Centralise linting config in .pre-commit-config.yaml (#15210)

This makes it easier to maintain the configurations for the various
linting tools we use in CI. It also makes it easier for contributors to
run the linting tools locally. `black`, `isort` and `flake8` are all
very fast checks, so I think it makes sense to just run them all
together in `runtests.py`.

With this PR, the following three invocations will all be equivalent:

```
pre-commit run --all-files
python runtests.py lint
tox -e lint
```

Closes #15076

Author: AlexWaygood

runtests.py

@@ -50,9 +50,7 @@
     # Self type check
     "self": [executable, "-m", "mypy", "--config-file", "mypy_self_check.ini", "-p", "mypy"],
     # Lint
-    "lint": ["flake8", "-j3"],
-    "format-black": ["black", "."],
-    "format-isort": ["isort", "."],
+    "lint": ["pre-commit", "run", "--all-files"],
     # Fast test cases only (this is the bulk of the test suite)
     "pytest-fast": ["pytest", "-q", "-k", f"not ({' or '.join(ALL_NON_FAST)})"],
     # Test cases that invoke mypy (with small inputs)

test-requirements.txt

@@ -8,6 +8,7 @@ flake8-bugbear==23.3.23; python_version >= "3.8" # must match version in .pre-co
 flake8-noqa==1.3.1; python_version >= "3.8"      # must match version in .pre-commit-config.yaml
 isort[colors]==5.12.0; python_version >= "3.8"   # must match version in .pre-commit-config.yaml
 lxml>=4.9.1; (python_version<'3.11' or sys_platform!='win32') and python_version<'3.12'
+pre-commit
 psutil>=4.0
 # pytest 6.2.3 does not support Python 3.10
 pytest>=6.2.4

tox.ini

@@ -41,10 +41,7 @@ commands =
 [testenv:lint]
 description = check the code style
 skip_install = true
-commands =
-    flake8 {posargs}
-    black --check --diff --color .
-    isort --check --diff --color .
+commands = pre-commit run --all-files --show-diff-on-failure
 
 [testenv:type]
 description = type check ourselves