Enable colors on-demand.

pkg/front_end/lib/src/fasta/colors.dart

Index: pkg/front_end/lib/src/fasta/colors.dart
diff --git a/pkg/front_end/lib/src/fasta/colors.dart b/pkg/front_end/lib/src/fasta/colors.dart
index 906ac377c50dff821520563f43ad2b5611723ba7..6f3214dca91430c06f29dd9fa30b0fdfdc5e53ce 100644
--- a/pkg/front_end/lib/src/fasta/colors.dart
+++ b/pkg/front_end/lib/src/fasta/colors.dart
@@ -2,23 +2,84 @@
 // 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.
 
-// TODO(ahe): Copied from sdk/pkg/compiler/lib/src/colors.dart.
+// TODO(ahe): Orignially copied from sdk/pkg/compiler/lib/src/colors.dart,
+// merge these two packages.
 library colors;
 
-// See http://en.wikipedia.org/wiki/ANSI_escape_code#CSI_codes
-const String RESET = '\u001b[0m';
+import 'dart:convert' show JSON;
 
-// See http://en.wikipedia.org/wiki/ANSI_escape_code#Colors
-const String BLACK_COLOR = '\u001b[30m';
-const String RED_COLOR = '\u001b[31m';
-const String GREEN_COLOR = '\u001b[32m';
-const String YELLOW_COLOR = '\u001b[33m';
-const String BLUE_COLOR = '\u001b[34m';
-const String MAGENTA_COLOR = '\u001b[35m';
-const String CYAN_COLOR = '\u001b[36m';
-const String WHITE_COLOR = '\u001b[37m';
+import 'dart:io'
+    show Platform, Process, ProcessResult, StdioType, stderr, stdioType, stdout;
 
-String wrap(String string, String color) => "${color}$string${RESET}";
+import 'compiler_context.dart' show CompilerContext;
+
+/// ANSI/xterm termcap for setting default colors. Output from Unix
+/// command-line program `tput op`.
+const String DEFAULT_COLOR = "\x1b[39;49m";
+
+/// ANSI/xterm termcap for setting black text color. Output from Unix
+/// command-line program `tput setaf 0`.
+const String BLACK_COLOR = "\x1b[30m";
+
+/// ANSI/xterm termcap for setting red text color. Output from Unix
+/// command-line program `tput setaf 1`.
+const String RED_COLOR = "\x1b[31m";
+
+/// ANSI/xterm termcap for setting green text color. Output from Unix
+/// command-line program `tput setaf 2`.
+const String GREEN_COLOR = "\x1b[32m";
+
+/// ANSI/xterm termcap for setting yellow text color. Output from Unix
+/// command-line program `tput setaf 3`.
+const String YELLOW_COLOR = "\x1b[33m";
+
+/// ANSI/xterm termcap for setting blue text color. Output from Unix
+/// command-line program `tput setaf 4`.
+const String BLUE_COLOR = "\x1b[34m";
+
+/// ANSI/xterm termcap for setting magenta text color. Output from Unix
+/// command-line program `tput setaf 5`.
+const String MAGENTA_COLOR = "\x1b[35m";
+
+/// ANSI/xterm termcap for setting cyan text color. Output from Unix
+/// command-line program `tput setaf 6`.
+const String CYAN_COLOR = "\x1b[36m";
+
+/// ANSI/xterm termcap for setting white text color. Output from Unix
+/// command-line program `tput setaf 7`.
+const String WHITE_COLOR = "\x1b[37m";
+
+/// All the above codes. This is used to compare the above codes to the
+/// terminal's. Printing this string should have the same effect as just
+/// printing [DEFAULT_COLOR].
+const String ALL_CODES = BLACK_COLOR +
+    RED_COLOR +
+    GREEN_COLOR +
+    YELLOW_COLOR +
+    BLUE_COLOR +
+    MAGENTA_COLOR +
+    CYAN_COLOR +
+    WHITE_COLOR +
+    DEFAULT_COLOR;
+
+const String TERMINAL_CAPABILITIES = """
+colors
+setaf 0
+setaf 1
+setaf 2
+setaf 3
+setaf 4
+setaf 5
+setaf 6
+setaf 7
+op
+""";
+
+String wrap(String string, String color) {
+  return CompilerContext.enableColors
+      ? "${color}$string${DEFAULT_COLOR}"
+      : string;
+}
 
 String black(String string) => wrap(string, BLACK_COLOR);
 String red(String string) => wrap(string, RED_COLOR);
@@ -28,3 +89,78 @@ String blue(String string) => wrap(string, BLUE_COLOR);
 String magenta(String string) => wrap(string, MAGENTA_COLOR);
 String cyan(String string) => wrap(string, CYAN_COLOR);
 String white(String string) => wrap(string, WHITE_COLOR);
+
+/// True if we should enable colors in output. We enable colors when:
+///  1. stdout and stderr are terminals,
+///  2. the terminal supports more than 8 colors, and
+///  3. the terminal's ANSI color codes matches what we expect.
+///
+/// Note: do not call this method directly, as it is expensive to
+/// compute. Instead, use [CompilerContext.enableColors].
+bool computeEnableColors(CompilerContext context) {
+  if (Platform.isWindows) {
+    if (context.options.verbose) {
+      print("Not enabling colors, running on Windows.");
+    }
+    return false;
+  }
+
+  if (stdioType(stderr) != StdioType.TERMINAL) {
+    if (context.options.verbose) {
+      print("Not enabling colors, stderr isn't a terminal.");
+    }
+    return false;
+  }
+
+  if (stdioType(stdout) != StdioType.TERMINAL) {
+    if (context.options.verbose) {
+      print("Not enabling colors, stdout isn't a terminal.");
+    }
+    return false;
+  }
+
+  // The `-S` option of `tput` allows us to query multiple capabilities at
+  // once.
+  ProcessResult result = Process.runSync(
+      "/bin/sh", ["-c", "printf '%s' '$TERMINAL_CAPABILITIES' | tput -S"]);
+
+  if (result.exitCode != 0) {
+    if (context.options.verbose) {
+      print("Not enabling colors, running tput failed.");
+    }
+    return false;
+  }
+
+  List<String> lines = result.stdout.split("\n");
+
+  if (lines.length != 2) {
+    if (context.options.verbose) {
+      print("Not enabling colors, unexpected output from tput: "
+          "${JSON.encode(result.stdout)}.");
+    }
+    return false;
+  }
+
+  String numberOfColors = lines[0];
+  if (int.parse(numberOfColors, onError: (_) => -1) < 8) {
+    if (context.options.verbose) {
+      print("Not enabling colors, less than 8 colors supported: "
+          "${JSON.encode(numberOfColors)}.");
+    }
+    return false;
+  }
+
+  String allCodes = lines[1].trim();
+  if (ALL_CODES != allCodes) {
+    if (context.options.verbose) {
+      print("Not enabling colors, color codes don't match: "
+          "${JSON.encode(ALL_CODES)} != ${JSON.encode(allCodes)}.");
+    }
+    return false;
+  }
+
+  if (context.options.verbose) {
+    print("Enabling colors.");
+  }
+  return true;
+}