fix: dedupe issue cross-reference timeline entries (#38881)

Removing and re-adding a mention, or changing `closes #1` to a plain
`#1`, added duplicate references to the issue's timeline.

The timeline now renders a single entry per referencing issue or pull
request, positioned at the first mention, like GitHub does.

routers/web/repo/issue_test.go

@@ -7,10 +7,34 @@ import (
 	"testing"
 
 	issues_model "gitea.dev/models/issues"
+	"gitea.dev/modules/references"
 
 	"github.com/stretchr/testify/assert"
 )
 
+func TestCombineXRefComments(t *testing.T) {
+	none, closes, neutered := references.XRefActionNone, references.XRefActionCloses, references.XRefActionNeutered
+	xref := func(id, refIssueID, refCommentID int64, action references.XRefAction) *issues_model.Comment {
+		return &issues_model.Comment{ID: id, Type: issues_model.CommentTypeIssueRef, RefIssueID: refIssueID, RefCommentID: refCommentID, RefAction: action}
+	}
+	issue := issues_model.Issue{Comments: issues_model.CommentList{
+		xref(1, 10, 1, neutered),
+		xref(2, 11, 2, none),
+		xref(3, 10, 3, none),
+		xref(4, 11, 4, closes),
+		xref(5, 11, 5, neutered),
+		xref(6, 0, 0, none),
+		xref(7, 0, 0, none),
+	}}
+	combineXRefComments(&issue)
+	assert.Equal(t, issues_model.CommentList{
+		xref(1, 10, 3, none),
+		xref(2, 11, 2, closes),
+		xref(6, 0, 0, none),
+		xref(7, 0, 0, none),
+	}, issue.Comments)
+}
+
 func TestCombineLabelComments(t *testing.T) {
 	kases := []struct {
 		name           string

routers/web/repo/issue_view.go

@@ -27,6 +27,7 @@ import (
 	"gitea.dev/modules/log"
 	"gitea.dev/modules/markup"
 	"gitea.dev/modules/markup/markdown"
+	"gitea.dev/modules/references"
 	"gitea.dev/modules/setting"
 	"gitea.dev/modules/svg"
 	"gitea.dev/modules/templates/vars"
@@ -189,6 +190,32 @@ func filterXRefComments(ctx *context.Context, issue *issues_model.Issue) error {
 	return nil
 }
 
+// combineXRefComments keeps only the first reference from each issue, carrying over the action of later ones
+func combineXRefComments(issue *issues_model.Issue) {
+	first := make(map[int64]*issues_model.Comment)
+	for i := 0; i < len(issue.Comments); {
+		c := issue.Comments[i]
+		if !issues_model.CommentTypeIsRef(c.Type) || c.RefIssueID == 0 {
+			i++
+			continue
+		}
+		prev, ok := first[c.RefIssueID]
+		if !ok {
+			first[c.RefIssueID] = c
+			i++
+			continue
+		}
+		switch {
+		case c.RefAction == references.XRefActionNeutered: // a removed mention never overrides a live one
+		case prev.RefAction == references.XRefActionNeutered:
+			prev.RefAction, prev.RefCommentID = c.RefAction, c.RefCommentID
+		case c.RefAction != references.XRefActionNone:
+			prev.RefAction = c.RefAction
+		}
+		issue.Comments = append(issue.Comments[:i], issue.Comments[i+1:]...)
+	}
+}
+
 // combineLabelComments combine the nearby label comments as one.
 func combineLabelComments(issue *issues_model.Issue) {
 	var prev, cur *issues_model.Comment
@@ -346,6 +373,7 @@ func ViewIssue(ctx *context.Context) {
 		ctx.ServerError("filterXRefComments", err)
 		return
 	}
+	combineXRefComments(issue)
 
 	ctx.Data["Title"] = fmt.Sprintf("#%d - %s", issue.Index, emoji.ReplaceAliases(issue.Title))