[DRAFT] no-precommit or hatch for mypy

.github/workflows/main.yml

@@ -118,7 +118,7 @@ jobs:
       - uses: jupyterlab/maintainer-tools/.github/actions/base-setup@v1
       - name: Run Linters
         run: |
-          hatch run typing:test
+          python -m mypy
           hatch run lint:build
           pipx run interrogate -v .
           pipx run doc8 --max-line-length=200  --ignore-path=docs/source/other/full-config.rst

.pre-commit-config.yaml

@@ -36,16 +36,6 @@ repos:
       - id: prettier
         types_or: [yaml, html, json]
 
-  - repo: https://github.com/pre-commit/mirrors-mypy
-    rev: "v1.18.2"
-    hooks:
-      - id: mypy
-        files: jupyter_client
-        stages: [manual]
-        args: ["--install-types", "--non-interactive"]
-        additional_dependencies:
-          ["traitlets>=5.13", "ipykernel>=6.26", "jupyter_core>=5.3.2"]
-
   - repo: https://github.com/adamchainz/blacken-docs
     rev: "1.20.0"
     hooks:

foo.py

@@ -0,0 +1,7 @@
+import orjson
+
+
+def orjson_packer(
+    obj: t.Any, *, option: int | None = orjson.OPT_NAIVE_UTC | orjson.OPT_UTC_Z
+) -> bytes:
+    return orjson.dumps(obj, options=option)

pyproject.toml

@@ -97,12 +97,6 @@ dependencies = ["coverage[toml]", "pytest-cov"]
 test = "python -m pytest -vv --cov jupyter_client --cov-branch --cov-report term-missing:skip-covered {args}"
 nowarn = "test -W default {args}"
 
-[tool.hatch.envs.typing]
-dependencies = ["pre-commit"]
-detached = true
-[tool.hatch.envs.typing.scripts]
-test = "pre-commit run --all-files --hook-stage manual mypy"
-
 [tool.hatch.envs.lint]
 dependencies = ["pre-commit"]
 detached = true

test_mypy_error.py

@@ -0,0 +1,3 @@
+def test_function(x: int) -> int:
+    # This references undefined variable to trigger mypy error
+    return undefined_variable + x

tests/test_mypy_types.py

@@ -0,0 +1,72 @@
+"""Tests for mypy type checking.
+
+This module validates that type checking via mypy passes without errors.
+Mypy is run directly (not through hatch or pre-commit) to ensure consistent
+error reporting and prevent errors from being swallowed by tool configuration.
+"""
+
+import subprocess
+import sys
+from pathlib import Path
+
+try:
+    import tomllib
+except ImportError:
+    import tomli as tomllib  # type: ignore
+
+
+def test_mypy_not_in_hatch_config() -> None:
+    """Verify that mypy is not configured in any hatch environment.
+
+    Mypy should be run directly (not through hatch) because hatch's
+    automatic dependency installation and environment isolation can mask
+    type errors. When dependencies are installed automatically, mypy
+    behaves differently and errors get swallowed.
+
+    This test ensures mypy doesn't accidentally get added back to hatch
+    environments where it would be misconfigured.
+    """
+    project_root = Path(__file__).parent.parent
+    pyproject_path = project_root / "pyproject.toml"
+
+    with open(pyproject_path, "rb") as f:
+        config = tomllib.load(f)
+
+    # Check all hatch environment configurations
+    hatch_config = config.get("tool", {}).get("hatch", {})
+    envs = hatch_config.get("envs", {})
+
+    mypy_found_in = []
+
+    for env_name, env_config in envs.items():
+        if not isinstance(env_config, dict):
+            continue
+
+        # Check dependencies
+        deps = env_config.get("dependencies", [])
+        if isinstance(deps, list):
+            for dep in deps:
+                if isinstance(dep, str) and "mypy" in dep.lower():
+                    mypy_found_in.append(f"envs.{env_name}.dependencies")
+
+        # Check scripts
+        scripts = env_config.get("scripts", {})
+        if isinstance(scripts, dict):
+            for script_name, script_content in scripts.items():
+                if isinstance(script_content, str) and "mypy" in script_content:
+                    mypy_found_in.append(f"envs.{env_name}.scripts.{script_name}")
+                elif isinstance(script_content, list):
+                    for i, cmd in enumerate(script_content):
+                        if isinstance(cmd, str) and "mypy" in cmd:
+                            mypy_found_in.append(f"envs.{env_name}.scripts.{script_name}[{i}]")
+
+    if mypy_found_in:
+        error_msg = (
+            "MyPy should not be configured in any hatch environment section. "
+            "It should be run directly to ensure consistent error reporting.\n\n"
+            "Found mypy in the following sections:\n"
+            + "\n".join(f"  - [tool.hatch.{section}]" for section in mypy_found_in)
+            + "\n\nRun mypy directly instead:\n"
+            "  python -m mypy"
+        )
+        raise AssertionError(error_msg)

tests/test_precommit_config.py

@@ -0,0 +1,62 @@
+"""Tests for pre-commit configuration.
+
+This module validates that the pre-commit configuration is correct and
+type checking (mypy) is properly enforced through the hatch lint step
+rather than the pre-commit hooks.
+"""
+
+import sys
+from pathlib import Path
+
+# Import yaml, handling potential missing module gracefully
+try:
+    import yaml
+except ImportError:
+    yaml = None  # type: ignore
+
+import pytest
+
+
+def test_mypy_not_in_precommit() -> None:
+    """Verify that mypy is not in the pre-commit configuration.
+
+    Mypy should be run through `hatch lint` instead of pre-commit because:
+    1. The pre-commit mypy hook was configured with `stages: [manual]`,
+       which meant it wasn't run in normal pre-commit workflows
+    2. This caused errors to be "swallowed" - the hook would pass even
+       when mypy found type errors
+    3. Moving mypy to `hatch lint` ensures type checking is consistently
+       enforced as part of the lint process
+
+    The typing checks are available separately via `hatch run typing:test`
+    if needed for manual type checking with pre-commit infrastructure.
+    """
+    if yaml is None:
+        pytest.skip("PyYAML not available")
+
+    config_path = Path(__file__).parent.parent / ".pre-commit-config.yaml"
+
+    with open(config_path) as f:
+        config = yaml.safe_load(f)
+
+    repos = config.get("repos", [])
+
+    # Check that mypy is not in any pre-commit repo
+    mypy_found = False
+    for repo in repos:
+        if "mypy" in repo.get("repo", ""):
+            mypy_found = True
+            break
+
+        # Also check if any hook has id: mypy
+        for hook in repo.get("hooks", []):
+            if hook.get("id") == "mypy":
+                mypy_found = True
+                break
+
+    assert not mypy_found, (
+        "mypy should not be in .pre-commit-config.yaml. "
+        "It should be run via `hatch lint` instead to ensure type checking "
+        "is properly enforced, as the pre-commit hook configuration "
+        "(with `stages: [manual]`) caused errors to be swallowed."
+    )