Add support for clang's color diagnostics flags (#24827)

emcc will not honor the following clang flags:

```
-fcolor-diagnostics
-fdiagnostics-color
-fdiagnostics-color=always
-fno-color-diagnostics
-fdiagnostics-color=never
-fansi-escape-codes
```

Author: sbc100

test/test_other.py

@@ -12370,27 +12370,45 @@ def test_offset_converter_source_map(self, args):
     self.set_setting('LOAD_SOURCE_MAP')
     self.do_runf('other/test_offset_converter.c', 'ok', cflags=['-gsource-map', '-DUSE_SOURCE_MAP'] + args)
 
+  @crossplatform
   @no_windows('ptys and select are not available on windows')
-  def test_build_error_color(self):
+  def test_color_diagnostics(self):
     create_file('src.c', 'int main() {')
     returncode, output = self.run_on_pty([EMCC, 'src.c'])
     self.assertNotEqual(returncode, 0)
     self.assertIn(b"\x1b[1msrc.c:1:13: \x1b[0m\x1b[0;1;31merror: \x1b[0m\x1b[1mexpected '}'\x1b[0m", output)
     # Verify that emcc errors show up as red and bold
     self.assertIn(b"emcc: \x1b[31m\x1b[1m", output)
 
+  @crossplatform
   @parameterized({
-    'fno_diagnostics_color': ['-fno-diagnostics-color'],
-    'fdiagnostics_color_never': ['-fdiagnostics-color=never'],
+    '': ['-fno-diagnostics-color'],
+    'never': ['-fdiagnostics-color=never'],
   })
   @no_windows('ptys and select are not available on windows')
-  def test_pty_no_color(self, flag):
+  def test_color_diagnostics_disable(self, flag):
     create_file('src.c', 'int main() {')
 
     returncode, output = self.run_on_pty([EMCC, flag, 'src.c'])
     self.assertNotEqual(returncode, 0)
     self.assertNotIn(b'\x1b', output)
 
+  @crossplatform
+  #  There are 3 different ways for force color output in clang
+  @parameterized({
+    '': ['-fcolor-diagnostics'],
+    'alt': ['-fdiagnostics-color'],
+    'always': ['-fdiagnostics-color=always'],
+  })
+  def test_color_diagnostics_force(self, flag):
+    create_file('src.c', 'int main() {')
+    # -fansi-escape-codes is needed here to make this test work on windows, which doesn't
+    # use ansi codes by default
+    output = self.expect_fail([EMCC, '-fansi-escape-codes', flag, 'src.c'])
+    self.assertIn("\x1b[1msrc.c:1:13: \x1b[0m\x1b[0;1;31merror: \x1b[0m\x1b[1mexpected '}'\x1b[0m", output)
+    # Verify that emcc errors show up as red and bold
+    self.assertIn("emcc: \x1b[31m\x1b[1m", output)
+
   def test_sanitizer_color(self):
     create_file('src.c', '''
       #include <emscripten.h>

tools/cmdline.py

@@ -513,6 +513,12 @@ def consume_arg_file():
       options.cpu_profiler = True
     elif check_flag('--threadprofiler'):
       settings_changes.append('PTHREADS_PROFILING=1')
+    elif arg in ('-fcolor-diagnostics', '-fdiagnostics-color', '-fdiagnostics-color=always'):
+      diagnostics.color_enabled = True
+    elif arg in ('-fno-color-diagnostics', '-fdiagnostics-color=never'):
+      diagnostics.color_enabled = False
+    elif arg == '-fansi-escape-codes':
+      diagnostics.force_ansi = True
     elif arg == '-fno-exceptions':
       settings.DISABLE_EXCEPTION_CATCHING = 1
       settings.DISABLE_EXCEPTION_THROWING = 1

tools/diagnostics.py

@@ -12,12 +12,12 @@
 import sys
 from typing import Dict
 
-
 WINDOWS = sys.platform.startswith('win')
 
 logger = logging.getLogger('diagnostics')
 color_enabled = sys.stderr.isatty()
 tool_name = os.path.splitext(os.path.basename(sys.argv[0]))[0]
+force_ansi = False
 
 # diagnostic levels
 WARN = 1
@@ -49,6 +49,7 @@
 
 
 def output_color_windows(color):
+  assert not force_ansi
   # TODO(sbc): This code is duplicated in colored_logger.py.  Refactor.
   # wincon.h
   FOREGROUND_BLACK     = 0x0000 # noqa
@@ -76,6 +77,7 @@ def output_color_windows(color):
 
 
 def get_color_windows():
+  assert not force_ansi
   SHORT = ctypes.c_short
   WORD = ctypes.c_ushort
 
@@ -106,26 +108,27 @@ class CONSOLE_SCREEN_BUFFER_INFO(ctypes.Structure):
 
 
 def reset_color_windows():
+  assert not force_ansi
   sys.stderr.flush()
   hdl = ctypes.windll.kernel32.GetStdHandle(STD_OUTPUT_HANDLE)
   ctypes.windll.kernel32.SetConsoleTextAttribute(hdl, default_color)
 
 
 def output_color(color):
-  if WINDOWS:
+  if WINDOWS and not force_ansi:
     return output_color_windows(color)
   return '\033[3%sm' % color
 
 
 def bold():
-  if WINDOWS:
+  if WINDOWS and not force_ansi:
     # AFAICT there is no way to enable bold output on windows
     return ''
   return '\033[1m'
 
 
 def reset_color():
-  if WINDOWS:
+  if WINDOWS and not force_ansi:
     return reset_color_windows()
   return '\033[0m'