commit-graph: pass repo_settings instead of repository

The parse_commit_graph() function takes a 'struct repository *' pointer,
but it only ever accesses config settings (either directly or through
the .settings field of the repo struct). Move all relevant config
settings into the repo_settings struct, and update parse_commit_graph()
and its existing callers so that it takes 'struct repo_settings *'
instead.

Callers of parse_commit_graph() will now need to call
prepare_repo_settings() themselves, or initialize a 'struct
repo_settings' directly.

Prior to ab14d0676c (commit-graph: pass a 'struct repository *' in more
places, 2020-09-09), parsing a commit-graph was a pure function
depending only on the contents of the commit-graph itself. Commit
ab14d0676c introduced a dependency on a `struct repository` pointer, and
later commits such as b66d84756f (commit-graph: respect
'commitGraph.readChangedPaths', 2020-09-09) added dependencies on config
settings, which were accessed through the `settings` field of the
repository pointer. This field was initialized via a call to
`prepare_repo_settings()`.

Additionally, this fixes an issue in fuzz-commit-graph: In 44c7e62
(2021-12-06, repo-settings:prepare_repo_settings only in git repos),
prepare_repo_settings was changed to issue a BUG() if it is called by a
process whose CWD is not a Git repository.

The combination of commits mentioned above broke fuzz-commit-graph,
which attempts to parse arbitrary fuzzing-engine-provided bytes as a
commit graph file. Prior to this change, parse_commit_graph() called
prepare_repo_settings(), but since we run the fuzz tests without a valid
repository, we are hitting the BUG() from 44c7e62 for every test case.

Signed-off-by: Taylor Blau <me@ttaylorr.com>
Signed-off-by: Josh Steadmon <steadmon@google.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

commit-graph.c

@@ -252,7 +252,8 @@ struct commit_graph *load_commit_graph_one_fd_st(struct repository *r,
 	}
 	graph_map = xmmap(NULL, graph_size, PROT_READ, MAP_PRIVATE, fd, 0);
 	close(fd);
-	ret = parse_commit_graph(r, graph_map, graph_size);
+	prepare_repo_settings(r);
+	ret = parse_commit_graph(&r->settings, graph_map, graph_size);
 
 	if (ret)
 		ret->odb = odb;
@@ -321,7 +322,7 @@ static int graph_read_bloom_data(const unsigned char *chunk_start,
 	return 0;
 }
 
-struct commit_graph *parse_commit_graph(struct repository *r,
+struct commit_graph *parse_commit_graph(struct repo_settings *s,
 					void *graph_map, size_t graph_size)
 {
 	const unsigned char *data;
@@ -359,8 +360,6 @@ struct commit_graph *parse_commit_graph(struct repository *r,
 		return NULL;
 	}
 
-	prepare_repo_settings(r);
-
 	graph = alloc_commit_graph();
 
 	graph->hash_len = the_hash_algo->rawsz;
@@ -390,7 +389,7 @@ struct commit_graph *parse_commit_graph(struct repository *r,
 	pair_chunk(cf, GRAPH_CHUNKID_EXTRAEDGES, &graph->chunk_extra_edges);
 	pair_chunk(cf, GRAPH_CHUNKID_BASE, &graph->chunk_base_graphs);
 
-	if (get_configured_generation_version(r) >= 2) {
+	if (s->commit_graph_generation_version >= 2) {
 		pair_chunk(cf, GRAPH_CHUNKID_GENERATION_DATA,
 			&graph->chunk_generation_data);
 		pair_chunk(cf, GRAPH_CHUNKID_GENERATION_DATA_OVERFLOW,
@@ -400,7 +399,7 @@ struct commit_graph *parse_commit_graph(struct repository *r,
 			graph->read_generation_data = 1;
 	}
 
-	if (r->settings.commit_graph_read_changed_paths) {
+	if (s->commit_graph_read_changed_paths) {
 		pair_chunk(cf, GRAPH_CHUNKID_BLOOMINDEXES,
 			   &graph->chunk_bloom_indexes);
 		read_chunk(cf, GRAPH_CHUNKID_BLOOMDATA,

commit-graph.h

@@ -93,7 +93,12 @@ struct commit_graph *load_commit_graph_one_fd_st(struct repository *r,
 						 struct object_directory *odb);
 struct commit_graph *read_commit_graph_one(struct repository *r,
 					   struct object_directory *odb);
-struct commit_graph *parse_commit_graph(struct repository *r,
+
+/*
+ * Callers should initialize the repo_settings with prepare_repo_settings()
+ * prior to calling parse_commit_graph().
+ */
+struct commit_graph *parse_commit_graph(struct repo_settings *s,
 					void *graph_map, size_t graph_size);
 
 /*

fuzz-commit-graph.c

@@ -1,7 +1,7 @@
 #include "commit-graph.h"
 #include "repository.h"
 
-struct commit_graph *parse_commit_graph(struct repository *r,
+struct commit_graph *parse_commit_graph(struct repo_settings *s,
 					void *graph_map, size_t graph_size);
 
 int LLVMFuzzerTestOneInput(const uint8_t *data, size_t size);
@@ -11,7 +11,15 @@ int LLVMFuzzerTestOneInput(const uint8_t *data, size_t size)
 	struct commit_graph *g;
 
 	initialize_the_repository();
-	g = parse_commit_graph(the_repository, (void *)data, size);
+	/*
+	 * Initialize the_repository with commit-graph settings that would
+	 * normally be read from the repository's gitdir. We want to avoid
+	 * touching the disk to keep the individual fuzz-test cases as fast as
+	 * possible.
+	 */
+	the_repository->settings.commit_graph_generation_version = 2;
+	the_repository->settings.commit_graph_read_changed_paths = 1;
+	g = parse_commit_graph(&the_repository->settings, (void *)data, size);
 	repo_clear(the_repository);
 	free_commit_graph(g);
 

repo-settings.c

@@ -11,6 +11,13 @@ static void repo_cfg_bool(struct repository *r, const char *key, int *dest,
 		*dest = def;
 }
 
+static void repo_cfg_int(struct repository *r, const char *key, int *dest,
+			 int def)
+{
+	if (repo_config_get_int(r, key, dest))
+		*dest = def;
+}
+
 void prepare_repo_settings(struct repository *r)
 {
 	int experimental;
@@ -42,11 +49,14 @@ void prepare_repo_settings(struct repository *r)
 		r->settings.core_untracked_cache = UNTRACKED_CACHE_WRITE;
 	}
 
-	/* Boolean config or default, does not cascade (simple)  */
+	/* Commit graph config or default, does not cascade (simple) */
 	repo_cfg_bool(r, "core.commitgraph", &r->settings.core_commit_graph, 1);
+	repo_cfg_int(r, "commitgraph.generationversion", &r->settings.commit_graph_generation_version, 2);
 	repo_cfg_bool(r, "commitgraph.readchangedpaths", &r->settings.commit_graph_read_changed_paths, 1);
 	repo_cfg_bool(r, "gc.writecommitgraph", &r->settings.gc_write_commit_graph, 1);
 	repo_cfg_bool(r, "fetch.writecommitgraph", &r->settings.fetch_write_commit_graph, 0);
+
+	/* Boolean config or default, does not cascade (simple)  */
 	repo_cfg_bool(r, "pack.usesparse", &r->settings.pack_use_sparse, 1);
 	repo_cfg_bool(r, "core.multipackindex", &r->settings.core_multi_pack_index, 1);
 	repo_cfg_bool(r, "index.sparse", &r->settings.sparse_index, 0);

repository.h

@@ -30,6 +30,7 @@ struct repo_settings {
 	int initialized;
 
 	int core_commit_graph;
+	int commit_graph_generation_version;
 	int commit_graph_read_changed_paths;
 	int gc_write_commit_graph;
 	int fetch_write_commit_graph;