builtin-commit: add --date option

This is like --author: allow a user to specify a given date without
using the GIT_AUTHOR_DATE environment variable.

Signed-off-by: Miklos Vajna <vmiklos@frugalware.org>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Documentation/git-commit.txt

@@ -11,7 +11,7 @@ SYNOPSIS
 'git commit' [-a | --interactive] [-s] [-v] [-u<mode>] [--amend] [--dry-run]
 	   [(-c | -C) <commit>] [-F <file> | -m <msg>] [--reset-author]
 	   [--allow-empty] [--no-verify] [-e] [--author=<author>]
-	   [--cleanup=<mode>] [--] [[-i | -o ]<file>...]
+	   [--date=<date>] [--cleanup=<mode>] [--] [[-i | -o ]<file>...]
 
 DESCRIPTION
 -----------
@@ -85,6 +85,9 @@ OPTIONS
 	an existing commit that matches the given string and its author
 	name is used.
 
+--date=<date>::
+	Override the author date used in the commit.
+
 -m <msg>::
 --message=<msg>::
 	Use the given <msg> as the commit message.

builtin-commit.c

@@ -52,7 +52,7 @@ 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, dry_run, renew_authorship;
-static char *untracked_files_arg;
+static char *untracked_files_arg, *force_date;
 /*
  * The default commit message cleanup mode will remove the lines
  * beginning with # (shell comments) and leading and trailing
@@ -90,6 +90,7 @@ static struct option builtin_commit_options[] = {
 
 	OPT_FILENAME('F', "file", &logfile, "read log from file"),
 	OPT_STRING(0, "author", &force_author, "AUTHOR", "override author for commit"),
+	OPT_STRING(0, "date", &force_date, "DATE", "override date for commit"),
 	OPT_CALLBACK('m', "message", &message, "MESSAGE", "specify commit message", opt_parse_m),
 	OPT_STRING('c', "reedit-message", &edit_message, "COMMIT", "reuse and edit message from specified commit"),
 	OPT_STRING('C', "reuse-message", &use_message, "COMMIT", "reuse message from specified commit"),
@@ -410,6 +411,9 @@ static void determine_author_info(void)
 		email = xstrndup(lb + 2, rb - (lb + 2));
 	}
 
+	if (force_date)
+		date = force_date;
+
 	author_name = name;
 	author_email = email;
 	author_date = date;

t/t7501-commit.sh

@@ -211,6 +211,21 @@ test_expect_success 'amend commit to fix author' '
 
 '
 
+test_expect_success 'amend commit to fix date' '
+
+	test_tick &&
+	newtick=$GIT_AUTHOR_DATE &&
+	git reset --hard &&
+	git cat-file -p HEAD |
+	sed -e "s/author.*/author $author $newtick/" \
+		-e "s/^\(committer.*> \).*$/\1$GIT_COMMITTER_DATE/" > \
+		expected &&
+	git commit --amend --date="$newtick" &&
+	git cat-file -p HEAD > current &&
+	test_cmp expected current
+
+'
+
 test_expect_success 'sign off (1)' '
 
 	echo 1 >positive &&