always throw when add missing helpers

packages/babel-core/src/transformation/file/file.js

@@ -203,6 +203,9 @@ export default class File {
       if (res) return res;
     }
 
+    // make sure that the helper exists
+    helpers.ensure(name);
+
     const uid = (this.declarations[name] = this.scope.generateUidIdentifier(
       name,
     ));

packages/babel-core/test/api.js

@@ -788,4 +788,28 @@ describe("api", function() {
       );
     });
   });
+
+  describe("missing helpers", function() {
+    it("should always throw", function() {
+      expect(() =>
+        babel.transformSync(``, {
+          configFile: false,
+          plugins: [
+            function() {
+              return {
+                visitor: {
+                  Program(path) {
+                    try {
+                      path.pushContainer("body", this.addHelper("fooBar"));
+                    } catch {}
+                    path.pushContainer("body", this.addHelper("fooBar"));
+                  },
+                },
+              };
+            },
+          ],
+        }),
+      ).toThrow();
+    });
+  });
 });

packages/babel-helpers/src/index.js

@@ -280,6 +280,10 @@ export function getDependencies(name: string): $ReadOnlyArray<string> {
   return Array.from(loadHelper(name).dependencies.values());
 }
 
+export function ensure(name: string) {
+  loadHelper(name);
+}
+
 export const list = Object.keys(helpers)
   .map(name => name.replace(/^_/, ""))
   .filter(name => name !== "__esModule");