Add findtags - reworked

A short perl script that will walk the tag refs, tag objects, and even commit
objects in its quest to figure out whether the given SHA1 (for a commit or
tree) was ever tagged.

This version is reworked incorporating sanity, feature and style fixes from
Junio.

Usage: git-findtags.perl [ -t ] <commit-or-tree-sha1>

Signed-off-by: Martin Langhoff <martin@catalyst.net.nz>
Signed-off-by: Junio C Hamano <junkio@cox.net>

Makefile

@@ -93,7 +93,8 @@ SCRIPT_SH = \
 
 SCRIPT_PERL = \
 	git-archimport.perl git-cvsimport.perl git-relink.perl \
-	git-rename.perl git-shortlog.perl git-fmt-merge-msg.perl
+	git-rename.perl git-shortlog.perl git-fmt-merge-msg.perl \
+	git-findtags.perl
 
 SCRIPT_PYTHON = \
 	git-merge-recursive.py

git-findtags.perl

@@ -0,0 +1,94 @@
+#!/usr/bin/perl -w
+#
+# Copyright (c) 2005 Martin Langhoff
+#
+# Walk the tags and find if they match a commit
+# expects a SHA1 of a commit. Option -t enables 
+# searching trees too.
+#
+
+use strict;
+use File::Basename;
+use File::Find;
+use Getopt::Std;
+
+my $git_dir = $ENV{GIT_DIR} || '.git';
+$git_dir =~ s|/$||; # chomp trailing slash
+
+# options
+our $opt_t;
+getopts("t") || usage();
+
+my @tagfiles   = `find $git_dir/refs/tags -follow -type f`; # haystack
+my $target = shift @ARGV;                     # needle
+unless ($target) {
+    usage();
+}
+
+# drive the processing from the find hook
+# slower, safer (?) than the find utility
+find( { wanted   => \&process,
+	no_chdir => 1,
+	follow   => 1,
+      }, "$git_dir/refs/tags");
+
+
+sub process {
+    my ($dev,$ino,$mode,$nlink,$uid,$gid);
+
+    # process only regular files
+    unless ((($dev,$ino,$mode,$nlink,$uid,$gid) = lstat($_)) && -f _) {
+	return 1; # ignored anyway
+    }
+
+    my $tagfile = $_;
+    chomp $tagfile;
+    my $tagname = substr($tagfile, length($git_dir.'/refs/tags/'));
+
+    my $tagid = quickread($tagfile);
+    chomp $tagid;
+
+    # is it just a soft tag?
+    if ($tagid eq $target) {
+	print "$tagname\n";
+	return 1; # done with this tag
+    }
+
+    # grab the first 2 lines (the whole tag could be large)
+    my $tagobj = `git-cat-file tag $tagid | head -n2 `;
+    if ($tagobj =~  m/^type commit$/m) { # only deal with commits
+
+	if ($tagobj =~ m/^object $target$/m) { # match on the commit
+	    print "$tagname\n";
+
+	} elsif ( $opt_t &&                      # follow the commit
+		 $tagobj =~ m/^object (\S+)$/m) { # and try to match trees
+	    my $commitid = $1;
+	    my $commitobj = `git-cat-file commit $commitid | head -n1`;
+	    chomp $commitobj;
+	    $commitobj =~ m/^tree (\S+)$/;
+	    my $treeid = $1;
+	    if ($target eq $treeid) {
+		print "$tagname\n";
+	    }
+	}
+    }
+}
+
+sub quickread {
+    my $file = shift;
+    local $/; # undef: slurp mode
+    open FILE, "<$file"
+	or die "Cannot open $file : $!";
+    my $content = <FILE>;
+    close FILE;
+    return $content;
+}
+
+sub usage {
+	print STDERR <<END;
+Usage: ${\basename $0}     # find tags for a commit or tree
+       [ -t ] <commit-or-tree-sha1>
+END
+	exit(1);
+}