[PATCH 2/2] cvsimport move over to using git for each ref to read refs V2

cvsimport: move over to using git-for-each-ref to read refs V2

cvsimport opens all of the files in $GIT_DIR/refs/heads and reads
out the sha1's in order to work out what time the last commit on
that branch was made (in CVS) thus allowing incremental updates.
However, this takes no account of hierachical refs naming producing
the following error for each directory in $GIT_DIR/refs:

  Use of uninitialized value in chomp at /usr/bin/git-cvsimport line 503.
  Use of uninitialized value in concatenation (.) or string at
					/usr/bin/git-cvsimport line 505.
  usage: git-cat-file [-t|-s|-e|-p|<type>] <sha1>

Take advantage of the new packed refs work to use the new
for-each-ref iterator to get this information.  Use the format
specifier to ensure we are neutral to changes in default.

[Junio: although although for-each-ref offers a --perl quoting mode
this patch does not use it as it seems only to make parsing the
output harder in perl.  If there is a neat trick for handling this
'perl' form please educate me.  Here, rely on sha1's and refnames
to contain no spaces.]

Signed-off-by: Andy Whitcroft <redacted>
---

diff --git a/git-cvsimport.perl b/git-cvsimport.perl
index e5a00a1..5b13c23 100755
--- a/git-cvsimport.perl
+++ b/git-cvsimport.perl

@@ -495,22 +495,17 @@ unless(-d $git_dir) {
 	$tip_at_start = `git-rev-parse --verify HEAD`;
 
 	# Get the last import timestamps
-	opendir(D,"$git_dir/refs/heads");
-	while(defined(my $head = readdir(D))) {
-		next if $head =~ /^\./;
-		open(F,"$git_dir/refs/heads/$head")
-			or die "Bad head branch: $head: $!\n";
-		chomp(my $ftag = <F>);
-		close(F);
-		open(F,"git-cat-file commit $ftag |");
-		while(<F>) {
-			next unless /^author\s.*\s(\d+)\s[-+]\d{4}$/;
-			$branch_date{$head} = $1;
-			last;
-		}
-		close(F);
+	open(H, "git-for-each-ref --format='%(objectname) %(refname) %(authorstamp)'|") or
+		die "Cannot run git-for-each-ref: $!\n";
+	while(defined(my $entry = <H>)) {
+		chomp($entry);
+		my ($ftag, $name, $stamp, $zone) = split(/ /, $entry, 4);
+		next if ($name !~ m@^refs/heads/(.*)$@);
+		my ($head) = ($1);
+
+		$branch_date{$head} = $stamp;
 	}
-	closedir(D);
+	close(H);
 }
 
 -d $git_dir