[PATCH v2 4/4] get_oid(): when an object was not found, try harder

["Johannes Schindelin via GitGitGadget" <gitgitgadget@gmail.com>]

From: Johannes Schindelin <johannes.schindelin@gmx.de>

It is quite possible that the loose object cache gets stale when new
objects are written. Or that a new pack was installed. In those cases,
get_oid() would potentially say that it cannot find a given object, even
if it should find it.

Let's blow away the loose object cache as well as the read packs and try
again in that case.

Note: this does *not* affect the code path that was introduced to help
avoid looking for the same non-existing objects (which made some
operations really expensive via NFS): that code path is handled by the
`OBJECT_INFO_QUICK` flag (which does not even apply to `get_oid()`,
which has no equivalent flag, at least at the time this patch was
written).

This incidentally fixes the problem identified earlier where an
interactive rebase wanted to re-read (and validate) the todo list after
an `exec` command modified it.

Helped-by: Jeff King <peff@peff.net>
Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
---
 sha1-name.c                 | 13 ++++++++++++-
 t/t3429-rebase-edit-todo.sh |  2 +-
 2 files changed, 13 insertions(+), 2 deletions(-)

diff --git a/sha1-name.c b/sha1-name.c
index 6dda2c16df..36a6602696 100644
--- a/sha1-name.c
+++ b/sha1-name.c
@@ -415,7 +415,7 @@ static enum get_oid_result get_short_oid(const char *name, int len,
 					 struct object_id *oid,
 					 unsigned flags)
 {
-	int status;
+	int status, attempts = 0;
 	struct disambiguate_state ds;
 	int quietly = !!(flags & GET_OID_QUIETLY);
 
@@ -438,10 +438,21 @@ static enum get_oid_result get_short_oid(const char *name, int len,
 	else
 		ds.fn = default_disambiguate_hint;
 
+try_again:
 	find_short_object_filename(&ds);
 	find_short_packed_object(&ds);
 	status = finish_object_disambiguation(&ds, oid);
 
+	/*
+	 * If we did not find it, do the usual reprepare() slow-path, since the
+	 * object may have recently been added to the repository or migrated
+	 * from loose to packed.
+	 */
+	if (status == MISSING_OBJECT && !attempts++) {
+		reprepare_packed_git(the_repository);
+		goto try_again;
+	}
+
 	if (!quietly && (status == SHORT_NAME_AMBIGUOUS)) {
 		struct oid_array collect = OID_ARRAY_INIT;
 
diff --git a/t/t3429-rebase-edit-todo.sh b/t/t3429-rebase-edit-todo.sh
index 83e5bb5eba..d5d2925a44 100755
--- a/t/t3429-rebase-edit-todo.sh
+++ b/t/t3429-rebase-edit-todo.sh
@@ -11,7 +11,7 @@ test_expect_success 'rebase exec modifies rebase-todo' '
 	test -e F
 '
 
-test_expect_failure SHA1 'loose object cache vs re-reading todo list' '
+test_expect_success SHA1 'loose object cache vs re-reading todo list' '
 	GIT_REBASE_TODO=.git/rebase-merge/git-rebase-todo &&
 	export GIT_REBASE_TODO &&
 	write_script append-todo.sh <<-\EOS &&
-- 
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