Fix pyproject.toml tool.mypy.overrides parsing (#146)

pytest_mypy_plugins/configs.py

@@ -54,6 +54,13 @@ def join_toml_configs(
     with mypy_config_file_path.open("w") as f:
         # We don't want the whole config file, because it can contain
         # other sections like `[tool.isort]`, we only need `[tool.mypy]` part.
-        f.write(f"{_TOML_TABLE_NAME}\n")
-        f.write(dedent(toml_config["tool"]["mypy"].as_string()))  # type: ignore[index]
+        tool_mypy = toml_config["tool"]["mypy"]  # type: ignore[index]
+
+        # construct toml output
+        min_toml = tomlkit.document()
+        min_tool = tomlkit.table(is_super_table=True)
+        min_toml.append("tool", min_tool)
+        min_tool.append("mypy", tool_mypy)
+
+        f.write(min_toml.as_string())
     return str(mypy_config_file_path)

pytest_mypy_plugins/tests/test_configs/pyproject3.toml

@@ -0,0 +1,11 @@
+# This file has `[tool.mypy]` existing config
+
+[tool.mypy]
+warn_unused_ignores = true
+pretty = true
+show_error_codes = true
+
+[[tool.mypy.overrides]]
+# This section should be copied
+module = "mymodule"
+ignore_missing_imports = true

pytest_mypy_plugins/tests/test_configs/test_join_toml_configs.py

@@ -21,6 +21,7 @@
 
 _PYPROJECT1: Final = str(Path(__file__).parent / "pyproject1.toml")
 _PYPROJECT2: Final = str(Path(__file__).parent / "pyproject2.toml")
+_PYPROJECT3: Final = str(Path(__file__).parent / "pyproject3.toml")
 
 
 @pytest.fixture
@@ -112,3 +113,22 @@ def test_join_missing_config2(execution_path: Path, assert_file_contents: _Asser
         filepath,
         "[tool.mypy]",
     )
+
+
+def test_join_missing_config3(execution_path: Path, assert_file_contents: _AssertFileContents) -> None:
+    filepath = join_toml_configs(_PYPROJECT3, "", execution_path)
+
+    assert_file_contents(
+        filepath,
+        """
+        [tool.mypy]
+        warn_unused_ignores = true
+        pretty = true
+        show_error_codes = true
+
+        [[tool.mypy.overrides]]
+        # This section should be copied
+        module = "mymodule"
+        ignore_missing_imports = true
+        """,
+    )