feat: add --tsc-rs flag to svelte-check

.changeset/tsc-rs.md

@@ -0,0 +1,5 @@
+---
+'svelte-check': minor
+---
+
+feat: add `--tsc-rs` flag to use tsc-rs, a Rust port of the TypeScript 7 compiler, for TypeScript diagnostics

packages/svelte-check/README.md

@@ -80,6 +80,7 @@ npm install --save-dev typescript@~6 @typescript/native@npm:typescript@7
 | `--threshold <error\|warning>`                                  | Filters the diagnostics to display. `error` will output only errors while `warning` will output warnings and errors.                                                                                                                                                                                                                                                                                     |
 | `--incremental`                                                 | Opts into TypeScript's incremental build cache, which speeds up subsequent runs. Saved within `.svelte-kit` or if not available within `.svelte-check`. This might result in slightly different type check outcomes, and certain patterns are not supported. Specifically, anything that is not in the root dir of your tsconfig.json and is a Svelte file will not be properly loaded and type-checked. |
 | `--tsgo`                                                        | Use TypeScript's Go implementation. Needs to have `@typescript/native-preview` installed. Subject to the same limitations as `--incremental`                                                                                                                                                                                                                                                             |
+| `--tsc-rs`                                                      | Use tsc-rs, a Rust port of TypeScript's Go implementation. Needs to have `tsc-rs` installed. Subject to the same limitations as `--incremental`                                                                                                                                                                                                                                                          |
 
 ### FAQ
 

packages/svelte-check/package.json

@@ -58,6 +58,7 @@
         "svelte": "^4.2.19",
         "svelte-language-server": "workspace:*",
         "svelte2tsx": "workspace:*",
+        "tsc-rs": "~0.7.0",
         "typescript": "^6.0.3",
         "vscode-languageserver": "8.0.2",
         "vscode-languageserver-protocol": "3.17.2",

packages/svelte-check/src/incremental.ts

@@ -466,22 +466,27 @@ export function writeOverlayTsconfig(
 }
 
 /**
- * Spawns a TypeScript compiler process (tsc or tsgo) to perform type-checking
+ * Spawns a TypeScript compiler process (tsc, tsgo or tsc-rs) to perform type-checking
  * and collects the diagnostics from its output.
  *
  * @param tsconfigPath - Path to the tsconfig.json to use for compilation
- * @param useTsgo - When true, uses the experimental native TypeScript compiler (tsgo)
+ * @param compiler - Which compiler to use: tsc, the native TypeScript compiler (tsgo) or its Rust port (tsc-rs)
  * @param incremental - Whether to enable incremental compilation for faster subsequent runs
  * @param cwd - Working directory for the TypeScript compiler process
  * @returns Parsed diagnostics containing file paths, positions, severity, and messages
  */
 export function runTypeScriptDiagnostics(
     tsconfigPath: string,
-    useTsgo: boolean,
+    compiler: 'tsc' | 'tsgo' | 'tsc-rs',
     incremental: boolean,
     cwd: string
 ): Promise<ParsedDiagnostic[]> {
-    const binPath = useTsgo ? getTsGoBinPath(tsconfigPath) : require.resolve('typescript/bin/tsc');
+    const binPath =
+        compiler === 'tsc-rs'
+            ? getTscRsBinPath(tsconfigPath)
+            : compiler === 'tsgo'
+              ? getTsGoBinPath(tsconfigPath)
+              : require.resolve('typescript/bin/tsc');
 
     if (!binPath || !fs.existsSync(binPath) || !fs.statSync(binPath).isFile()) {
         throw new Error('Failed to locate TypeScript command-line executable.');
@@ -569,6 +574,24 @@ function getTsGoBinPath(tsconfigPath: string): string | undefined {
     return binPathRelative ? path.join(path.dirname(pkg.path), binPathRelative) : undefined;
 }
 
+function getTscRsBinPath(tsconfigPath: string): string | undefined {
+    let pkgPath: string;
+    try {
+        pkgPath = require.resolve('tsc-rs/package.json', { paths: [tsconfigPath, __dirname] });
+    } catch (e) {
+        throw new Error(
+            'svelte-check --tsc-rs requires tsc-rs to be installed in the workspace. ' +
+                'You can install it via the following command.\n' +
+                'npm install --save-dev tsc-rs\n'
+        );
+    }
+
+    const bin = require(pkgPath).bin;
+    const binPathRelative = typeof bin === 'string' ? bin : bin?.['tsc-rs'];
+
+    return binPathRelative ? path.join(path.dirname(pkgPath), binPathRelative) : undefined;
+}
+
 /**
  * Maps TypeScript CLI diagnostics back to their original Svelte source files.
  * For Svelte files, uses source maps to translate positions from the generated

packages/svelte-check/src/index.ts

@@ -447,8 +447,11 @@ async function runWithVirtualFiles(
     writer: Writer
 ): Promise<Result | null> {
     if (!opts.tsconfig) {
-        throw new Error('`--incremental` / `--tsgo` requires a tsconfig/jsconfig file');
+        throw new Error(
+            '`--incremental` / `--tsgo` / `--tsc-rs` requires a tsconfig/jsconfig file'
+        );
     }
+    const compiler = opts.tscRs ? 'tsc-rs' : opts.tsgo ? 'tsgo' : 'tsc';
 
     const emitResult = await emitSvelteFiles(
         opts.workspaceUri.fsPath,
@@ -460,12 +463,13 @@ async function runWithVirtualFiles(
         opts.tsconfig,
         emitResult,
         opts.incremental,
-        opts.tsgo
+        // tsc-rs is a port of tsgo, so it needs the same overlay
+        compiler !== 'tsc'
     );
     const tsDiagnostics = mapCliDiagnosticsToLsp(
         await runTypeScriptDiagnostics(
             overlayTsconfig,
-            opts.tsgo,
+            compiler,
             opts.incremental,
             opts.workspaceUri.fsPath
         ),
@@ -600,6 +604,10 @@ parseOptions(async (opts) => {
             watch: opts.watch
         };
 
+        if (opts.tscRs && opts.tsgo) {
+            throw new Error('--tsc-rs cannot be used with --tsgo');
+        }
+
         if (opts.tsgoExperimental) {
             if (!opts.tsconfig) {
                 throw new Error('--tsgo-experimental-api requires a tsconfig/jsconfig file');
@@ -610,6 +618,9 @@ parseOptions(async (opts) => {
             if (opts.tsgo) {
                 throw new Error('--tsgo-experimental-api cannot be used with --tsgo');
             }
+            if (opts.tscRs) {
+                throw new Error('--tsgo-experimental-api cannot be used with --tsc-rs');
+            }
             const pkg = tryParseTsGoVersion(opts.tsconfig);
             if (!pkg) {
                 throw new Error(formatTsGoNotFoundError('--tsgo-experimental-api'));
@@ -642,7 +653,7 @@ parseOptions(async (opts) => {
             svelteCheckOptions.experimental = { tsgo: { apiModule, astModule } };
         }
 
-        const useVirtualFiles = opts.incremental || opts.tsgo;
+        const useVirtualFiles = opts.incremental || opts.tsgo || opts.tscRs;
         if (useVirtualFiles && opts.watch) {
             await watchWithVirtualFiles(opts, writer);
         } else if (useVirtualFiles) {

packages/svelte-check/src/options.ts

@@ -10,6 +10,7 @@ export interface SvelteCheckCliOptions {
     preserveWatchOutput: boolean;
     incremental: boolean;
     tsgo: boolean;
+    tscRs: boolean;
     tsgoExperimental: boolean;
     tsconfig?: string;
     config?: string;
@@ -47,9 +48,14 @@ export function parseOptions(cb: (opts: SvelteCheckCliOptions) => any) {
             'Use tsgo for TypeScript diagnostics. Requires writing transpiled Svelte files to disk (.svelte-kit if available, else .svelte-check)',
             false
         )
+        .option(
+            '--tsc-rs',
+            'Use tsc-rs (a Rust port of the TypeScript 7 compiler) for TypeScript diagnostics. Requires writing transpiled Svelte files to disk (.svelte-kit if available, else .svelte-check)',
+            false
+        )
         .option(
             '--tsgo-experimental-api',
-            'Use tsgo for TypeScript diagnostics with the experimental API. Cannot be used with --incremental or --tsgo. Experimental feature, might break without warning.',
+            'Use tsgo for TypeScript diagnostics with the experimental API. Cannot be used with --incremental, --tsgo or --tsc-rs. Experimental feature, might break without warning.',
             false
         )
         .option(
@@ -106,6 +112,7 @@ export function parseOptions(cb: (opts: SvelteCheckCliOptions) => any) {
                 preserveWatchOutput: !!opts.preserveWatchOutput,
                 incremental: !!opts.incremental,
                 tsgo: !!opts.tsgo,
+                tscRs: !!opts['tsc-rs'],
                 tsconfig,
                 config,
                 filePathsToIgnore: opts.ignore?.split(',') || [],

packages/svelte-check/test-sanity.js

@@ -32,6 +32,7 @@ let failed = 0;
  * @param {boolean} [opts.incremental]
  * @param {boolean} [opts.tsgoExp]
  * @param {boolean} [opts.tsgo]
+ * @param {boolean} [opts.tscRs]
  * @param {ExpectedError[]} [opts.errors]
  */
 function test(name, opts) {
@@ -53,6 +54,9 @@ function test(name, opts) {
     if (opts.tsgo) {
         args.push('--tsgo');
     }
+    if (opts.tscRs) {
+        args.push('--tsc-rs');
+    }
 
     let stdout;
     try {
@@ -249,6 +253,12 @@ test('clean project --tsgo', {
     tsgo: true
 });
 
+test('clean project --tsc-rs', {
+    workspace: './test-success',
+    tsconfig: './tsconfig.json',
+    tscRs: true
+});
+
 const errors = [
     {
         file: 'Index.svelte',
@@ -335,6 +345,13 @@ test('project with errors --tsgo', {
     errors
 });
 
+test('project with errors --tsc-rs', {
+    workspace: './test-error',
+    tsconfig: './tsconfig.json',
+    tscRs: true,
+    errors
+});
+
 // A compiler that dies must not look like a clean run, and one that dies after reporting
 // some diagnostics must not look like a completed one.
 testCrashedCompiler(