From 57b4c9ab4712b0de2a51464af4c8af9132f5ccde Mon Sep 17 00:00:00 2001
From: Justin Chadwell <me@jedevc.com>
Date: Mon, 21 Oct 2024 14:22:28 +0100
Subject: [PATCH] git: allow cloning commit shas not referenced by branch/tag

Signed-off-by: Justin Chadwell <me@jedevc.com>
---
 source/git/source.go      |  4 +++-
 source/git/source_test.go | 33 ++++++++++++++++++++++++++++-----
 util/gitutil/git_cli.go   | 23 +++++++++++++++++++++++
 3 files changed, 54 insertions(+), 6 deletions(-)

diff --git a/source/git/source.go b/source/git/source.go
index dd45b828c82bf..cb56eeed59868 100644
--- a/source/git/source.go
+++ b/source/git/source.go
@@ -475,7 +475,9 @@ func (gs *gitSourceHandler) Snapshot(ctx context.Context, g session.Group) (out
 			}
 		}
 		args = append(args, "origin")
-		if !gitutil.IsCommitSHA(ref) {
+		if gitutil.IsCommitSHA(ref) {
+			args = append(args, ref)
+		} else {
 			// local refs are needed so they would be advertised on next fetches. Force is used
 			// in case the ref is a branch and it now points to a different commit sha
 			// TODO: is there a better way to do this?
diff --git a/source/git/source_test.go b/source/git/source_test.go
index 59a0fdd83e4fa..57ab48df2ac89 100644
--- a/source/git/source_test.go
+++ b/source/git/source_test.go
@@ -218,15 +218,23 @@ func testFetchBySHA(t *testing.T, keepGitDir bool) {
 }
 
 func TestFetchUnreferencedTagSha(t *testing.T) {
-	testFetchUnreferencedTagSha(t, false)
+	testFetchUnreferencedRefSha(t, "v1.2.3-special", false)
 }
 
 func TestFetchUnreferencedTagShaKeepGitDir(t *testing.T) {
-	testFetchUnreferencedTagSha(t, true)
+	testFetchUnreferencedRefSha(t, "v1.2.3-special", true)
 }
 
-// testFetchUnreferencedTagSha tests fetching a SHA that points to a tag that is not reachable from any branch.
-func testFetchUnreferencedTagSha(t *testing.T, keepGitDir bool) {
+func TestFetchUnreferencedRefSha(t *testing.T) {
+	testFetchUnreferencedRefSha(t, "refs/special", false)
+}
+
+func TestFetchUnreferencedRefShaKeepGitDir(t *testing.T) {
+	testFetchUnreferencedRefSha(t, "refs/special", true)
+}
+
+// testFetchUnreferencedRefSha tests fetching a SHA that points to a ref that is not reachable from any branch.
+func testFetchUnreferencedRefSha(t *testing.T, ref string, keepGitDir bool) {
 	if runtime.GOOS == "windows" {
 		t.Skip("Depends on unimplemented containerd bind-mount support on Windows")
 	}
@@ -239,7 +247,7 @@ func testFetchUnreferencedTagSha(t *testing.T, keepGitDir bool) {
 
 	repo := setupGitRepo(t)
 
-	cmd := exec.Command("git", "rev-parse", "v1.2.3-special")
+	cmd := exec.Command("git", "rev-parse", ref)
 	cmd.Dir = repo.mainPath
 
 	out, err := cmd.Output()
@@ -699,35 +707,50 @@ func setupGitRepo(t *testing.T) gitRepoFixture {
 		"git -c init.defaultBranch=master init",
 		"git config --local user.email test",
 		"git config --local user.name test",
+
 		"echo foo > abc",
 		"git add abc",
 		"git commit -m initial",
 		"git tag --no-sign a/v1.2.3",
+
 		"echo bar > def",
 		"mkdir subdir",
 		"echo subcontents > subdir/subfile",
 		"git add def subdir",
 		"git commit -m second",
 		"git tag -a -m \"this is an annotated tag\" v1.2.3",
+
 		"echo foo > bar",
 		"git add bar",
 		"git commit -m tagonly-leaf",
 		"git tag --no-sign v1.2.3-special",
+
+		"echo foo2 > bar2",
+		"git add bar2",
+		"git commit -m more",
+		"git update-ref refs/special $(git rev-parse HEAD)",
+
 		// switch master back to v1.2.3
 		"git checkout -B master v1.2.3",
+
 		"echo sbb > foo13",
 		"git add foo13",
 		"git commit -m third",
 		"git tag --no-sign lightweight-tag",
+
 		"git checkout -B feature",
+
 		"echo baz > ghi",
 		"git add ghi",
 		"git commit -m feature",
 		"git update-ref refs/test $(git rev-parse HEAD)",
+
 		"git submodule add "+fixture.subURL+" sub",
 		"git add -A",
 		"git commit -m withsub",
+
 		"git checkout master",
+
 		// "git log --oneline --graph --decorate=full --all",
 	)
 	return fixture
diff --git a/util/gitutil/git_cli.go b/util/gitutil/git_cli.go
index 5c35f9365b73e..6b9ea01311e28 100644
--- a/util/gitutil/git_cli.go
+++ b/util/gitutil/git_cli.go
@@ -218,6 +218,13 @@ func (cli *GitCLI) Run(ctx context.Context, args ...string) (_ []byte, err error
 					continue
 				}
 			}
+			if strings.Contains(errbuf.String(), "upload-pack: not our ref") {
+				// https://github.com/git/git/blob/34b6ce9b30747131b6e781ff718a45328aa887d0/upload-pack.c
+				if newArgs := argsNoCommitRefspec(args); len(args) > len(newArgs) {
+					args = newArgs
+					continue
+				}
+			}
 
 			return buf.Bytes(), errors.Wrapf(err, "git stderr:\n%s", errbuf.String())
 		}
@@ -244,3 +251,19 @@ func argsNoDepth(args []string) []string {
 	}
 	return out
 }
+
+func argsNoCommitRefspec(args []string) []string {
+	if len(args) <= 2 {
+		return args
+	}
+	if args[0] != "fetch" {
+		return args
+	}
+
+	// assume the refspec is the last arg
+	if IsCommitSHA(args[len(args)-1]) {
+		return args[:len(args)-1]
+	}
+
+	return args
+}