Add a --diff option to match black behavior.

CHANGES.rst

@@ -3,6 +3,8 @@
 
 - Feature: Add support for black config
 - Feature: Add support for ``-l``/``--line-length`` and ``-S``/``--skip-string-normalization``
+- Feature: ``--diff`` outputs a diff for each file on standard output
+
 
 0.2.0 / 2020-03-11
 ------------------

CONTRIBUTORS.rst

@@ -7,3 +7,4 @@
 - Alexander Tishin (@Mystic-Mirage)
 - Antti Kaihola (@akaihola)
 - Correy Lim (@CorreyL)
+- Matthias Bussonnier (@Carreau)

README.rst

@@ -178,6 +178,30 @@ PyCharm/IntelliJ IDEA
 
 __ https://plugins.jetbrains.com/plugin/7177-file-watchers
 
+Visual Studio Code
+------------------
+
+1. Install ``darker``::
+
+     $ pip install darker
+
+2. Locate your ``darker`` installation folder.
+
+   On macOS / Linux / BSD::
+
+     $ which darker
+     /usr/local/bin/darker  # possible location
+
+   On Windows::
+
+     $ where darker
+     %LocalAppData%\Programs\Python\Python36-32\Scripts\darker.exe  # possible location
+
+3. Add these configuration options::
+
+    "python.formatting.provider": "black",
+    "python.formatting.blackPath": "<install_location_from_step_2>"
+
 
 How does it work?
 =================

pyproject.toml

@@ -1,3 +1,6 @@
 [build-system]
 # Minimum requirements for the build system to execute.
 requires = ["setuptools", "wheel"]  # PEP 508 specifications.
+
+[tool.black]
+skip-string-normalization = true

src/darker/__main__.py

@@ -2,6 +2,7 @@
 
 import logging
 import sys
+from difflib import unified_diff
 from pathlib import Path
 from typing import Dict, Iterable, List, Set, Union
 
@@ -21,7 +22,10 @@
 
 
 def format_edited_parts(
-    srcs: Iterable[Path], isort: bool, black_args: Dict[str, Union[bool, int]]
+    srcs: Iterable[Path],
+    isort: bool,
+    black_args: Dict[str, Union[bool, int]],
+    print_diff: bool,
 ) -> None:
     """Black (and optional isort) formatting for chunks with edits since the last commit
 
@@ -43,12 +47,16 @@ def format_edited_parts(
     :param srcs: Directories and files to re-format
     :param isort: ``True`` to also run ``isort`` first on each changed file
     :param black_args: Command-line arguments to send to ``black.FileMode``
+    :param print_diff: ``True`` to output diffs instead of modifying source files
+
     """
     remaining_srcs: Set[Path] = set(srcs)
     git_root = get_common_root(srcs)
 
     # 1. run isort
     if isort:
+        if print_diff:
+            raise NotImplementedError('--isort is not supported with --print-diff')
         changed_files = git_diff_name_only(remaining_srcs, git_root)
         apply_isort(changed_files)
 
@@ -109,7 +117,19 @@ def format_edited_parts(
                 # 10. A re-formatted Python file which produces an identical AST was
                 #     created successfully - write an updated file
                 logger.info("Writing %s bytes into %s", len(result_str), src)
-                src.write_text(result_str)
+                if print_diff:
+                    difflines = list(
+                        unified_diff(
+                            edited, chosen_lines, src.as_posix(), src.as_posix(),
+                        )
+                    )
+                    if len(difflines) > 2:
+                        h1, h2, *rest = difflines
+                        print(h1, end="")
+                        print(h2, end="")
+                        print("\n".join(rest))
+                else:
+                    src.write_text(result_str)
         if not remaining_srcs:
             break
 
@@ -144,7 +164,7 @@ def main(argv: List[str] = None) -> None:
         black_args["skip_string_normalization"] = args.skip_string_normalization
 
     paths = {Path(p) for p in args.src}
-    format_edited_parts(paths, args.isort, black_args)
+    format_edited_parts(paths, args.isort, black_args, args.diff)
 
 
 if __name__ == "__main__":

src/darker/command_line.py

@@ -27,6 +27,11 @@ def parse_command_line(argv: List[str]) -> Namespace:
     isort_help = ["Also sort imports using the `isort` package"]
     if not isort:
         isort_help.append(f". {ISORT_INSTRUCTION} to enable usage of this option.")
+    parser.add_argument(
+        "--diff",
+        action="store_true",
+        help="Don't write the files back, just output a diff for each file on stdout",
+    )
     parser.add_argument(
         "-i", "--isort", action="store_true", help="".join(isort_help),
     )

src/darker/import_sorting.py

@@ -15,7 +15,7 @@ def apply_isort(srcs: List[Path]) -> None:
         logger.debug(
             f"SortImports({str(src)!r}, multi_line_output=3, "
             f"include_trailing_comma=True, force_grid_wrap=0, use_parentheses=True,"
-            f" line_length=88)"
+            f" line_length=88, quiet=True)"
         )
         _ = SortImports(
             str(src),
@@ -24,4 +24,5 @@ def apply_isort(srcs: List[Path]) -> None:
             force_grid_wrap=0,
             use_parentheses=True,
             line_length=88,
+            quiet=True,
         )

src/darker/tests/test_command_line.py

@@ -1,4 +1,5 @@
 import re
+from pathlib import Path
 from textwrap import dedent
 from unittest.mock import call, patch
 
@@ -78,3 +79,31 @@ def test_black_options(monkeypatch, tmpdir, git_repo, options, expect):
 
     _, expect_args, expect_kwargs = expect
     FileMode.assert_called_once_with(*expect_args, **expect_kwargs)
+
+
+@pytest.mark.parametrize(
+    'options, expect',
+    [
+        (['a.py'], ({Path('a.py')}, False, {}, False)),
+        (['--isort', 'a.py'], ({Path('a.py')}, True, {}, False)),
+        (
+            ['--config', 'my.cfg', 'a.py'],
+            ({Path('a.py')}, False, {'config': 'my.cfg'}, False),
+        ),
+        (
+            ['--line-length', '90', 'a.py'],
+            ({Path('a.py')}, False, {'line_length': 90}, False),
+        ),
+        (
+            ['--skip-string-normalization', 'a.py'],
+            ({Path('a.py')}, False, {'skip_string_normalization': True}, False),
+        ),
+        (['--diff', 'a.py'], ({Path('a.py')}, False, {}, True)),
+    ],
+)
+def test_options(options, expect):
+    with patch('darker.__main__.format_edited_parts') as format_edited_parts:
+
+        main(options)
+
+    format_edited_parts.assert_called_once_with(*expect)

src/darker/tests/test_main.py

@@ -7,7 +7,6 @@
 
 import darker.__main__
 import darker.import_sorting
-from darker.tests.git_diff_example_output import CHANGE_SECOND_LINE
 
 
 def test_isort_option_without_isort(tmpdir, without_isort, caplog):
@@ -49,4 +48,88 @@ def test_isort_option_with_isort_calls_sortimports(run_isort):
         line_length=88,
         multi_line_output=3,
         use_parentheses=True,
+        quiet=True,
     )
+
+
+def test_format_edited_parts_empty():
+    with pytest.raises(ValueError):
+
+        darker.__main__.format_edited_parts([], False, {}, True)
+
+
+def test_format_edited_parts_isort_print_diff():
+    with pytest.raises(NotImplementedError):
+
+        darker.__main__.format_edited_parts([Path('test.py')], True, {}, True)
+
+
+A_PY = ['import sys', 'import os', "print( '42')", '']
+A_PY_BLACK = ['import sys', 'import os', '', 'print("42")', '']
+A_PY_BLACK_ISORT = ['import os', 'import sys', '', 'print("42")', '']
+
+A_PY_DIFF_BLACK = [
+    '--- /a.py',
+    '+++ /a.py',
+    '@@ -1,3 +1,4 @@',
+    '',
+    ' import sys',
+    ' import os',
+    "-print( '42')",
+    '+',
+    '+print("42")',
+    '',
+]
+
+A_PY_DIFF_BLACK_NO_STR_NORMALIZE = [
+    '--- /a.py',
+    '+++ /a.py',
+    '@@ -1,3 +1,4 @@',
+    '',
+    ' import sys',
+    ' import os',
+    "-print( '42')",
+    '+',
+    "+print('42')",
+    '',
+]
+
+
+@pytest.mark.parametrize(
+    'srcs, isort, black_args, print_diff, expect_stdout, expect_a_py',
+    [
+        (['a.py'], False, {}, True, A_PY_DIFF_BLACK, A_PY),
+        (['a.py'], True, {}, False, [''], A_PY_BLACK_ISORT),
+        (
+            ['a.py'],
+            False,
+            {'skip_string_normalization': True},
+            True,
+            A_PY_DIFF_BLACK_NO_STR_NORMALIZE,
+            A_PY,
+        ),
+        (['a.py'], False, {}, False, [''], A_PY_BLACK),
+    ],
+)
+def test_format_edited_parts(
+    git_repo,
+    monkeypatch,
+    capsys,
+    srcs,
+    isort,
+    black_args,
+    print_diff,
+    expect_stdout,
+    expect_a_py,
+):
+    monkeypatch.chdir(git_repo.root)
+    paths = git_repo.add({'a.py': '\n', 'b.py': '\n'}, commit='Initial commit')
+    paths['a.py'].write('\n'.join(A_PY))
+    paths['b.py'].write('print(42 )\n')
+    darker.__main__.format_edited_parts(
+        [Path(src) for src in srcs], isort, black_args, print_diff
+    )
+    stdout = capsys.readouterr().out.replace(str(git_repo.root), '')
+    assert stdout.split('\n') == expect_stdout
+    assert paths['a.py'].readlines(cr=False) == expect_a_py
+    assert paths['b.py'].readlines(cr=False) == ['print(42 )', '']