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/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)
 }