commit-graph: build graph from starting commits

Teach git-commit-graph to read commits from stdin when the
--stdin-commits flag is specified. Commits reachable from these
commits are added to the graph. This is a much faster way to construct
the graph than inspecting all packed objects, but is restricted to
known tips.

For the Linux repository, 700,000+ commits were added to the graph
file starting from 'master' in 7-9 seconds, depending on the number
of packfiles in the repo (1, 24, or 120).

Signed-off-by: Derrick Stolee <dstolee@microsoft.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

1 files changed, 21 insertions, 6 deletions

diff --git a/builtin/commit-graph.c b/builtin/commit-graph.c
index 5c70199..b5c0b08 100644
--- a/builtin/commit-graph.c
+++ b/builtin/commit-graph.c
@@ -8,7 +8,7 @@
 static char const * const builtin_commit_graph_usage[] = {
 	N_("git commit-graph [--object-dir <objdir>]"),
 	N_("git commit-graph read [--object-dir <objdir>]"),
-	N_("git commit-graph write [--object-dir <objdir>] [--stdin-packs]"),
+	N_("git commit-graph write [--object-dir <objdir>] [--stdin-packs|--stdin-commits]"),
 	NULL
 };
 
@@ -18,13 +18,14 @@ static const char * const builtin_commit_graph_read_usage[] = {
 };
 
 static const char * const builtin_commit_graph_write_usage[] = {
-	N_("git commit-graph write [--object-dir <objdir>] [--stdin-packs]"),
+	N_("git commit-graph write [--object-dir <objdir>] [--stdin-packs|--stdin-commits]"),
 	NULL
 };
 
 static struct opts_commit_graph {
 	const char *obj_dir;
 	int stdin_packs;
+	int stdin_commits;
 } opts;
 
 static int graph_read(int argc, const char **argv)
@@ -79,6 +80,8 @@ static int graph_write(int argc, const char **argv)
 {
 	const char **pack_indexes = NULL;
 	int packs_nr = 0;
+	const char **commit_hex = NULL;
+	int commits_nr = 0;
 	const char **lines = NULL;
 	int lines_nr = 0;
 	int lines_alloc = 0;
@@ -89,6 +92,8 @@ static int graph_write(int argc, const char **argv)
 			N_("The object directory to store the graph")),
 		OPT_BOOL(0, "stdin-packs", &opts.stdin_packs,
 			N_("scan pack-indexes listed by stdin for commits")),
+		OPT_BOOL(0, "stdin-commits", &opts.stdin_commits,
+			N_("start walk at commits listed by stdin")),
 		OPT_END(),
 	};
 
@@ -96,10 +101,12 @@ static int graph_write(int argc, const char **argv)
 			     builtin_commit_graph_write_options,
 			     builtin_commit_graph_write_usage, 0);
 
+	if (opts.stdin_packs && opts.stdin_commits)
+		die(_("cannot use both --stdin-commits and --stdin-packs"));
 	if (!opts.obj_dir)
 		opts.obj_dir = get_object_directory();
 
-	if (opts.stdin_packs) {
+	if (opts.stdin_packs || opts.stdin_commits) {
 		struct strbuf buf = STRBUF_INIT;
 		lines_nr = 0;
 		lines_alloc = 128;
@@ -110,13 +117,21 @@ static int graph_write(int argc, const char **argv)
 			lines[lines_nr++] = strbuf_detach(&buf, NULL);
 		}
 
-		pack_indexes = lines;
-		packs_nr = lines_nr;
+		if (opts.stdin_packs) {
+			pack_indexes = lines;
+			packs_nr = lines_nr;
+		}
+		if (opts.stdin_commits) {
+			commit_hex = lines;
+			commits_nr = lines_nr;
+		}
 	}
 
 	write_commit_graph(opts.obj_dir,
 			   pack_indexes,
-			   packs_nr);
+			   packs_nr,
+			   commit_hex,
+			   commits_nr);
 
 	return 0;
 }