metro-bundler: extract calls to require.async()

Reviewed By: davidaurelio

Differential Revision: D5639493

fbshipit-source-id: d74aae95a238cf97b7daafad41ce9cbdccc84c1b

packages/metro-bundler/src/JSTransformer/worker/__tests__/extract-dependencies-test.js

@@ -30,6 +30,14 @@ describe('Dependency extraction:', () => {
     expect(dependencyOffsets).toEqual([8, 46, 147, 203]);
   });
 
+  it('can extract calls to require.async', () => {
+    const code = `foo();
+      require.async('bar').then(() => {});`;
+    const {dependencies, dependencyOffsets} = extractDependencies(code);
+    expect(dependencies).toEqual(['bar']);
+    expect(dependencyOffsets).toEqual([27]);
+  });
+
   it('does not extract require method calls', () => {
     const code = `
       require('a');

packages/metro-bundler/src/JSTransformer/worker/extract-dependencies.js

@@ -33,19 +33,34 @@ function extractDependencies(code: string) {
   const dependencies = new Set();
   const dependencyOffsets = [];
 
+  function pushDependency(nodeArgs) {
+    const arg = nodeArgs[0];
+    if (nodeArgs.length != 1 || arg.type !== 'StringLiteral') {
+      throw new Error('require() must have a single string literal argument');
+    }
+    dependencyOffsets.push(arg.start);
+    dependencies.add(arg.value);
+  }
+
   babel.traverse(ast, {
     CallExpression(path) {
       const node = path.node;
       const callee = node.callee;
       if (callee.type === 'Identifier' && callee.name === 'require') {
-        const arg = node.arguments[0];
-        if (arg == null || arg.type !== 'StringLiteral') {
-          throw new Error(
-            'require() must have a single string literal argument',
-          );
-        }
-        dependencyOffsets.push(arg.start);
-        dependencies.add(arg.value);
+        pushDependency(node.arguments);
+      }
+      if (callee.type !== 'MemberExpression') {
+        return;
+      }
+      const obj = callee.object;
+      const prop = callee.property;
+      if (
+        obj.type === 'Identifier' &&
+        obj.name === 'require' &&
+        !callee.computed &&
+        prop.name === 'async'
+      ) {
+        pushDependency(node.arguments);
       }
     },
   });

packages/metro-bundler/src/Resolver/polyfills/require.js

@@ -110,6 +110,10 @@ function require(moduleId: ModuleID | VerboseModuleNameForDev) {
     : guardedLoadModule(moduleIdReallyIsNumber, module);
 }
 
+require.async = function(moduleId: ModuleID | VerboseModuleNameForDev) {
+  return Promise.resolve().then(() => require(moduleId));
+};
+
 let inGuard = false;
 function guardedLoadModule(moduleId: ModuleID, module) {
   if (!inGuard && global.ErrorUtils) {

packages/metro-bundler/src/integration_tests/__tests__/__snapshots__/basic_bundle-test.js.snap

@@ -57,6 +57,12 @@ function _require(moduleId) {
   return module && module.isInitialized ? module.exports : guardedLoadModule(moduleIdReallyIsNumber, module);
 }
 
+_require.async = function (moduleId) {
+  return Promise.resolve().then(function () {
+    return _require(moduleId);
+  });
+};
+
 var inGuard = false;
 function guardedLoadModule(moduleId, module) {
   if (!inGuard && global.ErrorUtils) {
@@ -324,6 +330,12 @@ function _require(moduleId) {
   return module && module.isInitialized ? module.exports : guardedLoadModule(moduleIdReallyIsNumber, module);
 }
 
+_require.async = function (moduleId) {
+  return Promise.resolve().then(function () {
+    return _require(moduleId);
+  });
+};
+
 var inGuard = false;
 function guardedLoadModule(moduleId, module) {
   if (!inGuard && global.ErrorUtils) {