difftool: move 'git-difftool' out of contrib

This prepares 'git-difftool' and its documentation for
mainstream use.

'git-difftool-helper' became 'git-difftool--helper'
since users should not use it directly.

'git-difftool' was added to the list of commands as
an ancillaryinterrogator.

Signed-off-by: David Aguilar <davvid@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

1 files changed, 76 insertions, 0 deletions

diff --git a/git-difftool.perl b/git-difftool.perl
new file mode 100755
index 0000000000..8857ac8a4c
--- /dev/null
+++ b/git-difftool.perl
@@ -0,0 +1,76 @@
+#!/usr/bin/env perl
+# Copyright (c) 2009 David Aguilar
+#
+# 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, and
+# GIT_DIFFTOOL_NO_PROMPT and GIT_DIFF_TOOL for use by git-difftool--helper.
+# Any arguments that are unknown to this script are forwarded to 'git diff'.
+
+use strict;
+use warnings;
+use Cwd qw(abs_path);
+use File::Basename qw(dirname);
+
+my $DIR = abs_path(dirname($0));
+
+
+sub usage
+{
+	print << 'USAGE';
+usage: git difftool [--tool=<tool>] [-y|--no-prompt] ["git diff" options]
+USAGE
+	exit 1;
+}
+
+sub setup_environment
+{
+	$ENV{PATH} = "$DIR:$ENV{PATH}";
+	$ENV{GIT_PAGER} = '';
+	$ENV{GIT_EXTERNAL_DIFF} = 'git-difftool--helper';
+}
+
+sub exe
+{
+	my $exe = shift;
+	if ($^O eq 'MSWin32' || $^O eq 'msys') {
+		return "$exe.exe";
+	}
+	return $exe;
+}
+
+sub generate_command
+{
+	my @command = (exe('git'), 'diff');
+	my $skip_next = 0;
+	my $idx = -1;
+	for my $arg (@ARGV) {
+		$idx++;
+		if ($skip_next) {
+			$skip_next = 0;
+			next;
+		}
+		if ($arg eq '-t' || $arg eq '--tool') {
+			usage() if $#ARGV <= $idx;
+			$ENV{GIT_DIFF_TOOL} = $ARGV[$idx + 1];
+			$skip_next = 1;
+			next;
+		}
+		if ($arg =~ /^--tool=/) {
+			$ENV{GIT_DIFF_TOOL} = substr($arg, 7);
+			next;
+		}
+		if ($arg eq '-y' || $arg eq '--no-prompt') {
+			$ENV{GIT_DIFFTOOL_NO_PROMPT} = 'true';
+			next;
+		}
+		if ($arg eq '-h' || $arg eq '--help') {
+			usage();
+		}
+		push @command, $arg;
+	}
+	return @command
+}
+
+setup_environment();
+exec(generate_command());