✨ Template | pre-commit: Add mypy type checking

Generated packages can now opt into mypy via a new `type_check` Copier question (none /
loose / strict, default loose).

The hook is a local pre-commit entry with `language: system`, so mypy runs inside the
hatch `pre-commit` environment and sees every installed project dependency — no
`additional_dependencies` list to maintain. `mypy` is added to the `pre-commit`
optional-deps group when type checking is enabled.

Two `[tool.mypy]` presets:

- `loose` turns on `warn_unused_ignores`, `warn_redundant_casts`, and
  `warn_unreachable`
- `strict` enables mypy's built-in `strict = true`.

Both scope checking to `src/` and pin `python_version = "3.10"` to match
`requires-python`.

CI coverage is automatic — the existing `hatch run pre-commit:run --all-files` job picks
up the new hook.

Author: mbercx

copier.yml

@@ -22,6 +22,15 @@ doc_deploy:
     {%- endif %}
   default: nowhere
 
+type_check:
+  type: str
+  help: 'How strict should type checking be?'
+  choices:
+    - none
+    - loose
+    - strict
+  default: loose
+
 _subdirectory: template
 _message_after_copy: |
   The `{{package_name}}` package has been created successfully!

template/.pre-commit-config.yaml.jinja

@@ -9,3 +9,14 @@ repos:
       - id: ruff-format
         name: Format with Ruff
         types_or: [ python, pyi ]
+{% if type_check != 'none' %}
+  - repo: local
+    hooks:
+      - id: mypy
+        name: Type-check with mypy
+        entry: mypy
+        language: system
+        types: [ python ]
+        require_serial: true
+        files: ^src/
+{% endif -%}

template/pyproject.toml.jinja

@@ -36,6 +36,10 @@ tests = [
 ]
 pre-commit = [
   "pre-commit"
+{%- if type_check != 'none' -%}
+  ,
+  "mypy"
+{%- endif %}
 ]
 
 [dependency-groups]
@@ -86,3 +90,18 @@ lint.ignore = [
 ]
 [tool.ruff.lint.per-file-ignores]
 "tests/**/*.py" = ["INP001", "S101"]
+{%- if type_check == 'loose' %}
+
+[tool.mypy]
+python_version = "3.10"
+files = ["src"]
+warn_unused_ignores = true
+warn_redundant_casts = true
+warn_unreachable = true
+{%- elif type_check == 'strict' %}
+
+[tool.mypy]
+python_version = "3.10"
+files = ["src"]
+strict = true
+{%- endif %}