[ dart:io ] Add tmux terminals to list of terminals known to support ANSI

Fixes flutter/flutter#142861

TEST=N/A

Change-Id: I208c597f33c622d19419202351dd17d39ec82bc3
CoreLibraryReviewExempt: only dart:io
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/419280
Commit-Queue: Ben Konyi <bkonyi@google.com>
Reviewed-by: Brian Quinlan <bquinlan@google.com>

Author: bkonyi

CHANGELOG.md

@@ -11,6 +11,8 @@
 #### `dart:io`
 
 - Added support `HttpClientBearerCredentials`.
+- Update `Stdout.supportsAnsiEscapes` and `Stdin.supportsAnsiEscapes` to
+  return `true` for `TERM` containing `tmux` values.
 
 #### `dart:html`
 

runtime/bin/stdio_linux.cc

@@ -109,7 +109,8 @@ static bool TermIsKnownToSupportAnsi() {
   }
 
   return strstr(term, "xterm") != nullptr ||
-         strstr(term, "screen") != nullptr || strstr(term, "rxvt") != nullptr;
+         strstr(term, "screen") != nullptr || strstr(term, "rxvt") != nullptr ||
+         strstr(term, "tmux") != nullptr;
 }
 
 bool Stdin::AnsiSupported(intptr_t fd, bool* supported) {

runtime/bin/stdio_macos.cc

@@ -109,7 +109,8 @@ static bool TermIsKnownToSupportAnsi() {
   }
 
   return strstr(term, "xterm") != nullptr ||
-         strstr(term, "screen") != nullptr || strstr(term, "rxvt") != nullptr;
+         strstr(term, "screen") != nullptr || strstr(term, "rxvt") != nullptr ||
+         strstr(term, "tmux") != nullptr;
 }
 
 bool Stdin::AnsiSupported(intptr_t fd, bool* supported) {

sdk/lib/io/stdio.dart

@@ -178,11 +178,11 @@ class Stdin extends _StdStream implements Stream<List<int>> {
   ///
   /// The ANSI color selection is generally supported.
   ///
-  /// 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", OS build 10586) will be detected as supporting the output of
-  /// ANSI escape sequences, and only versions after v.1607 ("Anniversary
+  /// Currently, a `TERM` environment variable containing the string `xterm`,
+  /// `screen`, `rxvt`, or `tmux` will be taken as evidence that ANSI escape
+  /// sequences are supported. On Windows, only versions of Windows 10 after
+  /// v.1511 ("TH2", OS build 10586) will be detected as supporting the output
+  /// of ANSI escape sequences, and only versions after v.1607 ("Anniversary
   /// Update", OS build 14393) will be detected as supporting the input of
   /// ANSI escape sequences.
   external bool get supportsAnsiEscapes;