[PATCH v2 09/14] commit-graph: fix memory leak in misused string_list API

["Ævar Arnfjörð Bjarmason" <avarab@gmail.com>]

When this code was migrated to the string_list API in
d88b14b3fd6 (commit-graph: use string-list API for input, 2018-06-27)
it was made to use used both STRING_LIST_INIT_NODUP and a
strbuf_detach() pattern.

Those should not be used together if string_list_clear() is expected
to free the memory, instead we need to either use STRING_LIST_INIT_DUP
with a string_list_append_nodup(), or a STRING_LIST_INIT_NODUP and
manually fiddle with the "strdup_strings" member before calling
string_list_clear(). Let's do the former.

Since "strdup_strings = 1" is set now other code might be broken by
relying on "pack_indexes" not to duplicate it strings, but that
doesn't happen. When we pass this down to write_commit_graph() that
code uses the "struct string_list" without modifying it. Let's add a
"const" to the variable to have the compiler enforce that assumption.

Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com>
---
 builtin/commit-graph.c | 6 +++---
 commit-graph.c         | 4 ++--
 commit-graph.h         | 2 +-
 3 files changed, 6 insertions(+), 6 deletions(-)

diff --git a/builtin/commit-graph.c b/builtin/commit-graph.c
index 4247fbde95a..51c4040ea6c 100644
--- a/builtin/commit-graph.c
+++ b/builtin/commit-graph.c
@@ -192,7 +192,7 @@ static int git_commit_graph_write_config(const char *var, const char *value,
 
 static int graph_write(int argc, const char **argv)
 {
-	struct string_list pack_indexes = STRING_LIST_INIT_NODUP;
+	struct string_list pack_indexes = STRING_LIST_INIT_DUP;
 	struct strbuf buf = STRBUF_INIT;
 	struct oidset commits = OIDSET_INIT;
 	struct object_directory *odb = NULL;
@@ -273,8 +273,8 @@ static int graph_write(int argc, const char **argv)
 
 	if (opts.stdin_packs) {
 		while (strbuf_getline(&buf, stdin) != EOF)
-			string_list_append(&pack_indexes,
-					   strbuf_detach(&buf, NULL));
+			string_list_append_nodup(&pack_indexes,
+						 strbuf_detach(&buf, NULL));
 	} else if (opts.stdin_commits) {
 		oidset_init(&commits, 0);
 		if (opts.progress)
diff --git a/commit-graph.c b/commit-graph.c
index 265c010122e..d0c94600bab 100644
--- a/commit-graph.c
+++ b/commit-graph.c
@@ -1679,7 +1679,7 @@ int write_commit_graph_reachable(struct object_directory *odb,
 }
 
 static int fill_oids_from_packs(struct write_commit_graph_context *ctx,
-				struct string_list *pack_indexes)
+				const struct string_list *pack_indexes)
 {
 	uint32_t i;
 	struct strbuf progress_title = STRBUF_INIT;
@@ -2259,7 +2259,7 @@ static void expire_commit_graphs(struct write_commit_graph_context *ctx)
 }
 
 int write_commit_graph(struct object_directory *odb,
-		       struct string_list *pack_indexes,
+		       const struct string_list *const pack_indexes,
 		       struct oidset *commits,
 		       enum commit_graph_write_flags flags,
 		       const struct commit_graph_opts *opts)
diff --git a/commit-graph.h b/commit-graph.h
index 04a94e18302..2e3ac35237e 100644
--- a/commit-graph.h
+++ b/commit-graph.h
@@ -142,7 +142,7 @@ int write_commit_graph_reachable(struct object_directory *odb,
 				 enum commit_graph_write_flags flags,
 				 const struct commit_graph_opts *opts);
 int write_commit_graph(struct object_directory *odb,
-		       struct string_list *pack_indexes,
+		       const struct string_list *pack_indexes,
 		       struct oidset *commits,
 		       enum commit_graph_write_flags flags,
 		       const struct commit_graph_opts *opts);
-- 
2.35.1.1248.gb68c9165ad8