repository: Fix commit-graphs referencing pruned commits after PruneUnreachableObjectspks-housekeeping-rewrite-commit-graph-on-prune

When pruning objects we need to rewrite our commit-graphs so that they
don't reference any commits that have just been pruned. While this is
not typically an issue, git-fsck(1) will report any such inconsistencies
in the commit-graph. Furthermore, Git may return an error when being
asked to parse such a missing commit directly.

Fix `PruneUnreachableObjects()` to do so.

Changelog: fixed

2 files changed, 12 insertions, 9 deletions

diff --git a/internal/gitaly/service/repository/prune_unreachable_objects.go b/internal/gitaly/service/repository/prune_unreachable_objects.go
index c648cbdff..2ba270830 100644
--- a/internal/gitaly/service/repository/prune_unreachable_objects.go
+++ b/internal/gitaly/service/repository/prune_unreachable_objects.go
@@ -4,6 +4,7 @@ import (
 	"context"
 
 	"gitlab.com/gitlab-org/gitaly/v15/internal/git"
+	"gitlab.com/gitlab-org/gitaly/v15/internal/git/housekeeping"
 	"gitlab.com/gitlab-org/gitaly/v15/internal/git/stats"
 	"gitlab.com/gitlab-org/gitaly/v15/internal/helper"
 	"gitlab.com/gitlab-org/gitaly/v15/proto/go/gitalypb"
@@ -38,6 +39,14 @@ func (s *server) PruneUnreachableObjects(
 		return nil, helper.ErrInternalf("pruning objects: %w", err)
 	}
 
+	// Rewrite the commit-graph so that it doesn't contain references to pruned commits
+	// anymore.
+	if err := housekeeping.WriteCommitGraph(ctx, repo, housekeeping.WriteCommitGraphConfig{
+		ReplaceChain: true,
+	}); err != nil {
+		return nil, helper.ErrInternalf("rewriting commit-graph: %w", err)
+	}
+
 	stats.LogObjectsInfo(ctx, repo)
 
 	return &gitalypb.PruneUnreachableObjectsResponse{}, nil
diff --git a/internal/gitaly/service/repository/prune_unreachable_objects_test.go b/internal/gitaly/service/repository/prune_unreachable_objects_test.go
index 434be71d6..440bb45dd 100644
--- a/internal/gitaly/service/repository/prune_unreachable_objects_test.go
+++ b/internal/gitaly/service/repository/prune_unreachable_objects_test.go
@@ -1,8 +1,6 @@
 package repository
 
 import (
-	"bytes"
-	"fmt"
 	"os"
 	"path/filepath"
 	"testing"
@@ -158,12 +156,8 @@ func TestPruneUnreachableObjects(t *testing.T) {
 		})
 		require.NoError(t, err)
 
-		// The commit-graph chain now refers to the pruned commit, and git-commit-graph(1)
-		// should complain about that.
-		var stderr bytes.Buffer
-		verifyCmd := gittest.NewCommand(t, cfg, "-C", repoPath, "commit-graph", "verify")
-		verifyCmd.Stderr = &stderr
-		require.EqualError(t, verifyCmd.Run(), "exit status 1")
-		require.Equal(t, stderr.String(), fmt.Sprintf("error: Could not read %[1]s\nfailed to parse commit %[1]s from object database for commit-graph\n", unreachableCommitID))
+		// The commit-graph chain should have been rewritten by PruneUnreachableObjects so
+		// that it doesn't refer to the pruned commit anymore.
+		gittest.Exec(t, cfg, "-C", repoPath, "commit-graph", "verify")
 	})
 }