Decouple diff stats query from actual diffing (#33810)

The diff stats are no longer part of the diff generation.
Use `GetDiffShortStat` instead to get the total number of changed files,
added lines, and deleted lines.
As such, `gitdiff.GetDiff` can be simplified:
It should not do more than expected.

And do not run "git diff --shortstat" for pull list. Fix #31492

4 files changed, 37 insertions, 29 deletions

diff --git a/routers/web/repo/commit.go b/routers/web/repo/commit.go
index 2728eda8b6..997e9f6869 100644
--- a/routers/web/repo/commit.go
+++ b/routers/web/repo/commit.go
@@ -321,12 +321,17 @@ func Diff(ctx *context.Context) {
 		MaxLineCharacters:  setting.Git.MaxGitDiffLineCharacters,
 		MaxFiles:           maxFiles,
 		WhitespaceBehavior: gitdiff.GetWhitespaceFlag(ctx.Data["WhitespaceBehavior"].(string)),
-		FileOnly:           fileOnly,
 	}, files...)
 	if err != nil {
 		ctx.NotFound(err)
 		return
 	}
+	diffShortStat, err := gitdiff.GetDiffShortStat(gitRepo, "", commitID)
+	if err != nil {
+		ctx.ServerError("GetDiffShortStat", err)
+		return
+	}
+	ctx.Data["DiffShortStat"] = diffShortStat
 
 	parents := make([]string, commit.ParentCount())
 	for i := 0; i < commit.ParentCount(); i++ {
@@ -383,7 +388,7 @@ func Diff(ctx *context.Context) {
 	ctx.Data["Verification"] = verification
 	ctx.Data["Author"] = user_model.ValidateCommitWithEmail(ctx, commit)
 	ctx.Data["Parents"] = parents
-	ctx.Data["DiffNotAvailable"] = diff.NumFiles == 0
+	ctx.Data["DiffNotAvailable"] = diffShortStat.NumFiles == 0
 
 	if err := asymkey_model.CalculateTrustStatus(verification, ctx.Repo.Repository.GetTrustModel(), func(user *user_model.User) (bool, error) {
 		return repo_model.IsOwnerMemberCollaborator(ctx, ctx.Repo.Repository, user.ID)
diff --git a/routers/web/repo/compare.go b/routers/web/repo/compare.go
index 5165636a52..d9c6305ce1 100644
--- a/routers/web/repo/compare.go
+++ b/routers/web/repo/compare.go
@@ -624,14 +624,19 @@ func PrepareCompareDiff(
 			MaxFiles:           maxFiles,
 			WhitespaceBehavior: whitespaceBehavior,
 			DirectComparison:   ci.DirectComparison,
-			FileOnly:           fileOnly,
 		}, ctx.FormStrings("files")...)
 	if err != nil {
-		ctx.ServerError("GetDiffRangeWithWhitespaceBehavior", err)
+		ctx.ServerError("GetDiff", err)
 		return false
 	}
+	diffShortStat, err := gitdiff.GetDiffShortStat(ci.HeadGitRepo, beforeCommitID, headCommitID)
+	if err != nil {
+		ctx.ServerError("GetDiffShortStat", err)
+		return false
+	}
+	ctx.Data["DiffShortStat"] = diffShortStat
 	ctx.Data["Diff"] = diff
-	ctx.Data["DiffNotAvailable"] = diff.NumFiles == 0
+	ctx.Data["DiffNotAvailable"] = diffShortStat.NumFiles == 0
 
 	if !fileOnly {
 		diffTree, err := gitdiff.GetDiffTree(ctx, ci.HeadGitRepo, false, beforeCommitID, headCommitID)
diff --git a/routers/web/repo/editor.go b/routers/web/repo/editor.go
index 3107d7b849..113622f872 100644
--- a/routers/web/repo/editor.go
+++ b/routers/web/repo/editor.go
@@ -423,7 +423,7 @@ func DiffPreviewPost(ctx *context.Context) {
 		return
 	}
 
-	if diff.NumFiles != 0 {
+	if len(diff.Files) != 0 {
 		ctx.Data["File"] = diff.Files[0]
 	}
 
diff --git a/routers/web/repo/pull.go b/routers/web/repo/pull.go
index 71057ec653..edbf399c77 100644
--- a/routers/web/repo/pull.go
+++ b/routers/web/repo/pull.go
@@ -200,22 +200,13 @@ func GetPullDiffStats(ctx *context.Context) {
 		return
 	}
 
-	diffOptions := &gitdiff.DiffOptions{
-		BeforeCommitID:     mergeBaseCommitID,
-		AfterCommitID:      headCommitID,
-		MaxLines:           setting.Git.MaxGitDiffLines,
-		MaxLineCharacters:  setting.Git.MaxGitDiffLineCharacters,
-		MaxFiles:           setting.Git.MaxGitDiffFiles,
-		WhitespaceBehavior: gitdiff.GetWhitespaceFlag(ctx.Data["WhitespaceBehavior"].(string)),
-	}
-
-	diff, err := gitdiff.GetPullDiffStats(ctx.Repo.GitRepo, diffOptions)
+	diffShortStat, err := gitdiff.GetDiffShortStat(ctx.Repo.GitRepo, mergeBaseCommitID, headCommitID)
 	if err != nil {
-		ctx.ServerError("GetPullDiffStats", err)
+		ctx.ServerError("GetDiffShortStat", err)
 		return
 	}
 
-	ctx.Data["Diff"] = diff
+	ctx.Data["DiffShortStat"] = diffShortStat
 }
 
 func GetMergedBaseCommitID(ctx *context.Context, issue *issues_model.Issue) string {
@@ -752,36 +743,43 @@ func viewPullFiles(ctx *context.Context, specifiedStartCommit, specifiedEndCommi
 		MaxLineCharacters:  setting.Git.MaxGitDiffLineCharacters,
 		MaxFiles:           maxFiles,
 		WhitespaceBehavior: gitdiff.GetWhitespaceFlag(ctx.Data["WhitespaceBehavior"].(string)),
-		FileOnly:           fileOnly,
 	}
 
 	if !willShowSpecifiedCommit {
 		diffOptions.BeforeCommitID = startCommitID
 	}
 
-	var methodWithError string
-	var diff *gitdiff.Diff
-	shouldGetUserSpecificDiff := false
+	diff, err := gitdiff.GetDiff(ctx, gitRepo, diffOptions, files...)
+	if err != nil {
+		ctx.ServerError("GetDiff", err)
+		return
+	}
 
 	// 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
 	// as the viewed information is designed to be loaded only on latest PR
 	// diff and if you're signed in.
+	shouldGetUserSpecificDiff := false
 	if !ctx.IsSigned || willShowSpecifiedCommit || willShowSpecifiedCommitRange {
-		diff, err = gitdiff.GetDiff(ctx, gitRepo, diffOptions, files...)
-		methodWithError = "GetDiff"
+		// do nothing
 	} else {
-		diff, err = gitdiff.SyncAndGetUserSpecificDiff(ctx, ctx.Doer.ID, pull, gitRepo, diffOptions, files...)
-		methodWithError = "SyncAndGetUserSpecificDiff"
 		shouldGetUserSpecificDiff = true
+		err = gitdiff.SyncUserSpecificDiff(ctx, ctx.Doer.ID, pull, gitRepo, diff, diffOptions, files...)
+		if err != nil {
+			ctx.ServerError("SyncUserSpecificDiff", err)
+			return
+		}
 	}
+
+	diffShortStat, err := gitdiff.GetDiffShortStat(ctx.Repo.GitRepo, startCommitID, endCommitID)
 	if err != nil {
-		ctx.ServerError(methodWithError, err)
+		ctx.ServerError("GetDiffShortStat", err)
 		return
 	}
+	ctx.Data["DiffShortStat"] = diffShortStat
 
 	ctx.PageData["prReview"] = map[string]any{
-		"numberOfFiles":       diff.NumFiles,
+		"numberOfFiles":       diffShortStat.NumFiles,
 		"numberOfViewedFiles": diff.NumViewedFiles,
 	}
 
@@ -840,7 +838,7 @@ func viewPullFiles(ctx *context.Context, specifiedStartCommit, specifiedEndCommi
 	}
 
 	ctx.Data["Diff"] = diff
-	ctx.Data["DiffNotAvailable"] = diff.NumFiles == 0
+	ctx.Data["DiffNotAvailable"] = diffShortStat.NumFiles == 0
 
 	baseCommit, err := ctx.Repo.GitRepo.GetCommit(startCommitID)
 	if err != nil {