Throw if annotation found without directive

packages/babel-plugin-transform-flow-strip-types/README.md

@@ -55,4 +55,5 @@ require("babel-core").transform("code", {
 `boolean`, defaults to `false`.
 
 Setting this to true will only strip annotations and declarations from files
-that contain the `// @flow` directive.
+that contain the `// @flow` directive. It will also throw errors for any Flow
+annotations found in files without the directive.

packages/babel-plugin-transform-flow-strip-types/src/index.js

@@ -47,7 +47,13 @@ export default function({ types: t }) {
       },
 
       Flow(path) {
-        if (skipStrip) return;
+        if (skipStrip) {
+          throw path.buildCodeFrameError(
+            "A @flow directive is required when using Flow annotations with " +
+              "babel-preset-react or the `requireDirective` option.",
+          );
+        }
+
         path.remove();
       },
 

packages/babel-plugin-transform-flow-strip-types/test/fixtures/requireDirective/true-does-not-throw-with-directive/actual.js

@@ -0,0 +1 @@
+function foo(numVal, strVal) {}

packages/babel-plugin-transform-flow-strip-types/test/fixtures/requireDirective/true-does-not-throw-with-directive/expected.js

@@ -0,0 +1 @@
+function foo(numVal, strVal) {}

packages/babel-plugin-transform-flow-strip-types/test/fixtures/requireDirective/true-throws-if-found-with-directive/options.json

@@ -0,0 +1,3 @@
+{
+  "throws": "A @flow directive is required when using Flow annotations with babel-preset-react or the `requireDirective` option."
+}

packages/babel-preset-react/README.md

@@ -14,8 +14,10 @@ And with the `development` option:
 - [transform-react-jsx-self](https://babeljs.io/docs/plugins/transform-react-jsx-self/)
 - [transform-react-jsx-source](https://babeljs.io/docs/plugins/transform-react-jsx-source/)
 
-Note: Flow annotations and declarations will _only_ be removed in files that
-have the `// @flow ` directive.
+Note: This preset sets the `requireDirective` option on
+`transform-flow-strip-types`. This means Flow annotations and declarations
+will _only_ be removed in files that have a `// @flow ` directive. It will also
+throw errors for any Flow annotations found in files without the directive.
 
 ```js
 // @flow

packages/babel-preset-react/test/fixtures/flow/strip-without-directive/expected.js

@@ -1 +0,0 @@
-function foo(numVal: number, strVal: string) {}

packages/babel-preset-react/test/fixtures/flow/throws-without-directive/options.json

@@ -0,0 +1,3 @@
+{
+  "throws": "A @flow directive is required when using Flow annotations with babel-preset-react or the `requireDirective` option."
+}