[dart:io] Move Platform.ansiSupported to {Stdin,Stdout}.supportsAnsiEscapes

sdk/lib/io/stdio.dart

 // Copyright (c) 2013, 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.
 
 part of dart.io;
 
 const int _STDIO_HANDLE_TYPE_TERMINAL = 0;
 const int _STDIO_HANDLE_TYPE_PIPE = 1;
 const int _STDIO_HANDLE_TYPE_FILE = 2;
 const int _STDIO_HANDLE_TYPE_SOCKET = 3;
@@ skipping 119 matching lines @@
    * If enabled, characters are delayed until a new-line character is entered.
    * If disabled, characters will be available as typed.
    *
    * Default depends on the parent process, but usually enabled.
    *
    * On Windows this mode can only be disabled if [echoMode] is disabled as well.
    */
   external void set lineMode(bool enabled);
 
   /**
+    * When connected to a terminal, whether ANSI codes are supported.

[Lasse Reichstein Nielsen, 2017/03/17 08:55:29]

This is very vague. 

"ANSI codes" should probably be "ANSI escape codes" or "ANSI escape sequences",
because "ANSI codes" means something else
(https://www.census.gov/geo/reference/ansi.html)
It's still a bad name because it's not actually specified by ANSI, it's just
derived from VT-100 terminal escapes for (among other things) selecting ANSI
colors.

Since there is no formal specification, we can't say which escape codes are
supported, so add a paragraph, e.g.:

  The actual escape sequence support may differ between terminals,
  with some terminals supporting more escape sequences than others,
  and some terminals even differing in behavior for the same escape
  sequence.
  The ANSI color selection is generally supported.

[Lasse Reichstein Nielsen, 2017/03/17 08:55:29]

It doesn't say what happens when it's not connected to a terminal.
Would it be more correct to say:
  Whether connected to a terminal that supports "ANSI" escape sequences.
?

[zra, 2017/03/17 15:38:51]

Done.

[zra, 2017/03/17 15:38:51]

Done.

+    *
+    * This is `true` if the TERM environment variable contains the string
+    * 'xterm', except on Windows where support is detected only in recent
+    * versions of Windows 10.

[Lasse Reichstein Nielsen, 2017/03/17 08:55:28]

This is very specific. Consider just saying:

 Not all terminals are recognized, and not all recognized terminals can
 report whether they support ANSI escape sequences, so this value is a  
 best-effort attempt at detecting the support.

Then you can follow up with the preceding paragraph if you think it's useful:
  Currently, a `TERM` environment variable containing the string `xterm`
  will be taken as evidence that ANSI escape sequences are supported.
  On Windows, only versions of Windows 10 after v.1511 ("TH2")
  will be detected as supporting ANSI escape sequences.

Drop "recent", this comment might still be there in five years.

(Is the Windows comment correct? Is it only the Window32 console or also
Powersheell? Will we not detect that ansi.sys is loaded? Will we not detect
terminals like ConEmu, Cmder or Console2?)

[zra, 2017/03/17 15:38:51]

Done.

Flutter is recommending PowerShell on Windows, so I don't think we should go to
great lengths to support anything else.

[Lasse Reichstein Nielsen, 2017/03/17 16:02:49]

This is not Flutter specific, the comment applies to all platforms that support
dart:io.

[zra, 2017/03/17 17:45:35]

I'm afraid I don't follow you. You asked whether various consoles are supported
by this change on Windows. I responded that developing and validating support
beyond what we have a customer requesting is not in scope right now.

+    */
+  external bool get ansiSupported;

[Lasse Reichstein Nielsen, 2017/03/17 08:55:29]

I'd prefer a name like `supportsAnsiEscapes` (or *maybe* just `supportsAnsi`).
Even `isAnsiSupported` or `hasAnsiSupport` are better than the current, but the
first one is more direct.

[zra, 2017/03/17 15:38:51]

Done.

+
+  /**
    * Synchronously read a byte from stdin. This call will block until a byte is
    * available.
    *
    * If at end of file, -1 is returned.
    */
   external int readByteSync();
 }
 
 /**
  * [Stdout] represents the [IOSink] for either `stdout` or `stderr`.
@@ skipping 29 matching lines @@
   int get terminalColumns => _terminalColumns(_fd);
 
   /**
    * Get the number of lines of the terminal.
    *
    * If no terminal is attached to stdout, a [StdoutException] is thrown. See
    * [hasTerminal] for more info.
    */
   int get terminalLines => _terminalLines(_fd);
 
+  /**
+    * When connected to a terminal, whether ANSI codes are supported.
+    *
+    * This is `true` if the TERM environment variable contains the string
+    * 'xterm', except on Windows where support is detected only in recent
+    * versions of Windows 10.
+    */
+  bool get ansiSupported => _ansiSupported(_fd);
+
   external bool _hasTerminal(int fd);
   external int _terminalColumns(int fd);
   external int _terminalLines(int fd);
+  external static bool _ansiSupported(int fd);
 
   /**
    * Get a non-blocking `IOSink`.
    */
   IOSink get nonBlocking {
     if (_nonBlocking == null) {
       _nonBlocking = new IOSink(new _FileStreamConsumer.fromStdio(_fd));
     }
     return _nonBlocking;
   }
@@ skipping 198 matching lines @@
 }
 
 class _StdIOUtils {
   external static _getStdioOutputStream(int fd);
   external static Stdin _getStdioInputStream();
 
   /// Returns the socket type or `null` if [socket] is not a builtin socket.
   external static int _socketType(Socket socket);
   external static _getStdioHandleType(int fd);
 }