From 8b46a956d8d1e474272f14cb1900f62df06c5c45 Mon Sep 17 00:00:00 2001
From: Roland <landuoduo123@gmail.com>
Date: Thu, 24 Sep 2026 15:12:02 +0800
Subject: [PATCH] perf(references): scan only the keyword window before a
 reference (#39396)
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Fixes https://github.com/go-gitea/gitea/issues/39395

`findActionKeywords` ran the close and reopen keyword patterns over all
content before each reference, making `FindAllIssueReferences` quadratic
on comments and commit messages. The patterns are anchored at the
reference, so only the last few bytes can match. Scan only that window,
sized from the longest keyword with room for `(?i)` matching wider runes
like `ſ` for `s`.

`"#1 "` repeated 4000 times: 2.04 s before, 16 ms after.

---------

Co-authored-by: silverwind <me@silverwind.io>
Co-authored-by: wxiaoguang <wxiaoguang@gmail.com>
---
 modules/references/references.go      | 20 +++++++++++++-------
 modules/references/references_test.go |  7 +++++++
 2 files changed, 20 insertions(+), 7 deletions(-)

diff --git a/modules/references/references.go b/modules/references/references.go
index d3d451269fd..0d470d479ae 100644
--- a/modules/references/references.go
+++ b/modules/references/references.go
@@ -7,9 +7,11 @@ import (
 	"bytes"
 	"net/url"
 	"regexp"
+	"slices"
 	"strconv"
 	"strings"
 	"sync"
+	"unicode/utf8"
 
 	"gitea.dev/modules/log"
 	"gitea.dev/modules/markup/mdstripper"
@@ -45,6 +47,7 @@ var (
 	timeLogPattern = regexp.MustCompile(`(?:\s|^|\(|\[)(@([0-9]+([\.,][0-9]+)?(w|d|m|h))+)(?:\s|$|\)|\]|[:;,.?!]\s|[:;,.?!]$)`)
 
 	issueCloseKeywordsPat, issueReopenKeywordsPat *regexp.Regexp
+	issueKeywordWindow                            int
 	issueKeywordsOnce                             sync.Once
 
 	giteaHostInit         sync.Once
@@ -167,6 +170,10 @@ func newKeywords() {
 func doNewKeywords(closeKeywords, reopenKeywords []string) {
 	issueCloseKeywordsPat = makeKeywordsPat(closeKeywords)
 	issueReopenKeywordsPat = makeKeywordsPat(reopenKeywords)
+	issueKeywordWindow = 0
+	for _, word := range slices.Concat(closeKeywords, reopenKeywords) {
+		issueKeywordWindow = max(issueKeywordWindow, utf8.RuneCountInString(word)*utf8.UTFMax+3) // delimiter, keyword with (?i)-folded runes like ſ for s, ": "
+	}
 }
 
 // getGiteaHostName returns a normalized string with the local host name, with no scheme or port information
@@ -599,17 +606,16 @@ func getCrossReference(content []byte, start, end int, fromLink, prOnly bool) *r
 
 func findActionKeywords(content []byte, start int) (XRefAction, *RefSpan) {
 	newKeywords()
-	var m []int
+	windowStart := max(start-issueKeywordWindow, 0)
+	prefix := content[windowStart:start]
 	if issueCloseKeywordsPat != nil {
-		m = issueCloseKeywordsPat.FindSubmatchIndex(content[:start])
-		if m != nil {
-			return XRefActionCloses, &RefSpan{Start: m[2], End: m[3]}
+		if m := issueCloseKeywordsPat.FindSubmatchIndex(prefix); m != nil {
+			return XRefActionCloses, &RefSpan{Start: windowStart + m[2], End: windowStart + m[3]}
 		}
 	}
 	if issueReopenKeywordsPat != nil {
-		m = issueReopenKeywordsPat.FindSubmatchIndex(content[:start])
-		if m != nil {
-			return XRefActionReopens, &RefSpan{Start: m[2], End: m[3]}
+		if m := issueReopenKeywordsPat.FindSubmatchIndex(prefix); m != nil {
+			return XRefActionReopens, &RefSpan{Start: windowStart + m[2], End: windowStart + m[3]}
 		}
 	}
 	return XRefActionNone, nil
diff --git a/modules/references/references_test.go b/modules/references/references_test.go
index 222b93d4092..53cd98a931c 100644
--- a/modules/references/references_test.go
+++ b/modules/references/references_test.go
@@ -162,6 +162,13 @@ func TestFindAllIssueReferences(t *testing.T) {
 				{1235, "", "", "1235", false, XRefActionNone, &RefSpan{Start: 8, End: 13}, nil, ""},
 			},
 		},
+		{
+			"After a long investigation into the root cause, this resolves #1, unlike the still unresolved #2",
+			[]testResult{
+				{1, "", "", "1", false, XRefActionCloses, &RefSpan{Start: 62, End: 64}, &RefSpan{Start: 53, End: 61}, ""},
+				{2, "", "", "2", false, XRefActionNone, &RefSpan{Start: 94, End: 96}, nil, ""},
+			},
+		},
 		{
 			"For [!123] yes",
 			[]testResult{