Add diagnostics for markdown links (#148578)

* Initial work on md link diagnostics

* Adding settings to enable/disable validation

* Add delay for recomputing diagnostics

* 💄

* Split test on diagnostics compute vs management

* Validate on file open

* Remove dianostics on file close

* Allow paths to folders

* Add validation configuration option

extensions/markdown-language-features/src/util/async.ts

@@ -0,0 +1,72 @@
+/*---------------------------------------------------------------------------------------------
+ *  Copyright (c) Microsoft Corporation. All rights reserved.
+ *  Licensed under the MIT License. See License.txt in the project root for license information.
+ *--------------------------------------------------------------------------------------------*/
+
+import { Disposable } from 'vscode';
+
+export interface ITask<T> {
+	(): T;
+}
+
+export class Delayer<T> {
+
+	public defaultDelay: number;
+	private timeout: any; // Timer
+	private completionPromise: Promise<T | null> | null;
+	private onSuccess: ((value: T | PromiseLike<T> | undefined) => void) | null;
+	private task: ITask<T> | null;
+
+	constructor(defaultDelay: number) {
+		this.defaultDelay = defaultDelay;
+		this.timeout = null;
+		this.completionPromise = null;
+		this.onSuccess = null;
+		this.task = null;
+	}
+
+	public trigger(task: ITask<T>, delay: number = this.defaultDelay): Promise<T | null> {
+		this.task = task;
+		if (delay >= 0) {
+			this.cancelTimeout();
+		}
+
+		if (!this.completionPromise) {
+			this.completionPromise = new Promise<T | undefined>((resolve) => {
+				this.onSuccess = resolve;
+			}).then(() => {
+				this.completionPromise = null;
+				this.onSuccess = null;
+				const result = this.task && this.task();
+				this.task = null;
+				return result;
+			});
+		}
+
+		if (delay >= 0 || this.timeout === null) {
+			this.timeout = setTimeout(() => {
+				this.timeout = null;
+				this.onSuccess?.(undefined);
+			}, delay >= 0 ? delay : this.defaultDelay);
+		}
+
+		return this.completionPromise;
+	}
+
+	private cancelTimeout(): void {
+		if (this.timeout !== null) {
+			clearTimeout(this.timeout);
+			this.timeout = null;
+		}
+	}
+}
+
+export function setImmediate(callback: (...args: any[]) => void, ...args: any[]): Disposable {
+	if (global.setImmediate) {
+		const handle = global.setImmediate(callback, ...args);
+		return { dispose: () => global.clearImmediate(handle) };
+	} else {
+		const handle = setTimeout(callback, 0, ...args);
+		return { dispose: () => clearTimeout(handle) };
+	}
+}