format-patch: Add a signature option (--signature)

By default, git uses the version string as the signature for all
patches output by format-patch. Many employers (mine included)
require the use of a signature on all outgoing mails. In a
format-patch | send-email workflow there isn't an easy way to modify
the signature without breaking the pipe and manually replacing the
version string with the signature required. Instead of doing all that
work, add an option (--signature) and a config variable
(format.signature) to replace the default git version signature when
formatting patches.

This does modify the original behavior of format-patch a bit. First
off the version string is now placed in the cover letter by default.
Secondly, once the configuration variable format.signature is added
to the .config file there is no way to revert back to the default
git version signature. Instead, specifying the --no-signature option
will remove the signature from the patches entirely.

Signed-off-by: Stephen Boyd <bebarino@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Documentation/config.txt

@@ -880,6 +880,12 @@ format.subjectprefix::
 	The default for format-patch is to output files with the '[PATCH]'
 	subject prefix. Use this variable to change that prefix.
 
+format.signature::
+	The default for format-patch is to output a signature containing
+	the git version number. Use this variable to change that default.
+	Set this variable to the empty string ("") to suppress
+	signature generation.
+
 format.suffix::
 	The default for format-patch is to output files with the suffix
 	`.patch`. Use this variable to change that suffix (make sure to

Documentation/git-format-patch.txt

@@ -13,6 +13,7 @@ SYNOPSIS
 		   [--no-thread | --thread[=<style>]]
 		   [(--attach|--inline)[=<boundary>] | --no-attach]
 		   [-s | --signoff]
+		   [--signature=<signature> | --no-signature]
 		   [-n | --numbered | -N | --no-numbered]
 		   [--start-number <n>] [--numbered-files]
 		   [--in-reply-to=Message-Id] [--suffix=.<sfx>]
@@ -180,6 +181,12 @@ will want to ensure that threading is disabled for `git send-email`.
 	containing the shortlog and the overall diffstat.  You can
 	fill in a description in the file before sending it out.
 
+--[no]-signature=<signature>::
+	Add a signature to each message produced. Per RFC 3676 the signature
+	is separated from the body by a line with '-- ' on it. If the
+	signature option is omitted the signature defaults to the git version
+	number.
+
 --suffix=.<sfx>::
 	Instead of using `.patch` as the suffix for generated
 	filenames, use specified suffix.  A common alternative is

builtin/log.c

@@ -549,8 +549,9 @@ static void add_header(const char *value)
 
 #define THREAD_SHALLOW 1
 #define THREAD_DEEP 2
-static int thread = 0;
-static int do_signoff = 0;
+static int thread;
+static int do_signoff;
+static const char *signature = git_version_string;
 
 static int git_format_config(const char *var, const char *value, void *cb)
 {
@@ -609,6 +610,8 @@ static int git_format_config(const char *var, const char *value, void *cb)
 		do_signoff = git_config_bool(var, value);
 		return 0;
 	}
+	if (!strcmp(var, "format.signature"))
+		return git_config_string(&signature, var, value);
 
 	return git_log_config(var, value, cb);
 }
@@ -703,6 +706,12 @@ static void gen_message_id(struct rev_info *info, char *base)
 	info->message_id = strbuf_detach(&buf, NULL);
 }
 
+static void print_signature(void)
+{
+	if (signature && *signature)
+		printf("-- \n%s\n\n", signature);
+}
+
 static void make_cover_letter(struct rev_info *rev, int use_stdout,
 			      int numbered, int numbered_files,
 			      struct commit *origin,
@@ -796,6 +805,7 @@ static void make_cover_letter(struct rev_info *rev, int use_stdout,
 	diff_flush(&opts);
 
 	printf("\n");
+	print_signature();
 }
 
 static const char *clean_message_id(const char *msg_id)
@@ -1035,6 +1045,8 @@ int cmd_format_patch(int argc, const char **argv, const char *prefix)
 		{ OPTION_CALLBACK, 0, "thread", &thread, "style",
 			    "enable message threading, styles: shallow, deep",
 			    PARSE_OPT_OPTARG, thread_callback },
+		OPT_STRING(0, "signature", &signature, "signature",
+			    "add a signature"),
 		OPT_END()
 	};
 
@@ -1313,7 +1325,7 @@ int cmd_format_patch(int argc, const char **argv, const char *prefix)
 				       mime_boundary_leader,
 				       rev.mime_boundary);
 			else
-				printf("-- \n%s\n\n", git_version_string);
+				print_signature();
 		}
 		if (!use_stdout)
 			fclose(stdout);

t/t4013/diff.format-patch_--stdout_--cover-letter_-n_initial..master^

@@ -18,6 +18,9 @@ A U Thor (2):
  create mode 100644 file1
  delete mode 100644 file2
 
+-- 
+g-i-t--v-e-r-s-i-o-n
+
 From 1bde4ae5f36c8d9abe3a0fce0c6aab3c4a12fe44 Mon Sep 17 00:00:00 2001
 From: A U Thor <author@example.com>
 Date: Mon, 26 Jun 2006 00:01:00 +0000

t/t4014-format-patch.sh

@@ -613,4 +613,56 @@ test_expect_success 'format-patch --ignore-if-in-upstream HEAD' '
 	git format-patch --ignore-if-in-upstream HEAD
 '
 
+test_expect_success 'format-patch --signature' '
+	git format-patch --stdout --signature="my sig" -1 >output &&
+	grep "my sig" output
+'
+
+test_expect_success 'format-patch with format.signature config' '
+	git config format.signature "config sig" &&
+	git format-patch --stdout -1 >output &&
+	grep "config sig" output
+'
+
+test_expect_success 'format-patch --signature overrides format.signature' '
+	git config format.signature "config sig" &&
+	git format-patch --stdout --signature="overrides" -1 >output &&
+	! grep "config sig" output &&
+	grep "overrides" output
+'
+
+test_expect_success 'format-patch --no-signature ignores format.signature' '
+	git config format.signature "config sig" &&
+	git format-patch --stdout --signature="my sig" --no-signature \
+		-1 >output &&
+	! grep "config sig" output &&
+	! grep "my sig" output &&
+	! grep "^-- \$" output
+'
+
+test_expect_success 'format-patch --signature --cover-letter' '
+	git config --unset-all format.signature &&
+	git format-patch --stdout --signature="my sig" --cover-letter \
+		-1 >output &&
+	grep "my sig" output &&
+	test 2 = $(grep "my sig" output | wc -l)
+'
+
+test_expect_success 'format.signature="" supresses signatures' '
+	git config format.signature "" &&
+	git format-patch --stdout -1 >output &&
+	! grep "^-- \$" output
+'
+
+test_expect_success 'format-patch --no-signature supresses signatures' '
+	git config --unset-all format.signature &&
+	git format-patch --stdout --no-signature -1 >output &&
+	! grep "^-- \$" output
+'
+
+test_expect_success 'format-patch --signature="" supresses signatures' '
+	git format-patch --signature="" -1 >output &&
+	! grep "^-- \$" output
+'
+
 test_done