[PATCH v3 2/2] fetch: no redundant error message for atomic fetch

[Jiang Xin <worldhello.net@xxxxxxxxx>]

From: Jiang Xin <zhiyou.jx@xxxxxxxxxxxxxxx>

If an error occurs during an atomic fetch, a redundant error message
will appear at the end of do_fetch(). It was introduced in b3a804663c
(fetch: make `--atomic` flag cover backfilling of tags, 2022-02-17).

Because a failure message is displayed before setting retcode in the
function do_fetch(), calling error() on the err message at the end of
this function may result in redundant or empty error message to be
displayed.

We can remove the redundant error() function, because we know that
the function ref_transaction_abort() never fails. While we can find a
common pattern for calling ref_transaction_abort() by running command
"git grep -A1 ref_transaction_abort", e.g.:

    if (ref_transaction_abort(transaction, &error))
        error("abort: %s", error.buf);

Following this pattern, we can tolerate the return value of the function
ref_transaction_abort() being changed in the future. We also delay the
output of the err message to the end of do_fetch() to reduce redundant
code. With these changes, the test case "fetch porcelain output
(atomic)" in t5574 will also be fixed.

Helped-by: Patrick Steinhardt <ps@xxxxxx>
Signed-off-by: Jiang Xin <zhiyou.jx@xxxxxxxxxxxxxxx>
---
 builtin/fetch.c         | 14 +++++++++-----
 t/t5574-fetch-output.sh |  2 +-
 2 files changed, 10 insertions(+), 6 deletions(-)

diff --git a/builtin/fetch.c b/builtin/fetch.c
index fd134ba74d..a284b970ef 100644
--- a/builtin/fetch.c
+++ b/builtin/fetch.c
@@ -1651,7 +1651,7 @@ static int do_fetch(struct transport *transport,
 	if (atomic_fetch) {
 		transaction = ref_transaction_begin(&err);
 		if (!transaction) {
-			retcode = error("%s", err.buf);
+			retcode = -1;
 			goto cleanup;
 		}
 	}
@@ -1711,7 +1711,6 @@ static int do_fetch(struct transport *transport,
 
 		retcode = ref_transaction_commit(transaction, &err);
 		if (retcode) {
-			error("%s", err.buf);
 			ref_transaction_free(transaction);
 			transaction = NULL;
 			goto cleanup;
@@ -1775,9 +1774,14 @@ static int do_fetch(struct transport *transport,
 	}
 
 cleanup:
-	if (retcode && transaction) {
-		ref_transaction_abort(transaction, &err);
-		error("%s", err.buf);
+	if (retcode) {
+		if (err.len) {
+			error("%s", err.buf);
+			strbuf_reset(&err);
+		}
+		if (transaction && ref_transaction_abort(transaction, &err) &&
+		    err.len)
+			error("%s", err.buf);
 	}
 
 	display_state_release(&display_state);
diff --git a/t/t5574-fetch-output.sh b/t/t5574-fetch-output.sh
index b579364c47..1400ef14cd 100755
--- a/t/t5574-fetch-output.sh
+++ b/t/t5574-fetch-output.sh
@@ -90,7 +90,7 @@ test_expect_success 'setup for fetch porcelain output' '
 
 for opt in "" "--atomic"
 do
-	test_expect_failure "fetch porcelain output ${opt:+(atomic)}" '
+	test_expect_success "fetch porcelain output ${opt:+(atomic)}" '
 		test_when_finished "rm -rf porcelain" &&
 
 		# Clone and pre-seed the repositories. We fetch references into two
-- 
2.41.0.232.g2f6f0bca4f.agit.8.0.4.dev