Add a new dependency group called dev and add pip-tools to it.

CONTRIBUTING.md

@@ -46,6 +46,7 @@ python -m venv venv
 
 ```bash
 python -m pip install -r test-requirements.txt
+python -m pip install --group dev
 python -m pip install -e .
 hash -r  # This resets shell PATH cache, not necessary on Windows
 ```

pyproject.toml

@@ -65,6 +65,14 @@ reports = ["lxml"]
 install-types = ["pip"]
 faster-cache = ["orjson"]
 
+[dependency-groups]
+dev = [
+  # This is not strictly needed for building mypy per se, but pip-compile from this package is needed if you want to update the requirement files:
+  # (Word on the street is you can also use uv pip compile instead of pip-compile, for this task, if you want.)
+  "pip-tools>=7.5.2", # TODO: once https://github.com/jazzband/pip-tools/pull/2257 lands, change to pip-tools[stable] instead of specifying a version
+  "pip<=25.3", # TODO: once https://github.com/jazzband/pip-tools/pull/2257 lands, remove this dependency line altogether
+]
+
 [project.urls]
 Homepage = "https://www.mypy-lang.org/"
 Documentation = "https://mypy.readthedocs.io/en/stable/index.html"