feat: Merge source branch into destination (#1)

.editorconfig

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+root = true
+
+[*]
+charset = utf-8
+end_of_line = lf
+insert_final_newline = true
+trim_trailing_whitespace = true
+
+[*.{md,yml}]
+indent_style = space
+indent_size = 2

.github/workflows/test.yml

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+name: "Test Action"
+
+on:
+  push:
+    branches:
+      - "**"
+
+env:
+  source: "${{ format('{0}-{1}-{2}', 'tests-source', github.run_id, github.run_number) }}"
+  destination: "${{ format('{0}-{1}-{2}', 'tests-destination', github.run_id, github.run_number) }}"
+  example-file: "example-change.test"
+
+jobs:
+  fixtures:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v2
+      - uses: fregante/setup-git-user@v1
+      - run: "git checkout -b ${{ env.destination }}"
+      - run: "git checkout -b ${{ env.source }}"
+      - run: "echo ${{ env.destination }} > ${{ env.example-file }}"
+      - run: "git add example-change.test"
+      - run: "git commit -m 'chore: Add example file'"
+      - run: "git push --set-upstream origin ${{ env.destination }} ${{ env.source }}"
+  merge:
+    runs-on: ubuntu-latest
+    needs:
+      - fixtures
+    steps:
+      - uses: actions/checkout@v2
+        with:
+          ref: "${{ env.destination }}"
+          fetch-depth: 0
+      - name: "Merge example branch ${{ env.source }} into ${{ env.destination }}"
+        uses: ./
+        with:
+          from: "origin/${{ env.source }}"
+  merge-without-changes:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v2
+      - name: Create a branch equal to the current branch
+        run: git branch equal-branch
+      - name: Merge equal branch
+        uses: ./
+        with:
+          from: "equal-branch"
+  assert:
+    runs-on: ubuntu-latest
+    needs:
+      - merge
+    steps:
+      - uses: actions/checkout@v2
+        with:
+          ref: "${{ env.destination }}"
+      - id: example-file
+        run: "echo ::set-output name=body::$(cat ${{ env.example-file }})"
+      - name: Test merge succeeded by verifying source file exists in destination branch
+        uses: pr-mpt/actions-assert@v2
+        with:
+          assertion: npm://@assertions/is-equal
+          expected: "${{ env.destination }}"
+          actual: "${{ steps.example-file.outputs.body }}"
+  clean-up:
+    runs-on: ubuntu-latest
+    needs:
+      - assert
+    steps:
+      - uses: actions/checkout@v2
+      - name: Delete test branches
+        run: git push origin --delete ${{ env.source }} ${{ env.destination }}

LICENSE

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+The MIT License (MIT)
+
+Copyright (c) 2021 > LIMITED and contributors
+
+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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+# Merge Into Current Branch
+
+A GitHub Action for keeping two branches in sync by merging in any `source`
+branch changes using `git` locally -- not the GitHub API.
+
+```
+pr-mpt/actions-merge-branch@v1
+```
+
+## Inputs
+
+| ID | Description | Default | Examples |
+| ---- | ----------- | ------- | -------- |
+| **`from`** | **Branch to merge into the current branch** | **<kbd>required</kbd>** | **`main`** |
+| `author` | Merge commit author | GitHub Actions<sup>[1]</sup> | `Alice <[email protected]>` |
+| `strategy` | Merge strategy with options | `recursive -Xtheirs` | `recursive`<br/>`recursive -Xours` |
+| `push` | Push merge commit to origin? | `true` | `true` `false` |
+
+[1] [`github-actions[bot] <41898282+github-actions[bot]@users.noreply.github.com>`][users/github-actions]
+
+## Outputs
+
+No outputs.
+
+## Examples
+
+### Synchronise `release` branch with `main`
+
+Every push to `main` is synchronised to the `release` branch by merging in any
+changes.
+
+```yaml
+on:
+  push:
+    branches:
+      - "main"
+
+jobs:
+  synchronise-release:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v2
+        with:
+          ref: "release"
+          fetch-depth: 0
+      - uses: pr-mpt/actions-merge-branch@v0
+        with:
+          from: "origin/main"
+```
+
+[users/github-actions]: https://api.github.com/users/github-actions%5Bbot%5D

action.yml

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+name: "Merge Into Current Branch"
+description: "Synchronise branches using Git merge with a (recursive) strategy"
+branding:
+  icon: "git-merge"
+  color: "blue"
+inputs:
+  from:
+    description: "Branch to merge into the current branch"
+    required: true
+  author:
+    description: "Commit author in Git author format"
+    default: "github-actions[bot] <41898282+github-actions[bot]@users.noreply.github.com>"
+    required: true
+  strategy:
+    description: "Merge strategy with any strategy options"
+    default: "recursive -Xtheirs"
+    required: true
+  push:
+    description: "Push commit to origin?"
+    default: "true"
+    required: true
+runs:
+  using: "composite"
+  steps:
+    - name: Set commit author information
+      shell: bash
+      run: |
+        git config user.name "github-actions[bot]"
+        git config user.email "41898282+github-actions[bot]@users.noreply.github.com"
+    - name: Merge ${{ inputs.from }} with ${{ inputs.strategy }} strategy
+      shell: bash
+      run: git merge ${{ inputs.from }} -s ${{ inputs.strategy }} --no-ff --no-commit
+    - name: "Commit changes from ${{ inputs.from }}"
+      shell: bash
+      run: |
+        git diff-index --quiet HEAD \
+        || git commit -am 'Merge branch ${{ inputs.from }}' --author='${{ inputs.author }}'
+    - name: "Push changes from ${{ inputs.from }} to origin"
+      shell: bash
+      run: |
+        if [ "${{ inputs.push }}" == "true" ]
+        then
+          git push origin HEAD
+        fi