[PATCH] sha1-file: make pretend_object_file() not prefetch

[Jonathan Tan <jonathantanmy@google.com>]

When pretend_object_file() is invoked with an object that does not exist
(as is the typical case), there is no need to fetch anything from the
promisor remote, because the caller already knows what the object is
supposed to contain. Therefore, suppress the fetch. (The
OBJECT_INFO_QUICK flag is added for the same reason.)

This was noticed at $DAYJOB when "blame" was run on a file that had
uncommitted modifications.

Signed-off-by: Jonathan Tan <jonathantanmy@google.com>
---
This is another instance of the issue Junio raised here [1]:

> Fixing issues hit by real users reactively is a necessary and good
> thing, but this is not the first time we patch callers of
> has_object_file() for this kind of "we are merely trying to
> determine the boundary of what we have, so that we know what we need
> to add to this repository" queries, I am afraid.
>
> Perhaps it is a good idea to sweep all the hits from "git grep -e
> has_object_file \*.c" and audit the codebase to see if there are
> other problematic ones?

To make progress towards solving this, I'm thinking of making a new
function has_object() that takes a repository, an object ID, and flags,
and only supports one flag: HAS_OBJECT_RECHECK_PACKED (which has the
opposite meaning of OBJECT_INFO_QUICK). Checks that should not fetch
should use has_object(), and checks that should fetch (if they exist - I
think that most would want additional information about the object, so
they would use oid_object_info() or similar already) should use
oid_object_info() or a similar function. That way we can see how many
uses of has_object_file() we have checked, and at the same time make
behavior we usually want into the default behavior. Any opinions?

[1] https://lore.kernel.org/git/xmqqpn8wie21.fsf@gitster.c.googlers.com/
---
 sha1-file.c      |  3 ++-
 t/t8002-blame.sh | 11 +++++++++++
 2 files changed, 13 insertions(+), 1 deletion(-)

diff --git a/sha1-file.c b/sha1-file.c
index ccd34dd9e8..45fdb8415c 100644
--- a/sha1-file.c
+++ b/sha1-file.c
@@ -1600,7 +1600,8 @@ int pretend_object_file(void *buf, unsigned long len, enum object_type type,
 	struct cached_object *co;
 
 	hash_object_file(the_hash_algo, buf, len, type_name(type), oid);
-	if (has_object_file(oid) || find_cached_object(oid))
+	if (has_object_file_with_flags(oid, OBJECT_INFO_QUICK | OBJECT_INFO_SKIP_FETCH_OBJECT) ||
+	    find_cached_object(oid))
 		return 0;
 	ALLOC_GROW(cached_objects, cached_object_nr + 1, cached_object_alloc);
 	co = &cached_objects[cached_object_nr++];
diff --git a/t/t8002-blame.sh b/t/t8002-blame.sh
index eea048e52c..2ed6aaae35 100755
--- a/t/t8002-blame.sh
+++ b/t/t8002-blame.sh
@@ -122,4 +122,15 @@ test_expect_success '--exclude-promisor-objects does not BUG-crash' '
 	test_must_fail git blame --exclude-promisor-objects one
 '
 
+test_expect_success 'blame with uncommitted edits in partial clone does not crash' '
+	git init server &&
+	echo foo >server/file.txt &&
+	git -C server add file.txt &&
+	git -C server commit -m file &&
+
+	git clone --filter=blob:none "file://$(pwd)/server" client &&
+	echo bar >>client/file.txt &&
+	git -C client blame file.txt
+'
+
 test_done
-- 
2.28.0.rc0.105.gf9edc3c819-goog