[CI] Add a pre-commit trailing blanks linter via tox

- add a pre-commit yaml configuration file with a basic profile to
  remove trailing blanks
- add a rule to exclude from its scope
  - patch files (generated from git diff)
    Trailing blanks are part of their syntax.
  - .conf files in the src folder
    Their trailing blanks removal make some tests fail during build.
  - jinja templates in docker folder
    Though trailing blank should not be part of the jinja2 syntax,
    these files use a known hack that requires trailing blanks.
    Their removal makes build fail.
- create a tox configuration to run/install/uninstall/autoupdate
  pre-commit in a python venv
- create a tox profile for the CI
  to run pre-commit only on files modified since this commit
- add a shell script to ease running pre-commit inside various CI

Issue sonic-net#15114

Signed-off-by: Guillaume Lambert <guillaume.lambert@orange.com>

.pre-commit-config.yaml

@@ -0,0 +1,8 @@
+---
+repos:
+  - repo: https://github.com/pre-commit/pre-commit-hooks
+    rev: v4.4.0
+    hooks:
+      - id: trailing-whitespace
+        exclude: '\.patch$|^src/.*\.conf$|^files/.*\.j2$'
+        #TODO fix the few files in ./files and ./src folders whose clean-up makes build fail

scripts/tox_entry_point.sh

@@ -0,0 +1,28 @@
+#!/bin/sh
+
+# Copyright © 2023 Orange
+#
+# 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.
+
+cd $(dirname $0)
+cd ..
+export DEBIAN_FRONTEND=noninteractive
+sudo -E apt-get -qq -y update 2>&1 >/dev/null || \
+        apt-get -qq -y update 2>&1 >/dev/null
+sudo -E apt-get -qq -y install git gzip python3-pip tox >&1 >/dev/null || \
+        apt-get -qq -y install git gzip python3-pip tox >&1 >/dev/null
+# Run tests inside a python tox virtual environment
+# the PBR_VERSION variable is normally not needed and is here to avoid troubles in some CI
+# that raise an exception for versioning w/o sdsit tarball or access to an upstream git repo
+export PBR_VERSION=5.10.0
+tox

setup.cfg

@@ -0,0 +1,7 @@
+[metadata]
+name = sonic_linters
+home_page = https://github.com/sonic-net/sonic-buildimage
+
+[files]
+packages = sonic_linters
+

setup.py

@@ -0,0 +1,9 @@
+#!/usr/bin/env python
+
+import setuptools
+
+# PBR doc available at https://docs.openstack.org/pbr/latest/
+
+setuptools.setup(
+    setup_requires=['pbr'],
+    pbr=True)

tox.ini

@@ -0,0 +1,47 @@
+[tox]
+minversion = 3.7.0
+envlist =
+    pre-commit-ci
+skipsdist = true
+
+[testenv]
+passenv = http_proxy HTTP_PROXY https_proxy HTTPS_PROXY no_proxy NO_PROXY
+usedevelop = true
+basepython = python3
+deps =
+  setuptools>=7.0
+
+[testenv:pre-commit-install]
+basepython = python3
+deps = pre-commit
+commands =
+    pre-commit install
+    pre-commit install --hook-type commit-msg
+
+[testenv:pre-commit-uninstall]
+basepython = python3
+deps = pre-commit
+commands =
+    pre-commit uninstall
+    pre-commit uninstall --hook-type commit-msg
+
+[testenv:pre-commit-autoupdate]
+basepython = python3
+deps = pre-commit
+commands =
+    pre-commit autoupdate
+
+[testenv:pre-commit]
+basepython = python3
+deps = pre-commit
+passenv = HOME
+commands =
+    pre-commit run --all-files
+
+[testenv:pre-commit-ci]
+basepython = python3
+deps = pre-commit
+passenv = HOME
+commands =
+    pre-commit run --all-files --show-diff-on-failure --from-ref a73d443c1d02698d9f3e030947c469677798bd32 --to-ref HEAD
+