Check pending version before updating markdown preview content

For microsoft#72671

extensions/markdown-language-features/src/features/preview.ts

@@ -60,6 +60,18 @@ interface PreviewStyleLoadErrorMessage extends WebviewMessage {
 	};
 }
 
+export class PreviewDocumentVersion {
+	public constructor(
+		public readonly resource: vscode.Uri,
+		public readonly version: number,
+	) { }
+
+	public equals(other: PreviewDocumentVersion): boolean {
+		return this.resource.fsPath === other.resource.fsPath
+			&& this.version === other.version;
+	}
+}
+
 export class MarkdownPreview extends Disposable {
 
 	public static viewType = 'markdown.preview';
@@ -71,7 +83,7 @@ export class MarkdownPreview extends Disposable {
 	private throttleTimer: any;
 	private line: number | undefined = undefined;
 	private firstUpdate = true;
-	private currentVersion?: { resource: vscode.Uri, version: number };
+	private currentVersion?: PreviewDocumentVersion;
 	private forceUpdate = false;
 	private isScrolling = false;
 	private _disposed: boolean = false;
@@ -389,18 +401,23 @@ export class MarkdownPreview extends Disposable {
 			return;
 		}
 
-		if (!this.forceUpdate && this.currentVersion && this.currentVersion.resource.fsPath === resource.fsPath && this.currentVersion.version === document.version) {
+		const pendingVersion = new PreviewDocumentVersion(resource, document.version);
+		if (!this.forceUpdate && this.currentVersion && this.currentVersion.equals(pendingVersion)) {
 			if (this.line) {
 				this.updateForView(resource, this.line);
 			}
 			return;
 		}
 		this.forceUpdate = false;
 
-		this.currentVersion = { resource, version: document.version };
+		this.currentVersion = pendingVersion;
 		if (this._resource === resource) {
 			const content = await this._contentProvider.provideTextDocumentContent(document, this._previewConfigurations, this.line, this.state);
-			this.setContent(content);
+			// Another call to `doUpdate` may have happened.
+			// Make sure we are still updating for the correct document
+			if (this.currentVersion && this.currentVersion.equals(pendingVersion)) {
+				this.setContent(content);
+			}
 		}
 	}