From 2a69ff09d5654de31361365e3faf9f8495f03ed7 Mon Sep 17 00:00:00 2001
From: Jonathan Tan <jonathantanmy@google.com>
Date: Thu, 17 Mar 2022 11:24:47 -0700
Subject: [PATCH] shallow: reset commit grafts when shallow is reset

When reset_repository_shallow() is called, Git clears its cache of
shallow information, so that if shallow information is re-requested, Git
will read fresh data from disk instead of reusing its stale cached data.
However, the cache of commit grafts is not likewise cleared, even though
there are commit grafts created from shallow information.

This means that if on-disk shallow information were to be updated and
then a commit-graft-using codepath were run (for example, a revision
walk), Git would be using stale commit graft information. This can be
seen from the test in this patch, in which Git performs a revision walk
(to check for changed submodules) after a fetch with --update-shallow.

Therefore, clear the cache of commit grafts whenever
reset_repository_shallow() is called.

Signed-off-by: Jonathan Tan <jonathantanmy@google.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
---
 commit.c                 | 10 ++++++++++
 commit.h                 |  1 +
 shallow.c                |  1 +
 submodule.c              |  1 +
 t/t5537-fetch-shallow.sh |  9 +++++++++
 5 files changed, 22 insertions(+)

diff --git a/commit.c b/commit.c
index 98b2e556653..ffcc4a97cd1 100644
--- a/commit.c
+++ b/commit.c
@@ -249,6 +249,16 @@ int for_each_commit_graft(each_commit_graft_fn fn, void *cb_data)
 	return ret;
 }
 
+void reset_commit_grafts(struct repository *r)
+{
+	int i;
+
+	for (i = 0; i < r->parsed_objects->grafts_nr; i++)
+		free(r->parsed_objects->grafts[i]);
+	r->parsed_objects->grafts_nr = 0;
+	r->parsed_objects->commit_graft_prepared = 0;
+}
+
 struct commit_buffer {
 	void *buffer;
 	unsigned long size;
diff --git a/commit.h b/commit.h
index 3b174135bcf..21e4d25ce78 100644
--- a/commit.h
+++ b/commit.h
@@ -249,6 +249,7 @@ int commit_graft_pos(struct repository *r, const struct object_id *oid);
 int register_commit_graft(struct repository *r, struct commit_graft *, int);
 void prepare_commit_graft(struct repository *r);
 struct commit_graft *lookup_commit_graft(struct repository *r, const struct object_id *oid);
+void reset_commit_grafts(struct repository *r);
 
 struct commit *get_fork_point(const char *refname, struct commit *commit);
 
diff --git a/shallow.c b/shallow.c
index 71e5876f377..e158be58b05 100644
--- a/shallow.c
+++ b/shallow.c
@@ -90,6 +90,7 @@ static void reset_repository_shallow(struct repository *r)
 {
 	r->parsed_objects->is_shallow = -1;
 	stat_validity_clear(r->parsed_objects->shallow_stat);
+	reset_commit_grafts(r);
 }
 
 int commit_shallow_file(struct repository *r, struct shallow_lock *lk)
diff --git a/submodule.c b/submodule.c
index 5ace18a7d94..7a0515913c4 100644
--- a/submodule.c
+++ b/submodule.c
@@ -22,6 +22,7 @@
 #include "parse-options.h"
 #include "object-store.h"
 #include "commit-reach.h"
+#include "shallow.h"
 
 static int config_update_recurse_submodules = RECURSE_SUBMODULES_OFF;
 static int initialized_fetch_ref_tips;
diff --git a/t/t5537-fetch-shallow.sh b/t/t5537-fetch-shallow.sh
index 11d5ea54a9c..92948de7a00 100755
--- a/t/t5537-fetch-shallow.sh
+++ b/t/t5537-fetch-shallow.sh
@@ -161,6 +161,15 @@ test_expect_success 'fetch --update-shallow' '
 	)
 '
 
+test_expect_success 'fetch --update-shallow into a repo with submodules' '
+	git init a-submodule &&
+	test_commit -C a-submodule foo &&
+	git init repo-with-sub &&
+	git -C repo-with-sub submodule add ../a-submodule a-submodule &&
+	git -C repo-with-sub commit -m "added submodule" &&
+	git -C repo-with-sub fetch --update-shallow ../shallow/.git refs/heads/*:refs/remotes/shallow/*
+'
+
 test_expect_success 'fetch --update-shallow (with fetch.writeCommitGraph)' '
 	(
 	cd shallow &&