Initial checkout-merge action

.github/workflows/checkout.yml

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+name: Word Counts
+on:
+  pull_request_target:
+
+jobs:
+  count:
+    name: Word Count
+    permissions:
+      contents: read
+      pull-requests: read
+    runs-on: ubuntu-latest
+    if: "contains(github.event_name, 'pull_request') || github.event_name == 'push'"
+    steps:
+    - name: checkout
+      uses: actions/checkout@v2
+    - name: checkout-merge
+      if: "contains(github.event_name, 'pull_request')"
+      uses: ./
+    - name: check-count
+      if: env.MERGE_FAILED != '1'
+      id: count
+      run: git ls-files -z | xargs -0 wc

LICENSE.txt

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+MIT License
+
+Copyright (c) 2021 Josh Soref
+
+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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+# Checkout Merge
+
+This action synthesizes the merge commit GitHub would give you via `refs/pull/X/merge`.
+
+With GitHub.com's current implementation as of Dec 8, 2021, if it was able to make a
+merge commit, and then a push causes the current state to be not mergable, the
+`refs/pull/X/merge` ref may stick around resulting in confusing output.
+
+With this action, instead, you will not get a merge commit.
+
+If you use [@actions/checkout](https://github.com/actions/checkout) to try to
+check out `refs/pull/X/merge` and it doesn't exist, the action will make three
+attempts (failing each time), and then leave your workflow in a failed state
+and your user with a fairly confusing log.
+
+If you instead use [@actions/checkout](https://github.com/actions/checkout) to
+check out the base commit, then you can use this action to get a merge commit.
+If it isn't able to, it can produce an error message that is hopefully easier
+for users to understand, and allow you to decide whether your workflow should
+✅ or ❌.
+
+## Usage
+
+```yaml
+    - name: checkout
+      uses: actions/checkout@v2
+    - name: checkout-merge
+      if: "contains(github.event_name, 'pull_request')"
+      uses: check-spelling/checkout-merge@main
+      with:
+        # Base for merge (it will be checked out)
+        # Default: ${{ github.event.pull_request.base.sha }}
+        base_ref: ''
+
+        # Head for merge (it will be fetched and merged)
+        # Default: ${{ github.event.pull_request.head.sha }}
+        head_ref: ''
+
+        # Relative path under $GITHUB_WORKSPACE to the repository
+        # Default: .
+        path: ''
+
+        # Suppress reporting errors (consumers would report the message themselves)
+        # By default, this action reports errors in the workflow overview.
+        # If you want to handle reporting the error in some other manner,
+        # you can set this flag.
+        # Default: false
+        do_not_report: ''
+    - if: env.MERGE_FAILED != '1'
+      run: ...
+```
+
+### Outputs
+
+* `message` - Message describing what prevented the action from producing a merge commit.
+
+* `status` - `success` or `failed`
+
+### Environment products
+
+* `$MERGE_FAILED` will be set to `1` if a merge can't be created.

action.yml

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+name: 'Checkout Merge'
+description: 'Generate a merge commit'
+author: 'jsoref'
+branding:
+  icon: 'git-commit'
+  color: 'green'
+inputs:
+  base_ref:
+    description: |
+      This commit will be refetched (to give the merge the best chance of
+      succceeding) and used as the base for the merge.
+    default: ${{ github.event.pull_request.base.sha }}
+    required: false
+  head_ref:
+    description: |
+      This commit will be fetched and merged into the base commit.
+    default: ${{ github.event.pull_request.head.sha }}
+    required: false
+  path:
+    description: 'Relative path under $GITHUB_WORKSPACE to the repository'
+    default: "."
+    required: false
+  do_not_report:
+    description: 'Suppress reporting errors (consumers would report the message themselves)'
+    default: ''
+    required: false
+outputs:
+  message:
+    description: "User facing message about attempt to merge"
+    value: ${{ steps.merge.outputs.message }}
+  status:
+    description: "Whether the merge succeeded"
+    value: ${{ steps.merge.status }}
+runs:
+  using: composite
+  steps:
+    - id: merge
+      shell: bash
+      env:
+        INPUT_BASE_REF: ${{ inputs.base_ref }}
+        INPUT_HEAD_REF: ${{ inputs.head_ref }}
+        INPUT_PATH: ${{ inputs.path }}
+        INPUT_DO_NOT_REPORT: ${{ inputs.do_not_report }}
+      run: ${{ github.action_path }}/merge

merge

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+#!/bin/bash
+report_failure() {
+    echo "MERGE_FAILED=1" >> "$GITHUB_ENV"
+    echo '::set-output name=status::failed'
+    echo "::set-output name=message::$1"
+    if [ -z "$INPUT_DO_NOT_REPORT" ]; then
+        echo "::error ::$1"
+    fi
+    exit 0
+}
+
+cd "$INPUT_PATH" || report_failure "Could not change to input_path ($INPUT_PATH)"
+SENDER=$(jq -r .sender.login "$GITHUB_EVENT_PATH")
+USER_JSON=$(mktemp)
+curl -s "$GITHUB_API_URL/users/$SENDER" -o "$USER_JSON"
+export GIT_AUTHOR_NAME=$(jq -r .name "$USER_JSON")
+export GIT_AUTHOR_EMAIL=$(jq -r '.email // empty' "$USER_JSON")
+if [ -z "$GIT_AUTHOR_EMAIL" ]; then
+    GIT_AUTHOR_EMAIL=$(jq -r '( (.id|tostring) + "+" + .login + "@users.noreply.github.com")' "$GITHUB_EVENT_PATH")
+fi
+export GIT_COMMITTER_NAME=GitHub
+export [email protected]
+git fetch --unshallow origin "$INPUT_BASE_REF" ||
+    report_failure "Can't get history for base_ref ($INPUT_BASE_REF). Please contact support"
+GITHUB_BASE_SHA=$(git rev-parse FETCH_HEAD)
+
+git -c advice.detachedHead=false checkout "$GITHUB_BASE_SHA" || {
+    git status
+    report_failure "Couldn't check out base_ref ($INPUT_BASE_REF); repository is probably dirty."
+}
+
+git fetch origin "$INPUT_HEAD_REF" ||
+    report_failure "Can't get head_ref ($INPUT_HEAD_REF). Please contact support"
+
+GITHUB_HEAD_SHA=$(git rev-parse FETCH_HEAD)
+git merge -m "Merge $GITHUB_HEAD_SHA into $GITHUB_BASE_SHA" FETCH_HEAD ||
+    report_failure "Can't generate merge; there's probably a conflict. Resolve it to get workflow feedback."
+
+echo '::set-output name=status::success'