[PATCH v3 08/14] commit-graph: implement 'git-commit-graph clear'

[Derrick Stolee <stolee@gmail.com>]

Teach Git to delete the current 'graph_head' file and the commit graph
it references. This is a good safety valve if somehow the file is
corrupted and needs to be recalculated. Since the commit graph is a
summary of contents already in the ODB, it can be regenerated.

Signed-off-by: Derrick Stolee <dstolee@microsoft.com>
---
 Documentation/git-commit-graph.txt | 11 +++++++++
 builtin/commit-graph.c             | 50 ++++++++++++++++++++++++++++++++++++++
 commit-graph.c                     | 23 ++++++++++++++++++
 commit-graph.h                     |  2 ++
 t/t5318-commit-graph.sh            |  5 ++++
 5 files changed, 91 insertions(+)

diff --git a/Documentation/git-commit-graph.txt b/Documentation/git-commit-graph.txt
index 5e32c43b27..8c2cbbc923 100644
--- a/Documentation/git-commit-graph.txt
+++ b/Documentation/git-commit-graph.txt
@@ -9,6 +9,7 @@ git-commit-graph - Write and verify Git commit graphs (.graph files)
 SYNOPSIS
 --------
 [verse]
+'git commit-graph clear' [--pack-dir <pack_dir>]
 'git commit-graph read' <options> [--pack-dir <pack_dir>]
 'git commit-graph write' <options> [--pack-dir <pack_dir>]
 
@@ -45,6 +46,10 @@ details about the graph file.
 With `--graph-hash=<hash>` option, consider the graph file
 graph-<hash>.graph in the pack directory.
 
+'clear'::
+
+Delete the graph-head file and the graph file it references.
+
 
 EXAMPLES
 --------
@@ -68,6 +73,12 @@ $ git commit-graph write --update-head
 $ git commit-graph read --graph-hash=<hash>
 ------------------------------------------------
 
+* Delete <dir>/graph-head and the file it references.
++
+------------------------------------------------
+$ git commit-graph clear --pack-dir=<dir>
+------------------------------------------------
+
 
 GIT
 ---
diff --git a/builtin/commit-graph.c b/builtin/commit-graph.c
index 776ca087e8..529cb80de6 100644
--- a/builtin/commit-graph.c
+++ b/builtin/commit-graph.c
@@ -1,16 +1,23 @@
 #include "builtin.h"
 #include "config.h"
+#include "dir.h"
 #include "lockfile.h"
 #include "parse-options.h"
 #include "commit-graph.h"
 
 static char const * const builtin_commit_graph_usage[] = {
 	N_("git commit-graph [--pack-dir <packdir>]"),
+	N_("git commit-graph clear [--pack-dir <packdir>]"),
 	N_("git commit-graph read [--graph-hash=<hash>]"),
 	N_("git commit-graph write [--pack-dir <packdir>] [--update-head]"),
 	NULL
 };
 
+static const char * const builtin_commit_graph_clear_usage[] = {
+	N_("git commit-graph clear [--pack-dir <packdir>]"),
+	NULL
+};
+
 static const char * const builtin_commit_graph_read_usage[] = {
 	N_("git commit-graph read [--pack-dir <packdir>]"),
 	NULL
@@ -27,6 +34,47 @@ static struct opts_commit_graph {
 	int update_head;
 } opts;
 
+static int graph_clear(int argc, const char **argv)
+{
+	char *old_path;
+	char *head_fname;
+	struct object_id old_graph_hash;
+
+	static struct option builtin_commit_graph_clear_options[] = {
+		{ OPTION_STRING, 'p', "pack-dir", &opts.pack_dir,
+			N_("dir"),
+			N_("The pack directory to store the graph") },
+		OPT_END(),
+	};
+
+	argc = parse_options(argc, argv, NULL,
+			     builtin_commit_graph_clear_options,
+			     builtin_commit_graph_clear_usage, 0);
+
+	if (!opts.pack_dir) {
+		struct strbuf path = STRBUF_INIT;
+		strbuf_addstr(&path, get_object_directory());
+		strbuf_addstr(&path, "/pack");
+		opts.pack_dir = strbuf_detach(&path, NULL);
+	}
+
+	if (!get_graph_head_hash(opts.pack_dir, &old_graph_hash))
+		return 0;
+
+	head_fname = get_graph_head_filename(opts.pack_dir);
+	if (remove_path(head_fname))
+		die("failed to remove path %s", head_fname);
+	FREE_AND_NULL(head_fname);
+
+	old_path = get_commit_graph_filename_hash(opts.pack_dir,
+						  &old_graph_hash);
+	if (remove_path(old_path))
+		die("failed to remove path %s", old_path);
+	free(old_path);
+
+	return 0;
+}
+
 static int graph_read(int argc, const char **argv)
 {
 	struct object_id graph_hash;
@@ -162,6 +210,8 @@ int cmd_commit_graph(int argc, const char **argv, const char *prefix)
 			     PARSE_OPT_STOP_AT_NON_OPTION);
 
 	if (argc > 0) {
+		if (!strcmp(argv[0], "clear"))
+			return graph_clear(argc, argv);
 		if (!strcmp(argv[0], "read"))
 			return graph_read(argc, argv);
 		if (!strcmp(argv[0], "write"))
diff --git a/commit-graph.c b/commit-graph.c
index 9789fe37f9..95b813c2c7 100644
--- a/commit-graph.c
+++ b/commit-graph.c
@@ -46,6 +46,29 @@ char *get_graph_head_filename(const char *pack_dir)
 	return strbuf_detach(&fname, 0);
 }
 
+struct object_id *get_graph_head_hash(const char *pack_dir, struct object_id *hash)
+{
+	char hex[GIT_MAX_HEXSZ + 1];
+	char *fname;
+	FILE *f;
+
+	fname = get_graph_head_filename(pack_dir);
+	f = fopen(fname, "r");
+	FREE_AND_NULL(fname);
+
+	if (!f)
+		return 0;
+
+	if (!fgets(hex, sizeof(hex), f))
+		die("failed to read graph-head");
+
+	fclose(f);
+
+	if (get_oid_hex(hex, hash))
+		return 0;
+	return hash;
+}
+
 char* get_commit_graph_filename_hash(const char *pack_dir,
 				     struct object_id *hash)
 {
diff --git a/commit-graph.h b/commit-graph.h
index 726b8aa0f4..75427cd5f6 100644
--- a/commit-graph.h
+++ b/commit-graph.h
@@ -5,6 +5,8 @@
 #include "commit.h"
 
 extern char *get_graph_head_filename(const char *pack_dir);
+extern struct object_id *get_graph_head_hash(const char *pack_dir,
+					     struct object_id *hash);
 extern char* get_commit_graph_filename_hash(const char *pack_dir,
 					    struct object_id *hash);
 
diff --git a/t/t5318-commit-graph.sh b/t/t5318-commit-graph.sh
index 21352d5a3c..de81253790 100755
--- a/t/t5318-commit-graph.sh
+++ b/t/t5318-commit-graph.sh
@@ -126,6 +126,11 @@ test_expect_success 'write graph with nothing new' '
 	graph_read_expect "11" "$packdir" &&
 	test_cmp expect output'
 
+test_expect_success 'clear graph' '
+	git commit-graph clear &&
+	test_path_is_missing $packdir/graph-$graph4.graph &&
+	test_path_is_missing $packdir/graph-head'
+
 test_expect_success 'setup bare repo' '
 	cd .. &&
 	git clone --bare --no-local full bare &&
-- 
2.15.1.45.g9b7079f