rstackjs · chenjiahan · Aug 12, 2026 · Aug 12, 2026
diff --git a/packages/rstack/package.json b/packages/rstack/package.json
@@ -95,8 +95,10 @@
     "is-binary-path": "catalog:",
     "lint-staged": "catalog:",
     "micromatch": "catalog:",
+    "prettier-plugin-svelte": "catalog:",
     "rslog": "catalog:",
     "sort-package-json": "catalog:",
+    "svelte": "catalog:",
     "tiny-readdir": "catalog:",
     "typescript": "catalog:"
   },

diff --git a/packages/rstack/src/fmt/yukuPlugin.ts b/packages/rstack/src/fmt/yukuPlugin.ts
@@ -7,10 +7,13 @@ import {
   type Diagnostic,
   type ParseOptions,
   type ParseResult,
+  type SourceLang,
   type SourceType,
 } from 'yuku-parser';
 
 const AST_FORMAT = 'estree-yuku';
+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'];
 
 type Range = [start: number, end: number];
@@ -461,6 +464,17 @@ const getSourceType = (filepath: string): SourceType | undefined => {
   return undefined;
 };
 
+const getLanguageCombinations = (text: string, filepath: string): SourceLang[] => {
+  const normalizedPath = filepath.toLowerCase();
+
+  if (JS_TS_FILE_REGEXP.test(normalizedPath)) {
+    return [langFromPath(normalizedPath)];
+  }
+
+  // Embedded code from Vue or Svelte keeps the host file path, so detect JSX from its content.
+  return JSX_REGEXP.test(text) ? ['tsx', 'ts', 'dts'] : ['ts', 'tsx', 'dts'];
+};
+
 const tryCombinations = (combinations: (() => ParseResult)[]): ParseResult => {
   let firstError: unknown;
   let hasError = false;
@@ -495,9 +509,9 @@ const parseJavaScript = (text: string, options: ParserOptions<AstNode>): AstNode
 
 const parseTypeScript = (text: string, options: ParserOptions<AstNode>): AstNode => {
   const sourceType = getSourceType(options.filepath);
-  const lang = langFromPath(options.filepath.toLowerCase());
-  const combinations = (sourceType ? [sourceType] : SOURCE_TYPE_COMBINATIONS).map(
-    (candidate) => () => parseWithOptions(text, { sourceType: candidate, lang }),
+  const languages = getLanguageCombinations(text, options.filepath);
+  const combinations = (sourceType ? [sourceType] : SOURCE_TYPE_COMBINATIONS).flatMap((candidate) =>
+    languages.map((lang) => () => parseWithOptions(text, { sourceType: candidate, lang })),
   );
   const { program, comments } = tryCombinations(combinations);
 

diff --git a/packages/rstack/tests/cli/fmt/svelte.test.ts b/packages/rstack/tests/cli/fmt/svelte.test.ts
@@ -0,0 +1,37 @@
+import { expect, test } from 'rstack/test';
+import { expectWriteSummary, setupFmtTest } from './helpers.ts';
+
+const { readProjectFile, runFmt, writeProjectFile } = setupFmtTest();
+
+test.each([
+  {
+    name: 'instance scripts',
+    source:
+      '<script lang="ts">\nlet title=$state<string>("Rstack + Svelte")\n</script>\n\n<h1>{title}</h1>\n',
+    expected:
+      '<script lang="ts">\n  let title = $state<string>("Rstack + Svelte");\n</script>\n\n<h1>{title}</h1>\n',
+  },
+  {
+    name: 'module scripts',
+    source:
+      '<script module lang="ts">\nconst identity=<T>(value:T):T=>value\n</script>\n\n<p>{identity("Rstack")}</p>\n',
+    expected:
+      '<script module lang="ts">\n  const identity = <T,>(value: T): T => value;\n</script>\n\n<p>{identity("Rstack")}</p>\n',
+  },
+])('formats TypeScript embedded in Svelte $name', ({ source, expected }) => {
+  writeProjectFile(
+    'rstack.config.ts',
+    `import { define } from 'rstack';
+
+define.fmt({ plugins: ['prettier-plugin-svelte'] });
+`,
+  );
+  writeProjectFile('App.svelte', source);
+
+  const result = runFmt(['App.svelte']);
+
+  expect(result.status).toBe(0);
+  expectWriteSummary(result.stdout, 1, 1);
+  expect(result.stderr).toBe('');
+  expect(readProjectFile('App.svelte')).toBe(expected);
+});
diff --git a/packages/rstack/tests/cli/fmt/vue.test.ts b/packages/rstack/tests/cli/fmt/vue.test.ts
@@ -0,0 +1,26 @@
+import { expect, test } from 'rstack/test';
+import { expectWriteSummary, setupFmtTest } from './helpers.ts';
+
+const { readProjectFile, runFmt, writeProjectFile } = setupFmtTest();
+
+test.each([
+  {
+    name: 'TypeScript',
+    source: '<script setup lang="ts">\nconst title=ref<string>("Rstack + Vue")\n</script>\n',
+    expected: '<script setup lang="ts">\nconst title = ref<string>("Rstack + Vue");\n</script>\n',
+  },
+  {
+    name: 'TSX',
+    source: '<script setup lang="tsx">\nconst view=<Component value={1}/>\n</script>\n',
+    expected: '<script setup lang="tsx">\nconst view = <Component value={1} />;\n</script>\n',
+  },
+])('formats $name embedded in Vue files', ({ source, expected }) => {
+  writeProjectFile('App.vue', source);
+
+  const result = runFmt(['App.vue']);
+
+  expect(result.status).toBe(0);
+  expectWriteSummary(result.stdout, 1, 1);
+  expect(result.stderr).toBe('');
+  expect(readProjectFile('App.vue')).toBe(expected);
+});