(perf) add priority queue

Give certain requests priority.
If a request doesn't have priority, we first wait 1 second to
1. let higher priority requests get through first
2. wait for possible document changes, which make the request wait again

This hopefully makes perceived responsiveness of the language server better
sveltejs#1098, sveltejs#1130, sveltejs#1139

packages/language-server/src/plugins/PluginHost.ts

@@ -53,6 +53,7 @@ export class PluginHost implements LSProvider, OnWatchFileChanges {
         filterIncompleteCompletions: true,
         definitionLinkSupport: false
     };
+    private deferredRequests: Record<string, [number, Promise<any>]> = {};
 
     constructor(private documentsManager: DocumentManager) {}
 
@@ -64,14 +65,23 @@ export class PluginHost implements LSProvider, OnWatchFileChanges {
         this.plugins.push(plugin);
     }
 
+    didUpdateDocument() {
+        this.deferredRequests = {};
+    }
+
     async getDiagnostics(textDocument: TextDocumentIdentifier): Promise<Diagnostic[]> {
         const document = this.getDocument(textDocument.uri);
         if (!document) {
             throw new Error('Cannot call methods on an unopened document');
         }
 
         return flatten(
-            await this.execute<Diagnostic[]>('getDiagnostics', [document], ExecuteMode.Collect)
+            await this.execute<Diagnostic[]>(
+                'getDiagnostics',
+                [document],
+                ExecuteMode.Collect,
+                'high'
+            )
         );
     }
 
@@ -81,7 +91,12 @@ export class PluginHost implements LSProvider, OnWatchFileChanges {
             throw new Error('Cannot call methods on an unopened document');
         }
 
-        return this.execute<Hover>('doHover', [document, position], ExecuteMode.FirstNonNull);
+        return this.execute<Hover>(
+            'doHover',
+            [document, position],
+            ExecuteMode.FirstNonNull,
+            'high'
+        );
     }
 
     async getCompletions(
@@ -99,7 +114,8 @@ export class PluginHost implements LSProvider, OnWatchFileChanges {
             await this.execute<CompletionList>(
                 'getCompletions',
                 [document, position, completionContext, cancellationToken],
-                ExecuteMode.Collect
+                ExecuteMode.Collect,
+                'high'
             )
         ).filter((completion) => completion != null);
 
@@ -141,7 +157,8 @@ export class PluginHost implements LSProvider, OnWatchFileChanges {
         const result = await this.execute<CompletionItem>(
             'resolveCompletion',
             [document, completionItem, cancellationToken],
-            ExecuteMode.FirstNonNull
+            ExecuteMode.FirstNonNull,
+            'high'
         );
 
         return result ?? completionItem;
@@ -160,7 +177,8 @@ export class PluginHost implements LSProvider, OnWatchFileChanges {
             await this.execute<TextEdit[]>(
                 'formatDocument',
                 [document, options],
-                ExecuteMode.Collect
+                ExecuteMode.Collect,
+                'high'
             )
         );
     }
@@ -177,7 +195,8 @@ export class PluginHost implements LSProvider, OnWatchFileChanges {
         return this.execute<string | null>(
             'doTagComplete',
             [document, position],
-            ExecuteMode.FirstNonNull
+            ExecuteMode.FirstNonNull,
+            'high'
         );
     }
 
@@ -191,7 +210,8 @@ export class PluginHost implements LSProvider, OnWatchFileChanges {
             await this.execute<ColorInformation[]>(
                 'getDocumentColors',
                 [document],
-                ExecuteMode.Collect
+                ExecuteMode.Collect,
+                'low'
             )
         );
     }
@@ -210,7 +230,8 @@ export class PluginHost implements LSProvider, OnWatchFileChanges {
             await this.execute<ColorPresentation[]>(
                 'getColorPresentations',
                 [document, range, color],
-                ExecuteMode.Collect
+                ExecuteMode.Collect,
+                'low'
             )
         );
     }
@@ -228,7 +249,8 @@ export class PluginHost implements LSProvider, OnWatchFileChanges {
             await this.execute<SymbolInformation[]>(
                 'getDocumentSymbols',
                 [document, cancellationToken],
-                ExecuteMode.Collect
+                ExecuteMode.Collect,
+                'low'
             )
         );
     }
@@ -246,7 +268,8 @@ export class PluginHost implements LSProvider, OnWatchFileChanges {
             await this.execute<DefinitionLink[]>(
                 'getDefinitions',
                 [document, position],
-                ExecuteMode.Collect
+                ExecuteMode.Collect,
+                'high'
             )
         );
 
@@ -274,7 +297,8 @@ export class PluginHost implements LSProvider, OnWatchFileChanges {
             await this.execute<CodeAction[]>(
                 'getCodeActions',
                 [document, range, context, cancellationToken],
-                ExecuteMode.Collect
+                ExecuteMode.Collect,
+                'high'
             )
         );
     }
@@ -292,15 +316,17 @@ export class PluginHost implements LSProvider, OnWatchFileChanges {
         return await this.execute<WorkspaceEdit>(
             'executeCommand',
             [document, command, args],
-            ExecuteMode.FirstNonNull
+            ExecuteMode.FirstNonNull,
+            'high'
         );
     }
 
     async updateImports(fileRename: FileRename): Promise<WorkspaceEdit | null> {
         return await this.execute<WorkspaceEdit>(
             'updateImports',
             [fileRename],
-            ExecuteMode.FirstNonNull
+            ExecuteMode.FirstNonNull,
+            'high'
         );
     }
 
@@ -316,7 +342,8 @@ export class PluginHost implements LSProvider, OnWatchFileChanges {
         return await this.execute<any>(
             'prepareRename',
             [document, position],
-            ExecuteMode.FirstNonNull
+            ExecuteMode.FirstNonNull,
+            'high'
         );
     }
 
@@ -333,7 +360,8 @@ export class PluginHost implements LSProvider, OnWatchFileChanges {
         return await this.execute<any>(
             'rename',
             [document, position, newName],
-            ExecuteMode.FirstNonNull
+            ExecuteMode.FirstNonNull,
+            'high'
         );
     }
 
@@ -350,7 +378,8 @@ export class PluginHost implements LSProvider, OnWatchFileChanges {
         return await this.execute<any>(
             'findReferences',
             [document, position, context],
-            ExecuteMode.FirstNonNull
+            ExecuteMode.FirstNonNull,
+            'high'
         );
     }
 
@@ -368,7 +397,8 @@ export class PluginHost implements LSProvider, OnWatchFileChanges {
         return await this.execute<any>(
             'getSignatureHelp',
             [document, position, context, cancellationToken],
-            ExecuteMode.FirstNonNull
+            ExecuteMode.FirstNonNull,
+            'high'
         );
     }
 
@@ -424,7 +454,8 @@ export class PluginHost implements LSProvider, OnWatchFileChanges {
         return await this.execute<SemanticTokens>(
             'getSemanticTokens',
             [document, range, cancellationToken],
-            ExecuteMode.FirstNonNull
+            ExecuteMode.FirstNonNull,
+            'low'
         );
     }
 
@@ -440,7 +471,8 @@ export class PluginHost implements LSProvider, OnWatchFileChanges {
         return await this.execute<LinkedEditingRanges>(
             'getLinkedEditingRanges',
             [document, position],
-            ExecuteMode.FirstNonNull
+            ExecuteMode.FirstNonNull,
+            'high'
         );
     }
 
@@ -463,21 +495,71 @@ export class PluginHost implements LSProvider, OnWatchFileChanges {
     private execute<T>(
         name: keyof LSProvider,
         args: any[],
-        mode: ExecuteMode.FirstNonNull
+        mode: ExecuteMode.FirstNonNull,
+        priority: 'low' | 'high'
     ): Promise<T | null>;
     private execute<T>(
         name: keyof LSProvider,
         args: any[],
-        mode: ExecuteMode.Collect
+        mode: ExecuteMode.Collect,
+        priority: 'low' | 'high'
     ): Promise<T[]>;
-    private execute(name: keyof LSProvider, args: any[], mode: ExecuteMode.None): Promise<void>;
+    private execute(
+        name: keyof LSProvider,
+        args: any[],
+        mode: ExecuteMode.None,
+        priority: 'low' | 'high'
+    ): Promise<void>;
     private async execute<T>(
         name: keyof LSProvider,
         args: any[],
-        mode: ExecuteMode
+        mode: ExecuteMode,
+        priority: 'low' | 'high'
     ): Promise<(T | null) | T[] | void> {
         const plugins = this.plugins.filter((plugin) => typeof plugin[name] === 'function');
 
+        if (priority === 'low') {
+            // If a request doesn't have priority, we first wait 1 second to
+            // 1. let higher priority requests get through first
+            // 2. wait for possible document changes, which make the request wait again
+            // Due to waiting, low priority items should preferrably be those who do not
+            // rely on positions or ranges and rather on the whole document only.
+            const debounce = async (): Promise<boolean> => {
+                const id = Math.random();
+                this.deferredRequests[name] = [
+                    id,
+                    new Promise<void>((resolve, reject) => {
+                        setTimeout(() => {
+                            if (
+                                !this.deferredRequests[name] ||
+                                this.deferredRequests[name][0] === id
+                            ) {
+                                resolve();
+                            } else {
+                                // We should not get into this case. According to the spec,
+                                // the language client // does not send another request
+                                // of the same type until the previous one is answered.
+                                reject();
+                            }
+                        }, 1000);
+                    })
+                ];
+                try {
+                    await this.deferredRequests[name][1];
+                    if (!this.deferredRequests[name]) {
+                        return debounce();
+                    }
+                    return true;
+                } catch (e) {
+                    return false;
+                }
+            };
+            const shouldContinue = await debounce();
+            if (!shouldContinue) {
+                return;
+            }
+        }
+
         switch (mode) {
             case ExecuteMode.FirstNonNull:
                 for (const plugin of plugins) {

packages/language-server/src/server.ts

@@ -262,9 +262,10 @@ export function startServer(options?: LSOptions) {
     });
 
     connection.onDidCloseTextDocument((evt) => docManager.closeDocument(evt.textDocument.uri));
-    connection.onDidChangeTextDocument((evt) =>
-        docManager.updateDocument(evt.textDocument, evt.contentChanges)
-    );
+    connection.onDidChangeTextDocument((evt) => {
+        docManager.updateDocument(evt.textDocument, evt.contentChanges);
+        pluginHost.didUpdateDocument();
+    });
     connection.onHover((evt) => pluginHost.doHover(evt.textDocument, evt.position));
     connection.onCompletion((evt, cancellationToken) =>
         pluginHost.getCompletions(evt.textDocument, evt.position, evt.context, cancellationToken)