reftable/error: discern locked/outdated errors

We currently throw two different errors into a similar-but-different
error code:

  - Errors when trying to lock the reftable stack.

  - Errors when trying to write to the reftable stack which has been
    modified concurrently.

This results in unclear error handling and user-visible error messages.

Create a new `REFTABLE_OUTDATED_ERROR` so that those error conditions
can be clearly told apart from each other. Adjust users of the old
`REFTABLE_LOCK_ERROR` to use the new error code as required.

Signed-off-by: Patrick Steinhardt <[email protected]>
Signed-off-by: Junio C Hamano <[email protected]>

Author: pks-t

reftable/error.c

@@ -22,7 +22,7 @@ const char *reftable_error_str(int err)
 	case REFTABLE_NOT_EXIST_ERROR:
 		return "file does not exist";
 	case REFTABLE_LOCK_ERROR:
-		return "data is outdated";
+		return "data is locked";
 	case REFTABLE_API_ERROR:
 		return "misuse of the reftable API";
 	case REFTABLE_ZLIB_ERROR:
@@ -35,6 +35,8 @@ const char *reftable_error_str(int err)
 		return "invalid refname";
 	case REFTABLE_ENTRY_TOO_BIG_ERROR:
 		return "entry too large";
+	case REFTABLE_OUTDATED_ERROR:
+		return "data concurrently modified";
 	case -1:
 		return "general error";
 	default:

reftable/reftable-error.h

@@ -25,7 +25,7 @@ enum reftable_error {
 	 */
 	REFTABLE_NOT_EXIST_ERROR = -4,
 
-	/* Trying to write out-of-date data. */
+	/* Trying to access locked data. */
 	REFTABLE_LOCK_ERROR = -5,
 
 	/* Misuse of the API:
@@ -57,6 +57,9 @@ enum reftable_error {
 	/* Entry does not fit. This can happen when writing outsize reflog
 	   messages. */
 	REFTABLE_ENTRY_TOO_BIG_ERROR = -11,
+
+	/* Trying to write out-of-date data. */
+	REFTABLE_OUTDATED_ERROR = -12,
 };
 
 /* convert the numeric error code to a string. The string should not be

reftable/stack.c

@@ -529,9 +529,9 @@ int reftable_stack_add(struct reftable_stack *st,
 {
 	int err = stack_try_add(st, write, arg);
 	if (err < 0) {
-		if (err == REFTABLE_LOCK_ERROR) {
+		if (err == REFTABLE_OUTDATED_ERROR) {
 			/* Ignore error return, we want to propagate
-			   REFTABLE_LOCK_ERROR.
+			   REFTABLE_OUTDATED_ERROR.
 			*/
 			reftable_stack_reload(st);
 		}
@@ -591,7 +591,7 @@ static int reftable_stack_init_addition(struct reftable_addition *add,
 	if (err < 0)
 		goto done;
 	if (err > 0) {
-		err = REFTABLE_LOCK_ERROR;
+		err = REFTABLE_OUTDATED_ERROR;
 		goto done;
 	}
 

reftable/stack_test.c

@@ -232,7 +232,7 @@ static void test_reftable_stack_uptodate(void)
 	EXPECT_ERR(err);
 
 	err = reftable_stack_add(st2, &write_test_ref, &ref2);
-	EXPECT(err == REFTABLE_LOCK_ERROR);
+	EXPECT(err == REFTABLE_OUTDATED_ERROR);
 
 	err = reftable_stack_reload(st2);
 	EXPECT_ERR(err);