git-difftool.perl - jrn/git - Git at Google

 #!/usr/bin/perl
 # Copyright (c) 2009, 2010 David Aguilar
 # Copyright (c) 2012 Tim Henigan
 #
 # This is a wrapper around the GIT_EXTERNAL_DIFF-compatible
 # git-difftool--helper script.
 #
 # This script exports GIT_EXTERNAL_DIFF and GIT_PAGER for use by git.
 # The GIT_DIFF* variables are exported for use by git-difftool--helper.
 #
 # Any arguments that are unknown to this script are forwarded to 'git diff'.

 use 5.008;
 use strict;
 use warnings;
 use Error qw(:try);
 use File::Basename qw(dirname);
 use File::Copy;
 use File::Find;
 use File::stat;
 use File::Path qw(mkpath rmtree);
 use File::Temp qw(tempdir);
 use Getopt::Long qw(:config pass_through);
 use Git;

 sub usage
 {
 	my $exitcode = shift;
 	print << 'USAGE';
 usage: git difftool [-t|--tool=<tool>] [--tool-help]
                     [-x|--extcmd=<cmd>]
                     [-g|--gui] [--no-gui]
                     [--prompt] [-y|--no-prompt]
                     [-d|--dir-diff]
                     ['git diff' options]
 USAGE
 	exit($exitcode);
 }

 sub find_worktree
 {
 	# Git->repository->wc_path() does not honor changes to the working
 	# tree location made by $ENV{GIT_WORK_TREE} or the 'core.worktree'
 	# config variable.
 	return Git::command_oneline('rev-parse', '--show-toplevel');
 }

 sub print_tool_help
 {
 	# See the comment at the bottom of file_diff() for the reason behind
 	# using system() followed by exit() instead of exec().
 	my $rc = system(qw(git mergetool --tool-help=diff));
 	exit($rc | ($rc >> 8));
 }

 sub exit_cleanup
 {
 	my ($tmpdir, $status) = @_;
 	my $errno = $!;
 	rmtree($tmpdir);
 	if ($status and $errno) {
 		my ($package, $file, $line) = caller();
 		warn "$file line $line: $errno\n";
 	}
 	exit($status | ($status >> 8));
 }

 sub use_wt_file
 {
 	my ($repo, $workdir, $file, $sha1) = @_;
 	my $null_sha1 = '0' x 40;

 	if (! -e "$workdir/$file") {
 		# If the file doesn't exist in the working tree, we cannot
 		# use it.
 		return (0, $null_sha1);
 	}

 	my $wt_sha1 = $repo->command_oneline('hash-object', "$workdir/$file");
 	my $use = ($sha1 eq $null_sha1) || ($sha1 eq $wt_sha1);
 	return ($use, $wt_sha1);
 }

 sub changed_files
 {
 	my ($repo_path, $index, $worktree) = @_;
 	$ENV{GIT_INDEX_FILE} = $index;
 	$ENV{GIT_WORK_TREE} = $worktree;
 	my $must_unset_git_dir = 0;
 	if (not defined($ENV{GIT_DIR})) {
 		$must_unset_git_dir = 1;
 		$ENV{GIT_DIR} = $repo_path;
 	}

 	my @refreshargs = qw/update-index --really-refresh -q --unmerged/;
 	my @gitargs = qw/diff-files --name-only -z/;
 	try {
 		Git::command_oneline(@refreshargs);
 	} catch Git::Error::Command with {};

 	my $line = Git::command_oneline(@gitargs);
 	my @files;
 	if (defined $line) {
 		@files = split('\0', $line);
 	} else {
 		@files = ();
 	}

 	delete($ENV{GIT_INDEX_FILE});
 	delete($ENV{GIT_WORK_TREE});
 	delete($ENV{GIT_DIR}) if ($must_unset_git_dir);

 	return map { $_ => 1 } @files;
 }

 sub setup_dir_diff
 {
 	my ($repo, $workdir, $symlinks) = @_;

 	# Run the diff; exit immediately if no diff found
 	# 'Repository' and 'WorkingCopy' must be explicitly set to insure that
 	# if $GIT_DIR and $GIT_WORK_TREE are set in ENV, they are actually used
 	# by Git->repository->command*.
 	my $repo_path = $repo->repo_path();
 	my %repo_args = (Repository => $repo_path, WorkingCopy => $workdir);
 	my $diffrepo = Git->repository(%repo_args);

 	my @gitargs = ('diff', '--raw', '--no-abbrev', '-z', @ARGV);
 	my $diffrtn = $diffrepo->command_oneline(@gitargs);
 	exit(0) unless defined($diffrtn);

 	# Build index info for left and right sides of the diff
 	my $submodule_mode = '160000';
 	my $symlink_mode = '120000';
 	my $null_mode = '0' x 6;
 	my $null_sha1 = '0' x 40;
 	my $lindex = '';
 	my $rindex = '';
 	my $wtindex = '';
 	my %submodule;
 	my %symlink;
 	my @working_tree = ();
 	my @rawdiff = split('\0', $diffrtn);

 	my $i = 0;
 	while ($i < $#rawdiff) {
 		if ($rawdiff[$i] =~ /^::/) {
 			warn << 'EOF';
 Combined diff formats ('-c' and '--cc') are not supported in
 directory diff mode ('-d' and '--dir-diff').
 EOF
 			exit(1);
 		}

 		my ($lmode, $rmode, $lsha1, $rsha1, $status) =
 			split(' ', substr($rawdiff[$i], 1));
 		my $src_path = $rawdiff[$i + 1];
 		my $dst_path;

 		if ($status =~ /^[CR]/) {
 			$dst_path = $rawdiff[$i + 2];
 			$i += 3;
 		} else {
 			$dst_path = $src_path;
 			$i += 2;
 		}

 		if ($lmode eq $submodule_mode or $rmode eq $submodule_mode) {
 			$submodule{$src_path}{left} = $lsha1;
 			if ($lsha1 ne $rsha1) {
 				$submodule{$dst_path}{right} = $rsha1;
 			} else {
 				$submodule{$dst_path}{right} = "$rsha1-dirty";
 			}
 			next;
 		}

 		if ($lmode eq $symlink_mode) {
 			$symlink{$src_path}{left} =
 				$diffrepo->command_oneline('show', "$lsha1");
 		}

 		if ($rmode eq $symlink_mode) {
 			$symlink{$dst_path}{right} =
 				$diffrepo->command_oneline('show', "$rsha1");
 		}

 		if ($lmode ne $null_mode and $status !~ /^C/) {
 			$lindex .= "$lmode $lsha1\t$src_path\0";
 		}

 		if ($rmode ne $null_mode) {
 			my ($use, $wt_sha1) = use_wt_file($repo, $workdir,
 							  $dst_path, $rsha1);
 			if ($use) {
 				push @working_tree, $dst_path;
 				$wtindex .= "$rmode $wt_sha1\t$dst_path\0";
 			} else {
 				$rindex .= "$rmode $rsha1\t$dst_path\0";
 			}
 		}
 	}

 	# Setup temp directories
 	my $tmpdir = tempdir('git-difftool.XXXXX', CLEANUP => 0, TMPDIR => 1);
 	my $ldir = "$tmpdir/left";
 	my $rdir = "$tmpdir/right";
 	mkpath($ldir) or exit_cleanup($tmpdir, 1);
 	mkpath($rdir) or exit_cleanup($tmpdir, 1);

 	# If $GIT_DIR is not set prior to calling 'git update-index' and
 	# 'git checkout-index', then those commands will fail if difftool
 	# is called from a directory other than the repo root.
 	my $must_unset_git_dir = 0;
 	if (not defined($ENV{GIT_DIR})) {
 		$must_unset_git_dir = 1;
 		$ENV{GIT_DIR} = $repo_path;
 	}

 	# Populate the left and right directories based on each index file
 	my ($inpipe, $ctx);
 	$ENV{GIT_INDEX_FILE} = "$tmpdir/lindex";
 	($inpipe, $ctx) =
 		$repo->command_input_pipe(qw(update-index -z --index-info));
 	print($inpipe $lindex);
 	$repo->command_close_pipe($inpipe, $ctx);

 	my $rc = system('git', 'checkout-index', '--all', "--prefix=$ldir/");
 	exit_cleanup($tmpdir, $rc) if $rc != 0;

 	$ENV{GIT_INDEX_FILE} = "$tmpdir/rindex";
 	($inpipe, $ctx) =
 		$repo->command_input_pipe(qw(update-index -z --index-info));
 	print($inpipe $rindex);
 	$repo->command_close_pipe($inpipe, $ctx);

 	$rc = system('git', 'checkout-index', '--all', "--prefix=$rdir/");
 	exit_cleanup($tmpdir, $rc) if $rc != 0;

 	$ENV{GIT_INDEX_FILE} = "$tmpdir/wtindex";
 	($inpipe, $ctx) =
 		$repo->command_input_pipe(qw(update-index --info-only -z --index-info));
 	print($inpipe $wtindex);
 	$repo->command_close_pipe($inpipe, $ctx);

 	# If $GIT_DIR was explicitly set just for the update/checkout
 	# commands, then it should be unset before continuing.
 	delete($ENV{GIT_DIR}) if ($must_unset_git_dir);
 	delete($ENV{GIT_INDEX_FILE});

 	# Changes in the working tree need special treatment since they are
 	# not part of the index. Remove any trailing slash from $workdir
 	# before starting to avoid double slashes in symlink targets.
 	$workdir =~ s|/$||;
 	for my $file (@working_tree) {
 		my $dir = dirname($file);
 		unless (-d "$rdir/$dir") {
 			mkpath("$rdir/$dir") or
 			exit_cleanup($tmpdir, 1);
 		}
 		if ($symlinks) {
 			symlink("$workdir/$file", "$rdir/$file") or
 			exit_cleanup($tmpdir, 1);
 		} else {
 			copy("$workdir/$file", "$rdir/$file") or
 			exit_cleanup($tmpdir, 1);

 			my $mode = stat("$workdir/$file")->mode;
 			chmod($mode, "$rdir/$file") or
 			exit_cleanup($tmpdir, 1);
 		}
 	}

 	# Changes to submodules require special treatment. This loop writes a
 	# temporary file to both the left and right directories to show the
 	# change in the recorded SHA1 for the submodule.
 	for my $path (keys %submodule) {
 		my $ok;
 		if (defined($submodule{$path}{left})) {
 			$ok = write_to_file("$ldir/$path",
 				"Subproject commit $submodule{$path}{left}");
 		}
 		if (defined($submodule{$path}{right})) {
 			$ok = write_to_file("$rdir/$path",
 				"Subproject commit $submodule{$path}{right}");
 		}
 		exit_cleanup($tmpdir, 1) if not $ok;
 	}

 	# Symbolic links require special treatment. The standard "git diff"
 	# shows only the link itself, not the contents of the link target.
 	# This loop replicates that behavior.
 	for my $path (keys %symlink) {
 		my $ok;
 		if (defined($symlink{$path}{left})) {
 			$ok = write_to_file("$ldir/$path",
 					$symlink{$path}{left});
 		}
 		if (defined($symlink{$path}{right})) {
 			$ok = write_to_file("$rdir/$path",
 					$symlink{$path}{right});
 		}
 		exit_cleanup($tmpdir, 1) if not $ok;
 	}

 	return ($ldir, $rdir, $tmpdir, @working_tree);
 }

 sub write_to_file
 {
 	my $path = shift;
 	my $value = shift;

 	# Make sure the path to the file exists
 	my $dir = dirname($path);
 	unless (-d "$dir") {
 		mkpath("$dir") or return 0;
 	}

 	# If the file already exists in that location, delete it.  This
 	# is required in the case of symbolic links.
 	unlink($path);

 	open(my $fh, '>', $path) or return 0;
 	print($fh $value);
 	close($fh);

 	return 1;
 }

 sub main
 {
 	# parse command-line options. all unrecognized options and arguments
 	# are passed through to the 'git diff' command.
 	my %opts = (
 		difftool_cmd => undef,
 		dirdiff => undef,
 		extcmd => undef,
 		gui => undef,
 		help => undef,
 		prompt => undef,
 		symlinks => $^O ne 'cygwin' &&
 				$^O ne 'MSWin32' && $^O ne 'msys',
 		tool_help => undef,
 		trust_exit_code => undef,
 	);
 	GetOptions('g|gui!' => \$opts{gui},
 		'd|dir-diff' => \$opts{dirdiff},
 		'h' => \$opts{help},
 		'prompt!' => \$opts{prompt},
 		'y' => sub { $opts{prompt} = 0; },
 		'symlinks' => \$opts{symlinks},
 		'no-symlinks' => sub { $opts{symlinks} = 0; },
 		't|tool:s' => \$opts{difftool_cmd},
 		'tool-help' => \$opts{tool_help},
 		'trust-exit-code' => \$opts{trust_exit_code},
 		'no-trust-exit-code' => sub { $opts{trust_exit_code} = 0; },
 		'x|extcmd:s' => \$opts{extcmd});

 	if (defined($opts{help})) {
 		usage(0);
 	}
 	if (defined($opts{tool_help})) {
 		print_tool_help();
 	}
 	if (defined($opts{difftool_cmd})) {
 		if (length($opts{difftool_cmd}) > 0) {
 			$ENV{GIT_DIFF_TOOL} = $opts{difftool_cmd};
 		} else {
 			print "No <tool> given for --tool=<tool>\n";
 			usage(1);
 		}
 	}
 	if (defined($opts{extcmd})) {
 		if (length($opts{extcmd}) > 0) {
 			$ENV{GIT_DIFFTOOL_EXTCMD} = $opts{extcmd};
 		} else {
 			print "No <cmd> given for --extcmd=<cmd>\n";
 			usage(1);
 		}
 	}
 	if ($opts{gui}) {
 		my $guitool = Git::config('diff.guitool');
 		if (defined($guitool) && length($guitool) > 0) {
 			$ENV{GIT_DIFF_TOOL} = $guitool;
 		}
 	}

 	if (!defined $opts{trust_exit_code}) {
 		$opts{trust_exit_code} = Git::config_bool('difftool.trustExitCode');
 	}
 	if ($opts{trust_exit_code}) {
 		$ENV{GIT_DIFFTOOL_TRUST_EXIT_CODE} = 'true';
 	} else {
 		$ENV{GIT_DIFFTOOL_TRUST_EXIT_CODE} = 'false';
 	}

 	# In directory diff mode, 'git-difftool--helper' is called once
 	# to compare the a/b directories.  In file diff mode, 'git diff'
 	# will invoke a separate instance of 'git-difftool--helper' for
 	# each file that changed.
 	if (defined($opts{dirdiff})) {
 		dir_diff($opts{extcmd}, $opts{symlinks});
 	} else {
 		file_diff($opts{prompt});
 	}
 }

 sub dir_diff
 {
 	my ($extcmd, $symlinks) = @_;
 	my $rc;
 	my $error = 0;
 	my $repo = Git->repository();
 	my $workdir = find_worktree();
 	my ($a, $b, $tmpdir, @worktree) =
 		setup_dir_diff($repo, $workdir, $symlinks);

 	if (defined($extcmd)) {
 		$rc = system($extcmd, $a, $b);
 	} else {
 		$ENV{GIT_DIFFTOOL_DIRDIFF} = 'true';
 		$rc = system('git', 'difftool--helper', $a, $b);
 	}
 	# If the diff including working copy files and those
 	# files were modified during the diff, then the changes
 	# should be copied back to the working tree.
 	# Do not copy back files when symlinks are used and the
 	# external tool did not replace the original link with a file.
 	#
 	# These hashes are loaded lazily since they aren't needed
 	# in the common case of --symlinks and the difftool updating
 	# files through the symlink.
 	my %wt_modified;
 	my %tmp_modified;
 	my $indices_loaded = 0;

 	for my $file (@worktree) {
 		next if $symlinks && -l "$b/$file";
 		next if ! -f "$b/$file";

 		if (!$indices_loaded) {
 			%wt_modified = changed_files($repo->repo_path(),
 				"$tmpdir/wtindex", "$workdir");
 			%tmp_modified = changed_files($repo->repo_path(),
 				"$tmpdir/wtindex", "$b");
 			$indices_loaded = 1;
 		}

 		if (exists $wt_modified{$file} and exists $tmp_modified{$file}) {
 			my $errmsg = "warning: Both files modified: ";
 			$errmsg .= "'$workdir/$file' and '$b/$file'.\n";
 			$errmsg .= "warning: Working tree file has been left.\n";
 			$errmsg .= "warning:\n";
 			warn $errmsg;
 			$error = 1;
 		} elsif (exists $tmp_modified{$file}) {
 			my $mode = stat("$b/$file")->mode;
 			copy("$b/$file", "$workdir/$file") or
 			exit_cleanup($tmpdir, 1);

 			chmod($mode, "$workdir/$file") or
 			exit_cleanup($tmpdir, 1);
 		}
 	}
 	if ($error) {
 		warn "warning: Temporary files exist in '$tmpdir'.\n";
 		warn "warning: You may want to cleanup or recover these.\n";
 		exit(1);
 	} else {
 		exit_cleanup($tmpdir, $rc);
 	}
 }

 sub file_diff
 {
 	my ($prompt) = @_;

 	if (defined($prompt)) {
 		if ($prompt) {
 			$ENV{GIT_DIFFTOOL_PROMPT} = 'true';
 		} else {
 			$ENV{GIT_DIFFTOOL_NO_PROMPT} = 'true';
 		}
 	}

 	$ENV{GIT_PAGER} = '';
 	$ENV{GIT_EXTERNAL_DIFF} = 'git-difftool--helper';

 	# ActiveState Perl for Win32 does not implement POSIX semantics of
 	# exec* system call. It just spawns the given executable and finishes
 	# the starting program, exiting with code 0.
 	# system will at least catch the errors returned by git diff,
 	# allowing the caller of git difftool better handling of failures.
 	my $rc = system('git', 'diff', @ARGV);
 	exit($rc | ($rc >> 8));
 }

 main();
	#!/usr/bin/perl
	# Copyright (c) 2009, 2010 David Aguilar
	# Copyright (c) 2012 Tim Henigan
	#
	# This is a wrapper around the GIT_EXTERNAL_DIFF-compatible
	# git-difftool--helper script.
	#
	# This script exports GIT_EXTERNAL_DIFF and GIT_PAGER for use by git.
	# The GIT_DIFF* variables are exported for use by git-difftool--helper.
	#
	# Any arguments that are unknown to this script are forwarded to 'git diff'.

	use 5.008;
	use strict;
	use warnings;
	use Error qw(:try);
	use File::Basename qw(dirname);
	use File::Copy;
	use File::Find;
	use File::stat;
	use File::Path qw(mkpath rmtree);
	use File::Temp qw(tempdir);
	use Getopt::Long qw(:config pass_through);
	use Git;

	sub usage
	{
	my $exitcode = shift;
	print << 'USAGE';
	usage: git difftool [-t\|--tool=<tool>] [--tool-help]
	[-x\|--extcmd=<cmd>]
	[-g\|--gui] [--no-gui]
	[--prompt] [-y\|--no-prompt]
	[-d\|--dir-diff]
	['git diff' options]
	USAGE
	exit($exitcode);
	}

	sub find_worktree
	{
	# Git->repository->wc_path() does not honor changes to the working
	# tree location made by $ENV{GIT_WORK_TREE} or the 'core.worktree'
	# config variable.
	return Git::command_oneline('rev-parse', '--show-toplevel');
	}

	sub print_tool_help
	{
	# See the comment at the bottom of file_diff() for the reason behind
	# using system() followed by exit() instead of exec().
	my $rc = system(qw(git mergetool --tool-help=diff));
	exit($rc \| ($rc >> 8));
	}

	sub exit_cleanup
	{
	my ($tmpdir, $status) = @_;
	my $errno = $!;
	rmtree($tmpdir);
	if ($status and $errno) {
	my ($package, $file, $line) = caller();
	warn "$file line $line: $errno\n";
	}
	exit($status \| ($status >> 8));
	}

	sub use_wt_file
	{
	my ($repo, $workdir, $file, $sha1) = @_;
	my $null_sha1 = '0' x 40;

	if (! -e "$workdir/$file") {
	# If the file doesn't exist in the working tree, we cannot
	# use it.
	return (0, $null_sha1);
	}

	my $wt_sha1 = $repo->command_oneline('hash-object', "$workdir/$file");
	my $use = ($sha1 eq $null_sha1) \|\| ($sha1 eq $wt_sha1);
	return ($use, $wt_sha1);
	}

	sub changed_files
	{
	my ($repo_path, $index, $worktree) = @_;
	$ENV{GIT_INDEX_FILE} = $index;
	$ENV{GIT_WORK_TREE} = $worktree;
	my $must_unset_git_dir = 0;
	if (not defined($ENV{GIT_DIR})) {
	$must_unset_git_dir = 1;
	$ENV{GIT_DIR} = $repo_path;
	}

	my @refreshargs = qw/update-index --really-refresh -q --unmerged/;
	my @gitargs = qw/diff-files --name-only -z/;
	try {
	Git::command_oneline(@refreshargs);
	} catch Git::Error::Command with {};

	my $line = Git::command_oneline(@gitargs);
	my @files;
	if (defined $line) {
	@files = split('\0', $line);
	} else {
	@files = ();
	}

	delete($ENV{GIT_INDEX_FILE});
	delete($ENV{GIT_WORK_TREE});
	delete($ENV{GIT_DIR}) if ($must_unset_git_dir);

	return map { $_ => 1 } @files;
	}

	sub setup_dir_diff
	{
	my ($repo, $workdir, $symlinks) = @_;

	# Run the diff; exit immediately if no diff found
	# 'Repository' and 'WorkingCopy' must be explicitly set to insure that
	# if $GIT_DIR and $GIT_WORK_TREE are set in ENV, they are actually used
	# by Git->repository->command*.
	my $repo_path = $repo->repo_path();
	my %repo_args = (Repository => $repo_path, WorkingCopy => $workdir);
	my $diffrepo = Git->repository(%repo_args);

	my @gitargs = ('diff', '--raw', '--no-abbrev', '-z', @ARGV);
	my $diffrtn = $diffrepo->command_oneline(@gitargs);
	exit(0) unless defined($diffrtn);

	# Build index info for left and right sides of the diff
	my $submodule_mode = '160000';
	my $symlink_mode = '120000';
	my $null_mode = '0' x 6;
	my $null_sha1 = '0' x 40;
	my $lindex = '';
	my $rindex = '';
	my $wtindex = '';
	my %submodule;
	my %symlink;
	my @working_tree = ();
	my @rawdiff = split('\0', $diffrtn);

	my $i = 0;
	while ($i < $#rawdiff) {
	if ($rawdiff[$i] =~ /^::/) {
	warn << 'EOF';
	Combined diff formats ('-c' and '--cc') are not supported in
	directory diff mode ('-d' and '--dir-diff').
	EOF
	exit(1);
	}

	my ($lmode, $rmode, $lsha1, $rsha1, $status) =
	split(' ', substr($rawdiff[$i], 1));
	my $src_path = $rawdiff[$i + 1];
	my $dst_path;

	if ($status =~ /^[CR]/) {
	$dst_path = $rawdiff[$i + 2];
	$i += 3;
	} else {
	$dst_path = $src_path;
	$i += 2;
	}

	if ($lmode eq $submodule_mode or $rmode eq $submodule_mode) {
	$submodule{$src_path}{left} = $lsha1;
	if ($lsha1 ne $rsha1) {
	$submodule{$dst_path}{right} = $rsha1;
	} else {
	$submodule{$dst_path}{right} = "$rsha1-dirty";
	}
	next;
	}

	if ($lmode eq $symlink_mode) {
	$symlink{$src_path}{left} =
	$diffrepo->command_oneline('show', "$lsha1");
	}

	if ($rmode eq $symlink_mode) {
	$symlink{$dst_path}{right} =
	$diffrepo->command_oneline('show', "$rsha1");
	}

	if ($lmode ne $null_mode and $status !~ /^C/) {
	$lindex .= "$lmode $lsha1\t$src_path\0";
	}

	if ($rmode ne $null_mode) {
	my ($use, $wt_sha1) = use_wt_file($repo, $workdir,
	$dst_path, $rsha1);
	if ($use) {
	push @working_tree, $dst_path;
	$wtindex .= "$rmode $wt_sha1\t$dst_path\0";
	} else {
	$rindex .= "$rmode $rsha1\t$dst_path\0";
	}
	}
	}

	# Setup temp directories
	my $tmpdir = tempdir('git-difftool.XXXXX', CLEANUP => 0, TMPDIR => 1);
	my $ldir = "$tmpdir/left";
	my $rdir = "$tmpdir/right";
	mkpath($ldir) or exit_cleanup($tmpdir, 1);
	mkpath($rdir) or exit_cleanup($tmpdir, 1);

	# If $GIT_DIR is not set prior to calling 'git update-index' and
	# 'git checkout-index', then those commands will fail if difftool
	# is called from a directory other than the repo root.
	my $must_unset_git_dir = 0;
	if (not defined($ENV{GIT_DIR})) {
	$must_unset_git_dir = 1;
	$ENV{GIT_DIR} = $repo_path;
	}

	# Populate the left and right directories based on each index file
	my ($inpipe, $ctx);
	$ENV{GIT_INDEX_FILE} = "$tmpdir/lindex";
	($inpipe, $ctx) =
	$repo->command_input_pipe(qw(update-index -z --index-info));
	print($inpipe $lindex);
	$repo->command_close_pipe($inpipe, $ctx);

	my $rc = system('git', 'checkout-index', '--all', "--prefix=$ldir/");
	exit_cleanup($tmpdir, $rc) if $rc != 0;

	$ENV{GIT_INDEX_FILE} = "$tmpdir/rindex";
	($inpipe, $ctx) =
	$repo->command_input_pipe(qw(update-index -z --index-info));
	print($inpipe $rindex);
	$repo->command_close_pipe($inpipe, $ctx);

	$rc = system('git', 'checkout-index', '--all', "--prefix=$rdir/");
	exit_cleanup($tmpdir, $rc) if $rc != 0;

	$ENV{GIT_INDEX_FILE} = "$tmpdir/wtindex";
	($inpipe, $ctx) =
	$repo->command_input_pipe(qw(update-index --info-only -z --index-info));
	print($inpipe $wtindex);
	$repo->command_close_pipe($inpipe, $ctx);

	# If $GIT_DIR was explicitly set just for the update/checkout
	# commands, then it should be unset before continuing.
	delete($ENV{GIT_DIR}) if ($must_unset_git_dir);
	delete($ENV{GIT_INDEX_FILE});

	# Changes in the working tree need special treatment since they are
	# not part of the index. Remove any trailing slash from $workdir
	# before starting to avoid double slashes in symlink targets.
	$workdir =~ s\|/$\|\|;
	for my $file (@working_tree) {
	my $dir = dirname($file);
	unless (-d "$rdir/$dir") {
	mkpath("$rdir/$dir") or
	exit_cleanup($tmpdir, 1);
	}
	if ($symlinks) {
	symlink("$workdir/$file", "$rdir/$file") or
	exit_cleanup($tmpdir, 1);
	} else {
	copy("$workdir/$file", "$rdir/$file") or
	exit_cleanup($tmpdir, 1);

	my $mode = stat("$workdir/$file")->mode;
	chmod($mode, "$rdir/$file") or
	exit_cleanup($tmpdir, 1);
	}
	}

	# Changes to submodules require special treatment. This loop writes a
	# temporary file to both the left and right directories to show the
	# change in the recorded SHA1 for the submodule.
	for my $path (keys %submodule) {
	my $ok;
	if (defined($submodule{$path}{left})) {
	$ok = write_to_file("$ldir/$path",
	"Subproject commit $submodule{$path}{left}");
	}
	if (defined($submodule{$path}{right})) {
	$ok = write_to_file("$rdir/$path",
	"Subproject commit $submodule{$path}{right}");
	}
	exit_cleanup($tmpdir, 1) if not $ok;
	}

	# Symbolic links require special treatment. The standard "git diff"
	# shows only the link itself, not the contents of the link target.
	# This loop replicates that behavior.
	for my $path (keys %symlink) {
	my $ok;
	if (defined($symlink{$path}{left})) {
	$ok = write_to_file("$ldir/$path",
	$symlink{$path}{left});
	}
	if (defined($symlink{$path}{right})) {
	$ok = write_to_file("$rdir/$path",
	$symlink{$path}{right});
	}
	exit_cleanup($tmpdir, 1) if not $ok;
	}

	return ($ldir, $rdir, $tmpdir, @working_tree);
	}

	sub write_to_file
	{
	my $path = shift;
	my $value = shift;

	# Make sure the path to the file exists
	my $dir = dirname($path);
	unless (-d "$dir") {
	mkpath("$dir") or return 0;
	}

	# If the file already exists in that location, delete it. This
	# is required in the case of symbolic links.
	unlink($path);

	open(my $fh, '>', $path) or return 0;
	print($fh $value);
	close($fh);

	return 1;
	}

	sub main
	{
	# parse command-line options. all unrecognized options and arguments
	# are passed through to the 'git diff' command.
	my %opts = (
	difftool_cmd => undef,
	dirdiff => undef,
	extcmd => undef,
	gui => undef,
	help => undef,
	prompt => undef,
	symlinks => $^O ne 'cygwin' &&
	$^O ne 'MSWin32' && $^O ne 'msys',
	tool_help => undef,
	trust_exit_code => undef,
	);
	GetOptions('g\|gui!' => \$opts{gui},
	'd\|dir-diff' => \$opts{dirdiff},
	'h' => \$opts{help},
	'prompt!' => \$opts{prompt},
	'y' => sub { $opts{prompt} = 0; },
	'symlinks' => \$opts{symlinks},
	'no-symlinks' => sub { $opts{symlinks} = 0; },
	't\|tool:s' => \$opts{difftool_cmd},
	'tool-help' => \$opts{tool_help},
	'trust-exit-code' => \$opts{trust_exit_code},
	'no-trust-exit-code' => sub { $opts{trust_exit_code} = 0; },
	'x\|extcmd:s' => \$opts{extcmd});

	if (defined($opts{help})) {
	usage(0);
	}
	if (defined($opts{tool_help})) {
	print_tool_help();
	}
	if (defined($opts{difftool_cmd})) {
	if (length($opts{difftool_cmd}) > 0) {
	$ENV{GIT_DIFF_TOOL} = $opts{difftool_cmd};
	} else {
	print "No <tool> given for --tool=<tool>\n";
	usage(1);
	}
	}
	if (defined($opts{extcmd})) {
	if (length($opts{extcmd}) > 0) {
	$ENV{GIT_DIFFTOOL_EXTCMD} = $opts{extcmd};
	} else {
	print "No <cmd> given for --extcmd=<cmd>\n";
	usage(1);
	}
	}
	if ($opts{gui}) {
	my $guitool = Git::config('diff.guitool');
	if (defined($guitool) && length($guitool) > 0) {
	$ENV{GIT_DIFF_TOOL} = $guitool;
	}
	}

	if (!defined $opts{trust_exit_code}) {
	$opts{trust_exit_code} = Git::config_bool('difftool.trustExitCode');
	}
	if ($opts{trust_exit_code}) {
	$ENV{GIT_DIFFTOOL_TRUST_EXIT_CODE} = 'true';
	} else {
	$ENV{GIT_DIFFTOOL_TRUST_EXIT_CODE} = 'false';
	}

	# In directory diff mode, 'git-difftool--helper' is called once
	# to compare the a/b directories. In file diff mode, 'git diff'
	# will invoke a separate instance of 'git-difftool--helper' for
	# each file that changed.
	if (defined($opts{dirdiff})) {
	dir_diff($opts{extcmd}, $opts{symlinks});
	} else {
	file_diff($opts{prompt});
	}
	}

	sub dir_diff
	{
	my ($extcmd, $symlinks) = @_;
	my $rc;
	my $error = 0;
	my $repo = Git->repository();
	my $workdir = find_worktree();
	my ($a, $b, $tmpdir, @worktree) =
	setup_dir_diff($repo, $workdir, $symlinks);

	if (defined($extcmd)) {
	$rc = system($extcmd, $a, $b);
	} else {
	$ENV{GIT_DIFFTOOL_DIRDIFF} = 'true';
	$rc = system('git', 'difftool--helper', $a, $b);
	}
	# If the diff including working copy files and those
	# files were modified during the diff, then the changes
	# should be copied back to the working tree.
	# Do not copy back files when symlinks are used and the
	# external tool did not replace the original link with a file.
	#
	# These hashes are loaded lazily since they aren't needed
	# in the common case of --symlinks and the difftool updating
	# files through the symlink.
	my %wt_modified;
	my %tmp_modified;
	my $indices_loaded = 0;

	for my $file (@worktree) {
	next if $symlinks && -l "$b/$file";
	next if ! -f "$b/$file";

	if (!$indices_loaded) {
	%wt_modified = changed_files($repo->repo_path(),
	"$tmpdir/wtindex", "$workdir");
	%tmp_modified = changed_files($repo->repo_path(),
	"$tmpdir/wtindex", "$b");
	$indices_loaded = 1;
	}

	if (exists $wt_modified{$file} and exists $tmp_modified{$file}) {
	my $errmsg = "warning: Both files modified: ";
	$errmsg .= "'$workdir/$file' and '$b/$file'.\n";
	$errmsg .= "warning: Working tree file has been left.\n";
	$errmsg .= "warning:\n";
	warn $errmsg;
	$error = 1;
	} elsif (exists $tmp_modified{$file}) {
	my $mode = stat("$b/$file")->mode;
	copy("$b/$file", "$workdir/$file") or
	exit_cleanup($tmpdir, 1);

	chmod($mode, "$workdir/$file") or
	exit_cleanup($tmpdir, 1);
	}
	}
	if ($error) {
	warn "warning: Temporary files exist in '$tmpdir'.\n";
	warn "warning: You may want to cleanup or recover these.\n";
	exit(1);
	} else {
	exit_cleanup($tmpdir, $rc);
	}
	}

	sub file_diff
	{
	my ($prompt) = @_;

	if (defined($prompt)) {
	if ($prompt) {
	$ENV{GIT_DIFFTOOL_PROMPT} = 'true';
	} else {
	$ENV{GIT_DIFFTOOL_NO_PROMPT} = 'true';
	}
	}

	$ENV{GIT_PAGER} = '';
	$ENV{GIT_EXTERNAL_DIFF} = 'git-difftool--helper';

	# ActiveState Perl for Win32 does not implement POSIX semantics of
	# exec* system call. It just spawns the given executable and finishes
	# the starting program, exiting with code 0.
	# system will at least catch the errors returned by git diff,
	# allowing the caller of git difftool better handling of failures.
	my $rc = system('git', 'diff', @ARGV);
	exit($rc \| ($rc >> 8));
	}

	main();