git-svn: better attempt to handle broken symlink updates

This is a followup to 7fc35e0e94,
(workaround a for broken symlinks in SVN).

Since broken SVN clients can commit svn:special files without
the magic "link " prefix, this can affect delta application
when we update the broken svn:special file.  So now we fall
back and retry the delta application on symlinks if having
a "link " prefix fails.

Our behavior differs from svn(1) (v1.5.1) slightly:

  When a svn:special file is created w/o a "link " prefix, svn
  will create a regular file (mode 100644 to git) with the
  contents of the blob as-is.

  Our behavior is to continue creating the symlink (mode 120000
  to git) with the contents of the blob as-is.  While this
  differs from current svn(1) behavior, this is easier and more
  efficient to implement (and the correctness of the svn(1) is
  debatable, since it's a workaround for a bug in the first
  place).

More information on this SVN bug is described here:
  http://subversion.tigris.org/issues/show_bug.cgi?id=2692

Signed-off-by: Eric Wong <normalperson@yhbt.net>

git-svn.perl

@@ -3380,19 +3380,35 @@ sub apply_textdelta {
 	open my $dup, '<&', $fh or croak $!;
 	my $base = $::_repository->temp_acquire('git_blob');
 	if ($fb->{blob}) {
+		my ($base_is_link, $size);
+
 		if ($fb->{mode_a} eq '120000' &&
 		    ! $self->{empty_symlinks}->{$fb->{path}}) {
 			print $base 'link ' or die "print $!\n";
+			$base_is_link = 1;
 		}
-		my $size = $::_repository->cat_blob($fb->{blob}, $base);
+	retry:
+		$size = $::_repository->cat_blob($fb->{blob}, $base);
 		die "Failed to read object $fb->{blob}" if ($size < 0);
 
 		if (defined $exp) {
 			seek $base, 0, 0 or croak $!;
 			my $got = ::md5sum($base);
-			die "Checksum mismatch: $fb->{path} $fb->{blob}\n",
-			    "expected: $exp\n",
-			    "     got: $got\n" if ($got ne $exp);
+			if ($got ne $exp) {
+				my $err = "Checksum mismatch: ".
+				       "$fb->{path} $fb->{blob}\n" .
+				       "expected: $exp\n" .
+				       "     got: $got\n";
+				if ($base_is_link) {
+					warn $err,
+					     "Retrying... (possibly ",
+					     "a bad symlink from SVN)\n";
+					$::_repository->temp_reset($base);
+					$base_is_link = 0;
+					goto retry;
+				}
+				die $err;
+			}
 		}
 	}
 	seek $base, 0, 0 or croak $!;

t/t9132-git-svn-broken-symlink.sh

@@ -0,0 +1,102 @@
+#!/bin/sh
+
+test_description='test that git handles an svn repository with empty symlinks'
+
+. ./lib-git-svn.sh
+test_expect_success 'load svn dumpfile' '
+	svnadmin load "$rawsvnrepo" <<EOF
+SVN-fs-dump-format-version: 2
+
+UUID: 60780f9a-7df5-43b4-83ab-60e2c0673ef7
+
+Revision-number: 0
+Prop-content-length: 56
+Content-length: 56
+
+K 8
+svn:date
+V 27
+2008-11-26T07:17:27.590577Z
+PROPS-END
+
+Revision-number: 1
+Prop-content-length: 111
+Content-length: 111
+
+K 7
+svn:log
+V 4
+test
+K 10
+svn:author
+V 12
+normalperson
+K 8
+svn:date
+V 27
+2008-11-26T07:18:03.511836Z
+PROPS-END
+
+Node-path: bar
+Node-kind: file
+Node-action: add
+Prop-content-length: 33
+Text-content-length: 4
+Text-content-md5: 912ec803b2ce49e4a541068d495ab570
+Content-length: 37
+
+K 11
+svn:special
+V 1
+*
+PROPS-END
+asdf
+
+Revision-number: 2
+Prop-content-length: 121
+Content-length: 121
+
+K 7
+svn:log
+V 13
+bar => doink
+
+K 10
+svn:author
+V 12
+normalperson
+K 8
+svn:date
+V 27
+2008-11-27T03:55:31.601672Z
+PROPS-END
+
+Node-path: bar
+Node-kind: file
+Node-action: change
+Text-content-length: 10
+Text-content-md5: 92ca4fe7a9721f877f765c252dcd66c9
+Content-length: 10
+
+link doink
+
+EOF
+'
+
+test_expect_success 'clone using git svn' 'git svn clone -r1 "$svnrepo" x'
+
+test_expect_success '"bar" is a symlink that points to "asdf"' '
+	test -L x/bar &&
+	(cd x && test xasdf = x"`git cat-file blob HEAD:bar`")
+'
+
+test_expect_success 'get "bar" => symlink fix from svn' '
+	(cd x && git svn rebase)
+'
+
+test_expect_success '"bar" remains a proper symlink' '
+	test -L x/bar &&
+	(cd x && test xdoink = x"`git cat-file blob HEAD:bar`")
+'
+
+test_done