commit-graph: implement git-commit-graph write

Teach git-commit-graph to write graph files. Create new test script to verify
this command succeeds without failure.

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

Documentation/git-commit-graph.txt

@@ -5,6 +5,47 @@ NAME
 ----
 git-commit-graph - Write and verify Git commit graph files
 
+
+SYNOPSIS
+--------
+[verse]
+'git commit-graph write' <options> [--object-dir <dir>]
+
+
+DESCRIPTION
+-----------
+
+Manage the serialized commit graph file.
+
+
+OPTIONS
+-------
+--object-dir::
+	Use given directory for the location of packfiles and commit graph
+	file. This parameter exists to specify the location of an alternate
+	that only has the objects directory, not a full .git directory. The
+	commit graph file is expected to be at <dir>/info/commit-graph and
+	the packfiles are expected to be in <dir>/pack.
+
+
+COMMANDS
+--------
+'write'::
+
+Write a commit graph file based on the commits found in packfiles.
+Includes all commits from the existing commit graph file.
+
+
+EXAMPLES
+--------
+
+* Write a commit graph file for the packed commits in your local .git folder.
++
+------------------------------------------------
+$ git commit-graph write
+------------------------------------------------
+
+
 GIT
 ---
 Part of the linkgit:git[1] suite

builtin/commit-graph.c

@@ -1,9 +1,18 @@
 #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 [--object-dir <objdir>]"),
+	N_("git commit-graph write [--object-dir <objdir>]"),
+	NULL
+};
+
+static const char * const builtin_commit_graph_write_usage[] = {
+	N_("git commit-graph write [--object-dir <objdir>]"),
 	NULL
 };
 
@@ -11,6 +20,25 @@ static struct opts_commit_graph {
 	const char *obj_dir;
 } opts;
 
+static int graph_write(int argc, const char **argv)
+{
+	static struct option builtin_commit_graph_write_options[] = {
+		OPT_STRING(0, "object-dir", &opts.obj_dir,
+			N_("dir"),
+			N_("The object directory to store the graph")),
+		OPT_END(),
+	};
+
+	argc = parse_options(argc, argv, NULL,
+			     builtin_commit_graph_write_options,
+			     builtin_commit_graph_write_usage, 0);
+
+	if (!opts.obj_dir)
+		opts.obj_dir = get_object_directory();
+
+	write_commit_graph(opts.obj_dir);
+	return 0;
+}
 
 int cmd_commit_graph(int argc, const char **argv, const char *prefix)
 {
@@ -31,6 +59,11 @@ int cmd_commit_graph(int argc, const char **argv, const char *prefix)
 			     builtin_commit_graph_usage,
 			     PARSE_OPT_STOP_AT_NON_OPTION);
 
+	if (argc > 0) {
+		if (!strcmp(argv[0], "write"))
+			return graph_write(argc, argv);
+	}
+
 	usage_with_options(builtin_commit_graph_usage,
 			   builtin_commit_graph_options);
 }

t/t5318-commit-graph.sh

@@ -0,0 +1,124 @@
+#!/bin/sh
+
+test_description='commit graph'
+. ./test-lib.sh
+
+test_expect_success 'setup full repo' '
+	mkdir full &&
+	cd "$TRASH_DIRECTORY/full" &&
+	git init &&
+	objdir=".git/objects"
+'
+
+test_expect_success 'write graph with no packs' '
+	cd "$TRASH_DIRECTORY/full" &&
+	git commit-graph write --object-dir . &&
+	test_path_is_file info/commit-graph
+'
+
+test_expect_success 'create commits and repack' '
+	cd "$TRASH_DIRECTORY/full" &&
+	for i in $(test_seq 3)
+	do
+		test_commit $i &&
+		git branch commits/$i
+	done &&
+	git repack
+'
+
+test_expect_success 'write graph' '
+	cd "$TRASH_DIRECTORY/full" &&
+	graph1=$(git commit-graph write) &&
+	test_path_is_file $objdir/info/commit-graph
+'
+
+test_expect_success 'Add more commits' '
+	cd "$TRASH_DIRECTORY/full" &&
+	git reset --hard commits/1 &&
+	for i in $(test_seq 4 5)
+	do
+		test_commit $i &&
+		git branch commits/$i
+	done &&
+	git reset --hard commits/2 &&
+	for i in $(test_seq 6 7)
+	do
+		test_commit $i &&
+		git branch commits/$i
+	done &&
+	git reset --hard commits/2 &&
+	git merge commits/4 &&
+	git branch merge/1 &&
+	git reset --hard commits/4 &&
+	git merge commits/6 &&
+	git branch merge/2 &&
+	git reset --hard commits/3 &&
+	git merge commits/5 commits/7 &&
+	git branch merge/3 &&
+	git repack
+'
+
+# Current graph structure:
+#
+#   __M3___
+#  /   |   \
+# 3 M1 5 M2 7
+# |/  \|/  \|
+# 2    4    6
+# |___/____/
+# 1
+
+
+test_expect_success 'write graph with merges' '
+	cd "$TRASH_DIRECTORY/full" &&
+	git commit-graph write &&
+	test_path_is_file $objdir/info/commit-graph
+'
+
+test_expect_success 'Add one more commit' '
+	cd "$TRASH_DIRECTORY/full" &&
+	test_commit 8 &&
+	git branch commits/8 &&
+	ls $objdir/pack | grep idx >existing-idx &&
+	git repack &&
+	ls $objdir/pack| grep idx | grep -v --file=existing-idx >new-idx
+'
+
+# Current graph structure:
+#
+#      8
+#      |
+#   __M3___
+#  /   |   \
+# 3 M1 5 M2 7
+# |/  \|/  \|
+# 2    4    6
+# |___/____/
+# 1
+
+test_expect_success 'write graph with new commit' '
+	cd "$TRASH_DIRECTORY/full" &&
+	git commit-graph write &&
+	test_path_is_file $objdir/info/commit-graph
+'
+
+test_expect_success 'write graph with nothing new' '
+	cd "$TRASH_DIRECTORY/full" &&
+	git commit-graph write &&
+	test_path_is_file $objdir/info/commit-graph
+'
+
+test_expect_success 'setup bare repo' '
+	cd "$TRASH_DIRECTORY" &&
+	git clone --bare --no-local full bare &&
+	cd bare &&
+	baredir="./objects"
+'
+
+test_expect_success 'write graph in bare repo' '
+	cd "$TRASH_DIRECTORY/bare" &&
+	git commit-graph write &&
+	test_path_is_file $baredir/info/commit-graph
+'
+
+test_done