Re: [PATCH v14 8/9] difftool: teach difftool to handle directory diffs

When 'difftool' is called to compare a range of commits that modify
more than one file, it opens a separate instance of the diff tool for
each file that changed.

The new '--dir-diff' option copies all the modified files to a temporary
location and runs a directory diff on them in a single instance of the
diff tool.

Signed-off-by: Tim Henigan <redacted>
---

This replaces 7fbdc6c on the th/difftool-diffall branch [1].

Changes in v14:

  - Fixed use of unitialized vars in the find_worktree function. A warning
    was seen when run on msysgit, but not other platforms.

  - Added a helper function (write_to_file) to replace repeated logic.

  - Fixed handling of symbolic links. The diff shown in the external tool
    now matches what is seen in the output of 'git diff'.

  - Added support for the diff format used for renames and copies. In the
    external tool, these will still appear as delete/add pairs.

  - Added logic to detect and abort if a combined diff ('--cc' or '-c')
    is commanded at the same time as directory diff ('--dir-diff').

[1]: https://github.com/gitster/git/tree/th/difftool-diffall


 Documentation/git-difftool.txt |    6 +
 git-difftool--helper.sh        |   19 ++-
 git-difftool.perl              |  261 +++++++++++++++++++++++++++++++++++++---
 t/t7800-difftool.sh            |   39 ++++++
 4 files changed, 299 insertions(+), 26 deletions(-)

diff --git a/Documentation/git-difftool.txt b/Documentation/git-difftool.txt
index fe38f66..aba5e76 100644
--- a/Documentation/git-difftool.txt
+++ b/Documentation/git-difftool.txt

@@ -19,6 +19,12 @@ linkgit:git-diff[1].
 
 OPTIONS
 -------
+-d::
+--dir-diff::
+	Copy the modified files to a temporary location and perform
+	a directory diff on them. This mode never prompts before
+	launching the diff tool.
+
 -y::
 --no-prompt::
 	Do not prompt before launching a diff tool.

diff --git a/git-difftool--helper.sh b/git-difftool--helper.sh
index e6558d1..3d0fe0c 100755
--- a/git-difftool--helper.sh
+++ b/git-difftool--helper.sh

@@ -73,9 +73,16 @@ then
 	fi
 fi
 
-# Launch the merge tool on each path provided by 'git diff'
-while test $# -gt 6
-do
-	launch_merge_tool "$1" "$2" "$5"
-	shift 7
-done
+if test -n "$GIT_DIFFTOOL_DIRDIFF"
+then
+	LOCAL="$1"
+	REMOTE="$2"
+	run_merge_tool "$merge_tool" false
+else
+	# Launch the merge tool on each path provided by 'git diff'
+	while test $# -gt 6
+	do
+		launch_merge_tool "$1" "$2" "$5"
+		shift 7
+	done
+fi

diff --git a/git-difftool.perl b/git-difftool.perl
index aba3d2f..7211f1e 100755
--- a/git-difftool.perl
+++ b/git-difftool.perl

@@ -1,21 +1,31 @@
-#!/usr/bin/env perl
+#!/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.
-# GIT_DIFFTOOL_NO_PROMPT, GIT_DIFFTOOL_PROMPT, and GIT_DIFF_TOOL
-# are exported for use by git-difftool--helper.
+# 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 File::Basename qw(dirname);
+use File::Copy;
+use File::stat;
+use File::Path qw(mkpath);
+use File::Temp qw(tempdir);
 use Getopt::Long qw(:config pass_through);
 use Git;
 
+my @working_tree;
+my $rc;
+my $repo = Git->repository();
+my $repo_path = $repo->repo_path();
+
 sub usage
 {
 	my $exitcode = shift;

@@ -24,15 +34,202 @@ usage: git difftool [-t|--tool=<tool>]
                     [-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.
+	my $worktree;
+	my $env_worktree = $ENV{GIT_WORK_TREE};
+	my $core_worktree = Git::config('core.worktree');
+
+	if (defined($env_worktree) and (length($env_worktree) > 0)) {
+		$worktree = $env_worktree;
+	} elsif (defined($core_worktree) and (length($core_worktree) > 0)) {
+		$worktree = $core_worktree;
+	} else {
+		$worktree = $repo->wc_path();
+	}
+
+	return $worktree;
+}
+
+my $workdir = find_worktree();
+
+sub setup_dir_diff
+{
+	# 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 $diffrepo = Git->repository(Repository => $repo_path, WorkingCopy => $workdir);
+	my $diffrtn = $diffrepo->command_oneline('diff', '--raw', '--no-abbrev', '-z', @ARGV);
+	exit(0) if (length($diffrtn) == 0);
+
+	if ($diffrtn =~ /::/) {
+		print "Combined diff formats ('-c' and '--cc') are not supported in directory diff mode.\n";