Move lint dependencies to extras

CONTRIBUTING.md

@@ -17,9 +17,9 @@ https://help.github.com/articles/using-pull-requests/) to ask us to pull your
 changes into our repo.
 
 Some other points to follow:
- 
+
  * Please base your changes on the `develop` branch.
-  
+
  * Please follow the [code style requirements](#code-style).
 
  * Please include a [changelog entry](#changelog) with each PR.
@@ -46,7 +46,7 @@ locally. You'll need python 3.6 or later, and to install a number of tools:
 
 ```
 # Install the dependencies
-pip install -U black flake8 flake8-comprehensions isort
+pip install -e ".[lint]"
 
 # Run the linter script
 ./scripts-dev/lint.sh

changelog.d/8330.misc

@@ -0,0 +1 @@
+Move lint-related dependencies to package-extra field, update CONTRIBUTING.md to utilise this.

synapse/python_dependencies.py

@@ -104,6 +104,13 @@
     # hiredis is not a *strict* dependency, but it makes things much faster.
     # (if it is not installed, we fall back to slow code.)
     "redis": ["txredisapi>=1.4.7", "hiredis"],
+    # We pin black so that our tests don't start failing on new releases.
+    "lint": [
+        "isort<=5.0.3",
+        'black==19.10b0;python_version>"3.5"',
+        "flake8-comprehensions",
+        "flake8",
+    ],
 }
 
 ALL_OPTIONAL_REQUIREMENTS = set()  # type: Set[str]

tox.ini

@@ -118,20 +118,14 @@ commands =
     check-manifest
 
 [testenv:check_codestyle]
-skip_install = True
-deps =
-    flake8
-    flake8-comprehensions
-    # We pin so that our tests don't start failing on new releases of black.
-    black==19.10b0
+extras = lint
 commands =
     python -m black --check --diff .
     /bin/sh -c "flake8 synapse tests scripts scripts-dev contrib synctl {env:PEP8SUFFIX:}"
     {toxinidir}/scripts-dev/config-lint.sh
 
 [testenv:check_isort]
-skip_install = True
-deps = isort==5.0.3
+extras = lint
 commands = /bin/sh -c "isort -c --df --sp setup.cfg synapse tests scripts-dev scripts"
 
 [testenv:check-newsfragment]