fix: Switch to git to get all commits

The ${GITHUB_EVENT_PATH} JSON file only shows diff since last push,
not all commits for the entire feature branch.

.github/workflows/git.yml

@@ -7,5 +7,6 @@ jobs:
     runs-on: ubuntu-18.04
 
     steps:
+    - uses: actions/checkout@master
     - name: Block Fixup Merge
       uses: 13rac1/block-fixup-merge-action@master

Dockerfile

@@ -2,7 +2,7 @@ FROM alpine:3.10
 
 RUN apk add --no-cache \
   bash \
-  jq
+  git
 COPY entrypoint.sh /entrypoint.sh
 
 CMD ["/entrypoint.sh"]

entrypoint.sh

@@ -2,12 +2,16 @@
 set -e
 set -o pipefail
 main() {
-  echo "Current branch: ${GITHUB_REF}"
+  echo "Current ref: ${GITHUB_REF}"
+  echo "Current branch: ${GITHUB_REF:11}"
+  # Using git directly because the $GITHUB_EVENT_PATH file only shows commits in
+  # most recent push.
 
-  FIXUP_COUNT=`jq .commits[].message ${GITHUB_EVENT_PATH} | grep fixup! | wc -l || true`
+  FIXUP_COUNT=`git log --pretty=format:%s origin/master..origin/${GITHUB_REF:11} | grep fixup! | wc -l || true`
   echo "Fixup! commits: ${FIXUP_COUNT}"
   if [ "$FIXUP_COUNT" -gt "0" ]; then
-    echo "Found Fixup! commits, failing"
+    git log --pretty=format:%s origin/master..origin/${GITHUB_REF:11} | grep fixup!
+    echo "failing..."
     exit 1
   fi
 }