Improve detection of when to use colors.

dart/utils/compiler/build_helper.dart

 // Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 #import('dart:io');
 #import('dart:uri');
 
 #import('../../lib/compiler/implementation/util/uri_extras.dart');
 #import('../../lib/compiler/implementation/filenames.dart');
 
@@ skipping 85 matching lines @@
   options = ' --heap_growth_rate=32$options';
 
   return [
 '''
 #!/bin/sh
 # Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
 # for details. All rights reserved. Use of this source code is governed by a
 # BSD-style license that can be found in the LICENSE file.
 
 BIN_DIR=`dirname \$0`
-NO_COLORS="--no-colors"
+unset COLORS
 if test -t 1; then
-    # Enable colors if stdout is a terminal.
-    unset NO_COLORS
+  # Stdout is a terminal.
+  if test 8 -le `tput colors`; then
+    # Stdout has at least 8 colors, so enable colors.
+    COLORS="--colors"
+  fi
 fi
-exec \$BIN_DIR/dart$options \$BIN_DIR/$path \$NO_COLORS "\$@"
+exec \$BIN_DIR/dart$options \$BIN_DIR/$path \$COLORS "\$@"
 ''',
 '''
 @echo off
 REM Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
 REM for details. All rights reserved. Use of this source code is governed by a
 REM BSD-style license that can be found in the LICENSE file.
 
 set SCRIPTPATH=%~dp0
 
 REM Does the path have a trailing slash? If so, remove it.
 if %SCRIPTPATH:~-1%==\ set SCRIPTPATH=%SCRIPTPATH:~0,-1%
 
 set arguments=%*
 
-"%SCRIPTPATH%\dart.exe"$options "%SCRIPTPATH%$pathWin" --no-colors %arguments%
+"%SCRIPTPATH%\dart.exe"$options "%SCRIPTPATH%$pathWin" %arguments%
 '''.replaceAll('\n', '\r\n')];
 }