Fix not honouring pyproject.toml when using stdin and calling black from parent directory

CHANGES.md

@@ -23,6 +23,8 @@
 <!-- Changes to how Black can be configured -->
 
 - `.pytest_cache`, `.ruff_cache` and `.vscode` are now excluded by default (#3691)
+- Fix black not honouring `pyproject.toml` settings when running `--stdin-filename` and
+  the `pyproject.toml` found isn't in the current working directory (#3719)
 
 ### Packaging
 

src/black/__init__.py

@@ -127,7 +127,9 @@ def read_pyproject_toml(
     otherwise.
     """
     if not value:
-        value = find_pyproject_toml(ctx.params.get("src", ()))
+        value = find_pyproject_toml(
+            ctx.params.get("src", ()), ctx.params.get("stdin_filename", None)
+        )
         if value is None:
             return None
 
@@ -362,6 +364,7 @@ def validate_regex(
 @click.option(
     "--stdin-filename",
     type=str,
+    is_eager=True,
     help=(
         "The name of the file when passing it through stdin. Useful to make "
         "sure Black will respect --force-exclude option on some "

src/black/files.py

@@ -89,9 +89,11 @@ def find_project_root(
     return directory, "file system root"
 
 
-def find_pyproject_toml(path_search_start: Tuple[str, ...]) -> Optional[str]:
+def find_pyproject_toml(
+    path_search_start: Tuple[str, ...], stdin_filename: Optional[str] = None
+) -> Optional[str]:
     """Find the absolute filepath to a pyproject.toml if it exists"""
-    path_project_root, _ = find_project_root(path_search_start)
+    path_project_root, _ = find_project_root(path_search_start, stdin_filename)
     path_pyproject_toml = path_project_root / "pyproject.toml"
     if path_pyproject_toml.is_file():
         return str(path_pyproject_toml)

tests/test_black.py

@@ -104,6 +104,7 @@ class FakeContext(click.Context):
 
     def __init__(self) -> None:
         self.default_map: Dict[str, Any] = {}
+        self.params: Dict[str, Any] = {}
         # Dummy root, since most of the tests don't care about it
         self.obj: Dict[str, Any] = {"root": PROJECT_ROOT}
 
@@ -1620,6 +1621,39 @@ def test_read_pyproject_toml(self) -> None:
         self.assertEqual(config["exclude"], r"\.pyi?$")
         self.assertEqual(config["include"], r"\.py?$")
 
+    def test_read_pyproject_toml_from_stdin(self) -> None:
+        with TemporaryDirectory() as workspace:
+            root = Path(workspace)
+
+            src_dir = root / "src"
+            src_dir.mkdir()
+
+            src_pyproject = src_dir / "pyproject.toml"
+            src_pyproject.touch()
+
+            test_toml_file = THIS_DIR / "test.toml"
+            src_pyproject.write_text(test_toml_file.read_text())
+
+            src_python = src_dir / "foo.py"
+            src_python.touch()
+
+            fake_ctx = FakeContext()
+            fake_ctx.params["src"] = ("-",)
+            fake_ctx.params["stdin_filename"] = str(src_python)
+
+            with change_directory(root):
+                black.read_pyproject_toml(fake_ctx, FakeParameter(), None)
+
+            config = fake_ctx.default_map
+            self.assertEqual(config["verbose"], "1")
+            self.assertEqual(config["check"], "no")
+            self.assertEqual(config["diff"], "y")
+            self.assertEqual(config["color"], "True")
+            self.assertEqual(config["line_length"], "79")
+            self.assertEqual(config["target_version"], ["py36", "py37", "py38"])
+            self.assertEqual(config["exclude"], r"\.pyi?$")
+            self.assertEqual(config["include"], r"\.py?$")
+
     @pytest.mark.incompatible_with_mypyc
     def test_find_project_root(self) -> None:
         with TemporaryDirectory() as workspace: