Split typing stubs into a standalone extra

Separate types-cffi/types-setuptools/scipy-stubs into a new `typing`
extra, installable independently by downstream users type-checking
their own code against the DOLFINx API, regardless of which type
checker they use. Drop the now-trivial `mypy` dependency group in
favour of listing `mypy` and `fenics-dolfinx[typing]` directly where
needed. Also install the typing stubs in the ci.yml mypy venv, which
previously checked with no stub coverage at all.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

Author: jhale

.github/workflows/ci.yml

@@ -237,7 +237,10 @@ jobs:
           # dolfinx, petsc4py and the rest.
           apt-get install -y --no-install-recommends python3-venv
           python3 -m venv /tmp/mypy-venv
-          /tmp/mypy-venv/bin/pip install --quiet mypy
+          # types-cffi, types-setuptools and scipy-stubs mirror the `typing`
+          # extra in python/pyproject.toml; installed by name rather than via
+          # '.[typing]' to avoid triggering a full DOLFINx build in this venv.
+          /tmp/mypy-venv/bin/pip install --quiet mypy types-cffi types-setuptools scipy-stubs
           # Distinguishes a broken install from mypy reporting errors.
           /tmp/mypy-venv/bin/mypy --version
           ENV_PYTHON=$(command -v python)

AGENTS.md

@@ -262,10 +262,10 @@ disclosure process.
   for parallel-aware tests where relevant.
 - Run the relevant formatter/linter and the affected test suite before
   calling a change done — don't rely on CI to catch formatting.
-- Dependency groups (`build`, `docs`, `lint`, `mypy`, `test`, `ci` in
+- Dependency groups (`build`, `docs`, `lint`, `test`, `ci` in
   `python/pyproject.toml`) use PEP 735 syntax and require `pip >= 25.1`
   (or another PEP 735-compliant build frontend) for the `--group` flag.
-  `demo`, `optional`, and `petsc4py` remain real
+  `demo`, `optional`, `petsc4py`, and `typing` remain real
   `[project.optional-dependencies]` extras since they are user-facing
   runtime features, or (in the case of `test`) are installed against
   built wheels where dependency groups are unavailable.

python/README.md

@@ -20,9 +20,10 @@ Note that Developer mode is significantly stricter than CMake's default Debug mo
 
 # Type checking with mypy
 
-1. Install DOLFINx Python with the `mypy` dependency group, e.g.:
+1. Install DOLFINx Python with the `typing` extra, plus `mypy` itself
+   (or any other type checker), e.g.:
 
-       pip install --group mypy .
+       pip install mypy '.[typing]'
 
 2. Check with mypy, e.g.:
 

python/pyproject.toml

@@ -46,6 +46,7 @@ optional = [
       "numba; (sys_platform != 'darwin' or platform_machine != 'x86_64') and (sys_platform != 'win32' or platform_machine != 'ARM64')",
 ]
 petsc4py = ["petsc4py"]
+typing = ["types-cffi", "types-setuptools", "scipy-stubs"]
 
 [dependency-groups]
 # Keep in sync with [build-system].requires above (petsc4py is an
@@ -73,15 +74,15 @@ docs = [
       "fenics-dolfinx[demo]",
 ]
 lint = ["ruff", "gersemi"]
-mypy = ["mypy", "types-cffi", "types-setuptools", "scipy-stubs"]
 ci = [
       "pytest-xdist",
+      "mypy",
       { include-group = "build" },
       { include-group = "docs" },
       { include-group = "lint" },
-      { include-group = "mypy" },
       { include-group = "test" },
       "fenics-dolfinx[optional]",
+      "fenics-dolfinx[typing]",
 ]
 
 [tool.scikit-build]