Create bugfix plugin for classes in computed keys in Firefox

packages/babel-compat-data/data/overlapping-plugins.json

@@ -23,9 +23,11 @@
     "bugfix/transform-v8-spread-parameters-in-optional-chaining"
   ],
   "transform-class-properties": [
-    "bugfix/transform-v8-static-class-fields-redefine-readonly"
+    "bugfix/transform-v8-static-class-fields-redefine-readonly",
+    "bugfix/transform-firefox-class-in-computed-class-key"
   ],
   "proposal-class-properties": [
-    "bugfix/transform-v8-static-class-fields-redefine-readonly"
+    "bugfix/transform-v8-static-class-fields-redefine-readonly",
+    "bugfix/transform-firefox-class-in-computed-class-key"
   ]
 }

packages/babel-compat-data/data/plugin-bugfixes.json

@@ -107,6 +107,18 @@
     "opera_mobile": "64",
     "electron": "13.0"
   },
+  "bugfix/transform-firefox-class-in-computed-class-key": {
+    "chrome": "74",
+    "opera": "62",
+    "edge": "79",
+    "safari": "14.1",
+    "node": "12",
+    "deno": "1",
+    "ios": "14.5",
+    "samsung": "11",
+    "opera_mobile": "53",
+    "electron": "6.0"
+  },
   "transform-optional-chaining": {
     "chrome": "80",
     "opera": "67",

packages/babel-compat-data/data/plugins.json

@@ -23,6 +23,18 @@
     "opera_mobile": "52",
     "electron": "17.0"
   },
+  "bugfix/transform-firefox-class-in-computed-class-key": {
+    "chrome": "74",
+    "opera": "62",
+    "edge": "79",
+    "safari": "14.1",
+    "node": "12",
+    "deno": "1",
+    "ios": "14.5",
+    "samsung": "11",
+    "opera_mobile": "53",
+    "electron": "6.0"
+  },
   "transform-class-static-block": {
     "chrome": "94",
     "opera": "80",

packages/babel-compat-data/scripts/data/plugin-features.js

@@ -162,6 +162,13 @@ const es2022 = {
     features: ["static class fields / static class fields use [[Define]]"],
     replaces: "transform-class-properties",
   },
+  "bugfix/transform-firefox-class-in-computed-class-key": {
+    replaces: "transform-class-properties",
+    overwrite: {
+      // TODO: Once Firefox releases the fix, write the correct version here.
+      firefox: undefined,
+    },
+  },
   "transform-class-static-block": "Class static initialization blocks",
   "transform-private-property-in-object":
     "Ergonomic brand checks for private fields",

packages/babel-compat-data/scripts/utils-build-data.js

@@ -103,6 +103,14 @@ exports.generateData = (environments, features) => {
 
   const normalized = {};
   for (const [key, options] of Object.entries(features)) {
+    if (options.overwrite) {
+      if (!options.replaces || options.features) {
+        throw new Error(
+          `.overwrite is only supported when using .replace and not defining .features (${key})`
+        );
+      }
+      options.features = features[options.replaces].features;
+    }
     if (!options.features) {
       normalized[key] = {
         features: expandFeatures([options]),
@@ -118,14 +126,24 @@ exports.generateData = (environments, features) => {
   const overlapping = {};
 
   // Apply bugfixes
-  for (const [key, { features, replaces }] of Object.entries(normalized)) {
+  for (const [key, { features, replaces, overwrite }] of Object.entries(
+    normalized
+  )) {
     if (replaces) {
       if (normalized[replaces].replaces) {
-        throw new Error("Transitive replacement is not supported");
+        throw new Error(`Transitive replacement is not supported (${key})`);
+      }
+
+      if (overwrite) {
+        normalized[key] = {
+          features: normalized[replaces].features,
+          overwrite,
+        };
+      } else {
+        normalized[replaces].features = normalized[replaces].features.filter(
+          feat => !features.includes(feat)
+        );
       }
-      normalized[replaces].features = normalized[replaces].features.filter(
-        feat => !features.includes(feat)
-      );
 
       if (!overlapping[replaces]) overlapping[replaces] = [];
       overlapping[replaces].push(key);
@@ -142,6 +160,8 @@ exports.generateData = (environments, features) => {
     });
     addElectronSupportFromChromium(plugin);
 
+    if (options.overwrite) Object.assign(plugin, options.overwrite);
+
     data[key] = plugin;
   }
 

packages/babel-plugin-bugfix-firefox-class-in-computed-class-key/.npmignore

@@ -0,0 +1,3 @@
+src
+test
+*.log

packages/babel-plugin-bugfix-firefox-class-in-computed-class-key/README.md

@@ -0,0 +1,19 @@
+# @babel/plugin-bugfix-firefox-class-in-computed-class-key
+
+> Wraps classes defined in computed keys of other classes affected by https://bugzilla.mozilla.org/show_bug.cgi?id=1887677
+
+See our website [@babel/plugin-bugfix-firefox-class-in-computed-class-key](https://babeljs.io/docs/babel-plugin-bugfix-firefox-class-in-computed-class-key) for more information.
+
+## Install
+
+Using npm:
+
+```sh
+npm install --save-dev @babel/plugin-bugfix-firefox-class-in-computed-class-key
+```
+
+or using yarn:
+
+```sh
+yarn add @babel/plugin-bugfix-firefox-class-in-computed-class-key --dev
+```

packages/babel-plugin-bugfix-firefox-class-in-computed-class-key/package.json

@@ -0,0 +1,57 @@
+{
+  "name": "@babel/plugin-bugfix-firefox-class-in-computed-class-key",
+  "version": "7.24.1",
+  "description": "Wraps classes defined in computed keys of other classes affected by https://bugzilla.mozilla.org/show_bug.cgi?id=1887677",
+  "repository": {
+    "type": "git",
+    "url": "https://github.com/babel/babel.git",
+    "directory": "packages/babel-plugin-bugfix-firefox-class-in-computed-class-key"
+  },
+  "homepage": "https://babel.dev/docs/en/next/babel-plugin-bugfix-firefox-class-in-computed-class-key",
+  "license": "MIT",
+  "publishConfig": {
+    "access": "public"
+  },
+  "main": "./lib/index.js",
+  "exports": {
+    ".": "./lib/index.js",
+    "./package.json": "./package.json"
+  },
+  "keywords": [
+    "babel-plugin",
+    "bugfix"
+  ],
+  "dependencies": {
+    "@babel/helper-environment-visitor": "workspace:^",
+    "@babel/helper-plugin-utils": "workspace:^"
+  },
+  "peerDependencies": {
+    "@babel/core": "^7.0.0"
+  },
+  "devDependencies": {
+    "@babel/core": "workspace:^",
+    "@babel/helper-plugin-test-runner": "workspace:^",
+    "@babel/traverse": "workspace:^"
+  },
+  "engines": {
+    "node": ">=6.9.0"
+  },
+  "author": "The Babel Team (https://babel.dev/team)",
+  "conditions": {
+    "USE_ESM": [
+      {
+        "type": "module"
+      },
+      null
+    ],
+    "BABEL_8_BREAKING": [
+      {
+        "engines": {
+          "node": "^16.20.0 || ^18.16.0 || >=20.0.0"
+        }
+      },
+      {}
+    ]
+  },
+  "type": "commonjs"
+}

packages/babel-plugin-bugfix-firefox-class-in-computed-class-key/src/index.ts

@@ -0,0 +1,113 @@
+import type { NodePath, Visitor } from "@babel/traverse";
+import type { types as t } from "@babel/core";
+import { declare } from "@babel/helper-plugin-utils";
+import environmentVisitor from "@babel/helper-environment-visitor";
+
+export default declare(({ types: t, traverse, assertVersion }) => {
+  assertVersion(REQUIRED_VERSION(7));
+
+  const containsClassExpressionVisitor: Visitor<{ found: boolean }> = {
+    ClassExpression(path, state) {
+      state.found = true;
+      path.stop();
+    },
+    Function(path) {
+      path.skip();
+    },
+  };
+
+  const containsYieldOrAwaitVisitor = traverse.visitors.merge([
+    {
+      YieldExpression(path, state) {
+        state.yield = true;
+        if (state.await) path.stop();
+      },
+      AwaitExpression(path, state) {
+        state.await = true;
+        if (state.yield) path.stop();
+      },
+    } satisfies Visitor<{ yield: boolean; await: boolean }>,
+    environmentVisitor,
+  ]);
+
+  function containsClassExpression(path: NodePath<t.Node>) {
+    if (t.isClassExpression(path.node)) return true;
+    if (t.isFunction(path.node)) return false;
+    const state = { found: false };
+    path.traverse(containsClassExpressionVisitor, state);
+    return state.found;
+  }
+
+  function wrap(path: NodePath<t.Expression>) {
+    const context = {
+      yield: t.isYieldExpression(path.node),
+      await: t.isAwaitExpression(path.node),
+    };
+    path.traverse(containsYieldOrAwaitVisitor, context);
+
+    let replacement;
+
+    if (context.yield) {
+      const fn = t.functionExpression(
+        null,
+        [],
+        t.blockStatement([t.returnStatement(path.node)]),
+        /* generator */ true,
+        /* async */ context.await,
+      );
+
+      replacement = t.yieldExpression(
+        t.callExpression(t.memberExpression(fn, t.identifier("call")), [
+          t.thisExpression(),
+          // NOTE: In some context arguments is invalid (it might not be defined
+          // in the top-level scope, or it's a syntax error in static class blocks).
+          // However, `yield` is also invalid in those contexts, so we can safely
+          // inject a reference to arguments.
+          t.identifier("arguments"),
+        ]),
+        true,
+      );
+    } else {
+      const fn = t.arrowFunctionExpression([], path.node, context.await);
+
+      if (context.await) {
+        replacement = t.awaitExpression(t.callExpression(fn, []));
+      } else {
+        replacement = t.callExpression(
+          // We need to use fn.call() instead of just fn() because
+          // terser transforms (() => class {})() to class {}, effectively
+          // undoing the wrapping introduced by this plugin.
+          // https://github.com/terser/terser/issues/1514
+          // TODO(Babel 8): Remove .call if Terser stops inlining this case.
+          t.memberExpression(fn, t.identifier("call")),
+          [],
+        );
+      }
+    }
+
+    path.replaceWith(replacement);
+  }
+
+  return {
+    name: "bugfix-firefox-class-in-computed-class-key",
+
+    visitor: {
+      Class(path) {
+        const hasPrivateElement = path.node.body.body.some(node =>
+          t.isPrivate(node),
+        );
+        if (!hasPrivateElement) return;
+
+        for (const elem of path.get("body.body")) {
+          if (
+            "computed" in elem.node &&
+            elem.node.computed &&
+            containsClassExpression(elem.get("key"))
+          ) {
+            wrap(elem.get("key"));
+          }
+        }
+      },
+    },
+  };
+});

packages/babel-plugin-bugfix-firefox-class-in-computed-class-key/test/fixtures/basic/nested-in-expression/input.js

@@ -0,0 +1,4 @@
+class A {
+  #x = 1;
+  [useIt([1 + class {}])];
+}

packages/babel-plugin-bugfix-firefox-class-in-computed-class-key/test/fixtures/basic/nested-in-expression/output.js

@@ -0,0 +1,4 @@
+class A {
+  #x = 1;
+  [(() => useIt([1 + class {}])).call()];
+}

packages/babel-plugin-bugfix-firefox-class-in-computed-class-key/test/fixtures/basic/options.json

@@ -0,0 +1,3 @@
+{
+  "plugins": ["bugfix-firefox-class-in-computed-class-key"]
+}

packages/babel-plugin-bugfix-firefox-class-in-computed-class-key/test/fixtures/basic/simple-class-in-computed-key/input.js

@@ -0,0 +1,4 @@
+class A {
+  #x = 1;
+  [class {}];
+}

packages/babel-plugin-bugfix-firefox-class-in-computed-class-key/test/fixtures/basic/simple-class-in-computed-key/output.js

@@ -0,0 +1,4 @@
+class A {
+  #x = 1;
+  [(() => class {}).call()];
+}

packages/babel-plugin-bugfix-firefox-class-in-computed-class-key/test/fixtures/basic/yield-await/input.mjs

@@ -0,0 +1,16 @@
+class A {
+  #x;
+  [class {}]
+  [await class {}]
+}
+
+async function* f() {
+  class A {
+    #x;
+    [class {}]
+    [await class {}]
+    [yield class {}]
+    [yield* class {}]
+    [await (yield class {})]
+  }
+}

packages/babel-plugin-bugfix-firefox-class-in-computed-class-key/test/fixtures/basic/yield-await/output.mjs

@@ -0,0 +1,21 @@
+class A {
+  #x;
+  [(() => class {}).call()];
+  [await (async () => await class {})()];
+}
+async function* f() {
+  class A {
+    #x;
+    [(() => class {}).call()];
+    [await (async () => await class {})()];
+    [yield* function* () {
+      return yield class {};
+    }.call(this, arguments)];
+    [yield* function* () {
+      return yield* class {};
+    }.call(this, arguments)];
+    [yield* async function* () {
+      return await (yield class {});
+    }.call(this, arguments)];
+  }
+}

packages/babel-plugin-bugfix-firefox-class-in-computed-class-key/test/fixtures/decorators-transform/decorators-plugin-after/input.js

@@ -0,0 +1,5 @@
+@deco
+class A {
+  #x = 1;
+  static #y = 2;
+}

packages/babel-plugin-bugfix-firefox-class-in-computed-class-key/test/fixtures/decorators-transform/decorators-plugin-after/options.json

@@ -0,0 +1,6 @@
+{
+  "plugins": [
+    "bugfix-firefox-class-in-computed-class-key",
+    ["proposal-decorators", { "version": "2023-11" }]
+  ]
+}