Improve relative execution tracking in fn exprs (#15275)

packages/babel-plugin-transform-block-scoping/test/fixtures/tdz/function-expression/input.js

@@ -0,0 +1,5 @@
+f(() => a);
+let a;
+
+let b;
+f(() => b);

packages/babel-plugin-transform-block-scoping/test/fixtures/tdz/function-expression/output.js

@@ -0,0 +1,5 @@
+var a = babelHelpers.temporalUndefined;
+f(() => babelHelpers.temporalRef(a, "a"));
+a = void 0;
+var b;
+f(() => b);

packages/babel-traverse/src/path/introspection.ts

@@ -267,7 +267,10 @@ export function willIMaybeExecuteBefore(
 }
 
 function getOuterFunction(path: NodePath) {
-  return (path.scope.getFunctionParent() || path.scope.getProgramParent()).path;
+  return (
+    path.parentPath.scope.getFunctionParent() ||
+    path.parentPath.scope.getProgramParent()
+  ).path;
 }
 
 function isExecutionUncertain(type: t.Node["type"], key: string) {
@@ -445,10 +448,12 @@ function _guessExecutionStatusRelativeToDifferentFunctionsInternal(
   target: NodePath,
   cache: ExecutionStatusCache,
 ): RelativeExecutionStatus {
-  if (
-    !target.isFunctionDeclaration() ||
-    target.parentPath.isExportDeclaration()
-  ) {
+  if (!target.isFunctionDeclaration()) {
+    if (base._guessExecutionStatusRelativeTo(target) === "before") {
+      return "before";
+    }
+    return "unknown";
+  } else if (target.parentPath.isExportDeclaration()) {
     return "unknown";
   }
 

packages/babel-traverse/test/introspection.js

@@ -213,4 +213,20 @@ describe("path/introspection", function () {
       expect(reference.referencesImport("source", "*")).toBe(false);
     });
   });
+
+  describe("_guessExecutionStatusRelativeTo", function () {
+    it("works withs paths in function expressions", () => {
+      const program = getPath(`
+        a;
+        f(() => b);
+        c;
+      `);
+      const a = program.get("body.0.expression");
+      const b = program.get("body.1.expression.arguments.0.body");
+      const c = program.get("body.2.expression");
+
+      expect(a._guessExecutionStatusRelativeTo(b)).toBe("before");
+      expect(c._guessExecutionStatusRelativeTo(b)).toBe("unknown");
+    });
+  });
 });