create plugin for extracting polyfills

Author: lobsterkatie

rollup/npmHelpers.js

@@ -9,6 +9,7 @@ import deepMerge from 'deepmerge';
 
 import {
   makeConstToVarPlugin,
+  makeExtractPolyfillsPlugin,
   makeNodeResolvePlugin,
   makeRemoveBlankLinesPlugin,
   makeRemoveESLintCommentsPlugin,
@@ -30,6 +31,7 @@ export function makeBaseNPMConfig(options = {}) {
   const constToVarPlugin = makeConstToVarPlugin();
   const removeESLintCommentsPlugin = makeRemoveESLintCommentsPlugin();
   const removeBlankLinesPlugin = makeRemoveBlankLinesPlugin();
+  const extractPolyfillsPlugin = makeExtractPolyfillsPlugin();
 
   // return {
   const config = {
@@ -71,7 +73,14 @@ export function makeBaseNPMConfig(options = {}) {
       interop: esModuleInterop ? 'auto' : 'esModule',
     },
 
-    plugins: [nodeResolvePlugin, sucrasePlugin, constToVarPlugin, removeESLintCommentsPlugin, removeBlankLinesPlugin],
+    plugins: [
+      nodeResolvePlugin,
+      sucrasePlugin,
+      constToVarPlugin,
+      removeESLintCommentsPlugin,
+      removeBlankLinesPlugin,
+      extractPolyfillsPlugin,
+    ],
 
     // don't include imported modules from outside the package in the final output
     external: [

rollup/plugins/extractPolyfillsPlugin.js

@@ -0,0 +1,208 @@
+import * as path from 'path';
+
+import * as recast from 'recast';
+import * as acornParser from 'recast/parsers/acorn';
+
+const POLYFILL_NAMES = new Set([
+  '_asyncNullishCoalesce',
+  '_asyncOptionalChain',
+  '_asyncOptionalChainDelete',
+  '_createNamedExportFrom',
+  '_createStarExport',
+  '_interopDefault', // rollup's version
+  '_interopNamespace', // rollup's version
+  '_interopRequireDefault', // sucrase's version
+  '_interopRequireWildcard', // sucrase's version
+  '_nullishCoalesce',
+  '_optionalChain',
+  '_optionalChainDelete',
+]);
+
+/**
+ * Create a plugin which will replace function definitions of any of the above funcions with an `import` or `require`
+ * statement pulling them in from a central source. Mimics tsc's `importHelpers` option.
+ */
+export function makeExtractPolyfillsPlugin() {
+  let moduleFormat;
+
+  // For more on the hooks used in this plugin, see https://rollupjs.org/guide/en/#output-generation-hooks
+  return {
+    name: 'extractPolyfills',
+
+    // Figure out which build we're currently in (esm or cjs)
+    outputOptions(options) {
+      moduleFormat = options.format;
+    },
+
+    // This runs after both the sucrase transpilation (which happens in the `transform` hook) and rollup's own
+    // esm-i-fying or cjs-i-fying work (which happens right before `renderChunk`), in other words, after all polyfills
+    // will have been injected
+    renderChunk(code, chunk) {
+      const sourceFile = chunk.fileName;
+      const parserOptions = {
+        sourceFileName: sourceFile,
+        // We supply a custom parser which wraps the provided `acorn` parser in order to override the `ecmaVersion` value.
+        // See https://github.com/benjamn/recast/issues/578.
+        parser: {
+          parse(source, options) {
+            return acornParser.parse(source, {
+              ...options,
+              // By this point in the build, everything should already have been down-compiled to whatever JS version
+              // we're targeting. Setting this parser to `latest` just means that whatever that version is (or changes
+              // to in the future), this parser will be able to handle the generated code.
+              ecmaVersion: 'latest',
+            });
+          },
+        },
+      };
+
+      const ast = recast.parse(code, parserOptions);
+
+      // Find function definitions and function expressions whose identifiers match a known polyfill name
+      const polyfillNodes = findPolyfillNodes(ast);
+
+      if (polyfillNodes.length === 0) {
+        return null;
+      }
+
+      console.log(`${sourceFile} - polyfills: ${polyfillNodes.map(node => node.name)}`);
+
+      // Depending on the output format, generate `import { x, y, z } from '...'` or `var { x, y, z } = require('...')`
+      const importOrRequireNode = createImportOrRequireNode(polyfillNodes, sourceFile, moduleFormat);
+
+      // Insert our new `import` or `require` node at the top of the file, and then delete the function definitions it's
+      // meant to replace (polyfill nodes get marked for deletion in `findPolyfillNodes`)
+      ast.program.body = [importOrRequireNode, ...ast.program.body.filter(node => !node.shouldDelete)];
+
+      // In spite of the name, this doesn't actually print anything - it just stringifies the code, and keeps track of
+      // where original nodes end up in order to generate a sourcemap.
+      const result = recast.print(ast, {
+        sourceMapName: `${sourceFile}.map`,
+        quote: 'single',
+      });
+
+      return { code: result.code, map: result.map };
+    },
+  };
+}
+
+/**
+ * Extract the function name, regardless of the format in which the function is declared
+ */
+function getNodeName(node) {
+  // Function expressions and functions pulled from objects
+  if (node.type === 'VariableDeclaration') {
+    // In practice sucrase and rollup only ever declare one polyfill at a time, so it's safe to just grab the first
+    // entry here
+    const declarationId = node.declarations[0].id;
+
+    // Note: Sucrase and rollup seem to only use the first type of variable declaration for their polyfills, but good to
+    // cover our bases
+
+    // Declarations of the form
+    //   `const dogs = function() { return "are great"; };`
+    // or
+    //   `const dogs = () => "are great";
+    if (declarationId.type === 'Identifier') {
+      return declarationId.name;
+    }
+    // Declarations of the form
+    //   `const { dogs } = { dogs: function() { return "are great"; } }`
+    // or
+    //   `const { dogs } = { dogs: () => "are great" }`
+    else if (declarationId.type === 'ObjectPattern') {
+      return declarationId.properties[0].key.name;
+    }
+    // Any other format
+    else {
+      return 'unknown variable';
+    }
+  }
+
+  // Regular old functions, of the form
+  //   `function dogs() { return "are great"; }`
+  else if (node.type === 'FunctionDeclaration') {
+    return node.id.name;
+  }
+
+  // If we get here, this isn't a node we're interested in, so just return a string we know will never match any of the
+  // polyfill names
+  else {
+    return 'nope';
+  }
+}
+
+/**
+ * Find all nodes whose identifiers match a known polyfill name.
+ *
+ * Note: In theory, this could yield false positives, if any of the magic names were assigned to something other than a
+ * polyfill function, but the chances of that are slim. Also, it only searches the module global scope, but that's
+ * always where the polyfills appear, so no reason to traverse the whole tree.
+ */
+function findPolyfillNodes(ast) {
+  const isPolyfillNode = node => {
+    const nodeName = getNodeName(node);
+    if (POLYFILL_NAMES.has(nodeName)) {
+      // mark this node for later deletion, since we're going to replace it with an import statement
+      node.shouldDelete = true;
+      // store the name in a consistent spot, regardless of node type
+      node.name = nodeName;
+
+      return true;
+    }
+
+    return false;
+  };
+
+  return ast.program.body.filter(isPolyfillNode);
+}
+
+/**
+ * Create a node representing an `import` or `require` statement of the form
+ *
+ *     import { < polyfills > } from '...'
+ * or
+ *     var { < polyfills > } = require('...')
+ *
+ * @param polyfillNodes The nodes from the current version of the code, defining the polyfill functions
+ * @param currentSourceFile The path, relative to `src/`, of the file currently being transpiled
+ * @param moduleFormat Either 'cjs' or 'esm'
+ * @returns A single node which can be subbed in for the polyfill definition nodes
+ */
+function createImportOrRequireNode(polyfillNodes, currentSourceFile, moduleFormat) {
+  const {
+    callExpression,
+    identifier,
+    importDeclaration,
+    importSpecifier,
+    literal,
+    objectPattern,
+    property,
+    variableDeclaration,
+    variableDeclarator,
+  } = recast.types.builders;
+
+  // Since our polyfills live in `@sentry/utils`, if we're importing or requiring them there the path will have to be
+  // relative
+  const isUtilsPackage = process.cwd().endsWith('packages/utils');
+  const importSource = literal(
+    isUtilsPackage
+      ? path.relative(path.dirname(currentSourceFile), `../jsPolyfills/${moduleFormat}`)
+      : `@sentry/utils/jsPolyfills/${moduleFormat}`,
+  );
+
+  // This is the `x, y, z` of inside of `import { x, y, z }` or `var { x, y, z }`
+  const importees = polyfillNodes.map(({ name: fnName }) =>
+    moduleFormat === 'esm'
+      ? importSpecifier(identifier(fnName))
+      : property.from({ kind: 'init', key: identifier(fnName), value: identifier(fnName), shorthand: true }),
+  );
+
+  const requireFn = identifier('require');
+
+  return moduleFormat === 'esm'
+    ? importDeclaration(importees, importSource)
+    : variableDeclaration('var', [
+        variableDeclarator(objectPattern(importees), callExpression(requireFn, [importSource])),
+      ]);
+}

rollup/plugins/npmPlugins.js

@@ -97,3 +97,5 @@ export function makeRemoveBlankLinesPlugin() {
     ],
   });
 }
+
+export { makeExtractPolyfillsPlugin } from './extractPolyfillsPlugin.js';