tag: add the option to force signing of annotated tags

The `tag.forcesignannotated` configuration variable makes "git tag"
that would implicitly create an annotated tag to instead create a
signed tag.  For example

	$ git tag -m "This is a message" tag-with-message
	$ git tag -F message-file tag-with-message

would create a signed tag if the configuration variable is in
effect.  To override this from the command line, the user can
explicitly ask for an annotated tag, like so:

	$ git tag -a -m "This is a message" tag-with-message
	$ git tag -a -F message-file tag-with-message

Creation of a light-weight tag, i.e.

	$ git tag lightweight

is not affected.

Signed-off-by: Laurent Arnoud <laurent@spkdev.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
diff --git a/builtin/tag.c b/builtin/tag.c
index 1705c94..528a1ba 100644
--- a/builtin/tag.c
+++ b/builtin/tag.c
@@ -29,6 +29,7 @@
 };
 
 static unsigned int colopts;
+static int force_sign_annotate;
 
 static int list_tags(struct ref_filter *filter, struct ref_sorting *sorting, const char *format)
 {
@@ -166,6 +167,11 @@
 	status = git_gpg_config(var, value, cb);
 	if (status)
 		return status;
+	if (!strcmp(var, "tag.forcesignannotated")) {
+		force_sign_annotate = git_config_bool(var, value);
+		return 0;
+	}
+
 	if (starts_with(var, "column."))
 		return git_column_config(var, value, "tag", &colopts);
 	return git_default_config(var, value, cb);
@@ -327,7 +333,7 @@
 	char *cleanup_arg = NULL;
 	int create_reflog = 0;
 	int annotate = 0, force = 0;
-	int cmdmode = 0;
+	int cmdmode = 0, create_tag_object = 0;
 	const char *msgfile = NULL, *keyid = NULL;
 	struct msg_arg msg = { 0, STRBUF_INIT };
 	struct ref_transaction *transaction;
@@ -385,12 +391,12 @@
 		opt.sign = 1;
 		set_signing_key(keyid);
 	}
-	if (opt.sign)
-		annotate = 1;
+	create_tag_object = (opt.sign || annotate || msg.given || msgfile);
+
 	if (argc == 0 && !cmdmode)
 		cmdmode = 'l';
 
-	if ((annotate || msg.given || msgfile || force) && (cmdmode != 0))
+	if ((create_tag_object || force) && (cmdmode != 0))
 		usage_with_options(git_tag_usage, options);
 
 	finalize_colopts(&colopts, -1);
@@ -431,7 +437,6 @@
 	if (msg.given || msgfile) {
 		if (msg.given && msgfile)
 			die(_("only one -F or -m option is allowed."));
-		annotate = 1;
 		if (msg.given)
 			strbuf_addbuf(&buf, &(msg.buf));
 		else {
@@ -474,8 +479,11 @@
 	else
 		die(_("Invalid cleanup mode %s"), cleanup_arg);
 
-	if (annotate)
+	if (create_tag_object) {
+		if (force_sign_annotate && !annotate)
+			opt.sign = 1;
 		create_tag(object, tag, &buf, &opt, prev, object);
+	}
 
 	transaction = ref_transaction_begin(&err);
 	if (!transaction ||