Fix crash when isort isn't installed

CHANGES.rst

@@ -9,6 +9,7 @@ Added
 Fixed
 -----
 - Git-related commands in the test suite now ignore the user's ``~/.gitconfig``.
+- Now works again even if ``isort`` isn't installed
 
 
 1.2.3_ - 2021-05-02

mypy.ini

@@ -45,6 +45,7 @@ disallow_any_explicit = False
 
 [mypy-darker.tests.*]
 disallow_any_decorated = False
+disallow_untyped_calls = False
 disallow_untyped_defs = False
 
 [mypy-darker.utils]

src/darker/help.py

@@ -13,7 +13,7 @@
 except ImportError:
     isort = None  # type: ignore
     DESCRIPTION_PARTS.extend(
-        ["", f"{ISORT_INSTRUCTION} to enable sorting of import definitions"]
+        ["\n", "\n", f"{ISORT_INSTRUCTION} to enable sorting of import definitions"]
     )
 DESCRIPTION = "".join(DESCRIPTION_PARTS)
 

src/darker/import_sorting.py

@@ -1,7 +1,7 @@
 import logging
 import sys
 from pathlib import Path
-from typing import Optional
+from typing import Any, Optional
 
 from black import find_project_root
 
@@ -15,11 +15,21 @@
 
 try:
     import isort
+
+    # Work around Mypy problem
+    # https://github.com/python/mypy/issues/7030#issuecomment-504128883
+    isort_code = getattr(isort, "code")
 except ImportError:
+    # `isort` is an optional dependency. Prevent the `ImportError` if it's missing.
     isort = None  # type: ignore
-# Work around Mypy problem
-# https://github.com/python/mypy/issues/7030#issuecomment-504128883
-isort_code = getattr(isort, "code")
+
+    def isort_code(*args: Any, **kwargs: Any) -> str:  # type: ignore[misc] # noqa: F821
+        """Fake `isort.code()` function to use when `isort` isn't installed"""
+        raise ModuleNotFoundError(
+            "No module named 'isort'. Please install the 'isort' package before using"
+            " the --isort / -i option."
+        )
+
 
 __all__ = ["apply_isort", "isort"]
 

src/darker/tests/conftest.py

@@ -1,31 +1,16 @@
 """Configuration and fixtures for the Pytest based test suite"""
 
 import os
-import sys
-import types
 from pathlib import Path
 from subprocess import check_call
 from typing import Dict, Optional
-from unittest.mock import patch
 
 import pytest
 from black import find_project_root
 
 from darker.git import _git_check_output_lines
 
 
-@pytest.fixture
-def without_isort():
-    with patch.dict(sys.modules, {"isort": None}):
-        yield
-
-
-@pytest.fixture
-def with_isort():
-    with patch.dict(sys.modules, {"isort": types.ModuleType("isort")}):
-        yield
-
-
 class GitRepoFixture:
     def __init__(self, root: Path, env: Dict[str, str]):
         self.root = root

src/darker/tests/helpers.py

@@ -2,7 +2,9 @@
 
 import sys
 from contextlib import contextmanager
-from typing import Any, ContextManager, Dict, List, Union
+from types import ModuleType
+from typing import Any, ContextManager, Dict, List, Optional, Union
+from unittest.mock import patch
 
 import pytest
 from _pytest.python_api import RaisesContext
@@ -53,3 +55,18 @@ def check(result):
             assert result == expect
 
         yield check
+
+
+@contextmanager
+def isort_present(present):
+    """Context manager to remove or add the `isort` package temporarily for a test"""
+    if present:
+        # Inject a dummy `isort` package temporarily
+        fake_isort_module: Optional[ModuleType] = ModuleType("isort")
+        # dummy function required by `import_sorting`:
+        fake_isort_module.code = None  # type: ignore
+    else:
+        # Remove the `isort` package temporarily
+        fake_isort_module = None
+    with patch.dict(sys.modules, {"isort": fake_isort_module}):
+        yield

src/darker/tests/test_command_line.py

@@ -12,7 +12,7 @@
 from darker.__main__ import main
 from darker.command_line import make_argument_parser, parse_command_line
 from darker.git import RevisionRange
-from darker.tests.helpers import filter_dict, raises_if_exception
+from darker.tests.helpers import filter_dict, isort_present, raises_if_exception
 from darker.utils import TextDocument, joinlines
 
 pytestmark = pytest.mark.usefixtures("find_project_root_cache_clear")
@@ -29,8 +29,7 @@ def test_make_argument_parser(require_src, expect):
         assert args.src == expect
 
 
-@pytest.fixture
-def darker_help_output(capsys):
+def get_darker_help_output(capsys):
     """Test for ``--help`` option output"""
     # Make sure the description is re-rendered since its content depends on whether
     # isort is installed or not:
@@ -232,22 +231,31 @@ def test_parse_command_line(
         assert modified_cfg[modified_option] == expect_modified_value
 
 
-def test_help_description_without_isort_package(without_isort, darker_help_output):
-    assert (
-        "Please run `pip install 'darker[isort]'` to enable sorting of import "
-        "definitions" in darker_help_output
-    )
+def test_help_description_without_isort_package(capsys):
+    """``darker --help`` description shows how to add ``isort`` if it's not present"""
+    with isort_present(False):
+
+        assert (
+            "Please run `pip install 'darker[isort]'` to enable sorting of import "
+            "definitions" in get_darker_help_output(capsys)
+        )
 
 
-def test_help_isort_option_without_isort_package(without_isort, darker_help_output):
-    assert (
-        "Please run `pip install 'darker[isort]'` to enable usage of this option."
-        in darker_help_output
-    )
+def test_help_isort_option_without_isort_package(capsys):
+    """``--isort`` option help text shows how to install `isort`` if it's not present"""
+    with isort_present(False):
+
+        assert (
+            "Please run `pip install 'darker[isort]'` to enable usage of this option."
+            in get_darker_help_output(capsys)
+        )
+
 
+def test_help_with_isort_package(capsys):
+    """``darker --help`` omits ``isort`` installation instructions if it is installed"""
+    with isort_present(True):
 
-def test_help_with_isort_package(with_isort, darker_help_output):
-    assert "Please run" not in darker_help_output
+        assert "Please run" not in get_darker_help_output(capsys)
 
 
 @pytest.mark.parametrize(

src/darker/tests/test_import_sorting.py

@@ -1,21 +1,38 @@
+"""Tests for :mod:`darker.import_sorting`"""
+
+from importlib import reload
 from pathlib import Path
 from textwrap import dedent
 
 import pytest
 from black import find_project_root
 
-from darker.import_sorting import apply_isort
+import darker.import_sorting
+from darker.tests.helpers import isort_present
 from darker.utils import TextDocument
 
 ORIGINAL_SOURCE = ("import sys", "import os")
 ISORTED_SOURCE = ("import os", "import sys")
 
 
+@pytest.mark.parametrize("present", [True, False])
+def test_import_sorting_importable_with_and_without_isort(present):
+    """Make sure ``import darker.import_sorting`` works with and without ``isort``"""
+    try:
+        with isort_present(present):
+
+            # Import when `isort` has been removed temporarily
+            reload(darker.import_sorting)
+    finally:
+        # Re-import after restoring `isort` so other tests won't be affected
+        reload(darker.import_sorting)
+
+
 @pytest.mark.parametrize("encoding", ["utf-8", "iso-8859-1"])
 @pytest.mark.parametrize("newline", ["\n", "\r\n"])
 def test_apply_isort(encoding, newline):
     """Import sorting is applied correctly, with encoding and newline intact"""
-    result = apply_isort(
+    result = darker.import_sorting.apply_isort(
         TextDocument.from_lines(ORIGINAL_SOURCE, encoding=encoding, newline=newline),
         Path("test1.py"),
     )
@@ -69,5 +86,7 @@ def test_isort_config(monkeypatch, tmpdir, line_length, settings_file, expect):
     content = "from module import ab, cd, ef, gh, ij, kl, mn, op, qr, st, uv, wx, yz"
     config = str(tmpdir / settings_file) if settings_file else None
 
-    actual = apply_isort(TextDocument.from_str(content), Path("test1.py"), config)
+    actual = darker.import_sorting.apply_isort(
+        TextDocument.from_str(content), Path("test1.py"), config
+    )
     assert actual.string == expect

src/darker/tests/test_main.py

@@ -1,5 +1,7 @@
 """Unit tests for :mod:`darker.__main__`"""
 
+# pylint: disable=unused-argument
+
 import logging
 import os
 import re
@@ -13,14 +15,16 @@
 import darker.__main__
 import darker.import_sorting
 from darker.git import RevisionRange
+from darker.tests.helpers import isort_present
 from darker.utils import TextDocument
 from darker.verification import NotEquivalentError
 
 
-def test_isort_option_without_isort(git_repo, without_isort, caplog):
+def test_isort_option_without_isort(git_repo, caplog):
     """Without isort, provide isort install instructions and error"""
-    # pylint: disable=unused-argument
-    with patch.object(darker.__main__, "isort", None), pytest.raises(SystemExit):
+    with isort_present(False), patch.object(
+        darker.__main__, "isort", None
+    ), pytest.raises(SystemExit):
 
         darker.__main__.main(["--isort", "."])