Implement black and isort-based style checks (#549)

This PR adds `black` and `isort` style formatting and checking, and
requires future code changes to comply with `black` and `isort` styles.

- New workflow `check-style.yml` that runs `black`, `isort` and `flake8`
checks
- Removes `flake8` check from test workflow
- `etstool.py` support for both checking and fixing style, via new
`style` command (with subcommands `fix` and `check`)
- removed old `flake8` command from `etstool.py`

Note: I'm installing the style-related packages from PyPI in
`etstool.py`, so that `etstool.py` and the new workflow are installing
the same package versions. I'm also fixing black to version 23.x so that
we don't suddenly get style failures for the first Black release in 2024
(or later years) - see Black's stability policy here:
https://black.readthedocs.io/en/stable/the_black_code_style/index.html#stability-policy

Closes #527

.flake8

@@ -1,4 +1,5 @@
 [flake8]
+max-line-length = 79
 exclude = build
-ignore = E266, W503
+ignore = E203, E266, W503
 per-file-ignores = */api.py:F401

.github/workflows/check-style.yml

@@ -0,0 +1,20 @@
+name: Run style checks
+
+on: [pull_request, workflow_dispatch]
+
+jobs:
+  style:
+    runs-on: 'ubuntu-latest'
+
+    steps:
+    - uses: actions/checkout@v3
+    - uses: actions/setup-python@v4
+      with:
+        python-version: '3.11'
+        cache: 'pip'
+        cache-dependency-path: '.github/workflows/style-requirements.txt'
+    - run: python -m pip install -r .github/workflows/style-requirements.txt
+    - run: |
+        python -m black --check --diff .
+        python -m isort --check --diff .
+        python -m flake8 .

.github/workflows/style-requirements.txt

@@ -0,0 +1,4 @@
+black ~= 23.0
+flake8
+flake8-ets
+isort

.github/workflows/test-with-edm.yml

@@ -45,9 +45,6 @@ jobs:
         run: python -m pip install -r .github/workflows/bootstrap-requirements.txt
       - name: Install test environment
         run: python etstool.py install --runtime=${{ matrix.runtime }} --toolkit=${{ matrix.toolkit }}
-      - name: Flake8
-        run: python etstool.py flake8 --runtime=${{ matrix.runtime }} --toolkit=${{ matrix.toolkit }}
-        if: runner.os == 'Linux' && matrix.toolkit == 'null'
       - name: Run tests (Ubuntu)
         if: matrix.os == 'ubuntu-latest'
         run: xvfb-run -a python etstool.py test --runtime=${{ matrix.runtime }} --toolkit=${{ matrix.toolkit }}

docs/source/conf.py

@@ -120,7 +120,7 @@
 .. |Message| replace:: :github-demo:`Message <MOTD/acme/motd/message.py>`
 .. |messages.py| replace:: :github-demo:`message.py <MOTD/acme/motd/software_quotes/messages.py>`
 .. |Message of the Day| replace:: :github-demo:`Message of the Day <MOTD>`
-"""   # noqa: E501
+"""  # noqa: E501
 
 # Options for HTML output
 # -----------------------
@@ -234,7 +234,8 @@
 # -- Options for extlinks extension -------------------------------------------
 
 extlinks = {
-    'github-demo': (
-        f'https://github.com/enthought/envisage/tree/{version}/envisage/examples/demo/%s',   # noqa: E501
-        '')
+    "github-demo": (
+        f"https://github.com/enthought/envisage/tree/{version}/envisage/examples/demo/%s",  # noqa: E501
+        "",
+    )
 }

envisage/api.py

@@ -66,6 +66,18 @@
 
 """
 
+from .application import Application
+from .core_plugin import CorePlugin
+from .egg_plugin_manager import EggPluginManager
+from .extension_point import ExtensionPoint
+from .extension_point_binding import (
+    bind_extension_point,
+    ExtensionPointBinding,
+    unbind_extension_point,
+)
+from .extension_point_changed_event import ExtensionPointChangedEvent
+from .extension_provider import ExtensionProvider
+from .extension_registry import ExtensionRegistry
 from .i_application import IApplication
 from .i_extension_point import IExtensionPoint
 from .i_extension_point_user import IExtensionPointUser
@@ -76,28 +88,15 @@
 from .i_plugin_activator import IPluginActivator
 from .i_plugin_manager import IPluginManager
 from .i_service_registry import IServiceRegistry
-
-from .application import Application
-from .core_plugin import CorePlugin
-from .egg_plugin_manager import EggPluginManager
-from .extension_registry import ExtensionRegistry
-from .extension_point import ExtensionPoint
-from .extension_point_binding import (
-    ExtensionPointBinding,
-    bind_extension_point,
-    unbind_extension_point,
-)
-from .extension_provider import ExtensionProvider
-from .extension_point_changed_event import ExtensionPointChangedEvent
 from .ids import (
     BINDINGS,
     COMMANDS,
     PREFERENCES,
     PREFERENCES_CATEGORIES,
     PREFERENCES_PANES,
     SERVICE_OFFERS,
+    TASK_EXTENSIONS,
     TASKS,
-    TASK_EXTENSIONS
 )
 from .import_manager import ImportManager
 from .plugin import Plugin