[PATCH v2 4/5] gc: add --dry-run

["Nguyễn Thái Ngọc Duy" <pclouds@gmail.com>]

"git gc --auto --dry-run" will print instead of doing
housekeeping. This option is to be called by other commands rather
than by user and will not print more than one warning every hour. gc()
function also behaves this way.

Signed-off-by: Nguyễn Thái Ngọc Duy <pclouds@gmail.com>
---
 Documentation/git-gc.txt |    7 ++++++-
 builtin/gc.c             |   19 +++++++++++++++++++
 2 files changed, 25 insertions(+), 1 deletions(-)

diff --git a/Documentation/git-gc.txt b/Documentation/git-gc.txt
index b370b02..f69f5e1 100644
--- a/Documentation/git-gc.txt
+++ b/Documentation/git-gc.txt
@@ -9,7 +9,7 @@ git-gc - Cleanup unnecessary files and optimize the local repository
 SYNOPSIS
 --------
 [verse]
-'git gc' [--aggressive] [--auto] [--quiet] [--prune=<date> | --no-prune]
+'git gc' [--aggressive] [--auto [--dry-run]] [--quiet] [--prune=<date> | --no-prune]
 
 DESCRIPTION
 -----------
@@ -60,6 +60,11 @@ are consolidated into a single pack by using the `-A` option of
 'git repack'. Setting `gc.autopacklimit` to 0 disables
 automatic consolidation of packs.
 
+--dry-run::
+	Only show warning if housekeeping is required. The warning
+	is only shown at most once every hour even if
+	"gc --auto --dry-run" is run continuously.
+
 --prune=<date>::
 	Prune loose objects older than date (default is 2 weeks ago,
 	overridable by the config variable `gc.pruneExpire`).  This
diff --git a/builtin/gc.c b/builtin/gc.c
index ce60225..f82b9ef 100644
--- a/builtin/gc.c
+++ b/builtin/gc.c
@@ -150,6 +150,8 @@ static void add_repack_all_option(void)
 
 static int need_to_gc(void)
 {
+	struct stat st;
+
 	/*
 	 * Setting gc.auto to 0 or negative can disable the
 	 * automatic gc.
@@ -168,6 +170,13 @@ static int need_to_gc(void)
 	else if (!too_many_loose_objects())
 		return 0;
 
+	if (stat(git_path("gc_needed"), &st))
+		open(git_path("gc_needed"), O_CREAT | O_RDWR, 0644);
+	else if (time(NULL) - st.st_mtime < 3600)
+		return 0;
+	else
+		utime(git_path("gc_needed"), NULL);
+
 	return 1;
 }
 
@@ -190,6 +199,7 @@ int cmd_gc(int argc, const char **argv, const char *prefix)
 {
 	int aggressive = 0;
 	int auto_gc = 0;
+	int check_gc = 0;
 	int quiet = 0;
 
 	struct option builtin_gc_options[] = {
@@ -199,12 +209,16 @@ int cmd_gc(int argc, const char **argv, const char *prefix)
 			PARSE_OPT_OPTARG, NULL, (intptr_t)prune_expire },
 		OPT_BOOLEAN(0, "aggressive", &aggressive, "be more thorough (increased runtime)"),
 		OPT_BOOLEAN(0, "auto", &auto_gc, "enable auto-gc mode"),
+		OPT_BOOLEAN(0, "dry-run", &check_gc, "warn if auto gc is needed"),
 		OPT_END()
 	};
 
 	if (argc == 2 && !strcmp(argv[1], "-h"))
 		usage_with_options(builtin_gc_usage, builtin_gc_options);
 
+	if (!auto_gc && check_gc)
+		die(_("--dry-run is useless without --auto"));
+
 	argv_array_pushl(&pack_refs_cmd, "pack-refs", "--all", "--prune", NULL);
 	argv_array_pushl(&reflog, "reflog", "expire", "--all", NULL);
 	argv_array_pushl(&repack, "repack", "-d", "-l", NULL);
@@ -240,6 +254,11 @@ int cmd_gc(int argc, const char **argv, const char *prefix)
 		if (run_hook(NULL, "pre-auto-gc", NULL))
 			return 0;
 
+		if (check_gc) {
+			warning(_("This repository needs maintenance. "
+				  "Please run \"git gc\" as soon as possible."));
+			return 0;
+		}
 		if (quiet)
 			fprintf(stderr, _("Auto packing the repository for optimum performance.\n"));
 		else
-- 
1.7.8.36.g69ee2