Only report the first CheckoutWrongHead lint error

src/actions-util.test.ts

@@ -432,3 +432,27 @@ on:
 
   t.deepEqual(errors, []);
 });
+
+test("validateWorkflow() should only report the first CheckoutWrongHead", (t) => {
+  const errors = actionsutil.validateWorkflow(
+    yaml.safeLoad(`
+name: "CodeQL"
+on:
+  push:
+    branches: [master]
+  pull_request:
+    # The branches below must be a subset of the branches above
+    branches: [master]
+jobs:
+  test:
+    steps:
+      - run: "git checkout HEAD^2"
+      - run: "git checkout HEAD^2"
+      - run: "git checkout HEAD^2"
+      - run: "git checkout HEAD^2"
+      - run: "git checkout HEAD^2"
+`)
+  );
+
+  t.deepEqual(errors, [actionsutil.WorkflowErrors.CheckoutWrongHead]);
+});

src/actions-util.ts

@@ -212,7 +212,7 @@ export function validateWorkflow(doc: Workflow): CodedError[] {
   const errors: CodedError[] = [];
 
   // .jobs[key].steps[].run
-  for (const job of Object.values(doc?.jobs || {})) {
+  outer: for (const job of Object.values(doc?.jobs || {})) {
     if (Array.isArray(job?.steps)) {
       for (const step of job?.steps) {
         // this was advice that we used to give in the README
@@ -222,6 +222,7 @@ export function validateWorkflow(doc: Workflow): CodedError[] {
         // and avoid some race conditions
         if (step?.run === "git checkout HEAD^2") {
           errors.push(WorkflowErrors.CheckoutWrongHead);
+          break outer;
         }
       }
     }