Merge pull request #46 from Carreau/color-diff

Optionally print the diff in color.

CHANGES.rst

@@ -15,7 +15,8 @@ Added
 Fixed
 -----
 - Paths from ``--diff`` are now relative to current working directory, similar to output
-  from ``black --diff``
+  from ``black --diff``, and blank lines after the lines markers (``@@ ... @@``) have been removed.
+- The ``--diff`` option will highlight syntax on screen if the ``pygments`` package is available.
 
 
 1.0.0_ - 2020-07-15

README.rst

@@ -113,7 +113,8 @@ The following `command line arguments`_ can also be used to modify the defaults:
 .. code-block:: shell
 
      --diff                Don't write the files back, just output a diff for
-                           each file on stdout
+                           each file on stdout. Highlight syntax on screen if
+                           the `pygments` package is available.
 
      --check               Don't write the files back, just return the status.
                            Return code 0 means nothing would change. Return code

mypy.ini

@@ -52,3 +52,12 @@ ignore_missing_imports = True
 
 [mypy-setuptools.*]
 ignore_missing_imports = True
+
+[mypy-pygments.*]
+ignore_missing_imports = True
+
+[mypy-pygments.formatters.*]
+ignore_missing_imports = True
+
+[mypy-pygments.lexers.*]
+ignore_missing_imports = True

pytest.ini

@@ -6,3 +6,4 @@ addopts =
   --isort
   --mypy
   --doctest-modules
+  --durations 10

setup.cfg

@@ -43,3 +43,4 @@ test =
     pytest-black
     pytest-isort>=1.1.0
     pytest-mypy
+    pygments

src/darker/__main__.py

@@ -141,13 +141,24 @@ def modify_file(path: Path, new_content: str) -> None:
 def print_diff(path: Path, old_content: str, new_lines: List[str]) -> None:
     """Print ``black --diff`` style output for the changes"""
     relative_path = path.resolve().relative_to(Path.cwd()).as_posix()
-    difflines = list(
-        unified_diff(old_content.splitlines(), new_lines, relative_path, relative_path)
+    diff = "\n".join(
+        line.rstrip("\n")
+        for line in unified_diff(
+            old_content.splitlines(), new_lines, relative_path, relative_path,
+        )
     )
-    header1, header2, *rest = difflines
-    print(header1, end="")
-    print(header2, end="")
-    print("\n".join(rest))
+
+    if sys.stdout.isatty():
+        try:
+            from pygments import highlight
+            from pygments.formatters import TerminalFormatter
+            from pygments.lexers import DiffLexer
+        except ImportError:
+            print(diff)
+        else:
+            print(highlight(diff, DiffLexer(), TerminalFormatter()))
+    else:
+        print(diff)
 
 
 def main(argv: List[str] = None) -> int:

src/darker/command_line.py

@@ -36,7 +36,10 @@ def parse_command_line(argv: List[str]) -> Namespace:
     parser.add_argument(
         "--diff",
         action="store_true",
-        help="Don't write the files back, just output a diff for each file on stdout",
+        help=(
+            "Don't write the files back, just output a diff for each file on stdout."
+            " Highlight syntax on screen if the `pygments` package is available."
+        ),
     )
     parser.add_argument(
         "--check",

src/darker/tests/test_main.py

@@ -69,7 +69,6 @@ def test_format_edited_parts_empty():
     '--- a.py',
     '+++ a.py',
     '@@ -1,3 +1,4 @@',
-    '',
     ' import sys',
     ' import os',
     "-print( '42')",
@@ -82,7 +81,6 @@ def test_format_edited_parts_empty():
     '--- a.py',
     '+++ a.py',
     '@@ -1,3 +1,4 @@',
-    '',
     ' import sys',
     ' import os',
     "-print( '42')",
@@ -95,7 +93,6 @@ def test_format_edited_parts_empty():
     '--- a.py',
     '+++ a.py',
     '@@ -1,3 +1,4 @@',
-    '',
     '+import os',
     ' import sys',
     '-import os',
@@ -189,15 +186,13 @@ def test_output_diff(capsys):
         '--- a.py',
         '+++ a.py',
         '@@ -1,5 +1,5 @@',
-        '',
         '+inserted',
         ' unchanged',
         '-removed',
         ' kept 1',
         ' 2',
         ' 3',
         '@@ -7,4 +7,4 @@',
-        '',
         ' 5',
         ' 6',
         ' 7',