Support the NO_COLOR environment variable

CHANGES.rst

@@ -11,9 +11,10 @@ Added
 - Sort imports only if the range of modified lines overlaps with changes resulting from
   sorting the imports.
 - Allow force enabling/disabling of syntax highlighting using the ``color`` option in
-  ``pyproject.toml``, the ``PY_COLORS`` environment variable, and the
+  ``pyproject.toml``, the ``PY_COLORS`` and ``NO_COLOR`` environment variables, and the
   ``--color``/``--no-color`` command line options.
 - Syntax highlighting is now enabled by default in the GitHub Action.
+- ``pytest>=6.2.0`` now required for the test suite due to type hinting issues.
 
 Fixed
 -----

constraints-oldest.txt

@@ -13,7 +13,7 @@ flake8-bugbear==22.1.11
 flake8-comprehensions==3.7.0
 mypy==0.940
 Pygments==2.4.0
-pytest==6.1.0
+pytest==6.2.0
 pytest-flake8==1.0.6
 pytest-isort==1.1.0
 pytest-kwparametrize==0.0.3

setup.cfg

@@ -62,7 +62,7 @@ test =
     mypy>=0.940
     pygments
     pylint
-    pytest>=6.1.0
+    pytest>=6.2.0
     pytest-darker
     pytest-flake8>=1.0.6
     pytest-isort>=1.1.0

src/darker/config.py

@@ -106,11 +106,14 @@ def override_color_with_environment(pyproject_config: DarkerConfig) -> DarkerCon
     :return: The modified configuration
 
     """
-    py_colors = os.getenv("PY_COLORS")
-    if py_colors not in {"0", "1"}:
-        return pyproject_config
     config = pyproject_config.copy()
-    config["color"] = py_colors == "1"
+    py_colors = os.getenv("PY_COLORS")
+    if py_colors in {"0", "1"}:
+        config["color"] = py_colors == "1"
+    elif os.getenv("NO_COLOR") is not None:
+        config["color"] = False
+    elif os.getenv("FORCE_COLOR") is not None:
+        config["color"] = True
     return config