Add configuration option to suppress require cycle warnings

docs/Configuration.md

@@ -182,6 +182,14 @@ Type: `Array<string>`
 
 Additional platforms to look out for, For example, if you want to add a "custom" platform, and use modules ending in .custom.js, you would return ['custom'] here.
 
+#### `ignoreRequireCyclePrefixes`
+
+Type: `Array<string>`
+
+In development mode, suppress require cycle warnings for modules that start with one of the prefixes in this array. This is useful if a module you use has a require cycle that's not worth fixing.
+
+Note that paths are relative to the root of the project. For example, if you want to exclude all files of a module named `my-library` in `node_modules`, you should use `['node_modules/my-library']`. 
+
 ---
 ### Transformer Options
 

packages/metro-config/src/__tests__/__snapshots__/loadConfig-test.js.snap

@@ -50,6 +50,7 @@ Object {
     "emptyModulePath": "metro-runtime/src/modules/empty-module",
     "extraNodeModules": Object {},
     "hasteImplModulePath": undefined,
+    "ignoreRequireCyclePrefixes": Array [],
     "nodeModulesPaths": Array [],
     "platforms": Array [
       "ios",
@@ -195,6 +196,7 @@ Object {
     "emptyModulePath": "metro-runtime/src/modules/empty-module",
     "extraNodeModules": Object {},
     "hasteImplModulePath": undefined,
+    "ignoreRequireCyclePrefixes": Array [],
     "nodeModulesPaths": Array [],
     "platforms": Array [
       "ios",
@@ -340,6 +342,7 @@ Object {
     "emptyModulePath": "metro-runtime/src/modules/empty-module",
     "extraNodeModules": Object {},
     "hasteImplModulePath": undefined,
+    "ignoreRequireCyclePrefixes": Array [],
     "nodeModulesPaths": Array [],
     "platforms": Array [
       "ios",
@@ -485,6 +488,7 @@ Object {
     "emptyModulePath": "metro-runtime/src/modules/empty-module",
     "extraNodeModules": Object {},
     "hasteImplModulePath": undefined,
+    "ignoreRequireCyclePrefixes": Array [],
     "nodeModulesPaths": Array [],
     "platforms": Array [
       "ios",

packages/metro-config/src/configTypes.flow.js

@@ -84,6 +84,7 @@ type ResolverConfigT = {|
   resolverMainFields: $ReadOnlyArray<string>,
   sourceExts: $ReadOnlyArray<string>,
   useWatchman: boolean,
+  ignoreRequireCyclePrefixes: $ReadOnlyArray<string>,
 |};
 
 type SerializerConfigT = {|

packages/metro-config/src/defaults/index.js

@@ -46,6 +46,7 @@ const getDefaultValues = (projectRoot: ?string): ConfigT => ({
     resolveRequest: null,
     resolverMainFields: ['browser', 'main'],
     useWatchman: true,
+    ignoreRequireCyclePrefixes: [],
   },
 
   serializer: {

packages/metro-runtime/src/polyfills/__tests__/require-test.js

@@ -43,6 +43,7 @@ describe('require', () => {
     'global',
     '__DEV__',
     '__METRO_GLOBAL_PREFIX__',
+    '__IGNORE_REQUIRE_CYCLE_PREFIXES__',
     moduleSystemCode,
   );
 
@@ -665,6 +666,29 @@ describe('require', () => {
       console.warn = warn;
     });
 
+    it('does not log warning for cyclic dependency in ignore list', () => {
+      createModuleSystem(moduleSystem, true, '', ['foo']);
+
+      createModule(moduleSystem, 0, 'foo.js', (global, require) => {
+        require(1);
+      });
+
+      createModule(moduleSystem, 1, 'bar.js', (global, require) => {
+        require(2);
+      });
+
+      createModule(moduleSystem, 2, 'baz.js', (global, require) => {
+        require(0);
+      });
+
+      const warn = console.warn;
+      console.warn = jest.fn();
+
+      moduleSystem.__r(0);
+      expect(console.warn).toHaveBeenCalledTimes(0);
+      console.warn = warn;
+    });
+
     it('sets the exports value to their current value', () => {
       createModuleSystem(moduleSystem, false, '');
 

packages/metro-runtime/src/polyfills/require.js

@@ -15,6 +15,9 @@
 
 declare var __DEV__: boolean;
 declare var __METRO_GLOBAL_PREFIX__: string;
+// JSON-encoded array of strings that we should not print require cycle errors
+// for
+declare var __IGNORE_REQUIRE_CYCLE_PREFIXES__: $ReadOnlyArray<string>;
 
 type DependencyMap = Array<ModuleID>;
 type Exports = any;
@@ -178,11 +181,13 @@ function metroRequire(moduleId: ModuleID | VerboseModuleNameForDev): Exports {
         );
       // We want to show A -> B -> A:
       cycle.push(cycle[0]);
-      console.warn(
-        `Require cycle: ${cycle.join(' -> ')}\n\n` +
-          'Require cycles are allowed, but can result in uninitialized values. ' +
-          'Consider refactoring to remove the need for a cycle.',
-      );
+      if (shouldPrintRequireCycle(cycle[0])) {
+        console.warn(
+          `Require cycle: ${cycle.join(' -> ')}\n\n` +
+            'Require cycles are allowed, but can result in uninitialized values. ' +
+            'Consider refactoring to remove the need for a cycle.',
+        );
+      }
     }
   }
 
@@ -193,6 +198,17 @@ function metroRequire(moduleId: ModuleID | VerboseModuleNameForDev): Exports {
     : guardedLoadModule(moduleIdReallyIsNumber, module);
 }
 
+function shouldPrintRequireCycle(module: ?string): boolean {
+  const prefixes = __IGNORE_REQUIRE_CYCLE_PREFIXES__;
+  if (!module || !prefixes || !Array.isArray(prefixes)) return true;
+
+  for (const prefix of prefixes) {
+    if (module.startsWith(prefix)) return false;
+  }
+
+  return true;
+}
+
 function metroImportDefault(moduleId: ModuleID | VerboseModuleNameForDev) {
   if (__DEV__ && typeof moduleId === 'string') {
     const verboseName = moduleId;

packages/metro/src/lib/__tests__/getPreludeCode-test.js

@@ -18,11 +18,15 @@ const vm = require('vm');
   describe(`${mode} mode`, () => {
     const isDev = mode === 'development';
     const globalPrefix = '';
+    const ignoreRequireCyclePrefixes = [];
 
     it('sets up `process.env.NODE_ENV` and `__DEV__`', () => {
       const sandbox: $FlowFixMe = {};
       vm.createContext(sandbox);
-      vm.runInContext(getPreludeCode({isDev, globalPrefix}), sandbox);
+      vm.runInContext(
+        getPreludeCode({isDev, globalPrefix, ignoreRequireCyclePrefixes}),
+        sandbox,
+      );
       expect(sandbox.process.env.NODE_ENV).toEqual(mode);
       expect(sandbox.__DEV__).toEqual(isDev);
     });
@@ -31,17 +35,38 @@ const vm = require('vm');
       const sandbox: $FlowFixMe = {};
       vm.createContext(sandbox);
       vm.runInContext(
-        getPreludeCode({isDev, globalPrefix: '__metro'}),
+        getPreludeCode({
+          isDev,
+          globalPrefix: '__metro',
+          ignoreRequireCyclePrefixes,
+        }),
         sandbox,
       );
       expect(sandbox.__METRO_GLOBAL_PREFIX__).toBe('__metro');
     });
 
+    it('sets up `__IGNORE_REQUIRE_CYCLE_PREFIXES__`', () => {
+      const sandbox: $FlowFixMe = {};
+      vm.createContext(sandbox);
+      vm.runInContext(
+        getPreludeCode({
+          isDev,
+          globalPrefix,
+          ignoreRequireCyclePrefixes: ['blah'],
+        }),
+        sandbox,
+      );
+      expect(sandbox.__IGNORE_REQUIRE_CYCLE_PREFIXES__).toEqual(['blah']);
+    });
+
     it('does not override an existing `process.env`', () => {
       const nextTick = () => {};
       const sandbox: $FlowFixMe = {process: {nextTick, env: {FOOBAR: 123}}};
       vm.createContext(sandbox);
-      vm.runInContext(getPreludeCode({isDev, globalPrefix}), sandbox);
+      vm.runInContext(
+        getPreludeCode({isDev, globalPrefix, ignoreRequireCyclePrefixes}),
+        sandbox,
+      );
       expect(sandbox.process.env.NODE_ENV).toEqual(mode);
       expect(sandbox.process.env.FOOBAR).toEqual(123);
       expect(sandbox.process.nextTick).toEqual(nextTick);
@@ -53,7 +78,12 @@ const vm = require('vm');
       const BAR = 2;
       vm.createContext(sandbox);
       vm.runInContext(
-        getPreludeCode({isDev, globalPrefix, extraVars: {FOO, BAR}}),
+        getPreludeCode({
+          isDev,
+          globalPrefix,
+          ignoreRequireCyclePrefixes,
+          extraVars: {FOO, BAR},
+        }),
         sandbox,
       );
       expect(sandbox.FOO).toBe(FOO);
@@ -64,7 +94,12 @@ const vm = require('vm');
       const sandbox: $FlowFixMe = {};
       vm.createContext(sandbox);
       vm.runInContext(
-        getPreludeCode({isDev, globalPrefix, extraVars: {__DEV__: 123}}),
+        getPreludeCode({
+          isDev,
+          globalPrefix,
+          ignoreRequireCyclePrefixes,
+          extraVars: {__DEV__: 123},
+        }),
         sandbox,
       );
       expect(sandbox.__DEV__).toBe(isDev);

packages/metro/src/lib/getPreludeCode.js

@@ -14,17 +14,24 @@ function getPreludeCode({
   extraVars,
   isDev,
   globalPrefix,
+  ignoreRequireCyclePrefixes,
 }: {|
   +extraVars?: {[string]: mixed, ...},
   +isDev: boolean,
   +globalPrefix: string,
+  +ignoreRequireCyclePrefixes: $ReadOnlyArray<string>,
 |}): string {
   const vars = [
+    // Ensure these variable names match the ones referenced in metro-runtime
+    // require.js
     '__BUNDLE_START_TIME__=this.nativePerformanceNow?nativePerformanceNow():Date.now()',
     `__DEV__=${String(isDev)}`,
     ...formatExtraVars(extraVars),
     'process=this.process||{}',
     `__METRO_GLOBAL_PREFIX__='${globalPrefix}'`,
+    `__IGNORE_REQUIRE_CYCLE_PREFIXES__=${JSON.stringify(
+      ignoreRequireCyclePrefixes,
+    )}`,
   ];
   return `var ${vars.join(',')};${processEnv(
     isDev ? 'development' : 'production',

packages/metro/src/lib/getPrependedScripts.js

@@ -69,6 +69,7 @@ async function getPrependedScripts(
     _getPrelude({
       dev: options.dev,
       globalPrefix: config.transformer.globalPrefix,
+      ignoreRequireCyclePrefixes: config.resolver.ignoreRequireCyclePrefixes,
     }),
     ...dependencies.values(),
   ];
@@ -77,12 +78,18 @@ async function getPrependedScripts(
 function _getPrelude({
   dev,
   globalPrefix,
+  ignoreRequireCyclePrefixes,
 }: {
   dev: boolean,
   globalPrefix: string,
+  ignoreRequireCyclePrefixes: $ReadOnlyArray<string>,
   ...
 }): Module<> {
-  const code = getPreludeCode({isDev: dev, globalPrefix});
+  const code = getPreludeCode({
+    isDev: dev,
+    globalPrefix,
+    ignoreRequireCyclePrefixes,
+  });
   const name = '__prelude__';
 
   return {