Throw on module collision (#1750)

* add throwOnModuleCollision option that, when set to true, will throw an error when a module name collision is detected (as opposed to simply printing a warning)

* fix lint errors

* alphabetize options; made code more compact

* Update index.js

* Update index-test.js.snap

packages/jest-haste-map/src/__tests__/__snapshots__/index-test.js.snap

@@ -1,3 +1,11 @@
+exports[`HasteMap throws on duplicate module ids if "throwOnModuleCollision" is set to true 1`] = `
+[Error: jest-haste-map: @providesModule naming collision:
+  Duplicate module name: Strawberry
+  Paths: /fruits/raspberry.js collides with /fruits/strawberry.js
+
+This error is caused by a @providesModule declaration with the same name across two different files.]
+`;
+
 exports[`HasteMap tries to crawl using node as a fallback 1`] = `
 "jest-haste-map: Watchman crawl failed. Retrying once with node crawler.
   Usually this happens when watchman isn\'t running. Create an empty \`.watchmanconfig\` file in your project\'s root folder or initialize a git or hg repository in your project.

packages/jest-haste-map/src/__tests__/index-test.js

@@ -318,6 +318,22 @@ describe('HasteMap', () => {
       });
   });
 
+  it('throws on duplicate module ids if "throwOnModuleCollision" is set to true', () => {
+    // Raspberry thinks it is a Strawberry
+    mockFs['/fruits/raspberry.js'] = [
+      '/**',
+      ' * @providesModule Strawberry',
+      ' */',
+      'const Banana = require("Banana");',
+    ].join('\n');
+
+    return new HasteMap(
+      Object.assign({throwOnModuleCollision: true}, defaultConfig),
+    ).build().catch(err => {
+      expect(err).toMatchSnapshot();
+    });
+  });
+
   it('splits up modules by platform', () => {
     mockFs = Object.create(null);
     mockFs['/fruits/strawberry.js'] = [

packages/jest-haste-map/src/index.js

@@ -48,6 +48,7 @@ type Options = {
   resetCache?: boolean,
   retainAllFiles: boolean,
   roots: Array<string>,
+  throwOnModuleCollision?: boolean,
   useWatchman?: boolean,
 };
 
@@ -187,6 +188,7 @@ class HasteMap {
       resetCache: options.resetCache,
       retainAllFiles: options.retainAllFiles,
       roots: options.roots,
+      throwOnModuleCollision: !!options.throwOnModuleCollision,
       useWatchman:
         options.useWatchman == null ? true : options.useWatchman,
     };
@@ -273,14 +275,18 @@ class HasteMap {
         getPlatformExtension(module[H.PATH]) || H.GENERIC_PLATFORM;
       const existingModule = moduleMap[platform];
       if (existingModule && existingModule[H.PATH] !== module[H.PATH]) {
-        this._console.warn(
+        const message =
           `jest-haste-map: @providesModule naming collision:\n` +
           `  Duplicate module name: ${id}\n` +
           `  Paths: ${module[H.PATH]} collides with ` +
-          `${existingModule[H.PATH]}\n\n` +
-          `This warning is caused by a @providesModule declaration ` +
-          `with the same name across two different files.`,
-        );
+          `${existingModule[H.PATH]}\n\nThis ` +
+          `${this._options.throwOnModuleCollision ? 'error' : 'warning'} ` +
+          `is caused by a @providesModule declaration ` +
+          `with the same name across two different files.`;
+        if (this._options.throwOnModuleCollision) {
+          throw new Error(message);
+        }
+        this._console.warn(message);
         return;
       }