cache panel body size

fixes #60018

src/vs/base/browser/ui/splitview/panelview.ts

@@ -46,7 +46,6 @@ export abstract class Panel implements IView {
 	protected _expanded: boolean;
 	protected disposables: IDisposable[] = [];
 
-	private expandedSize: number | undefined = undefined;
 	private _headerVisible = true;
 	private _minimumBodySize: number;
 	private _maximumBodySize: number;
@@ -55,6 +54,9 @@ export abstract class Panel implements IView {
 
 	private header: HTMLElement;
 
+	private cachedExpandedSize: number | undefined = undefined;
+	private cachedBodySize: number | undefined = undefined;
+
 	private _onDidChange = new Emitter<number | undefined>();
 	readonly onDidChange: Event<number | undefined> = this._onDidChange.event;
 
@@ -129,7 +131,7 @@ export abstract class Panel implements IView {
 
 		this._expanded = !!expanded;
 		this.updateHeader();
-		this._onDidChange.fire(expanded ? this.expandedSize : undefined);
+		this._onDidChange.fire(expanded ? this.cachedExpandedSize : undefined);
 	}
 
 	get headerVisible(): boolean {
@@ -190,8 +192,14 @@ export abstract class Panel implements IView {
 		const headerSize = this.headerVisible ? Panel.HEADER_SIZE : 0;
 
 		if (this.isExpanded()) {
-			this.layoutBody(size - headerSize);
-			this.expandedSize = size;
+			const bodySize = size - headerSize;
+
+			if (bodySize !== this.cachedBodySize) {
+				this.layoutBody(bodySize);
+				this.cachedBodySize = bodySize;
+			}
+
+			this.cachedExpandedSize = size;
 		}
 	}