feat: pull diagnostics support (#2978)

jasonlyu123 · web-flow · commit d5b1f7be43f4 · 2026-03-18T12:06:06.000+01:00
This switches the diagnostics from push model (server to client) to the pull model when the client supports it. The advantage is that the client can prioritise sending the diagnostic request for the visible tab. With this, we can check the document split to the side immediately and don't need to check all open files after a file save. The pull mode has a way to tell the client that the diagnostics haven't changed. I implement this mostly because VSCode sends another diagnostic request for the same files when switching files in the editor, even if the file isn't changed.

I also lowered the debounce delay in the push-mode diagnostics. I've been wondering if some of the performance complaints are actually just because the artificial delay is too long for some people. The pull mode also has a much lower artificial delay. I think we can give it a try. If people are complaining about it, we can switch to an approach similar to the "smart" mode.
diff --git a/.changeset/purple-lions-fold.md b/.changeset/purple-lions-fold.md
@@ -0,0 +1,5 @@
+---
+'svelte-language-server': patch
+---
+
+feat: pull diagnostics support
diff --git a/packages/language-server/src/lib/DiagnosticsManager.ts b/packages/language-server/src/lib/DiagnosticsManager.ts
@@ -14,7 +14,14 @@ export type GetDiagnostics = (
     cancellationToken?: CancellationToken
 ) => Thenable<Diagnostic[]>;
 
-export class DiagnosticsManager {
+export interface DiagnosticsManager {
+    scheduleUpdate(document: Document): void;
+    scheduleUpdateAll(): void;
+    removeDiagnostics(document: Document): void;
+    cancelStarted(uri: string): void;
+}
+
+export class PushDiagnosticsManager implements DiagnosticsManager {
     constructor(
         private sendDiagnostics: SendDiagnostics,
         private docManager: DocumentManager,
@@ -93,5 +100,39 @@ export class DiagnosticsManager {
             this.update(doc);
         });
         this.pendingUpdates.clear();
-    }, 700);
+    }, 500);
+}
+
+export class PullDiagnosticsManager implements DiagnosticsManager {
+    constructor(
+        private sendDiagnostics: SendDiagnostics,
+        private sendRefreshDiagnostics: () => void
+    ) {}
+
+    private refreshTimeout: NodeJS.Timeout | null = null;
+
+    scheduleUpdate(): void {
+        // No-op, diagnostics are pulled by the client.
+    }
+
+    scheduleUpdateAll(): void {
+        if (this.refreshTimeout) {
+            clearTimeout(this.refreshTimeout);
+        }
+        this.refreshTimeout = setTimeout(() => {
+            this.sendRefreshDiagnostics();
+            this.refreshTimeout = null;
+        }, 500);
+    }
+
+    removeDiagnostics(document: Document): void {
+        this.sendDiagnostics({
+            uri: document.getURL(),
+            diagnostics: []
+        });
+    }
+
+    cancelStarted(): void {
+        // No-op, diagnostics are pulled by the client.
+    }
 }
diff --git a/packages/language-server/src/plugins/PluginHost.ts b/packages/language-server/src/plugins/PluginHost.ts
@@ -35,9 +35,10 @@ import {
     WorkspaceEdit,
     InlayHint,
     WorkspaceSymbol,
-    DocumentSymbol
+    DocumentSymbol,
+    DocumentDiagnosticReport
 } from 'vscode-languageserver';
-import { DocumentManager, getNodeIfIsInHTMLStartTag } from '../lib/documents';
+import { Document, DocumentManager, getNodeIfIsInHTMLStartTag } from '../lib/documents';
 import { Logger } from '../logger';
 import { isNotNullOrUndefined, regexLastIndexOf } from '../utils';
 import {
@@ -85,15 +86,7 @@ export class PluginHost implements LSProvider, OnWatchFileChanges {
     ): Promise<Diagnostic[]> {
         const document = this.getDocument(textDocument.uri);
 
-        if (
-            (document.getFilePath()?.includes('/node_modules/') ||
-                document.getFilePath()?.includes('\\node_modules\\')) &&
-            // Sapper convention: Put stuff inside node_modules below src
-            !(
-                document.getFilePath()?.includes('/src/node_modules/') ||
-                document.getFilePath()?.includes('\\src\\node_modules\\')
-            )
-        ) {
+        if (this.canSkipDiagnostics(document)) {
             // Don't return diagnostics for files inside node_modules. These are considered read-only (cannot be changed)
             // and in case of svelte-check they would pollute/skew the output
             return [];
@@ -109,6 +102,98 @@ export class PluginHost implements LSProvider, OnWatchFileChanges {
         ).flat();
     }
 
+    private canSkipDiagnostics(document: Document) {
+        return (
+            (document.getFilePath()?.includes('/node_modules/') ||
+                document.getFilePath()?.includes('\\node_modules\\')) &&
+            // Sapper convention: Put stuff inside node_modules below src
+            !(
+                document.getFilePath()?.includes('/src/node_modules/') ||
+                document.getFilePath()?.includes('\\src\\node_modules\\')
+            )
+        );
+    }
+
+    async getDiagnosticsForPullMode(
+        textDocument: TextDocumentIdentifier,
+        previousResultId: string | undefined,
+        cancellationToken?: CancellationToken
+    ): Promise<DocumentDiagnosticReport> {
+        const document = this.getDocument(textDocument.uri);
+        let previousResultIdData: Record<string, string> = {};
+        if (previousResultId) {
+            try {
+                previousResultIdData = JSON.parse(previousResultId);
+            } catch (error) {}
+        }
+
+        if (this.canSkipDiagnostics(document)) {
+            // Don't return diagnostics for files inside node_modules. These are considered read-only (cannot be changed)
+            return {
+                kind: 'full',
+                items: []
+            };
+        }
+
+        const plugins = this.plugins.filter(
+            (plugin) => typeof plugin.getDiagnosticsForPullMode === 'function'
+        );
+
+        const results = await Promise.all(
+            plugins.map(
+                async (plugin): Promise<[string, DocumentDiagnosticReport]> => [
+                    plugin.__name,
+                    await this.tryExecutePlugin(
+                        plugin,
+                        'getDiagnosticsForPullMode',
+                        [document, previousResultIdData[plugin.__name], cancellationToken],
+                        { kind: 'full', items: [] }
+                    )
+                ]
+            )
+        );
+
+        const newResultId = JSON.stringify(
+            Object.fromEntries(results.map(([name, res]) => [name, res.resultId]))
+        );
+        const unchanged = results
+            .filter(([, res]) => res.kind === 'unchanged')
+            .map(([name]) => name);
+        const fullResults = results.flatMap(([, res]) => (res.kind === 'full' ? res.items : []));
+
+        if (unchanged.length === plugins.length) {
+            return {
+                kind: 'unchanged',
+                resultId: newResultId
+            };
+        }
+        if (unchanged.length === 0) {
+            return {
+                kind: 'full',
+                resultId: newResultId,
+                items: fullResults
+            };
+        }
+        const unchangedPlugins = plugins.filter((plugin) => unchanged.includes(plugin.__name));
+        const unchangedResults = await Promise.all(
+            unchangedPlugins.map(async (plugin) => {
+                const result = await this.tryExecutePlugin(
+                    plugin,
+                    'getDiagnostics',
+                    [document, cancellationToken],
+                    []
+                );
+                return result;
+            })
+        );
+
+        return {
+            kind: 'full',
+            resultId: newResultId,
+            items: fullResults.concat(unchangedResults.flat())
+        };
+    }
+
     async doHover(textDocument: TextDocumentIdentifier, position: Position): Promise<Hover | null> {
         const document = this.getDocument(textDocument.uri);
 
diff --git a/packages/language-server/src/plugins/css/CSSPlugin.ts b/packages/language-server/src/plugins/css/CSSPlugin.ts
@@ -15,7 +15,9 @@ import {
     CompletionItemKind,
     SelectionRange,
     DocumentHighlight,
-    WorkspaceFolder
+    WorkspaceFolder,
+    FullDocumentDiagnosticReport,
+    UnchangedDocumentDiagnosticReport
 } from 'vscode-languageserver';
 import {
     Document,
@@ -144,6 +146,32 @@ export class CSSPlugin
             .map((diagnostic) => mapObjWithRangeToOriginal(cssDocument, diagnostic));
     }
 
+    getDiagnosticsForPullMode(
+        document: Document,
+        previousResultId: string | undefined
+    ): FullDocumentDiagnosticReport | UnchangedDocumentDiagnosticReport {
+        if (!this.featureEnabled('diagnostics')) {
+            return {
+                kind: 'full',
+                items: []
+            };
+        }
+
+        const resultId = document.version.toString();
+        if (previousResultId === resultId) {
+            return {
+                kind: 'unchanged',
+                resultId
+            };
+        }
+        const diagnostics = this.getDiagnostics(document);
+        return {
+            kind: 'full',
+            items: diagnostics,
+            resultId
+        };
+    }
+
     doHover(document: Document, position: Position): Hover | null {
         if (!this.featureEnabled('hover')) {
             return null;
diff --git a/packages/language-server/src/plugins/interfaces.ts b/packages/language-server/src/plugins/interfaces.ts
@@ -1,6 +1,7 @@
 import {
     CancellationToken,
     CompletionContext,
+    DocumentDiagnosticReport,
     FileChangeType,
     LinkedEditingRanges,
     SemanticTokens,
@@ -52,6 +53,11 @@ export interface AppCompletionList<T extends TextDocumentIdentifier = any> exten
 
 export interface DiagnosticsProvider {
     getDiagnostics(document: Document): Resolvable<Diagnostic[]>;
+    getDiagnosticsForPullMode(
+        document: Document,
+        previousResultId?: string,
+        cancellationToken?: CancellationToken
+    ): Resolvable<DocumentDiagnosticReport>;
 }
 
 export interface HoverProvider {
diff --git a/packages/language-server/src/plugins/svelte/SveltePlugin.ts b/packages/language-server/src/plugins/svelte/SveltePlugin.ts
@@ -7,6 +7,7 @@ import {
     CompletionContext,
     CompletionList,
     Diagnostic,
+    DocumentDiagnosticReport,
     FormattingOptions,
     Hover,
     Position,
@@ -107,6 +108,33 @@ export class SveltePlugin
         );
     }
 
+    async getDiagnosticsForPullMode(
+        document: Document,
+        previousResultId: string | undefined,
+        cancellationToken?: CancellationToken
+    ): Promise<DocumentDiagnosticReport> {
+        if (!this.featureEnabled('diagnostics')) {
+            return {
+                kind: 'full',
+                items: []
+            };
+        }
+
+        const resultId = document.version.toString();
+        if (previousResultId === resultId) {
+            return {
+                kind: 'unchanged',
+                resultId
+            };
+        }
+        const diagnostics = await this.getDiagnostics(document, cancellationToken);
+        return {
+            kind: 'full',
+            items: diagnostics,
+            resultId
+        };
+    }
+
     async getCompiledResult(document: Document): Promise<SvelteCompileResult | null> {
         try {
             const svelteDoc = await this.getSvelteDoc(document);
diff --git a/packages/language-server/src/plugins/typescript/TypeScriptPlugin.ts b/packages/language-server/src/plugins/typescript/TypeScriptPlugin.ts
@@ -11,6 +11,7 @@ import {
     CompletionList,
     DefinitionLink,
     Diagnostic,
+    DocumentDiagnosticReport,
     DocumentHighlight,
     FileChangeType,
     FoldingRange,
@@ -236,6 +237,25 @@ export class TypeScriptPlugin
         return this.diagnosticsProvider.getDiagnostics(document, cancellationToken);
     }
 
+    async getDiagnosticsForPullMode(
+        document: Document,
+        previousResultId?: string,
+        cancellationToken?: CancellationToken
+    ): Promise<DocumentDiagnosticReport> {
+        if (!this.featureEnabled('diagnostics')) {
+            return {
+                kind: 'full',
+                items: []
+            };
+        }
+
+        return this.diagnosticsProvider.getDiagnosticsForPullMode(
+            document,
+            previousResultId,
+            cancellationToken
+        );
+    }
+
     async doHover(document: Document, position: Position): Promise<Hover | null> {
         if (!this.featureEnabled('hover')) {
             return null;
diff --git a/packages/language-server/src/plugins/typescript/features/DiagnosticsProvider.ts b/packages/language-server/src/plugins/typescript/features/DiagnosticsProvider.ts
@@ -1,5 +1,11 @@
 import ts, { flattenDiagnosticMessageText } from 'typescript';
-import { CancellationToken, Diagnostic, DiagnosticSeverity, Range } from 'vscode-languageserver';
+import {
+    CancellationToken,
+    Diagnostic,
+    DiagnosticSeverity,
+    DocumentDiagnosticReport,
+    Range
+} from 'vscode-languageserver';
 import {
     Document,
     getNodeIfIsInStartTag,
@@ -105,6 +111,35 @@ export class DiagnosticsProviderImpl implements DiagnosticsProvider {
         return mapAndFilterDiagnostics(diagnostics, document, tsDoc, lang);
     }
 
+    async getDiagnosticsForPullMode(
+        document: Document,
+        previousResultId?: string,
+        cancellationToken?: CancellationToken
+    ): Promise<DocumentDiagnosticReport> {
+        const { tsDoc, lsContainer } = await this.getLSAndTSDoc(document);
+        if (cancellationToken?.isCancellationRequested) {
+            return {
+                kind: 'full',
+                items: []
+            };
+        }
+        const resultId = tsDoc.version.toString() + '-' + lsContainer.getProjectVersion();
+
+        if (previousResultId === resultId) {
+            return {
+                kind: 'unchanged',
+                resultId
+            };
+        }
+
+        const diagnostics = await this.getDiagnostics(document);
+        return {
+            kind: 'full',
+            resultId,
+            items: diagnostics
+        };
+    }
+
     private async getLSAndTSDoc(document: Document) {
         return this.lsAndTsDocResolver.getLSAndTSDoc(document);
     }
diff --git a/packages/language-server/src/plugins/typescript/service.ts b/packages/language-server/src/plugins/typescript/service.ts
diff --git a/packages/language-server/src/server.ts b/packages/language-server/src/server.ts
diff --git a/packages/language-server/test/plugins/PluginHost.test.ts b/packages/language-server/test/plugins/PluginHost.test.ts

-Original file line number
+Diff line change
@@ @@ -0,0 +1,5 @@ @@
 +---
 +'svelte-language-server': patch
 +---
++
 +feat: pull diagnostics support