odb: allow odb_find_source() to fail

When trying to locate a source for an unknown object directory we will
die right away. In subsequent patches we will add new callsites though
that want to handle this situation gracefully instead.

Refactor the function to return a `NULL` pointer if the source could not
be found and adapt the callsites to die instead. Introduce a new wrapper
`odb_find_source_or_die()` that continues to die in case the source
could not be found.

Signed-off-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Author: pks-t

builtin/commit-graph.c

@@ -101,7 +101,7 @@ static int graph_verify(int argc, const char **argv, const char *prefix,
 	if (opts.progress)
 		flags |= COMMIT_GRAPH_WRITE_PROGRESS;
 
-	source = odb_find_source(the_repository->objects, opts.obj_dir);
+	source = odb_find_source_or_die(the_repository->objects, opts.obj_dir);
 	graph_name = get_commit_graph_filename(source);
 	chain_name = get_commit_graph_chain_filename(source);
 	if (open_commit_graph(graph_name, &fd, &st))
@@ -289,7 +289,7 @@ static int graph_write(int argc, const char **argv, const char *prefix,
 	    git_env_bool(GIT_TEST_COMMIT_GRAPH_CHANGED_PATHS, 0))
 		flags |= COMMIT_GRAPH_WRITE_BLOOM_FILTERS;
 
-	source = odb_find_source(the_repository->objects, opts.obj_dir);
+	source = odb_find_source_or_die(the_repository->objects, opts.obj_dir);
 
 	if (opts.reachable) {
 		if (write_commit_graph_reachable(source, flags, &write_opts))

midx-write.c

@@ -916,7 +916,7 @@ static int write_midx_bitmap(struct write_midx_context *ctx,
 static struct multi_pack_index *lookup_multi_pack_index(struct repository *r,
 							const char *object_dir)
 {
-	struct odb_source *source = odb_find_source(r->objects, object_dir);
+	struct odb_source *source = odb_find_source_or_die(r->objects, object_dir);
 	return get_multi_pack_index(source);
 }
 

odb.c

@@ -464,6 +464,12 @@ struct odb_source *odb_find_source(struct object_database *odb, const char *obj_
 	free(obj_dir_real);
 	strbuf_release(&odb_path_real);
 
+	return source;
+}
+
+struct odb_source *odb_find_source_or_die(struct object_database *odb, const char *obj_dir)
+{
+	struct odb_source *source = odb_find_source(odb, obj_dir);
 	if (!source)
 		die(_("could not find object directory matching %s"), obj_dir);
 	return source;

odb.h

@@ -186,11 +186,14 @@ struct object_database *odb_new(struct repository *repo);
 void odb_clear(struct object_database *o);
 
 /*
- * Find source by its object directory path. Dies in case the source couldn't
- * be found.
+ * Find source by its object directory path. Returns a `NULL` pointer in case
+ * the source could not be found.
  */
 struct odb_source *odb_find_source(struct object_database *odb, const char *obj_dir);
 
+/* Same as `odb_find_source()`, but dies in case the source doesn't exist. */
+struct odb_source *odb_find_source_or_die(struct object_database *odb, const char *obj_dir);
+
 /*
  * Replace the current writable object directory with the specified temporary
  * object directory; returns the former primary source.