builtin/verify-tag: add --format to verify-tag

Callers of verify-tag may want to cross-check the tagname from refs/tags
with the tagname from the tag object header upon GPG verification. This
is to avoid tag refs that point to an incorrect object.

Add a --format parameter to git verify-tag to print the formatted tag
object header in addition to or instead of the --verbose or --raw GPG
verification output.

Signed-off-by: Santiago Torres <santiago@nyu.edu>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Author: SantiagoTorres

Documentation/git-verify-tag.txt

@@ -8,7 +8,7 @@ git-verify-tag - Check the GPG signature of tags
 SYNOPSIS
 --------
 [verse]
-'git verify-tag' <tag>...
+'git verify-tag' [--format=<format>] <tag>...
 
 DESCRIPTION
 -----------

builtin/verify-tag.c

@@ -12,9 +12,10 @@
 #include <signal.h>
 #include "parse-options.h"
 #include "gpg-interface.h"
+#include "ref-filter.h"
 
 static const char * const verify_tag_usage[] = {
-		N_("git verify-tag [-v | --verbose] <tag>..."),
+		N_("git verify-tag [-v | --verbose] [--format=<format>] <tag>..."),
 		NULL
 };
 
@@ -30,9 +31,11 @@ int cmd_verify_tag(int argc, const char **argv, const char *prefix)
 {
 	int i = 1, verbose = 0, had_error = 0;
 	unsigned flags = 0;
+	char *fmt_pretty = NULL;
 	const struct option verify_tag_options[] = {
 		OPT__VERBOSE(&verbose, N_("print tag contents")),
 		OPT_BIT(0, "raw", &flags, N_("print raw gpg status output"), GPG_VERIFY_RAW),
+		OPT_STRING(  0 , "format", &fmt_pretty, N_("format"), N_("format to use for the output")),
 		OPT_END()
 	};
 
@@ -46,13 +49,26 @@ int cmd_verify_tag(int argc, const char **argv, const char *prefix)
 	if (verbose)
 		flags |= GPG_VERIFY_VERBOSE;
 
+	if (fmt_pretty) {
+		verify_ref_format(fmt_pretty);
+		flags |= GPG_VERIFY_OMIT_STATUS;
+	}
+
 	while (i < argc) {
 		unsigned char sha1[20];
 		const char *name = argv[i++];
-		if (get_sha1(name, sha1))
+		if (get_sha1(name, sha1)) {
 			had_error = !!error("tag '%s' not found.", name);
-		else if (gpg_verify_tag(sha1, name, flags))
+			continue;
+		}
+
+		if (gpg_verify_tag(sha1, name, flags)) {
 			had_error = 1;
+			continue;
+		}
+
+		if (fmt_pretty)
+			pretty_print_ref(name, sha1, fmt_pretty);
 	}
 	return had_error;
 }