From 017d09e2fe0e917df03beb9e9fd7fd69dae1f7cc Mon Sep 17 00:00:00 2001
From: Matt Bierner <matb@microsoft.com>
Date: Fri, 13 Apr 2018 16:34:05 -0700
Subject: [PATCH] Be more lazy computing symbols

---
 .../src/features/workspaceSymbolProvider.ts   | 11 ++++--
 .../src/util/lazy.ts                          | 39 +++++++++++++++++++
 2 files changed, 46 insertions(+), 4 deletions(-)
 create mode 100644 extensions/markdown-language-features/src/util/lazy.ts

diff --git a/extensions/markdown-language-features/src/features/workspaceSymbolProvider.ts b/extensions/markdown-language-features/src/features/workspaceSymbolProvider.ts
index f383a011778..ecf6f1b2140 100644
--- a/extensions/markdown-language-features/src/features/workspaceSymbolProvider.ts
+++ b/extensions/markdown-language-features/src/features/workspaceSymbolProvider.ts
@@ -6,6 +6,7 @@
 import * as vscode from 'vscode';
 import { disposeAll } from '../util/dispose';
 import { isMarkdownFile } from '../util/file';
+import { Lazy, lazy } from '../util/lazy';
 import MDDocumentSymbolProvider from './documentSymbolProvider';
 
 export interface WorkspaceMarkdownDocumentProvider {
@@ -87,7 +88,7 @@ class VSCodeWorkspaceMarkdownDocumentProvider implements WorkspaceMarkdownDocume
 
 
 export default class MarkdownWorkspaceSymbolProvider implements vscode.WorkspaceSymbolProvider {
-	private _symbolCache = new Map<string, Thenable<vscode.SymbolInformation[]>>();
+	private _symbolCache = new Map<string, Lazy<Thenable<vscode.SymbolInformation[]>>>();
 	private _symbolCachePopulated: boolean = false;
 	private _disposables: vscode.Disposable[] = [];
 
@@ -106,7 +107,7 @@ export default class MarkdownWorkspaceSymbolProvider implements vscode.Workspace
 			this._workspaceMarkdownDocumentProvider.onDidDeleteMarkdownDocument(this.onDidDeleteDocument, this, this._disposables);
 		}
 
-		const allSymbolsSets = await Promise.all(Array.from(this._symbolCache.values()));
+		const allSymbolsSets = await Promise.all(Array.from(this._symbolCache.values()).map(x => x.value));
 		const allSymbols: vscode.SymbolInformation[] = Array.prototype.concat.apply([], allSymbolsSets);
 		return allSymbols.filter(symbolInformation => symbolInformation.name.toLowerCase().indexOf(query.toLowerCase()) !== -1);
 	}
@@ -122,8 +123,10 @@ export default class MarkdownWorkspaceSymbolProvider implements vscode.Workspace
 		disposeAll(this._disposables);
 	}
 
-	private getSymbols(document: vscode.TextDocument): Promise<vscode.SymbolInformation[]> {
-		return this._symbolProvider.provideDocumentSymbols(document);
+	private getSymbols(document: vscode.TextDocument): Lazy<Thenable<vscode.SymbolInformation[]>> {
+		return lazy(async () => {
+			return this._symbolProvider.provideDocumentSymbols(document);
+		});
 	}
 
 	private onDidChangeDocument(document: vscode.TextDocument) {
diff --git a/extensions/markdown-language-features/src/util/lazy.ts b/extensions/markdown-language-features/src/util/lazy.ts
new file mode 100644
index 00000000000..aa5effd3d31
--- /dev/null
+++ b/extensions/markdown-language-features/src/util/lazy.ts
@@ -0,0 +1,39 @@
+/*---------------------------------------------------------------------------------------------
+ *  Copyright (c) Microsoft Corporation. All rights reserved.
+ *  Licensed under the MIT License. See License.txt in the project root for license information.
+ *--------------------------------------------------------------------------------------------*/
+
+export interface Lazy<T> {
+	readonly value: T;
+	readonly hasValue: boolean;
+	map<R>(f: (x: T) => R): Lazy<R>;
+}
+
+class LazyValue<T> implements Lazy<T> {
+	private _hasValue: boolean = false;
+	private _value?: T;
+
+	constructor(
+		private readonly _getValue: () => T
+	) { }
+
+	get value(): T {
+		if (!this._hasValue) {
+			this._hasValue = true;
+			this._value = this._getValue();
+		}
+		return this._value!;
+	}
+
+	get hasValue(): boolean {
+		return this._hasValue;
+	}
+
+	public map<R>(f: (x: T) => R): Lazy<R> {
+		return new LazyValue(() => f(this.value));
+	}
+}
+
+export function lazy<T>(getValue: () => T): Lazy<T> {
+	return new LazyValue<T>(getValue);
+}
\ No newline at end of file