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feat(scripts): Create script to help with CJS -> ESM migration (#8197)
* feat(scripts): Create script to help with CJS -> ESM migration
This is based on js2ts, but considerably simplified since we
no longer need to deal with goog.module IDs.
* feat(scripts): Add support for module.exports = {...}
Support (optionally renaming) assignments to module.exports, in
addition to the existing support for simple exports property
assignmenets.
* fix(scripts): Typo corrections + other improvments for PR #8197
* chore(scripts): Format
This commit is contained in:
Christopher Allen
committed by
GitHub
GitHub
parent
dc91c3ab54
commit
5a9a31ad1d
162
scripts/migration/cjs2esm
Executable file
162
scripts/migration/cjs2esm
Executable file
@@ -0,0 +1,162 @@
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#!/usr/bin/env node
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const fs = require('fs');
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const path = require('path');
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const filenames = process.argv.slice(2); // Trim off node and script name.
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/** Absolute path of repository root. */
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const repoPath = path.resolve(__dirname, '..', '..');
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//////////////////////////////////////////////////////////////////////
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// Process files mentioned on the command line.
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//////////////////////////////////////////////////////////////////////
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/** RegExp matching require statements. */
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const requireRE =
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/(?:const\s+(?:([$\w]+)|(\{[^}]*\}))\s*=\s*)?require\('([^']+)'\);/g;
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/** RegExp matching key: value pairs in destructuring assignments. */
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const keyValueRE = /([$\w]+)\s*:\s*([$\w]+)\s*(?=,|})/g;
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/** Prefix for RegExp matching a top-level declaration. */
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const declPrefix = '(?:const|let|var|(?:async\\s+)?function(?:\\s*\\*)?|class)';
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for (const filename of filenames) {
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let contents = null;
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try {
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contents = String(fs.readFileSync(filename));
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} catch (e) {
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console.error(`error while reading ${filename}: ${e.message}`);
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continue;
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}
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console.log(`Converting ${filename} from CJS to ESM...`);
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// Remove "use strict".
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contents = contents.replace(/^\s*["']use strict["']\s*; *\n/m, '');
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// Migrate from require to import.
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contents = contents.replace(
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requireRE,
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function (
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orig, // Whole statement to be replaced.
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name, // Name of named import of whole module (if applicable).
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names, // {}-enclosed list of destructured imports.
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moduleName, // Imported module name or path.
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) {
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if (moduleName[0] === '.') {
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// Relative path. Could check and add '.mjs' suffix if desired.
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}
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if (name) {
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return `import * as ${name} from '${moduleName}';`;
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} else if (names) {
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names = names.replace(keyValueRE, '$1 as $2');
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return `import ${names} from '${moduleName}';`;
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} else {
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// Side-effect only require.
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return `import '${moduleName}';`;
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}
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},
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);
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// Find and update or remove old-style single-export assignments
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// like:
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//
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// exports.bar = foo; // becomes export {foo as bar};
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// exports.foo = foo; // remove the export and export at declaration
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// // instead, if possible.
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/** @type {!Array<{name: string, re: RegExp>}>} */
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const easyExports = [];
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contents = contents.replace(
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/^\s*exports\.([$\w]+)\s*=\s*([$\w]+)\s*;\n/gm,
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function (
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orig, // Whole statement to be replaced.
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exportName, // Name to export item as.
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declName, // Already-declared name for item being exported.
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) {
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// Renamed exports have to be translated as-is.
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if (exportName !== declName) {
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return `export {${declName} as ${exportName}};\n`;
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}
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// OK, we're doing "export.foo = foo;". Can we update the
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// declaration? We can't actualy modify it yet as we're in
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// the middle of a search-and-replace on contents already, but
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// we can delete the old export and later update the
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// declaration into an export.
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const declRE = new RegExp(
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`^(\\s*)(${declPrefix}\\s+${declName})\\b`,
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'gm',
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);
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if (contents.match(declRE)) {
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easyExports.push({exportName, declRE});
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return ''; // Delete existing export assignment.
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} else {
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return `export ${exportName};\n`; // Safe fallback.
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}
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},
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);
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// Find and update or remove old-style module.exports assignment
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// like:
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//
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// module.exports = {foo, bar: baz, quux};
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//
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// which becomes export {baz as bar}, with foo and quux exported at
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// declaration instead, if possible.
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contents = contents.replace(
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/^module\.exports\s*=\s*\{([^\}]+)\};?(\n?)/m,
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function (
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orig, // Whole statement to be replaced.
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items, // List of items to be exported.
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) {
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items = items.replace(
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/( *)([$\w]+)\s*(?::\s*([$\w]+)\s*)?,?(\s*?\n?)/gm,
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function (
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origItem, // Whole item being replaced.
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indent, // Optional leading whitespace.
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exportName, // Name to export item as.
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declName, // Already-declared name being exported, if different.
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newline, // Optional trailing whitespace.
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) {
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if (!declName) declName = exportName;
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// Renamed exports have to be translated as-is.
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if (exportName !== declName) {
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return `${indent}${declName} as ${exportName},${newline}`;
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}
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// OK, this item has no rename. Can we update the
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// declaration? We can't actualy modify it yet as we're in
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// the middle of a search-and-replace on contents already,
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// but we can delete the item and later update the
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// declaration into an export.
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const declRE = new RegExp(
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`^(\\s*)(${declPrefix}\\s+${declName})\\b`,
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'gm',
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);
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if (contents.match(declRE)) {
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easyExports.push({exportName, declRE});
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return ''; // Delete existing item.
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} else {
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return `${indent}${exportName},${newline}`; // Safe fallback.
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}
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},
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);
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if (/^\s*$/s.test(items)) {
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// No items left?
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return ''; // Delete entire module.export assignment.
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} else {
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return `export {${items}};\n`;
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}
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},
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);
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// Add 'export' to existing declarations where appropriate.
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for (const {exportName, declRE} of easyExports) {
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contents = contents.replace(declRE, '$1export $2');
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}
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// Write converted file with new extension.
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const newFilename = filename.replace(/.c?js$/, '.mjs');
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fs.writeFileSync(newFilename, contents);
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console.log(`Wrote ${newFilename}.`);
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}
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