Add: first version of a flake8 checker with annotation (#1)

This uses a ProblemMatcher together with GitHub Actions 'add-matcher'.
To allow warnings/errors to show up correctly, a 'sed' is used to handled that correctly.

.github/workflows/testing.yml

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+name: Testing
+
+on: [pull_request]
+
+jobs:
+  run_action:
+    name: Test run action
+    runs-on: ubuntu-latest
+    steps:
+    - uses: actions/checkout@v1
+    - uses: ./
+      with:
+        path: example
+        only_warn: 1

Dockerfile

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+FROM python:3.8-alpine
+
+COPY LICENSE \
+        README.md \
+        entrypoint.sh \
+        flake8-matcher.json \
+        requirements.txt \
+        /code/
+
+RUN pip install -r /code/requirements.txt
+
+ENTRYPOINT ["/code/entrypoint.sh"]
+CMD []

LICENSE

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+The MIT License
+
+Copyright (c) 2019, Patric "TrueBrain" Stout
+
+Permission is hereby granted, free of charge, to any person obtaining a copy
+of this software and associated documentation files (the "Software"), to deal
+in the Software without restriction, including without limitation the rights
+to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+copies of the Software, and to permit persons to whom the Software is
+furnished to do so, subject to the following conditions:
+
+The above copyright notice and this permission notice shall be included in
+all copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+THE SOFTWARE.

README.md

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+# Flake8 with GitHub Actions -- including annotations for Pull Requests
+
+This GitHub Actions runs flake8 over your code.
+Any warnings or errors will be annoted in the Pull Request.
+
+## Example usages
+
+```
+uses: TrueBrain/actions-flake8@master
+```

action.yml

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+name: 'Flake8'
+description: 'Flake8 with annotations for Pull Request'
+inputs:
+  path:
+    description: 'Path to run flake8 in'
+    requred: false
+    default: ''
+  only_warn:
+    description: 'If set, only warn, never error'
+    requred: false
+    default: ''
+runs:
+  using: 'docker'
+  image: 'Dockerfile'

entrypoint.sh

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+#!/bin/sh
+
+# Copy the matcher to the host system; otherwise "add-matcher" can't find it.
+cp /code/flake8-matcher.json /github/workflow/flake8-matcher.json
+echo "::add-matcher::${RUNNER_TEMP}/_github_workflow/flake8-matcher.json"
+
+# Run flake8. We add 'error/warning' as GitHub Actions ProblemMatcher needs
+# the text 'error/warning' to know how to classify it.
+# The weird piping is needed because we want to get the exitcode from flake8,
+# but there is no other good universal way of doing so.
+# e.g. PIPESTATUS and pipestatus only work in bash/zsh respectively.
+exec 5>&1
+res=`{ { flake8 ${INPUT_PATH}; echo $? 1>&4; } | sed -r 's/: ([^W][0-9][0-9][0-9])/: error: \1/;s/: (W[0-9][0-9][0-9])/: warning: \1/' 1>&5; } 4>&1`
+
+# Remove the matcher, so no other jobs hit it.
+echo "::remove-matcher owner=flake8::"
+
+# If we are in warn-only mode, return always as if we pass
+if [ -n "${INPUT_ONLY_WARN}" ]; then
+    exit 0
+else
+    exit $res
+fi

example/example.py

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+
+def test():
+    pass
+def test() :
+	pass

flake8-matcher.json

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+{
+    "problemMatcher": [
+        {
+            "owner": "flake8",
+            "pattern": [
+                {
+                    "regexp": "^([^:]*):(\\d+):(\\d+): (error|warning): (\\w\\d\\d\\d) (.*)$",
+                    "file": 1,
+                    "line": 2,
+                    "column": 3,
+                    "severity": 4,
+                    "message": 6
+                }
+            ]
+        }
+    ]
+}

requirements.txt

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+flake8==3.7.9