[PATCH v2] fetch: no FETCH_HEAD display if --no-write-fetch-head

[Jonathan Tan <jonathantanmy@google.com>]

887952b8c6 ("fetch: optionally allow disabling FETCH_HEAD update",
2020-08-18) introduced the ability to disable writing to FETCH_HEAD
during fetch, but did not suppress the "<source> -> FETCH_HEAD" message
when this ability is used. This message is misleading in this case,
because FETCH_HEAD is not written. Also, because "fetch" is used to
lazy-fetch missing objects in a partial clone, this significantly
clutters up the output in that case since the objects to be fetched are
potentially numerous.

Therefore, suppress this message when --no-write-fetch-head is passed
(but not when --dry-run is set).

Signed-off-by: Jonathan Tan <jonathantanmy@google.com>
---
This is on origin/jt/lazy-fetch.

Junio writes [1]:

> Test also --dry-run, but that perhaps needs to be done outside the
> context of partial-clone.  The above "lazy fetching should be silent
> and should not bother users with mention of FETCH_HEAD" is good test
> in the context of partial-clone, though.
>
> jc/no-update-fetch-head added its own test to t/t5510, and both the
> "output lacks FETCH_HEAD when --no-write-fetch-head is given" test
> and the "output still mentions FETCH_HEAD with --dry-run" test
> belong there.

Ah, thanks for catching that. Here's an updated version.

[1] https://lore.kernel.org/git/xmqq7dtcaqob.fsf@gitster.c.googlers.com/
---
 builtin/fetch.c          |  8 +++++++-
 t/t0410-partial-clone.sh |  7 +++++--
 t/t5510-fetch.sh         | 18 ++++++++++--------
 3 files changed, 22 insertions(+), 11 deletions(-)

diff --git a/builtin/fetch.c b/builtin/fetch.c
index 320ba9471d..c6c4689250 100644
--- a/builtin/fetch.c
+++ b/builtin/fetch.c
@@ -1023,11 +1023,17 @@ static int store_updated_refs(const char *raw_url, const char *remote_name,
 				rc |= update_local_ref(ref, what, rm, &note,
 						       summary_width);
 				free(ref);
-			} else
+			} else if (write_fetch_head || dry_run) {
+				/*
+				 * Display fetches written to FETCH_HEAD (or
+				 * would be written to FETCH_HEAD, if --dry-run
+				 * is set).
+				 */
 				format_display(&note, '*',
 					       *kind ? kind : "branch", NULL,
 					       *what ? what : "HEAD",
 					       "FETCH_HEAD", summary_width);
+			}
 			if (note.len) {
 				if (verbosity >= 0 && !shown_url) {
 					fprintf(stderr, _("From %.*s\n"),
diff --git a/t/t0410-partial-clone.sh b/t/t0410-partial-clone.sh
index d681e90640..584a039b85 100755
--- a/t/t0410-partial-clone.sh
+++ b/t/t0410-partial-clone.sh
@@ -183,7 +183,7 @@ test_expect_success 'missing CLI object, but promised, passes fsck' '
 '
 
 test_expect_success 'fetching of missing objects' '
-	rm -rf repo &&
+	rm -rf repo err &&
 	test_create_repo server &&
 	test_commit -C server foo &&
 	git -C server repack -a -d --write-bitmap-index &&
@@ -194,7 +194,10 @@ test_expect_success 'fetching of missing objects' '
 
 	git -C repo config core.repositoryformatversion 1 &&
 	git -C repo config extensions.partialclone "origin" &&
-	git -C repo cat-file -p "$HASH" &&
+	git -C repo cat-file -p "$HASH" 2>err &&
+
+	# Ensure that no spurious FETCH_HEAD messages are written
+	! grep FETCH_HEAD err &&
 
 	# Ensure that the .promisor file is written, and check that its
 	# associated packfile contains the object
diff --git a/t/t5510-fetch.sh b/t/t5510-fetch.sh
index 2a1abe91f0..759aec9305 100755
--- a/t/t5510-fetch.sh
+++ b/t/t5510-fetch.sh
@@ -543,16 +543,18 @@ test_expect_success 'fetch into the current branch with --update-head-ok' '
 
 '
 
-test_expect_success 'fetch --dry-run does not touch FETCH_HEAD' '
-	rm -f .git/FETCH_HEAD &&
-	git fetch --dry-run . &&
-	! test -f .git/FETCH_HEAD
+test_expect_success 'fetch --dry-run does not touch FETCH_HEAD, but still prints what would be written' '
+	rm -f .git/FETCH_HEAD err &&
+	git fetch --dry-run . 2>err &&
+	! test -f .git/FETCH_HEAD &&
+	grep FETCH_HEAD err
 '
 
-test_expect_success '--no-write-fetch-head does not touch FETCH_HEAD' '
-	rm -f .git/FETCH_HEAD &&
-	git fetch --no-write-fetch-head . &&
-	! test -f .git/FETCH_HEAD
+test_expect_success '--no-write-fetch-head does not touch FETCH_HEAD, and does not print what would be written' '
+	rm -f .git/FETCH_HEAD err &&
+	git fetch --no-write-fetch-head . 2>err &&
+	! test -f .git/FETCH_HEAD &&
+	! grep FETCH_HEAD err
 '
 
 test_expect_success '--write-fetch-head gets defeated by --dry-run' '
-- 
2.28.0.402.g5ffc5be6b7-goog