feat: throw error when targets are used with regenerator

- the polyfill-regenerator plugin actually does not support targets and
  does not use them
  - it instead detects whether the `regeneratorRuntime` variable has
    been injected by `transform-regenerator`, which already supports
    targets
  - so targets are not needed twice in that sense

- instead of silently ignoring the targets option, error out when it is
  given as it is an unsupported option
  - this should hopefully make it easier for developers to realize
    what's going on when debugging issues with this (as I did)
  - but it shouldn't error if top-level targets are configured, as those
    aren't specific to this plugin
    - caveat: if a user specifies both and they are the same, there's
      currently no way to tell, so it won't error in that case
      - but will catch the common mistake

- add a test for this new error as well as a basic "harness" based on
  the one in `define-polyfill-provider`
  - remove `targets` from any fixtures that had them for this polyfill
    so that this test passes
    - and because they didn't do anything previously anyway
- also add a test that ensures that top-level targets still work
  - and change some fixtures to use top-level targets instead, ensuring
    that those fixture tests still pass as well

packages/babel-plugin-polyfill-regenerator/src/index.ts

@@ -8,7 +8,16 @@ type Options = {
   };
 };
 
-export default defineProvider<Options>(({ debug }, options) => {
+export default defineProvider<Options>(({ debug, targets, babel }, options) => {
+  if (!shallowEqual(targets, babel.targets())) {
+    throw new Error(
+      "This plugin does not use the targets option. Only preset-env's targets" +
+        " or top-level targets need to be configured for this plugin to work." +
+        " See https://github.com/babel/babel-polyfills/issues/36 for more" +
+        " details",
+    );
+  }
+
   const { [runtimeCompat]: { useBabelRuntime } = { useBabelRuntime: "" } } =
     options;
 
@@ -39,3 +48,7 @@ export default defineProvider<Options>(({ debug }, options) => {
 
 const isRegenerator = meta =>
   meta.kind === "global" && meta.name === "regeneratorRuntime";
+
+function shallowEqual(obj1: any, obj2: any) {
+  return JSON.stringify(obj1) === JSON.stringify(obj2);
+}

packages/babel-plugin-polyfill-regenerator/test/fixtures/usage-global/generator-native-support/options.json

@@ -3,10 +3,7 @@
     [
       "@@/polyfill-regenerator",
       {
-        "method": "usage-global",
-        "targets": {
-          "node": 6
-        }
+        "method": "usage-global"
       }
     ]
   ],
@@ -21,4 +18,4 @@
       }
     ]
   ]
-}
+}

packages/babel-plugin-polyfill-regenerator/test/fixtures/usage-pure/all/options.json

@@ -7,4 +7,4 @@
       }
     ]
   ]
-}
+}

packages/babel-plugin-polyfill-regenerator/test/fixtures/usage-pure/options.json

@@ -7,4 +7,4 @@
       }
     ]
   ]
-}
+}

packages/babel-plugin-polyfill-regenerator/test/fixtures/usage-pure/preset-env-supported/options.json

@@ -1,24 +1,21 @@
 {
+  "targets": {
+    "chrome": 70
+  },
   "plugins": [
     [
       "@@/polyfill-regenerator",
       {
-        "method": "usage-pure",
-        "targets": {
-          "chrome": 70
-        }
+        "method": "usage-pure"
       }
     ]
   ],
   "presets": [
     [
       "@babel/preset-env",
       {
-        "modules": false,
-        "targets": {
-          "chrome": 70
-        }
+        "modules": false
       }
     ]
   ]
-}
+}

packages/babel-plugin-polyfill-regenerator/test/fixtures/usage-pure/preset-env-unsupported/options.json

@@ -1,24 +1,21 @@
 {
+  "targets": {
+    "chrome": 40
+  },
   "plugins": [
     [
       "@@/polyfill-regenerator",
       {
-        "method": "usage-pure",
-        "targets": {
-          "chrome": 40
-        }
+        "method": "usage-pure"
       }
     ]
   ],
   "presets": [
     [
       "@babel/preset-env",
       {
-        "modules": false,
-        "targets": {
-          "chrome": 40
-        }
+        "modules": false
       }
     ]
   ]
-}
+}

packages/babel-plugin-polyfill-regenerator/test/options.js

@@ -0,0 +1,39 @@
+import * as babel from "@babel/core";
+import polyfillRegenerator from "../lib";
+
+function transform(code, babelOpts, pluginOpts) {
+  return babel.transformSync(code, {
+    configFile: false,
+    ...babelOpts,
+    plugins: [[polyfillRegenerator, pluginOpts]],
+  });
+}
+
+describe("targets", () => {
+  it("is not supported", () => {
+    expect(() =>
+      transform(
+        "code",
+        {},
+        {
+          method: "usage-pure",
+          targets: { chrome: 50 },
+        },
+      ),
+    ).toThrow(/targets/);
+  });
+});
+
+describe("top-level targets", () => {
+  it("is supported", () => {
+    expect(() =>
+      transform(
+        "code",
+        { targets: { chrome: 50 } },
+        {
+          method: "usage-pure",
+        },
+      ),
+    ).not.toThrow(/targets/);
+  });
+});