Add hermes parser (#17520)

CONTRIBUTING.md

@@ -48,7 +48,7 @@ function runFormatTest(
 Parameters:
 
 - **`fixtures`**: Must be set to `import.meta` or to an object of the shape `{ importMeta: import.meta, ... }`. The object may have the `snippets` property to specify an array of extra input entries in addition to the files in the current directory. For each input entry (a file or a snippet), `runFormatTest` configures and runs a number of tests. The main check is that for a given input the output should match the snapshot (for snippets, the expected output can also be specified directly). [Additional checks](#deeper-testing) are controlled by options and environment variables.
-- **`parsers`**: A list of parser names. The tests verify that the parsers in this list produce the same output. If the list includes `typescript`, then `babel-ts`, and `oxc-ts` is included implicitly. If the list includes `flow`, then `babel-flow` is included implicitly. If the list includes `babel`, and the current directory is inside `tests/format/js` or `tests/format/jsx`, then `acorn`, `espree`, `meriyah`, and `oxc` are included implicitly.
+- **`parsers`**: A list of parser names. The tests verify that the parsers in this list produce the same output. If the list includes `typescript`, then `babel-ts`, and `oxc-ts` are included implicitly. If the list includes `flow`, then `hermes` and `babel-flow` is included implicitly. If the list includes `babel`, and the current directory is inside `tests/format/js` or `tests/format/jsx`, then `acorn`, `espree`, `meriyah`, and `oxc` are included implicitly.
 - **`options`**: In addition to Prettier's formatting options, can contain the `errors` property to specify that it's expected that the formatting shouldn't be successful and an error should be thrown for all (`errors: true`) or some combinations of input entries and parsers.
 
 The implementation of `runFormatTest` can be found in [`tests/config/run-format-test.js`](tests/config/run-format-test.js).

knip.config.js

@@ -9,6 +9,7 @@ export default {
         "src/cli/index.js",
         "src/experimental-cli/index.js",
         "packages/plugin-oxc/index.js",
+        "packages/plugin-hermes/index.js",
       ],
       project: ["src/**", "scripts/**"],
       ignore: [
@@ -17,7 +18,7 @@ export default {
         "scripts/tools/**",
         "src/experimental-cli/**",
       ],
-      ignoreDependencies: ["eslint-formatter-friendly", "ts-expect"],
+      ignoreDependencies: ["eslint-formatter-friendly", "ts-expect", "buffer"],
       ignoreBinaries: [
         "test-coverage",
         "renovate-config-validator",

package.json

@@ -121,6 +121,7 @@
     "@typescript-eslint/parser": "8.33.0",
     "browserslist": "4.24.5",
     "browserslist-to-esbuild": "2.1.1",
+    "buffer": "6.0.3",
     "c8": "10.1.3",
     "cross-env": "7.0.3",
     "cspell": "9.0.0",
@@ -189,9 +190,9 @@
     "build": "node ./scripts/build/build.js",
     "build:website": "node ./scripts/build-website.js",
     "gen:changelog": "node ./scripts/generate-changelog.js",
-    "debug": "node bin/prettier.js --ignore-path=.prettierignore --plugin=./packages/plugin-oxc/index.js",
+    "debug": "node bin/prettier.js --ignore-path=.prettierignore --plugin=./packages/plugin-oxc/index.js --plugin=./packages/plugin-hermes/index.js",
-    "debug:watch": "node --watch bin/prettier.js --ignore-path=.prettierignore --plugin=./packages/plugin-oxc/index.js",
+    "debug:watch": "node --watch bin/prettier.js --ignore-path=.prettierignore --plugin=./packages/plugin-oxc/index.js --plugin=./packages/plugin-hermes/index.js",
-    "debug:inspect": "node --inspect-brk bin/prettier.js --ignore-path=.prettierignore --plugin=./packages/plugin-oxc/index.js"
+    "debug:inspect": "node --inspect-brk bin/prettier.js --ignore-path=.prettierignore --plugin=./packages/plugin-oxc/index.js --plugin=./packages/plugin-hermes/index.js"
   },
   "c8": {
     "reporter": [

packages/plugin-hermes/README.md

@@ -0,0 +1,27 @@
+# @prettier/plugin-hermes
+
+> Prettier [Hermes](https://github.com/facebook/hermes/blob/main/README.md) plugin.
+
+## Install
+
+```bash
+yarn add --dev prettier @prettier/plugin-hermes
+```
+
+## Usage
+
+Create or modify your [prettier configuration file](https://prettier.io/docs/en/configuration) to use the plugin:
+
+```json
+{
+  "overrides": [
+    {
+      "files": ["**/*.{js.flow,js,mjs,cjs}"],
+      "options": {
+        "plugins": ["@prettier/plugin-hermes"],
+        "parser": "hermes"
+      }
+    }
+  ]
+}
+```

packages/plugin-hermes/index.js

@@ -0,0 +1 @@
+export * as parsers from "../../src/language-js/parse/hermes.js";

packages/plugin-hermes/package.json

@@ -0,0 +1,22 @@
+{
+  "name": "@prettier/plugin-hermes",
+  "version": "0.0.1",
+  "description": "Prettier Hermes plugin.",
+  "type": "module",
+  "exports": {
+    ".": {
+      "types": "./index.d.js",
+      "default": "./index.mjs"
+    },
+    "./*": "./*"
+  },
+  "repository": {
+    "type": "git",
+    "url": "git+https://github.com/prettier/prettier.git",
+    "directory": "packages/plugin-hermes"
+  },
+  "funding": "https://github.com/prettier/prettier?sponsor=1",
+  "homepage": "https://github.com/prettier/prettier/packages/plugin-hermes",
+  "author": "fisker Cheung <lionkay@gmail.com>",
+  "license": "MIT"
+}

packages/plugin-oxc/README.md

@@ -1,6 +1,6 @@
 # @prettier/plugin-oxc
 
-> Prettier Oxc plugin.
+> Prettier [Oxc](https://oxc.rs/) plugin.
 
 ## Install
 
@@ -32,7 +32,3 @@ Create or modify your [prettier configuration file](https://prettier.io/docs/en/
   ]
 }
 ```
-
-## Related
-
-- [Oxc](https://oxc.rs/) - The JavaScript Oxidation Compiler

scripts/build-website.js

@@ -43,7 +43,7 @@ async function buildPrettier() {
   });
 
   try {
-    await runYarn("build", ["--package=prettier", "--clean", "--playground"], {
+    await runYarn("build", ["--clean", "--playground"], {
       cwd: PROJECT_ROOT,
     });
   } finally {
@@ -55,16 +55,30 @@ async function buildPrettier() {
 async function buildPlaygroundFiles() {
   const patterns = ["standalone.mjs", "plugins/*.mjs"];
 
-  const files = await fastGlob(patterns, {
+  let files = await fastGlob(patterns, {
     cwd: PRETTIER_DIR,
   });
 
+  files = files.map((fileName) => ({
+    fileName,
+    file: path.join(PRETTIER_DIR, fileName),
+    dist: path.join(PLAYGROUND_PRETTIER_DIR, fileName),
+  }));
+
+  // TODO: Support stable version
+  if (IS_PULL_REQUEST) {
+    const fileName = "plugins/hermes.mjs";
+    files.push({
+      fileName,
+      file: path.join(DIST_DIR, "plugin-hermes/index.mjs"),
+      dist: path.join(PLAYGROUND_PRETTIER_DIR, fileName),
+    });
+  }
+
   const packageManifest = {
     builtinPlugins: [],
   };
-  for (const fileName of files) {
+  for (const { fileName, file, dist } of files) {
-    const file = path.join(PRETTIER_DIR, fileName);
-    const dist = path.join(PLAYGROUND_PRETTIER_DIR, fileName);
     await copyFile(file, dist);
 
     if (fileName === "standalone.mjs") {

scripts/build/build-dependencies-license.js

@@ -135,9 +135,7 @@ async function buildDependenciesLicense({
   }
 
   const shouldBuildLicense =
-    !cliOptions.playground &&
+    !cliOptions.files && typeof cliOptions.minify !== "boolean";
-    !cliOptions.files &&
-    typeof cliOptions.minify !== "boolean";
 
   if (!shouldBuildLicense) {
     return { skipped: true };

scripts/build/build-javascript-module.js

@@ -224,7 +224,7 @@ function getEsbuildOptions({ packageConfig, file, cliOptions }) {
     bundle: true,
     metafile: true,
     plugins: [
-      esbuildPluginPrimitiveDefine(define),
+      esbuildPluginPrimitiveDefine({ ...define, ...buildOptions.define }),
       esbuildPluginEvaluate(),
       esbuildPluginStripNodeProtocol(),
       esbuildPluginReplaceModule({

scripts/build/build-package-json.js

@@ -141,6 +141,34 @@ async function buildPluginOxcPackageJson({ packageConfig, file }) {
   );
 }
 
+async function buildPluginHermesPackageJson({ packageConfig, file }) {
+  const { distDirectory, files } = packageConfig;
+  const packageJson = await readJson(path.join(PROJECT_ROOT, file.input));
+  const projectPackageJson = await readJson(
+    path.join(PROJECT_ROOT, "package.json"),
+  );
+
+  const overrides = {
+    engines: {
+      ...packageJson.engines,
+      // https://github.com/prettier/prettier/pull/13118#discussion_r922708068
+      // Don't delete, event it's the same in package.json
+      node: `>=${PRODUCTION_MINIMAL_NODE_JS_VERSION}`,
+    },
+    // Use `commonjs` since we may provide browser build in future.
+    type: "commonjs",
+    files: files.map(({ output: { file } }) => file).sort(),
+    dependencies: {
+      "hermes-parser": projectPackageJson.dependencies["hermes-parser"],
+    },
+  };
+
+  await writeJson(
+    path.join(distDirectory, file.output.file),
+    Object.assign(pick(packageJson, keysToKeep), overrides),
+  );
+}
+
 function pick(object, keys) {
   keys = new Set(keys);
   return Object.fromEntries(
@@ -148,4 +176,8 @@ function pick(object, keys) {
   );
 }
 
-export { buildPluginOxcPackageJson, buildPrettierPackageJson };
+export {
+  buildPluginHermesPackageJson,
+  buildPluginOxcPackageJson,
+  buildPrettierPackageJson,
+};

scripts/build/build.js

@@ -60,10 +60,7 @@ async function buildFile({ packageConfig, file, cliOptions, results }) {
 
   if (
     (cliOptions.files && !cliOptions.files.has(file.output.file)) ||
-    (cliOptions.playground &&
+    (cliOptions.playground && !file.playground)
-      (file.output.format !== "esm" ||
-        file.platform !== "universal" ||
-        file.output.file === "doc.mjs"))
   ) {
     console.log(status.SKIPPED);
     return;

scripts/build/config.js

@@ -7,6 +7,7 @@ import { copyFile, DIST_DIR, PROJECT_ROOT } from "../utils/index.js";
 import buildDependenciesLicense from "./build-dependencies-license.js";
 import buildJavascriptModule from "./build-javascript-module.js";
 import {
+  buildPluginHermesPackageJson,
   buildPluginOxcPackageJson,
   buildPrettierPackageJson,
 } from "./build-package-json.js";
@@ -738,6 +739,7 @@ const universalFiles = [...nonPluginUniversalFiles, ...pluginFiles].flatMap(
         isPlugin,
         build: buildJavascriptModule,
         kind: "javascript",
+        playground: output.format === "esm" && outputBaseName !== "doc",
       })),
       getTypesFileConfig({ input, outputBaseName, isPlugin }),
     ];
@@ -998,4 +1000,99 @@ export default [
       })),
     ],
   },
+  {
+    packageName: "@prettier/plugin-hermes",
+    distDirectory: path.join(DIST_DIR, "plugin-hermes"),
+    files: [
+      ...[
+        {
+          input: "packages/plugin-hermes/index.js",
+          addDefaultExport: true,
+          replaceModule: [
+            {
+              module: require.resolve("hermes-parser/dist/HermesParser.js"),
+              process(text) {
+                text =
+                  'const Buffer = globalThis.Buffer ?? require("buffer/").Buffer;' +
+                  text;
+                return text;
+              },
+            },
+            {
+              module: require.resolve("hermes-parser/dist/HermesParserWASM.js"),
+              process(text) {
+                text = text.replaceAll("process.argv", "[]");
+                text = text.replaceAll('require("fs")', "undefined");
+                text = text.replaceAll('require("path")', "undefined");
+                text =
+                  'const Buffer = globalThis.Buffer ?? require("buffer/").Buffer;' +
+                  text;
+
+                return text;
+              },
+            },
+          ],
+        },
+      ].flatMap((file) => {
+        let { input, output, outputBaseName, ...buildOptions } = file;
+
+        outputBaseName ??= path.basename(input, path.extname(input));
+        const format = input.endsWith(".cjs") ? "cjs" : "esm";
+
+        return [
+          {
+            input,
+            output: {
+              format,
+              file: `${outputBaseName}${extensions[format]}`,
+            },
+            platform: "universal",
+            buildOptions: {
+              addDefaultExport: true,
+              ...buildOptions,
+            },
+            isPlugin: true,
+            build: buildJavascriptModule,
+            playground: true,
+            kind: "javascript",
+          },
+          getTypesFileConfig({ input, outputBaseName, isPlugin: true }),
+        ];
+      }),
+      ...[
+        {
+          input: "packages/plugin-hermes/package.json",
+          output: {
+            file: "package.json",
+            format: "json",
+          },
+          build: buildPluginHermesPackageJson,
+        },
+        {
+          input: "packages/plugin-hermes/README.md",
+          output: {
+            file: "README.md",
+          },
+          build: copyFileBuilder,
+        },
+        {
+          input: "LICENSE",
+          output: {
+            file: "LICENSE",
+          },
+          build: copyFileBuilder,
+        },
+        {
+          output: {
+            file: "THIRD-PARTY-NOTICES.md",
+          },
+          build: buildDependenciesLicense,
+        },
+      ].map((file) => ({
+        ...file,
+        output: { file: file.input, ...file.output },
+        kind: "meta",
+      })),
+    ],
+  },
 ];

src/language-js/comments/printer-methods.js

@@ -44,6 +44,7 @@ function getCommentChildNodes(node, options) {
   if (
     (options.parser === "typescript" ||
       options.parser === "flow" ||
+      options.parser === "hermes" ||
       options.parser === "acorn" ||
       options.parser === "oxc" ||
       options.parser === "oxc-ts" ||
@@ -81,7 +82,7 @@ function willPrintOwnComments(path) {
 }
 
 function isGap(text, { parser }) {
-  if (parser === "flow" || parser === "babel-flow") {
+  if (parser === "flow" || parser === "hermes" || parser === "babel-flow") {
     // Example: (a /* b */ /* : c */)
     //                gap ^^^^
     text = text.replaceAll(/[\s(]/gu, "");

src/language-js/parse/flow.js

@@ -27,10 +27,14 @@ const parseOptions = {
 };
 
 function createParseError(error) {
-  const {
+  const { message, loc } = error;
-    message,
+
-    loc: { start, end },
+  /* c8 ignore next 3 */
-  } = error;
+  if (!loc) {
+    return error;
+  }
+
+  const { start, end } = loc;
 
   return createError(message, {
     loc: {

src/language-js/parse/hermes.js

@@ -0,0 +1,51 @@
+import { parse as hermesParse } from "hermes-parser";
+import createError from "../../common/parser-create-error.js";
+import postprocess from "./postprocess/index.js";
+import createParser from "./utils/create-parser.js";
+
+function createParseError(error) {
+  let { message, loc } = error;
+
+  if (!loc) {
+    return error;
+  }
+
+  const { line, column } = loc;
+
+  message = message.split("\n")[0];
+
+  const suffix = `(${line}:${column})`;
+  if (message.endsWith(suffix)) {
+    message = message.slice(0, -suffix.length);
+  }
+  message = message.trim();
+
+  return createError(message, {
+    loc: {
+      start: { line, column },
+    },
+    cause: error,
+  });
+}
+
+const parseOptions = {
+  flow: "all",
+  babel: false,
+  // Not supported yet
+  enableExperimentalFlowMatchSyntax: false,
+  tokens: false,
+  allowReturnOutsideFunction: true,
+};
+
+async function parse(text /*, options*/) {
+  let ast;
+  try {
+    ast = await hermesParse(text, parseOptions);
+  } catch (error) {
+    throw createParseError(error);
+  }
+
+  return postprocess(ast, { text, parser: "hermes" });
+}
+
+export const hermes = createParser(parse);

src/language-js/parse/oxc.js

@@ -8,6 +8,11 @@ import jsxRegexp from "./utils/jsx-regexp.evaluate.js";
 import { getSourceType } from "./utils/source-types.js";
 
 function createParseError(error, { text }) {
+  /* c8 ignore next 3 */
+  if (!error?.labels?.[0]) {
+    return error;
+  }
+
   const {
     message,
     labels: [{ start: startIndex, end: endIndex }],

src/language-js/parse/postprocess/index.js

@@ -134,10 +134,11 @@ function postprocess(ast, options) {
         break;
 
       case "TemplateElement":
-        // `flow`, `typescript`, and `oxc`(with `{astType: 'ts'}`) follows the `espree` style positions
+        // `flow`, `hermes`, `typescript`, and `oxc`(with `{astType: 'ts'}`) follows the `espree` style positions
         // https://github.com/eslint/js/blob/5826877f7b33548e5ba984878dd4a8eac8448f87/packages/espree/lib/espree.js#L213
         if (
           parser === "flow" ||
+          parser === "hermes" ||
           parser === "espree" ||
           parser === "typescript" ||
           (parser === "oxc" && options.oxcAstType === "ts")
@@ -215,6 +216,13 @@ function postprocess(ast, options) {
           delete node.members;
         }
         break;
+
+      // https://github.com/facebook/hermes/issues/1712
+      case "ImportExpression":
+        if (parser === "hermes" && node.attributes && !node.options) {
+          node.options = node.attributes;
+        }
+        break;
     }
 
     /* c8 ignore next 3 */

src/language-js/parse/typescript.js

@@ -30,15 +30,14 @@ const baseParseOptions = {
 };
 
 function createParseError(error) {
+  const { message, location } = error;
+
   /* c8 ignore next 3 -- not a parse error */
-  if (!error?.location) {
+  if (!location) {
     return error;
   }
 
-  const {
+  const { start, end } = location;
-    message,
-    location: { start, end },
-  } = error;
 
   return createError(message, {
     loc: {

src/language-js/parse/utils/create-babel-parse-error.js

@@ -1,13 +1,16 @@
 import createError from "../../../common/parser-create-error.js";
 
 function createBabelParseError(error) {
+  let { message, loc, reasonCode } = error;
+
+  /* c8 ignore next 3 */
+  if (!loc) {
+    return error;
+  }
+
   // babel error prints (line:column) with cols that are zero indexed
   // so we need our custom error
-  let {
+  const { line, column } = loc;
-    message,
-    loc: { line, column },
-    reasonCode,
-  } = error;
 
   let cause = error;
   if (reasonCode === "MissingPlugin" || reasonCode === "MissingOneOfPlugins") {

src/main/range-util.js

@@ -170,6 +170,7 @@ function isSourceElement(opts, node, parentNode) {
   }
   switch (opts.parser) {
     case "flow":
+    case "hermes":
     case "babel":
     case "babel-flow":
     case "babel-ts":

tests/config/run-format-test.js

@@ -103,6 +103,23 @@ const oxcTsDisabledTests = new Set(
     "typescript/decorators/abstract-method.ts",
   ].map((file) => path.join(__dirname, "../format", file)),
 );
+const hermesDisabledTests = new Set([
+  ...commentClosureTypecaseTests,
+  ...[
+    // Need update L183 to use `replaceAll`
+    // https://app.unpkg.com/hermes-parser@0.28.1/files/dist/HermesASTAdapter.js
+    "js/call/first-argument-expansion/expression-2nd-arg.js",
+    "js/directives/escaped.js",
+    // Not supported
+    "flow/comments",
+    "flow-repo/union_new",
+    // Wrongly parsed
+    "js/sloppy-mode/function-declaration-in-if.js",
+    // Wrong location of `Property.value`
+    "js/classes/method.js",
+    "js/comments/function-declaration.js",
+  ].map((file) => path.join(__dirname, "../format", file)),
+]);
 
 const isUnstable = (filename, options) => {
   const testFunction = unstableTests.get(filename);
@@ -274,6 +291,14 @@ function runFormatTest(fixtures, parsers, options) {
       allParsers.push("babel-flow");
     }
 
+    if (
+      parsers.includes("flow") &&
+      !parsers.includes("hermes") &&
+      !hermesDisabledTests.has(dirname)
+    ) {
+      allParsers.push("hermes");
+    }
+
     if (parsers.includes("babel") && !parsers.includes("__babel_estree")) {
       allParsers.push("__babel_estree");
     }
@@ -314,6 +339,7 @@ function runFormatTest(fixtures, parsers, options) {
           (currentParser === "meriyah" && meriyahDisabledTests.has(filename)) ||
           (currentParser === "oxc" && oxcDisabledTests.has(filename)) ||
           (currentParser === "oxc-ts" && oxcTsDisabledTests.has(filename)) ||
+          (currentParser === "hermes" && hermesDisabledTests.has(filename)) ||
           (currentParser === "babel-ts" && babelTsDisabledTests.has(filename))
         ) {
           continue;
@@ -487,9 +513,11 @@ function shouldSkipEolTest(code, options) {
 
 async function parse(source, options) {
   const prettier = await getPrettier();
-  const { ast } = await prettier.__debug.parse(source, options, {
+  const { ast } = await ensurePromise(
-    massage: true,
+    prettier.__debug.parse(source, await loadPlugins(options), {
-  });
+      massage: true,
+    }),
+  );
   return ast;
 }
 
@@ -534,16 +562,15 @@ const insertCursor = (text, cursorOffset) =>
       text.slice(cursorOffset)
     : text;
 async function format(originalText, originalOptions) {
-  let { text: input, options } = replacePlaceholders(
+  const { text: input, options } = replacePlaceholders(
     originalText,
     originalOptions,
   );
-  options = await loadPlugins(options);
   const inputWithCursor = insertCursor(input, options.cursorOffset);
   const prettier = await getPrettier();
 
   const { formatted: output, cursorOffset } = await ensurePromise(
-    prettier.formatWithCursor(input, options),
+    prettier.formatWithCursor(input, await loadPlugins(options)),
   );
   const outputWithCursor = insertCursor(output, cursorOffset);
   const eolVisualizedOutput = visualizeEndOfLine(outputWithCursor);
@@ -561,13 +588,20 @@ async function format(originalText, originalOptions) {
   };
 }
 
+const externalPlugins = new Map([
+  ["oxc", "plugin-oxc"],
+  ["oxc-ts", "plugin-oxc"],
+  ["hermes", "plugin-hermes"],
+]);
 async function loadPlugins(options) {
-  if (options.parser === "oxc" || options.parser === "oxc-ts") {
+  const { parser } = options;
+  if (externalPlugins.has(options.parser)) {
     const plugins = options.plugins ?? [];
+    const pluginName = externalPlugins.get(parser);
     const url = new URL(
       isProduction
-        ? "../../dist/plugin-oxc/index.mjs"
+        ? `../../dist/${pluginName}/index.mjs`
-        : "../../packages/plugin-oxc/index.js",
+        : `../../packages/${pluginName}/index.js`,
       import.meta.url,
     );
     plugins.push(TEST_STANDALONE ? await import(url) : url);

tests/format/flow-repo/binding/__snapshots__/format.test.js.snap

@@ -1,5 +1,18 @@
 // Jest Snapshot v1, https://goo.gl/fbAQLP
 
+exports[`const.js [hermes] format 1`] = `
+"invalid operand in update operation (4:0)
+  2 |
+  3 | // errors: const cannot be reassigned
+> 4 | x++;
+  5 | x--;
+  6 | x += 0;
+  7 | x -= 0;
+Cause: invalid operand in update operation (4:0)
+x++;
+^"
+`;
+
 exports[`const.js format 1`] = `
 ====================================options=====================================
 parsers: ["flow"]
@@ -66,6 +79,23 @@ for (const { baz } of bazzes) {
 ================================================================================
 `;
 
+exports[`rebinding.js [hermes] format 1`] = `
+"Identifier 'A' is already declared (53:8)
+  51 | function class_class() {
+  52 |   class A {}
+> 53 |   class A {}        // error: name already bound
+     |        ^
+  54 | }
+  55 |
+  56 | function class_let() {
+Cause: Identifier 'A' is already declared (53:8)
+  class A {}        // error: name already bound
+        ^
+note: previous declaration (52:8)
+  class A {}
+        ^"
+`;
+
 exports[`rebinding.js format 1`] = `
 ====================================options=====================================
 parsers: ["flow"]
@@ -472,6 +502,23 @@ function fn_params_clash_fn_binding(x, y) {
 ================================================================================
 `;
 
+exports[`scope.js [hermes] format 1`] = `
+"Identifier 'a' is already declared (19:10)
+  17 |       break;
+  18 |     case "bar":
+> 19 |       let a = ""; // error: a already bound in switch
+     |          ^
+  20 |       break;
+  21 |   }
+  22 | }
+Cause: Identifier 'a' is already declared (19:10)
+      let a = ""; // error: a already bound in switch
+          ^
+note: previous declaration (15:10)
+      let a = ""; // ok: local to switch
+          ^"
+`;
+
 exports[`scope.js format 1`] = `
 ====================================options=====================================
 parsers: ["flow"]

tests/format/flow-repo/binding/format.test.js

@@ -1 +1,3 @@
-runFormatTest(import.meta, ["flow"]);
+runFormatTest(import.meta, ["flow"], {
+  errors: { hermes: ["const.js", "rebinding.js", "scope.js"] },
+});

tests/format/flow-repo/esproposal_decorators.ignore/__snapshots__/format.test.js.snap

@@ -1,5 +1,18 @@
 // Jest Snapshot v1, https://goo.gl/fbAQLP
 
+exports[`test.js [hermes] format 1`] = `
+"unrecognized character '@' (3:0)
+  1 | /* @flow */
+  2 |
+> 3 | @decorator4
+  4 | class Foo {
+  5 |   @decorator1
+  6 |   method1() {}
+Cause: unrecognized character '@' (3:0)
+@decorator4
+^"
+`;
+
 exports[`test.js format 1`] = `
 ====================================options=====================================
 parsers: ["flow"]

tests/format/flow-repo/esproposal_decorators.ignore/format.test.js

@@ -1 +1,5 @@
-runFormatTest(import.meta, ["flow"]);
+runFormatTest(import.meta, ["flow"], {
+  errors: {
+    hermes:["test.js"],
+  },
+});

tests/format/flow-repo/esproposal_decorators.warn/__snapshots__/format.test.js.snap

@@ -1,5 +1,18 @@
 // Jest Snapshot v1, https://goo.gl/fbAQLP
 
+exports[`test.js [hermes] format 1`] = `
+"unrecognized character '@' (3:0)
+  1 | /* @flow */
+  2 |
+> 3 | @decorator4
+  4 | class Foo {
+  5 |   @decorator1
+  6 |   method1() {}
+Cause: unrecognized character '@' (3:0)
+@decorator4
+^"
+`;
+
 exports[`test.js format 1`] = `
 ====================================options=====================================
 parsers: ["flow"]

tests/format/flow-repo/esproposal_decorators.warn/format.test.js

@@ -1 +1,2 @@
-runFormatTest(import.meta, ["flow"]);
+runFormatTest(import.meta, ["flow"], {errors: { hermes: ["test.js"] }
+});

tests/format/flow-repo/find-module/__snapshots__/format.test.js.snap

@@ -14,6 +14,21 @@ module.exports = 0;
 ================================================================================
 `;
 
+exports[`test.js [hermes] format 1`] = `
+"Identifier 'x' is already declared (4:7)
+  2 | (x: string);
+  3 |
+> 4 | import x from './req';
+    |       ^
+  5 |
+Cause: Identifier 'x' is already declared (4:7)
+import x from './req';
+       ^
+note: previous declaration (1:4)
+var x = require('./req');
+    ^"
+`;
+
 exports[`test.js format 1`] = `
 ====================================options=====================================
 parsers: ["flow"]

tests/format/flow-repo/find-module/format.test.js

@@ -1 +1 @@
-runFormatTest(import.meta, ["flow"]);
+runFormatTest(import.meta, ["flow"], { errors: { hermes: ["test.js"] } });

tests/format/flow-repo/type_only_vars/__snapshots__/format.test.js.snap

@@ -38,6 +38,23 @@ module.exports = {
 ================================================================================
 `;
 
+exports[`bad_shadowing.js [hermes] format 1`] = `
+"Identifier 'A' is already declared (13:4)
+  11 |
+  12 | // These string types should confict with the imported types
+> 13 | var A: string = "Hello";
+     |    ^
+  14 | var Foo: string = "Goodbye";
+  15 | var Baz: string = "Go away please";
+  16 |
+Cause: Identifier 'A' is already declared (13:4)
+var A: string = "Hello";
+    ^~~~~~~~~
+note: previous declaration (5:14)
+import typeof A from "./A.js";
+              ^"
+`;
+
 exports[`bad_shadowing.js format 1`] = `
 ====================================options=====================================
 parsers: ["flow"]
@@ -86,6 +103,23 @@ var duck: string = "quack";
 ================================================================================
 `;
 
+exports[`good_shadowing.js [hermes] format 1`] = `
+"Identifier 'A' is already declared (8:4)
+   6 | import type {Foo, Bar as Baz} from "./A.js";
+   7 |
+>  8 | var A = require('./A.js');
+     |    ^
+   9 | var Foo = A.Foo;
+  10 | var Baz = A.Bar;
+  11 |
+Cause: Identifier 'A' is already declared (8:4)
+var A = require('./A.js');
+    ^
+note: previous declaration (5:14)
+import typeof A from "./A.js";
+              ^"
+`;
+
 exports[`good_shadowing.js format 1`] = `
 ====================================options=====================================
 parsers: ["flow"]

tests/format/flow-repo/type_only_vars/format.test.js

@@ -1 +1,5 @@
-runFormatTest(import.meta, ["flow"]);
+runFormatTest(import.meta, ["flow"], {
+  errors: {
+    hermes: ["bad_shadowing.js", "good_shadowing.js"],
+  },
+});

tests/format/flow-repo/unary/__snapshots__/format.test.js.snap

@@ -50,6 +50,20 @@ function x4(y: string): boolean {
 ================================================================================
 `;
 
+exports[`update.js [hermes] format 1`] = `
+"invalid operand in update operation (31:4)
+  29 |   function() {
+  30 |     const y = 123;
+> 31 |     y++; // error, can't update const
+     |    ^
+  32 |     y--; // error, can't update const
+  33 |   },
+  34 |
+Cause: invalid operand in update operation (31:4)
+    y++; // error, can't update const
+    ^"
+`;
+
 exports[`update.js format 1`] = `
 ====================================options=====================================
 parsers: ["flow"]

tests/format/flow-repo/unary/format.test.js

@@ -1 +1,5 @@
-runFormatTest(import.meta, ["flow"]);
+runFormatTest(import.meta, ["flow"], {
+  errors: {
+    hermes: ["update.js"],
+  },
+});

tests/format/flow/as-satisfies-expression/__snapshots__/format.test.js.snap

@@ -428,6 +428,20 @@ exports[`satisfies.js [babel-flow] format 1`] = `
 Cause: Unexpected token, expected "type" (32:7)"
 `;
 
+exports[`satisfies.js [hermes] format 1`] = `
+"';' expected (3:12)
+  1 | // @flow
+  2 |
+> 3 | const x = y satisfies T;
+    |            ^
+  4 |
+  5 | // demonstrating how "satisfies" expression can be practically used as expression statement.
+  6 | const _ = (type: 'foo' | 'bar') => {
+Cause: ';' expected (3:12)
+const x = y satisfies T;
+            ^"
+`;
+
 exports[`satisfies.js format 1`] = `
 ====================================options=====================================
 parsers: ["flow"]
@@ -532,6 +546,19 @@ exports[`ternary.js [babel-flow] format 1`] = `
 Cause: Unexpected token, expected "," (28:31)"
 `;
 
+exports[`ternary.js [hermes] format 1`] = `
+"invalid assignment left-hand side (3:0)
+  1 | // @flow
+  2 |
+> 3 | foo = (coooooooooooooooooooooooooooooooooooooooooooooooooooond
+  4 |     ? baaaaaaaaaaaaaaaaaaaaar
+  5 |     : baaaaaaaaaaaaaaaaaaaaaz) as Fooooooooooo;
+  6 |
+Cause: invalid assignment left-hand side (3:0)
+foo = (coooooooooooooooooooooooooooooooooooooooooooooooooooond
+^~~"
+`;
+
 exports[`ternary.js format 1`] = `
 ====================================options=====================================
 parsers: ["flow"]

tests/format/flow/as-satisfies-expression/format.test.js

@@ -1 +1,6 @@
-runFormatTest(import.meta, ["flow"], { errors: { "babel-flow": true } });
+runFormatTest(import.meta, ["flow"], {
+  errors: {
+    "babel-flow": true,
+    hermes: ["satisfies.js", "ternary.js"],
+  },
+});

tests/format/flow/assignments/__snapshots__/format.test.js.snap

@@ -92,10 +92,10 @@ printWidth: 80
 const map: Map<Function, Map<string | void, { value: UnloadedDescriptor }>> =
   new Map();
 
-const map: Map<Function, FunctionFunctionFunctionFunctionffFunction> =
+const ma2: Map<Function, FunctionFunctionFunctionFunctionffFunction> =
   new Map();
 
-const map: Map<Function, Foo<S>> = new Map();
+const ma3: Map<Function, Foo<S>> = new Map();
 
 =====================================output=====================================
 const map: Map<
@@ -103,10 +103,10 @@ const map: Map<
   Map<string | void, { value: UnloadedDescriptor }>,
 > = new Map();
 
-const map: Map<Function, FunctionFunctionFunctionFunctionffFunction> =
+const ma2: Map<Function, FunctionFunctionFunctionFunctionffFunction> =
   new Map();
 
-const map: Map<Function, Foo<S>> = new Map();
+const ma3: Map<Function, Foo<S>> = new Map();
 
 ================================================================================
 `;

tests/format/flow/assignments/issue-10850.js

@@ -1,7 +1,7 @@
 const map: Map<Function, Map<string | void, { value: UnloadedDescriptor }>> =
   new Map();
 
-const map: Map<Function, FunctionFunctionFunctionFunctionffFunction> =
+const ma2: Map<Function, FunctionFunctionFunctionFunctionffFunction> =
   new Map();
 
-const map: Map<Function, Foo<S>> = new Map();
+const ma3: Map<Function, Foo<S>> = new Map();

tests/format/flow/await/__snapshots__/format.test.js.snap

@@ -12,6 +12,19 @@ exports[`await-keywords.js [babel-flow] format 1`] = `
 Cause: 'await' is only allowed within async functions and at the top levels of modules. (12:6)"
 `;
 
+exports[`await-keywords.js [hermes] format 1`] = `
+"'await' not in an async function (2:6)
+  1 | export class C1 {
+> 2 |   p = await (0);
+    |      ^
+  3 | }
+  4 |
+  5 | await (0);
+Cause: 'await' not in an async function (2:6)
+  p = await (0);
+      ^~~~~~~~~"
+`;
+
 exports[`await-keywords.js format 1`] = `
 ====================================options=====================================
 parsers: ["flow"]

tests/format/flow/await/format.test.js

@@ -1,3 +1,6 @@
 runFormatTest(import.meta, ["flow"], {
-  errors: { "babel-flow": ["await-keywords.js"] },
+  errors: {
+    "babel-flow": ["await-keywords.js"],
+    hermes: ["await-keywords.js"],
+  },
 });

tests/format/flow/implements/__snapshots__/format.test.js.snap

@@ -7,17 +7,17 @@ printWidth: 80
                                                                                 | printWidth
 =====================================input======================================
 class A implements B {}
-class A implements B, C {}
+class B implements B, C {}
-declare class A implements B {}
+declare class C implements B {}
-declare class A mixins B implements C {}
+declare class D mixins B implements C {}
-declare class A implements B, C {}
+declare class E implements B, C {}
 
 =====================================output=====================================
 class A implements B {}
-class A implements B, C {}
+class B implements B, C {}
-declare class A implements B {}
+declare class C implements B {}
-declare class A mixins B implements C {}
+declare class D mixins B implements C {}
-declare class A implements B, C {}
+declare class E implements B, C {}
 
 ================================================================================
 `;

tests/format/flow/implements/implements.js

@@ -1,5 +1,5 @@
 class A implements B {}
-class A implements B, C {}
+class B implements B, C {}
-declare class A implements B {}
+declare class C implements B {}
-declare class A mixins B implements C {}
+declare class D mixins B implements C {}
-declare class A implements B, C {}
+declare class E implements B, C {}

tests/format/flow/import-type-specifier/__snapshots__/format.test.js.snap

@@ -14,7 +14,7 @@ import { Foo, type Baz } from "../module";
 import type {} from 'foo';
 
 import type {somethingSuperLongsomethingSuperLong} from 'somethingSuperLongsomethingSuperLongsomethingSuperLong'
-import type {a, somethingSuperLongsomethingSuperLong} from 'somethingSuperLongsomethingSuperLongsomethingSuperLong'
+import type {a, somethingSuperLongsomethingSuperLon2} from 'somethingSuperLongsomethingSuperLongsomethingSuperLong'
 
 import transformRouterContext, { type TransformedContextRouter } from '../../helpers/transformRouterContext';
 
@@ -29,7 +29,7 @@ import type {} from "foo";
 import type { somethingSuperLongsomethingSuperLong } from "somethingSuperLongsomethingSuperLongsomethingSuperLong";
 import type {
   a,
-  somethingSuperLongsomethingSuperLong,
+  somethingSuperLongsomethingSuperLon2,
 } from "somethingSuperLongsomethingSuperLongsomethingSuperLong";
 
 import transformRouterContext, {

tests/format/flow/import-type-specifier/test.js

@@ -6,6 +6,6 @@ import { Foo, type Baz } from "../module";
 import type {} from 'foo';
 
 import type {somethingSuperLongsomethingSuperLong} from 'somethingSuperLongsomethingSuperLongsomethingSuperLong'
-import type {a, somethingSuperLongsomethingSuperLong} from 'somethingSuperLongsomethingSuperLongsomethingSuperLong'
+import type {a, somethingSuperLongsomethingSuperLon2} from 'somethingSuperLongsomethingSuperLongsomethingSuperLong'
 
 import transformRouterContext, { type TransformedContextRouter } from '../../helpers/transformRouterContext';

tests/format/flow/import/__snapshots__/format.test.js.snap

@@ -8,18 +8,32 @@ printWidth: 80
 =====================================input======================================
 // @flow
 import { foo as as } from "foo";
-import { as as as } from "foo";
 import { as as foo } from "foo";
 
 =====================================output=====================================
 // @flow
 import { foo as as } from "foo";
-import { as as as } from "foo";
 import { as as foo } from "foo";
 
 ================================================================================
 `;
 
+exports[`import-as-as2.js format 1`] = `
+====================================options=====================================
+parsers: ["flow"]
+printWidth: 80
+                                                                                | printWidth
+=====================================input======================================
+// @flow
+import { as as as } from "foo";
+
+=====================================output=====================================
+// @flow
+import { as as as } from "foo";
+
+================================================================================
+`;
+
 exports[`type-import-as-as.js format 1`] = `
 ====================================options=====================================
 parsers: ["flow"]

tests/format/flow/import/import-as-as.js

@@ -1,4 +1,3 @@
 // @flow
 import { foo as as } from "foo";
-import { as as as } from "foo";
 import { as as foo } from "foo";

tests/format/flow/import/import-as-as2.js

@@ -0,0 +1,2 @@
+// @flow
+import { as as as } from "foo";

tests/format/flow/ternary/__snapshots__/format.test.js.snap

@@ -58,3 +58,51 @@ exports[`arrows.js [flow] format 1`] = `
   8 |
   9 | (a ? (b = c) : d => e : f); // a ? ((b = c): d => e) : f"
 `;
+
+exports[`arrows.js [hermes] format 1`] = `
+====================================options=====================================
+parsers: ["flow"]
+printWidth: 80
+                                                                                | printWidth
+=====================================input======================================
+// Test cases from babel
+//   ref: https://github.com/babel/babel/blob/614b48678095746b83bbe517c4d6b30ba8cd5c04/packages/babel-parser/test/fixtures/flow/arrows-in-ternaries/issue-13644/input.js
+// \`flow\` cannot parse below codes
+//   ref: https://github.com/facebook/flow/issues/8731
+
+(a ? (b = c) : d => e); // a ? (b = c) : (d => e)
+(a ? (b += c) : d => e); // a ? (b += c) : (d => e)
+
+(a ? (b = c) : d => e : f); // a ? ((b = c): d => e) : f
+(a ? (b += c) : d => e : f); // ((a ? (b += c) : (d => e)) : f)
+
+(a ? b => (c = d) : e => f); // a ? (b => (c = d)) : (e => f)
+(a ? b => (c += d) : e => f); // a ? (b => (c += d)) : (e => f)
+
+(a ? b => (c = d) : e => f : g); // a ? (b => ((c = d): e => f)) : g
+(a ? b => (c += d) : e => f : g); // ((a ? (b => (c += d)) : (e => f)) : g)
+
+=====================================output=====================================
+// Test cases from babel
+//   ref: https://github.com/babel/babel/blob/614b48678095746b83bbe517c4d6b30ba8cd5c04/packages/babel-parser/test/fixtures/flow/arrows-in-ternaries/issue-13644/input.js
+// \`flow\` cannot parse below codes
+//   ref: https://github.com/facebook/flow/issues/8731
+
+a ? (b = c) : (d) => e; // a ? (b = c) : (d => e)
+a ? (b += c) : (d) => e; // a ? (b += c) : (d => e)
+
+a ? (b = c): d => e : f; // a ? ((b = c): d => e) : f
+a ? (): d => e : f; // ((a ? (b += c) : (d => e)) : f)
+
+a ? (b) => (c = d) : (e) => f; // a ? (b => (c = d)) : (e => f)
+a ? (b) => (c += d) : (e) => f; // a ? (b => (c += d)) : (e => f)
+
+a
+  ? (b) =>
+      (c = d): e =>
+        f
+  : g; // a ? (b => ((c = d): e => f)) : g
+a ? (b) => (): e => f : g; // ((a ? (b => (c += d)) : (e => f)) : g)
+
+================================================================================
+`;

tests/format/flow/type-parameters/flow-only/__snapshots__/format.test.js.snap

@@ -51,7 +51,7 @@ class C<const T>{}
 type T<const +X> = X;
 function f<const +T>(): void {}
 <const +T>(x: T) => {}
-class C<const +T>{}
+class D<const +T>{}
 
 =====================================output=====================================
 // Simple
@@ -64,7 +64,7 @@ class C<const T> {}
 type T<const +X> = X;
 function f<const +T>(): void {}
 <const +T>(x: T) => {};
-class C<const +T> {}
+class D<const +T> {}
 
 ================================================================================
 `;

tests/format/flow/type-parameters/flow-only/const-type-params.js

@@ -8,4 +8,4 @@ class C<const T>{}
 type T<const +X> = X;
 function f<const +T>(): void {}
 <const +T>(x: T) => {}
-class C<const +T>{}
+class D<const +T>{}

tests/format/js/assignment/__snapshots__/format.test.js.snap

@@ -1,5 +1,18 @@
 // Jest Snapshot v1, https://goo.gl/fbAQLP
 
+exports[`binaryish.js [hermes] format 1`] = `
+"invalid assignment left-hand side (6:0)
+  4 |   descriptionLines;
+  5 |
+> 6 | computedDescriptionLines = (focused &&
+  7 |   !loading &&
+  8 |   descriptionLinesFocused) ||
+  9 |   descriptionLines;
+Cause: invalid assignment left-hand side (6:0)
+computedDescriptionLines = (focused &&
+^~~~~~~~~~~~~~~~~~~~~~~~"
+`;
+
 exports[`binaryish.js format 1`] = `
 ====================================options=====================================
 parsers: ["babel", "flow", "typescript"]

tests/format/js/assignment/format.test.js

@@ -1 +1,5 @@
-runFormatTest(import.meta, ["babel", "flow", "typescript"]);
+runFormatTest(import.meta, ["babel", "flow", "typescript"], {
+  errors: {
+    hermes: ["binaryish.js"],
+  },
+});

tests/format/js/decorators/class-expression/__snapshots__/format.test.js.snap

@@ -26,6 +26,17 @@ exports[`arguments.js [flow] format 1`] = `
   3 |"
 `;
 
+exports[`arguments.js [hermes] format 1`] = `
+"unrecognized character '@' (1:12)
+> 1 | console.log(@deco class Foo {})
+    |            ^
+  2 | console.log(@deco class {})
+  3 |
+Cause: unrecognized character '@' (1:12)
+console.log(@deco class Foo {})
+            ^"
+`;
+
 exports[`arguments.js - {"semi":false} [acorn] format 1`] = `
 "Unexpected character '@' (1:13)
 > 1 | console.log(@deco class Foo {})
@@ -52,6 +63,17 @@ exports[`arguments.js - {"semi":false} [flow] format 1`] = `
   3 |"
 `;
 
+exports[`arguments.js - {"semi":false} [hermes] format 1`] = `
+"unrecognized character '@' (1:12)
+> 1 | console.log(@deco class Foo {})
+    |            ^
+  2 | console.log(@deco class {})
+  3 |
+Cause: unrecognized character '@' (1:12)
+console.log(@deco class Foo {})
+            ^"
+`;
+
 exports[`arguments.js - {"semi":false} format 1`] = `
 ====================================options=====================================
 parsers: ["babel", "flow", "typescript"]
@@ -126,6 +148,18 @@ exports[`class-expression.js [flow] format 1`] = `
   4 | (@deco class Foo {});"
 `;
 
+exports[`class-expression.js [hermes] format 1`] = `
+"unrecognized character '@' (1:12)
+> 1 | const a1 = (@deco class Foo {});
+    |            ^
+  2 | const a2 = (@deco class {});
+  3 |
+  4 | (@deco class Foo {});
+Cause: unrecognized character '@' (1:12)
+const a1 = (@deco class Foo {});
+            ^"
+`;
+
 exports[`class-expression.js - {"semi":false} [acorn] format 1`] = `
 "Unexpected character '@' (1:13)
 > 1 | const a1 = (@deco class Foo {});
@@ -155,6 +189,18 @@ exports[`class-expression.js - {"semi":false} [flow] format 1`] = `
   4 | (@deco class Foo {});"
 `;
 
+exports[`class-expression.js - {"semi":false} [hermes] format 1`] = `
+"unrecognized character '@' (1:12)
+> 1 | const a1 = (@deco class Foo {});
+    |            ^
+  2 | const a2 = (@deco class {});
+  3 |
+  4 | (@deco class Foo {});
+Cause: unrecognized character '@' (1:12)
+const a1 = (@deco class Foo {});
+            ^"
+`;
+
 exports[`class-expression.js - {"semi":false} format 1`] = `
 ====================================options=====================================
 parsers: ["babel", "flow", "typescript"]
@@ -296,6 +342,17 @@ exports[`member-expression.js [flow] format 1`] = `
   3 |"
 `;
 
+exports[`member-expression.js [hermes] format 1`] = `
+"unrecognized character '@' (1:1)
+> 1 | (@deco class Foo {}).name;
+    | ^
+  2 | (@deco class {}).name;
+  3 |
+Cause: unrecognized character '@' (1:1)
+(@deco class Foo {}).name;
+ ^"
+`;
+
 exports[`member-expression.js - {"semi":false} [acorn] format 1`] = `
 "Unexpected character '@' (1:2)
 > 1 | (@deco class Foo {}).name;
@@ -322,6 +379,17 @@ exports[`member-expression.js - {"semi":false} [flow] format 1`] = `
   3 |"
 `;
 
+exports[`member-expression.js - {"semi":false} [hermes] format 1`] = `
+"unrecognized character '@' (1:1)
+> 1 | (@deco class Foo {}).name;
+    | ^
+  2 | (@deco class {}).name;
+  3 |
+Cause: unrecognized character '@' (1:1)
+(@deco class Foo {}).name;
+ ^"
+`;
+
 exports[`member-expression.js - {"semi":false} format 1`] = `
 ====================================options=====================================
 parsers: ["babel", "flow", "typescript"]
@@ -396,6 +464,18 @@ exports[`super-class.js [flow] format 1`] = `
   4 |"
 `;
 
+exports[`super-class.js [hermes] format 1`] = `
+"unrecognized character '@' (1:19)
+> 1 | class Foo extends (@deco class Foo {}){}
+    |                   ^
+  2 |
+  3 | class Foo extends (@deco class {}){}
+  4 |
+Cause: unrecognized character '@' (1:19)
+class Foo extends (@deco class Foo {}){}
+                   ^"
+`;
+
 exports[`super-class.js - {"semi":false} [acorn] format 1`] = `
 "Unexpected character '@' (1:20)
 > 1 | class Foo extends (@deco class Foo {}){}
@@ -425,6 +505,18 @@ exports[`super-class.js - {"semi":false} [flow] format 1`] = `
   4 |"
 `;
 
+exports[`super-class.js - {"semi":false} [hermes] format 1`] = `
+"unrecognized character '@' (1:19)
+> 1 | class Foo extends (@deco class Foo {}){}
+    |                   ^
+  2 |
+  3 | class Foo extends (@deco class {}){}
+  4 |
+Cause: unrecognized character '@' (1:19)
+class Foo extends (@deco class Foo {}){}
+                   ^"
+`;
+
 exports[`super-class.js - {"semi":false} format 1`] = `
 ====================================options=====================================
 parsers: ["babel", "flow", "typescript"]

tests/format/js/decorators/class-expression/format.test.js

@@ -1,5 +1,6 @@
 const errors = {
   flow: true,
+  hermes: true,
   acorn: true,
   espree: true,
 };

tests/format/js/destructuring/__snapshots__/format.test.js.snap

@@ -1,5 +1,17 @@
 // Jest Snapshot v1, https://goo.gl/fbAQLP
 
+exports[`destructuring.js [hermes] format 1`] = `
+"invalid assignment left-hand side (2:0)
+  1 | const [one, two = null, three = null] = arr;
+> 2 | a = ([s=1,]) => 1
+  3 | const { children, ...props } = this.props
+  4 |
+  5 | const { user: { firstName, lastName } } = this.props;
+Cause: invalid assignment left-hand side (2:0)
+a = ([s=1,]) => 1
+^"
+`;
+
 exports[`destructuring.js format 1`] = `
 ====================================options=====================================
 parsers: ["babel", "flow", "typescript"]

tests/format/js/destructuring/format.test.js

@@ -1 +1,5 @@
-runFormatTest(import.meta, ["babel", "flow", "typescript"]);
+runFormatTest(import.meta, ["babel", "flow", "typescript"], {
+  errors: {
+    hermes: ["destructuring.js"],
+  },
+});

tests/format/js/dynamic-import/__snapshots__/format.test.js.snap

@@ -50,6 +50,21 @@ exports[`import-phase.js [flow] format 1`] = `
   4 |"
 `;
 
+exports[`import-phase.js [hermes] format 1`] = `
+"'meta' expected in member expression (1:7)
+> 1 | import.source(\`data:text/javascript,
+    |       ^
+  2 |     console.log("RUN");
+  3 | \`)
+  4 |
+Cause: 'meta' expected in member expression (1:7)
+import.source(\`data:text/javascript,
+       ^~~~~~
+note: start of member expression (1:0)
+import.source(\`data:text/javascript,
+^"
+`;
+
 exports[`import-phase.js [meriyah] format 1`] = `
 "The only valid meta property for import is 'import.meta' (1:8)
 > 1 | import.source(\`data:text/javascript,
@@ -95,6 +110,18 @@ exports[`template-literal.js [flow] format 1`] = `
   4 |"
 `;
 
+exports[`template-literal.js [hermes] format 1`] = `
+"unexpected token after assignment expression (1:19)
+> 1 | module   =   await import(\`data:text/javascript,
+    |                   ^
+  2 |     console.log("RUN");
+  3 | \`);
+  4 |
+Cause: unexpected token after assignment expression (1:19)
+module   =   await import(\`data:text/javascript,
+                   ^"
+`;
+
 exports[`template-literal.js format 1`] = `
 ====================================options=====================================
 parsers: ["babel", "flow", "typescript"]

tests/format/js/dynamic-import/format.test.js

@@ -1,6 +1,7 @@
 runFormatTest(import.meta, ["babel", "flow", "typescript"], {
   errors: {
     flow: ["assertions.js", "template-literal.js", "import-phase.js"],
+    hermes: ["template-literal.js", "import-phase.js"],
     acorn: ["import-phase.js"],
     espree: ["import-phase.js"],
     meriyah: ["import-phase.js"],

tests/format/js/explicit-resource-management/__snapshots__/format.test.js.snap

@@ -23,6 +23,16 @@ exports[`for-await-using-of-comments.js [flow] format 1`] = `
   2 |"
 `;
 
+exports[`for-await-using-of-comments.js [hermes] format 1`] = `
+"'(' expected after 'for' (1:18)
+> 1 | /*1*/ for /* 2 */ await /*3*/ ( /*4*/ using /*5*/ fo /*6*/ of /*7*/ of /*8*/) /*9*/;
+    |                  ^
+  2 |
+Cause: '(' expected after 'for' (1:18)
+/*1*/ for /* 2 */ await /*3*/ ( /*4*/ using /*5*/ fo /*6*/ of /*7*/ of /*8*/) /*9*/;
+      ~~~~~~~~~~~~^"
+`;
+
 exports[`for-await-using-of-comments.js [meriyah] format 1`] = `
 "for await (... of ...) is only valid in async functions and async generators (1:51)
 > 1 | /*1*/ for /* 2 */ await /*3*/ ( /*4*/ using /*5*/ fo /*6*/ of /*7*/ of /*8*/) /*9*/;
@@ -77,6 +87,19 @@ exports[`invalid-duplicate-using-bindings.js [flow] format 1`] = `
   5 |   using g = foo();"
 `;
 
+exports[`invalid-duplicate-using-bindings.js [hermes] format 1`] = `
+"';' expected (2:8)
+  1 | {
+> 2 |   using f = foo(), f = foo();
+    |        ^
+  3 | }
+  4 | {
+  5 |   using g = foo();
+Cause: ';' expected (2:8)
+  using f = foo(), f = foo();
+        ^"
+`;
+
 exports[`invalid-duplicate-using-bindings.js [meriyah] format 1`] = `
 "Unexpected token: 'identifier' (2:9)
   1 | {
@@ -138,6 +161,16 @@ exports[`invalid-script-top-level-using-binding.js [flow] format 1`] = `
   2 |"
 `;
 
+exports[`invalid-script-top-level-using-binding.js [hermes] format 1`] = `
+"';' expected (1:6)
+> 1 | using x = bar();
+    |      ^
+  2 |
+Cause: ';' expected (1:6)
+using x = bar();
+      ^"
+`;
+
 exports[`invalid-script-top-level-using-binding.js [meriyah] format 1`] = `
 "Unexpected token: 'identifier' (1:7)
 > 1 | using x = bar();
@@ -192,6 +225,19 @@ exports[`using-declarations.js [flow] format 1`] = `
   5 | for(using /* 1 */ a = foo(), /* 2 */ b = foo();;);"
 `;
 
+exports[`using-declarations.js [hermes] format 1`] = `
+"';' expected (2:16)
+  1 | {
+> 2 |   using /* 1 */ a = foo(), /* 2 */ b = foo()
+    |                ^
+  3 | }
+  4 |
+  5 | for(using /* 1 */ a = foo(), /* 2 */ b = foo();;);
+Cause: ';' expected (2:16)
+  using /* 1 */ a = foo(), /* 2 */ b = foo()
+                ^"
+`;
+
 exports[`using-declarations.js [meriyah] format 1`] = `
 "Unexpected token: 'identifier' (2:17)
   1 | {
@@ -347,6 +393,18 @@ exports[`valid-await-using-binding-basic.js [flow] format 1`] = `
   4 |"
 `;
 
+exports[`valid-await-using-binding-basic.js [hermes] format 1`] = `
+"';' expected (2:14)
+  1 | async function f() {
+> 2 |   await using basic = getReader();
+    |              ^
+  3 | }
+  4 |
+Cause: ';' expected (2:14)
+  await using basic = getReader();
+              ^"
+`;
+
 exports[`valid-await-using-binding-basic.js [meriyah] format 1`] = `
 "Unexpected token: 'identifier' (2:15)
   1 | async function f() {
@@ -404,6 +462,18 @@ exports[`valid-await-using-binding-escaped.js [flow] format 1`] = `
   4 |"
 `;
 
+exports[`valid-await-using-binding-escaped.js [hermes] format 1`] = `
+"';' expected (2:14)
+  1 | async function f() {
+> 2 |   await using \\u0061b = c;
+    |              ^
+  3 | }
+  4 |
+Cause: ';' expected (2:14)
+  await using \\u0061b = c;
+              ^"
+`;
+
 exports[`valid-await-using-binding-escaped.js [meriyah] format 1`] = `
 "Unexpected token: 'identifier' (2:15)
   1 | async function f() {
@@ -461,6 +531,17 @@ exports[`valid-await-using-binding-non-bmp.js [flow] format 1`] = `
   4 |"
 `;
 
+exports[`valid-await-using-binding-non-bmp.js [hermes] format 1`] = `
+"';' expected (2:14)
+  1 | async function f() {
+> 2 |   await using 𠮷 = foo();
+    |              ^
+  3 | }
+  4 |
+Cause: ';' expected (2:14)
+  await using 𠮷 = foo();"
+`;
+
 exports[`valid-await-using-binding-non-bmp.js [meriyah] format 1`] = `
 "Unexpected token: 'identifier' (2:15)
   1 | async function f() {
@@ -521,6 +602,19 @@ exports[`valid-await-using-binding-using.js [flow] format 1`] = `
   5 |"
 `;
 
+exports[`valid-await-using-binding-using.js [hermes] format 1`] = `
+"';' expected (2:14)
+  1 | async function f() {
+> 2 |   await using using = of;
+    |              ^
+  3 |   for (await using using of of);
+  4 | }
+  5 |
+Cause: ';' expected (2:14)
+  await using using = of;
+              ^"
+`;
+
 exports[`valid-await-using-binding-using.js [meriyah] format 1`] = `
 "Unexpected token: 'identifier' (2:15)
   1 | async function f() {
@@ -587,6 +681,20 @@ exports[`valid-await-using-comments.js [flow] format 1`] = `
   6 |   /*0*/for/*1*/(/*2*/await/*3*/using/*4*/b/*5*/=/*6*/x/*7*/;/*8*/;/*9*/)/*10*/;"
 `;
 
+exports[`valid-await-using-comments.js [hermes] format 1`] = `
+"';' expected (3:27)
+  1 | async function f() {
+  2 | {
+> 3 |   /*0*/await/*1*/using/*2*/b/*3*/=/*4*/f()/*5*/;
+    |                           ^
+  4 | }
+  5 | {
+  6 |   /*0*/for/*1*/(/*2*/await/*3*/using/*4*/b/*5*/=/*6*/x/*7*/;/*8*/;/*9*/)/*10*/;
+Cause: ';' expected (3:27)
+  /*0*/await/*1*/using/*2*/b/*3*/=/*4*/f()/*5*/;
+                           ^"
+`;
+
 exports[`valid-await-using-comments.js [meriyah] format 1`] = `
 "Unexpected token: 'identifier' (3:28)
   1 | async function f() {
@@ -720,6 +828,19 @@ exports[`valid-for-using-binding-of-of.js [flow] format 1`] = `
   5 |"
 `;
 
+exports[`valid-for-using-binding-of-of.js [hermes] format 1`] = `
+"')' expected after 'for(... in/of ...' (2:25)
+  1 | async function f() {
+> 2 |   for (await using of of of);
+    |                         ^
+  3 |   for await (await using of of of);
+  4 | }
+  5 |
+Cause: ')' expected after 'for(... in/of ...' (2:25)
+  for (await using of of of);
+      ~~~~~~~~~~~~~~~~~~~^"
+`;
+
 exports[`valid-for-using-binding-of-of.js [meriyah] format 1`] = `
 "Invalid left-hand side in for-of (2:20)
   1 | async function f() {
@@ -780,6 +901,18 @@ exports[`valid-for-using-declaration.js [flow] format 1`] = `
   4 |"
 `;
 
+exports[`valid-for-using-declaration.js [hermes] format 1`] = `
+"';' or 'in' expected inside 'for' (2:19)
+  1 | async function f() {
+> 2 |   for (await using basic = reader();;);
+    |                   ^
+  3 | }
+  4 |
+Cause: ';' or 'in' expected inside 'for' (2:19)
+  for (await using basic = reader();;);
+  ~~~~~~~~~~~~~~~~~^"
+`;
+
 exports[`valid-for-using-declaration.js [meriyah] format 1`] = `
 "Expected ';' (2:20)
   1 | async function f() {
@@ -847,6 +980,18 @@ exports[`valid-module-block-top-level-await-using-binding.js [flow] format 1`] =
   4 |"
 `;
 
+exports[`valid-module-block-top-level-await-using-binding.js [hermes] format 1`] = `
+"';' expected (1:17)
+> 1 | const m = module {
+    |                 ^
+  2 |   await using foo = bar();
+  3 | }
+  4 |
+Cause: ';' expected (1:17)
+const m = module {
+                 ^"
+`;
+
 exports[`valid-module-block-top-level-await-using-binding.js [meriyah] format 1`] = `
 "Unexpected token: '{' (1:18)
 > 1 | const m = module {
@@ -932,6 +1077,18 @@ exports[`valid-module-block-top-level-using-binding.js [flow] format 1`] = `
   4 |"
 `;
 
+exports[`valid-module-block-top-level-using-binding.js [hermes] format 1`] = `
+"';' expected (1:7)
+> 1 | module {
+    |       ^
+  2 |   using foo = bar();
+  3 | }
+  4 |
+Cause: ';' expected (1:7)
+module {
+       ^"
+`;
+
 exports[`valid-module-block-top-level-using-binding.js [meriyah] format 1`] = `
 "Unexpected token: '{' (1:8)
 > 1 | module {
@@ -1027,6 +1184,16 @@ exports[`valid-using-as-identifier-for-await-of.js [flow] format 1`] = `
   2 |"
 `;
 
+exports[`valid-using-as-identifier-for-await-of.js [hermes] format 1`] = `
+"'(' expected after 'for' (1:4)
+> 1 | for await (using of of);
+    |    ^
+  2 |
+Cause: '(' expected after 'for' (1:4)
+for await (using of of);
+~~~~^"
+`;
+
 exports[`valid-using-as-identifier-for-await-of.js format 1`] = `
 ====================================options=====================================
 parsers: ["babel", "flow", "typescript"]
@@ -1140,6 +1307,18 @@ exports[`valid-using-binding-basic.js [flow] format 1`] = `
   4 |"
 `;
 
+exports[`valid-using-binding-basic.js [hermes] format 1`] = `
+"';' expected (2:8)
+  1 | {
+> 2 |   using basic = getReader();
+    |        ^
+  3 | }
+  4 |
+Cause: ';' expected (2:8)
+  using basic = getReader();
+        ^"
+`;
+
 exports[`valid-using-binding-basic.js [meriyah] format 1`] = `
 "Unexpected token: 'identifier' (2:9)
   1 | {
@@ -1191,6 +1370,16 @@ exports[`valid-using-binding-escaped.js [flow] format 1`] = `
   2 |"
 `;
 
+exports[`valid-using-binding-escaped.js [hermes] format 1`] = `
+"';' expected (1:8)
+> 1 | { using \\u0061b = c; }
+    |        ^
+  2 |
+Cause: ';' expected (1:8)
+{ using \\u0061b = c; }
+        ^"
+`;
+
 exports[`valid-using-binding-escaped.js [meriyah] format 1`] = `
 "Unexpected token: 'identifier' (1:9)
 > 1 | { using \\u0061b = c; }
@@ -1238,6 +1427,15 @@ exports[`valid-using-binding-non-bmp.js [flow] format 1`] = `
   2 |"
 `;
 
+exports[`valid-using-binding-non-bmp.js [hermes] format 1`] = `
+"';' expected (1:8)
+> 1 | { using 𠮷 = foo(); }
+    |        ^
+  2 |
+Cause: ';' expected (1:8)
+{ using 𠮷 = foo(); }"
+`;
+
 exports[`valid-using-binding-non-bmp.js [meriyah] format 1`] = `
 "Unexpected token: 'identifier' (1:9)
 > 1 | { using 𠮷 = foo(); }
@@ -1294,6 +1492,19 @@ exports[`valid-using-binding-using.js [flow] format 1`] = `
   5 |"
 `;
 
+exports[`valid-using-binding-using.js [hermes] format 1`] = `
+"';' expected (2:8)
+  1 | {
+> 2 |   using using = of;
+    |        ^
+  3 |   for (using using of of);
+  4 | }
+  5 |
+Cause: ';' expected (2:8)
+  using using = of;
+        ^"
+`;
+
 exports[`valid-using-binding-using.js [meriyah] format 1`] = `
 "Unexpected token: 'identifier' (2:9)
   1 | {

tests/format/js/explicit-resource-management/format.test.js

@@ -24,6 +24,30 @@ runFormatTest(import.meta, ["babel", "flow", "typescript"], {
       "valid-for-using-declaration.js",
       "valid-module-block-top-level-await-using-binding.js",
     ],
+    hermes: [
+      "for-await-using-of-comments.js",
+      "invalid-duplicate-using-bindings.js",
+      "invalid-script-top-level-using-binding.js",
+      "using-declarations.js",
+      // "valid-for-await-using-binding-escaped-of-of.js",
+      // "valid-for-using-binding-escaped-of-of.js",
+      "valid-module-block-top-level-using-binding.js",
+      "valid-using-as-identifier-for-await-of.js",
+      "valid-using-binding-basic.js",
+      "valid-using-binding-escaped.js",
+      "valid-using-binding-non-bmp.js",
+      "valid-using-binding-using.js",
+
+      "valid-await-using-binding-basic.js",
+      "valid-await-using-binding-escaped.js",
+      "valid-await-using-binding-non-bmp.js",
+      "valid-await-using-binding-using.js",
+      "valid-await-using-comments.js",
+      "valid-for-lhs-await-as-identifier.js",
+      "valid-for-using-binding-of-of.js",
+      "valid-for-using-declaration.js",
+      "valid-module-block-top-level-await-using-binding.js",
+    ],
     typescript: [
       // https://github.com/typescript-eslint/typescript-eslint/blob/4f34d0ba34474926ba1eed623704b583a037f886/packages/typescript-estree/src/convert.ts#L1035-L1050
       "valid-for-using-declaration.js",

tests/format/js/export-default/escaped/__snapshots__/format.test.js.snap

@@ -23,6 +23,16 @@ exports[`default-escaped.js [flow] format 1`] = `
     |        ^^^^^^^"
 `;
 
+exports[`default-escaped.js [hermes] format 1`] = `
+"expected declaration in export (2:7)
+  1 | // export asyn\\u{63} from "async";
+> 2 | export n\\u{63} from "async";
+    |       ^
+Cause: expected declaration in export (2:7)
+export n\\u{63} from "async";
+       ^~~~~~~"
+`;
+
 exports[`default-escaped.js [meriyah] format 1`] = `
 "Unexpected token: 'identifier' (2:8)
   1 | // export asyn\\u{63} from "async";

tests/format/js/export-default/escaped/format.test.js

@@ -4,6 +4,7 @@ runFormatTest(import.meta, ["babel", "flow"], {
     espree: true,
     meriyah: true,
     flow: true,
+    hermes: true,
     oxc: true,
     "oxc-ts": true,
   },

tests/format/js/export-star/__snapshots__/format.test.js.snap

@@ -71,6 +71,16 @@ exports[`export-star-as-string.js [flow] format 1`] = `
   2 |"
 `;
 
+exports[`export-star-as-string.js [hermes] format 1`] = `
+"'identifier' expected in export clause (1:12)
+> 1 | export * as 'foo' from 'foo'
+    |            ^
+  2 |
+Cause: 'identifier' expected in export clause (1:12)
+export * as 'foo' from 'foo'
+~~~~~~~~~~~~^"
+`;
+
 exports[`export-star-as-string.js format 1`] = `
 ====================================options=====================================
 parsers: ["babel", "flow", "typescript"]
@@ -92,6 +102,16 @@ exports[`export-star-as-string2.js [flow] format 1`] = `
   2 |"
 `;
 
+exports[`export-star-as-string2.js [hermes] format 1`] = `
+"'identifier' expected in export clause (1:12)
+> 1 | export * as "foo" from 'foo'
+    |            ^
+  2 |
+Cause: 'identifier' expected in export clause (1:12)
+export * as "foo" from 'foo'
+~~~~~~~~~~~~^"
+`;
+
 exports[`export-star-as-string2.js format 1`] = `
 ====================================options=====================================
 parsers: ["babel", "flow", "typescript"]

tests/format/js/export-star/format.test.js

@@ -1,5 +1,6 @@
 runFormatTest(import.meta, ["babel", "flow", "typescript"], {
   errors: {
     flow: ["export-star-as-string.js", "export-star-as-string2.js"],
+    hermes: ["export-star-as-string.js", "export-star-as-string2.js"],
   },
 });

tests/format/js/ignore/__snapshots__/format.test.js.snap

@@ -35,6 +35,20 @@ exports[`class-expression-decorator.js [flow] format 1`] = `
   6 |"
 `;
 
+exports[`class-expression-decorator.js [hermes] format 1`] = `
+"unrecognized character '@' (3:2)
+  1 | (
+  2 |   // prettier-ignore
+> 3 |   @decorator
+    |  ^
+  4 |   class {}
+  5 | );
+  6 |
+Cause: unrecognized character '@' (3:2)
+  @decorator
+  ^"
+`;
+
 exports[`class-expression-decorator.js format 1`] = `
 ====================================options=====================================
 parsers: ["babel", "flow", "typescript"]
@@ -77,6 +91,17 @@ exports[`decorator.js [espree] format 1`] = `
 Cause: Unexpected character '@'"
 `;
 
+exports[`decorator.js [hermes] format 1`] = `
+"unrecognized character '@' (2:0)
+  1 | // prettier-ignore
+> 2 | @decorator
+  3 | class A {}
+  4 |
+Cause: unrecognized character '@' (2:0)
+@decorator
+^"
+`;
+
 exports[`decorator.js format 1`] = `
 ====================================options=====================================
 parsers: ["babel", "flow", "typescript"]

tests/format/js/ignore/format.test.js

@@ -3,5 +3,6 @@ runFormatTest(import.meta, ["babel", "flow", "typescript"], {
     acorn: ["decorator.js", "class-expression-decorator.js"],
     espree: ["decorator.js", "class-expression-decorator.js"],
     flow: ["class-expression-decorator.js"],
+    hermes: ["decorator.js", "class-expression-decorator.js"],
   },
 });

tests/format/js/multiparser-invalid/__snapshots__/format.test.js.snap

@@ -33,6 +33,20 @@ exports[`text.js [flow] format 1`] = `
   4 | foo = markdown\`\\u{prettier}\\u{0065}\`;"
 `;
 
+exports[`text.js [hermes] format 1`] = `
+"untagged template literal contains invalid escape sequence (6:16)
+  4 | foo = markdown\`\\u{prettier}\\u{0065}\`;
+  5 | foo = css\`\\u{prettier}\\u{0065}\`;
+> 6 | foo = /* HTML */\`\\u{prettier}\\u{0065}\`;
+    |                ^
+  7 | foo = /* GraphQL */\`\\u{prettier}\\u{0065}\`;
+  8 |
+  9 | foo = foo\`\\u{prettier}\${foo}pr\\u{0065}ttier\`;
+Cause: untagged template literal contains invalid escape sequence (6:16)
+foo = /* HTML */\`\\u{prettier}\\u{0065}\`;
+                ^~~~~~~~~~~~~~~~~~~~~~"
+`;
+
 exports[`text.js [meriyah] format 1`] = `
 "Invalid hexadecimal escape sequence (6:17)
   4 | foo = markdown\`\\u{prettier}\\u{0065}\`;

tests/format/js/multiparser-invalid/format.test.js

@@ -3,6 +3,7 @@ runFormatTest(import.meta, ["babel", "flow", "typescript"], {
     acorn: true,
     espree: true,
     flow: true,
+    hermes: true,
     typescript: true,
     meriyah: true,
     oxc: true,

tests/format/js/new-target/__snapshots__/format.test.js.snap

@@ -23,6 +23,16 @@ exports[`outside-functions.js [flow] format 1`] = `
   2 |"
 `;
 
+exports[`outside-functions.js [hermes] format 1`] = `
+"'new.target' not in a function (1:10)
+> 1 | const x = new.target;
+    |          ^
+  2 |
+Cause: 'new.target' not in a function (1:10)
+const x = new.target;
+          ^~~~~~~~~~"
+`;
+
 exports[`outside-functions.js [meriyah] format 1`] = `
 "new.target only allowed within functions or static blocks (1:15)
 > 1 | const x = new.target;
@@ -68,6 +78,15 @@ exports[`range.js [flow] format 1`] = `
     |    ^"
 `;
 
+exports[`range.js [hermes] format 1`] = `
+"'new.target' not in a function (2:0)
+  1 | const x =
+> 2 | new.target;
+Cause: 'new.target' not in a function (2:0)
+new.target;
+^~~~~~~~~~"
+`;
+
 exports[`range.js [meriyah] format 1`] = `
 "new.target only allowed within functions or static blocks (2:5)
   1 | const x =

tests/format/js/new-target/format.test.js

@@ -4,5 +4,6 @@ runFormatTest(import.meta, ["babel", "flow", "typescript"], {
     espree: true,
     meriyah: true,
     flow: true,
+    hermes: true,
   },
 });

tests/format/js/objects/__snapshots__/format.test.js.snap

@@ -1,5 +1,17 @@
 // Jest Snapshot v1, https://goo.gl/fbAQLP
 
+exports[`bigint-key.js [hermes] format 1`] = `
+"invalid property name - must be a string, number or identifier (1:5)
+> 1 | a = {1n: ""}
+    |     ^
+  2 | a = {1n() {}}
+  3 | a = {get 1n() {}}
+  4 |
+Cause: invalid property name - must be a string, number or identifier (1:5)
+a = {1n: ""}
+     ^~"
+`;
+
 exports[`bigint-key.js format 1`] = `
 ====================================options=====================================
 parsers: ["babel", "typescript", "flow"]
@@ -105,6 +117,20 @@ exports[`expression.js [flow] format 1`] = `
   8 | ({} = 0);"
 `;
 
+exports[`expression.js [hermes] format 1`] = `
+"unexpected token in type annotation (5:4)
+  3 | a = () => ({}).x;
+  4 | ({} && a, b);
+> 5 | ({}::b, 0);
+    |    ^
+  6 | ({}::b()\`\`[''].c++ && 0 ? 0 : 0, 0);
+  7 | ({}(), 0);
+  8 | ({} = 0);
+Cause: unexpected token in type annotation (5:4)
+({}::b, 0);
+    ^"
+`;
+
 exports[`expression.js [meriyah] format 1`] = `
 "Expected ')' (5:4)
   3 | a = () => ({}).x;

tests/format/js/objects/format.test.js

@@ -7,5 +7,6 @@ runFormatTest(import.meta, ["babel", "typescript", "flow"], {
     oxc: ["expression.js"],
     "oxc-ts": ["expression.js"],
     flow: ["expression.js"],
+    hermes: ["expression.js", "bigint-key.js"],
   },
 });

tests/format/js/sloppy-mode/__snapshots__/format.test.js.snap

@@ -19,6 +19,19 @@ function foo() {
 ================================================================================
 `;
 
+exports[`eval-arguments.js [hermes] format 1`] = `
+"invalid assignment left-hand side (3:2)
+  1 | function myfunc() {
+  2 |   eval = 1
+> 3 |   arguments = arguments;
+    |  ^
+  4 | }
+  5 |
+Cause: invalid assignment left-hand side (3:2)
+  arguments = arguments;
+  ^~~~~~~~~"
+`;
+
 exports[`eval-arguments.js format 1`] = `
 ====================================options=====================================
 parsers: ["babel", "flow", "typescript"]
@@ -96,6 +109,16 @@ exports[`function-declaration-in-while.js [flow] format 1`] = `
   2 |"
 `;
 
+exports[`function-declaration-in-while.js [hermes] format 1`] = `
+"declaration not allowed as expression statement (1:14)
+> 1 | while (false) function foo(){}
+    |              ^
+  2 |
+Cause: declaration not allowed as expression statement (1:14)
+while (false) function foo(){}
+              ^~~~~~~~"
+`;
+
 exports[`function-declaration-in-while.js [meriyah] format 1`] = `
 "In strict mode code, functions can only be declared at top level or inside a block (1:15)
 > 1 | while (false) function foo(){}
@@ -118,6 +141,16 @@ while (false) function foo() {}
 ================================================================================
 `;
 
+exports[`labeled-function-declaration.js [hermes] format 1`] = `
+"Function declaration not allowed as body of labeled statement (1:5)
+> 1 | foo: function bar() {}
+    |     ^
+  2 |
+Cause: Function declaration not allowed as body of labeled statement (1:5)
+foo: function bar() {}
+     ^"
+`;
+
 exports[`labeled-function-declaration.js format 1`] = `
 ====================================options=====================================
 parsers: ["babel", "flow", "typescript"]

tests/format/js/sloppy-mode/format.test.js

@@ -1,6 +1,11 @@
 runFormatTest(import.meta, ["babel", "flow", "typescript"], {
   errors: {
     flow: ["function-declaration-in-while.js"],
+    hermes: [
+      "eval-arguments.js",
+      "labeled-function-declaration.js",
+      "function-declaration-in-while.js",
+    ],
     acorn: ["function-declaration-in-while.js"],
     espree: ["function-declaration-in-while.js"],
     meriyah: ["function-declaration-in-while.js"],

tests/format/typescript/classes/__snapshots__/format.test.js.snap

@@ -97,26 +97,26 @@ parsers: ["typescript", "flow"]
 printWidth: 80
                                                                                 | printWidth
 =====================================input======================================
-class loooooooooooooooooooong extends looooooooooooooooooong implements loooooooooooooooooooong {
+class looooooooooooooooooong1 extends looooooooooooooooooong implements loooooooooooooooooooong {
   // leading comment
   property: string;
 }
 
-class loooooooooooooooooooong extends looooooooooooooooooong implements loooooooooooooooooooong {
+class looooooooooooooooooong2 extends looooooooooooooooooong implements loooooooooooooooooooong {
   property: string;
 }
 
-class loooooooooooooooooooong extends looooooooooooooooooong implements loooooooooooooooooooong {
+class looooooooooooooooooong3 extends looooooooooooooooooong implements loooooooooooooooooooong {
 
   property: string;
 }
 
-class loooooooooooooooooooong extends looooooooooooooooooong implements loooooooooooooooooooong, loooooooooooooooooooong, loooooooooooooooooooong {
+class looooooooooooooooooong4 extends looooooooooooooooooong implements loooooooooooooooooooong, loooooooooooooooooooong, loooooooooooooooooooong {
   property: string;
 }
 
 =====================================output=====================================
-class loooooooooooooooooooong
+class looooooooooooooooooong1
   extends looooooooooooooooooong
   implements loooooooooooooooooooong
 {
@@ -124,21 +124,21 @@ class loooooooooooooooooooong
   property: string;
 }
 
-class loooooooooooooooooooong
+class looooooooooooooooooong2
   extends looooooooooooooooooong
   implements loooooooooooooooooooong
 {
   property: string;
 }
 
-class loooooooooooooooooooong
+class looooooooooooooooooong3
   extends looooooooooooooooooong
   implements loooooooooooooooooooong
 {
   property: string;
 }
 
-class loooooooooooooooooooong
+class looooooooooooooooooong4
   extends looooooooooooooooooong
   implements
     loooooooooooooooooooong,

tests/format/typescript/classes/break-heritage.ts

@@ -1,17 +1,17 @@
-class loooooooooooooooooooong extends looooooooooooooooooong implements loooooooooooooooooooong {
+class looooooooooooooooooong1 extends looooooooooooooooooong implements loooooooooooooooooooong {
   // leading comment
   property: string;
 }
 
-class loooooooooooooooooooong extends looooooooooooooooooong implements loooooooooooooooooooong {
+class looooooooooooooooooong2 extends looooooooooooooooooong implements loooooooooooooooooooong {
   property: string;
 }
 
-class loooooooooooooooooooong extends looooooooooooooooooong implements loooooooooooooooooooong {
+class looooooooooooooooooong3 extends looooooooooooooooooong implements loooooooooooooooooooong {
 
   property: string;
 }
 
-class loooooooooooooooooooong extends looooooooooooooooooong implements loooooooooooooooooooong, loooooooooooooooooooong, loooooooooooooooooooong {
+class looooooooooooooooooong4 extends looooooooooooooooooong implements loooooooooooooooooooong, loooooooooooooooooooong, loooooooooooooooooooong {
   property: string;
 }

tests/format/typescript/type-params/consistent/__snapshots__/format.test.js.snap

@@ -99,6 +99,16 @@ exports[`template-literal-types.ts [flow] format 1`] = `
   2 |"
 `;
 
+exports[`template-literal-types.ts [hermes] format 1`] = `
+"unexpected token in type annotation (1:83)
+> 1 | const foo1: Fooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooo<\`Hello, \${keyof World}\`> = a;
+    |                                                                                   ^
+  2 |
+Cause: unexpected token in type annotation (1:83)
+const foo1: Fooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooo<\`Hello, \${keyof World}\`> = a;
+                                                                                   ^"
+`;
+
 exports[`template-literal-types.ts format 1`] = `
 ====================================options=====================================
 parsers: ["typescript", "flow"]

tests/format/typescript/type-params/consistent/format.test.js

@@ -1,6 +1,7 @@
 runFormatTest(import.meta, ["typescript", "flow"], {
   errors: {
     flow: ["template-literal-types.ts"],
+    hermes: ["template-literal-types.ts"],
     "babel-flow": ["template-literal-types.ts"],
   },
 });

tests/format/typescript/type-params/empty-parameters-with-arrow-function/__snapshots__/format.test.js.snap

@@ -8,26 +8,26 @@ printWidth: 80
 trailingComma: "all"
                                                                                 | printWidth
 =====================================input======================================
-const xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx: xxxxxxxxxxxxxxxxxxxxxx<> =
+const xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx1: xxxxxxxxxxxxxxxxxxxxxx<> =
   arg => null;
 
-const xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx: xxxxxxxxxxxxxxxxxxxxxx</* comment */> =
+const xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx2: xxxxxxxxxxxxxxxxxxxxxx</* comment */> =
   arg => null;
 
 
-const xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx: xxxxxxxxxxxxxxxxxxxxxx<
+const xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx3: xxxxxxxxxxxxxxxxxxxxxx<
   // comment
 > =
   arg => null;
 
 =====================================output=====================================
-const xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx: xxxxxxxxxxxxxxxxxxxxxx<> =
+const xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx1: xxxxxxxxxxxxxxxxxxxxxx<> =
   arg => null;
 
-const xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx: xxxxxxxxxxxxxxxxxxxxxx</* comment */> =
+const xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx2: xxxxxxxxxxxxxxxxxxxxxx</* comment */> =
   arg => null;
 
-const xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx: xxxxxxxxxxxxxxxxxxxxxx<
+const xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx3: xxxxxxxxxxxxxxxxxxxxxx<
   // comment
 > = arg => null;
 

tests/format/typescript/type-params/empty-parameters-with-arrow-function/issue-13817.ts

@@ -1,11 +1,11 @@
-const xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx: xxxxxxxxxxxxxxxxxxxxxx<> =
+const xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx1: xxxxxxxxxxxxxxxxxxxxxx<> =
   arg => null;
 
-const xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx: xxxxxxxxxxxxxxxxxxxxxx</* comment */> =
+const xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx2: xxxxxxxxxxxxxxxxxxxxxx</* comment */> =
   arg => null;
 
 
-const xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx: xxxxxxxxxxxxxxxxxxxxxx<
+const xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx3: xxxxxxxxxxxxxxxxxxxxxx<
   // comment
 > =
   arg => null;

website/playground/codeSamples.mjs

@@ -28,6 +28,7 @@ export default function getCodeSamples(parser) {
         "}",
       ].join("\n");
     case "flow":
+    case "hermes":
     case "babel-flow":
       return [
         "declare export function graphql<Props, Variables, Component: React$ComponentType<Props>>",

website/playground/markdown.js

@@ -41,6 +41,7 @@ function getMarkdownSyntax(options) {
     case "babel":
     case "babel-flow":
     case "flow":
+    case "hermes":
     case "acorn":
     case "espree":
     case "meriyah":

website/playground/util.js

@@ -65,6 +65,7 @@ const astAutoFold = {
 export function getAstAutoFold(parser) {
   switch (parser) {
     case "flow":
+    case "hermes":
     case "babel":
     case "babel-flow":
     case "babel-ts":

website/static/worker.mjs

@@ -62,6 +62,13 @@ const plugins = [
     createPlugin(plugin),
   ),
   docExplorerPlugin,
+  prettierPackageManifest.builtinPlugins.some((plugin) =>
+    plugin.parsers?.includes("hermes"),
+  )
+    ? {
+        languages: [{ name: "hermes", parsers: ["hermes"] }],
+      }
+    : {},
 ];
 
 self.onmessage = async function (event) {

yarn.lock

@@ -2902,7 +2902,7 @@ __metadata:
   languageName: node
   linkType: hard
 
-"buffer@npm:^6.0.3":
+"buffer@npm:6.0.3, buffer@npm:^6.0.3":
   version: 6.0.3
   resolution: "buffer@npm:6.0.3"
   dependencies:
@@ -7233,6 +7233,7 @@ __metadata:
     angular-html-parser: "npm:8.1.0"
     browserslist: "npm:4.24.5"
     browserslist-to-esbuild: "npm:2.1.1"
+    buffer: "npm:6.0.3"
     c8: "npm:10.1.3"
     camelcase: "npm:8.0.0"
     ci-info: "npm:4.2.0"