feat: svelte-check --incremental / --tsgo (#2932)

Adds two new flags:

- `--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`

Part of #2733
closes #2131

Huge kudos to https://github.com/astralhpi/svelte-fast-check and https://svelte-check-rs.vercel.app/ , both of which heavily inspired this PR

Author: dummdidumm

.changeset/clean-clocks-itch.md

@@ -0,0 +1,5 @@
+---
+'svelte-check': minor
+---
+
+feat: provide `--incremental` and `--tsgo` flags

.changeset/silver-trees-act.md

@@ -0,0 +1,5 @@
+---
+'svelte2tsx': patch
+---
+
+chore: add option to output pure jsdoc-based JS files

.changeset/wild-crabs-rule.md

@@ -0,0 +1,5 @@
+---
+'svelte-language-server': patch
+---
+
+chore: provide utils for svelte-check

packages/language-server/src/index.ts

@@ -1,3 +1,8 @@
 export * from './server';
 export { offsetAt } from './lib/documents';
-export { SvelteCheck, SvelteCheckOptions, SvelteCheckDiagnosticSource } from './svelte-check';
+export {
+    mapSvelteCheckDiagnostics,
+    SvelteCheck,
+    SvelteCheckDiagnosticSource,
+    SvelteCheckOptions
+} from './svelte-check';

packages/language-server/src/plugins/typescript/features/DiagnosticsProvider.ts

@@ -1,4 +1,4 @@
-import ts from 'typescript';
+import ts, { flattenDiagnosticMessageText } from 'typescript';
 import { CancellationToken, Diagnostic, DiagnosticSeverity, Range } from 'vscode-languageserver';
 import {
     Document,
@@ -101,8 +101,25 @@ export class DiagnosticsProviderImpl implements DiagnosticsProvider {
             diagnostics.push(...checker.call(lang, tsDoc.filePath));
         }
 
+        return mapAndFilterDiagnostics(diagnostics, document, tsDoc, isTypescript, lang);
+    }
+
+    private async getLSAndTSDoc(document: Document) {
+        return this.lsAndTsDocResolver.getLSAndTSDoc(document);
+    }
+}
+
+export function mapAndFilterDiagnostics(
+    diagnostics: ts.Diagnostic[],
+    document: Document,
+    tsDoc: SvelteDocumentSnapshot,
+    isTypescript: boolean,
+    lang?: ts.LanguageService
+): Diagnostic[] {
+    const notGenerated = isNotGenerated(tsDoc.getFullText());
+
+    if (lang) {
         const additionalStoreDiagnostics: ts.Diagnostic[] = [];
-        const notGenerated = isNotGenerated(tsDoc.getFullText());
         for (const diagnostic of diagnostics) {
             if (
                 (diagnostic.code === DiagnosticCode.NO_OVERLOAD_MATCHES_CALL ||
@@ -132,46 +149,44 @@ export class DiagnosticsProviderImpl implements DiagnosticsProvider {
             }
         }
         diagnostics.push(...additionalStoreDiagnostics);
+    }
 
-        diagnostics = diagnostics
-            .filter(notGenerated)
-            .filter(not(isUnusedReactiveStatementLabel))
-            .filter((diagnostics) => !expectedTransitionThirdArgument(diagnostics, tsDoc, lang));
+    diagnostics = diagnostics
+        .filter(notGenerated)
+        .filter(not(isUnusedReactiveStatementLabel))
+        .filter((diagnostic) => !expectedTransitionThirdArgument(diagnostic, tsDoc, lang));
 
+    if (lang) {
         diagnostics = resolveNoopsInReactiveStatements(lang, diagnostics);
+    }
 
-        const mapRange = rangeMapper(tsDoc, document, lang);
-        const noFalsePositive = isNoFalsePositive(document, tsDoc);
-        const converted: Diagnostic[] = [];
-
-        for (const tsDiag of diagnostics) {
-            let diagnostic: Diagnostic = {
-                range: convertRange(tsDoc, tsDiag),
-                severity: mapSeverity(tsDiag.category),
-                source: isTypescript ? 'ts' : 'js',
-                message: ts.flattenDiagnosticMessageText(tsDiag.messageText, '\n'),
-                code: tsDiag.code,
-                tags: getDiagnosticTag(tsDiag)
-            };
-            diagnostic = mapRange(diagnostic);
-
-            moveBindingErrorMessage(tsDiag, tsDoc, diagnostic, document);
+    const mapRange = rangeMapper(tsDoc, document, lang);
+    const noFalsePositive = isNoFalsePositive(document, tsDoc);
+    const converted: Diagnostic[] = [];
+
+    for (const tsDiag of diagnostics) {
+        let diagnostic: Diagnostic = {
+            range: convertRange(tsDoc, tsDiag),
+            severity: mapSeverity(tsDiag.category),
+            source: isTypescript ? 'ts' : 'js',
+            message: ts.flattenDiagnosticMessageText(tsDiag.messageText, '\n'),
+            code: tsDiag.code,
+            tags: getDiagnosticTag(tsDiag)
+        };
+        diagnostic = mapRange(diagnostic);
 
-            if (!hasNoNegativeLines(diagnostic) || !noFalsePositive(diagnostic)) {
-                continue;
-            }
+        moveBindingErrorMessage(tsDiag, tsDoc, diagnostic, document);
 
-            diagnostic = adjustIfNecessary(diagnostic, tsDoc.isSvelte5Plus);
-            diagnostic = swapDiagRangeStartEndIfNecessary(diagnostic);
-            converted.push(diagnostic);
+        if (!hasNoNegativeLines(diagnostic) || !noFalsePositive(diagnostic)) {
+            continue;
         }
 
-        return converted;
+        diagnostic = adjustIfNecessary(diagnostic, tsDoc.isSvelte5Plus);
+        diagnostic = swapDiagRangeStartEndIfNecessary(diagnostic);
+        converted.push(diagnostic);
     }
 
-    private async getLSAndTSDoc(document: Document) {
-        return this.lsAndTsDocResolver.getLSAndTSDoc(document);
-    }
+    return converted;
 }
 
 function moveBindingErrorMessage(
@@ -231,17 +246,21 @@ function moveBindingErrorMessage(
 function rangeMapper(
     snapshot: SvelteDocumentSnapshot,
     document: Document,
-    lang: ts.LanguageService
+    lang?: ts.LanguageService
 ): (value: Diagnostic) => Diagnostic {
-    const get$$PropsDefWithCache = memoize(() => get$$PropsDef(lang, snapshot));
+    const get$$PropsDefWithCache = memoize(() =>
+        lang ? get$$PropsDef(lang, snapshot) : undefined
+    );
     const get$$PropsAliasInfoWithCache = memoize(() =>
-        get$$PropsAliasForInfo(get$$PropsDefWithCache, lang, document)
+        lang ? get$$PropsAliasForInfo(get$$PropsDefWithCache, lang, document) : undefined
     );
 
     return (diagnostic) => {
         let range = mapRangeToOriginal(snapshot, diagnostic.range);
 
-        if (range.start.line < 0) {
+        // When lang is unavailable (incremental CLI path), we can't remap negative-line
+        // diagnostics. This only affects deprecated $$Props syntax, so it's acceptable.
+        if (range.start.line < 0 && lang) {
             range =
                 movePropsErrorRangeBackIfNecessary(
                     diagnostic,
@@ -605,7 +624,7 @@ function movePropsErrorRangeBackIfNecessary(
 function expectedTransitionThirdArgument(
     diagnostic: ts.Diagnostic,
     tsDoc: SvelteDocumentSnapshot,
-    lang: ts.LanguageService
+    lang?: ts.LanguageService
 ) {
     if (
         diagnostic.code !== DiagnosticCode.EXPECTED_N_ARGUMENTS ||
@@ -631,6 +650,13 @@ function expectedTransitionThirdArgument(
                   ts.isCallExpression
               );
 
+    if (!lang) {
+        // Without a language service we can't resolve the signature to check parameter count.
+        // Fall back to checking the message text for " 3" (i.e. "Expected 3 arguments").
+        // This is only for the __sveltets_2_ensureTransition wrapper and unlikely to false-positive.
+        return flattenDiagnosticMessageText(diagnostic.messageText, '\n').includes(' 3');
+    }
+
     const signature =
         callExpression && lang.getProgram()?.getTypeChecker().getResolvedSignature(callExpression);
 

packages/language-server/src/svelte-check.ts

@@ -14,12 +14,35 @@ import {
 } from './plugins';
 import { FileSystemProvider } from './lib/FileSystemProvider';
 import { createLanguageServices } from './plugins/css/service';
-import { JSOrTSDocumentSnapshot } from './plugins/typescript/DocumentSnapshot';
+import {
+    DocumentSnapshot,
+    JSOrTSDocumentSnapshot,
+    SvelteDocumentSnapshot,
+    SvelteSnapshotOptions
+} from './plugins/typescript/DocumentSnapshot';
 import { isInGeneratedCode } from './plugins/typescript/features/utils';
+import { mapAndFilterDiagnostics } from './plugins/typescript/features/DiagnosticsProvider';
 import { convertRange, getDiagnosticTag, mapSeverity } from './plugins/typescript/utils';
 import { pathToUrl, urlToPath } from './utils';
 import { groupBy } from 'lodash';
 
+export function mapSvelteCheckDiagnostics(
+    sourcePath: string,
+    sourceText: string,
+    isTsFile: boolean,
+    tsDiagnostics: ts.Diagnostic[]
+): Diagnostic[] {
+    const document = new Document(pathToUrl(sourcePath), sourceText);
+    const snapshot = DocumentSnapshot.fromDocument(document, {
+        parse: document.compiler?.parse,
+        version: document.compiler?.VERSION,
+        transformOnTemplateError: false,
+        typingsNamespace: 'svelteHTML'
+    } satisfies SvelteSnapshotOptions) as SvelteDocumentSnapshot;
+
+    return mapAndFilterDiagnostics(tsDiagnostics, document, snapshot, isTsFile, undefined);
+}
+
 export type SvelteCheckDiagnosticSource = 'js' | 'css' | 'svelte';
 
 export interface SvelteCheckOptions {

packages/svelte-check/.gitignore

@@ -1,3 +1,4 @@
 dist/
 .vscode/
 node_modules/
+.svelte-check/