Add autosquash (#83)

* Add action.yml metadata file

* Add and use autosquash action input

By using an input to trigger whether to rebase with autosquash, we can
enable other kinds of workflow configurations (e.g. other events and
criteria).

* Include autosquash feature in README installation section

README.md

@@ -18,8 +18,12 @@ on:
 jobs:
   rebase:
     name: Rebase
-    if: github.event.issue.pull_request != '' && contains(github.event.comment.body, '/rebase')
-    runs-on: ubuntu-latest
+    if: >-
+      github.event.issue.pull_request != '' && 
+      (
+        contains(github.event.comment.body, '/rebase') || 
+        contains(github.event.comment.body, '/autosquash')
+      )    runs-on: ubuntu-latest
     steps:
       - name: Checkout the latest code
         uses: actions/checkout@v2
@@ -28,6 +32,8 @@ jobs:
           fetch-depth: 0 # otherwise, you will fail to push refs to dest repo
       - name: Automatic Rebase
         uses: cirrus-actions/rebase@1.5
+        with:
+          autosquash: ${{ contains(github.event.comment.body, '/autosquash') || contains(github.event.comment.body, '/rebase-autosquash') }}
         env:
           GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}
 ```

action.yml

@@ -0,0 +1,14 @@
+name: Automatic Rebase
+description: Automatically rebases PR on '/rebase' comment
+maintainer: Cirrus Labs
+runs:
+  using: 'docker'
+  image: 'Dockerfile'
+inputs:
+  autosquash:
+    description: Should the rebase autosquash fixup and squash commits
+    required: false
+    default: false
+branding:
+  icon: git-pull-request
+  color: purple

entrypoint.sh

@@ -100,7 +100,11 @@ git fetch fork $HEAD_BRANCH
 
 # do the rebase
 git checkout -b fork/$HEAD_BRANCH fork/$HEAD_BRANCH
-git rebase origin/$BASE_BRANCH
+if [[ $INPUT_AUTOSQUASH -eq 'true' ]]; then
+	GIT_SEQUENCE_EDITOR=: git rebase -i --autosquash origin/$BASE_BRANCH
+else
+	git rebase origin/$BASE_BRANCH
+fi
 
 # push back
 git push --force-with-lease fork fork/$HEAD_BRANCH:$HEAD_BRANCH