Merge branch 'jk/disable-commit-graph-during-upload-pack'

The "upload-pack" (the counterpart of "git fetch") needs to disable
commit-graph when responding to a shallow clone/fetch request, but
the way this was done made Git panic, which has been corrected.

* jk/disable-commit-graph-during-upload-pack:
  upload-pack: disable commit graph more gently for shallow traversal
  commit-graph: bump DIE_ON_LOAD check to actual load-time

commit-graph.c

@@ -468,14 +468,21 @@ static int prepare_commit_graph(struct repository *r)
 {
 	struct object_directory *odb;
 
-	if (git_env_bool(GIT_TEST_COMMIT_GRAPH_DIE_ON_LOAD, 0))
-		die("dying as requested by the '%s' variable on commit-graph load!",
-		    GIT_TEST_COMMIT_GRAPH_DIE_ON_LOAD);
+	/*
+	 * This must come before the "already attempted?" check below, because
+	 * we want to disable even an already-loaded graph file.
+	 */
+	if (r->commit_graph_disabled)
+		return 0;
 
 	if (r->objects->commit_graph_attempted)
 		return !!r->objects->commit_graph;
 	r->objects->commit_graph_attempted = 1;
 
+	if (git_env_bool(GIT_TEST_COMMIT_GRAPH_DIE_ON_LOAD, 0))
+		die("dying as requested by the '%s' variable on commit-graph load!",
+		    GIT_TEST_COMMIT_GRAPH_DIE_ON_LOAD);
+
 	prepare_repo_settings(r);
 
 	if (!git_env_bool(GIT_TEST_COMMIT_GRAPH, 0) &&
@@ -2101,3 +2108,8 @@ void free_commit_graph(struct commit_graph *g)
 	free(g->filename);
 	free(g);
 }
+
+void disable_commit_graph(struct repository *r)
+{
+	r->commit_graph_disabled = 1;
+}

commit-graph.h

@@ -107,4 +107,10 @@ int verify_commit_graph(struct repository *r, struct commit_graph *g, int flags)
 void close_commit_graph(struct raw_object_store *);
 void free_commit_graph(struct commit_graph *);
 
+/*
+ * Disable further use of the commit graph in this process when parsing a
+ * "struct commit".
+ */
+void disable_commit_graph(struct repository *r);
+
 #endif

repository.h

@@ -125,6 +125,9 @@ struct repository {
 	/* A unique-id for tracing purposes. */
 	int trace2_repo_id;
 
+	/* True if commit-graph has been disabled within this process. */
+	int commit_graph_disabled;
+
 	/* Configurations */
 
 	/* Indicate if a repository has a different 'commondir' from 'gitdir' */

t/t5500-fetch-pack.sh

@@ -792,6 +792,44 @@ test_expect_success 'clone shallow since selects no commits' '
 	)
 '
 
+# A few subtle things about the request in this test:
+#
+#  - the server must have commit-graphs present and enabled
+#
+#  - the history is such that our want/have share a common ancestor ("base"
+#    here)
+#
+#  - we send only a single have, which is fewer than a normal client would
+#    send. This ensures that we don't parse "base" up front with
+#    parse_object(), but rather traverse to it as a parent while deciding if we
+#    can stop the "have" negotiation, and call parse_commit(). The former
+#    sees the actual object data and so always loads the three oid, whereas the
+#    latter will try to load it lazily.
+#
+#  - we must use protocol v2, because it handles the "have" negotiation before
+#    processing the shallow directives
+#
+test_expect_success 'shallow since with commit graph and already-seen commit' '
+	test_create_repo shallow-since-graph &&
+	(
+	cd shallow-since-graph &&
+	test_commit base &&
+	test_commit master &&
+	git checkout -b other HEAD^ &&
+	test_commit other &&
+	git commit-graph write --reachable &&
+	git config core.commitGraph true &&
+
+	GIT_PROTOCOL=version=2 git upload-pack . <<-EOF >/dev/null
+	0012command=fetch
+	00010013deepen-since 1
+	0032want $(git rev-parse other)
+	0032have $(git rev-parse master)
+	0000
+	EOF
+	)
+'
+
 test_expect_success 'shallow clone exclude tag two' '
 	test_create_repo shallow-exclude &&
 	(

upload-pack.c

@@ -721,7 +721,7 @@ static void deepen_by_rev_list(struct packet_writer *writer, int ac,
 {
 	struct commit_list *result;
 
-	close_commit_graph(the_repository->objects);
+	disable_commit_graph(the_repository);
 	result = get_shallow_commits_by_rev_list(ac, av, SHALLOW, NOT_SHALLOW);
 	send_shallow(writer, result);
 	free_commit_list(result);