means all project columns,
-	// do not need to apply any condition
-	if opts.ProjectColumnID > 0 {
-		sess.In("issue.id", builder.Select("issue_id").From("project_issue").Where(builder.Eq{"project_board_id": opts.ProjectColumnID}))
-	} else if opts.ProjectColumnID == db.NoConditionID {
-		sess.In("issue.id", builder.Select("issue_id").From("project_issue").Where(builder.Eq{"project_board_id": 0}))
-	}
-}
-
 func applyRepoConditions(sess *xorm.Session, opts *IssuesOptions) {
 	if len(opts.RepoIDs) == 1 {
 		opts.RepoCond = builder.Eq{"issue.repo_id": opts.RepoIDs[0]}
@@ -276,8 +269,6 @@ func applyConditions(sess *xorm.Session, opts *IssuesOptions) {
 
 	applyProjectCondition(sess, opts)
 
-	applyProjectColumnCondition(sess, opts)
-
 	if opts.IsPull.Has() {
 		sess.And("issue.is_pull=?", opts.IsPull.Value())
 	}

models/issues/issue_test.go

@@ -424,10 +424,10 @@ func TestIssueLoadAttributes(t *testing.T) {
 		}
 		if issue.ID == int64(1) {
 			assert.Equal(t, int64(400), issue.TotalTrackedTime)
-			assert.NotNil(t, issue.Project)
-			assert.Equal(t, int64(1), issue.Project.ID)
+			assert.NotEmpty(t, issue.Projects)
+			assert.Equal(t, int64(1), issue.Projects[0].ID)
 		} else {
-			assert.Nil(t, issue.Project)
+			assert.Empty(t, issue.Projects)
 		}
 	}
 }

models/project/project.go

@@ -302,6 +302,15 @@ func GetProjectByID(ctx context.Context, id int64) (*Project, error) {
 	return p, nil
 }
 
+// GetProjectsMapByIDs returns projects by a list of IDs.
+func GetProjectsMapByIDs(ctx context.Context, ids []int64) (map[int64]*Project, error) {
+	projects := make(map[int64]*Project, len(ids))
+	if len(ids) == 0 {
+		return projects, nil
+	}
+	return projects, db.GetEngine(ctx).In("id", ids).Find(&projects)
+}
+
 func GetProjectByIDAndOwner(ctx context.Context, id, ownerID int64) (*Project, error) {
 	p := new(Project)
 	has, err := db.GetEngine(ctx).ID(id).And("owner_id = ?", ownerID).Get(p)

modules/indexer/issues/bleve/bleve.go

@@ -27,7 +27,7 @@ import (
 const (
 	issueIndexerAnalyzer      = "issueIndexer"
 	issueIndexerDocType       = "issueIndexerDocType"
-	issueIndexerLatestVersion = 5
+	issueIndexerLatestVersion = 6
 )
 
 const unicodeNormalizeName = "unicodeNormalize"
@@ -83,8 +83,8 @@ func generateIssueIndexMapping() (mapping.IndexMapping, error) {
 	docMapping.AddFieldMappingsAt("label_ids", numberFieldMapping)
 	docMapping.AddFieldMappingsAt("no_label", boolFieldMapping)
 	docMapping.AddFieldMappingsAt("milestone_id", numberFieldMapping)
-	docMapping.AddFieldMappingsAt("project_id", numberFieldMapping)
-	docMapping.AddFieldMappingsAt("project_board_id", numberFieldMapping)
+	docMapping.AddFieldMappingsAt("project_ids", numberFieldMapping)
+	docMapping.AddFieldMappingsAt("no_project", boolFieldMapping)
 	docMapping.AddFieldMappingsAt("poster_id", numberFieldMapping)
 	docMapping.AddFieldMappingsAt("assignee_id", numberFieldMapping)
 	docMapping.AddFieldMappingsAt("mention_ids", numberFieldMapping)
@@ -241,11 +241,15 @@ func (b *Indexer) Search(ctx context.Context, options *internal.SearchOptions) (
 		queries = append(queries, bleve.NewDisjunctionQuery(milestoneQueries...))
 	}
 
-	if options.ProjectID.Has() {
-		queries = append(queries, inner_bleve.NumericEqualityQuery(options.ProjectID.Value(), "project_id"))
-	}
-	if options.ProjectColumnID.Has() {
-		queries = append(queries, inner_bleve.NumericEqualityQuery(options.ProjectColumnID.Value(), "project_board_id"))
+	if options.NoProjectOnly {
+		queries = append(queries, inner_bleve.BoolFieldQuery(true, "no_project"))
+	} else if len(options.ProjectIDs) > 0 {
+		var projectQueries []query.Query
+		for _, projectID := range options.ProjectIDs {
+			projectQueries = append(projectQueries, inner_bleve.NumericEqualityQuery(projectID, "project_ids"))
+		}
+		// FIXME: ISSUE-MULTIPLE-PROJECTS-FILTER: this logic is not right, it should use "AND" but not "OR"
+		queries = append(queries, bleve.NewDisjunctionQuery(projectQueries...))
 	}
 
 	if options.PosterID != "" {

modules/indexer/issues/db/options.go

@@ -13,6 +13,7 @@ import (
 	"code.gitea.io/gitea/modules/container"
 	"code.gitea.io/gitea/modules/indexer/issues/internal"
 	"code.gitea.io/gitea/modules/optional"
+	"code.gitea.io/gitea/modules/util"
 )
 
 func ToDBOptions(ctx context.Context, options *internal.SearchOptions) (*issue_model.IssuesOptions, error) {
@@ -65,8 +66,7 @@ func ToDBOptions(ctx context.Context, options *internal.SearchOptions) (*issue_m
 		ReviewRequestedID:  convertID(options.ReviewRequestedID),
 		ReviewedID:         convertID(options.ReviewedID),
 		SubscriberID:       convertID(options.SubscriberID),
-		ProjectID:          convertID(options.ProjectID),
-		ProjectColumnID:    convertID(options.ProjectColumnID),
+		ProjectIDs:         util.Iif(options.NoProjectOnly, []int64{db.NoConditionID}, options.ProjectIDs),
 		IsClosed:           options.IsClosed,
 		IsPull:             options.IsPull,
 		IncludedLabelNames: nil,

modules/indexer/issues/dboptions.go

@@ -46,10 +46,10 @@ func ToSearchOptions(keyword string, opts *issues_model.IssuesOptions) *SearchOp
 		searchOpt.MilestoneIDs = opts.MilestoneIDs
 	}
 
-	if opts.ProjectID > 0 {
-		searchOpt.ProjectID = optional.Some(opts.ProjectID)
-	} else if opts.ProjectID == db.NoConditionID { // FIXME: this is inconsistent from other places
-		searchOpt.ProjectID = optional.Some[int64](0) // Those issues with no project(projectid==0)
+	if len(opts.ProjectIDs) == 1 && opts.ProjectIDs[0] == db.NoConditionID {
+		searchOpt.NoProjectOnly = true
+	} else {
+		searchOpt.ProjectIDs = opts.ProjectIDs
 	}
 
 	searchOpt.AssigneeID = opts.AssigneeID
@@ -65,7 +65,6 @@ func ToSearchOptions(keyword string, opts *issues_model.IssuesOptions) *SearchOp
 		return nil
 	}
 
-	searchOpt.ProjectColumnID = convertID(opts.ProjectColumnID)
 	searchOpt.PosterID = opts.PosterID
 	searchOpt.MentionID = convertID(opts.MentionedID)
 	searchOpt.ReviewedID = convertID(opts.ReviewedID)

modules/indexer/issues/elasticsearch/elasticsearch.go

@@ -19,7 +19,7 @@ import (
 )
 
 const (
-	issueIndexerLatestVersion = 2
+	issueIndexerLatestVersion = 3
 	// multi-match-types, currently only 2 types are used
 	// Reference: https://www.elastic.co/guide/en/elasticsearch/reference/7.0/query-dsl-multi-match-query.html#multi-match-types
 	esMultiMatchTypeBestFields   = "best_fields"
@@ -68,8 +68,8 @@ const (
 			"label_ids": { "type": "integer", "index": true },
 			"no_label": { "type": "boolean", "index": true },
 			"milestone_id": { "type": "integer", "index": true },
-			"project_id": { "type": "integer", "index": true },
-			"project_board_id": { "type": "integer", "index": true },
+			"project_ids": { "type": "integer", "index": true },
+			"no_project": { "type": "boolean", "index": true },
 			"poster_id": { "type": "integer", "index": true },
 			"assignee_id": { "type": "integer", "index": true },
 			"mention_ids": { "type": "integer", "index": true },
@@ -204,11 +204,11 @@ func (b *Indexer) Search(ctx context.Context, options *internal.SearchOptions) (
 		query.Must(elastic.NewTermsQuery("milestone_id", toAnySlice(options.MilestoneIDs)...))
 	}
 
-	if options.ProjectID.Has() {
-		query.Must(elastic.NewTermQuery("project_id", options.ProjectID.Value()))
-	}
-	if options.ProjectColumnID.Has() {
-		query.Must(elastic.NewTermQuery("project_board_id", options.ProjectColumnID.Value()))
+	if options.NoProjectOnly {
+		query.Must(elastic.NewTermQuery("no_project", true))
+	} else if len(options.ProjectIDs) > 0 {
+		// FIXME: ISSUE-MULTIPLE-PROJECTS-FILTER: this logic is not right, it should use "AND" but not "OR"
+		query.Must(elastic.NewTermsQuery("project_ids", toAnySlice(options.ProjectIDs)...))
 	}
 
 	if options.PosterID != "" {

modules/indexer/issues/indexer_test.go

@@ -416,28 +416,42 @@ func searchIssueInProject(t *testing.T) {
 	}{
 		{
 			SearchOptions{
-				ProjectID: optional.Some(int64(1)),
+				ProjectIDs: []int64{1},
 			},
 			[]int64{5, 3, 2, 1},
 		},
-		{
-			SearchOptions{
-				ProjectColumnID: optional.Some(int64(1)),
-			},
-			[]int64{1},
-		},
-		{
-			SearchOptions{
-				ProjectColumnID: optional.Some(int64(0)), // issue with in default column
-			},
-			[]int64{2},
-		},
 	}
 	for _, test := range tests {
 		issueIDs, _, err := SearchIssues(t.Context(), &test.opts)
 		require.NoError(t, err)
 		assert.Equal(t, test.expectedIDs, issueIDs)
 	}
+
+	// Test filtering for issues with no project assigned using dynamic validation
+	t.Run("no project assigned", func(t *testing.T) {
+		issueIDs, total, err := SearchIssues(t.Context(), &SearchOptions{
+			ProjectIDs: []int64{db.NoConditionID},
+		})
+		require.NoError(t, err)
+		assert.NotEmpty(t, issueIDs)
+		assert.Equal(t, total, int64(len(issueIDs)))
+
+		// Verify each returned issue actually has no project
+		for _, issueID := range issueIDs {
+			issue, err := issues.GetIssueByID(t.Context(), issueID)
+			require.NoError(t, err)
+			err = issue.LoadProjects(t.Context())
+			require.NoError(t, err)
+			assert.Empty(t, issue.Projects, "Issue %d should have no projects", issueID)
+		}
+
+		// Count total issues with no project to verify we got them all
+		allIssues, err := issues.Issues(t.Context(), &issues.IssuesOptions{
+			ProjectIDs: []int64{db.NoConditionID},
+		})
+		require.NoError(t, err)
+		assert.Len(t, issueIDs, len(allIssues), "Should return all issues with no project")
+	})
 }
 
 func searchIssueWithPaginator(t *testing.T) {

modules/indexer/issues/internal/model.go

@@ -30,8 +30,9 @@ type IndexerData struct {
 	LabelIDs           []int64            `json:"label_ids"`
 	NoLabel            bool               `json:"no_label"` // True if LabelIDs is empty
 	MilestoneID        int64              `json:"milestone_id"`
-	ProjectID          int64              `json:"project_id"`
-	ProjectColumnID    int64              `json:"project_board_id"` // the key should be kept as project_board_id to keep compatible
+	ProjectIDs         []int64            `json:"project_ids"`
+	NoProject          bool               `json:"no_project"`                   // True if ProjectIDs is empty
+	ProjectColumnMap   map[int64]int64    `json:"project_column_map,omitempty"` // Maps project ID to column ID for each project the issue is in
 	PosterID           int64              `json:"poster_id"`
 	AssigneeID         int64              `json:"assignee_id"`
 	MentionIDs         []int64            `json:"mention_ids"`
@@ -94,8 +95,8 @@ type SearchOptions struct {
 
 	MilestoneIDs []int64 // milestones the issues have
 
-	ProjectID       optional.Option[int64] // project the issues belong to
-	ProjectColumnID optional.Option[int64] // project column the issues belong to
+	ProjectIDs    []int64 // project the issues belong to. FIXME: ISSUE-MULTIPLE-PROJECTS-FILTER: no multiple project filter support yet. Search logic is wrong.
+	NoProjectOnly bool    // if the issues have no project, if true, ProjectIDs will be ignored
 
 	PosterID   string // poster of the issues, "(none)" or "(any)" or a user ID
 	AssigneeID string // assignee of the issues, "(none)" or "(any)" or a user ID

modules/indexer/issues/internal/tests/tests.go

@@ -301,75 +301,41 @@ var cases = []*testIndexerCase{
 		},
 	},
 	{
-		Name: "ProjectID",
+		Name: "ProjectIDs",
 		SearchOptions: &internal.SearchOptions{
 			Paginator: &db.ListOptions{
 				PageSize: 5,
 			},
-			ProjectID: optional.Some(int64(1)),
+			ProjectIDs: []int64{1},
 		},
 		Expected: func(t *testing.T, data map[int64]*internal.IndexerData, result *internal.SearchResult) {
 			assert.Len(t, result.Hits, 5)
 			for _, v := range result.Hits {
-				assert.Equal(t, int64(1), data[v.ID].ProjectID)
+				assert.Contains(t, data[v.ID].ProjectIDs, int64(1))
 			}
 			assert.Equal(t, countIndexerData(data, func(v *internal.IndexerData) bool {
-				return v.ProjectID == 1
+				return slices.Contains(v.ProjectIDs, int64(1))
 			}), result.Total)
 		},
 	},
 	{
-		Name: "no ProjectID",
+		Name: "no ProjectIDs (empty array)",
 		SearchOptions: &internal.SearchOptions{
 			Paginator: &db.ListOptions{
-				PageSize: 5,
+				PageSize: 50,
 			},
-			ProjectID: optional.Some(int64(0)),
+			NoProjectOnly: true,
 		},
 		Expected: func(t *testing.T, data map[int64]*internal.IndexerData, result *internal.SearchResult) {
-			assert.Len(t, result.Hits, 5)
+			// Verify only issues with no projects are returned
 			for _, v := range result.Hits {
-				assert.Equal(t, int64(0), data[v.ID].ProjectID)
+				assert.Empty(t, data[v.ID].ProjectIDs, "Issue %d should have no projects", v.ID)
 			}
-			assert.Equal(t, countIndexerData(data, func(v *internal.IndexerData) bool {
-				return v.ProjectID == 0
-			}), result.Total)
-		},
-	},
-	{
-		Name: "ProjectColumnID",
-		SearchOptions: &internal.SearchOptions{
-			Paginator: &db.ListOptions{
-				PageSize: 5,
-			},
-			ProjectColumnID: optional.Some(int64(1)),
-		},
-		Expected: func(t *testing.T, data map[int64]*internal.IndexerData, result *internal.SearchResult) {
-			assert.Len(t, result.Hits, 5)
-			for _, v := range result.Hits {
-				assert.Equal(t, int64(1), data[v.ID].ProjectColumnID)
-			}
-			assert.Equal(t, countIndexerData(data, func(v *internal.IndexerData) bool {
-				return v.ProjectColumnID == 1
-			}), result.Total)
-		},
-	},
-	{
-		Name: "no ProjectColumnID",
-		SearchOptions: &internal.SearchOptions{
-			Paginator: &db.ListOptions{
-				PageSize: 5,
-			},
-			ProjectColumnID: optional.Some(int64(0)),
-		},
-		Expected: func(t *testing.T, data map[int64]*internal.IndexerData, result *internal.SearchResult) {
-			assert.Len(t, result.Hits, 5)
-			for _, v := range result.Hits {
-				assert.Equal(t, int64(0), data[v.ID].ProjectColumnID)
-			}
-			assert.Equal(t, countIndexerData(data, func(v *internal.IndexerData) bool {
-				return v.ProjectColumnID == 0
-			}), result.Total)
+			// Verify we got ALL issues with no projects
+			expectedCount := countIndexerData(data, func(v *internal.IndexerData) bool {
+				return len(v.ProjectIDs) == 0
+			})
+			assert.Equal(t, expectedCount, result.Total, "Should return all %d issues with no project", expectedCount)
 		},
 	},
 	{
@@ -706,6 +672,10 @@ func generateDefaultIndexerData() []*internal.IndexerData {
 			for i := range subscriberIDs {
 				subscriberIDs[i] = int64(i) + 1 // SubscriberID should not be 0
 			}
+			projectIDs := make([]int64, id%5)
+			for i := range projectIDs {
+				projectIDs[i] = int64(i) + 1 // projectID should not be 0
+			}
 
 			data = append(data, &internal.IndexerData{
 				ID:                 id,
@@ -719,8 +689,8 @@ func generateDefaultIndexerData() []*internal.IndexerData {
 				LabelIDs:           labelIDs,
 				NoLabel:            len(labelIDs) == 0,
 				MilestoneID:        issueIndex % 4,
-				ProjectID:          issueIndex % 5,
-				ProjectColumnID:    issueIndex % 6,
+				ProjectIDs:         projectIDs,
+				NoProject:          len(projectIDs) == 0,
 				PosterID:           id%10 + 1, // PosterID should not be 0
 				AssigneeID:         issueIndex % 10,
 				MentionIDs:         mentionIDs,

modules/indexer/issues/meilisearch/meilisearch.go

@@ -20,7 +20,7 @@ import (
 )
 
 const (
-	issueIndexerLatestVersion = 4
+	issueIndexerLatestVersion = 5
 
 	// TODO: make this configurable if necessary
 	maxTotalHits = 10000
@@ -71,8 +71,8 @@ func NewIndexer(url, apiKey, indexerName string) *Indexer {
 			"label_ids",
 			"no_label",
 			"milestone_id",
-			"project_id",
-			"project_board_id",
+			"project_ids",
+			"no_project",
 			"poster_id",
 			"assignee_id",
 			"mention_ids",
@@ -182,11 +182,11 @@ func (b *Indexer) Search(ctx context.Context, options *internal.SearchOptions) (
 		query.And(inner_meilisearch.NewFilterIn("milestone_id", options.MilestoneIDs...))
 	}
 
-	if options.ProjectID.Has() {
-		query.And(inner_meilisearch.NewFilterEq("project_id", options.ProjectID.Value()))
-	}
-	if options.ProjectColumnID.Has() {
-		query.And(inner_meilisearch.NewFilterEq("project_board_id", options.ProjectColumnID.Value()))
+	if options.NoProjectOnly {
+		query.And(inner_meilisearch.NewFilterEq("no_project", true))
+	} else if len(options.ProjectIDs) > 0 {
+		// FIXME: ISSUE-MULTIPLE-PROJECTS-FILTER: this logic is not right, it should use "AND" but not "OR"
+		query.And(inner_meilisearch.NewFilterIn("project_ids", options.ProjectIDs...))
 	}
 
 	if options.PosterID != "" {

modules/indexer/issues/util.go

@@ -87,14 +87,9 @@ func getIssueIndexerData(ctx context.Context, issueID int64) (*internal.IndexerD
 		return nil, false, err
 	}
 
-	var projectID int64
-	if issue.Project != nil {
-		projectID = issue.Project.ID
-	}
-
-	projectColumnID, err := issue.ProjectColumnID(ctx)
-	if err != nil {
-		return nil, false, err
+	projectIDs := make([]int64, 0, len(issue.Projects))
+	for _, project := range issue.Projects {
+		projectIDs = append(projectIDs, project.ID)
 	}
 
 	if err := issue.Repo.LoadOwner(ctx); err != nil {
@@ -114,8 +109,8 @@ func getIssueIndexerData(ctx context.Context, issueID int64) (*internal.IndexerD
 		LabelIDs:           labels,
 		NoLabel:            len(labels) == 0,
 		MilestoneID:        issue.MilestoneID,
-		ProjectID:          projectID,
-		ProjectColumnID:    projectColumnID,
+		ProjectIDs:         projectIDs,
+		NoProject:          len(projectIDs) == 0,
 		PosterID:           issue.PosterID,
 		AssigneeID:         issue.AssigneeID,
 		MentionIDs:         mentionIDs,

modules/structs/issue.go

@@ -60,6 +60,7 @@ type Issue struct {
 	Attachments      []*Attachment `json:"assets"`
 	Labels           []*Label      `json:"labels"`
 	Milestone        *Milestone    `json:"milestone"`
+	Projects         []*Project    `json:"projects"`
 	// deprecated
 	Assignee  *User     `json:"assignee"`
 	Assignees []*User   `json:"assignees"`
@@ -100,7 +101,9 @@ type CreateIssueOption struct {
 	Milestone int64 `json:"milestone"`
 	// list of label ids
 	Labels []int64 `json:"labels"`
-	Closed bool    `json:"closed"`
+	// list of project ids
+	Projects []int64 `json:"projects"`
+	Closed   bool    `json:"closed"`
 }
 
 // EditIssueOption options for editing an issue
@@ -112,7 +115,9 @@ type EditIssueOption struct {
 	Assignee  *string  `json:"assignee"`
 	Assignees []string `json:"assignees"`
 	Milestone *int64   `json:"milestone"`
-	State     *string  `json:"state"`
+	// list of project ids to set (replaces existing projects)
+	Projects *[]int64 `json:"projects"`
+	State    *string  `json:"state"`
 	// swagger:strfmt date-time
 	Deadline       *time.Time `json:"due_date"`
 	RemoveDeadline *bool      `json:"unset_due_date"`

modules/structs/project.go

@@ -0,0 +1,33 @@
+// Copyright 2026 The Gitea Authors. All rights reserved.
+// SPDX-License-Identifier: MIT
+
+package structs
+
+import (
+	"time"
+)
+
+// Project represents a project
+// swagger:model
+type Project struct {
+	// ID is the unique identifier for the project
+	ID int64 `json:"id"`
+	// Title is the title of the project
+	Title string `json:"title"`
+	// Description provides details about the project
+	Description string `json:"description"`
+	// OwnerID is the owner of the project (for org-level projects)
+	OwnerID int64 `json:"owner_id,omitempty"`
+	// RepoID is the repository this project belongs to (for repo-level projects)
+	RepoID int64 `json:"repo_id,omitempty"`
+	// CreatorID is the user who created the project
+	CreatorID int64 `json:"creator_id"`
+	// IsClosed indicates if the project is closed
+	IsClosed bool `json:"is_closed"`
+	// swagger:strfmt date-time
+	Created time.Time `json:"created_at"`
+	// swagger:strfmt date-time
+	Updated time.Time `json:"updated_at"`
+	// swagger:strfmt date-time
+	Closed *time.Time `json:"closed_at,omitempty"`
+}

modules/templates/page.go

@@ -5,6 +5,7 @@ package templates
 
 import (
 	"context"
+	"fmt"
 	"html/template"
 	"io"
 	"net/http"
@@ -36,7 +37,11 @@ func (r *pageRenderer) funcMapDummy() template.FuncMap {
 }
 
 func (r *pageRenderer) TemplateLookup(tmpl string, templateCtx context.Context) (TemplateExecutor, error) { //nolint:revive // we don't use ctx, only pass it to the template executor
-	return r.tmplRenderer.Templates().Executor(tmpl, r.funcMap(templateCtx))
+	tmpls := r.tmplRenderer.Templates()
+	if tmpls == nil {
+		return nil, fmt.Errorf("no templates defined for %s", tmpl)
+	}
+	return tmpls.Executor(tmpl, r.funcMap(templateCtx))
 }
 
 func (r *pageRenderer) HTML(w io.Writer, status int, tplName TplName, data any, templateCtx context.Context) error { //nolint:revive // we don't use ctx, only pass it to the template executor

modules/templates/util_slice.go

@@ -6,6 +6,11 @@ package templates
 import (
 	"fmt"
 	"reflect"
+	"slices"
+	"strconv"
+	"strings"
+
+	"code.gitea.io/gitea/modules/util"
 )
 
 type SliceUtils struct{}
@@ -33,3 +38,29 @@ func (su *SliceUtils) Contains(s, v any) bool {
 	}
 	return false
 }
+
+// JoinInt64 joins a slice of int64 values into a comma-separated string.
+func (su *SliceUtils) JoinInt64(values []int64) string {
+	if len(values) == 0 {
+		return ""
+	}
+	strs := make([]string, len(values))
+	for i, v := range values {
+		strs[i] = strconv.FormatInt(v, 10)
+	}
+	return strings.Join(strs, ",")
+}
+
+func (su *SliceUtils) JoinToggleIDs(values []int64, target int64) (ret struct {
+	IsIncluded bool
+	ToggledIDs string
+},
+) {
+	ret.IsIncluded = slices.Contains(values, target)
+	if ret.IsIncluded {
+		ret.ToggledIDs = su.JoinInt64(util.SliceRemoveAll(slices.Clone(values), target))
+	} else {
+		ret.ToggledIDs = su.JoinInt64(append(values, target))
+	}
+	return ret
+}

modules/templates/util_test.go

@@ -70,6 +70,16 @@ func TestUtils(t *testing.T) {
 	actual = execTmpl("{{StringUtils.Contains .String .Value}}", map[string]any{"String": "abc", "Value": "x"})
 	assert.Equal(t, "false", actual)
 
+	// Test JoinInt64
+	actual = execTmpl("{{SliceUtils.JoinInt64 .Values}}", map[string]any{"Values": []int64{1, 2, 3}})
+	assert.Equal(t, "1,2,3", actual)
+
+	actual = execTmpl("{{SliceUtils.JoinInt64 .Values}}", map[string]any{"Values": []int64{}})
+	assert.Empty(t, actual)
+
+	actual = execTmpl("{{SliceUtils.JoinInt64 .Values}}", map[string]any{"Values": []int64{42}})
+	assert.Equal(t, "42", actual)
+
 	tmpl := template.New("test")
 	tmpl.Funcs(template.FuncMap{"SliceUtils": NewSliceUtils, "StringUtils": NewStringUtils})
 	template.Must(tmpl.Parse("{{SliceUtils.Contains .Slice .Value}}"))

modules/util/diff_slice_test.go

@@ -0,0 +1,74 @@
+// Copyright 2026 The Gitea Authors. All rights reserved.
+// SPDX-License-Identifier: MIT
+
+package util
+
+import (
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+)
+
+func TestDiffSliceBasic(t *testing.T) {
+	// Typical integer cases
+	t.Run("additions", func(t *testing.T) {
+		added, removed := DiffSlice([]int{1, 2}, []int{1, 2, 3})
+		assert.Equal(t, []int{3}, added)
+		assert.Empty(t, removed)
+	})
+
+	t.Run("removals", func(t *testing.T) {
+		added, removed := DiffSlice([]int{1, 2, 3}, []int{1, 2})
+		assert.Empty(t, added)
+		assert.Equal(t, []int{3}, removed)
+	})
+
+	t.Run("no changes", func(t *testing.T) {
+		added, removed := DiffSlice([]int{1, 2}, []int{1, 2})
+		assert.Empty(t, added)
+		assert.Empty(t, removed)
+	})
+
+	t.Run("empty slices", func(t *testing.T) {
+		added, removed := DiffSlice([]int{}, []int{})
+		assert.Empty(t, added)
+		assert.Empty(t, removed)
+	})
+
+	t.Run("overlapping elements", func(t *testing.T) {
+		added, removed := DiffSlice([]int{1, 2, 4}, []int{2, 3, 4})
+		assert.Equal(t, []int{3}, added)
+		assert.Equal(t, []int{1}, removed)
+	})
+}
+
+func TestDiffSliceOrderAndDuplicates(t *testing.T) {
+	oldSlice := []int{1, 2, 2, 3}
+	newSlice := []int{2, 4, 2, 5}
+
+	added, removed := DiffSlice(oldSlice, newSlice)
+	assert.Equal(t, []int{4, 5}, added)
+	assert.Equal(t, []int{1, 3}, removed)
+}
+
+func TestDiffSliceDeduplicatesOutput(t *testing.T) {
+	// Test case from issue: newSlice contains [4, 4, 5] and oldSlice is [1]
+	// added should return [4, 5], not [4, 4, 5]
+	t.Run("deduplicates added", func(t *testing.T) {
+		added, removed := DiffSlice([]int{1}, []int{4, 4, 5})
+		assert.Equal(t, []int{4, 5}, added)
+		assert.Equal(t, []int{1}, removed)
+	})
+
+	t.Run("deduplicates removed", func(t *testing.T) {
+		added, removed := DiffSlice([]int{1, 1, 2}, []int{3})
+		assert.Equal(t, []int{3}, added)
+		assert.Equal(t, []int{1, 2}, removed)
+	})
+
+	t.Run("deduplicates both", func(t *testing.T) {
+		added, removed := DiffSlice([]int{1, 1, 2, 2}, []int{3, 3, 4, 4})
+		assert.Equal(t, []int{3, 4}, added)
+		assert.Equal(t, []int{1, 2}, removed)
+	})
+}

modules/util/util.go

@@ -15,6 +15,8 @@ import (
 	"strings"
 	"sync"
 
+	"code.gitea.io/gitea/modules/container"
+
 	"golang.org/x/text/cases"
 	"golang.org/x/text/language"
 )
@@ -291,3 +293,21 @@ func NormalizeStringEOL(input string) string {
 	// Other than this, we should respect the original content, even leading or trailing spaces.
 	return UnsafeBytesToString(NormalizeEOL(UnsafeStringToBytes(input)))
 }
+
+func DiffSlice[T comparable](oldSlice, newSlice []T) (added, removed []T) {
+	oldSet := container.SetOf(oldSlice...)
+	newSet := container.SetOf(newSlice...)
+
+	addedSet, removedSet := container.Set[T]{}, container.Set[T]{}
+	for _, v := range newSlice {
+		if !oldSet.Contains(v) && addedSet.Add(v) {
+			added = append(added, v)
+		}
+	}
+	for _, v := range oldSlice {
+		if !newSet.Contains(v) && removedSet.Add(v) {
+			removed = append(removed, v)
+		}
+	}
+	return added, removed
+}

options/locale/locale_en-US.json

@@ -1385,6 +1385,7 @@
   "repo.projects.column.delete": "Delete Column",
   "repo.projects.column.deletion_desc": "Deleting a project column moves all related issues to the default column. Continue?",
   "repo.projects.column.color": "Color",
+  "repo.projects.column": "Column",
   "repo.projects.open": "Open",
   "repo.projects.close": "Close",
   "repo.projects.column.assigned_to": "Assigned to",

routers/api/v1/repo/issue.go

@@ -690,11 +690,11 @@ func CreateIssue(ctx *context.APIContext) {
 		form.Labels = make([]int64, 0)
 	}
 
-	if err := issue_service.NewIssue(ctx, ctx.Repo.Repository, issue, form.Labels, nil, assigneeIDs, 0); err != nil {
-		if repo_model.IsErrUserDoesNotHaveAccessToRepo(err) {
-			ctx.APIError(http.StatusBadRequest, err)
-		} else if errors.Is(err, user_model.ErrBlockedUser) {
+	if err := issue_service.NewIssue(ctx, ctx.Repo.Repository, issue, form.Labels, nil, assigneeIDs, form.Projects); err != nil {
+		if errors.Is(err, user_model.ErrBlockedUser) {
 			ctx.APIError(http.StatusForbidden, err)
+		} else if errors.Is(err, util.ErrPermissionDenied) || errors.Is(err, util.ErrNotExist) {
+			ctx.APIError(http.StatusBadRequest, err)
 		} else {
 			ctx.APIErrorInternal(err)
 		}
@@ -913,6 +913,18 @@ func EditIssue(ctx *context.APIContext) {
 		}
 	}
 
+	// Update projects if provided
+	if canWrite && form.Projects != nil {
+		if err := issues_model.IssueAssignOrRemoveProject(ctx, issue, ctx.Doer, *form.Projects); err != nil {
+			if errors.Is(err, util.ErrPermissionDenied) || errors.Is(err, util.ErrNotExist) {
+				ctx.APIError(http.StatusBadRequest, err)
+			} else {
+				ctx.APIErrorInternal(err)
+			}
+			return
+		}
+	}
+
 	// Refetch from database to assign some automatic values
 	issue, err = issues_model.GetIssueByID(ctx, issue.ID)
 	if err != nil {

routers/web/repo/issue_list.go

@@ -38,6 +38,14 @@ func retrieveProjectsForIssueList(ctx *context.Context, repo *repo_model.Reposit
 	ctx.Data["OpenProjects"], ctx.Data["ClosedProjects"] = retrieveProjectsInternal(ctx, repo)
 }
 
+// parseProjectIDsFromQuery parses the comma-separated `project` (preferred) or `projects`
+// query parameter into a slice of int64 IDs.
+func parseProjectIDsFromQuery(ctx *context.Context) []int64 {
+	// FIXME: ISSUE-MULTIPLE-PROJECTS-FILTER: no multiple project filter support yet
+	// Although here parses the project parameter as a slice, the "search" logic is wrong
+	return ctx.FormStringInt64s("project")
+}
+
 // SearchIssues searches for issues across the repositories that the user has access to
 func SearchIssues(ctx *context.Context) {
 	before, since, err := context.GetQueryBeforeSince(ctx.Base)
@@ -156,10 +164,7 @@ func SearchIssues(ctx *context.Context) {
 		}
 	}
 
-	projectID := optional.None[int64]()
-	if v := ctx.FormInt64("project"); v > 0 {
-		projectID = optional.Some(v)
-	}
+	includedProjectIDs := parseProjectIDsFromQuery(ctx)
 
 	// this api is also used in UI,
 	// so the default limit is set to fit UI needs
@@ -182,7 +187,7 @@ func SearchIssues(ctx *context.Context) {
 		IsClosed:            isClosed,
 		IncludedAnyLabelIDs: includedAnyLabels,
 		MilestoneIDs:        includedMilestones,
-		ProjectID:           projectID,
+		ProjectIDs:          includedProjectIDs,
 		SortBy:              issue_indexer.SortByCreatedDesc,
 	}
 
@@ -298,11 +303,6 @@ func SearchRepoIssuesJSON(ctx *context.Context) {
 		}
 	}
 
-	projectID := optional.None[int64]()
-	if v := ctx.FormInt64("project"); v > 0 {
-		projectID = optional.Some(v)
-	}
-
 	isPull := optional.None[bool]()
 	switch ctx.FormString("type") {
 	case "pulls":
@@ -330,13 +330,20 @@ func SearchRepoIssuesJSON(ctx *context.Context) {
 			Page:     ctx.FormInt("page"),
 			PageSize: convert.ToCorrectPageSize(ctx.FormInt("limit")),
 		},
-		Keyword:   keyword,
-		RepoIDs:   []int64{ctx.Repo.Repository.ID},
-		IsPull:    isPull,
-		IsClosed:  isClosed,
-		ProjectID: projectID,
-		SortBy:    issue_indexer.SortByCreatedDesc,
+		Keyword:  keyword,
+		RepoIDs:  []int64{ctx.Repo.Repository.ID},
+		IsPull:   isPull,
+		IsClosed: isClosed,
+		SortBy:   issue_indexer.SortByCreatedDesc,
 	}
+
+	projectIDs := parseProjectIDsFromQuery(ctx)
+	if len(projectIDs) == 1 && projectIDs[0] == -1 {
+		searchOpt.NoProjectOnly = true
+	} else if len(projectIDs) > 0 {
+		searchOpt.ProjectIDs = projectIDs
+	}
+
 	if since != 0 {
 		searchOpt.UpdatedAfterUnix = optional.Some(since)
 	}
@@ -467,7 +474,7 @@ func renderMilestones(ctx *context.Context) {
 	ctx.Data["ClosedMilestones"] = closedMilestones
 }
 
-func prepareIssueFilterAndList(ctx *context.Context, milestoneID, projectID int64, isPullOption optional.Option[bool]) {
+func prepareIssueFilterAndList(ctx *context.Context, milestoneID int64, projectIDs []int64, isPullOption optional.Option[bool]) {
 	var err error
 	viewType := ctx.FormString("type")
 	sortType := ctx.FormString("sort")
@@ -520,7 +527,7 @@ func prepareIssueFilterAndList(ctx *context.Context, milestoneID, projectID int6
 		RepoIDs:           []int64{repo.ID},
 		LabelIDs:          preparedLabelFilter.SelectedLabelIDs,
 		MilestoneIDs:      mileIDs,
-		ProjectID:         projectID,
+		ProjectIDs:        projectIDs,
 		AssigneeID:        assigneeID,
 		MentionedID:       mentionedID,
 		PosterID:          posterUserID,
@@ -529,6 +536,7 @@ func prepareIssueFilterAndList(ctx *context.Context, milestoneID, projectID int6
 		IsPull:            isPullOption,
 		IssueIDs:          nil,
 	}
+
 	if keyword != "" {
 		keywordMatchedIssueIDs, _, err = issue_indexer.SearchIssues(ctx, issue_indexer.ToSearchOptions(keyword, statsOpts))
 		if err != nil {
@@ -600,7 +608,7 @@ func prepareIssueFilterAndList(ctx *context.Context, milestoneID, projectID int6
 			ReviewRequestedID: reviewRequestedID,
 			ReviewedID:        reviewedID,
 			MilestoneIDs:      mileIDs,
-			ProjectID:         projectID,
+			ProjectIDs:        projectIDs,
 			IsClosed:          isShowClosed,
 			IsPull:            isPullOption,
 			LabelIDs:          preparedLabelFilter.SelectedLabelIDs,
@@ -708,7 +716,7 @@ func prepareIssueFilterAndList(ctx *context.Context, milestoneID, projectID int6
 	ctx.Data["ViewType"] = viewType
 	ctx.Data["SortType"] = sortType
 	ctx.Data["MilestoneID"] = milestoneID
-	ctx.Data["ProjectID"] = projectID
+	ctx.Data["ProjectIDs"] = projectIDs
 	ctx.Data["AssigneeID"] = assigneeID
 	ctx.Data["PosterUsername"] = posterUsername
 	ctx.Data["Keyword"] = keyword
@@ -749,7 +757,9 @@ func Issues(ctx *context.Context) {
 		ctx.Data["NewIssueChooseTemplate"] = issue_service.HasTemplatesOrContactLinks(ctx.Repo.Repository, ctx.Repo.GitRepo)
 	}
 
-	prepareIssueFilterAndList(ctx, ctx.FormInt64("milestone"), ctx.FormInt64("project"), optional.Some(isPullList))
+	projectIDs := parseProjectIDsFromQuery(ctx)
+
+	prepareIssueFilterAndList(ctx, ctx.FormInt64("milestone"), projectIDs, optional.Some(isPullList))
 	if ctx.Written() {
 		return
 	}

routers/web/repo/issue_new.go

@@ -121,7 +121,8 @@ func NewIssue(ctx *context.Context) {
 	}
 
 	pageMetaData.MilestonesData.SelectedMilestoneID = ctx.FormInt64("milestone")
-	pageMetaData.ProjectsData.SelectedProjectIDs, _ = base.StringsToInt64s(strings.Split(ctx.FormString("project"), ","))
+
+	pageMetaData.SetSelectedProjectIDs(parseProjectIDsFromQuery(ctx))
 	if len(pageMetaData.ProjectsData.SelectedProjectIDs) == 1 {
 		ctx.Data["redirect_after_creation"] = "project"
 	}
@@ -237,8 +238,9 @@ func toSet[ItemType any, KeyType comparable](slice []ItemType, keyFunc func(Item
 
 // ValidateRepoMetasForNewIssue check and returns repository's meta information
 func ValidateRepoMetasForNewIssue(ctx *context.Context, form forms.CreateIssueForm, isPull bool) (ret struct {
-	LabelIDs, AssigneeIDs  []int64
-	MilestoneID, ProjectID int64
+	LabelIDs, AssigneeIDs []int64
+	MilestoneID           int64
+	ProjectIDs            []int64
 
 	Reviewers     []*user_model.User
 	TeamReviewers []*organization.Team
@@ -249,7 +251,7 @@ func ValidateRepoMetasForNewIssue(ctx *context.Context, form forms.CreateIssueFo
 		return ret
 	}
 
-	inputLabelIDs, _ := base.StringsToInt64s(strings.Split(form.LabelIDs, ","))
+	inputLabelIDs := ctx.FormStringInt64s("label_ids")
 	candidateLabels := toSet(pageMetaData.LabelsData.AllLabels, func(label *issues_model.Label) int64 { return label.ID })
 	if len(inputLabelIDs) > 0 && !candidateLabels.Contains(inputLabelIDs...) {
 		ctx.NotFound(nil)
@@ -265,13 +267,8 @@ func ValidateRepoMetasForNewIssue(ctx *context.Context, form forms.CreateIssueFo
 	}
 	pageMetaData.MilestonesData.SelectedMilestoneID = form.MilestoneID
 
-	allProjects := append(slices.Clone(pageMetaData.ProjectsData.OpenProjects), pageMetaData.ProjectsData.ClosedProjects...)
-	candidateProjects := toSet(allProjects, func(project *project_model.Project) int64 { return project.ID })
-	if form.ProjectID > 0 && !candidateProjects.Contains(form.ProjectID) {
-		ctx.NotFound(nil)
-		return ret
-	}
-	pageMetaData.ProjectsData.SelectedProjectIDs = util.Iif(form.ProjectID > 0, []int64{form.ProjectID}, nil)
+	inputProjectIDs := ctx.FormStringInt64s("project_ids")
+	pageMetaData.SetSelectedProjectIDs(inputProjectIDs)
 
 	// prepare assignees
 	candidateAssignees := toSet(pageMetaData.AssigneesData.CandidateAssignees, func(user *user_model.User) int64 { return user.ID })
@@ -316,7 +313,8 @@ func ValidateRepoMetasForNewIssue(ctx *context.Context, form forms.CreateIssueFo
 		}
 	}
 
-	ret.LabelIDs, ret.AssigneeIDs, ret.MilestoneID, ret.ProjectID = inputLabelIDs, inputAssigneeIDs, form.MilestoneID, form.ProjectID
+	// Return only the validated IDs.
+	ret.LabelIDs, ret.AssigneeIDs, ret.MilestoneID, ret.ProjectIDs = inputLabelIDs, inputAssigneeIDs, form.MilestoneID, inputProjectIDs
 	ret.Reviewers, ret.TeamReviewers = reviewers, teamReviewers
 	return ret
 }
@@ -324,26 +322,17 @@ func ValidateRepoMetasForNewIssue(ctx *context.Context, form forms.CreateIssueFo
 // NewIssuePost response for creating new issue
 func NewIssuePost(ctx *context.Context) {
 	form := web.GetForm(ctx).(*forms.CreateIssueForm)
-	ctx.Data["Title"] = ctx.Tr("repo.issues.new")
-	ctx.Data["PageIsIssueList"] = true
-	ctx.Data["NewIssueChooseTemplate"] = issue_service.HasTemplatesOrContactLinks(ctx.Repo.Repository, ctx.Repo.GitRepo)
-	ctx.Data["PullRequestWorkInProgressPrefixes"] = setting.Repository.PullRequest.WorkInProgressPrefixes
-	ctx.Data["IsAttachmentEnabled"] = setting.Attachment.Enabled
-	upload.AddUploadContext(ctx, "comment")
 
-	var (
-		repo        = ctx.Repo.Repository
-		attachments []string
-	)
+	repo := ctx.Repo.Repository
 
 	validateRet := ValidateRepoMetasForNewIssue(ctx, *form, false)
 	if ctx.Written() {
 		return
 	}
 
-	labelIDs, assigneeIDs, milestoneID, projectID := validateRet.LabelIDs, validateRet.AssigneeIDs, validateRet.MilestoneID, validateRet.ProjectID
+	labelIDs, assigneeIDs, milestoneID, projectIDs := validateRet.LabelIDs, validateRet.AssigneeIDs, validateRet.MilestoneID, validateRet.ProjectIDs
 
-	if projectID > 0 {
+	if len(projectIDs) > 0 {
 		if !ctx.Repo.Permission.CanRead(unit.TypeProjects) {
 			// User must also be able to see the project.
 			ctx.HTTPError(http.StatusBadRequest, "user hasn't permissions to read projects")
@@ -351,6 +340,7 @@ func NewIssuePost(ctx *context.Context) {
 		}
 	}
 
+	var attachments []string
 	if setting.Attachment.Enabled {
 		attachments = form.Files
 	}
@@ -383,7 +373,7 @@ func NewIssuePost(ctx *context.Context) {
 		Ref:         form.Ref,
 	}
 
-	if err := issue_service.NewIssue(ctx, repo, issue, labelIDs, attachments, assigneeIDs, projectID); err != nil {
+	if err := issue_service.NewIssue(ctx, repo, issue, labelIDs, attachments, assigneeIDs, projectIDs); err != nil {
 		if repo_model.IsErrUserDoesNotHaveAccessToRepo(err) {
 			ctx.HTTPError(http.StatusBadRequest, "UserDoesNotHaveAccessToRepo", err.Error())
 		} else if errors.Is(err, user_model.ErrBlockedUser) {
@@ -395,8 +385,9 @@ func NewIssuePost(ctx *context.Context) {
 	}
 
 	log.Trace("Issue created: %d/%d", repo.ID, issue.ID)
-	if ctx.FormString("redirect_after_creation") == "project" && projectID > 0 {
-		project, err := project_model.GetProjectByID(ctx, projectID)
+	if ctx.FormString("redirect_after_creation") == "project" && len(projectIDs) > 0 {
+		// When issue is in multiple projects, redirect to first project from form order.
+		project, err := project_model.GetProjectByID(ctx, projectIDs[0])
 		if err == nil {
 			if project.Type == project_model.TypeOrganization {
 				ctx.JSONRedirect(project_model.ProjectLinkForOrg(ctx.Repo.Owner, project.ID))

routers/web/repo/issue_page_meta.go

@@ -40,7 +40,7 @@ type issueSidebarProjectCardData struct {
 }
 
 type issueSidebarProjectsData struct {
-	SelectedProjectIDs []int64 // TODO: support multiple projects in the future
+	SelectedProjectIDs []int64
 	ProjectCards       []*issueSidebarProjectCardData
 
 	OpenProjects   []*project_model.Project
@@ -171,33 +171,49 @@ func (d *IssuePageMetaData) retrieveAssigneesData(ctx *context.Context) {
 	ctx.Data["Assignees"] = d.AssigneesData.CandidateAssignees
 }
 
-func (d *IssuePageMetaData) retrieveProjectData(ctx *context.Context) {
-	if d.Issue == nil || d.Issue.Project == nil {
+func (d *IssuePageMetaData) retrieveProjectCardsForExistingIssue(ctx *context.Context) {
+	if err := d.Issue.LoadProjects(ctx); err != nil {
+		ctx.ServerError("LoadProjects", err)
 		return
 	}
-	columns, err := d.Issue.Project.GetColumns(ctx)
+
+	// Load column mappings for all projects
+	projectColumnMap, err := d.Issue.ProjectColumnMap(ctx)
 	if err != nil {
-		ctx.ServerError("GetProjectColumns", err)
+		ctx.ServerError("ProjectColumnMap", err)
 		return
 	}
-	columnID, err := d.Issue.ProjectColumnID(ctx)
-	if err != nil {
-		ctx.ServerError("ProjectColumnID", err)
-		return
-	}
-	var selectedColumn *project_model.Column
-	for _, col := range columns {
-		if col.ID == columnID {
-			selectedColumn = col
-			break
+
+	// Build project cards for each project
+	d.ProjectsData.ProjectCards = make([]*issueSidebarProjectCardData, 0, len(d.Issue.Projects))
+	for _, project := range d.Issue.Projects {
+		columns, err := project.GetColumns(ctx)
+		if err != nil {
+			ctx.ServerError("GetProjectColumns", err)
+			return
 		}
-	}
-	d.ProjectsData.ProjectCards = []*issueSidebarProjectCardData{
-		{
-			Project:        d.Issue.Project,
+
+		var selectedColumn *project_model.Column
+		columnID := projectColumnMap[project.ID]
+		for _, col := range columns {
+			if col.ID == columnID {
+				selectedColumn = col
+				break
+			}
+		}
+
+		if selectedColumn == nil {
+			selectedColumn, err = project.MustDefaultColumn(ctx)
+			if err != nil {
+				ctx.ServerError("MustDefaultColumn", err)
+				return
+			}
+		}
+		d.ProjectsData.ProjectCards = append(d.ProjectsData.ProjectCards, &issueSidebarProjectCardData{
+			Project:        project,
 			Columns:        columns,
 			SelectedColumn: selectedColumn,
-		},
+		})
 	}
 	d.ProjectsData.SelectedProjectIDs = make([]int64, 0, len(d.ProjectsData.ProjectCards))
 	for _, card := range d.ProjectsData.ProjectCards {
@@ -205,6 +221,29 @@ func (d *IssuePageMetaData) retrieveProjectData(ctx *context.Context) {
 	}
 }
 
+func (d *IssuePageMetaData) retrieveProjectData(ctx *context.Context) {
+	if d.Issue == nil {
+		return
+	}
+	d.retrieveProjectCardsForExistingIssue(ctx)
+}
+
+func (d *IssuePageMetaData) SetSelectedProjectIDs(ids []int64) {
+	allProjects := map[int64]*project_model.Project{}
+	for _, p := range d.ProjectsData.OpenProjects {
+		allProjects[p.ID] = p
+	}
+	for _, p := range d.ProjectsData.ClosedProjects {
+		allProjects[p.ID] = p
+	}
+	for _, id := range ids {
+		if project, ok := allProjects[id]; ok {
+			d.ProjectsData.ProjectCards = append(d.ProjectsData.ProjectCards, &issueSidebarProjectCardData{Project: project})
+		}
+	}
+	d.ProjectsData.SelectedProjectIDs = ids
+}
+
 func (d *IssuePageMetaData) retrieveProjectsDataForIssueWriter(ctx *context.Context) {
 	d.ProjectsData.OpenProjects, d.ProjectsData.ClosedProjects = retrieveProjectsInternal(ctx, ctx.Repo.Repository)
 }

routers/web/repo/milestone.go

@@ -238,7 +238,7 @@ func DeleteMilestone(ctx *context.Context) {
 // MilestoneIssuesAndPulls lists all the issues and pull requests of the milestone
 func MilestoneIssuesAndPulls(ctx *context.Context) {
 	milestoneID := ctx.PathParamInt64("id")
-	projectID := ctx.FormInt64("project")
+	projectIDs := parseProjectIDsFromQuery(ctx)
 	milestone, err := issues_model.GetMilestoneByRepoID(ctx, ctx.Repo.Repository.ID, milestoneID)
 	if err != nil {
 		if issues_model.IsErrMilestoneNotExist(err) {
@@ -260,7 +260,7 @@ func MilestoneIssuesAndPulls(ctx *context.Context) {
 	ctx.Data["Title"] = milestone.Name
 	ctx.Data["Milestone"] = milestone
 
-	prepareIssueFilterAndList(ctx, milestoneID, projectID, optional.None[bool]())
+	prepareIssueFilterAndList(ctx, milestoneID, projectIDs, optional.None[bool]())
 
 	ret := issue.ParseTemplatesFromDefaultBranch(ctx.Repo.Repository, ctx.Repo.GitRepo)
 	ctx.Data["NewIssueChooseTemplate"] = len(ret.IssueTemplates) > 0

routers/web/repo/projects.go

@@ -17,6 +17,7 @@ import (
 	repo_model "code.gitea.io/gitea/models/repo"
 	"code.gitea.io/gitea/models/unit"
 	"code.gitea.io/gitea/modules/json"
+	"code.gitea.io/gitea/modules/log"
 	"code.gitea.io/gitea/modules/markup/markdown"
 	"code.gitea.io/gitea/modules/optional"
 	"code.gitea.io/gitea/modules/setting"
@@ -447,13 +448,12 @@ func UpdateIssueProject(ctx *context.Context) {
 		return
 	}
 
-	projectID := ctx.FormInt64("id")
+	projectIDs := ctx.FormStringInt64s("id")
+	var failedIssues []int64
 	for _, issue := range issues {
-		if issue.Project != nil && issue.Project.ID == projectID {
-			continue
-		}
-		if err := issues_model.IssueAssignOrRemoveProject(ctx, issue, ctx.Doer, projectID, 0); err != nil {
+		if err := issues_model.IssueAssignOrRemoveProject(ctx, issue, ctx.Doer, projectIDs); err != nil {
 			if errors.Is(err, util.ErrPermissionDenied) {
+				failedIssues = append(failedIssues, issue.ID)
 				continue
 			}
 			ctx.ServerError("IssueAssignOrRemoveProject", err)
@@ -461,6 +461,10 @@ func UpdateIssueProject(ctx *context.Context) {
 		}
 	}
 
+	if len(failedIssues) > 0 {
+		log.Warn("Failed to assign projects to %d issues due to permission denied: %v", len(failedIssues), failedIssues)
+	}
+
 	ctx.JSONOK()
 }
 
@@ -477,12 +481,12 @@ func UpdateIssueProjectColumn(ctx *context.Context) {
 		return
 	}
 
-	if err := issue.LoadProject(ctx); err != nil {
-		ctx.ServerError("LoadProject", err)
+	if err := issue.LoadProjects(ctx); err != nil {
+		ctx.ServerError("LoadProjects", err)
 		return
 	}
 
-	issueProjects := []*project_model.Project{issue.Project} // TODO: this is for the multiple project support in the future
+	issueProjects := issue.Projects
 
 	// it must make sure the requested column is in this issue's projects
 	var columnProject *project_model.Project

routers/web/repo/pull.go

@@ -1301,7 +1301,7 @@ func CompareAndPullRequestPost(ctx *context.Context) {
 		return
 	}
 
-	labelIDs, assigneeIDs, milestoneID, projectID := validateRet.LabelIDs, validateRet.AssigneeIDs, validateRet.MilestoneID, validateRet.ProjectID
+	labelIDs, assigneeIDs, milestoneID, projectIDs := validateRet.LabelIDs, validateRet.AssigneeIDs, validateRet.MilestoneID, validateRet.ProjectIDs
 
 	var attachments []string
 	if setting.Attachment.Enabled {
@@ -1368,7 +1368,7 @@ func CompareAndPullRequestPost(ctx *context.Context) {
 		AssigneeIDs:     assigneeIDs,
 		Reviewers:       validateRet.Reviewers,
 		TeamReviewers:   validateRet.TeamReviewers,
-		ProjectID:       projectID,
+		ProjectIDs:      projectIDs,
 	}
 	if err := pull_service.NewPullRequest(ctx, prOpts); err != nil {
 		switch {

services/context/base_form.go

@@ -7,6 +7,7 @@ import (
 	"strconv"
 	"strings"
 
+	"code.gitea.io/gitea/modules/base"
 	"code.gitea.io/gitea/modules/optional"
 	"code.gitea.io/gitea/modules/util"
 )
@@ -35,6 +36,11 @@ func (b *Base) FormStrings(key string) []string {
 	return nil
 }
 
+func (b *Base) FormStringInt64s(key string) []int64 {
+	vals, _ := base.StringsToInt64s(strings.Split(b.FormString(key), ","))
+	return vals
+}
+
 // FormTrim returns the first value for the provided key in the form as a space trimmed string
 func (b *Base) FormTrim(key string) string {
 	return strings.TrimSpace(b.Req.FormValue(key))

services/convert/issue.go

@@ -95,6 +95,13 @@ func toIssue(ctx context.Context, doer *user_model.User, issue *issues_model.Iss
 		apiIssue.Milestone = ToAPIMilestone(issue.Milestone)
 	}
 
+	if err := issue.LoadProjects(ctx); err != nil {
+		return &api.Issue{}
+	}
+	if len(issue.Projects) > 0 {
+		apiIssue.Projects = ToAPIProjectList(issue.Projects)
+	}
+
 	if err := issue.LoadAssignees(ctx); err != nil {
 		return &api.Issue{}
 	}

services/convert/project.go

@@ -0,0 +1,37 @@
+// Copyright 2026 The Gitea Authors. All rights reserved.
+// SPDX-License-Identifier: MIT
+
+package convert
+
+import (
+	project_model "code.gitea.io/gitea/models/project"
+	api "code.gitea.io/gitea/modules/structs"
+)
+
+// ToAPIProject converts a Project to API format
+func ToAPIProject(p *project_model.Project) *api.Project {
+	apiProject := &api.Project{
+		ID:          p.ID,
+		Title:       p.Title,
+		Description: p.Description,
+		OwnerID:     p.OwnerID,
+		RepoID:      p.RepoID,
+		CreatorID:   p.CreatorID,
+		IsClosed:    p.IsClosed,
+		Created:     p.CreatedUnix.AsTime(),
+		Updated:     p.UpdatedUnix.AsTime(),
+	}
+	if p.IsClosed && p.ClosedDateUnix > 0 {
+		apiProject.Closed = p.ClosedDateUnix.AsTimePtr()
+	}
+	return apiProject
+}
+
+// ToAPIProjectList converts a list of Projects to API format
+func ToAPIProjectList(projects []*project_model.Project) []*api.Project {
+	result := make([]*api.Project, len(projects))
+	for i := range projects {
+		result[i] = ToAPIProject(projects[i])
+	}
+	return result
+}

services/forms/repo_form.go

@@ -412,12 +412,10 @@ func (f *NewPackagistHookForm) Validate(req *http.Request, errs binding.Errors)
 // CreateIssueForm form for creating issue
 type CreateIssueForm struct {
 	Title               string `binding:"Required;MaxSize(255)"`
-	LabelIDs            string `form:"label_ids"`
 	AssigneeIDs         string `form:"assignee_ids"`
 	ReviewerIDs         string `form:"reviewer_ids"`
 	Ref                 string `form:"ref"`
 	MilestoneID         int64
-	ProjectID           int64
 	Content             string
 	Files               []string
 	AllowMaintainerEdit bool

services/issue/issue.go

@@ -23,7 +23,7 @@ import (
 )
 
 // NewIssue creates new issue with labels for repository.
-func NewIssue(ctx context.Context, repo *repo_model.Repository, issue *issues_model.Issue, labelIDs []int64, uuids []string, assigneeIDs []int64, projectID int64) error {
+func NewIssue(ctx context.Context, repo *repo_model.Repository, issue *issues_model.Issue, labelIDs []int64, uuids []string, assigneeIDs, projectIDs []int64) error {
 	if err := issue.LoadPoster(ctx); err != nil {
 		return err
 	}
@@ -41,8 +41,9 @@ func NewIssue(ctx context.Context, repo *repo_model.Repository, issue *issues_mo
 				return err
 			}
 		}
-		if projectID > 0 {
-			if err := issues_model.IssueAssignOrRemoveProject(ctx, issue, issue.Poster, projectID, 0); err != nil {
+		if len(projectIDs) > 0 {
+			err := issues_model.IssueAssignOrRemoveProject(ctx, issue, issue.Poster, projectIDs)
+			if err != nil {
 				return err
 			}
 		}

services/projects/issue.go

@@ -59,11 +59,13 @@ func MoveIssuesOnProjectColumn(ctx context.Context, doer *user_model.User, colum
 				continue
 			}
 
-			projectColumnID, err := curIssue.ProjectColumnID(ctx)
+			projectColumnMap, err := curIssue.ProjectColumnMap(ctx)
 			if err != nil {
 				return err
 			}
 
+			projectColumnID := projectColumnMap[column.ProjectID]
+
 			if projectColumnID != column.ID {
 				// add timeline to issue
 				if _, err := issues_model.CreateComment(ctx, &issues_model.CreateCommentOptions{
@@ -80,7 +82,16 @@ func MoveIssuesOnProjectColumn(ctx context.Context, doer *user_model.User, colum
 				}
 			}
 
-			_, err = db.Exec(ctx, "UPDATE `project_issue` SET project_board_id=?, sorting=? WHERE issue_id=?", column.ID, sorting, issueID)
+			// Update the column and sorting for this specific issue in this specific project.
+			// IMPORTANT: The WHERE clause must include both issue_id AND project_id to ensure
+			// that moving an issue's column in one project doesn't affect its column in other
+			// projects when the issue is assigned to multiple projects.
+			_, err = db.GetEngine(ctx).Table("project_issue").
+				Where("issue_id = ? AND project_id = ?", issueID, column.ProjectID).
+				Update(map[string]any{
+					"project_board_id": column.ID,
+					"sorting":          sorting,
+				})
 			if err != nil {
 				return err
 			}
@@ -117,7 +128,7 @@ func LoadIssuesAssigneesForProject(ctx context.Context, issuesMap map[int64]issu
 // LoadIssuesFromProject load issues assigned to each project column inside the given project
 func LoadIssuesFromProject(ctx context.Context, project *project_model.Project, opts *issues_model.IssuesOptions) (results map[int64]issues_model.IssueList, _ error) {
 	issueList, err := issues_model.Issues(ctx, opts.Copy(func(o *issues_model.IssuesOptions) {
-		o.ProjectID = project.ID
+		o.ProjectIDs = []int64{project.ID}
 		o.SortType = "project-column-sorting"
 	}))
 	if err != nil {
@@ -211,10 +222,10 @@ func LoadIssueNumbersForProject(ctx context.Context, project *project_model.Proj
 
 	// for user or org projects, we need to check access permissions
 	opts := issues_model.IssuesOptions{
-		ProjectID: project.ID,
-		Doer:      doer,
-		AllPublic: doer == nil,
-		Owner:     project.Owner,
+		ProjectIDs: []int64{project.ID},
+		Doer:       doer,
+		AllPublic:  doer == nil,
+		Owner:      project.Owner,
 	}
 
 	var err error

services/projects/issue_test.go

@@ -102,28 +102,18 @@ func Test_Projects(t *testing.T) {
 			assert.NoError(t, err)
 		}()
 
-		column1 := project_model.Column{
-			Title:     "column 1",
-			ProjectID: project1.ID,
-		}
-		err = project_model.NewColumn(t.Context(), &column1)
-		assert.NoError(t, err)
-
-		column2 := project_model.Column{
-			Title:     "column 2",
-			ProjectID: project1.ID,
-		}
-		err = project_model.NewColumn(t.Context(), &column2)
+		// Get the default column created by the template (issues will be assigned here)
+		defaultColumn, err := project1.MustDefaultColumn(t.Context())
 		assert.NoError(t, err)
 
 		// issue 6 belongs to private repo 3 under org 3
 		issue6 := unittest.AssertExistsAndLoadBean(t, &issues_model.Issue{ID: 6})
-		err = issues_model.IssueAssignOrRemoveProject(t.Context(), issue6, user2, project1.ID, column1.ID)
+		err = issues_model.IssueAssignOrRemoveProject(t.Context(), issue6, user2, []int64{project1.ID})
 		assert.NoError(t, err)
 
 		// issue 16 belongs to public repo 16 under org 3
 		issue16 := unittest.AssertExistsAndLoadBean(t, &issues_model.Issue{ID: 16})
-		err = issues_model.IssueAssignOrRemoveProject(t.Context(), issue16, user2, project1.ID, column1.ID)
+		err = issues_model.IssueAssignOrRemoveProject(t.Context(), issue16, user2, []int64{project1.ID})
 		assert.NoError(t, err)
 
 		projects, err := db.Find[project_model.Project](t.Context(), project_model.SearchOptions{
@@ -139,8 +129,8 @@ func Test_Projects(t *testing.T) {
 				Doer:  userAdmin,
 			})
 			assert.NoError(t, err)
-			assert.Len(t, columnIssues, 1)             // column1 has 2 issues, 6 will not contains here because 0 issues
-			assert.Len(t, columnIssues[column1.ID], 2) // user2 can visit both issues, one from public repository one from private repository
+			assert.Len(t, columnIssues, 1)                   // default column has 2 issues
+			assert.Len(t, columnIssues[defaultColumn.ID], 2) // admin can visit both issues, one from public repository one from private repository
 		})
 
 		t.Run("Anonymous user", func(t *testing.T) {
@@ -149,7 +139,7 @@ func Test_Projects(t *testing.T) {
 			})
 			assert.NoError(t, err)
 			assert.Len(t, columnIssues, 1)
-			assert.Len(t, columnIssues[column1.ID], 1) // anonymous user can only visit public repo issues
+			assert.Len(t, columnIssues[defaultColumn.ID], 1) // anonymous user can only visit public repo issues
 		})
 
 		t.Run("Authenticated user with no permission to the private repo", func(t *testing.T) {
@@ -159,7 +149,7 @@ func Test_Projects(t *testing.T) {
 			})
 			assert.NoError(t, err)
 			assert.Len(t, columnIssues, 1)
-			assert.Len(t, columnIssues[column1.ID], 1) // user4 can only visit public repo issues
+			assert.Len(t, columnIssues[defaultColumn.ID], 1) // user2 can only visit public repo issues
 		})
 	})
 

services/pull/pull.go

@@ -50,7 +50,7 @@ type NewPullRequestOptions struct {
 	AssigneeIDs     []int64
 	Reviewers       []*user_model.User
 	TeamReviewers   []*organization.Team
-	ProjectID       int64
+	ProjectIDs      []int64
 }
 
 // NewPullRequest creates new pull request with labels for repository.
@@ -110,8 +110,8 @@ func NewPullRequest(ctx context.Context, opts *NewPullRequestOptions) error {
 			assigneeCommentMap[assigneeID] = comment
 		}
 
-		if opts.ProjectID > 0 && canAssignProject {
-			if err := issues_model.IssueAssignOrRemoveProject(ctx, issue, issue.Poster, opts.ProjectID, 0); err != nil {
+		if len(opts.ProjectIDs) > 0 && canAssignProject {
+			if err := issues_model.IssueAssignOrRemoveProject(ctx, issue, issue.Poster, opts.ProjectIDs); err != nil {
 				return err
 			}
 		}

templates/repo/issue/filter_list.tmpl

@@ -1,4 +1,8 @@
-{{$queryLink := QueryBuild "?" "q" $.Keyword "type" $.ViewType "sort" $.SortType "state" $.State "labels" $.SelectLabels "milestone" $.MilestoneID "project" $.ProjectID "assignee" $.AssigneeID "poster" $.PosterUsername "archived_labels" (Iif $.ShowArchivedLabels "true")}}
+{{$projectIDs := $.ProjectIDs}}
+{{$projectIDsQuery := SliceUtils.JoinInt64 $projectIDs}}
+{{$queryLink := QueryBuild "?" "q" $.Keyword "type" $.ViewType "sort" $.SortType "state" $.State "labels" $.SelectLabels "milestone" $.MilestoneID "project" $projectIDsQuery "assignee" $.AssigneeID "poster" $.PosterUsername "archived_labels" (Iif $.ShowArchivedLabels "true")}}
+{{$showAllProjects := not $projectIDs}}
+{{$showNoProjectSelected := and (eq (len $projectIDs) 1) (eq (index $projectIDs 0) -1)}}
 
 {{template "repo/issue/filter_item_label" dict "Labels" .Labels "QueryLink" $queryLink "SupportArchivedLabel" true}}
 
@@ -12,26 +16,28 @@
 {{end}}
 
 <!-- Project -->
-<div class="item ui dropdown jump {{if not (or .OpenProjects .ClosedProjects)}}disabled{{end}}">
+<div class="item ui dropdown jump project-filter {{if not (or .OpenProjects .ClosedProjects)}}disabled{{end}}">
 	<span class="text">
 		{{ctx.Locale.Tr "repo.issues.filter_project"}}
 	</span>
 	{{svg "octicon-triangle-down" 14 "dropdown icon"}}
-	<div class="menu">
+	<div class="menu flex-items-menu">
 		<div class="ui icon search input">
 			<i class="icon">{{svg "octicon-search" 16}}</i>
 			<input type="text" placeholder="{{ctx.Locale.Tr "repo.issues.filter_project"}}">
 		</div>
-		<a class="{{if not .ProjectID}}active selected {{end}}item" href="{{QueryBuild $queryLink "project" NIL}}">{{ctx.Locale.Tr "repo.issues.filter_project_all"}}</a>
-		<a class="{{if eq .ProjectID -1}}active selected {{end}}item" href="{{QueryBuild $queryLink "project" -1}}">{{ctx.Locale.Tr "repo.issues.filter_project_none"}}</a>
+		<a class="item {{if $showAllProjects}}selected{{end}}" href="{{QueryBuild $queryLink "project" NIL}}">{{ctx.Locale.Tr "repo.issues.filter_project_all"}}</a>
+		<a class="item {{if $showNoProjectSelected}}selected{{end}}" href="{{QueryBuild $queryLink "project" -1}}">{{ctx.Locale.Tr "repo.issues.filter_project_none"}}</a>
 		{{if .OpenProjects}}
 			<div class="divider"></div>
 			<div class="header">
 				{{ctx.Locale.Tr "repo.issues.new.open_projects"}}
 			</div>
-			{{range .OpenProjects}}
-				<a class="{{if $.ProjectID}}{{if eq $.ProjectID .ID}}active selected{{end}}{{end}} item tw-flex" href="{{QueryBuild $queryLink "project" .ID}}">
-					{{svg .IconName 18 "tw-mr-2 tw-shrink-0"}}<span class="gt-ellipsis">{{.Title}}</span>
+			{{range $project := .OpenProjects}}
+				{{$toggle := SliceUtils.JoinToggleIDs $projectIDs $project.ID}}
+				{{/* FIXME: ISSUE-MULTIPLE-PROJECTS-FILTER: no multiple project filter support yet. If the support comes, here it should use "&project=${toggle.ToggledIDs}" */}}
+				<a class="item {{if $toggle.IsIncluded}}selected{{end}}" href="{{QueryBuild $queryLink "project" $project.ID}}">
+					{{svg $project.IconName}}<span class="gt-ellipsis">{{$project.Title}}</span>
 				</a>
 			{{end}}
 		{{end}}
@@ -40,9 +46,11 @@
 			<div class="header">
 				{{ctx.Locale.Tr "repo.issues.new.closed_projects"}}
 			</div>
-			{{range .ClosedProjects}}
-				<a class="{{if $.ProjectID}}{{if eq $.ProjectID .ID}}active selected{{end}}{{end}} item" href="{{QueryBuild $queryLink "project" .ID}}">
-					{{svg .IconName 18 "tw-mr-2"}}{{.Title}}
+			{{range $project := .ClosedProjects}}
+				{{$toggle := SliceUtils.JoinToggleIDs $projectIDs $project.ID}}
+				{{/* FIXME: ISSUE-MULTIPLE-PROJECTS-FILTER: no multiple project filter support yet. If the support comes, here it should use "&project=${toggle.ToggledIDs}" */}}
+				<a class="item {{if $toggle.IsIncluded}}selected{{end}}" href="{{QueryBuild $queryLink "project" $project.ID}}">
+					{{svg $project.IconName}}<span class="gt-ellipsis">{{$project.Title}}</span>
 				</a>
 			{{end}}
 		{{end}}

templates/repo/issue/openclose.tmpl

@@ -1,9 +1,10 @@
 {{/* this tmpl is quite dirty, it should not mix unrelated things together .... need to split it in the future*/}}
 {{$allStatesLink := ""}}{{$openLink := ""}}{{$closedLink := ""}}
+{{$projectIDsQuery := SliceUtils.JoinInt64 $.ProjectIDs}}
 {{if .PageIsMilestones}}
 	{{$allStatesLink = QueryBuild "?" "q" $.Keyword "sort" $.SortType "state" "all"}}
 {{else}}
-	{{$allStatesLink = QueryBuild "?" "q" $.Keyword "type" $.ViewType "sort" $.SortType "state" "all" "labels" $.SelectLabels "milestone" $.MilestoneID "project" $.ProjectID "assignee" $.AssigneeID "poster" $.PosterUsername "archived_labels" (Iif $.ShowArchivedLabels "true")}}
+	{{$allStatesLink = QueryBuild "?" "q" $.Keyword "type" $.ViewType "sort" $.SortType "state" "all" "labels" $.SelectLabels "milestone" $.MilestoneID "project" $projectIDsQuery "assignee" $.AssigneeID "poster" $.PosterUsername "archived_labels" (Iif $.ShowArchivedLabels "true")}}
 {{end}}
 {{$openLink = QueryBuild $allStatesLink "state" "open"}}
 {{$closedLink = QueryBuild $allStatesLink "state" "closed"}}

templates/repo/issue/search.tmpl

@@ -5,7 +5,7 @@
 			<input type="hidden" name="type" value="{{$.ViewType}}">
 			<input type="hidden" name="labels" value="{{$.SelectLabels}}">
 			<input type="hidden" name="milestone" value="{{$.MilestoneID}}">
-			<input type="hidden" name="project" value="{{$.ProjectID}}">
+			<input type="hidden" name="project" value="{{SliceUtils.JoinInt64 $.ProjectIDs}}">
 			<input type="hidden" name="assignee" value="{{$.AssigneeID}}">
 			<input type="hidden" name="poster" value="{{$.PosterUsername}}">
 			<input type="hidden" name="sort" value="{{$.SortType}}">

templates/repo/issue/sidebar/project_list.tmpl

@@ -3,10 +3,10 @@
 <div class="divider"></div>
 
 {{/* project selector */}}
-<div class="issue-sidebar-combo sidebar-project-combo" data-selection-mode="single" data-update-algo="all"
+<div class="issue-sidebar-combo sidebar-project-combo" data-selection-mode="multiple" data-update-algo="all"
 		{{if $pageMeta.Issue}}data-update-url="{{$pageMeta.RepoLink}}/issues/projects?issue_ids={{$pageMeta.Issue.ID}}"{{end}}
 >
-	<input class="combo-value" name="project_id" type="hidden" value="{{if and $pageMeta.CanModifyIssueOrPull $data.SelectedProjectIDs}}{{index $data.SelectedProjectIDs 0}}{{end}}">
+	<input class="combo-value" name="project_ids" type="hidden" value="{{SliceUtils.JoinInt64 $data.SelectedProjectIDs}}">
 	<div class="ui dropdown full-width {{if not $pageMeta.CanModifyIssueOrPull}}disabled{{end}}">
 		<a class="fixed-text muted">
 			<strong>{{ctx.Locale.Tr "repo.issues.new.projects"}}</strong> {{if $pageMeta.CanModifyIssueOrPull}}{{svg "octicon-gear"}}{{end}}
@@ -26,7 +26,7 @@
 					{{range $data.OpenProjects}}
 						<a class="item muted" data-value="{{.ID}}" href="{{.Link ctx}}">
 							<span class="item-check-mark">{{svg "octicon-check"}}</span>
-							{{svg .IconName 18}}<span class="tw-flex-1 tw-break-anywhere">{{.Title}}</span>
+							{{svg .IconName 18}}<span class="tw-flex-1 gt-ellipsis">{{.Title}}</span>
 						</a>
 					{{end}}
 				{{end}}
@@ -36,44 +36,37 @@
 					{{range $data.ClosedProjects}}
 						<a class="item muted" data-value="{{.ID}}" href="{{.Link ctx}}">
 							<span class="item-check-mark">{{svg "octicon-check"}}</span>
-							{{svg .IconName 18}}<span class="tw-flex-1 tw-break-anywhere">{{.Title}}</span>
+							{{svg .IconName 18}}<span class="tw-flex-1 gt-ellipsis">{{.Title}}</span>
 						</a>
 					{{end}}
 				{{end}}
 			</div>
 		</div>
 	</div>
-</div>
 
-{{/* project cards (column selectors) */}}
-{{if not $data.ProjectCards}}
-	<div class="ui list">
-		<div class="item empty-list">{{ctx.Locale.Tr "repo.issues.new.no_projects"}}</div>
-	</div>
-{{else}}
-	<div class="flex-relaxed-list">
+	{{/* project cards (column selectors) */}}
+	<div class="ui list tw-my-2 flex-relaxed-list issue-sidebar-project-cards" data-combo-list-inited="true">
+		<div class="item empty-list {{if $data.ProjectCards}}tw-hidden{{end}}">{{ctx.Locale.Tr "repo.issues.new.no_projects"}}</div>
 	{{range $card := $data.ProjectCards}}
 		{{$selectedColumn := $card.SelectedColumn}}
-		<div class="item sidebar-project-card">
-			<div class="tw-mb-1">
-				<a class="suppressed flex-text-block" href="{{$card.Project.Link ctx}}">
-					{{svg $card.Project.IconName 16}}
-					<span class="gt-ellipsis">{{$card.Project.Title}}</span>
-				</a>
-			</div>
-			{{if $pageMeta.CanModifyIssueOrPull}}
+		{{/* only show a "project column card" if the selected column exists, otherwise only show the project title */}}
+		<div class="item {{if $selectedColumn}}sidebar-project-card{{end}}">
+			<a class="suppressed flex-text-block" href="{{$card.Project.Link ctx}}">
+				{{svg $card.Project.IconName 16}} <span class="gt-ellipsis">{{$card.Project.Title}}</span>
+			</a>
+			{{if and $selectedColumn $pageMeta.CanModifyIssueOrPull}}
 				<div class="issue-sidebar-combo sidebar-project-column-combo" data-selection-mode="single" data-update-algo="all"
 					data-update-url="{{$pageMeta.RepoLink}}/issues/projects/column?issue_id={{$pageMeta.Issue.ID}}"
 				>
 					<input class="combo-value" name="column_id" type="hidden" value="{{if $selectedColumn}}{{$selectedColumn.ID}}{{end}}">
 					<div class="ui dropdown full-width">
 						<div class="flex-text-block tw-ml-[16px]">{{/* align with the "project" icon */}}
-							<div class="interact-bg tw-px-2 tw-py-1 tw-rounded flex-text-block">
+							<div class="interact-bg tw-px-2 tw-py-1 tw-rounded flex-text-block fixed-text">
 								{{if $selectedColumn}}
 									{{if $card.SelectedColumn.Color}}<span class="color-icon icon-size-8" style="background-color: {{$card.SelectedColumn.Color}}"></span>{{end}}
-									<div class="gt-ellipsis" data-testid="sidebar-project-column-text">{{$card.SelectedColumn.Title}}</div>
+									<div class="gt-ellipsis">{{$card.SelectedColumn.Title}}</div>
 								{{else}}
-									<div class="gt-ellipsis" data-testid="sidebar-project-column-text">{{ctx.Locale.Tr "repo.issues.new.no_column"}}</div>
+									<div class="gt-ellipsis">{{ctx.Locale.Tr "repo.issues.new.no_column"}}</div>
 								{{end}}
 								{{svg "octicon-triangle-down" 14}}
 							</div>
@@ -98,4 +91,4 @@
 		</div>
 	{{end}}
 	</div>
-{{end}}
+</div>

templates/shared/issuelist.tmpl

@@ -76,10 +76,10 @@
 							<span class="gt-ellipsis">{{.Milestone.Name}}</span>
 						</a>
 					{{end}}
-					{{if .Project}}
-						<a class="project flex-text-inline tw-max-w-[300px]" href="{{.Project.Link ctx}}">
-							{{svg .Project.IconName 14}}
-							<span class="gt-ellipsis">{{.Project.Title}}</span>
+					{{range $project := .Projects}}
+						<a class="project flex-text-inline tw-max-w-[300px]" href="{{$project.Link ctx}}">
+							{{svg $project.IconName 14}}
+							<span class="gt-ellipsis">{{$project.Title}}</span>
 						</a>
 					{{end}}
 					{{if .Ref}}{{/* TODO: RemoveIssueRef: see "repo/issue/branch_selector_field.tmpl" */}}

templates/swagger/v1_json.tmpl

@@ -23841,6 +23841,15 @@
           "format": "int64",
           "x-go-name": "Milestone"
         },
+        "projects": {
+          "description": "list of project ids",
+          "type": "array",
+          "items": {
+            "type": "integer",
+            "format": "int64"
+          },
+          "x-go-name": "Projects"
+        },
         "ref": {
           "type": "string",
           "x-go-name": "Ref"
@@ -25098,6 +25107,15 @@
           "format": "int64",
           "x-go-name": "Milestone"
         },
+        "projects": {
+          "description": "list of project ids to set (replaces existing projects)",
+          "type": "array",
+          "items": {
+            "type": "integer",
+            "format": "int64"
+          },
+          "x-go-name": "Projects"
+        },
         "ref": {
           "type": "string",
           "x-go-name": "Ref"
@@ -26622,6 +26640,13 @@
           "format": "int64",
           "x-go-name": "PinOrder"
         },
+        "projects": {
+          "type": "array",
+          "items": {
+            "$ref": "#/definitions/Project"
+          },
+          "x-go-name": "Projects"
+        },
         "pull_request": {
           "$ref": "#/definitions/PullRequestMeta"
         },
@@ -27974,6 +27999,67 @@
       },
       "x-go-package": "code.gitea.io/gitea/modules/structs"
     },
+    "Project": {
+      "description": "Project represents a project",
+      "type": "object",
+      "properties": {
+        "closed_at": {
+          "type": "string",
+          "format": "date-time",
+          "x-go-name": "Closed"
+        },
+        "created_at": {
+          "type": "string",
+          "format": "date-time",
+          "x-go-name": "Created"
+        },
+        "creator_id": {
+          "description": "CreatorID is the user who created the project",
+          "type": "integer",
+          "format": "int64",
+          "x-go-name": "CreatorID"
+        },
+        "description": {
+          "description": "Description provides details about the project",
+          "type": "string",
+          "x-go-name": "Description"
+        },
+        "id": {
+          "description": "ID is the unique identifier for the project",
+          "type": "integer",
+          "format": "int64",
+          "x-go-name": "ID"
+        },
+        "is_closed": {
+          "description": "IsClosed indicates if the project is closed",
+          "type": "boolean",
+          "x-go-name": "IsClosed"
+        },
+        "owner_id": {
+          "description": "OwnerID is the owner of the project (for org-level projects)",
+          "type": "integer",
+          "format": "int64",
+          "x-go-name": "OwnerID"
+        },
+        "repo_id": {
+          "description": "RepoID is the repository this project belongs to (for repo-level projects)",
+          "type": "integer",
+          "format": "int64",
+          "x-go-name": "RepoID"
+        },
+        "title": {
+          "description": "Title is the title of the project",
+          "type": "string",
+          "x-go-name": "Title"
+        },
+        "updated_at": {
+          "type": "string",
+          "format": "date-time",
+          "x-go-name": "Updated"
+        }
+      },
+      "x-go-package": "code.gitea.io/gitea/modules/structs"
+    },
     "PublicKey": {
       "description": "PublicKey publickey is a user key to push code to repository",
       "type": "object",

templates/swagger/v1_openapi3_json.tmpl

@@ -4102,6 +4102,15 @@
             "type": "integer",
             "x-go-name": "Milestone"
           },
+          "projects": {
+            "description": "list of project ids",
+            "items": {
+              "format": "int64",
+              "type": "integer"
+            },
+            "type": "array",
+            "x-go-name": "Projects"
+          },
           "ref": {
             "type": "string",
             "x-go-name": "Ref"
@@ -5330,6 +5339,15 @@
             "type": "integer",
             "x-go-name": "Milestone"
           },
+          "projects": {
+            "description": "list of project ids to set (replaces existing projects)",
+            "items": {
+              "format": "int64",
+              "type": "integer"
+            },
+            "type": "array",
+            "x-go-name": "Projects"
+          },
           "ref": {
             "type": "string",
             "x-go-name": "Ref"
@@ -6849,6 +6867,13 @@
             "type": "integer",
             "x-go-name": "PinOrder"
           },
+          "projects": {
+            "items": {
+              "$ref": "#/components/schemas/Project"
+            },
+            "type": "array",
+            "x-go-name": "Projects"
+          },
           "pull_request": {
             "$ref": "#/components/schemas/PullRequestMeta"
           },
@@ -8215,6 +8240,67 @@
         "type": "object",
         "x-go-package": "code.gitea.io/gitea/modules/structs"
       },
+      "Project": {
+        "description": "Project represents a project",
+        "properties": {
+          "closed_at": {
+            "format": "date-time",
+            "type": "string",
+            "x-go-name": "Closed"
+          },
+          "created_at": {
+            "format": "date-time",
+            "type": "string",
+            "x-go-name": "Created"
+          },
+          "creator_id": {
+            "description": "CreatorID is the user who created the project",
+            "format": "int64",
+            "type": "integer",
+            "x-go-name": "CreatorID"
+          },
+          "description": {
+            "description": "Description provides details about the project",
+            "type": "string",
+            "x-go-name": "Description"
+          },
+          "id": {
+            "description": "ID is the unique identifier for the project",
+            "format": "int64",
+            "type": "integer",
+            "x-go-name": "ID"
+          },
+          "is_closed": {
+            "description": "IsClosed indicates if the project is closed",
+            "type": "boolean",
+            "x-go-name": "IsClosed"
+          },
+          "owner_id": {
+            "description": "OwnerID is the owner of the project (for org-level projects)",
+            "format": "int64",
+            "type": "integer",
+            "x-go-name": "OwnerID"
+          },
+          "repo_id": {
+            "description": "RepoID is the repository this project belongs to (for repo-level projects)",
+            "format": "int64",
+            "type": "integer",
+            "x-go-name": "RepoID"
+          },
+          "title": {
+            "description": "Title is the title of the project",
+            "type": "string",
+            "x-go-name": "Title"
+          },
+          "updated_at": {
+            "format": "date-time",
+            "type": "string",
+            "x-go-name": "Updated"
+          }
+        },
+        "type": "object",
+        "x-go-package": "code.gitea.io/gitea/modules/structs"
+      },
       "PublicKey": {
         "description": "PublicKey publickey is a user key to push code to repository",
         "properties": {

tests/e2e/events.test.ts

@@ -20,7 +20,7 @@ test.describe('events', () => {
     await expect(badge).toBeHidden();
 
     // Create issue as another user — this generates a notification delivered via server push
-    await apiCreateIssue(request, owner, repoName, {title: 'events notification test', headers: apiUserHeaders(commenter)});
+    await apiCreateIssue(request, {owner, repo: repoName, title: 'events notification test', headers: apiUserHeaders(commenter)});
 
     // Wait for the notification badge to appear via server event
     await expect(badge).toBeVisible({timeout: 15000 * timeoutFactor});
@@ -37,7 +37,7 @@ test.describe('events', () => {
       loginUser(page, name),
       (async () => {
         await apiCreateRepo(request, {name, headers});
-        await apiCreateIssue(request, name, name, {title: 'events stopwatch test', headers});
+        await apiCreateIssue(request, {owner: name, repo: name, title: 'events stopwatch test', headers});
         await apiStartStopwatch(request, name, name, 1, {headers});
       })(),
     ]);

tests/e2e/issue-project.test.ts

@@ -1,6 +1,6 @@
 import {env} from 'node:process';
 import {test, expect} from '@playwright/test';
-import {login, apiCreateRepo, apiCreateIssue, createProjectColumn, randomString} from './utils.ts';
+import {login, apiCreateRepo, apiCreateIssue, apiDeleteRepo, createProject, createProjectColumn, randomString} from './utils.ts';
 
 test('assign issue to project and change column', async ({page}) => {
   const repoName = `e2e-issue-project-${randomString(8)}`;
@@ -16,14 +16,428 @@ test('assign issue to project and change column', async ({page}) => {
   // columns created via POST because the web UI uses modals that are hard to drive
   await Promise.all([
     ...['Backlog', 'In Progress', 'Done'].map((title) => createProjectColumn(page.request, user, repoName, projectID, title)),
-    apiCreateIssue(page.request, user, repoName, {title: 'Column picker test'}),
+    apiCreateIssue(page.request, {owner: user, repo: repoName, title: 'Column picker test'}),
   ]);
   await page.goto(`/${user}/${repoName}/issues/1`);
-  await page.locator('.sidebar-project-combo .ui.dropdown').click();
-  await page.locator('.sidebar-project-combo .menu a.item', {hasText: 'Kanban Board'}).click();
-  const columnCombo = page.locator('.sidebar-project-column-combo');
-  await expect(columnCombo).toBeVisible();
-  await columnCombo.locator('.ui.dropdown').click();
-  await columnCombo.locator('.menu a.item', {hasText: 'In Progress'}).click();
-  await expect(columnCombo.getByTestId('sidebar-project-column-text')).toHaveText('In Progress');
+  await page.locator('.sidebar-project-combo > .ui.dropdown').click();
+  await page.locator('.sidebar-project-combo > .ui.dropdown .item:has-text("Kanban Board")').click();
+  await page.locator('.sidebar-project-combo > .ui.dropdown').click();
+  await page.locator('.sidebar-project-column-combo .ui.dropdown').click();
+  await page.locator('.sidebar-project-column-combo .ui.dropdown .item:has-text("In Progress")').click();
+  await expect(page.locator('.sidebar-project-column-combo .ui.dropdown .fixed-text')).toHaveText('In Progress');
+  await apiDeleteRepo(page.request, user, repoName);
+});
+
+test('create a project', async ({page}) => {
+  const repoName = `e2e-project-repo-${Date.now()}`;
+  const projectTitle = 'Test Project';
+
+  await login(page);
+  await apiCreateRepo(page.request, {name: repoName});
+
+  try {
+    // Navigate to new project page
+    await page.goto(`/${env.GITEA_TEST_E2E_USER}/${repoName}/projects/new`);
+
+    // Fill in project details
+    await page.getByLabel('Title').fill(projectTitle);
+
+    // Submit the form
+    await page.getByRole('button', {name: 'Create Project'}).click();
+
+    // Verify project was created by checking we're redirected to the projects list
+    await expect(page).toHaveURL(new RegExp(`/${env.GITEA_TEST_E2E_USER}/${repoName}/projects$`));
+
+    // Verify the project appears in the list
+    await expect(page.locator('.milestone-list')).toContainText(projectTitle);
+  } finally {
+    await apiDeleteRepo(page.request, env.GITEA_TEST_E2E_USER, repoName);
+  }
+});
+
+test('assign issue to multiple projects via sidebar', async ({page}) => {
+  const repoName = `e2e-multi-project-${Date.now()}`;
+  const project1Title = 'Project Alpha';
+  const project2Title = 'Project Beta';
+  const issueTitle = 'Test issue for multiple projects';
+
+  await login(page);
+  await apiCreateRepo(page.request, {name: repoName});
+
+  try {
+    // Create two projects via UI
+    const project1 = await createProject(page, {
+      owner: env.GITEA_TEST_E2E_USER,
+      repo: repoName,
+      title: project1Title,
+    });
+    const project2 = await createProject(page, {
+      owner: env.GITEA_TEST_E2E_USER,
+      repo: repoName,
+      title: project2Title,
+    });
+
+    // Create an issue without any project
+    const issue = await apiCreateIssue(page.request, {
+      owner: env.GITEA_TEST_E2E_USER,
+      repo: repoName,
+      title: issueTitle,
+    });
+
+    // Navigate to the issue page
+    await page.goto(`/${env.GITEA_TEST_E2E_USER}/${repoName}/issues/${issue.index}`);
+
+    // Open the projects dropdown in the sidebar
+    await page.locator('.sidebar-project-combo > .ui.dropdown').click();
+
+    // Select both projects
+    await page.locator(`.sidebar-project-combo > .ui.dropdown .item[data-value="${project1.id}"]`).click();
+    await page.locator(`.sidebar-project-combo > .ui.dropdown .item[data-value="${project2.id}"]`).click();
+
+    // Click outside to close the dropdown and trigger the update
+    await page.locator('.issue-content-left').click();
+
+    // Verify both projects are shown in the sidebar
+    await expect(page.locator(`.item.sidebar-project-card:has-text("${project1Title}")`)).toBeVisible();
+    await expect(page.locator(`.item.sidebar-project-card:has-text("${project2Title}")`)).toBeVisible();
+  } finally {
+    await apiDeleteRepo(page.request, env.GITEA_TEST_E2E_USER, repoName);
+  }
+});
+
+test('create issue with multiple projects pre-selected', async ({page}) => {
+  const repoName = `e2e-issue-multi-proj-${Date.now()}`;
+  const project1Title = 'Project One';
+  const project2Title = 'Project Two';
+  const issueTitle = 'Issue with multiple projects';
+
+  await login(page);
+  await apiCreateRepo(page.request, {name: repoName});
+
+  try {
+    // Create two projects via UI
+    const project1 = await createProject(page, {
+      owner: env.GITEA_TEST_E2E_USER,
+      repo: repoName,
+      title: project1Title,
+    });
+    const project2 = await createProject(page, {
+      owner: env.GITEA_TEST_E2E_USER,
+      repo: repoName,
+      title: project2Title,
+    });
+
+    // Navigate to new issue page
+    await page.goto(`/${env.GITEA_TEST_E2E_USER}/${repoName}/issues/new`);
+
+    // Fill in the issue title
+    await page.locator('input[name="title"]').fill(issueTitle);
+
+    // Open the projects dropdown
+    await page.locator('.sidebar-project-combo > .ui.dropdown').click();
+
+    // Select both projects
+    await page.locator(`.sidebar-project-combo > .ui.dropdown .item[data-value="${project1.id}"]`).click();
+    await page.locator(`.sidebar-project-combo > .ui.dropdown .item[data-value="${project2.id}"]`).click();
+
+    // Click outside to close the dropdown
+    await page.locator('.issue-content-left').click();
+
+    // Submit the form
+    await page.getByRole('button', {name: 'Create Issue'}).click();
+
+    // Wait for issue to be created and page to redirect
+    await page.waitForURL(new RegExp(`/${env.GITEA_TEST_E2E_USER}/${repoName}/issues/\\d+`));
+
+    // Verify both projects are shown in the sidebar
+    await expect(page.locator(`.item.sidebar-project-card:has-text("${project1Title}")`)).toBeVisible();
+    await expect(page.locator(`.item.sidebar-project-card:has-text("${project2Title}")`)).toBeVisible();
+  } finally {
+    await apiDeleteRepo(page.request, env.GITEA_TEST_E2E_USER, repoName);
+  }
+});
+
+test('filter issues by multiple projects in issue list', async ({page}) => {
+  const repoName = `e2e-filter-projects-${Date.now()}`;
+  const project1Title = 'Filter Project A';
+  const project2Title = 'Filter Project B';
+
+  await login(page);
+  await apiCreateRepo(page.request, {name: repoName});
+
+  try {
+    // Create two projects via UI
+    const project1 = await createProject(page, {
+      owner: env.GITEA_TEST_E2E_USER,
+      repo: repoName,
+      title: project1Title,
+    });
+    const project2 = await createProject(page, {
+      owner: env.GITEA_TEST_E2E_USER,
+      repo: repoName,
+      title: project2Title,
+    });
+
+    // Create issues: one in project1, one in project2, one in both
+    await apiCreateIssue(page.request, {
+      owner: env.GITEA_TEST_E2E_USER,
+      repo: repoName,
+      title: 'Issue in Project A only',
+      projects: [project1.id],
+    });
+    await apiCreateIssue(page.request, {
+      owner: env.GITEA_TEST_E2E_USER,
+      repo: repoName,
+      title: 'Issue in Project B only',
+      projects: [project2.id],
+    });
+    await apiCreateIssue(page.request, {
+      owner: env.GITEA_TEST_E2E_USER,
+      repo: repoName,
+      title: 'Issue in both projects',
+      projects: [project1.id, project2.id],
+    });
+    // Create an issue with no project
+    await apiCreateIssue(page.request, {
+      owner: env.GITEA_TEST_E2E_USER,
+      repo: repoName,
+      title: 'Issue with no project',
+    });
+
+    // Verify only project1 issues are visible
+    await page.goto(`/${env.GITEA_TEST_E2E_USER}/${repoName}/issues?project=${project1.id}`);
+    await expect(page.locator('#issue-list')).toContainText('Issue in Project A only');
+    await expect(page.locator('#issue-list')).toContainText('Issue in both projects');
+    await expect(page.locator('#issue-list')).not.toContainText('Issue in Project B only');
+    await expect(page.locator('#issue-list')).not.toContainText('Issue with no project');
+
+    // Verify only project2 issues are visible
+    await page.goto(`/${env.GITEA_TEST_E2E_USER}/${repoName}/issues?project=${project2.id}`);
+    await expect(page.locator('#issue-list')).toContainText('Issue in Project B only');
+    await expect(page.locator('#issue-list')).toContainText('Issue in both projects');
+    await expect(page.locator('#issue-list')).not.toContainText('Issue in Project A only');
+    await expect(page.locator('#issue-list')).not.toContainText('Issue with no project');
+  } finally {
+    await apiDeleteRepo(page.request, env.GITEA_TEST_E2E_USER, repoName);
+  }
+});
+
+test('remove issue from one project keeping others', async ({page}) => {
+  const repoName = `e2e-remove-project-${Date.now()}`;
+  const project1Title = 'Keep This Project';
+  const project2Title = 'Remove This Project';
+  const issueTitle = 'Issue to modify projects';
+
+  await login(page);
+  await apiCreateRepo(page.request, {name: repoName});
+
+  try {
+    // Create two projects via UI
+    const project1 = await createProject(page, {
+      owner: env.GITEA_TEST_E2E_USER,
+      repo: repoName,
+      title: project1Title,
+    });
+    const project2 = await createProject(page, {
+      owner: env.GITEA_TEST_E2E_USER,
+      repo: repoName,
+      title: project2Title,
+    });
+
+    // Create an issue in both projects
+    const issue = await apiCreateIssue(page.request, {
+      owner: env.GITEA_TEST_E2E_USER,
+      repo: repoName,
+      title: issueTitle,
+      projects: [project1.id, project2.id],
+    });
+
+    // Navigate to the issue page
+    await page.goto(`/${env.GITEA_TEST_E2E_USER}/${repoName}/issues/${issue.index}`);
+
+    // Verify both projects are initially shown
+    await expect(page.locator(`.item.sidebar-project-card:has-text("${project1Title}")`)).toBeVisible();
+    await expect(page.locator(`.item.sidebar-project-card.item:has-text("${project2Title}")`)).toBeVisible();
+
+    // Open the projects dropdown
+    await page.locator('.sidebar-project-combo > .ui.dropdown').click();
+
+    // Deselect project2 (click on the already selected item to deselect)
+    await page.locator(`.sidebar-project-combo > .ui.dropdown .item[data-value="${project2.id}"]`).click();
+
+    // Click outside to close the dropdown and trigger the update
+    await page.locator('.issue-content-left').click();
+
+    // Verify project1 is still shown but project2 is removed
+    await expect(page.locator(`.item.sidebar-project-card.item:has-text("${project1Title}")`)).toBeVisible();
+    await expect(page.locator(`.item.sidebar-project-card.item:has-text("${project2Title}")`)).toBeHidden();
+
+    // Reload the page to see the timeline comment
+    await page.reload();
+
+    // Verify the timeline shows "removed this from the project" comment
+    const timelineComments = page.locator('.timeline-item.event');
+    await expect(timelineComments.filter({hasText: 'removed this from the'})).toBeVisible();
+  } finally {
+    await apiDeleteRepo(page.request, env.GITEA_TEST_E2E_USER, repoName);
+  }
+});
+
+test('filter issues with no project using project=-1', async ({page}) => {
+  const repoName = `e2e-no-project-filter-${Date.now()}`;
+  const projectTitle = 'Some Project';
+
+  await login(page);
+  await apiCreateRepo(page.request, {name: repoName});
+
+  try {
+    // Create a project via UI
+    const project = await createProject(page, {
+      owner: env.GITEA_TEST_E2E_USER,
+      repo: repoName,
+      title: projectTitle,
+    });
+
+    // Create an issue with a project
+    await apiCreateIssue(page.request, {
+      owner: env.GITEA_TEST_E2E_USER,
+      repo: repoName,
+      title: 'Issue with project assigned',
+      projects: [project.id],
+    });
+
+    // Create issues with no project
+    await apiCreateIssue(page.request, {
+      owner: env.GITEA_TEST_E2E_USER,
+      repo: repoName,
+      title: 'Issue without any project',
+    });
+    await apiCreateIssue(page.request, {
+      owner: env.GITEA_TEST_E2E_USER,
+      repo: repoName,
+      title: 'Another unassigned issue',
+    });
+
+    // First verify we can see all issues without the filter
+    await page.goto(`/${env.GITEA_TEST_E2E_USER}/${repoName}/issues?type=all&state=open`);
+    await expect(page.locator('#issue-list')).toContainText('Issue with project assigned');
+    await expect(page.locator('#issue-list')).toContainText('Issue without any project');
+    await expect(page.locator('#issue-list')).toContainText('Another unassigned issue');
+
+    // Navigate to issue list filtering for issues with no project (project=-1)
+    await page.goto(`/${env.GITEA_TEST_E2E_USER}/${repoName}/issues?type=all&state=open&project=-1`);
+
+    // Verify only issues with no project are visible
+    await expect(page.locator('#issue-list')).toContainText('Issue without any project');
+    await expect(page.locator('#issue-list')).toContainText('Another unassigned issue');
+
+    // Verify the issue with a project is NOT visible
+    await expect(page.locator('#issue-list')).not.toContainText('Issue with project assigned');
+
+    // Verify the last item in the list is NOT the issue with a project
+    const issueItems = page.locator('#issue-list .flex-item');
+    const lastIssueItem = issueItems.last();
+    await expect(lastIssueItem).not.toContainText('Issue with project assigned');
+  } finally {
+    await apiDeleteRepo(page.request, env.GITEA_TEST_E2E_USER, repoName);
+  }
+});
+
+test('close project and view in closed projects list', async ({page}) => {
+  const repoName = `e2e-close-project-${Date.now()}`;
+  const openProjectTitle = 'Open Project';
+  const closedProjectTitle = 'Project To Close';
+
+  await login(page);
+  await apiCreateRepo(page.request, {name: repoName});
+
+  try {
+    // Create two projects via UI
+    await createProject(page, {
+      owner: env.GITEA_TEST_E2E_USER,
+      repo: repoName,
+      title: openProjectTitle,
+    });
+    const projectToClose = await createProject(page, {
+      owner: env.GITEA_TEST_E2E_USER,
+      repo: repoName,
+      title: closedProjectTitle,
+    });
+
+    // Navigate to projects list
+    await page.goto(`/${env.GITEA_TEST_E2E_USER}/${repoName}/projects`);
+
+    // Verify both projects are visible in open state
+    await expect(page.locator('.milestone-list')).toContainText(openProjectTitle);
+    await expect(page.locator('.milestone-list')).toContainText(closedProjectTitle);
+
+    // Close the second project by clicking the close link
+    const projectCard = page.locator('.milestone-card').filter({hasText: closedProjectTitle});
+    await projectCard.locator('a.link-action[data-url$="/close"]').click();
+
+    // Wait for redirect back to project view page
+    await page.waitForURL(new RegExp(`/${env.GITEA_TEST_E2E_USER}/${repoName}/projects/${projectToClose.id}`));
+
+    // Navigate to projects list
+    await page.goto(`/${env.GITEA_TEST_E2E_USER}/${repoName}/projects`);
+
+    // Click on "Closed" tab to view closed projects
+    await page.locator('.list-header-toggle a.item').filter({hasText: 'Closed'}).click();
+
+    // Wait for the page to load with closed projects
+    await page.waitForURL(/state=closed/);
+
+    // Verify only the closed project is visible
+    await expect(page.locator('.milestone-list')).toContainText(closedProjectTitle);
+    await expect(page.locator('.milestone-list')).not.toContainText(openProjectTitle);
+
+    // Verify the "Closed" tab is active
+    await expect(page.locator('.list-header-toggle a.item.active')).toContainText('Closed');
+  } finally {
+    await apiDeleteRepo(page.request, env.GITEA_TEST_E2E_USER, repoName);
+  }
+});
+
+test('select projects on new issue page shows in sidebar', async ({page}) => {
+  const repoName = `e2e-new-issue-project-${Date.now()}`;
+  const project1Title = 'Project One';
+  const project2Title = 'Project Two';
+
+  await login(page);
+  await apiCreateRepo(page.request, {name: repoName});
+
+  try {
+    // Create two projects
+    const project1 = await createProject(page, {
+      owner: env.GITEA_TEST_E2E_USER,
+      repo: repoName,
+      title: project1Title,
+    });
+    const project2 = await createProject(page, {
+      owner: env.GITEA_TEST_E2E_USER,
+      repo: repoName,
+      title: project2Title,
+    });
+
+    // Navigate to new issue page
+    await page.goto(`/${env.GITEA_TEST_E2E_USER}/${repoName}/issues/new`);
+
+    // Open the projects dropdown in the sidebar
+    await page.locator('.sidebar-project-combo > .ui.dropdown').click();
+
+    // Select both projects
+    await page.locator(`.sidebar-project-combo > .ui.dropdown .item[data-value="${project1.id}"]`).click();
+    await page.locator(`.sidebar-project-combo > .ui.dropdown .item[data-value="${project2.id}"]`).click();
+
+    // Click outside to close dropdown
+    await page.locator('.issue-content-left').click();
+
+    // Verify both projects appear in the sidebar list below the dropdown
+    // On new issue page, these are simple cloned items rendered in the list container
+    const projectList = page.locator('.sidebar-project-combo > .ui.list');
+    await expect(projectList.locator(`.item:has-text("${project1Title}")`).first()).toBeVisible();
+    await expect(projectList.locator(`.item:has-text("${project2Title}")`).first()).toBeVisible();
+  } finally {
+    await apiDeleteRepo(page.request, env.GITEA_TEST_E2E_USER, repoName);
+  }
 });

tests/e2e/reactions.test.ts

@@ -7,7 +7,7 @@ test('toggle issue reactions', async ({page, request}) => {
   const owner = env.GITEA_TEST_E2E_USER;
   await apiCreateRepo(request, {name: repoName});
   await Promise.all([
-    apiCreateIssue(request, owner, repoName, {title: 'Reaction test'}),
+    apiCreateIssue(request, {owner, repo: repoName, title: 'Reaction test'}),
     login(page),
   ]);
   await page.goto(`/${owner}/${repoName}/issues/1`);

tests/e2e/utils.ts

@@ -47,13 +47,6 @@ export async function apiCreateRepo(requestContext: APIRequestContext, {name, au
   }), 'apiCreateRepo');
 }
 
-export async function apiCreateIssue(requestContext: APIRequestContext, owner: string, repo: string, {title, headers}: {title: string; headers?: Record<string, string>}) {
-  await apiRetry(() => requestContext.post(`${baseUrl()}/api/v1/repos/${owner}/${repo}/issues`, {
-    headers: headers || apiHeaders(),
-    data: {title},
-  }), 'apiCreateIssue');
-}
-
 export async function apiStartStopwatch(requestContext: APIRequestContext, owner: string, repo: string, issueIndex: number, {headers}: {headers?: Record<string, string>} = {}) {
   await apiRetry(() => requestContext.post(`${baseUrl()}/api/v1/repos/${owner}/${repo}/issues/${issueIndex}/stopwatch/start`, {
     headers: headers || apiHeaders(),
@@ -135,6 +128,63 @@ export async function apiDeleteUser(requestContext: APIRequestContext, username:
   }), 'apiDeleteUser');
 }
 
+export async function createProject(
+  page: Page,
+  {owner, repo, title}: {owner: string; repo: string; title: string},
+): Promise<{id: number}> {
+  // Navigate to new project page
+  await page.goto(`/${owner}/${repo}/projects/new`);
+
+  // Fill in project details
+  await page.getByLabel('Title').fill(title);
+
+  // Submit the form
+  await page.getByRole('button', {name: 'Create Project'}).click();
+
+  // Wait for redirect to projects list
+  await page.waitForURL(new RegExp(`/${owner}/${repo}/projects$`));
+
+  // Extract the project ID from the project link in the list
+  const projectLink = page.locator('.milestone-list .milestone-card').filter({hasText: title}).locator('a').first();
+  const href = await projectLink.getAttribute('href');
+  const match = /\/projects\/(\d+)/.exec(href || '');
+  const id = match ? parseInt(match[1]) : 0;
+
+  return {id};
+}
+
+export async function apiCreateIssue(
+  requestContext: APIRequestContext,
+  {owner, repo, title, body, projects, headers}: {
+    owner: string;
+    repo: string;
+    title: string;
+    body?: string;
+    projects?: number[];
+    headers?: Record<string, string>;
+  },
+): Promise<{index: number}> {
+  let result: {index: number} = {index: 0};
+  await apiRetry(async () => {
+    const response = await requestContext.post(`${baseUrl()}/api/v1/repos/${owner}/${repo}/issues`, {
+      headers: headers || apiHeaders(),
+      data: {title, body: body || '', projects: projects || []},
+    });
+    if (response.ok()) {
+      const json = await response.json();
+      // API returns "number" field for the issue index
+      result = {index: json.number};
+    }
+    return response;
+  }, 'apiCreateIssue');
+  return result;
+}
+
+export async function clickDropdownItem(page: Page, trigger: Locator, itemText: string) {
+  await trigger.click();
+  await page.getByText(itemText).click();
+}
+
 export async function loginUser(page: Page, username: string) {
   return login(page, username, testUserPassword);
 }

tests/integration/api_issue_test.go

@@ -35,6 +35,7 @@ func TestAPIIssue(t *testing.T) {
 	t.Run("IssueContentVersion", testAPIIssueContentVersion)
 	t.Run("CreateIssue", testAPICreateIssue)
 	t.Run("CreateIssueParallel", testAPICreateIssueParallel)
+	t.Run("IssueProjects", testAPIIssueProjects)
 }
 
 func testAPIListIssues(t *testing.T) {
@@ -496,3 +497,66 @@ func testAPIIssueContentVersion(t *testing.T) {
 		MakeRequest(t, req, http.StatusCreated)
 	})
 }
+
+func testAPIIssueProjects(t *testing.T) {
+	repo := unittest.AssertExistsAndLoadBean(t, &repo_model.Repository{ID: 1})
+	owner := unittest.AssertExistsAndLoadBean(t, &user_model.User{ID: repo.OwnerID})
+
+	session := loginUser(t, owner.Name)
+	token := getTokenForLoggedInUser(t, session, auth_model.AccessTokenScopeWriteIssue)
+	urlStr := fmt.Sprintf("/api/v1/repos/%s/%s/issues", owner.Name, repo.Name)
+
+	// Create issue with a project
+	req := NewRequestWithJSON(t, "POST", urlStr, &api.CreateIssueOption{
+		Title:    "issue with project",
+		Body:     "test body",
+		Projects: []int64{1},
+	}).AddTokenAuth(token)
+	resp := MakeRequest(t, req, http.StatusCreated)
+	var apiIssue api.Issue
+	DecodeJSON(t, resp, &apiIssue)
+	assert.Len(t, apiIssue.Projects, 1)
+	assert.EqualValues(t, 1, apiIssue.Projects[0].ID)
+
+	// Get issue should include projects
+	req = NewRequest(t, "GET", fmt.Sprintf("%s/%d", urlStr, apiIssue.Index)).AddTokenAuth(token)
+	resp = MakeRequest(t, req, http.StatusOK)
+	DecodeJSON(t, resp, &apiIssue)
+	assert.Len(t, apiIssue.Projects, 1)
+	assert.EqualValues(t, 1, apiIssue.Projects[0].ID)
+
+	// Edit issue to remove projects
+	emptyProjects := []int64{}
+	req = NewRequestWithJSON(t, "PATCH", fmt.Sprintf("%s/%d", urlStr, apiIssue.Index), &api.EditIssueOption{
+		Projects: &emptyProjects,
+	}).AddTokenAuth(token)
+	resp = MakeRequest(t, req, http.StatusCreated)
+	DecodeJSON(t, resp, &apiIssue)
+	assert.Empty(t, apiIssue.Projects)
+
+	// Edit issue to add project back
+	projects := []int64{1}
+	req = NewRequestWithJSON(t, "PATCH", fmt.Sprintf("%s/%d", urlStr, apiIssue.Index), &api.EditIssueOption{
+		Projects: &projects,
+	}).AddTokenAuth(token)
+	resp = MakeRequest(t, req, http.StatusCreated)
+	DecodeJSON(t, resp, &apiIssue)
+	assert.Len(t, apiIssue.Projects, 1)
+	assert.EqualValues(t, 1, apiIssue.Projects[0].ID)
+
+	// Test invalid project ID
+	req = NewRequestWithJSON(t, "POST", urlStr, &api.CreateIssueOption{
+		Title:    "issue with invalid project",
+		Body:     "test body",
+		Projects: []int64{99999},
+	}).AddTokenAuth(token)
+	MakeRequest(t, req, http.StatusBadRequest)
+
+	// Test project from different repo (project 2 is for repo 3)
+	req = NewRequestWithJSON(t, "POST", urlStr, &api.CreateIssueOption{
+		Title:    "issue with inaccessible project",
+		Body:     "test body",
+		Projects: []int64{2},
+	}).AddTokenAuth(token)
+	MakeRequest(t, req, http.StatusBadRequest)
+}

tests/integration/project_test.go

@@ -90,6 +90,26 @@ func TestMoveRepoProjectColumns(t *testing.T) {
 	assert.NoError(t, project_model.DeleteProjectByID(t.Context(), project1.ID))
 }
 
+func TestUpdateIssueProject(t *testing.T) {
+	defer tests.PrepareTestEnv(t)()
+
+	sess := loginUser(t, "user2")
+
+	t.Run("AssignAndRemove", func(t *testing.T) {
+		req := NewRequestWithValues(t, "POST", "/user2/repo1/issues/projects?issue_ids=2", map[string]string{
+			"id": "1",
+		})
+		sess.MakeRequest(t, req, http.StatusOK)
+		unittest.AssertExistsAndLoadBean(t, &project_model.ProjectIssue{IssueID: 2, ProjectID: 1})
+
+		req = NewRequestWithValues(t, "POST", "/user2/repo1/issues/projects?issue_ids=2", map[string]string{
+			"id": "",
+		})
+		sess.MakeRequest(t, req, http.StatusOK)
+		unittest.AssertNotExistsBean(t, &project_model.ProjectIssue{IssueID: 2, ProjectID: 1})
+	})
+}
+
 func TestUpdateIssueProjectColumn(t *testing.T) {
 	defer tests.PrepareTestEnv(t)()
 
@@ -160,13 +180,13 @@ func TestIssueSidebarProjectColumn(t *testing.T) {
 	resp := sess.MakeRequest(t, req, http.StatusOK)
 	htmlDoc := NewHTMLParser(t, resp.Body)
 
-	cards := htmlDoc.Find(".sidebar-project-card")
+	cards := htmlDoc.Find(".flex-relaxed-list > .item.sidebar-project-card")
 	assert.Equal(t, 1, cards.Length())
 
-	title := cards.Find(".sidebar-project-card a.suppressed .gt-ellipsis")
+	title := cards.Find("a span.gt-ellipsis")
 	assert.Contains(t, strings.TrimSpace(title.Text()), "First project")
 
-	columnCombo := cards.Find(".sidebar-project-column-combo")
+	columnCombo := cards.Find(".issue-sidebar-combo.sidebar-project-column-combo")
 	assert.Equal(t, 1, columnCombo.Length())
 
 	defaultItem := columnCombo.Find(`.menu .item[data-value="1"]`)
@@ -181,16 +201,14 @@ func TestIssueSidebarProjectColumn(t *testing.T) {
 	assert.True(t, exists)
 	assert.Equal(t, "3", comboVal)
 
-	req = NewRequestWithValues(t, "POST", "/user2/repo1/issues/projects?issue_ids=5", map[string]string{
-		"id": "0",
-	})
+	req = NewRequestWithValues(t, "POST", "/user2/repo1/issues/projects?issue_ids=5", map[string]string{"id": ""})
 	sess.MakeRequest(t, req, http.StatusOK)
 
 	req = NewRequest(t, "GET", "/user2/repo1/issues/4")
 	resp = sess.MakeRequest(t, req, http.StatusOK)
 	htmlDoc = NewHTMLParser(t, resp.Body)
 
-	cards = htmlDoc.Find(".sidebar-project-card")
+	cards = htmlDoc.Find(".flex-relaxed-list > .item.sidebar-project-card")
 	assert.Equal(t, 0, cards.Length())
 }
 
@@ -293,15 +311,9 @@ func TestOrgProjectFilterByMilestone(t *testing.T) {
 	}
 	require.NoError(t, project_model.NewProject(t.Context(), &project))
 
-	// Get the default column
-	columns, err := project.GetColumns(t.Context())
-	require.NoError(t, err)
-	require.NotEmpty(t, columns)
-	defaultColumnID := columns[0].ID
-
 	// Add issues to the project
-	require.NoError(t, issues_model.IssueAssignOrRemoveProject(t.Context(), issue16, user1, project.ID, defaultColumnID))
-	require.NoError(t, issues_model.IssueAssignOrRemoveProject(t.Context(), issue17, user1, project.ID, defaultColumnID))
+	require.NoError(t, issues_model.IssueAssignOrRemoveProject(t.Context(), issue16, user1, []int64{project.ID}))
+	require.NoError(t, issues_model.IssueAssignOrRemoveProject(t.Context(), issue17, user1, []int64{project.ID}))
 
 	sess := loginUser(t, "user1")
 	projectURL := fmt.Sprintf("/org3/-/projects/%d", project.ID)

web_src/css/base.css

@@ -897,7 +897,7 @@ table th[data-sortt-desc] .svg {
   display: flex;
   align-items: center;
   gap: var(--gap-block);
-  min-width: 0;
+  max-width: 100%;
 }
 
 .flex-left-right > .ui.button,

web_src/css/repo.css

@@ -62,10 +62,17 @@
   visibility: hidden;
 }
 
-.sidebar-project-card {
+.ui.list.issue-sidebar-project-cards > .item {
+  display: flex;
+  align-items: center;
+  gap: var(--gap-block);
+}
+
+.ui.list.issue-sidebar-project-cards > .item.sidebar-project-card {
+  flex-direction: column;
+  align-items: flex-start;
   border: 1px solid var(--color-secondary);
   border-radius: var(--border-radius);
-  margin-top: var(--gap-block);
   padding: 8px;
 }
 

web_src/js/features/repo-issue-sidebar-combolist.ts

@@ -70,7 +70,7 @@ export class IssueSidebarComboList {
 
   updateUiList(changedValues: Array<string>) {
     if (!this.elList) return;
-    const elEmptyTip = this.elList.querySelector('.item.empty-list')!;
+    const elEmptyTip = this.elList.querySelector(':scope > .item.empty-list')!;
     queryElemChildren(this.elList, '.item:not(.empty-list)', (el) => el.remove());
     for (const value of changedValues) {
       const el = this.elDropdown.querySelector<HTMLElement>(`.menu > .item[data-value="${CSS.escape(value)}"]`);
@@ -139,7 +139,7 @@ export class IssueSidebarComboList {
   async doUpdate() {
     const changedValues = this.collectCheckedValues();
     if (this.initialValues.join(',') === changedValues.join(',')) return;
-    this.updateUiList(changedValues);
+    if (!this.updateUrl) this.updateUiList(changedValues);
     if (this.updateUrl) await this.updateToBackend(changedValues);
     this.initialValues = changedValues;
   }
@@ -196,7 +196,9 @@ export class IssueSidebarComboList {
         const elItem = this.elDropdown.querySelector<HTMLElement>(`.menu > .item[data-value="${CSS.escape(value)}"]`);
         elItem?.classList.add('checked');
       }
-      this.updateUiList(values);
+      if (this.elList && this.elList.getAttribute('data-combo-list-inited') !== 'true') {
+        this.updateUiList(values);
+      }
     }
     this.initialValues = this.collectCheckedValues();