Add Mypy configuration through root "pyproject.toml" file

It is not uncommon to require a Mypy configuration that differs from the project's main
configuration and is specific to tests, such as enabling the 'force_uppercase_builtins'
option. Currently, the argument '--mypy-pyproject-toml-file' can be used via the command
line, but this approach has two drawbacks:

- It requires an additional file in the codebase, whereas it is more pleasant to
  group all configurations in the root 'pyproject.toml' file.
- It confines the invocation of 'pytest' to a fixed location, as the path is resolved
  relative to the current working directory. However, there are situations where it is
  useful to call 'pytest' from a different directory.

The solution implemented here allows for configuring the Mypy parameters used by
'pytest-mypy-plugins' directly within the project's 'pyproject.toml' file, addressing
both of the aforementioned points.

Author: Delgan

Diff for: .github/workflows/test.yml

@@ -26,6 +26,8 @@ jobs:
       run: |
         pip install -U pip setuptools wheel
         pip install -e .
+        # Workaround until Mypy regression is fixed.
+        pip install mypy==1.5.1
         # Force correct `pytest` version for different envs:
         pip install -U "pytest${{ matrix.pytest-version }}"
     - name: Run tests

Diff for: README.md

@@ -195,6 +195,22 @@ mypy-tests:
 
 ```
 
+## Configuration
+
+For convenience, it is also possible to define a default `mypy` configuration in the root `pyproject.toml` file of your project:
+
+```toml
+[tool.pytest-mypy-plugins.mypy-config]
+force_uppercase_builtins = true
+force_union_syntax = true
+```
+
+The ultimate `mypy` configuration applied during a test is derived by merging the following sources (if they exist), in order:
+
+1. The `mypy-config` table in the root `pyproject.toml` of the project.
+2. The configuration file provided via `--mypy-pyproject-toml-file` or `--mypy-ini-file`.
+3. The `config_mypy` field of the test case.
+
 ## Further reading
 
 - [Testing mypy stubs, plugins, and types](https://sobolevn.me/2019/08/testing-mypy-types)

Diff for: pytest_mypy_plugins/configs.py

@@ -1,15 +1,28 @@
 from configparser import ConfigParser
 from pathlib import Path
 from textwrap import dedent
-from typing import Final, Optional
+from typing import Any, Dict, Final, Optional
 
 import tomlkit
 
 _TOML_TABLE_NAME: Final = "[tool.mypy]"
 
 
-def join_ini_configs(base_ini_fpath: Optional[str], additional_mypy_config: str, execution_path: Path) -> Optional[str]:
+def load_mypy_plugins_config(config_pyproject_toml_path: str) -> Optional[Dict[str, Any]]:
+    with open(config_pyproject_toml_path) as f:
+        toml_config = tomlkit.parse(f.read())
+    return toml_config.get("tool", {}).get("pytest-mypy-plugins", {}).get("mypy-config")
+
+
+def join_ini_configs(
+    base_ini_fpath: Optional[str],
+    additional_mypy_config: str,
+    execution_path: Path,
+    mypy_plugins_config: Optional[Dict[str, Any]] = None,
+) -> Optional[str]:
     mypy_ini_config = ConfigParser()
+    if mypy_plugins_config:
+        mypy_ini_config.read_dict({"mypy": mypy_plugins_config})
     if base_ini_fpath:
         mypy_ini_config.read(base_ini_fpath)
     if additional_mypy_config:
@@ -26,34 +39,38 @@ def join_ini_configs(base_ini_fpath: Optional[str], additional_mypy_config: str,
 
 
 def join_toml_configs(
-    base_pyproject_toml_fpath: str, additional_mypy_config: str, execution_path: Path
+    base_pyproject_toml_fpath: str,
+    additional_mypy_config: str,
+    execution_path: Path,
+    mypy_plugins_config: Optional[Dict[str, Any]] = None,
 ) -> Optional[str]:
+    # Empty document with `[tool.mypy]` empty table, useful for overrides further.
+    toml_document = tomlkit.document()
+    tool = tomlkit.table(is_super_table=True)
+    tool.append("mypy", tomlkit.table())
+    toml_document.append("tool", tool)
+
+    if mypy_plugins_config:
+        toml_document["tool"]["mypy"].update(mypy_plugins_config.items())  # type: ignore[index, union-attr]
+
     if base_pyproject_toml_fpath:
         with open(base_pyproject_toml_fpath) as f:
             toml_config = tomlkit.parse(f.read())
-    else:
-        # Emtpy document with `[tool.mypy` empty table,
-        # useful for overrides further.
-        toml_config = tomlkit.document()
-
-    if "tool" not in toml_config or "mypy" not in toml_config["tool"]:  # type: ignore[operator]
-        tool = tomlkit.table(is_super_table=True)
-        tool.append("mypy", tomlkit.table())
-        toml_config.append("tool", tool)
+        # We don't want the whole config file, because it can contain
+        # other sections like `[tool.isort]`, we only need `[tool.mypy]` part.
+        if "tool" in toml_config and "mypy" in toml_config["tool"]:  # type: ignore[operator]
+            toml_document["tool"]["mypy"].update(toml_config["tool"]["mypy"].value.items())  # type: ignore[index, union-attr]
 
     if additional_mypy_config:
         if _TOML_TABLE_NAME not in additional_mypy_config:
             additional_mypy_config = f"{_TOML_TABLE_NAME}\n{dedent(additional_mypy_config)}"
 
         additional_data = tomlkit.parse(additional_mypy_config)
-        toml_config["tool"]["mypy"].update(  # type: ignore[index, union-attr]
+        toml_document["tool"]["mypy"].update(  # type: ignore[index, union-attr]
             additional_data["tool"]["mypy"].value.items(),  # type: ignore[index]
         )
 
     mypy_config_file_path = execution_path / "pyproject.toml"
     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]
+        f.write(toml_document.as_string())
     return str(mypy_config_file_path)

Diff for: pytest_mypy_plugins/item.py

@@ -141,6 +141,12 @@ def __init__(
         if self.config.option.mypy_ini_file and self.config.option.mypy_pyproject_toml_file:
             raise ValueError("Cannot specify both `--mypy-ini-file` and `--mypy-pyproject-toml-file`")
 
+        # Optionally retrieve plugin configuration through the root `pyproject.toml` file.
+        if (self.config.rootpath / "pyproject.toml").exists():
+            self.config_pyproject_toml_fpath: Optional[str] = str(self.config.rootpath / "pyproject.toml")
+        else:
+            self.config_pyproject_toml_fpath = None
+
         if self.config.option.mypy_ini_file:
             self.base_ini_fpath = os.path.abspath(self.config.option.mypy_ini_file)
         else:
@@ -318,18 +324,25 @@ def prepare_mypy_cmd_options(self, execution_path: Path) -> List[str]:
         return mypy_cmd_options
 
     def prepare_config_file(self, execution_path: Path) -> Optional[str]:
+        # We allow a default Mypy config in root `pyproject.toml` file. This is useful to define
+        # options that are specific to the tests without requiring an additional file.
+        if self.config_pyproject_toml_fpath:
+            mypy_plugins_config = configs.load_mypy_plugins_config(self.config_pyproject_toml_fpath)
+
         # Merge (`self.base_ini_fpath` or `base_pyproject_toml_fpath`)
         # and `self.additional_mypy_config`
         # into one file and copy to the typechecking folder:
         if self.base_pyproject_toml_fpath:
             return configs.join_toml_configs(
-                self.base_pyproject_toml_fpath, self.additional_mypy_config, execution_path
+                self.base_pyproject_toml_fpath, self.additional_mypy_config, execution_path, mypy_plugins_config
             )
-        elif self.base_ini_fpath or self.additional_mypy_config:
+        elif self.base_ini_fpath or self.additional_mypy_config or self.config_pyproject_toml_fpath:
             # We might have `self.base_ini_fpath` set as well.
             # Or this might be a legacy case: only `mypy_config:` is set in the `yaml` test case.
             # This means that no real file is provided.
-            return configs.join_ini_configs(self.base_ini_fpath, self.additional_mypy_config, execution_path)
+            return configs.join_ini_configs(
+                self.base_ini_fpath, self.additional_mypy_config, execution_path, mypy_plugins_config
+            )
         return None
 
     def repr_failure(

Diff for: pytest_mypy_plugins/tests/test_configs/pyproject2.toml

@@ -1 +1 @@
-# This file has no `[tool.mypy]` existing config
+# This file has no `[tool.mypy]` nor `[tool.pytest-mypy-plugins.mypy-config]` existing config

Diff for: pytest_mypy_plugins/tests/test_configs/pyproject3.toml

@@ -0,0 +1,10 @@
+# This file has `[tool.pytest-mypy-plugins.mypy-config]` existing config
+
+[tool.pytest-mypy-plugins.mypy-config]
+pretty = false
+show_column_numbers = true
+warn_unused_ignores = false
+
+[tool.other]
+# This section should not be copied:
+key = 'value'

Diff for: pytest_mypy_plugins/tests/test_configs/test_join_toml_configs.py

@@ -19,6 +19,12 @@
 show_traceback = true
 """
 
+_MYPY_PLUGINS_CONFIG: Final = {
+    "pretty": False,
+    "show_column_numbers": True,
+    "warn_unused_ignores": False,
+}
+
 _PYPROJECT1: Final = str(Path(__file__).parent / "pyproject1.toml")
 _PYPROJECT2: Final = str(Path(__file__).parent / "pyproject2.toml")
 
@@ -68,6 +74,71 @@ def test_join_existing_config(
     )
 
 
+def test_join_existing_config1(execution_path: Path, assert_file_contents: _AssertFileContents) -> None:
+    filepath = join_toml_configs(_PYPROJECT1, "", execution_path, _MYPY_PLUGINS_CONFIG)
+
+    assert_file_contents(
+        filepath,
+        """
+        [tool.mypy]
+        pretty = true
+        show_column_numbers = true
+        warn_unused_ignores = true
+        show_error_codes = true
+        """,
+    )
+
+
+@pytest.mark.parametrize(
+    "additional_config",
+    [
+        _ADDITIONAL_CONFIG,
+        _ADDITIONAL_CONFIG_NO_TABLE,
+    ],
+)
+def test_join_existing_config2(
+    execution_path: Path, assert_file_contents: _AssertFileContents, additional_config: str
+) -> None:
+    filepath = join_toml_configs(_PYPROJECT1, additional_config, execution_path, _MYPY_PLUGINS_CONFIG)
+
+    assert_file_contents(
+        filepath,
+        """
+        [tool.mypy]
+        pretty = true
+        show_column_numbers = true
+        warn_unused_ignores = true
+        show_error_codes = false
+        show_traceback = true
+        """,
+    )
+
+
+@pytest.mark.parametrize(
+    "additional_config",
+    [
+        _ADDITIONAL_CONFIG,
+        _ADDITIONAL_CONFIG_NO_TABLE,
+    ],
+)
+def test_join_existing_config3(
+    execution_path: Path, assert_file_contents: _AssertFileContents, additional_config: str
+) -> None:
+    filepath = join_toml_configs(_PYPROJECT1, additional_config, execution_path, _MYPY_PLUGINS_CONFIG)
+
+    assert_file_contents(
+        filepath,
+        """
+        [tool.mypy]
+        pretty = true
+        show_column_numbers = true
+        warn_unused_ignores = true
+        show_error_codes = false
+        show_traceback = true
+        """,
+    )
+
+
 @pytest.mark.parametrize(
     "additional_config",
     [
@@ -112,3 +183,42 @@ 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(_PYPROJECT2, "", execution_path, _MYPY_PLUGINS_CONFIG)
+
+    assert_file_contents(
+        filepath,
+        """
+        [tool.mypy]
+        pretty = false
+        show_column_numbers = true
+        warn_unused_ignores = false
+        """,
+    )
+
+
+@pytest.mark.parametrize(
+    "additional_config",
+    [
+        _ADDITIONAL_CONFIG,
+        _ADDITIONAL_CONFIG_NO_TABLE,
+    ],
+)
+def test_join_missing_config4(
+    execution_path: Path, assert_file_contents: _AssertFileContents, additional_config: str
+) -> None:
+    filepath = join_toml_configs(_PYPROJECT2, additional_config, execution_path, _MYPY_PLUGINS_CONFIG)
+
+    assert_file_contents(
+        filepath,
+        """
+        [tool.mypy]
+        pretty = true
+        show_column_numbers = true
+        warn_unused_ignores = false
+        show_error_codes = false
+        show_traceback = true
+        """,
+    )

Diff for: pytest_mypy_plugins/tests/test_configs/test_load_mypy_plugins_config.py

@@ -0,0 +1,20 @@
+from pathlib import Path
+from typing import Final
+
+from pytest_mypy_plugins.configs import load_mypy_plugins_config
+
+
+def test_load_existing_config() -> None:
+    root_pyproject1: Final = str(Path(__file__).parent / "pyproject3.toml")
+    result = load_mypy_plugins_config(root_pyproject1)
+    assert result == {
+        "pretty": False,
+        "show_column_numbers": True,
+        "warn_unused_ignores": False,
+    }
+
+
+def test_load_missing_config() -> None:
+    root_pyproject2: Final = str(Path(__file__).parent / "pyproject2.toml")
+    result = load_mypy_plugins_config(root_pyproject2)
+    assert result is None