Subject: [PATCH] fetch: support "--super-prefix"

From: "Glen Choo via GitGitGadget" <[email-masked]>
Date: Fri, 11 Nov 2022 23:55:35 +0000

From: Glen Choo <[email-masked]>

In a repo with partially cloned submodules, "git restore
--recurse-submodules" from the superproject can fail with "fatal: fetch
doesn't support --super-prefix". This error is encountered when the
super prefix is set (either by passing "--super-prefix" or by setting
the GIT_INTERNAL_SUPER_PREFIX env var) on a command that isn't marked
SUPPORT_SUPER_PREFIX. In this case, "git restore --recurse-submodules"
invokes "git read-tree --super-prefix=<path to submodule>", which in
turn, invokes a "git fetch" to fetch promisor objects.

The usefulness of this "--super-prefix" check is up for debate, and
there is WIP to get rid of the option altogether [1], but we can't just
leave "git restore" broken in the meantime, so let's do the barest
minimum to fix this without causing too much trouble for that effort.

Mark cmd_fetch as SUPPORT_SUPER_PREFIX, and add a test that shows that
this fixes the bug described above.

There is precedent for using SUPPORT_SUPER_PREFIX solely as a workaround
for the super prefix check (c.f. [2]), which is all the more reason to
get rid of this check.

[1] https://lore.kernel.org/git/[email-masked]/
[2] 53fcfbc84f (fsmonitor--daemon: allow --super-prefix argument,
    2022-05-26)

Suggested-by: Ævar Arnfjörð Bjarmason <[email-masked]>
Signed-off-by: Glen Choo <[email-masked]>
---
    fetch: support "--super-prefix"
    
    Since "git read-tree" is seriously broken at the moment, let's not keep
    it hostage to the work on [1]. This is Ævar's suggested change from [2]
    combined with my partial clone test case from [3].
    
    I think we can take this regardless of where we are with the RFCs; it's
    simple and obvious enough that it adds virtually no churn to the RFCs.
    
    [1] https://lore.kernel.org/git/[email-masked]/ [2]
    https://lore.kernel.org/git/[email-masked]
    [3]
    https://lore.kernel.org/git/[email-masked]

Published-As: https://github.com/gitgitgadget/git/releases/tag/pr-git-1378%2Fchooglen%2Ffetch%2Fsupport-super-prefix-v1
Fetch-It-Via: git fetch https://github.com/gitgitgadget/git pr-git-1378/chooglen/fetch/support-super-prefix-v1
Pull-Request: https://github.com/git/git/pull/1378

 builtin/fetch.c          |  6 ++++++
 git.c                    |  2 +-
 t/t5616-partial-clone.sh | 43 ++++++++++++++++++++++++++++++++++++++++
 3 files changed, 50 insertions(+), 1 deletion(-)

diff --git a/builtin/fetch.c b/builtin/fetch.c
index 7378cafeec9..9fd64e2f409 100644
--- a/builtin/fetch.c
+++ b/builtin/fetch.c
@@ -2114,6 +2114,12 @@ int cmd_fetch(int argc, const char **argv, const char *prefix)
 	int result = 0;
 	int prune_tags_ok = 1;
 
+	/*
+	 * NEEDSWORK: we don't actually use "--super-prefix". Unset it
+	 * so that we don't accidentally use it or pass it down.
+	 */
+	unsetenv(GIT_SUPER_PREFIX_ENVIRONMENT);
+
 	packet_trace_identity("fetch");
 
 	/* Record the command line for the reflog */
diff --git a/git.c b/git.c
index 6662548986f..b971752f6f0 100644
--- a/git.c
+++ b/git.c
@@ -531,7 +531,7 @@ static struct cmd_struct commands[] = {
 	{ "env--helper", cmd_env__helper },
 	{ "fast-export", cmd_fast_export, RUN_SETUP },
 	{ "fast-import", cmd_fast_import, RUN_SETUP | NO_PARSEOPT },
-	{ "fetch", cmd_fetch, RUN_SETUP },
+	{ "fetch", cmd_fetch, RUN_SETUP | SUPPORT_SUPER_PREFIX },
 	{ "fetch-pack", cmd_fetch_pack, RUN_SETUP | NO_PARSEOPT },
 	{ "fmt-merge-msg", cmd_fmt_merge_msg, RUN_SETUP },
 	{ "for-each-ref", cmd_for_each_ref, RUN_SETUP },
diff --git a/t/t5616-partial-clone.sh b/t/t5616-partial-clone.sh
index 037941b95d2..9bec57a0476 100755
--- a/t/t5616-partial-clone.sh
+++ b/t/t5616-partial-clone.sh
@@ -644,6 +644,49 @@ test_expect_success 'repack does not loosen promisor objects' '
 	grep "loosen_unused_packed_objects/loosened:0" trace
 '
 
+test_expect_success 'setup src repo with submodules' '
+	test_config_global protocol.file.allow always &&
+
+	git init src-sub &&
+	git -C src-sub config uploadpack.allowfilter 1 &&
+	git -C src-sub config uploadpack.allowanysha1inwant 1 &&
+
+	# This blob must be missing in the subsequent commit.
+	echo foo >src-sub/file &&
+	git -C src-sub add file &&
+	git -C src-sub commit -m "submodule one" &&
+	SUB_ONE=$(git -C src-sub rev-parse HEAD) &&
+
+	echo bar >src-sub/file &&
+	git -C src-sub add file &&
+	git -C src-sub commit -m "submodule two" &&
+	SUB_TWO=$(git -C src-sub rev-parse HEAD) &&
+
+	git init src-super &&
+	git -C src-super config uploadpack.allowfilter 1 &&
+	git -C src-super config uploadpack.allowanysha1inwant 1 &&
+	git -C src-super submodule add ../src-sub src-sub &&
+
+	git -C src-super/src-sub checkout $SUB_ONE &&
+	git -C src-super add src-sub &&
+	git -C src-super commit -m "superproject one" &&
+
+	git -C src-super/src-sub checkout $SUB_TWO &&
+	git -C src-super add src-sub &&
+	git -C src-super commit -m "superproject two"
+'
+
+test_expect_success 'lazy-fetch in submodule succeeds' '
+	test_when_finished "rm -rf src-super src-sub client" &&
+
+	test_config_global protocol.file.allow always &&
+	git clone --filter=blob:none --also-filter-submodules \
+		--recurse-submodules "file://$(pwd)/src-super" client &&
+
+	# Trigger lazy-fetch from the superproject
+	git -C client restore --recurse-submodules --source=HEAD^ :/
+'
+
 . "$TEST_DIRECTORY"/lib-httpd.sh
 start_httpd

base-commit: 319605f8f00e402f3ea758a02c63534ff800a711
-- 
gitgitgadget