add --check (#65)

fixes undefined

src/pyproject_fmt/__main__.py

@@ -32,7 +32,7 @@ def _handle_one(config: Config, opts: PyProjectFmtNamespace) -> bool:
         print(formatted, end="")
         return changed
 
-    if before != formatted:
+    if before != formatted and not opts.check:
         config.pyproject_toml.write_text(formatted, encoding="utf-8")
     try:
         name = str(config.pyproject_toml.relative_to(Path.cwd()))

src/pyproject_fmt/cli.py

@@ -19,6 +19,7 @@ class PyProjectFmtNamespace(Namespace):
     inputs: list[Path]
     stdout: bool
     indent: int
+    check: bool
 
     @property
     def configs(self) -> list[Config]:
@@ -45,8 +46,11 @@ def pyproject_toml_path_creator(argument: str) -> Path:
 
 def _build_cli() -> ArgumentParser:
     parser = ArgumentParser(formatter_class=ArgumentDefaultsHelpFormatter)
+    group = parser.add_mutually_exclusive_group()
     msg = "print the formatted text to the stdout (instead of update in-place)"
-    parser.add_argument("-s", "--stdout", action="store_true", help=msg)
+    group.add_argument("-s", "--stdout", action="store_true", help=msg)
+    msg = "check and fail if any input would be formatted, printing any diffs"
+    group.add_argument("--check", action="store_true", help=msg)
     parser.add_argument("--indent", type=int, default=DEFAULT_INDENT, help="number of spaces to indent")
     msg = "pyproject.toml file(s) to format"
     parser.add_argument("inputs", nargs="+", type=pyproject_toml_path_creator, help=msg)

tests/test_main.py

@@ -56,6 +56,13 @@ def no_color(diff: Any) -> Any:
         False,
     ],
 )
+@pytest.mark.parametrize(
+    "check",
+    [
+        True,
+        False,
+    ],
+)
 @pytest.mark.parametrize(
     "cwd",
     [
@@ -87,7 +94,8 @@ def test_main(
     outcome: str,
     output: str,
     monkeypatch: pytest.MonkeyPatch,
-    cwd: Path,
+    cwd: bool,
+    check: bool,
 ) -> None:
     monkeypatch.setattr(pyproject_fmt.__main__, "color_diff", no_color)
     if cwd:
@@ -98,13 +106,24 @@ def test_main(
     if not in_place:
         args.append("--stdout")
 
+    if check:
+        args.append("--check")
+
+        if not in_place:
+            with pytest.raises(SystemExit):
+                run(args)
+            assert pyproject_toml.read_text() == start
+            return
+
     result = run(args)
     assert result == (0 if start == outcome else 1)
 
     out, err = capsys.readouterr()
     assert not err
 
-    if in_place:
+    if check:
+        assert pyproject_toml.read_text() == start
+    elif in_place:
         name = "pyproject.toml" if cwd else str(tmp_path / "pyproject.toml")
         output = output.format(name)
         assert pyproject_toml.read_text() == outcome