feat(diff): Enable commenting on expanded lines in PR diffs (#35662)

Fixes #32257 
/claim #32257

Implemented commenting on unchanged lines in Pull Request diffs, lines
are accessed by expanding the diff preview. Comments also appear in the
"Files Changed" tab on the unchanged lines where they were placed.

---------

Co-authored-by: wxiaoguang <wxiaoguang@gmail.com>

routers/web/repo/commit.go

@@ -276,20 +276,24 @@ func Diff(ctx *context.Context) {
 	userName := ctx.Repo.Owner.Name
 	repoName := ctx.Repo.Repository.Name
 	commitID := ctx.PathParam("sha")
-	var (
-		gitRepo *git.Repository
-		err     error
-	)
+
+	diffBlobExcerptData := &gitdiff.DiffBlobExcerptData{
+		BaseLink:      ctx.Repo.RepoLink + "/blob_excerpt",
+		DiffStyle:     ctx.FormString("style"),
+		AfterCommitID: commitID,
+	}
+	gitRepo := ctx.Repo.GitRepo
+	var gitRepoStore gitrepo.Repository = ctx.Repo.Repository
 
 	if ctx.Data["PageIsWiki"] != nil {
-		gitRepo, err = gitrepo.OpenRepository(ctx, ctx.Repo.Repository.WikiStorageRepo())
+		var err error
+		gitRepoStore = ctx.Repo.Repository.WikiStorageRepo()
+		gitRepo, err = gitrepo.RepositoryFromRequestContextOrOpen(ctx, gitRepoStore)
 		if err != nil {
 			ctx.ServerError("Repo.GitRepo.GetCommit", err)
 			return
 		}
-		defer gitRepo.Close()
-	} else {
-		gitRepo = ctx.Repo.GitRepo
+		diffBlobExcerptData.BaseLink = ctx.Repo.RepoLink + "/wiki/blob_excerpt"
 	}
 
 	commit, err := gitRepo.GetCommit(commitID)
@@ -324,7 +328,7 @@ func Diff(ctx *context.Context) {
 		ctx.NotFound(err)
 		return
 	}
-	diffShortStat, err := gitdiff.GetDiffShortStat(ctx, ctx.Repo.Repository, gitRepo, "", commitID)
+	diffShortStat, err := gitdiff.GetDiffShortStat(ctx, gitRepoStore, gitRepo, "", commitID)
 	if err != nil {
 		ctx.ServerError("GetDiffShortStat", err)
 		return
@@ -360,6 +364,7 @@ func Diff(ctx *context.Context) {
 	ctx.Data["Title"] = commit.Summary() + " · " + base.ShortSha(commitID)
 	ctx.Data["Commit"] = commit
 	ctx.Data["Diff"] = diff
+	ctx.Data["DiffBlobExcerptData"] = diffBlobExcerptData
 
 	if !fileOnly {
 		diffTree, err := gitdiff.GetDiffTree(ctx, gitRepo, false, parentCommitID, commitID)

routers/web/repo/compare.go

@@ -14,6 +14,7 @@ import (
 	"net/http"
 	"net/url"
 	"path/filepath"
+	"sort"
 	"strings"
 
 	"code.gitea.io/gitea/models/db"
@@ -43,6 +44,7 @@ import (
 	"code.gitea.io/gitea/services/context/upload"
 	"code.gitea.io/gitea/services/gitdiff"
 	pull_service "code.gitea.io/gitea/services/pull"
+	user_service "code.gitea.io/gitea/services/user"
 )
 
 const (
@@ -638,6 +640,11 @@ func PrepareCompareDiff(
 	}
 	ctx.Data["DiffShortStat"] = diffShortStat
 	ctx.Data["Diff"] = diff
+	ctx.Data["DiffBlobExcerptData"] = &gitdiff.DiffBlobExcerptData{
+		BaseLink:      ci.HeadRepo.Link() + "/blob_excerpt",
+		DiffStyle:     ctx.FormString("style"),
+		AfterCommitID: headCommitID,
+	}
 	ctx.Data["DiffNotAvailable"] = diffShortStat.NumFiles == 0
 
 	if !fileOnly {
@@ -865,6 +872,28 @@ func CompareDiff(ctx *context.Context) {
 	ctx.HTML(http.StatusOK, tplCompare)
 }
 
+// attachCommentsToLines attaches comments to their corresponding diff lines
+func attachCommentsToLines(section *gitdiff.DiffSection, lineComments map[int64][]*issues_model.Comment) {
+	for _, line := range section.Lines {
+		if comments, ok := lineComments[int64(line.LeftIdx*-1)]; ok {
+			line.Comments = append(line.Comments, comments...)
+		}
+		if comments, ok := lineComments[int64(line.RightIdx)]; ok {
+			line.Comments = append(line.Comments, comments...)
+		}
+		sort.SliceStable(line.Comments, func(i, j int) bool {
+			return line.Comments[i].CreatedUnix < line.Comments[j].CreatedUnix
+		})
+	}
+}
+
+// attachHiddenCommentIDs calculates and attaches hidden comment IDs to expand buttons
+func attachHiddenCommentIDs(section *gitdiff.DiffSection, lineComments map[int64][]*issues_model.Comment) {
+	for _, line := range section.Lines {
+		gitdiff.FillHiddenCommentIDsForDiffLine(line, lineComments)
+	}
+}
+
 // ExcerptBlob render blob excerpt contents
 func ExcerptBlob(ctx *context.Context) {
 	commitID := ctx.PathParam("sha")
@@ -874,19 +903,26 @@ func ExcerptBlob(ctx *context.Context) {
 	idxRight := ctx.FormInt("right")
 	leftHunkSize := ctx.FormInt("left_hunk_size")
 	rightHunkSize := ctx.FormInt("right_hunk_size")
-	anchor := ctx.FormString("anchor")
 	direction := ctx.FormString("direction")
 	filePath := ctx.FormString("path")
 	gitRepo := ctx.Repo.GitRepo
+
+	diffBlobExcerptData := &gitdiff.DiffBlobExcerptData{
+		BaseLink:      ctx.Repo.RepoLink + "/blob_excerpt",
+		DiffStyle:     ctx.FormString("style"),
+		AfterCommitID: commitID,
+	}
+
 	if ctx.Data["PageIsWiki"] == true {
 		var err error
-		gitRepo, err = gitrepo.OpenRepository(ctx, ctx.Repo.Repository.WikiStorageRepo())
+		gitRepo, err = gitrepo.RepositoryFromRequestContextOrOpen(ctx, ctx.Repo.Repository.WikiStorageRepo())
 		if err != nil {
 			ctx.ServerError("OpenRepository", err)
 			return
 		}
-		defer gitRepo.Close()
+		diffBlobExcerptData.BaseLink = ctx.Repo.RepoLink + "/wiki/blob_excerpt"
 	}
+
 	chunkSize := gitdiff.BlobExcerptChunkSize
 	commit, err := gitRepo.GetCommit(commitID)
 	if err != nil {
@@ -947,10 +983,43 @@ func ExcerptBlob(ctx *context.Context) {
 			section.Lines = append(section.Lines, lineSection)
 		}
 	}
+
+	diffBlobExcerptData.PullIssueIndex = ctx.FormInt64("pull_issue_index")
+	if diffBlobExcerptData.PullIssueIndex > 0 {
+		if !ctx.Repo.CanRead(unit.TypePullRequests) {
+			ctx.NotFound(nil)
+			return
+		}
+
+		issue, err := issues_model.GetIssueByIndex(ctx, ctx.Repo.Repository.ID, diffBlobExcerptData.PullIssueIndex)
+		if err != nil {
+			log.Error("GetIssueByIndex error: %v", err)
+		} else if issue.IsPull {
+			// FIXME: DIFF-CONVERSATION-DATA: the following data assignment is fragile
+			ctx.Data["Issue"] = issue
+			ctx.Data["CanBlockUser"] = func(blocker, blockee *user_model.User) bool {
+				return user_service.CanBlockUser(ctx, ctx.Doer, blocker, blockee)
+			}
+			// and "diff/comment_form.tmpl" (reply comment) needs them
+			ctx.Data["PageIsPullFiles"] = true
+			ctx.Data["AfterCommitID"] = diffBlobExcerptData.AfterCommitID
+
+			allComments, err := issues_model.FetchCodeComments(ctx, issue, ctx.Doer, ctx.FormBool("show_outdated"))
+			if err != nil {
+				log.Error("FetchCodeComments error: %v", err)
+			} else {
+				if lineComments, ok := allComments[filePath]; ok {
+					attachCommentsToLines(section, lineComments)
+					attachHiddenCommentIDs(section, lineComments)
+				}
+			}
+		}
+	}
+
 	ctx.Data["section"] = section
 	ctx.Data["FileNameHash"] = git.HashFilePathForWebUI(filePath)
-	ctx.Data["AfterCommitID"] = commitID
-	ctx.Data["Anchor"] = anchor
+	ctx.Data["DiffBlobExcerptData"] = diffBlobExcerptData
+
 	ctx.HTML(http.StatusOK, tplBlobExcerpt)
 }
 

routers/web/repo/compare_test.go

@@ -0,0 +1,40 @@
+// Copyright 2025 The Gitea Authors. All rights reserved.
+// SPDX-License-Identifier: MIT
+
+package repo
+
+import (
+	"testing"
+
+	issues_model "code.gitea.io/gitea/models/issues"
+	"code.gitea.io/gitea/services/gitdiff"
+
+	"github.com/stretchr/testify/assert"
+)
+
+func TestAttachCommentsToLines(t *testing.T) {
+	section := &gitdiff.DiffSection{
+		Lines: []*gitdiff.DiffLine{
+			{LeftIdx: 5, RightIdx: 10},
+			{LeftIdx: 6, RightIdx: 11},
+		},
+	}
+
+	lineComments := map[int64][]*issues_model.Comment{
+		-5: {{ID: 100, CreatedUnix: 1000}},                               // left side comment
+		10: {{ID: 200, CreatedUnix: 2000}},                               // right side comment
+		11: {{ID: 300, CreatedUnix: 1500}, {ID: 301, CreatedUnix: 2500}}, // multiple comments
+	}
+
+	attachCommentsToLines(section, lineComments)
+
+	// First line should have left and right comments
+	assert.Len(t, section.Lines[0].Comments, 2)
+	assert.Equal(t, int64(100), section.Lines[0].Comments[0].ID)
+	assert.Equal(t, int64(200), section.Lines[0].Comments[1].ID)
+
+	// Second line should have two comments, sorted by creation time
+	assert.Len(t, section.Lines[1].Comments, 2)
+	assert.Equal(t, int64(300), section.Lines[1].Comments[0].ID)
+	assert.Equal(t, int64(301), section.Lines[1].Comments[1].ID)
+}

routers/web/repo/pull.go

@@ -827,6 +827,12 @@ func viewPullFiles(ctx *context.Context, beforeCommitID, afterCommitID string) {
 	}
 
 	ctx.Data["Diff"] = diff
+	ctx.Data["DiffBlobExcerptData"] = &gitdiff.DiffBlobExcerptData{
+		BaseLink:       ctx.Repo.RepoLink + "/blob_excerpt",
+		PullIssueIndex: pull.Index,
+		DiffStyle:      ctx.FormString("style"),
+		AfterCommitID:  afterCommitID,
+	}
 	ctx.Data["DiffNotAvailable"] = diffShortStat.NumFiles == 0
 
 	if ctx.IsSigned && ctx.Doer != nil {

services/gitdiff/gitdiff.go

@@ -22,19 +22,21 @@ import (
 	git_model "code.gitea.io/gitea/models/git"
 	issues_model "code.gitea.io/gitea/models/issues"
 	pull_model "code.gitea.io/gitea/models/pull"
-	repo_model "code.gitea.io/gitea/models/repo"
 	user_model "code.gitea.io/gitea/models/user"
 	"code.gitea.io/gitea/modules/analyze"
+	"code.gitea.io/gitea/modules/base"
 	"code.gitea.io/gitea/modules/charset"
 	"code.gitea.io/gitea/modules/git"
 	"code.gitea.io/gitea/modules/git/attribute"
 	"code.gitea.io/gitea/modules/git/gitcmd"
 	"code.gitea.io/gitea/modules/gitrepo"
 	"code.gitea.io/gitea/modules/highlight"
+	"code.gitea.io/gitea/modules/htmlutil"
 	"code.gitea.io/gitea/modules/lfs"
 	"code.gitea.io/gitea/modules/log"
 	"code.gitea.io/gitea/modules/optional"
 	"code.gitea.io/gitea/modules/setting"
+	"code.gitea.io/gitea/modules/svg"
 	"code.gitea.io/gitea/modules/translation"
 	"code.gitea.io/gitea/modules/util"
 
@@ -67,18 +69,6 @@ const (
 	DiffFileCopy
 )
 
-// DiffLineExpandDirection represents the DiffLineSection expand direction
-type DiffLineExpandDirection uint8
-
-// DiffLineExpandDirection possible values.
-const (
-	DiffLineExpandNone DiffLineExpandDirection = iota + 1
-	DiffLineExpandSingle
-	DiffLineExpandUpDown
-	DiffLineExpandUp
-	DiffLineExpandDown
-)
-
 // DiffLine represents a line difference in a DiffSection.
 type DiffLine struct {
 	LeftIdx     int // line number, 1-based
@@ -99,6 +89,8 @@ type DiffLineSectionInfo struct {
 	RightIdx      int
 	LeftHunkSize  int
 	RightHunkSize int
+
+	HiddenCommentIDs []int64 // IDs of hidden comments in this section
 }
 
 // DiffHTMLOperation is the HTML version of diffmatchpatch.Diff
@@ -153,8 +145,7 @@ func (d *DiffLine) GetLineTypeMarker() string {
 	return ""
 }
 
-// GetBlobExcerptQuery builds query string to get blob excerpt
-func (d *DiffLine) GetBlobExcerptQuery() string {
+func (d *DiffLine) getBlobExcerptQuery() string {
 	query := fmt.Sprintf(
 		"last_left=%d&last_right=%d&"+
 			"left=%d&right=%d&"+
@@ -167,19 +158,88 @@ func (d *DiffLine) GetBlobExcerptQuery() string {
 	return query
 }
 
-// GetExpandDirection gets DiffLineExpandDirection
-func (d *DiffLine) GetExpandDirection() DiffLineExpandDirection {
+func (d *DiffLine) getExpandDirection() string {
 	if d.Type != DiffLineSection || d.SectionInfo == nil || d.SectionInfo.LeftIdx-d.SectionInfo.LastLeftIdx <= 1 || d.SectionInfo.RightIdx-d.SectionInfo.LastRightIdx <= 1 {
-		return DiffLineExpandNone
+		return ""
 	}
 	if d.SectionInfo.LastLeftIdx <= 0 && d.SectionInfo.LastRightIdx <= 0 {
-		return DiffLineExpandUp
+		return "up"
 	} else if d.SectionInfo.RightIdx-d.SectionInfo.LastRightIdx > BlobExcerptChunkSize && d.SectionInfo.RightHunkSize > 0 {
-		return DiffLineExpandUpDown
+		return "updown"
 	} else if d.SectionInfo.LeftHunkSize <= 0 && d.SectionInfo.RightHunkSize <= 0 {
-		return DiffLineExpandDown
+		return "down"
+	}
+	return "single"
+}
+
+type DiffBlobExcerptData struct {
+	BaseLink       string
+	IsWikiRepo     bool
+	PullIssueIndex int64
+	DiffStyle      string
+	AfterCommitID  string
+}
+
+func (d *DiffLine) RenderBlobExcerptButtons(fileNameHash string, data *DiffBlobExcerptData) template.HTML {
+	dataHiddenCommentIDs := strings.Join(base.Int64sToStrings(d.SectionInfo.HiddenCommentIDs), ",")
+	anchor := fmt.Sprintf("diff-%sK%d", fileNameHash, d.SectionInfo.RightIdx)
+
+	makeButton := func(direction, svgName string) template.HTML {
+		style := util.IfZero(data.DiffStyle, "unified")
+		link := data.BaseLink + "/" + data.AfterCommitID + fmt.Sprintf("?style=%s&direction=%s&anchor=%s", url.QueryEscape(style), direction, url.QueryEscape(anchor)) + "&" + d.getBlobExcerptQuery()
+		if data.PullIssueIndex > 0 {
+			link += fmt.Sprintf("&pull_issue_index=%d", data.PullIssueIndex)
+		}
+		return htmlutil.HTMLFormat(
+			`<button class="code-expander-button" hx-target="closest tr" hx-get="%s" data-hidden-comment-ids=",%s,">%s</button>`,
+			link, dataHiddenCommentIDs, svg.RenderHTML(svgName),
+		)
+	}
+	var content template.HTML
+
+	if len(d.SectionInfo.HiddenCommentIDs) > 0 {
+		tooltip := fmt.Sprintf("%d hidden comment(s)", len(d.SectionInfo.HiddenCommentIDs))
+		content += htmlutil.HTMLFormat(`<span class="code-comment-more" data-tooltip-content="%s">%d</span>`, tooltip, len(d.SectionInfo.HiddenCommentIDs))
+	}
+
+	expandDirection := d.getExpandDirection()
+	if expandDirection == "up" || expandDirection == "updown" {
+		content += makeButton("up", "octicon-fold-up")
+	}
+	if expandDirection == "updown" || expandDirection == "down" {
+		content += makeButton("down", "octicon-fold-down")
+	}
+	if expandDirection == "single" {
+		content += makeButton("single", "octicon-fold")
+	}
+	return htmlutil.HTMLFormat(`<div class="code-expander-buttons" data-expand-direction="%s">%s</div>`, expandDirection, content)
+}
+
+// FillHiddenCommentIDsForDiffLine finds comment IDs that are in the hidden range of an expand button
+func FillHiddenCommentIDsForDiffLine(line *DiffLine, lineComments map[int64][]*issues_model.Comment) {
+	if line.Type != DiffLineSection {
+		return
+	}
+
+	var hiddenCommentIDs []int64
+	for commentLineNum, comments := range lineComments {
+		if commentLineNum < 0 {
+			// ATTENTION: BLOB-EXCERPT-COMMENT-RIGHT: skip left-side, unchanged lines always use "right (proposed)" side for comments
+			continue
+		}
+		lineNum := int(commentLineNum)
+		isEndOfFileExpansion := line.SectionInfo.RightHunkSize == 0
+		inRange := lineNum > line.SectionInfo.LastRightIdx &&
+			(isEndOfFileExpansion && lineNum <= line.SectionInfo.RightIdx ||
+				!isEndOfFileExpansion && lineNum < line.SectionInfo.RightIdx)
+
+		if inRange {
+			for _, comment := range comments {
+				hiddenCommentIDs = append(hiddenCommentIDs, comment.ID)
+			}
+		}
 	}
-	return DiffLineExpandSingle
+	line.SectionInfo.HiddenCommentIDs = hiddenCommentIDs
 }
 
 func getDiffLineSectionInfo(treePath, line string, lastLeftIdx, lastRightIdx int) *DiffLineSectionInfo {
@@ -485,6 +545,8 @@ func (diff *Diff) LoadComments(ctx context.Context, issue *issues_model.Issue, c
 					sort.SliceStable(line.Comments, func(i, j int) bool {
 						return line.Comments[i].CreatedUnix < line.Comments[j].CreatedUnix
 					})
+					// Mark expand buttons that have comments in hidden lines
+					FillHiddenCommentIDsForDiffLine(line, lineCommits)
 				}
 			}
 		}
@@ -1281,7 +1343,7 @@ type DiffShortStat struct {
 	NumFiles, TotalAddition, TotalDeletion int
 }
 
-func GetDiffShortStat(ctx context.Context, repo *repo_model.Repository, gitRepo *git.Repository, beforeCommitID, afterCommitID string) (*DiffShortStat, error) {
+func GetDiffShortStat(ctx context.Context, repoStorage gitrepo.Repository, gitRepo *git.Repository, beforeCommitID, afterCommitID string) (*DiffShortStat, error) {
 	afterCommit, err := gitRepo.GetCommit(afterCommitID)
 	if err != nil {
 		return nil, err
@@ -1293,7 +1355,7 @@ func GetDiffShortStat(ctx context.Context, repo *repo_model.Repository, gitRepo
 	}
 
 	diff := &DiffShortStat{}
-	diff.NumFiles, diff.TotalAddition, diff.TotalDeletion, err = gitrepo.GetDiffShortStatByCmdArgs(ctx, repo, nil, actualBeforeCommitID.String(), afterCommitID)
+	diff.NumFiles, diff.TotalAddition, diff.TotalDeletion, err = gitrepo.GetDiffShortStatByCmdArgs(ctx, repoStorage, nil, actualBeforeCommitID.String(), afterCommitID)
 	if err != nil {
 		return nil, err
 	}
@@ -1386,6 +1448,75 @@ func CommentAsDiff(ctx context.Context, c *issues_model.Comment) (*Diff, error)
 	return diff, nil
 }
 
+// GeneratePatchForUnchangedLine creates a patch showing code context for an unchanged line
+func GeneratePatchForUnchangedLine(gitRepo *git.Repository, commitID, treePath string, line int64, contextLines int) (string, error) {
+	commit, err := gitRepo.GetCommit(commitID)
+	if err != nil {
+		return "", fmt.Errorf("GetCommit: %w", err)
+	}
+
+	entry, err := commit.GetTreeEntryByPath(treePath)
+	if err != nil {
+		return "", fmt.Errorf("GetTreeEntryByPath: %w", err)
+	}
+
+	blob := entry.Blob()
+	dataRc, err := blob.DataAsync()
+	if err != nil {
+		return "", fmt.Errorf("DataAsync: %w", err)
+	}
+	defer dataRc.Close()
+
+	return generatePatchForUnchangedLineFromReader(dataRc, treePath, line, contextLines)
+}
+
+// generatePatchForUnchangedLineFromReader is the testable core logic that generates a patch from a reader
+func generatePatchForUnchangedLineFromReader(reader io.Reader, treePath string, line int64, contextLines int) (string, error) {
+	// Calculate line range (commented line + lines above it)
+	commentLine := int(line)
+	if line < 0 {
+		commentLine = int(-line)
+	}
+	startLine := max(commentLine-contextLines, 1)
+	endLine := commentLine
+
+	// Read only the needed lines efficiently
+	scanner := bufio.NewScanner(reader)
+	currentLine := 0
+	var lines []string
+	for scanner.Scan() {
+		currentLine++
+		if currentLine >= startLine && currentLine <= endLine {
+			lines = append(lines, scanner.Text())
+		}
+		if currentLine > endLine {
+			break
+		}
+	}
+	if err := scanner.Err(); err != nil {
+		return "", fmt.Errorf("scanner error: %w", err)
+	}
+
+	if len(lines) == 0 {
+		return "", fmt.Errorf("no lines found in range %d-%d", startLine, endLine)
+	}
+
+	// Generate synthetic patch
+	var patchBuilder strings.Builder
+	patchBuilder.WriteString(fmt.Sprintf("diff --git a/%s b/%s\n", treePath, treePath))
+	patchBuilder.WriteString(fmt.Sprintf("--- a/%s\n", treePath))
+	patchBuilder.WriteString(fmt.Sprintf("+++ b/%s\n", treePath))
+	patchBuilder.WriteString(fmt.Sprintf("@@ -%d,%d +%d,%d @@\n", startLine, len(lines), startLine, len(lines)))
+
+	for _, lineContent := range lines {
+		patchBuilder.WriteString(" ")
+		patchBuilder.WriteString(lineContent)
+		patchBuilder.WriteString("\n")
+	}
+
+	return patchBuilder.String(), nil
+}
+
 // CommentMustAsDiff executes AsDiff and logs the error instead of returning
 func CommentMustAsDiff(ctx context.Context, c *issues_model.Comment) *Diff {
 	if c == nil {

services/gitdiff/gitdiff_test.go

@@ -640,3 +640,346 @@ func TestNoCrashes(t *testing.T) {
 		ParsePatch(t.Context(), setting.Git.MaxGitDiffLines, setting.Git.MaxGitDiffLineCharacters, setting.Git.MaxGitDiffFiles, strings.NewReader(testcase.gitdiff), "")
 	}
 }
+
+func TestGeneratePatchForUnchangedLineFromReader(t *testing.T) {
+	tests := []struct {
+		name         string
+		content      string
+		treePath     string
+		line         int64
+		contextLines int
+		want         string
+		wantErr      bool
+	}{
+		{
+			name:         "single line with context",
+			content:      "line1\nline2\nline3\nline4\nline5\n",
+			treePath:     "test.txt",
+			line:         3,
+			contextLines: 1,
+			want: `diff --git a/test.txt b/test.txt
+--- a/test.txt
++++ b/test.txt
+@@ -2,2 +2,2 @@
+ line2
+ line3
+`,
+		},
+		{
+			name:         "negative line number (left side)",
+			content:      "line1\nline2\nline3\nline4\nline5\n",
+			treePath:     "test.txt",
+			line:         -3,
+			contextLines: 1,
+			want: `diff --git a/test.txt b/test.txt
+--- a/test.txt
++++ b/test.txt
+@@ -2,2 +2,2 @@
+ line2
+ line3
+`,
+		},
+		{
+			name:         "line near start of file",
+			content:      "line1\nline2\nline3\n",
+			treePath:     "test.txt",
+			line:         2,
+			contextLines: 5,
+			want: `diff --git a/test.txt b/test.txt
+--- a/test.txt
++++ b/test.txt
+@@ -1,2 +1,2 @@
+ line1
+ line2
+`,
+		},
+		{
+			name:         "first line with context",
+			content:      "line1\nline2\nline3\n",
+			treePath:     "test.txt",
+			line:         1,
+			contextLines: 3,
+			want: `diff --git a/test.txt b/test.txt
+--- a/test.txt
++++ b/test.txt
+@@ -1,1 +1,1 @@
+ line1
+`,
+		},
+		{
+			name:         "zero context lines",
+			content:      "line1\nline2\nline3\n",
+			treePath:     "test.txt",
+			line:         2,
+			contextLines: 0,
+			want: `diff --git a/test.txt b/test.txt
+--- a/test.txt
++++ b/test.txt
+@@ -2,1 +2,1 @@
+ line2
+`,
+		},
+		{
+			name:         "multi-line context",
+			content:      "package main\n\nfunc main() {\n  fmt.Println(\"Hello\")\n}\n",
+			treePath:     "main.go",
+			line:         4,
+			contextLines: 2,
+			want: `diff --git a/main.go b/main.go
+--- a/main.go
++++ b/main.go
+@@ -2,3 +2,3 @@
+<SP>
+ func main() {
+   fmt.Println("Hello")
+`,
+		},
+		{
+			name:         "empty file",
+			content:      "",
+			treePath:     "empty.txt",
+			line:         1,
+			contextLines: 1,
+			wantErr:      true,
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			reader := strings.NewReader(tt.content)
+			got, err := generatePatchForUnchangedLineFromReader(reader, tt.treePath, tt.line, tt.contextLines)
+			if tt.wantErr {
+				assert.Error(t, err)
+			} else {
+				require.NoError(t, err)
+				assert.Equal(t, strings.ReplaceAll(tt.want, "<SP>", " "), got)
+			}
+		})
+	}
+}
+
+func TestCalculateHiddenCommentIDsForLine(t *testing.T) {
+	tests := []struct {
+		name         string
+		line         *DiffLine
+		lineComments map[int64][]*issues_model.Comment
+		expected     []int64
+	}{
+		{
+			name: "comments in hidden range",
+			line: &DiffLine{
+				Type: DiffLineSection,
+				SectionInfo: &DiffLineSectionInfo{
+					LastRightIdx: 10,
+					RightIdx:     20,
+				},
+			},
+			lineComments: map[int64][]*issues_model.Comment{
+				15: {{ID: 100}, {ID: 101}},
+				12: {{ID: 102}},
+			},
+			expected: []int64{100, 101, 102},
+		},
+		{
+			name: "comments outside hidden range",
+			line: &DiffLine{
+				Type: DiffLineSection,
+				SectionInfo: &DiffLineSectionInfo{
+					LastRightIdx: 10,
+					RightIdx:     20,
+				},
+			},
+			lineComments: map[int64][]*issues_model.Comment{
+				5:  {{ID: 100}},
+				25: {{ID: 101}},
+			},
+			expected: nil,
+		},
+		{
+			name: "negative line numbers (left side)",
+			line: &DiffLine{
+				Type: DiffLineSection,
+				SectionInfo: &DiffLineSectionInfo{
+					LastRightIdx: 10,
+					RightIdx:     20,
+				},
+			},
+			lineComments: map[int64][]*issues_model.Comment{
+				-15: {{ID: 100}}, // Left-side comment, should NOT be counted
+				15:  {{ID: 101}}, // Right-side comment, should be counted
+			},
+			expected: []int64{101}, // Only right-side comment
+		},
+		{
+			name: "boundary conditions - normal expansion (both boundaries exclusive)",
+			line: &DiffLine{
+				Type: DiffLineSection,
+				SectionInfo: &DiffLineSectionInfo{
+					LastRightIdx:  10,
+					RightIdx:      20,
+					RightHunkSize: 5, // Normal case: next section has content
+				},
+			},
+			lineComments: map[int64][]*issues_model.Comment{
+				10: {{ID: 100}}, // at LastRightIdx (visible line), should NOT be included
+				20: {{ID: 101}}, // at RightIdx (visible line), should NOT be included
+				11: {{ID: 102}}, // just inside range, should be included
+				19: {{ID: 103}}, // just inside range, should be included
+			},
+			expected: []int64{102, 103},
+		},
+		{
+			name: "boundary conditions - end of file expansion (RightIdx inclusive)",
+			line: &DiffLine{
+				Type: DiffLineSection,
+				SectionInfo: &DiffLineSectionInfo{
+					LastRightIdx:  54,
+					RightIdx:      70,
+					RightHunkSize: 0, // End of file: no more content after
+				},
+			},
+			lineComments: map[int64][]*issues_model.Comment{
+				54: {{ID: 54}}, // at LastRightIdx (visible line), should NOT be included
+				70: {{ID: 70}}, // at RightIdx (last hidden line), SHOULD be included
+				60: {{ID: 60}}, // inside range, should be included
+			},
+			expected: []int64{60, 70}, // Lines 60 and 70 are hidden
+		},
+		{
+			name: "real-world scenario - start of file with hunk",
+			line: &DiffLine{
+				Type: DiffLineSection,
+				SectionInfo: &DiffLineSectionInfo{
+					LastRightIdx:  0,  // No previous visible section
+					RightIdx:      26, // Line 26 is first visible line of hunk
+					RightHunkSize: 9,  // Normal hunk with content
+				},
+			},
+			lineComments: map[int64][]*issues_model.Comment{
+				1:  {{ID: 1}},  // Line 1 is hidden
+				26: {{ID: 26}}, // Line 26 is visible (hunk start) - should NOT be hidden
+				10: {{ID: 10}}, // Line 10 is hidden
+				15: {{ID: 15}}, // Line 15 is hidden
+			},
+			expected: []int64{1, 10, 15}, // Lines 1, 10, 15 are hidden; line 26 is visible
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			FillHiddenCommentIDsForDiffLine(tt.line, tt.lineComments)
+			assert.ElementsMatch(t, tt.expected, tt.line.SectionInfo.HiddenCommentIDs)
+		})
+	}
+}
+
+func TestDiffLine_RenderBlobExcerptButtons(t *testing.T) {
+	tests := []struct {
+		name             string
+		line             *DiffLine
+		fileNameHash     string
+		data             *DiffBlobExcerptData
+		expectContains   []string
+		expectNotContain []string
+	}{
+		{
+			name: "expand up button with hidden comments",
+			line: &DiffLine{
+				Type: DiffLineSection,
+				SectionInfo: &DiffLineSectionInfo{
+					LastRightIdx:     0,
+					RightIdx:         26,
+					LeftIdx:          26,
+					LastLeftIdx:      0,
+					LeftHunkSize:     0,
+					RightHunkSize:    0,
+					HiddenCommentIDs: []int64{100},
+				},
+			},
+			fileNameHash: "abc123",
+			data: &DiffBlobExcerptData{
+				BaseLink:      "/repo/blob_excerpt",
+				AfterCommitID: "commit123",
+				DiffStyle:     "unified",
+			},
+			expectContains: []string{
+				"octicon-fold-up",
+				"direction=up",
+				"code-comment-more",
+				"1 hidden comment(s)",
+			},
+		},
+		{
+			name: "expand up and down buttons with pull request",
+			line: &DiffLine{
+				Type: DiffLineSection,
+				SectionInfo: &DiffLineSectionInfo{
+					LastRightIdx:     10,
+					RightIdx:         50,
+					LeftIdx:          10,
+					LastLeftIdx:      5,
+					LeftHunkSize:     5,
+					RightHunkSize:    5,
+					HiddenCommentIDs: []int64{200, 201},
+				},
+			},
+			fileNameHash: "def456",
+			data: &DiffBlobExcerptData{
+				BaseLink:       "/repo/blob_excerpt",
+				AfterCommitID:  "commit456",
+				DiffStyle:      "split",
+				PullIssueIndex: 42,
+			},
+			expectContains: []string{
+				"octicon-fold-down",
+				"octicon-fold-up",
+				"direction=down",
+				"direction=up",
+				`data-hidden-comment-ids=",200,201,"`, // use leading and trailing commas to ensure exact match by CSS selector `attr*=",id,"`
+				"pull_issue_index=42",
+				"2 hidden comment(s)",
+			},
+		},
+		{
+			name: "no hidden comments",
+			line: &DiffLine{
+				Type: DiffLineSection,
+				SectionInfo: &DiffLineSectionInfo{
+					LastRightIdx:     10,
+					RightIdx:         20,
+					LeftIdx:          10,
+					LastLeftIdx:      5,
+					LeftHunkSize:     5,
+					RightHunkSize:    5,
+					HiddenCommentIDs: nil,
+				},
+			},
+			fileNameHash: "ghi789",
+			data: &DiffBlobExcerptData{
+				BaseLink:      "/repo/blob_excerpt",
+				AfterCommitID: "commit789",
+			},
+			expectContains: []string{
+				"code-expander-button",
+			},
+			expectNotContain: []string{
+				"code-comment-more",
+			},
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			result := tt.line.RenderBlobExcerptButtons(tt.fileNameHash, tt.data)
+			resultStr := string(result)
+
+			for _, expected := range tt.expectContains {
+				assert.Contains(t, resultStr, expected, "Expected to contain: %s", expected)
+			}
+
+			for _, notExpected := range tt.expectNotContain {
+				assert.NotContains(t, resultStr, notExpected, "Expected NOT to contain: %s", notExpected)
+			}
+		})
+	}
+}

services/pull/review.go

@@ -22,6 +22,7 @@ import (
 	"code.gitea.io/gitea/modules/optional"
 	"code.gitea.io/gitea/modules/setting"
 	"code.gitea.io/gitea/modules/util"
+	"code.gitea.io/gitea/services/gitdiff"
 	notify_service "code.gitea.io/gitea/services/notify"
 )
 
@@ -283,6 +284,15 @@ func createCodeComment(ctx context.Context, doer *user_model.User, repo *repo_mo
 			log.Error("Error whilst generating patch: %v", err)
 			return nil, err
 		}
+
+		// If patch is still empty (unchanged line), generate code context
+		if patch == "" && commitID != "" {
+			patch, err = gitdiff.GeneratePatchForUnchangedLine(gitRepo, commitID, treePath, line, setting.UI.CodeCommentLines)
+			if err != nil {
+				// Log the error but don't fail comment creation
+				log.Debug("Unable to generate patch for unchanged line (file=%s, line=%d, commit=%s): %v", treePath, line, commitID, err)
+			}
+		}
 	}
 	return issues_model.CreateComment(ctx, &issues_model.CreateCommentOptions{
 		Type:        issues_model.CommentTypeCode,

templates/repo/diff/blob_excerpt.tmpl

@@ -1,28 +1,10 @@
-{{$blobExcerptLink := print $.RepoLink (Iif $.PageIsWiki "/wiki" "") "/blob_excerpt/" (PathEscape $.AfterCommitID) (QueryBuild "?" "anchor" $.Anchor)}}
+{{$diffBlobExcerptData := .DiffBlobExcerptData}}
+{{$canCreateComment := and ctx.RootData.SignedUserID $diffBlobExcerptData.PullIssueIndex}}
 {{if $.IsSplitStyle}}
 	{{range $k, $line := $.section.Lines}}
-	<tr class="{{.GetHTMLDiffLineType}}-code nl-{{$k}} ol-{{$k}} line-expanded">
+	<tr class="{{.GetHTMLDiffLineType}}-code nl-{{$k}} ol-{{$k}} line-expanded" data-line-type="{{.GetHTMLDiffLineType}}">
 		{{if eq .GetType 4}}
-			{{$expandDirection := $line.GetExpandDirection}}
-			<td class="lines-num lines-num-old" data-line-num="{{if $line.LeftIdx}}{{$line.LeftIdx}}{{end}}">
-				<div class="code-expander-buttons" data-expand-direction="{{$expandDirection}}">
-				{{if or (eq $expandDirection 3) (eq $expandDirection 5)}}
-					<button class="code-expander-button" hx-target="closest tr" hx-get="{{$blobExcerptLink}}&{{$line.GetBlobExcerptQuery}}&style=split&direction=down">
-						{{svg "octicon-fold-down"}}
-					</button>
-				{{end}}
-				{{if or (eq $expandDirection 3) (eq $expandDirection 4)}}
-					<button class="code-expander-button" hx-target="closest tr" hx-get="{{$blobExcerptLink}}&{{$line.GetBlobExcerptQuery}}&style=split&direction=up">
-						{{svg "octicon-fold-up"}}
-					</button>
-				{{end}}
-				{{if eq $expandDirection 2}}
-					<button class="code-expander-button" hx-target="closest tr" hx-get="{{$blobExcerptLink}}&{{$line.GetBlobExcerptQuery}}&style=split">
-						{{svg "octicon-fold"}}
-					</button>
-				{{end}}
-				</div>
-			</td>
+			<td class="lines-num lines-num-old">{{$line.RenderBlobExcerptButtons $.FileNameHash $diffBlobExcerptData}}</td>
 			<td colspan="7" class="lines-code lines-code-old">
 				{{- $inlineDiff := $.section.GetComputedInlineDiffFor $line ctx.Locale -}}
 				{{- template "repo/diff/section_code" dict "diff" $inlineDiff -}}
@@ -33,6 +15,12 @@
 			<td class="lines-escape lines-escape-old">{{if and $line.LeftIdx $inlineDiff.EscapeStatus.Escaped}}<button class="toggle-escape-button btn interact-bg" title="{{template "repo/diff/escape_title" dict "diff" $inlineDiff}}"></button>{{end}}</td>
 			<td class="lines-type-marker lines-type-marker-old">{{if $line.LeftIdx}}<span class="tw-font-mono" data-type-marker=""></span>{{end}}</td>
 			<td class="lines-code lines-code-old">
+				{{/* ATTENTION: BLOB-EXCERPT-COMMENT-RIGHT: here it intentially use "right" side to comment, because the backend code depends on the assumption that the comment only happens on right side*/}}
+				{{- if and $canCreateComment $line.RightIdx -}}
+					<button type="button" aria-label="{{ctx.Locale.Tr "repo.diff.comment.add_line_comment"}}" class="ui primary button add-code-comment add-code-comment-right{{if (not $line.CanComment)}} tw-invisible{{end}}" data-side="right" data-idx="{{$line.RightIdx}}">
+						{{- svg "octicon-plus" -}}
+					</button>
+				{{- end -}}
 				{{- if $line.LeftIdx -}}
 					{{- template "repo/diff/section_code" dict "diff" $inlineDiff -}}
 				{{- else -}}
@@ -43,6 +31,11 @@
 			<td class="lines-escape lines-escape-new">{{if and $line.RightIdx $inlineDiff.EscapeStatus.Escaped}}<button class="toggle-escape-button btn interact-bg" title="{{template "repo/diff/escape_title" dict "diff" $inlineDiff}}"></button>{{end}}</td>
 			<td class="lines-type-marker lines-type-marker-new">{{if $line.RightIdx}}<span class="tw-font-mono" data-type-marker=""></span>{{end}}</td>
 			<td class="lines-code lines-code-new">
+				{{- if and $canCreateComment $line.RightIdx -}}
+					<button type="button" aria-label="{{ctx.Locale.Tr "repo.diff.comment.add_line_comment"}}" class="ui primary button add-code-comment add-code-comment-right{{if (not $line.CanComment)}} tw-invisible{{end}}" data-side="right" data-idx="{{$line.RightIdx}}">
+						{{- svg "octicon-plus" -}}
+					</button>
+				{{- end -}}
 				{{- if $line.RightIdx -}}
 					{{- template "repo/diff/section_code" dict "diff" $inlineDiff -}}
 				{{- else -}}
@@ -51,31 +44,26 @@
 			</td>
 		{{end}}
 	</tr>
+	{{if $line.Comments}}
+		<tr class="add-comment" data-line-type="{{.GetHTMLDiffLineType}}">
+			<td class="add-comment-left" colspan="4">
+				{{if eq $line.GetCommentSide "previous"}}
+					{{template "repo/diff/conversation" dict "." $ "comments" $line.Comments}}
+				{{end}}
+			</td>
+			<td class="add-comment-right" colspan="4">
+				{{if eq $line.GetCommentSide "proposed"}}
+					{{template "repo/diff/conversation" dict "." $ "comments" $line.Comments}}
+				{{end}}
+			</td>
+		</tr>
+	{{end}}
 	{{end}}
 {{else}}
 	{{range $k, $line := $.section.Lines}}
-	<tr class="{{.GetHTMLDiffLineType}}-code nl-{{$k}} ol-{{$k}} line-expanded">
+	<tr class="{{.GetHTMLDiffLineType}}-code nl-{{$k}} ol-{{$k}} line-expanded" data-line-type="{{.GetHTMLDiffLineType}}">
 		{{if eq .GetType 4}}
-			{{$expandDirection := $line.GetExpandDirection}}
-			<td colspan="2" class="lines-num">
-				<div class="code-expander-buttons" data-expand-direction="{{$expandDirection}}">
-					{{if or (eq $expandDirection 3) (eq $expandDirection 5)}}
-						<button class="code-expander-button" hx-target="closest tr" hx-get="{{$blobExcerptLink}}&{{$line.GetBlobExcerptQuery}}&style=unified&direction=down">
-							{{svg "octicon-fold-down"}}
-						</button>
-					{{end}}
-					{{if or (eq $expandDirection 3) (eq $expandDirection 4)}}
-						<button class="code-expander-button" hx-target="closest tr" hx-get="{{$blobExcerptLink}}&{{$line.GetBlobExcerptQuery}}&style=unified&direction=up">
-							{{svg "octicon-fold-up"}}
-						</button>
-					{{end}}
-					{{if eq $expandDirection 2}}
-						<button class="code-expander-button" hx-target="closest tr" hx-get="{{$blobExcerptLink}}&{{$line.GetBlobExcerptQuery}}&style=unified">
-							{{svg "octicon-fold"}}
-						</button>
-					{{end}}
-				</div>
-			</td>
+			<td colspan="2" class="lines-num">{{$line.RenderBlobExcerptButtons $.FileNameHash $diffBlobExcerptData}}</td>
 		{{else}}
 			<td class="lines-num lines-num-old" data-line-num="{{if $line.LeftIdx}}{{$line.LeftIdx}}{{end}}"><span rel="{{if $line.LeftIdx}}diff-{{$.FileNameHash}}L{{$line.LeftIdx}}{{end}}"></span></td>
 			<td class="lines-num lines-num-new" data-line-num="{{if $line.RightIdx}}{{$line.RightIdx}}{{end}}"><span rel="{{if $line.RightIdx}}diff-{{$.FileNameHash}}R{{$line.RightIdx}}{{end}}"></span></td>
@@ -83,7 +71,21 @@
 		{{$inlineDiff := $.section.GetComputedInlineDiffFor $line ctx.Locale}}
 		<td class="lines-escape">{{if $inlineDiff.EscapeStatus.Escaped}}<button class="toggle-escape-button btn interact-bg" title="{{template "repo/diff/escape_title" dict "diff" $inlineDiff}}"></button>{{end}}</td>
 		<td class="lines-type-marker"><span class="tw-font-mono" data-type-marker="{{$line.GetLineTypeMarker}}"></span></td>
-		<td class="lines-code{{if (not $line.RightIdx)}} lines-code-old{{end}}"><code {{if $inlineDiff.EscapeStatus.Escaped}}class="code-inner has-escaped" title="{{template "repo/diff/escape_title" dict "diff" $inlineDiff}}"{{else}}class="code-inner"{{end}}>{{$inlineDiff.Content}}</code></td>
+		<td class="lines-code{{if (not $line.RightIdx)}} lines-code-old{{end}}">
+			{{- if and $canCreateComment -}}
+				<button type="button" aria-label="{{ctx.Locale.Tr "repo.diff.comment.add_line_comment"}}" class="ui primary button add-code-comment add-code-comment-{{if $line.RightIdx}}right{{else}}left{{end}}{{if (not $line.CanComment)}} tw-invisible{{end}}" data-side="{{if $line.RightIdx}}right{{else}}left{{end}}" data-idx="{{if $line.RightIdx}}{{$line.RightIdx}}{{else}}{{$line.LeftIdx}}{{end}}">
+					{{- svg "octicon-plus" -}}
+				</button>
+			{{- end -}}
+			<code {{if $inlineDiff.EscapeStatus.Escaped}}class="code-inner has-escaped" title="{{template "repo/diff/escape_title" dict "diff" $inlineDiff}}"{{else}}class="code-inner"{{end}}>{{$inlineDiff.Content}}</code>
+		</td>
 	</tr>
+	{{if $line.Comments}}
+		<tr class="add-comment" data-line-type="{{.GetHTMLDiffLineType}}">
+			<td class="add-comment-left add-comment-right" colspan="5">
+				{{template "repo/diff/conversation" dict "." $ "comments" $line.Comments}}
+			</td>
+		</tr>
+	{{end}}
 	{{end}}
 {{end}}

templates/repo/diff/section_split.tmpl

@@ -1,5 +1,5 @@
 {{$file := .file}}
-{{$blobExcerptLink := print (or ctx.RootData.CommitRepoLink ctx.RootData.RepoLink) (Iif $.root.PageIsWiki "/wiki" "") "/blob_excerpt/" (PathEscape $.root.AfterCommitID) "?"}}
+{{$diffBlobExcerptData := $.root.DiffBlobExcerptData}}
 <colgroup>
 	<col width="50">
 	<col width="10">
@@ -16,26 +16,8 @@
 		{{if or (ne .GetType 2) (not $hasmatch)}}
 			<tr class="{{.GetHTMLDiffLineType}}-code nl-{{$k}} ol-{{$k}}" data-line-type="{{.GetHTMLDiffLineType}}">
 				{{if eq .GetType 4}}
-					{{$expandDirection := $line.GetExpandDirection}}
-					<td class="lines-num lines-num-old">
-						<div class="code-expander-buttons" data-expand-direction="{{$expandDirection}}">
-						{{if or (eq $expandDirection 3) (eq $expandDirection 5)}}
-							<button class="code-expander-button" hx-target="closest tr" hx-get="{{$blobExcerptLink}}&{{$line.GetBlobExcerptQuery}}&style=split&direction=down&&anchor=diff-{{$file.NameHash}}K{{$line.SectionInfo.RightIdx}}">
-								{{svg "octicon-fold-down"}}
-							</button>
-						{{end}}
-						{{if or (eq $expandDirection 3) (eq $expandDirection 4)}}
-							<button class="code-expander-button" hx-target="closest tr" hx-get="{{$blobExcerptLink}}&{{$line.GetBlobExcerptQuery}}&style=split&direction=up&anchor=diff-{{$file.NameHash}}K{{$line.SectionInfo.RightIdx}}">
-								{{svg "octicon-fold-up"}}
-							</button>
-						{{end}}
-						{{if eq $expandDirection 2}}
-							<button class="code-expander-button" hx-target="closest tr" hx-get="{{$blobExcerptLink}}&{{$line.GetBlobExcerptQuery}}&style=split&anchor=diff-{{$file.NameHash}}K{{$line.SectionInfo.RightIdx}}">
-								{{svg "octicon-fold"}}
-							</button>
-						{{end}}
-						</div>
-					</td>{{$inlineDiff := $section.GetComputedInlineDiffFor $line ctx.Locale}}
+					{{$inlineDiff := $section.GetComputedInlineDiffFor $line ctx.Locale}}
+					<td class="lines-num lines-num-old">{{$line.RenderBlobExcerptButtons $file.NameHash $diffBlobExcerptData}}</td>
 					<td class="lines-escape lines-escape-old">{{if $inlineDiff.EscapeStatus.Escaped}}<button class="toggle-escape-button btn interact-bg" title="{{template "repo/diff/escape_title" dict "diff" $inlineDiff}}"></button>{{end}}</td>
 					<td colspan="6" class="lines-code lines-code-old">{{template "repo/diff/section_code" dict "diff" $inlineDiff}}</td>
 				{{else if and (eq .GetType 3) $hasmatch}}{{/* DEL */}}

templates/repo/diff/section_unified.tmpl

@@ -1,7 +1,6 @@
 {{$file := .file}}
-{{$repoLink := or ctx.RootData.CommitRepoLink ctx.RootData.RepoLink}}
-{{$afterCommitID := or $.root.AfterCommitID "no-after-commit-id"}}{{/* this tmpl is also used by the PR Conversation page, so the "AfterCommitID" may not exist */}}
-{{$blobExcerptLink := print $repoLink (Iif $.root.PageIsWiki "/wiki" "") "/blob_excerpt/" (PathEscape $afterCommitID) "?"}}
+{{/* this tmpl is also used by the PR Conversation page, so the "AfterCommitID" and "DiffBlobExcerptData" may not exist */}}
+{{$diffBlobExcerptData := $.root.DiffBlobExcerptData}}
 <colgroup>
 	<col width="50">
 	<col width="50">
@@ -14,26 +13,7 @@
 		<tr class="{{.GetHTMLDiffLineType}}-code nl-{{$k}} ol-{{$k}}" data-line-type="{{.GetHTMLDiffLineType}}">
 			{{if eq .GetType 4}}
 				{{if $.root.AfterCommitID}}
-					{{$expandDirection := $line.GetExpandDirection}}
-					<td colspan="2" class="lines-num">
-						<div class="code-expander-buttons" data-expand-direction="{{$expandDirection}}">
-							{{if or (eq $expandDirection 3) (eq $expandDirection 5)}}
-								<button class="code-expander-button" hx-target="closest tr" hx-get="{{$blobExcerptLink}}&{{$line.GetBlobExcerptQuery}}&style=unified&direction=down&anchor=diff-{{$file.NameHash}}K{{$line.SectionInfo.RightIdx}}">
-									{{svg "octicon-fold-down"}}
-								</button>
-							{{end}}
-							{{if or (eq $expandDirection 3) (eq $expandDirection 4)}}
-								<button class="code-expander-button" hx-target="closest tr" hx-get="{{$blobExcerptLink}}&{{$line.GetBlobExcerptQuery}}&style=unified&direction=up&anchor=diff-{{$file.NameHash}}K{{$line.SectionInfo.RightIdx}}">
-									{{svg "octicon-fold-up"}}
-								</button>
-							{{end}}
-							{{if eq $expandDirection 2}}
-								<button class="code-expander-button" hx-target="closest tr" hx-get="{{$blobExcerptLink}}&{{$line.GetBlobExcerptQuery}}&style=unified&anchor=diff-{{$file.NameHash}}K{{$line.SectionInfo.RightIdx}}">
-									{{svg "octicon-fold"}}
-								</button>
-							{{end}}
-						</div>
-					</td>
+					<td colspan="2" class="lines-num">{{$line.RenderBlobExcerptButtons $file.NameHash $diffBlobExcerptData}}</td>
 				{{else}}
 					{{/* for code file preview page or comment diffs on pull comment pages, do not show the expansion arrows */}}
 					<td colspan="2" class="lines-num"></td>

templates/repo/issue/view_content/conversation.tmpl

@@ -1,3 +1,8 @@
+{{/* FIXME: DIFF-CONVERSATION-DATA: in the future this template should be refactor to avoid called by {{... "." $}}
+At the moment, two kinds of request handler call this template:
+* ExcerptBlob -> blob_excerpt.tmpl -> this
+* Other compare and diff pages -> ... -> {section_unified.tmpl|section_split.tmpl} -> this)
+The variables in "ctx.Data" are different in each case, making this template fragile, hard to read and maintain. */}}
 {{if len .comments}}
 	{{$comment := index .comments 0}}
 	{{$invalid := $comment.Invalidated}}

web_src/css/review.css

@@ -115,6 +115,23 @@
   color: var(--color-text);
 }
 
+.code-expander-buttons {
+  position: relative;
+}
+
+.code-expander-buttons .code-comment-more {
+  position: absolute;
+  line-height: 12px;
+  padding: 2px 4px;
+  font-size: 10px;
+  background-color: var(--color-primary);
+  color: var(--color-primary-contrast);
+  border-radius: 8px !important;
+  left: -12px;
+  top: 6px;
+  text-align: center;
+}
+
 .code-expander-button {
   border: none;
   color: var(--color-text-light);
@@ -127,8 +144,8 @@
   flex: 1;
 }
 
-/* expand direction 3 is both ways with two buttons */
-.code-expander-buttons[data-expand-direction="3"] .code-expander-button {
+/* expand direction "updown" is both ways with two buttons */
+.code-expander-buttons[data-expand-direction="updown"] .code-expander-button {
   height: 18px;
 }
 

web_src/js/features/repo-diff.ts

@@ -9,7 +9,7 @@ import {submitEventSubmitter, queryElemSiblings, hideElem, showElem, animateOnce
 import {POST, GET} from '../modules/fetch.ts';
 import {createTippy} from '../modules/tippy.ts';
 import {invertFileFolding} from './file-fold.ts';
-import {parseDom} from '../utils.ts';
+import {parseDom, sleep} from '../utils.ts';
 import {registerGlobalSelectorFunc} from '../modules/observer.ts';
 
 const {i18n} = window.config;
@@ -218,21 +218,46 @@ function initRepoDiffShowMore() {
   });
 }
 
-async function loadUntilFound() {
-  const hashTargetSelector = window.location.hash;
-  if (!hashTargetSelector.startsWith('#diff-') && !hashTargetSelector.startsWith('#issuecomment-')) {
-    return;
-  }
+async function onLocationHashChange() {
+  // try to scroll to the target element by the current hash
+  const currentHash = window.location.hash;
+  if (!currentHash.startsWith('#diff-') && !currentHash.startsWith('#issuecomment-')) return;
+
+  // avoid reentrance when we are changing the hash to scroll and trigger ":target" selection
+  const attrAutoScrollRunning = 'data-auto-scroll-running';
+  if (document.body.hasAttribute(attrAutoScrollRunning)) return;
 
-  while (true) {
+  const targetElementId = currentHash.substring(1);
+  while (currentHash === window.location.hash) {
     // use getElementById to avoid querySelector throws an error when the hash is invalid
     // eslint-disable-next-line unicorn/prefer-query-selector
-    const targetElement = document.getElementById(hashTargetSelector.substring(1));
+    const targetElement = document.getElementById(targetElementId);
     if (targetElement) {
+      // need to change hash to re-trigger ":target" CSS selector, let's manually scroll to it
       targetElement.scrollIntoView();
+      document.body.setAttribute(attrAutoScrollRunning, 'true');
+      window.location.hash = '';
+      window.location.hash = currentHash;
+      setTimeout(() => document.body.removeAttribute(attrAutoScrollRunning), 0);
       return;
     }
 
+    // If looking for a hidden comment, try to expand the section that contains it
+    const issueCommentPrefix = '#issuecomment-';
+    if (currentHash.startsWith(issueCommentPrefix)) {
+      const commentId = currentHash.substring(issueCommentPrefix.length);
+      const expandButton = document.querySelector<HTMLElement>(`.code-expander-button[data-hidden-comment-ids*=",${commentId},"]`);
+      if (expandButton) {
+        // avoid infinite loop, do not re-click the button if already clicked
+        const attrAutoLoadClicked = 'data-auto-load-clicked';
+        if (expandButton.hasAttribute(attrAutoLoadClicked)) return;
+        expandButton.setAttribute(attrAutoLoadClicked, 'true');
+        expandButton.click();
+        await sleep(500); // Wait for HTMX to load the content. FIXME: need to drop htmx in the future
+        continue; // Try again to find the element
+      }
+    }
+
     // the button will be refreshed after each "load more", so query it every time
     const showMoreButton = document.querySelector('#diff-show-more-files');
     if (!showMoreButton) {
@@ -246,8 +271,8 @@ async function loadUntilFound() {
 }
 
 function initRepoDiffHashChangeListener() {
-  window.addEventListener('hashchange', loadUntilFound);
-  loadUntilFound();
+  window.addEventListener('hashchange', onLocationHashChange);
+  onLocationHashChange();
 }
 
 export function initRepoDiffView() {