Convert current build system to Rollup and adopt flat bundles (#9327)

* WIP

* fbjs support

* WIP

* dev/prod mode WIP

* More WIP

* builds a cjs bundle

* adding forwarding modules

* more progress on forwarding modules and FB config

* improved how certain modules get inlined for fb and cjs

* more forwarding modules

* added comments to the module aliasing code

* made ReactPerf and ReactTestUtils bundle again

* Use -core suffix for all bundles

This makes it easier to override things in www.

* Add a lazy shim for ReactPerf

This prevents a circular dependency between ReactGKJSModule and ReactDOM

* Fix forwarding module for ReactCurrentOwner

* Revert "Add a lazy shim for ReactPerf"

This reverts commit 723b402c07.

* Rename -core suffix to -fb for clarity

* Change forwarding modules to import from -fb

This is another, more direct fix for ReactPerf circular dependency

* should fix fb and cjs bundles for ReactCurrentOwner

* added provides module for ReactCurrentOwner

* should improve console output

* fixed typo with argument passing on functon call

* Revert "should improve console output"

This breaks the FB bundles.

This reverts commit 65f11ee64f.

* Work around internal FB transform require() issue

* moved  ReactInstanceMap out of React and into ReactDOM and ReactDOMFiber

* Expose more internal modules to www

* Add missing modules to Stack ReactDOM to fix UFI

* Fix onlyChild module

* improved the build tool

* Add a rollup npm script

* Rename ReactDOM-fb to ReactDOMStack-fb

* Fix circular dependencies now that ReactDOM-fb is a GK switch

* Revert "Work around internal FB transform require() issue"

This reverts commit 0a50b6a90b.

* Bump rollup-plugin-commonjs to include a fix for rollup/rollup-plugin-commonjs#176

* Add more forwarding modules that are used on www

* Add even more forwarding modules that are used on www

* Add DOMProperty to hidden exports

* Externalize feature flags

This lets www specify them dynamically.

* Remove forwarding modules with implementations

Instead I'm adding them to react-fb in my diff.

* Add all injection necessary for error logging

* Add missing forwarding module (oops)

* Add ReactART builds

* Add ReactDOMServer bundle

* Fix UMD build of ReactDOMFiber

* Work in progress: start adding ReactNative bundle

* tidied up the options for bundles, so they can define what types they output and exclude

* Add a working RN build

* further improved and tidied up build process

* improved how bundles are built by exposing externals and making the process less "magical", also tidied up code and added more comments

* better handling of bundling ReactCurrentOwner and accessing it from renderer modules

* added NODE_DEV and NODE_PROD

* added NPM package creation and copying into build chain

* Improved UMD bundles, added better fixture testing and doc plus prod builds

* updated internal modules (WIP)

* removed all react/lib/* dependencies from appearing in bundles created on build

* added react-test-renderer bundles

* renamed bundles and paths

* fixed fixture path changes

* added extract-errors support

* added extractErrors warning

* moved shims to shims directory in rollup scripts

* changed pathing to use build rather than build/rollup

* updated release doc to reflect some rollup changes

* Updated ReactNative findNodeHandle() to handle number case (#9238)

* Add dynamic injection to ReactErrorUtils (#9246)

* Fix ReactErrorUtils injection (#9247)

* Fix Haste name

* Move files around

* More descriptive filenames

* Add missing ReactErrorUtils shim

* Tweak reactComponentExpect to make it standalone-ish in www

* Unflowify shims

* facebook-www shims now get copied over correctly to build

* removed unnecessary resolve

* building facebook-www/build is now all sync to prevent IO issues plus handles extra facebook-www src assets

* removed react-native-renderer package and made build make a react-native build dir instead

* 😭😭😭

* Add more SSR unit tests for elements and children. (#9221)

* Adding more SSR unit tests for elements and children.

* Some of my SSR tests were testing for react-text and react-empty elements that no longer exist in Fiber. Fixed the tests so that they expect correct markup in Fiber.

* Tweaked some test names after @gaearon review comment https://github.com/facebook/react/pull/9221#discussion_r107045673 . Also realized that one of the tests was essentially a direct copy of another, so deleted it.

* Responding to code review https://github.com/facebook/react/pull/9221#pullrequestreview-28996315 . Thanks @spicyj!

* ReactElementValidator uses temporary ReactNative View propTypes getter (#9256)

* Updating packages for 16.0.0-alpha.6 release

* Revert "😭😭😭"

This reverts commit 7dba33b2cf.

* Work around Jest issue with CurrentOwner shared state in www

* updated error codes

* splits FB into FB_DEV and FB_PROD

* Remove deps on specific builds from shims

* should no longer mangle FB_PROD output

* Added init() dev block to ReactTestUtils

* added shims for DEV only code so it does not get included in prod bundles

* added a __DEV__ wrapping code to FB_DEV

* added __DEV__ flag behind a footer/header

* Use right haste names

* keeps comments in prod

* added external babel helpers plugin

* fixed fixtures and updated cjs/umd paths

* Fixes Jest so it run tests correctly

* fixed an issue with stubbed modules not properly being replaced due to greedy replacement

* added a WIP solution for ReactCurrentOwner on FB DEV

* adds a FB_TEST bundle

* allows both ReactCurrentOwner and react/lib/ReactCurrentOwner

* adds -test to provides module name

* Remove TEST env

* Ensure requires stay at the top

* added basic mangle support (disbaled by default)

* per bundle property mangling added

* moved around plugin order to try and fix deadcode requires as per https://github.com/rollup/rollup/issues/855

* Fix flow issues

* removed gulp and grunt and moved tasks to standalone node script

* configured circleci to use new paths

* Fix lint

* removed gulp-extract-errors

* added test_build.sh back in

* added missing newline to flow.js

* fixed test coverage command

* changed permissions on test_build.sh

* fixed test_html_generations.sh

* temp removed html render test

* removed the warning output from test_build, the build should do this instead

* fixed test_build

* fixed broken npm script

* Remove unused ViewportMetrics shim

* better error output

* updated circleci to node 7 for async/await

* Fixes

* removed coverage test from circleci run

* circleci run tets

* removed build from circlci

* made a dedicated jest script in a new process

* moved order around of circlci tasks

* changing path to jest in more circleci tests

* re-enabled code coverage

* Add file header to prod bundles

* Remove react-dom/server.js (WIP: decide on the plan)

* Only UMD bundles need version header

* Merge with master

* disabled const evaluation by uglify for <script></script> string literal

* deal with ART modules for UMD bundles

* improved how bundle output gets printed

* fixed filesize difference reporting

* added filesize dep

* Update yarn lockfile for some reason

* now compares against the last run branch built on

* added react-dom-server

* removed un-needed comment

* results only get saved on full builds

* moved the rollup sized plugin into a plugins directory

* added a missing commonjs()

* fixed missing ignore

* Hack around to fix RN bundle

* Partially fix RN bundles

* added react-art bundle and a fixture for it

* Point UMD bundle to Fiber and add EventPluginHub to exported internals

* Make it build on Node 4

* fixed eslint error with resolve being defined in outer scope

* Tweak how build results are calculated and stored

* Tweak fixtures build to work on Node 4

* Include LICENSE/PATENTS and fix up package.json files

* Add Node bundle for react-test-renderer

* Revert "Hack around to fix RN bundle"

We'll do this later.

This reverts commit 59445a6259.

* Revert more RN changes

We'll do them separately later

* Revert more unintentional changes

* Revert changes to error codes

* Add accidentally deleted RN externals

* added RN_DEV/RN_PROD bundles

* fixed typo where RN_DEV and RN_PROD were the wrong way around

* Delete/ignore fixture build outputs

* Format scripts/ with Prettier

* tidied up the Rollup build process and split functions into various different files to improve readability

* Copy folder before files

* updated yarn.lock

* updated results and yarn dependencies to the latest versions

scripts/error-codes/Types.js

@@ -11,3 +11,4 @@
 'use strict';
 
 /*:: export type ErrorMap = { [id: string]: string; }; */
+

scripts/error-codes/__tests__/dev-expression-with-codes-test.js

@@ -37,11 +37,11 @@ describe('dev-expression', () => {
 
   it('should replace __DEV__ in if', () => {
     compare(
-`
+      `
 if (__DEV__) {
   console.log('foo')
 }`,
-`
+      `
 if (process.env.NODE_ENV !== 'production') {
   console.log('foo');
 }`
@@ -57,9 +57,8 @@ if (process.env.NODE_ENV !== 'production') {
 
   it("should add `reactProdInvariant` when it finds `require('invariant')`", () => {
     compare(
-"var invariant = require('invariant');",
-
-`var _prodInvariant = require('reactProdInvariant');
+      "var invariant = require('invariant');",
+      `var _prodInvariant = require('reactProdInvariant');
 
 var invariant = require('invariant');`
     );
@@ -69,27 +68,24 @@ var invariant = require('invariant');`
     compare(
       "invariant(condition, 'Do not override existing functions.');",
       "var _prodInvariant = require('reactProdInvariant');\n\n" +
-      "!condition ? " +
-      "process.env.NODE_ENV !== 'production' ? " +
-      "invariant(false, 'Do not override existing functions.') : " +
-      `_prodInvariant('16') : void 0;`
+        '!condition ? ' +
+        "process.env.NODE_ENV !== 'production' ? " +
+        "invariant(false, 'Do not override existing functions.') : " +
+        `_prodInvariant('16') : void 0;`
     );
   });
 
-  it("should only add `reactProdInvariant` once", () => {
-    var expectedInvariantTransformResult = (
-      "!condition ? " +
+  it('should only add `reactProdInvariant` once', () => {
+    var expectedInvariantTransformResult = '!condition ? ' +
       "process.env.NODE_ENV !== 'production' ? " +
       "invariant(false, 'Do not override existing functions.') : " +
-      `_prodInvariant('16') : void 0;`
-    );
+      `_prodInvariant('16') : void 0;`;
 
     compare(
-`var invariant = require('invariant');
+      `var invariant = require('invariant');
 invariant(condition, 'Do not override existing functions.');
 invariant(condition, 'Do not override existing functions.');`,
-
-`var _prodInvariant = require('reactProdInvariant');
+      `var _prodInvariant = require('reactProdInvariant');
 
 var invariant = require('invariant');
 ${expectedInvariantTransformResult}
@@ -101,10 +97,10 @@ ${expectedInvariantTransformResult}`
     compare(
       "invariant(condition, 'Expected %s target to be an array; got %s', 'foo', 'bar');",
       "var _prodInvariant = require('reactProdInvariant');\n\n" +
-      "!condition ? " +
-      "process.env.NODE_ENV !== 'production' ? " +
-      "invariant(false, 'Expected %s target to be an array; got %s', 'foo', 'bar') : " +
-      `_prodInvariant('7', 'foo', 'bar') : void 0;`
+        '!condition ? ' +
+        "process.env.NODE_ENV !== 'production' ? " +
+        "invariant(false, 'Expected %s target to be an array; got %s', 'foo', 'bar') : " +
+        `_prodInvariant('7', 'foo', 'bar') : void 0;`
     );
   });
 
@@ -112,10 +108,10 @@ ${expectedInvariantTransformResult}`
     compare(
       "invariant(condition, 'Expected a component class, ' + 'got %s.' + '%s', 'Foo', 'Bar');",
       "var _prodInvariant = require('reactProdInvariant');\n\n" +
-      "!condition ? " +
-      "process.env.NODE_ENV !== 'production' ? " +
-      "invariant(false, 'Expected a component class, got %s.%s', 'Foo', 'Bar') : " +
-      `_prodInvariant('18', 'Foo', 'Bar') : void 0;`
+        '!condition ? ' +
+        "process.env.NODE_ENV !== 'production' ? " +
+        "invariant(false, 'Expected a component class, got %s.%s', 'Foo', 'Bar') : " +
+        `_prodInvariant('18', 'Foo', 'Bar') : void 0;`
     );
   });
 
@@ -126,9 +122,9 @@ ${expectedInvariantTransformResult}`
     expect(console.warn.calls.count()).toBe(1);
     expect(console.warn.calls.argsFor(0)[0]).toBe(
       'Error message "a %s b" ' +
-      'cannot be found. The current React version ' +
-      'and the error map are probably out of sync. ' +
-      'Please run `gulp react:extract-errors` before building React.'
+        'cannot be found. The current React version ' +
+        'and the error map are probably out of sync. ' +
+        'Please run `yarn build -- --extractErrors` to build React with the error map in sync.'
     );
   });
 

scripts/error-codes/__tests__/evalToString-test.js

@@ -11,11 +11,9 @@
 var evalToString = require('../evalToString');
 var babylon = require('babylon');
 
-var parse = (source) => babylon.parse(
-  `(${source});`
-).program.body[0].expression; // quick way to get an exp node
+var parse = source => babylon.parse(`(${source});`).program.body[0].expression; // quick way to get an exp node
 
-var parseAndEval = (source) => evalToString(parse(source));
+var parseAndEval = source => evalToString(parse(source));
 
 describe('evalToString', () => {
   it('should support StringLiteral', () => {
@@ -28,9 +26,15 @@ describe('evalToString', () => {
   });
 
   it('should throw when it finds other types', () => {
-    expect(() => parseAndEval(`'foo ' + true`)).toThrowError(/Unsupported type/);
+    expect(() => parseAndEval(`'foo ' + true`)).toThrowError(
+      /Unsupported type/
+    );
     expect(() => parseAndEval(`'foo ' + 3`)).toThrowError(/Unsupported type/);
-    expect(() => parseAndEval(`'foo ' + null`)).toThrowError(/Unsupported type/);
-    expect(() => parseAndEval(`'foo ' + undefined`)).toThrowError(/Unsupported type/);
+    expect(() => parseAndEval(`'foo ' + null`)).toThrowError(
+      /Unsupported type/
+    );
+    expect(() => parseAndEval(`'foo ' + undefined`)).toThrowError(
+      /Unsupported type/
+    );
   });
 });

scripts/error-codes/__tests__/invertObject-test.js

@@ -10,7 +10,7 @@
 
 var invertObject = require('../invertObject');
 
-var objectValues = (target) => Object.keys(target).map((key) => target[key]);
+var objectValues = target => Object.keys(target).map(key => target[key]);
 
 describe('invertObject', () => {
   it('should return an empty object for an empty input', () => {
@@ -18,37 +18,49 @@ describe('invertObject', () => {
   });
 
   it('should invert key-values', () => {
-    expect(invertObject({
-      a: '3',
-      b: '4',
-    })).toEqual({
+    expect(
+      invertObject({
+        a: '3',
+        b: '4',
+      })
+    ).toEqual({
       3: 'a',
       4: 'b',
     });
   });
 
-  it('should take the last value when there\'re duplications in vals', () => {
-    expect(invertObject({
-      a: '3',
-      b: '4',
-      c: '3',
-    })).toEqual({
+  it("should take the last value when there're duplications in vals", () => {
+    expect(
+      invertObject({
+        a: '3',
+        b: '4',
+        c: '3',
+      })
+    ).toEqual({
       4: 'b',
       3: 'c',
     });
   });
 
   it('should preserve the original order', () => {
-    expect(Object.keys(invertObject({
-      a: '3',
-      b: '4',
-      c: '3',
-    }))).toEqual(['3', '4']);
+    expect(
+      Object.keys(
+        invertObject({
+          a: '3',
+          b: '4',
+          c: '3',
+        })
+      )
+    ).toEqual(['3', '4']);
 
-    expect(objectValues(invertObject({
-      a: '3',
-      b: '4',
-      c: '3',
-    }))).toEqual(['c', 'b']);
+    expect(
+      objectValues(
+        invertObject({
+          a: '3',
+          b: '4',
+          c: '3',
+        })
+      )
+    ).toEqual(['c', 'b']);
   });
 });

scripts/error-codes/codes.json

@@ -144,4 +144,4 @@
   "142": "Expected onBeforeMountComponent() parent and onSetChildren() to be consistent (%s has parents %s and %s).",
   "143": "React.Children.only expected to receive a single React element child.",
   "144": "React.PropTypes type checking code is stripped in production."
-}
+}

scripts/error-codes/dev-expression-with-codes.js

@@ -22,13 +22,14 @@ module.exports = function(babel) {
   // Generate a hygienic identifier
   function getProdInvariantIdentifier(path, localState) {
     if (!localState.prodInvariantIdentifier) {
-      localState.prodInvariantIdentifier = path.scope.generateUidIdentifier('prodInvariant');
+      localState.prodInvariantIdentifier = path.scope.generateUidIdentifier(
+        'prodInvariant'
+      );
       path.scope.getProgramParent().push({
         id: localState.prodInvariantIdentifier,
-        init: t.callExpression(
-          t.identifier('require'),
-          [t.stringLiteral('reactProdInvariant')]
-        ),
+        init: t.callExpression(t.identifier('require'), [
+          t.stringLiteral('reactProdInvariant'),
+        ]),
       });
     }
     return localState.prodInvariantIdentifier;
@@ -37,11 +38,7 @@ module.exports = function(babel) {
   var DEV_EXPRESSION = t.binaryExpression(
     '!==',
     t.memberExpression(
-      t.memberExpression(
-        t.identifier('process'),
-        t.identifier('env'),
-        false
-      ),
+      t.memberExpression(t.identifier('process'), t.identifier('env'), false),
       t.identifier('NODE_ENV'),
       false
     ),
@@ -122,42 +119,46 @@ module.exports = function(babel) {
               node[SEEN_SYMBOL] = true;
               if (process.env.NODE_ENV !== 'test') {
                 console.warn(
-                  'Error message "' + errorMsgLiteral +
-                  '" cannot be found. The current React version ' +
-                  'and the error map are probably out of sync. ' +
-                  'Please run `gulp react:extract-errors` before building React.'
+                  'Error message "' +
+                    errorMsgLiteral +
+                    '" cannot be found. The current React version ' +
+                    'and the error map are probably out of sync. ' +
+                    'Please run `yarn build -- --extractErrors` to ' +
+                    'build React with the error map in sync.'
                 );
               }
               return;
             }
 
-            var devInvariant = t.callExpression(node.callee, [
-              t.booleanLiteral(false),
-              t.stringLiteral(errorMsgLiteral),
-            ].concat(node.arguments.slice(2)));
+            var devInvariant = t.callExpression(
+              node.callee,
+              [
+                t.booleanLiteral(false),
+                t.stringLiteral(errorMsgLiteral),
+              ].concat(node.arguments.slice(2))
+            );
 
             devInvariant[SEEN_SYMBOL] = true;
 
             var localInvariantId = getProdInvariantIdentifier(path, this);
-            var prodInvariant = t.callExpression(localInvariantId, [
-              t.stringLiteral(prodErrorId),
-            ].concat(node.arguments.slice(2)));
+            var prodInvariant = t.callExpression(
+              localInvariantId,
+              [t.stringLiteral(prodErrorId)].concat(node.arguments.slice(2))
+            );
 
             prodInvariant[SEEN_SYMBOL] = true;
-            path.replaceWith(t.ifStatement(
-              t.unaryExpression('!', condition),
-              t.blockStatement([
-                t.ifStatement(
-                  DEV_EXPRESSION,
-                  t.blockStatement([
-                    t.expressionStatement(devInvariant),
-                  ]),
-                  t.blockStatement([
-                    t.expressionStatement(prodInvariant),
-                  ])
-                ),
-              ])
-            ));
+            path.replaceWith(
+              t.ifStatement(
+                t.unaryExpression('!', condition),
+                t.blockStatement([
+                  t.ifStatement(
+                    DEV_EXPRESSION,
+                    t.blockStatement([t.expressionStatement(devInvariant)]),
+                    t.blockStatement([t.expressionStatement(prodInvariant)])
+                  ),
+                ])
+              )
+            );
           } else if (path.get('callee').isIdentifier({name: 'warning'})) {
             // Turns this code:
             //
@@ -174,14 +175,12 @@ module.exports = function(babel) {
             // invariant because we don't care about an extra call in __DEV__
 
             node[SEEN_SYMBOL] = true;
-            path.replaceWith(t.ifStatement(
-              DEV_EXPRESSION,
-              t.blockStatement([
-                t.expressionStatement(
-                  node
-                ),
-              ])
-            ));
+            path.replaceWith(
+              t.ifStatement(
+                DEV_EXPRESSION,
+                t.blockStatement([t.expressionStatement(node)])
+              )
+            );
           }
         },
       },

scripts/error-codes/evalToString.js

@@ -10,7 +10,7 @@
  */
 'use strict';
 
-function evalToString(ast/* : Object */)/* : string */ {
+function evalToString(ast /* : Object */) /* : string */ {
   switch (ast.type) {
     case 'StringLiteral':
       return ast.value;

scripts/error-codes/extract-errors.js

@@ -8,19 +8,14 @@
  */
 'use strict';
 
-var babylon = require('babylon');
-var fs = require('fs');
-var gutil = require('gulp-util');
-var path = require('path');
-var through = require('through2');
-var traverse = require('babel-traverse').default;
+const babylon = require('babylon');
+const fs = require('fs');
+const path = require('path');
+const traverse = require('babel-traverse').default;
+const evalToString = require('./evalToString');
+const invertObject = require('./invertObject');
 
-var evalToString = require('./evalToString');
-var invertObject = require('./invertObject');
-
-var PLUGIN_NAME = 'extract-errors';
-
-var babylonOptions = {
+const babylonOptions = {
   sourceType: 'module',
   // As a parser, babylon has its own options and we can't directly
   // import/require a babel preset. It should be kept **the same** as
@@ -37,8 +32,7 @@ var babylonOptions = {
 
 module.exports = function(opts) {
   if (!opts || !('errorMapFilePath' in opts)) {
-    throw new gutil.PluginError(
-      PLUGIN_NAME,
+    throw new Error(
       'Missing options. Ensure you pass an object with `errorMapFilePath`.'
     );
   }
@@ -46,9 +40,10 @@ module.exports = function(opts) {
   var errorMapFilePath = opts.errorMapFilePath;
   var existingErrorMap;
   try {
-    existingErrorMap = require(
-      path.join(__dirname, path.basename(errorMapFilePath))
-    );
+    existingErrorMap = require(path.join(
+      __dirname,
+      path.basename(errorMapFilePath)
+    ));
   } catch (e) {
     existingErrorMap = {};
   }
@@ -56,7 +51,8 @@ module.exports = function(opts) {
   var allErrorIDs = Object.keys(existingErrorMap);
   var currentID;
 
-  if (allErrorIDs.length === 0) { // Map is empty
+  if (allErrorIDs.length === 0) {
+    // Map is empty
     currentID = 0;
   } else {
     currentID = Math.max.apply(null, allErrorIDs) + 1;
@@ -65,18 +61,7 @@ module.exports = function(opts) {
   // Here we invert the map object in memory for faster error code lookup
   existingErrorMap = invertObject(existingErrorMap);
 
-  function transform(file, enc, cb) {
-    if (file.isNull()) {
-      cb(null, file);
-      return;
-    }
-
-    if (file.isStream()) {
-      cb(new gutil.PluginError(PLUGIN_NAME, 'Streaming not supported'));
-      return;
-    }
-
-    var source = file.contents.toString();
+  function transform(source) {
     var ast = babylon.parse(source, babylonOptions);
 
     traverse(ast, {
@@ -92,26 +77,25 @@ module.exports = function(opts) {
               return;
             }
 
-            existingErrorMap[errorMsgLiteral] = '' + (currentID++);
+            existingErrorMap[errorMsgLiteral] = '' + currentID++;
           }
         },
       },
     });
-
-    cb();
   }
 
   function flush(cb) {
-    fs.writeFile(
+    fs.writeFileSync(
       errorMapFilePath,
       JSON.stringify(invertObject(existingErrorMap), null, 2) + '\n',
-      'utf-8',
-      function() {
-        // avoid calling cb with fs.write callback data
-        cb();
-      }
+      'utf-8'
     );
   }
 
-  return through.obj(transform, flush);
+  return function extractErrors(filepath) {
+    const source = fs.readFileSync(filepath, 'utf-8');
+
+    transform(source);
+    flush();
+  };
 };

scripts/error-codes/invertObject.js

@@ -18,7 +18,7 @@
  * into
  *   { 0: 'MUCH ERROR', 1: 'SUCH WRONG' }
  */
-function invertObject(targetObj/* : ErrorMap */)/* : ErrorMap */ {
+function invertObject(targetObj /* : ErrorMap */) /* : ErrorMap */ {
   var result = {};
   var mapKeys = Object.keys(targetObj);
 

scripts/error-codes/print-warnings.js

@@ -18,7 +18,6 @@ const evalToString = require('./evalToString');
 
 const paths = require('../../gulpfile').paths;
 
-
 const babylonOptions = {
   sourceType: 'module',
   // As a parser, babylon has its own options and we can't directly
@@ -70,8 +69,9 @@ const sourcePaths = [].concat(
   paths.reactTestRenderer.src
 );
 
-gs(sourcePaths)
-  .pipe(through.obj(transform, cb => {
+gs(sourcePaths).pipe(
+  through.obj(transform, cb => {
     process.stdout.write(Array.from(warnings).sort().join('\n') + '\n');
     cb();
-  }));
+  })
+);