feat(fmt): prototype SWC Next 0.2.2 npm integration

rstackjs · chenjiahan · Sep 22, 2026 · Sep 7, 2026 · Sep 22, 2026 · Sep 22, 2026
commit dae1f3145d3c9f142192f802ccde68a5424c2468
diff --git a/packages/rstack/SWC_NEXT_POC.md b/packages/rstack/SWC_NEXT_POC.md
@@ -0,0 +1,30 @@
+# SWC next formatter PoC
+
+This branch replaces the default Yuku parser in `rs fmt` with SWC Next 0.2.2 while retaining Prettier's ESTree printer and the existing formatting adapter.
+
+`@swc-next/parser@0.2.2` supplies its own platform-specific native binding and decodes its output internally. The rstack native binding is unchanged.
+
+Inferred JavaScript, JSX, TypeScript, TSX, and embedded script formatting use SWC Next. Explicit `babel` and `typescript` options still select Prettier's own parsers, and project plugins retain precedence. The experimental explicit parser names are `swc-next` and `swc-next-ts`, replacing `yuku` and `yuku-ts`.
+
+The cache namespace includes the parser version and integration route so switching between the original formatter and either PoC cannot reuse stale formatting results. The decoder and Rust serializer must be upgraded together; all SWC Next packages in this PoC are locked to 0.2.2.
+
+## Try it
+
+```sh
+pnpm install
+pnpm build
+pnpm --filter rstack build:native
+printf 'const view=<Component value={{foo:1}} />' | pnpm exec rs fmt --stdin-filepath example.tsx
+pnpm test
+pnpm check
+```
+
+## Compatibility and limits
+
+SWC Next 0.2.2 reports diagnostics for function implementations in declaration files, restoring the formatter's existing rejection behavior. It also parses the typed arrow callback inside the conditional expression that previously failed when formatting Rsbuild's `inspectConfig.ts` with 0.2.0. Tests cover both cases, alongside valid declarations, comments, Unicode locations, JSX/TSX, CommonJS, pragmas, and syntax errors. Parser errors stop formatting without falling back to another parser.
+
+Validation is on macOS arm64 with the repository's Node.js, pnpm, and Rust versions. The complete formatter/CLI suite covers worker execution, stdin, LSP, Vue, Svelte, and caching. Cross-platform binaries and formatter-wide conformance against Prettier's upstream corpus have not been validated. No throughput advantage is claimed by this PoC.
+
+## Upstream
+
+[SWC Next 0.2.2 source](https://github.com/swc-project/swc-next/tree/v0.2.2)
diff --git a/packages/rstack/THIRD_PARTY_NOTICES.md b/packages/rstack/THIRD_PARTY_NOTICES.md
@@ -29,9 +29,9 @@ LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
 OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
 SOFTWARE.
 
-## Prettier yuku parser adapter
+## Prettier SWC next parser adapter
 
-The local Yuku parser adapter includes portions derived from
+The local SWC Next parser adapter includes portions derived from
 [@prettier/plugin-yuku](https://github.com/prettier/prettier/tree/main/packages/plugin-yuku)
 and Prettier's JavaScript parser postprocessing. The adapter reuses the public
 ESTree printer, formatter options, and parser utilities from the installed

diff --git a/packages/rstack/package.json b/packages/rstack/package.json
@@ -77,9 +77,9 @@
     "@rslib/core": "catalog:",
     "@rslint/core": "catalog:",
     "@rstest/core": "catalog:",
+    "@swc-next/parser": "catalog:",
     "prettier": "catalog:",
-    "tinypool": "catalog:",
-    "yuku-parser": "catalog:"
+    "tinypool": "catalog:"
   },
   "devDependencies": {
     "@napi-rs/cli": "catalog:",

diff --git a/packages/rstack/src/fmt/cacheIdentity.ts b/packages/rstack/src/fmt/cacheIdentity.ts
@@ -21,6 +21,7 @@ const cacheNamespace: string = JSON.stringify([
   fmtCacheVersion,
   RSTACK_VERSION,
   PRETTIER_VERSION,
+  'swc-next@0.2.2:npm',
 ]);
 
 /** Creates project-relative POSIX cache keys without repeating path setup. */

diff --git a/packages/rstack/src/fmt/prettierPlugins.ts b/packages/rstack/src/fmt/prettierPlugins.ts
@@ -1,6 +1,6 @@
 import type { Options as PrettierOptions, Plugin } from 'prettier';
 import type { ResolvedFmtOptions } from './types.ts';
-import { yukuPlugin } from './yukuPlugin.ts';
+import { swcNextPlugin } from './swcNextPlugin.ts';
 
 type PrettierPlugins = NonNullable<PrettierOptions['plugins']>;
 
@@ -15,14 +15,14 @@ const fmtOptionsPlugin = {
   },
 } satisfies Plugin;
 
-const defaultFmtPlugins: PrettierPlugins = [yukuPlugin, fmtOptionsPlugin];
+const defaultFmtPlugins: PrettierPlugins = [swcNextPlugin, fmtOptionsPlugin];
 
 /** Prepends bundled plugins so project plugins can override their parsers. */
 const getPrettierPlugins = async (
   options: ResolvedFmtOptions,
   filePath: string,
 ): Promise<PrettierPlugins> => {
-  // An explicit native parser is also the escape hatch for bypassing Yuku.
+  // An explicit native parser is also the escape hatch for bypassing SWC Next.
   const defaultPlugins =
     options.parser === 'babel' || options.parser === 'typescript'
       ? [fmtOptionsPlugin]

diff --git a/packages/rstack/src/fmt/swcNextParser.ts b/packages/rstack/src/fmt/swcNextParser.ts
@@ -0,0 +1,25 @@
+import {
+  langFromPath,
+  parseSync as parse,
+  type ParserOptions,
+  type ParseResult as SwcParseResult,
+} from '@swc-next/parser';
+
+export { langFromPath };
+export type { Comment, Diagnostic } from '@swc-next/parser';
+export type Lang = 'js' | 'jsx' | 'ts' | 'tsx' | 'dts';
+export type SourceType = 'module' | 'commonjs';
+export type ParseOptions = {
+  lang: Lang;
+  sourceType: SourceType;
+  preserveParens: true;
+  comments: 'flat';
+};
+
+// Keep the upstream untyped AST behind an unknown boundary.
+export type ParseResult = Omit<SwcParseResult, 'program'> & {
+  program: unknown;
+};
+
+export const parseSync = (source: string, options: ParseOptions): ParseResult =>
+  parse(source, options as ParserOptions);
diff --git a/packages/rstack/src/fmt/yukuPlugin.ts → packages/rstack/src/fmt/swcNextPlugin.ts b/packages/rstack/src/fmt/yukuPlugin.ts → packages/rstack/src/fmt/swcNextPlugin.ts
@@ -2,16 +2,16 @@ import * as prettierEstreePlugin from 'prettier/plugins/estree';
 import type { Parser, ParserOptions, Plugin } from 'prettier';
 import {
   langFromPath,
-  parse as parseWithYuku,
+  parseSync as parseWithSwcNext,
   type Comment,
   type Diagnostic,
   type ParseOptions,
   type ParseResult,
-  type SourceLang,
+  type Lang,
   type SourceType,
-} from 'yuku-parser';
+} from './swcNextParser.ts';
 
-const AST_FORMAT = 'estree-yuku';
+const AST_FORMAT = 'estree-swc-next';
 const JS_TS_FILE_REGEXP = /\.(?:js|mjs|cjs|jsx|ts|mts|cts|tsx)$/i;
 const JSX_REGEXP = /^[^"'`]*<\/|^[^/]{2}.*\/>/m;
 const SOURCE_TYPE_COMBINATIONS: SourceType[] = ['module', 'commonjs'];
@@ -158,7 +158,7 @@ const isAstNode = (value: unknown): value is AstNode =>
 
 const asAstNode = (value: unknown): AstNode => {
   if (!isAstNode(value)) {
-    throw new TypeError('Expected a Yuku AST node.');
+    throw new TypeError('Expected a SWC Next AST node.');
   }
   return value;
 };
@@ -220,7 +220,7 @@ const stripComments = (
   const chunks: string[] = [];
   let cursor = 0;
 
-  // Yuku returns comments in source order, so mask each range while copying the source only once.
+  // SWC Next returns comments in source order, so mask each range while copying the source only once.
   for (const comment of comments) {
     const start = locStart(comment);
     const end = locEnd(comment);
@@ -356,7 +356,7 @@ const postprocess = (
   ast: AstNode,
   comments: PrettierComment[],
   text: string,
-  astType: 'yuku-js' | 'yuku-ts',
+  astType: 'swc-next-js' | 'swc-next-ts',
 ): AstNode => {
   mergeNestedJsdocComments(comments);
 
@@ -384,7 +384,7 @@ const postprocess = (
           const expression = asAstNode(node.expression);
           const start = locStart(node);
 
-          // Yuku comments are in source order, so these end offsets are sorted.
+          // SWC Next comments are in source order, so these end offsets are sorted.
           typeCastCommentEnds ??= comments
             .filter(isTypeCastComment)
             .map((comment) => locEnd(comment));
@@ -415,7 +415,7 @@ const postprocess = (
         }
 
         case 'TemplateElement': {
-          if (astType === 'yuku-ts') {
+          if (astType === 'swc-next-ts') {
             const start = locStart(node) + 1;
             const end = locEnd(node) - (node.tail ? 1 : 2);
             node.range = [start, end];
@@ -482,11 +482,13 @@ const createParseError = (error: Diagnostic, text: string): SyntaxError => {
   );
 };
 
-const parseWithOptions = (text: string, options: ParseOptions): ParseResult => {
-  const result = parseWithYuku(text, {
+const parseWithOptions = (
+  text: string,
+  options: Pick<ParseOptions, 'sourceType' | 'lang'>,
+): ParseResult => {
+  const result = parseWithSwcNext(text, {
     preserveParens: true,
-    semanticErrors: false,
-    attachComments: false,
+    comments: 'flat',
     ...options,
   });
 
@@ -509,10 +511,7 @@ const getSourceType = (filepath: string): SourceType | undefined => {
   return undefined;
 };
 
-const getLanguageCombinations = (
-  text: string,
-  filepath: string,
-): SourceLang[] => {
+const getLanguageCombinations = (text: string, filepath: string): Lang[] => {
   const normalizedPath = filepath.toLowerCase();
 
   if (JS_TS_FILE_REGEXP.test(normalizedPath)) {
@@ -542,7 +541,7 @@ const tryCombinations = (combinations: (() => ParseResult)[]): ParseResult => {
     throw firstError;
   }
 
-  throw new Error('No Yuku parser combinations were provided.');
+  throw new Error('No SWC Next parser combinations were provided.');
 };
 
 const parseJavaScript = (
@@ -558,7 +557,7 @@ const parseJavaScript = (
   );
   const { program, comments } = tryCombinations(combinations);
 
-  return postprocess(program as unknown as AstNode, comments, text, 'yuku-js');
+  return postprocess(asAstNode(program), comments, text, 'swc-next-js');
 };
 
 const parseTypeScript = (
@@ -576,7 +575,7 @@ const parseTypeScript = (
   );
   const { program, comments } = tryCombinations(combinations);
 
-  return postprocess(program as unknown as AstNode, comments, text, 'yuku-ts');
+  return postprocess(asAstNode(program), comments, text, 'swc-next-ts');
 };
 
 const createParser = (
@@ -611,23 +610,23 @@ const parseBabel = (text: string, options: ParserOptions<AstNode>): AstNode => {
   };
 };
 
-const yukuParser = createParser(parseJavaScript);
-const yukuBabelParser = createParser(parseBabel);
-const yukuTypeScriptParser = createParser(parseTypeScript);
+const swcNextParser = createParser(parseJavaScript);
+const swcNextBabelParser = createParser(parseBabel);
+const swcNextTypeScriptParser = createParser(parseTypeScript);
 
-const yukuPlugin: Plugin = {
+const swcNextPlugin: Plugin = {
   options: estreePlugin.options,
   parsers: {
     // Prettier resolves parsers from the last plugin that provides the name.
     // Project plugins are loaded after this one, so parser wrappers take priority.
-    babel: yukuBabelParser,
-    typescript: yukuTypeScriptParser,
-    yuku: yukuParser,
-    'yuku-ts': yukuTypeScriptParser,
+    babel: swcNextBabelParser,
+    typescript: swcNextTypeScriptParser,
+    'swc-next': swcNextParser,
+    'swc-next-ts': swcNextTypeScriptParser,
   },
   printers: {
     [AST_FORMAT]: estreePrinter,
   },
 };
 
-export { yukuPlugin };
+export { swcNextPlugin };
diff --git a/packages/rstack/tests/fmt/cacheIdentity.test.ts b/packages/rstack/tests/fmt/cacheIdentity.test.ts
@@ -88,6 +88,7 @@ test('includes formatter implementation versions in the namespace', () => {
     fmtCacheVersion,
     pkgJson.version,
     prettierPkgJson.version,
+    'swc-next@0.2.2:npm',
   ]);
 });