commit: --dry-run

This teaches --dry-run option to "git commit".

It is the same as "git status", but in the longer term we would want to
change the semantics of "git status" not to be the preview of commit, and
this is the first step for doing so.
Signed-off-by: NJunio C Hamano <gitster@pobox.com>

Documentation/git-commit.txt

@@ -8,7 +8,7 @@ git-commit - Record changes to the repository
 SYNOPSIS
 --------
 [verse]
-'git commit' [-a | --interactive] [-s] [-v] [-u<mode>] [--amend]
+'git commit' [-a | --interactive] [-s] [-v] [-u<mode>] [--amend] [--dry-run]
 	   [(-c | -C) <commit>] [-F <file> | -m <msg>]
 	   [--allow-empty] [--no-verify] [-e] [--author=<author>]
 	   [--cleanup=<mode>] [--] [[-i | -o ]<file>...]
@@ -198,6 +198,11 @@ specified.
 --quiet::
 	Suppress commit summary message.
 
+--dry-run::
+	Do not create a commit, but show a list of paths that are
+	to be committed, paths with local changes that will be left
+	uncommitted and paths that are untracked.
+
 \--::
 	Do not interpret any more arguments as options.
 

builtin-commit.c

@@ -51,7 +51,7 @@ static const char *template_file;
 static char *edit_message, *use_message;
 static char *author_name, *author_email, *author_date;
 static int all, edit_flag, also, interactive, only, amend, signoff;
-static int quiet, verbose, no_verify, allow_empty;
+static int quiet, verbose, no_verify, allow_empty, dry_run;
 static char *untracked_files_arg;
 /*
  * The default commit message cleanup mode will remove the lines
@@ -103,6 +103,7 @@ static struct option builtin_commit_options[] = {
 	OPT_BOOLEAN(0, "interactive", &interactive, "interactively add files"),
 	OPT_BOOLEAN('o', "only", &only, "commit only specified files"),
 	OPT_BOOLEAN('n', "no-verify", &no_verify, "bypass pre-commit hook"),
+	OPT_BOOLEAN(0, "dry-run", &dry_run, "show what would be committed"),
 	OPT_BOOLEAN(0, "amend", &amend, "amend previous commit"),
 	{ OPTION_STRING, 'u', "untracked-files", &untracked_files_arg, "mode", "show untracked files, optional modes: all, normal, no. (Default: all)", PARSE_OPT_OPTARG, NULL, (intptr_t)"all" },
 	OPT_BOOLEAN(0, "allow-empty", &allow_empty, "ok to record an empty change"),
@@ -813,28 +814,28 @@ static int parse_and_validate_options(int argc, const char *argv[],
 	return argc;
 }
 
-int cmd_status(int argc, const char **argv, const char *prefix)
+static int dry_run_commit(int argc, const char **argv, const char *prefix)
 {
-	const char *index_file;
 	int commitable;
+	const char *index_file;
 
-	git_config(git_status_config, NULL);
+	index_file = prepare_index(argc, argv, prefix, 1);
+	commitable = run_status(stdout, index_file, prefix, 0);
+	rollback_index_files();
 
+	return commitable ? 0 : 1;
+}
+
+int cmd_status(int argc, const char **argv, const char *prefix)
+{
+	git_config(git_status_config, NULL);
 	if (wt_status_use_color == -1)
 		wt_status_use_color = git_use_color_default;
-
 	if (diff_use_color_default == -1)
 		diff_use_color_default = git_use_color_default;
 
 	argc = parse_and_validate_options(argc, argv, builtin_status_usage, prefix);
-
-	index_file = prepare_index(argc, argv, prefix, 1);
-
-	commitable = run_status(stdout, index_file, prefix, 0);
-
-	rollback_index_files();
-
-	return commitable ? 0 : 1;
+	return dry_run_commit(argc, argv, prefix);
 }
 
 static void print_summary(const char *prefix, const unsigned char *sha1)
@@ -909,6 +910,8 @@ int cmd_commit(int argc, const char **argv, const char *prefix)
 		wt_status_use_color = git_use_color_default;
 
 	argc = parse_and_validate_options(argc, argv, builtin_commit_usage, prefix);
+	if (dry_run)
+		return dry_run_commit(argc, argv, prefix);
 
 	index_file = prepare_index(argc, argv, prefix, 0);