main: add FORCE_COLOR

Signed-off-by: Filipe Laíns <lains@riseup.net>

CHANGELOG.rst

@@ -8,6 +8,7 @@ Unreleased
 
 - Improved output (`PR #333`_, Fixes `#142`_)
 - The CLI now honnors `NO_COLOR`_ (`PR #333`_)
+- The CLI can now be forced to colorize the output by setting the ``FORCE_COLOR`` environment variable (`PR #335`_)
 - Added logging to ``build`` and ``build.env`` (`PR #333`_)
 
 
@@ -17,6 +18,7 @@ Breaking Changes
 - Dropped support for Python 2 and 3.5.
 
 .. _PR #333: https://github.com/pypa/build/pull/333
+.. _PR #335: https://github.com/pypa/build/pull/335
 .. _#142: https://github.com/pypa/build/issues/142
 .. _NO_COLOR: https://no-color.org
 

src/build/__main__.py

@@ -33,7 +33,7 @@
     'underline': '\33[4m',
     'reset': '\33[0m',
 }
-if not sys.stdout.isatty() or 'NO_COLOR' in os.environ:
+if 'FORCE_COLOR' not in os.environ and not sys.stdout.isatty() or 'NO_COLOR' in os.environ:
     _STYLES = {color: '' for color in _STYLES}
 
 

tests/test_main.py

@@ -338,8 +338,9 @@ def test_output_env_subprocess_error(
     stdout_body,
     stdout_error,
 ):
-    mocker.patch('sys.stdout.isatty', return_value=True)
-    if not color:
+    if color:
+        monkeypatch.setenv('FORCE_COLOR', '')
+    else:
         monkeypatch.setenv('NO_COLOR', '')
 
     importlib.reload(build.__main__)  # reload module to set _STYLES