Generate sourcemaps for production build artifacts

Author: markerikson

scripts/rollup/build.js

@@ -11,6 +11,7 @@ const stripBanner = require('rollup-plugin-strip-banner');
 const chalk = require('chalk');
 const resolve = require('@rollup/plugin-node-resolve').nodeResolve;
 const fs = require('fs');
+const path = require('path');
 const argv = require('minimist')(process.argv.slice(2));
 const Modules = require('./modules');
 const Bundles = require('./bundles');
@@ -148,6 +149,7 @@ function getBabelConfig(
     presets: [],
     plugins: [...babelPlugins],
     babelHelpers: 'bundled',
+    sourcemap: false,
   };
   if (isDevelopment) {
     options.plugins.push(
@@ -386,6 +388,16 @@ function getPlugins(
 
   const {isUMDBundle, shouldStayReadable} = getBundleTypeFlags(bundleType);
 
+  const needsMinifiedByClosure = isProduction && bundleType !== ESM_PROD;
+  // Only generate sourcemaps for true "production" build artifacts
+  // that will be used by bundlers, such as `react-dom.production.min.js`.
+  // UMD and "profiling" builds are rarely used and not worth having sourcemaps.
+  const needsSourcemaps =
+    needsMinifiedByClosure &&
+    !isProfiling &&
+    !isUMDBundle &&
+    !shouldStayReadable;
+
   return [
     // Keep dynamic imports as externals
     dynamicImports(),
@@ -395,7 +407,7 @@ function getPlugins(
         const transformed = flowRemoveTypes(code);
         return {
           code: transformed.toString(),
-          map: transformed.generateMap(),
+          map: null,
         };
       },
     },
@@ -424,6 +436,7 @@ function getPlugins(
     ),
     // Remove 'use strict' from individual source files.
     {
+      name: "remove 'use strict'",
       transform(source) {
         return source.replace(/['"]use strict["']/g, '');
       },
@@ -443,47 +456,9 @@ function getPlugins(
     // I'm going to port "art" to ES modules to avoid this problem.
     // Please don't enable this for anything else!
     isUMDBundle && entry === 'react-art' && commonjs(),
-    // Apply dead code elimination and/or minification.
-    // closure doesn't yet support leaving ESM imports intact
-    isProduction &&
-      bundleType !== ESM_PROD &&
-      closure({
-        compilation_level: 'SIMPLE',
-        language_in: 'ECMASCRIPT_2020',
-        language_out:
-          bundleType === NODE_ES2015
-            ? 'ECMASCRIPT_2020'
-            : bundleType === BROWSER_SCRIPT
-            ? 'ECMASCRIPT5'
-            : 'ECMASCRIPT5_STRICT',
-        emit_use_strict:
-          bundleType !== BROWSER_SCRIPT &&
-          bundleType !== ESM_PROD &&
-          bundleType !== ESM_DEV,
-        env: 'CUSTOM',
-        warning_level: 'QUIET',
-        apply_input_source_maps: false,
-        use_types_for_optimization: false,
-        process_common_js_modules: false,
-        rewrite_polyfills: false,
-        inject_libraries: false,
-        allow_dynamic_import: true,
-
-        // Don't let it create global variables in the browser.
-        // https://github.com/facebook/react/issues/10909
-        assume_function_wrapper: !isUMDBundle,
-        renaming: !shouldStayReadable,
-      }),
-    // Add the whitespace back if necessary.
-    shouldStayReadable &&
-      prettier({
-        parser: 'flow',
-        singleQuote: false,
-        trailingComma: 'none',
-        bracketSpacing: true,
-      }),
     // License and haste headers, top-level `if` blocks.
     {
+      name: 'license-and-headers',
       renderChunk(source) {
         return Wrappers.wrapBundle(
           source,
@@ -495,6 +470,85 @@ function getPlugins(
         );
       },
     },
+    // Apply dead code elimination and/or minification.
+    // closure doesn't yet support leaving ESM imports intact
+    needsMinifiedByClosure &&
+      closure(
+        {
+          compilation_level: 'SIMPLE',
+          language_in: 'ECMASCRIPT_2020',
+          language_out:
+            bundleType === NODE_ES2015
+              ? 'ECMASCRIPT_2020'
+              : bundleType === BROWSER_SCRIPT
+              ? 'ECMASCRIPT5'
+              : 'ECMASCRIPT5_STRICT',
+          emit_use_strict:
+            bundleType !== BROWSER_SCRIPT &&
+            bundleType !== ESM_PROD &&
+            bundleType !== ESM_DEV,
+          env: 'CUSTOM',
+          warning_level: 'QUIET',
+          source_map_include_content: true,
+          use_types_for_optimization: false,
+          process_common_js_modules: false,
+          rewrite_polyfills: false,
+          inject_libraries: false,
+          allow_dynamic_import: true,
+
+          // Don't let it create global variables in the browser.
+          // https://github.com/facebook/react/issues/10909
+          assume_function_wrapper: !isUMDBundle,
+          renaming: !shouldStayReadable,
+        },
+        {needsSourcemaps}
+      ),
+    // Add the whitespace back if necessary.
+    shouldStayReadable &&
+      prettier({
+        parser: 'flow',
+        singleQuote: false,
+        trailingComma: 'none',
+        bracketSpacing: true,
+      }),
+    needsSourcemaps && {
+      name: 'generate-prod-bundle-sourcemaps',
+      async renderChunk(codeAfterLicense, chunk, options, meta) {
+        // We want to generate a sourcemap that shows the production bundle source
+        // as it existed before Closure Compiler minified that chunk, rather than
+        // showing the "original" individual source files. This better shows
+        // what is actually running in the app.
+
+        // Use a path like `node_modules/react/cjs/react.production.min.js.map` for the sourcemap file
+        const finalSourcemapPath = options.file.replace('.js', '.js.map');
+        const finalSourcemapFilename = path.basename(finalSourcemapPath);
+
+        // Read the sourcemap that Closure wrote to disk
+        const sourcemapAfterClosure = JSON.parse(
+          fs.readFileSync(finalSourcemapPath, 'utf8')
+        );
+
+        // CC generated a file list that only contains the tempfile name.
+        // Replace that with a more meaningful "source" name for this bundle.
+        sourcemapAfterClosure.sources = [filename];
+        sourcemapAfterClosure.file = filename;
+
+        // Overwrite the Closure-generated file with the final combined sourcemap
+        fs.writeFileSync(
+          finalSourcemapPath,
+          JSON.stringify(sourcemapAfterClosure)
+        );
+
+        // Add the sourcemap URL to the actual bundle, so that tools pick it up
+        const sourceWithMappingUrl =
+          codeAfterLicense + `\n//# sourceMappingURL=${finalSourcemapFilename}`;
+
+        return {
+          code: sourceWithMappingUrl,
+          map: null,
+        };
+      },
+    },
     // Record bundle size.
     sizes({
       getSize: (size, gzip) => {

scripts/rollup/plugins/closure-plugin.js

@@ -19,15 +19,25 @@ function compile(flags) {
   });
 }
 
-module.exports = function closure(flags = {}) {
+module.exports = function closure(flags = {}, {needsSourcemaps}) {
   return {
     name: 'scripts/rollup/plugins/closure-plugin',
-    async renderChunk(code) {
+    async renderChunk(code, chunk, options) {
       const inputFile = tmp.fileSync();
-      const tempPath = inputFile.name;
-      flags = Object.assign({}, flags, {js: tempPath});
-      await writeFileAsync(tempPath, code, 'utf8');
-      const compiledCode = await compile(flags);
+
+      // Use a path like `node_modules/react/cjs/react.production.min.js.map` for the sourcemap file
+      const sourcemapPath = options.file.replace('.js', '.js.map');
+
+      // Tell Closure what JS source file to read, and optionally what sourcemap file to write
+      const finalFlags = {
+        ...flags,
+        js: inputFile.name,
+        ...(needsSourcemaps && {create_source_map: sourcemapPath}),
+      };
+
+      await writeFileAsync(inputFile.name, code, 'utf8');
+      const compiledCode = await compile(finalFlags);
+
       inputFile.removeCallback();
       return {code: compiledCode};
     },

scripts/rollup/wrappers.js

@@ -191,6 +191,7 @@ ${source}`;
   /****************** FB_WWW_DEV ******************/
   [FB_WWW_DEV](source, globalName, filename, moduleType) {
     return `/**
+ * @preserve
 ${license}
  *
  * @noflow
@@ -211,6 +212,7 @@ ${source}
   /****************** FB_WWW_PROD ******************/
   [FB_WWW_PROD](source, globalName, filename, moduleType) {
     return `/**
+ * @preserve
 ${license}
  *
  * @noflow
@@ -225,6 +227,7 @@ ${source}`;
   /****************** FB_WWW_PROFILING ******************/
   [FB_WWW_PROFILING](source, globalName, filename, moduleType) {
     return `/**
+ * @preserve
 ${license}
  *
  * @noflow
@@ -239,6 +242,7 @@ ${source}`;
   /****************** RN_OSS_DEV ******************/
   [RN_OSS_DEV](source, globalName, filename, moduleType) {
     return `/**
+ * @preserve
 ${license}
  *
  * @noflow
@@ -260,6 +264,7 @@ ${source}
   /****************** RN_OSS_PROD ******************/
   [RN_OSS_PROD](source, globalName, filename, moduleType) {
     return `/**
+ * @preserve
 ${license}
  *
  * @noflow
@@ -275,6 +280,7 @@ ${source}`;
   /****************** RN_OSS_PROFILING ******************/
   [RN_OSS_PROFILING](source, globalName, filename, moduleType) {
     return `/**
+ * @preserve
 ${license}
  *
  * @noflow
@@ -290,6 +296,7 @@ ${source}`;
   /****************** RN_FB_DEV ******************/
   [RN_FB_DEV](source, globalName, filename, moduleType) {
     return `/**
+ * @preserve
 ${license}
  *
  * @noflow
@@ -310,6 +317,7 @@ ${source}
   /****************** RN_FB_PROD ******************/
   [RN_FB_PROD](source, globalName, filename, moduleType) {
     return `/**
+ * @preserve
 ${license}
  *
  * @noflow
@@ -324,6 +332,7 @@ ${source}`;
   /****************** RN_FB_PROFILING ******************/
   [RN_FB_PROFILING](source, globalName, filename, moduleType) {
     return `/**
+ * @preserve
 ${license}
  *
  * @noflow