builtin/tag: add --format argument for tag -v

Adding --format to git tag -v mutes the default output of the GPG
verification and instead prints the formatted tag object.
This allows callers to cross-check the tagname from refs/tags with
the tagname from the tag object header upon GPG verification.

The callback function for for_each_tag_name() didn't allow callers to
pass custom data to their callback functions. Add a new opaque pointer
to each_tag_name_fn's parameter to allow this.

Signed-off-by: Lukas Puehringer <luk.puehringer@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Author: lukpueh

Documentation/git-tag.txt

@@ -15,7 +15,7 @@ SYNOPSIS
 'git tag' [-n[<num>]] -l [--contains <commit>] [--points-at <object>]
 	[--column[=<options>] | --no-column] [--create-reflog] [--sort=<key>]
 	[--format=<format>] [--[no-]merged [<commit>]] [<pattern>...]
-'git tag' -v <tagname>...
+'git tag' -v [--format=<format>] <tagname>...
 
 DESCRIPTION
 -----------

builtin/tag.c

@@ -24,7 +24,7 @@ static const char * const git_tag_usage[] = {
 	N_("git tag -d <tagname>..."),
 	N_("git tag -l [-n[<num>]] [--contains <commit>] [--points-at <object>]"
 		"\n\t\t[--format=<format>] [--[no-]merged [<commit>]] [<pattern>...]"),
-	N_("git tag -v <tagname>..."),
+	N_("git tag -v [--format=<format>] <tagname>..."),
 	NULL
 };
 
@@ -66,9 +66,10 @@ static int list_tags(struct ref_filter *filter, struct ref_sorting *sorting, con
 }
 
 typedef int (*each_tag_name_fn)(const char *name, const char *ref,
-				const unsigned char *sha1);
+				const unsigned char *sha1, const void *cb_data);
 
-static int for_each_tag_name(const char **argv, each_tag_name_fn fn)
+static int for_each_tag_name(const char **argv, each_tag_name_fn fn,
+			     const void *cb_data)
 {
 	const char **p;
 	char ref[PATH_MAX];
@@ -87,14 +88,14 @@ static int for_each_tag_name(const char **argv, each_tag_name_fn fn)
 			had_error = 1;
 			continue;
 		}
-		if (fn(*p, ref, sha1))
+		if (fn(*p, ref, sha1, cb_data))
 			had_error = 1;
 	}
 	return had_error;
 }
 
 static int delete_tag(const char *name, const char *ref,
-				const unsigned char *sha1)
+		      const unsigned char *sha1, const void *cb_data)
 {
 	if (delete_ref(ref, sha1, 0))
 		return 1;
@@ -103,9 +104,22 @@ static int delete_tag(const char *name, const char *ref,
 }
 
 static int verify_tag(const char *name, const char *ref,
-				const unsigned char *sha1)
+		      const unsigned char *sha1, const void *cb_data)
 {
-	return gpg_verify_tag(sha1, name, GPG_VERIFY_VERBOSE);
+	int flags;
+	const char *fmt_pretty = cb_data;
+	flags = GPG_VERIFY_VERBOSE;
+
+	if (fmt_pretty)
+		flags = GPG_VERIFY_OMIT_STATUS;
+
+	if (gpg_verify_tag(sha1, name, flags))
+		return -1;
+
+	if (fmt_pretty)
+		pretty_print_ref(name, sha1, fmt_pretty);
+
+	return 0;
 }
 
 static int do_sign(struct strbuf *buffer)
@@ -424,9 +438,12 @@ int cmd_tag(int argc, const char **argv, const char *prefix)
 	if (filter.merge_commit)
 		die(_("--merged and --no-merged option are only allowed with -l"));
 	if (cmdmode == 'd')
-		return for_each_tag_name(argv, delete_tag);
-	if (cmdmode == 'v')
-		return for_each_tag_name(argv, verify_tag);
+		return for_each_tag_name(argv, delete_tag, NULL);
+	if (cmdmode == 'v') {
+		if (format)
+			verify_ref_format(format);
+		return for_each_tag_name(argv, verify_tag, format);
+	}
 
 	if (msg.given || msgfile) {
 		if (msg.given && msgfile)