tests: ensure tests never mutate DEFAULT_OPTS or cached TOML opts (#509)

* tests: ensure tests never mutate DEFAULT_OPTS or cached TOML opts

* lazy load plugins for speed and avoiding circular import

Author: hukkin

.pre-commit-config.yaml

@@ -23,11 +23,11 @@ repos:
   hooks:
   - id: absolufy-imports
 - repo: https://github.com/PyCQA/isort
-  rev: c235f5e450b4b84e58d114ed4c589cbf454175a3  # frozen: 5.13.2
+  rev: 0a0b7a830386ba6a31c2ec8316849ae4d1b8240d  # frozen: 6.0.0
   hooks:
   - id: isort
 - repo: https://github.com/psf/black
-  rev: 1b2427a2b785cc4aac97c19bb4b9a0de063f9547  # frozen: 24.10.0
+  rev: 8a737e727ac5ab2f1d4cf5876720ed276dc8dc4b  # frozen: 25.1.0
   hooks:
   - id: black
 - repo: https://github.com/hukkin/docformatter
@@ -43,6 +43,6 @@ repos:
     - flake8-builtins
     - flake8-comprehensions
 - repo: https://github.com/pre-commit/pre-commit
-  rev: cc4a52241565440ce200666799eef70626457488  # frozen: v4.0.1
+  rev: b152e922ef11a97efe22ca7dc4f90011f0d1711c  # frozen: v4.1.0
   hooks:
   - id: validate_manifest

src/mdformat/_cli.py

@@ -54,7 +54,11 @@ def run(cli_args: Sequence[str], cache_toml: bool = True) -> int:  # noqa: C901
             print_error(str(e))
             return 1
 
-        opts: Mapping = {**DEFAULT_OPTS, **toml_opts, **cli_core_opts}
+        opts = {**DEFAULT_OPTS, **toml_opts, **cli_core_opts}
+
+        # Merge plugin options from CLI.
+        # Make a copy of opts["plugin"] to not mutate DEFAULT_OPTS or cached TOML.
+        opts["plugin"] = dict(opts["plugin"])
         for plugin_id, plugin_opts in cli_plugin_opts.items():
             if plugin_id in opts["plugin"]:
                 opts["plugin"][plugin_id] |= plugin_opts

src/mdformat/_conf.py

@@ -2,20 +2,24 @@
 
 import functools
 from pathlib import Path
+from types import MappingProxyType
 from typing import Mapping
 
 from mdformat._compat import tomllib
+from mdformat._util import EMPTY_MAP
 
-DEFAULT_OPTS = {
-    "wrap": "keep",
-    "number": False,
-    "end_of_line": "lf",
-    "validate": True,
-    "exclude": [],
-    "plugin": {},
-    "extensions": None,
-    "codeformatters": None,
-}
+DEFAULT_OPTS = MappingProxyType(
+    {
+        "wrap": "keep",
+        "number": False,
+        "end_of_line": "lf",
+        "validate": True,
+        "exclude": (),
+        "plugin": EMPTY_MAP,
+        "extensions": None,
+        "codeformatters": None,
+    }
+)
 
 
 class InvalidConfError(Exception):

src/mdformat/plugins.py

@@ -1,12 +1,13 @@
 from __future__ import annotations
 
-import argparse
-from collections.abc import Callable, Mapping
 from typing import TYPE_CHECKING, Any, Protocol
 
 from mdformat._compat import importlib_metadata
 
 if TYPE_CHECKING:
+    import argparse
+    from collections.abc import Callable, Mapping
+
     from markdown_it import MarkdownIt
 
     from mdformat.renderer.typing import Postprocess, Render
@@ -31,13 +32,6 @@ def _load_entrypoints(
     return loaded_ifaces, dist_versions
 
 
-CODEFORMATTERS: Mapping[str, Callable[[str, str], str]]
-_CODEFORMATTER_DISTS: Mapping[str, tuple[str, list[str]]]
-CODEFORMATTERS, _CODEFORMATTER_DISTS = _load_entrypoints(
-    importlib_metadata.entry_points(group="mdformat.codeformatter")
-)
-
-
 class ParserExtensionInterface(Protocol):
     """An interface for parser extension plugins."""
 
@@ -86,8 +80,37 @@ def update_mdit(mdit: MarkdownIt) -> None:
         """Update the parser, e.g. by adding a plugin: `mdit.use(myplugin)`"""
 
 
+CODEFORMATTERS: Mapping[str, Callable[[str, str], str]]
+_CODEFORMATTER_DISTS: Mapping[str, tuple[str, list[str]]]
 PARSER_EXTENSIONS: Mapping[str, ParserExtensionInterface]
 _PARSER_EXTENSION_DISTS: Mapping[str, tuple[str, list[str]]]
-PARSER_EXTENSIONS, _PARSER_EXTENSION_DISTS = _load_entrypoints(
-    importlib_metadata.entry_points(group="mdformat.parser_extension")
-)
+
+
+def __getattr__(name: str) -> Mapping[str, Any]:
+    """Attribute getter fallback.
+
+    Used to lazy load CODEFORMATTERS and PARSER_EXTENSIONS. It'd
+    probably be more readable to use `@functools.cache` decorated
+    functions, but `__getattr__` is used now for back compatibility.
+    """
+    if name in {"CODEFORMATTERS", "_CODEFORMATTER_DISTS"}:
+        formatters, formatter_dists = _load_entrypoints(
+            importlib_metadata.entry_points(group="mdformat.codeformatter")
+        )
+        # Cache the values in this module for next time, so that `__getattr__`
+        # is only called once per `name`.
+        global CODEFORMATTERS, _CODEFORMATTER_DISTS
+        CODEFORMATTERS = formatters
+        _CODEFORMATTER_DISTS = formatter_dists
+        return formatters if name == "CODEFORMATTERS" else formatter_dists
+    if name in {"PARSER_EXTENSIONS", "_PARSER_EXTENSION_DISTS"}:
+        extensions, extension_dists = _load_entrypoints(
+            importlib_metadata.entry_points(group="mdformat.parser_extension")
+        )
+        # Cache the value in this module for next time, so that `__getattr__`
+        # is only called once per `name`.
+        global PARSER_EXTENSIONS, _PARSER_EXTENSION_DISTS
+        PARSER_EXTENSIONS = extensions
+        _PARSER_EXTENSION_DISTS = extension_dists
+        return extensions if name == "PARSER_EXTENSIONS" else extension_dists
+    raise AttributeError(f"module {__name__!r} has no attribute {name!r}")