#27498 restore extension editor webview scroll positions (#85982)

* #27498 restore extension editor webview scroll positions

* Delay setInitialScrollPosition so iframe contents  have time to load fully (we hope)

* Some changes requested by @mjbvz

* revert setTimeout hack

* fix my spelling error in comment

* remove blank line to perfect the undo
Co-authored-by: NMatt Bierner <matb@microsoft.com>

src/vs/workbench/contrib/extensions/browser/extensionEditor.ts

@@ -169,6 +169,11 @@ interface IExtensionEditorTemplate {
 	header: HTMLElement;
 }
 
+const enum WebviewIndex {
+	Readme,
+	Changelog
+}
+
 export class ExtensionEditor extends EditorPane {
 
 	static readonly ID: string = 'workbench.editor.extension';
@@ -179,6 +184,12 @@ export class ExtensionEditor extends EditorPane {
 	private extensionChangelog: Cache<string> | null;
 	private extensionManifest: Cache<IExtensionManifest | null> | null;
 
+	// Some action bar items use a webview whose vertical scroll position we track in this map
+	private initialScrollProgress: Map<WebviewIndex, number> = new Map();
+
+	// Spot when an ExtensionEditor instance gets reused for a different extension, in which case the vertical scroll positions must be zeroed
+	private currentIdentifier: string = '';
+
 	private layoutParticipants: ILayoutParticipant[] = [];
 	private readonly contentDisposables = this._register(new DisposableStore());
 	private readonly transientDisposables = this._register(new DisposableStore());
@@ -336,6 +347,11 @@ export class ExtensionEditor extends EditorPane {
 		this.editorLoadComplete = false;
 		const extension = input.extension;
 
+		if (this.currentIdentifier !== extension.identifier.id) {
+			this.initialScrollProgress.clear();
+			this.currentIdentifier = extension.identifier.id;
+		}
+
 		this.transientDisposables.clear();
 
 		this.extensionReadme = new Cache(() => createCancelablePromise(token => extension.getReadme(token)));
@@ -563,7 +579,7 @@ export class ExtensionEditor extends EditorPane {
 		return Promise.resolve(null);
 	}
 
-	private async openMarkdown(cacheResult: CacheResult<string>, noContentCopy: string, template: IExtensionEditorTemplate, token: CancellationToken): Promise<IActiveElement | null> {
+	private async openMarkdown(cacheResult: CacheResult<string>, noContentCopy: string, template: IExtensionEditorTemplate, webviewIndex: WebviewIndex, token: CancellationToken): Promise<IActiveElement> {
 		try {
 			const body = await this.renderMarkdown(cacheResult, template);
 			if (token.isCancellationRequested) {
@@ -572,15 +588,22 @@ export class ExtensionEditor extends EditorPane {
 
 			const webview = this.contentDisposables.add(this.webviewService.createWebviewOverlay('extensionEditor', {
 				enableFindWidget: true,
+				tryRestoreScrollPosition: true,
 			}, {}, undefined));
 
+			webview.initialScrollProgress = this.initialScrollProgress.get(webviewIndex) || 0;
+
 			webview.claim(this, this.scopedContextKeyService);
 			setParentFlowTo(webview.container, template.content);
 			webview.layoutWebviewOverElement(template.content);
 
 			webview.html = body;
+			webview.claim(this);
 
 			this.contentDisposables.add(webview.onDidFocus(() => this.fireOnDidFocus()));
+
+			this.contentDisposables.add(webview.onDidScroll(() => this.initialScrollProgress.set(webviewIndex, webview.initialScrollProgress)));
+
 			const removeLayoutParticipant = arrays.insert(this.layoutParticipants, {
 				layout: () => {
 					webview.layoutWebviewOverElement(template.content);
@@ -823,7 +846,7 @@ export class ExtensionEditor extends EditorPane {
 		if (manifest && manifest.extensionPack && manifest.extensionPack.length) {
 			return this.openExtensionPackReadme(manifest, template, token);
 		}
-		return this.openMarkdown(this.extensionReadme!.get(), localize('noReadme', "No README available."), template, token);
+		return this.openMarkdown(this.extensionReadme!.get(), localize('noReadme', "No README available."), template, WebviewIndex.Readme, token);
 	}
 
 	private async openExtensionPackReadme(manifest: IExtensionManifest, template: IExtensionEditorTemplate, token: CancellationToken): Promise<IActiveElement | null> {
@@ -854,15 +877,15 @@ export class ExtensionEditor extends EditorPane {
 		const readmeContent = append(extensionPackReadme, $('div.readme-content'));
 
 		await Promise.all([
-			this.renderExtensionPack(manifest, extensionPackContent, token),
-			this.openMarkdown(this.extensionReadme!.get(), localize('noReadme', "No README available."), { ...template, ...{ content: readmeContent } }, token),
+			this.renderExtensionPack(manifest, extensionPackContent),
+			this.openMarkdown(this.extensionReadme!.get(), localize('noReadme', "No README available."), { ...template, ...{ content: readmeContent } }, WebviewIndex.Readme, token),
 		]);
 
 		return { focus: () => extensionPackContent.focus() };
 	}
 
-	private openChangelog(template: IExtensionEditorTemplate, token: CancellationToken): Promise<IActiveElement | null> {
-		return this.openMarkdown(this.extensionChangelog!.get(), localize('noChangelog', "No Changelog available."), template, token);
+	private openChangelog(template: IExtensionEditorTemplate,  token: CancellationToken): Promise<IActiveElement> {
+	  return this.openMarkdown(this.extensionChangelog!.get(), localize('noChangelog', "No Changelog available."), template, WebviewIndex.Changelog, token);
 	}
 
 	private openContributions(template: IExtensionEditorTemplate, token: CancellationToken): Promise<IActiveElement | null> {