Merge branch 'tb/fix-persistent-shallow' into master

When "fetch.writeCommitGraph" configuration is set in a shallow
repository and a fetch moves the shallow boundary, we wrote out
broken commit-graph files that do not match the reality, which has
been corrected.

* tb/fix-persistent-shallow:
  commit.c: don't persist substituted parents when unshallowing

commit-graph.c

@@ -203,7 +203,8 @@ static int commit_graph_compatible(struct repository *r)
 	}
 
 	prepare_commit_graft(r);
-	if (r->parsed_objects && r->parsed_objects->grafts_nr)
+	if (r->parsed_objects &&
+	    (r->parsed_objects->grafts_nr || r->parsed_objects->substituted_parent))
 		return 0;
 	if (is_repository_shallow(r))
 		return 0;

commit.c

@@ -423,6 +423,8 @@ int parse_commit_buffer(struct repository *r, struct commit *item, const void *b
 	pptr = &item->parents;
 
 	graft = lookup_commit_graft(r, &item->object.oid);
+	if (graft)
+		r->parsed_objects->substituted_parent = 1;
 	while (bufptr + parent_entry_len < tail && !memcmp(bufptr, "parent ", 7)) {
 		struct commit *new_parent;
 

object.h

@@ -25,6 +25,7 @@ struct parsed_object_pool {
 	char *alternate_shallow_file;
 
 	int commit_graft_prepared;
+	int substituted_parent;
 
 	struct buffer_slab *buffer_slab;
 };

t/t5537-fetch-shallow.sh

@@ -81,6 +81,20 @@ test_expect_success 'fetch --unshallow from shallow clone' '
 	)
 '
 
+test_expect_success 'fetch --unshallow from a full clone' '
+	git clone --no-local --depth=2 .git shallow3 &&
+	(
+	cd shallow3 &&
+	git log --format=%s >actual &&
+	test_write_lines 4 3 >expect &&
+	test_cmp expect actual &&
+	git -c fetch.writeCommitGraph fetch --unshallow &&
+	git log origin/master --format=%s >actual &&
+	test_write_lines 4 3 2 1 >expect &&
+	test_cmp expect actual
+	)
+'
+
 test_expect_success 'fetch something upstream has but hidden by clients shallow boundaries' '
 	# the blob "1" is available in .git but hidden by the
 	# shallow2/.git/shallow and it should be resent