refactor(git): replace git stderr matching with exit codes (#39866)

Matching git's stderr text is fragile because it breaks silently when
git rewords a message. Where git offers an exit code or a query with a
defined answer, use that instead, and drop matches that could never
trigger. Follow-up to the discussion in https://github.com/go-gitea/gitea/pull/39857.

- Detect a missing remote by `git remote` exit code 2
- Resolve annotated tags to their tree with cat-file `^{tree}` instead
of spawning `ls-tree` when listing tree entries
- Skip the wiki page lookup when the default branch doesn't exist yet
- Remove unreachable "no merge base" and "unknown revision" checks

services/wiki/wiki.go

@@ -15,7 +15,6 @@ import (
 	"gitea.dev/models/unit"
 	user_model "gitea.dev/models/user"
 	"gitea.dev/modules/git"
-	"gitea.dev/modules/git/gitcmd"
 	"gitea.dev/modules/globallock"
 	"gitea.dev/modules/graceful"
 	"gitea.dev/modules/log"
@@ -50,17 +49,18 @@ func InitWiki(ctx context.Context, repo *repo_model.Repository) error {
 }
 
 // prepareGitPath try to find a suitable file path with file name by the given raw wiki name.
+// An empty defaultWikiBranch means the branch doesn't exist yet.
 // return: existence, prepared file path with name, error
 func prepareGitPath(ctx context.Context, gitRepo *git.Repository, defaultWikiBranch string, wikiPath WebPath) (bool, string, error) {
 	unescaped := string(wikiPath) + ".md"
 	gitPath := WebPathToGitPath(wikiPath)
+	if defaultWikiBranch == "" {
+		return false, gitPath, nil
+	}
 
 	// Look for both files
 	filesInIndex, err := gitRepo.LsTree(ctx, defaultWikiBranch, unescaped, gitPath)
 	if err != nil {
-		if gitcmd.IsStderr(err, gitcmd.StderrNotValidObjectName) {
-			return false, gitPath, nil // branch doesn't exist
-		}
 		log.Error("Wiki LsTree failed, err: %v", err)
 		return false, gitPath, err
 	}
@@ -136,7 +136,7 @@ func updateWikiPage(ctx context.Context, doer *user_model.User, repo *repo_model
 		}
 	}
 
-	isWikiExist, newWikiPath, err := prepareGitPath(ctx, gitRepo, repo.DefaultWikiBranch, newWikiName)
+	isWikiExist, newWikiPath, err := prepareGitPath(ctx, gitRepo, cloneOpts.Branch, newWikiName)
 	if err != nil {
 		return err
 	}
@@ -152,7 +152,7 @@ func updateWikiPage(ctx context.Context, doer *user_model.User, repo *repo_model
 		isOldWikiExist := true
 		oldWikiPath := newWikiPath
 		if oldWikiName != newWikiName {
-			isOldWikiExist, oldWikiPath, err = prepareGitPath(ctx, gitRepo, repo.DefaultWikiBranch, oldWikiName)
+			isOldWikiExist, oldWikiPath, err = prepareGitPath(ctx, gitRepo, cloneOpts.Branch, oldWikiName)
 			if err != nil {
 				return err
 			}

services/wiki/wiki_test.go

@@ -300,18 +300,7 @@ func TestPrepareWikiFileName(t *testing.T) {
 }
 
 func TestPrepareWikiFileName_FirstPage(t *testing.T) {
-	// Now create a temporaryDirectory
-	tmpDir := t.TempDir()
-
-	err := git.InitRepositoryLocal(t.Context(), tmpDir, true, git.Sha1ObjectFormat.Name(), "")
-	assert.NoError(t, err)
-
-	gitRepo, err := git.OpenRepositoryLocal(t.Context(), tmpDir)
-	require.NoError(t, err)
-
-	defer gitRepo.Close()
-
-	existence, newWikiPath, err := prepareGitPath(t.Context(), gitRepo, "master", "Home")
+	existence, newWikiPath, err := prepareGitPath(t.Context(), nil, "", "Home")
 	assert.False(t, existence)
 	assert.NoError(t, err)
 	assert.Equal(t, "Home.md", newWikiPath)