chainlint: colorize problem annotations and test delimiters

When `chainlint.pl` detects problems in a test definition, it emits the
test definition with "?!FOO?!" annotations highlighting the problems it
discovered. For instance, given this problematic test:

    test_expect_success 'discombobulate frobnitz' '
        git frob babble &&
        (echo balderdash; echo gnabgib) >expect &&
        for i in three two one
        do
            git nitfol $i
        done >actual
        test_cmp expect actual
    '

chainlint.pl will output:

    # chainlint: t1234-confusing.sh
    # chainlint: discombobulate frobnitz
    git frob babble &&
    (echo balderdash ; ?!AMP?! echo gnabgib) >expect &&
    for i in three two one
    do
    git nitfol $i ?!LOOP?!
    done >actual ?!AMP?!
    test_cmp expect actual

in which it may be difficult to spot the "?!FOO?!" annotations. The
problem is compounded when multiple tests, possibly in multiple
scripts, fail "linting", in which case it may be difficult to spot the
"# chainlint:" lines which delimit one problematic test from another.

To ameliorate this potential problem, colorize the "?!FOO?!" annotations
in order to quickly draw the test author's attention to the problem
spots, and colorize the "# chainlint:" lines to help the author identify
the name of each script and each problematic test.

Colorization is disabled automatically if output is not directed to a
terminal or if NO_COLOR environment variable is set. The implementation
is specific to Unix (it employs `tput` if available) but works equally
well in the Git for Windows development environment which emulates Unix
sufficiently.

Signed-off-by: Eric Sunshine <sunshine@sunshineco.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

t/chainlint.pl

@@ -585,12 +585,14 @@ sub check_test {
 	my $parser = TestParser->new(\$body);
 	my @tokens = $parser->parse();
 	return unless $emit_all || grep(/\?![^?]+\?!/, @tokens);
+	my $c = main::fd_colors(1);
 	my $checked = join(' ', @tokens);
 	$checked =~ s/^\n//;
 	$checked =~ s/^ //mg;
 	$checked =~ s/ $//mg;
+	$checked =~ s/(\?![^?]+\?!)/$c->{rev}$c->{red}$1$c->{reset}/mg;
 	$checked .= "\n" unless $checked =~ /\n$/;
-	push(@{$self->{output}}, "# chainlint: $title\n$checked");
+	push(@{$self->{output}}, "$c->{blue}# chainlint: $title$c->{reset}\n$checked");
 }
 
 sub parse_cmd {
@@ -615,6 +617,41 @@ package main;
 	$interval = sub { return Time::HiRes::tv_interval(shift); };
 }
 
+# Restore TERM if test framework set it to "dumb" so 'tput' will work; do this
+# outside of get_colors() since under 'ithreads' all threads use %ENV of main
+# thread and ignore %ENV changes in subthreads.
+$ENV{TERM} = $ENV{USER_TERM} if $ENV{USER_TERM};
+
+my @NOCOLORS = (bold => '', rev => '', reset => '', blue => '', green => '', red => '');
+my %COLORS = ();
+sub get_colors {
+	return \%COLORS if %COLORS;
+	if (exists($ENV{NO_COLOR}) ||
+	    system("tput sgr0 >/dev/null 2>&1") != 0 ||
+	    system("tput bold >/dev/null 2>&1") != 0 ||
+	    system("tput rev  >/dev/null 2>&1") != 0 ||
+	    system("tput setaf 1 >/dev/null 2>&1") != 0) {
+		%COLORS = @NOCOLORS;
+		return \%COLORS;
+	}
+	%COLORS = (bold  => `tput bold`,
+		   rev   => `tput rev`,
+		   reset => `tput sgr0`,
+		   blue  => `tput setaf 4`,
+		   green => `tput setaf 2`,
+		   red   => `tput setaf 1`);
+	chomp(%COLORS);
+	return \%COLORS;
+}
+
+my %FD_COLORS = ();
+sub fd_colors {
+	my $fd = shift;
+	return $FD_COLORS{$fd} if exists($FD_COLORS{$fd});
+	$FD_COLORS{$fd} = -t $fd ? get_colors() : {@NOCOLORS};
+	return $FD_COLORS{$fd};
+}
+
 sub ncores {
 	# Windows
 	return $ENV{NUMBER_OF_PROCESSORS} if exists($ENV{NUMBER_OF_PROCESSORS});
@@ -630,6 +667,8 @@ sub show_stats {
 	my $walltime = $interval->($start_time);
 	my ($usertime) = times();
 	my ($total_workers, $total_scripts, $total_tests, $total_errs) = (0, 0, 0, 0);
+	my $c = fd_colors(2);
+	print(STDERR $c->{green});
 	for (@$stats) {
 		my ($worker, $nscripts, $ntests, $nerrs) = @$_;
 		print(STDERR "worker $worker: $nscripts scripts, $ntests tests, $nerrs errors\n");
@@ -638,7 +677,7 @@ sub show_stats {
 		$total_tests += $ntests;
 		$total_errs += $nerrs;
 	}
-	printf(STDERR "total: %d workers, %d scripts, %d tests, %d errors, %.2fs/%.2fs (wall/user)\n", $total_workers, $total_scripts, $total_tests, $total_errs, $walltime, $usertime);
+	printf(STDERR "total: %d workers, %d scripts, %d tests, %d errors, %.2fs/%.2fs (wall/user)$c->{reset}\n", $total_workers, $total_scripts, $total_tests, $total_errs, $walltime, $usertime);
 }
 
 sub check_script {
@@ -656,8 +695,9 @@ sub check_script {
 		my $parser = ScriptParser->new(\$s);
 		1 while $parser->parse_cmd();
 		if (@{$parser->{output}}) {
+			my $c = fd_colors(1);
 			my $s = join('', @{$parser->{output}});
-			$emit->("# chainlint: $path\n" . $s);
+			$emit->("$c->{bold}$c->{blue}# chainlint: $path$c->{reset}\n" . $s);
 			$nerrs += () = $s =~ /\?![^?]+\?!/g;
 		}
 		$ntests += $parser->{ntests};