Use git diff-tree for DiffFileTree on diff pages (#33514)

Modify Diff View FileTree to show all files

## Changes

* removes Show Status button on diff
* uses `git diff-tree` to generate the file tree for the diff
* doesn't reload the diff tree each time we load more files in the
preview
* selecting and unloaded file will keep loading until that file is
loaded
* removes `DiffFileList.vue` and "Show Stats" in diff options

## Open Questions

* selecting and unloaded file will keep loading until that file is
loaded. Is this behaviour okay? It matches what github does.

### Demo

In this demo I set `git.MAX_GIT_DIFF_FILES=1` in my `app.ini` to
demonstrate a worst case example. In most cases the behaviour isn't
nearly as jarring as we load a bunch of files at a time.


https://github.com/user-attachments/assets/72f29663-d6fc-472d-94fa-7fb5950c2836

---------

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

routers/web/repo/commit.go

@@ -344,18 +344,30 @@ func Diff(ctx *context.Context) {
 	ctx.Data["Reponame"] = repoName
 
 	var parentCommit *git.Commit
+	var parentCommitID string
 	if commit.ParentCount() > 0 {
 		parentCommit, err = gitRepo.GetCommit(parents[0])
 		if err != nil {
 			ctx.NotFound(err)
 			return
 		}
+		parentCommitID = parentCommit.ID.String()
 	}
 	setCompareContext(ctx, parentCommit, commit, userName, repoName)
 	ctx.Data["Title"] = commit.Summary() + " · " + base.ShortSha(commitID)
 	ctx.Data["Commit"] = commit
 	ctx.Data["Diff"] = diff
 
+	if !fileOnly {
+		diffTree, err := gitdiff.GetDiffTree(ctx, gitRepo, false, parentCommitID, commitID)
+		if err != nil {
+			ctx.ServerError("GetDiffTree", err)
+			return
+		}
+
+		ctx.PageData["DiffFiles"] = transformDiffTreeForUI(diffTree, nil)
+	}
+
 	statuses, _, err := git_model.GetLatestCommitStatus(ctx, ctx.Repo.Repository.ID, commitID, db.ListOptionsAll)
 	if err != nil {
 		log.Error("GetLatestCommitStatus: %v", err)

routers/web/repo/compare.go

@@ -633,6 +633,16 @@ func PrepareCompareDiff(
 	ctx.Data["Diff"] = diff
 	ctx.Data["DiffNotAvailable"] = diff.NumFiles == 0
 
+	if !fileOnly {
+		diffTree, err := gitdiff.GetDiffTree(ctx, ci.HeadGitRepo, false, beforeCommitID, headCommitID)
+		if err != nil {
+			ctx.ServerError("GetDiffTree", err)
+			return false
+		}
+
+		ctx.PageData["DiffFiles"] = transformDiffTreeForUI(diffTree, nil)
+	}
+
 	headCommit, err := ci.HeadGitRepo.GetCommit(headCommitID)
 	if err != nil {
 		ctx.ServerError("GetCommit", err)

routers/web/repo/pull.go

@@ -761,6 +761,7 @@ func viewPullFiles(ctx *context.Context, specifiedStartCommit, specifiedEndCommi
 
 	var methodWithError string
 	var diff *gitdiff.Diff
+	shouldGetUserSpecificDiff := false
 
 	// if we're not logged in or only a single commit (or commit range) is shown we
 	// have to load only the diff and not get the viewed information
@@ -772,6 +773,7 @@ func viewPullFiles(ctx *context.Context, specifiedStartCommit, specifiedEndCommi
 	} else {
 		diff, err = gitdiff.SyncAndGetUserSpecificDiff(ctx, ctx.Doer.ID, pull, gitRepo, diffOptions, files...)
 		methodWithError = "SyncAndGetUserSpecificDiff"
+		shouldGetUserSpecificDiff = true
 	}
 	if err != nil {
 		ctx.ServerError(methodWithError, err)
@@ -816,6 +818,27 @@ func viewPullFiles(ctx *context.Context, specifiedStartCommit, specifiedEndCommi
 		}
 	}
 
+	if !fileOnly {
+		// note: use mergeBase is set to false because we already have the merge base from the pull request info
+		diffTree, err := gitdiff.GetDiffTree(ctx, gitRepo, false, pull.MergeBase, headCommitID)
+		if err != nil {
+			ctx.ServerError("GetDiffTree", err)
+			return
+		}
+
+		filesViewedState := make(map[string]pull_model.ViewedState)
+		if shouldGetUserSpecificDiff {
+			// This sort of sucks because we already fetch this when getting the diff
+			review, err := pull_model.GetNewestReviewState(ctx, ctx.Doer.ID, issue.ID)
+			if err == nil && review != nil && review.UpdatedFiles != nil {
+				// If there wasn't an error and we have a review with updated files, use that
+				filesViewedState = review.UpdatedFiles
+			}
+		}
+
+		ctx.PageData["DiffFiles"] = transformDiffTreeForUI(diffTree, filesViewedState)
+	}
+
 	ctx.Data["Diff"] = diff
 	ctx.Data["DiffNotAvailable"] = diff.NumFiles == 0
 

routers/web/repo/treelist.go

@@ -6,9 +6,11 @@ package repo
 import (
 	"net/http"
 
+	pull_model "code.gitea.io/gitea/models/pull"
 	"code.gitea.io/gitea/modules/base"
 	"code.gitea.io/gitea/modules/git"
 	"code.gitea.io/gitea/services/context"
+	"code.gitea.io/gitea/services/gitdiff"
 
 	"github.com/go-enry/go-enry/v2"
 )
@@ -52,3 +54,33 @@ func isExcludedEntry(entry *git.TreeEntry) bool {
 
 	return false
 }
+
+type FileDiffFile struct {
+	Name        string
+	NameHash    string
+	IsSubmodule bool
+	IsViewed    bool
+	Status      string
+}
+
+// transformDiffTreeForUI transforms a DiffTree into a slice of FileDiffFile for UI rendering
+// it also takes a map of file names to their viewed state, which is used to mark files as viewed
+func transformDiffTreeForUI(diffTree *gitdiff.DiffTree, filesViewedState map[string]pull_model.ViewedState) []FileDiffFile {
+	files := make([]FileDiffFile, 0, len(diffTree.Files))
+
+	for _, file := range diffTree.Files {
+		nameHash := git.HashFilePathForWebUI(file.HeadPath)
+		isSubmodule := file.HeadMode == git.EntryModeCommit
+		isViewed := filesViewedState[file.HeadPath] == pull_model.Viewed
+
+		files = append(files, FileDiffFile{
+			Name:        file.HeadPath,
+			NameHash:    nameHash,
+			IsSubmodule: isSubmodule,
+			IsViewed:    isViewed,
+			Status:      file.Status,
+		})
+	}
+
+	return files
+}