Fix diff schema on PRs

.github/workflows/schema.yml

@@ -7,40 +7,54 @@ on:
   workflow_dispatch:
     inputs:
       base:
-        description: 'Base ref'
-        default: 'master'
+        description: "Base ref"
+        default: "master"
         required: true
       head:
-        description: 'Head ref'
-        default: 'master'
+        description: "Head ref"
+        default: "master"
         required: true
 
 jobs:
   compute_diff:
     runs-on: ubuntu-latest
 
     steps:
+      # Check out the base commit first and the head commit second. diff-schema
+      # uses the current commit as the head commit.
       - if: github.event_name == 'pull_request'
-        name: Checkout
+        name: Checkout PR base commit
+        uses: actions/checkout@v4
+        with:
+          ref: ${{ github.base_ref }}
+      - if: github.event_name == 'pull_request'
+        name: Checkout PR merge commit
         uses: actions/checkout@v4
 
       - if: github.event_name == 'workflow_dispatch'
-        name: Checkout
+        name: Checkout base commit
         uses: actions/checkout@v4
         with:
           ref: ${{ github.event.inputs.base }}
+      - if: github.event_name == 'workflow_dispatch'
+        name: Checkout head commit
+        uses: actions/checkout@v4
+        with:
+          ref: ${{ github.event.inputs.head }}
 
-      - name: 'Setup Go'
+      - name: "Setup Go"
         uses: actions/setup-go@v4
         with:
           go-version: 1.21.x
 
-      - name: 'Setup Terraform'
+      - name: "Setup Terraform"
         uses: hashicorp/setup-terraform@v2
         with:
           terraform_wrapper: false
 
-      - name: 'Install jd'
+      - name: "Install jd"
         run: go install github.com/josephburnett/jd@latest
 
       - run: make diff-schema
+        env:
+          BASE_COMMIT: ${{ github.event_name == 'pull_request' && github.base_ref || github.event.inputs.base }}

scripts/diff-schema.sh

@@ -1,25 +1,26 @@
 #!/usr/bin/env bash
+set -eo pipefail
 
 source scripts/libschema.sh
 
-BASE_BRANCH="master"
+BASE=${BASE_COMMIT:-"master"}
+CURRENT_BRANCH=$(git rev-parse --abbrev-ref HEAD)
 
-checkout_branch() {
-    local branch=$1
-    echo "Checking out branch: $branch"
-    git checkout $branch
+checkout() {
+    local ref=$1
+    echo "Checking out ref: $ref"
+    git checkout $ref
 }
 
 if [ -n "$(git status --porcelain)" ]; then
     echo "There are uncommitted changes. Please commit them before running this script."
     exit 1
 fi
 
-CURRENT_BRANCH=$(git rev-parse --abbrev-ref HEAD)
 NEW_SCHEMA=$(generate_schema)
-checkout_branch $BASE_BRANCH
+checkout $BASE
 CURRENT_SCHEMA=$(generate_schema)
-checkout_branch $CURRENT_BRANCH
+checkout $CURRENT_BRANCH
 
 set +e
 jd -color "$CURRENT_SCHEMA" "$NEW_SCHEMA"