Make black with line length 80 repo's code style

Provide a consistent formatting style and tox commands to lint and
format.

Bug: b/267675342
Change-Id: I33ddfe07af8473f4334c347d156246bfb66d4cfe
Reviewed-on: https://gerrit-review.googlesource.com/c/git-repo/+/362954
Reviewed-by: Josip Sokcevic <sokcevic@google.com>
Reviewed-by: Mike Frysinger <vapier@google.com>
Tested-by: Gavin Mak <gavinmak@google.com>
Commit-Queue: Gavin Mak <gavinmak@google.com>

.flake8

@@ -1,15 +1,10 @@
 [flake8]
-max-line-length=100
-ignore=
-    # E111: Indentation is not a multiple of four
-    E111,
-    # E114: Indentation is not a multiple of four (comment)
-    E114,
+max-line-length = 80
+extend-ignore =
+    # E203: Whitespace before ':'
+    # See https://github.com/PyCQA/pycodestyle/issues/373
+    E203,
     # E402: Module level import not at top of file
     E402,
     # E731: do not assign a lambda expression, use a def
     E731,
-    # W503: Line break before binary operator
-    W503,
-    # W504: Line break after binary operator
-    W504

SUBMITTING_PATCHES.md

@@ -4,7 +4,6 @@
 
  - Make small logical changes.
  - [Provide a meaningful commit message][commit-message-style].
- - Check for coding errors and style nits with flake8.
  - Make sure all code is under the Apache License, 2.0.
  - Publish your changes for review.
  - Make corrections if requested.
@@ -39,17 +38,26 @@ If your description starts to get too long, that's a sign that you
 probably need to split up your commit to finer grained pieces.
 
 
-## Check for coding errors and style violations with flake8
+## Linting and formatting code
 
-Run `flake8` on changed modules:
+Lint any changes by running:
+```sh
+$ tox -e lint -- file.py
+```
 
-    flake8 file.py
+And format with:
+```sh
+$ tox -e format -- file.py
+```
 
-Note that repo generally follows [Google's Python Style Guide] rather than
-[PEP 8], with a couple of notable exceptions:
+Or format everything:
+```sh
+$ tox -e format
+```
 
-* Indentation is at 2 columns rather than 4
-* The maximum line length is 100 columns rather than 80
+Repo uses [black](https://black.readthedocs.io/) with line length of 80 as its
+formatter and flake8 as its linter. Repo also follows
+[Google's Python Style Guide].
 
 There should be no new errors or warnings introduced.
 

pyproject.toml

@@ -0,0 +1,18 @@
+# Copyright 2023 The Android Open Source Project
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#      http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+[tool.black]
+line-length = 80
+# NB: Keep in sync with tox.ini.
+target-version = ['py36', 'py37', 'py38', 'py39', 'py310']

tox.ini

@@ -15,7 +15,7 @@
 # https://tox.readthedocs.io/
 
 [tox]
-envlist = py36, py37, py38, py39, py310
+envlist = lint, py36, py37, py38, py39, py310
 
 [gh-actions]
 python =
@@ -35,5 +35,23 @@ setenv =
     GIT_COMMITTER_NAME = Repo test committer
     EMAIL = repo@gerrit.nodomain
 
+[testenv:lint]
+skip_install = true
+deps =
+    black
+    flake8
+commands =
+    black --check {posargs:.}
+    flake8
+
+[testenv:format]
+skip_install = true
+deps =
+    black
+    flake8
+commands =
+    black {posargs:.}
+    flake8
+
 [pytest]
 timeout = 300