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Merged
merged 4 commits into from
Sep 20, 2025
Merged

perf: rework snapshot hot paths #2852

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3846dc6
perf: rework snapshot hot paths
43081j Sep 16, 2025
b856e36
perf: avoid garbage collection on diagnostics
43081j Sep 17, 2025
8dce0cd
Tweak snapshot hot paths for performance
dummdidumm Sep 19, 2025
6558687
chore: make linter happy
43081j Sep 19, 2025
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6 changes: 6 additions & 0 deletions .changeset/cool-chefs-compete.md
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Original file line number Diff line number Diff line change
@@ -0,0 +1,6 @@
---
'svelte-language-server': patch
'svelte-check': patch
---

perf: tweak some snapshot hot paths
20 changes: 10 additions & 10 deletions packages/language-server/src/plugins/typescript/DocumentSnapshot.ts
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Expand Up @@ -73,6 +73,11 @@ export interface SvelteSnapshotOptions {
typingsNamespace: string;
}

const ambientPathPattern = /node_modules[\/\\]svelte[\/\\]types[\/\\]ambient\.d\.ts$/;
const svelteTypesPattern = /node_modules[\/\\]svelte[\/\\]types[\/\\]index\.d\.ts$/;
const shimsPattern =
/svelte2tsx[\/\\]svelte-shims\.d\.ts$|svelte-check[\/\\]dist[\/\\]src[\/\\]svelte-shims\.d\.ts$/;

export namespace DocumentSnapshot {
/**
* Returns a svelte snapshot from a svelte document.
Expand Down Expand Up @@ -121,30 +126,25 @@ export namespace DocumentSnapshot {
* @param options options that apply in case it's a svelte file
*/
export function fromNonSvelteFilePath(filePath: string, tsSystem: ts.System) {
let originalText = '';

// The following (very hacky) code makes sure that the ambient module definitions
// that tell TS "every import ending with .svelte is a valid module" are removed.
// They exist in svelte2tsx and svelte to make sure that people don't
// get errors in their TS files when importing Svelte files and not using our TS plugin.
// If someone wants to get back the behavior they can add an ambient module definition
// on their own.
const normalizedPath = filePath.replace(/\\/g, '/');
if (!normalizedPath.endsWith('node_modules/svelte/types/runtime/ambient.d.ts')) {
let originalText = '';
if (!ambientPathPattern.test(filePath)) {
originalText = tsSystem.readFile(filePath) || '';
}

if (normalizedPath.endsWith('node_modules/svelte/types/index.d.ts')) {
if (svelteTypesPattern.test(filePath)) {
const startIdx = originalText.indexOf(`declare module '*.svelte' {`);
const endIdx = originalText.indexOf(`\n}`, startIdx + 1) + 2;
originalText =
originalText.substring(0, startIdx) +
' '.repeat(endIdx - startIdx) +
originalText.substring(endIdx);
} else if (
normalizedPath.endsWith('svelte2tsx/svelte-shims.d.ts') ||
normalizedPath.endsWith('svelte-check/dist/src/svelte-shims.d.ts')
) {
} else if (shimsPattern.test(filePath)) {
// If not present, the LS uses an older version of svelte2tsx
if (originalText.includes('// -- start svelte-ls-remove --')) {
originalText =
Expand All @@ -157,7 +157,7 @@ export namespace DocumentSnapshot {
}

const declarationExtensions = [ts.Extension.Dcts, ts.Extension.Dts, ts.Extension.Dmts];
if (declarationExtensions.some((ext) => normalizedPath.endsWith(ext))) {
if (declarationExtensions.some((ext) => filePath.endsWith(ext))) {
return new DtsDocumentSnapshot(INITIAL_VERSION, filePath, originalText, tsSystem);
}

Expand Down
111 changes: 56 additions & 55 deletions packages/language-server/src/svelte-check.ts
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Expand Up @@ -252,66 +252,67 @@ export class SvelteCheck {
const isKitFile = snapshot?.kitFile ?? false;
const diagnostics: Diagnostic[] = [];
if (!skipDiagnosticsForFile) {
const originalDiagnostics = [
...lang.getSyntacticDiagnostics(file.fileName),
...lang.getSuggestionDiagnostics(file.fileName),
...lang.getSemanticDiagnostics(file.fileName)
];

for (let diagnostic of originalDiagnostics) {
if (!diagnostic.start || !diagnostic.length || !isKitFile) {
diagnostics.push(map(diagnostic));
continue;
}
const diagnosticSources = [
'getSyntacticDiagnostics',
'getSuggestionDiagnostics',
'getSemanticDiagnostics'
] as const;
for (const diagnosticSource of diagnosticSources) {
for (let diagnostic of lang[diagnosticSource](file.fileName)) {
if (!diagnostic.start || !diagnostic.length || !isKitFile) {
diagnostics.push(map(diagnostic));
continue;
}

let range: Range | undefined = undefined;
const inGenerated = isInGeneratedCode(
file.text,
diagnostic.start,
diagnostic.start + diagnostic.length
);
if (inGenerated && snapshot) {
const pos = snapshot.getOriginalPosition(
snapshot.positionAt(diagnostic.start)
let range: Range | undefined = undefined;
const inGenerated = isInGeneratedCode(
file.text,
diagnostic.start,
diagnostic.start + diagnostic.length
);
range = {
start: pos,
end: {
line: pos.line,
// adjust length so it doesn't spill over to the next line
character: pos.character + 1
}
};
// If not one of the specific error messages then filter out
if (diagnostic.code === 2307) {
diagnostic = {
...diagnostic,
messageText:
typeof diagnostic.messageText === 'string' &&
diagnostic.messageText.includes('./$types')
? diagnostic.messageText +
` (this likely means that SvelteKit's type generation didn't run yet - try running it by executing 'npm run dev' or 'npm run build')`
: diagnostic.messageText
if (inGenerated && snapshot) {
const pos = snapshot.getOriginalPosition(
snapshot.positionAt(diagnostic.start)
);
range = {
start: pos,
end: {
line: pos.line,
// adjust length so it doesn't spill over to the next line
character: pos.character + 1
}
};
} else if (diagnostic.code === 2694) {
diagnostic = {
...diagnostic,
messageText:
typeof diagnostic.messageText === 'string' &&
diagnostic.messageText.includes('/$types')
? diagnostic.messageText +
` (this likely means that SvelteKit's generated types are out of date - try rerunning it by executing 'npm run dev' or 'npm run build')`
: diagnostic.messageText
};
} else if (
diagnostic.code !==
2355 /* A function whose declared type is neither 'void' nor 'any' must return a value */
) {
continue;
// If not one of the specific error messages then filter out
if (diagnostic.code === 2307) {
diagnostic = {
...diagnostic,
messageText:
typeof diagnostic.messageText === 'string' &&
diagnostic.messageText.includes('./$types')
? diagnostic.messageText +
` (this likely means that SvelteKit's type generation didn't run yet - try running it by executing 'npm run dev' or 'npm run build')`
: diagnostic.messageText
};
} else if (diagnostic.code === 2694) {
diagnostic = {
...diagnostic,
messageText:
typeof diagnostic.messageText === 'string' &&
diagnostic.messageText.includes('/$types')
? diagnostic.messageText +
` (this likely means that SvelteKit's generated types are out of date - try rerunning it by executing 'npm run dev' or 'npm run build')`
: diagnostic.messageText
};
} else if (
diagnostic.code !==
2355 /* A function whose declared type is neither 'void' nor 'any' must return a value */
) {
continue;
}
}
}

diagnostics.push(map(diagnostic, range));
diagnostics.push(map(diagnostic, range));
}
}
}

Expand Down
5 changes: 4 additions & 1 deletion packages/language-server/src/utils.ts
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Expand Up @@ -60,7 +60,10 @@ export function normalizeUri(uri: string): string {
* (bar or bar.svelte in this example).
*/
export function getLastPartOfPath(path: string): string {
return path.replace(/\\/g, '/').split('/').pop() || '';
const lastSlash = path.lastIndexOf('/');
const lastBackslash = path.lastIndexOf('\\');
const lastSeparator = Math.max(lastSlash, lastBackslash);
return lastSeparator === -1 ? path : path.slice(lastSeparator + 1);
}

export function flatten<T>(arr: Array<T | T[]>): T[] {
Expand Down