From 8fa32bd3ffe9e74da1bb23c5e961a24a52324b3c Mon Sep 17 00:00:00 2001
From: Gusted <postmaster@gusted.xyz>
Date: Thu, 13 Nov 2025 13:22:09 +0100
Subject: [PATCH] fix: make `Fetch` work with git < 2.41 (#10095)

`git fetch --porcelain` was introduced in 2.41, add a fallback for older git clients.

Resolves forgejo/forgejo#10080

Reviewed-on: https://codeberg.org/forgejo/forgejo/pulls/10095
Reviewed-by: Michael Kriese <michael.kriese@gmx.de>
Reviewed-by: Mathieu Fenniak <mfenniak@noreply.codeberg.org>
Co-authored-by: Gusted <postmaster@gusted.xyz>
Co-committed-by: Gusted <postmaster@gusted.xyz>
---
 modules/git/fetch.go | 50 ++++++++++++++++++++++++++++++++++++--------
 modules/git/git.go   |  2 ++
 2 files changed, 43 insertions(+), 9 deletions(-)

diff --git a/modules/git/fetch.go b/modules/git/fetch.go
index 886ca9ca60..af8bb34d38 100644
--- a/modules/git/fetch.go
+++ b/modules/git/fetch.go
@@ -6,6 +6,9 @@ import (
 	"errors"
 	"fmt"
 	"strings"
+
+	"forgejo.org/modules/log"
+	"forgejo.org/modules/util"
 )
 
 var ErrRemoteRefNotFound = errors.New("unable to find remote ref")
@@ -25,7 +28,20 @@ func (repo *Repository) Fetch(remoteURL, refspec string) (string, error) {
 		return "", err
 	}
 
-	stdout, stderr, err := NewCommand(repo.Ctx, "fetch", "--porcelain", "--end-of-options").AddDynamicArguments(remoteURL, refspec).RunStdString(&RunOpts{Dir: repo.Path})
+	cmd := NewCommand(repo.Ctx, "fetch")
+	if SupportFetchPorcelain {
+		cmd.AddArguments("--porcelain")
+	} else if !strings.Contains(refspec, ":") {
+		randomString, err := util.CryptoRandomString(8)
+		if err != nil {
+			return "", err
+		}
+		refspec += ":refs/tmp/" + randomString
+	}
+
+	cmd.AddArguments("--end-of-options").AddDynamicArguments(remoteURL, refspec)
+
+	stdout, stderr, err := cmd.RunStdString(&RunOpts{Dir: repo.Path})
 	if err != nil {
 		if strings.HasPrefix(stderr, "fatal: couldn't find remote ref ") {
 			return "", ErrRemoteRefNotFound
@@ -33,19 +49,35 @@ func (repo *Repository) Fetch(remoteURL, refspec string) (string, error) {
 		return "", err
 	}
 
-	localReference, _, ok := strings.Cut(refspec, ":")
+	_, localReference, ok := strings.Cut(refspec, ":")
 	if !ok {
 		localReference = "FETCH_HEAD"
 	}
 
-	// The porcelain format, per section OUTPUT of git-fetch(1), is expected to be:
-	// <flag><space><old-object-id><space><new-object-id><space><local-reference>\n
-	// flag is one character.
-	if expectedLen := 1 + 1 + objectFormat.FullLength() + 1 + objectFormat.FullLength() + 1 + len(localReference) + 1; len(stdout) != expectedLen {
-		return "", fmt.Errorf("output of git-fetch(1) is unexpected, we expected it to be %d bytes but it is %d bytes. stdout: %s", expectedLen, len(stdout), stdout)
+	// Happy path
+	if SupportFetchPorcelain {
+		// The porcelain format, per section OUTPUT of git-fetch(1), is expected to be:
+		// <flag><space><old-object-id><space><new-object-id><space><local-reference>\n
+		// flag is one character.
+		if expectedLen := 1 + 1 + objectFormat.FullLength() + 1 + objectFormat.FullLength() + 1 + len(localReference) + 1; len(stdout) != expectedLen {
+			return "", fmt.Errorf("output of git-fetch(1) is unexpected, we expected it to be %d bytes but it is %d bytes. stdout: %s", expectedLen, len(stdout), stdout)
+		}
+
+		// Extract the new objectID.
+		newObjectID := stdout[1+1+objectFormat.FullLength()+1 : 1+1+objectFormat.FullLength()+1+objectFormat.FullLength()]
+		return newObjectID, nil
+	}
+
+	defer func() {
+		if err := repo.RemoveReference(localReference); err != nil {
+			log.Error("Could not remove reference %q from repository %q: %v", localReference, repo.Path, err)
+		}
+	}()
+
+	newObjectID, err := repo.ResolveReference(localReference)
+	if err != nil {
+		return "", err
 	}
 
-	// Extract the new objectID.
-	newObjectID := stdout[1+1+objectFormat.FullLength()+1 : 1+1+objectFormat.FullLength()+1+objectFormat.FullLength()]
 	return newObjectID, nil
 }
diff --git a/modules/git/git.go b/modules/git/git.go
index e3ffa39514..650fd3b5af 100644
--- a/modules/git/git.go
+++ b/modules/git/git.go
@@ -35,6 +35,7 @@ var (
 
 	SupportHashSha256      bool // >= 2.42, SHA-256 repositories no longer an ‘experimental curiosity’
 	InvertedGitFlushEnv    bool // 2.43.1
+	SupportFetchPorcelain  bool // >= 2.41
 	SupportCheckAttrOnBare bool // >= 2.40
 	SupportGitMergeTree    bool // >= 2.38
 	SupportGrepMaxCount    bool // >= 2.38
@@ -179,6 +180,7 @@ func InitFull(ctx context.Context) (err error) {
 	globalCommandArgs = append(globalCommandArgs, "-c", "credential.helper=")
 
 	SupportHashSha256 = CheckGitVersionAtLeast("2.42") == nil
+	SupportFetchPorcelain = CheckGitVersionAtLeast("2.41") == nil
 	SupportCheckAttrOnBare = CheckGitVersionAtLeast("2.40") == nil
 	if SupportHashSha256 {
 		SupportedObjectFormats = append(SupportedObjectFormats, Sha256ObjectFormat)