updateref: Convert `FileDirectoryConflictError` to use error metadata

Convert the `FileDirectoryConflictError` to use error metadata instead
of embedding the information into the error message.

2 files changed, 15 insertions, 2 deletions

diff --git a/internal/git/updateref/updateref.go b/internal/git/updateref/updateref.go
index 54e18c76a..de0be8ec5 100644
--- a/internal/git/updateref/updateref.go
+++ b/internal/git/updateref/updateref.go
@@ -60,7 +60,16 @@ type FileDirectoryConflictError struct {
 }
 
 func (e FileDirectoryConflictError) Error() string {
-	return fmt.Sprintf("%q conflicts with %q", e.ConflictingReferenceName, e.ExistingReferenceName)
+	return "file directory conflict"
+}
+
+// ErrorMetadata implements the `structerr.ErrorMetadater` interface and provides the name of preexisting and
+// conflicting reference names.
+func (e FileDirectoryConflictError) ErrorMetadata() []structerr.MetadataItem {
+	return []structerr.MetadataItem{
+		{Key: "conflicting_reference", Value: e.ConflictingReferenceName},
+		{Key: "existing_reference", Value: e.ExistingReferenceName},
+	}
 }
 
 // InTransactionConflictError is returned when attempting to modify two references in the same transaction
diff --git a/internal/gitaly/service/operations/branches_test.go b/internal/gitaly/service/operations/branches_test.go
index dfbd3bbde..f89b58073 100644
--- a/internal/gitaly/service/operations/branches_test.go
+++ b/internal/gitaly/service/operations/branches_test.go
@@ -401,7 +401,11 @@ func TestUserCreateBranch_Failure(t *testing.T) {
 			branchName: "improve",
 			startPoint: "master",
 			user:       gittest.TestUser,
-			err:        status.Errorf(codes.FailedPrecondition, "Could not update refs/heads/improve. Please refresh and try again."),
+			err: testhelper.WithInterceptedMetadataItems(
+				structerr.NewFailedPrecondition("Could not update refs/heads/improve. Please refresh and try again."),
+				structerr.MetadataItem{Key: "conflicting_reference", Value: "refs/heads/improve"},
+				structerr.MetadataItem{Key: "existing_reference", Value: "refs/heads/improve/awesome"},
+			),
 		},
 	}