get placeholder to be read by screen reader for chat inputs

src/vs/workbench/contrib/chat/browser/contrib/chatInputEditorContrib.ts

@@ -134,12 +134,14 @@ class InputEditorDecorations extends Disposable {
 
 		const viewModel = this.widget.viewModel;
 		if (!viewModel) {
+			this.updateAriaPlaceholder(undefined);
 			return;
 		}
 
 		if (!inputValue) {
 			const mode = this.widget.input.currentModeObs.get();
 			const placeholder = mode.argumentHint?.get() ?? mode.description.get() ?? '';
+			const displayPlaceholder = viewModel.inputPlaceholder || placeholder;
 
 			const decoration: IDecorationOptions[] = [
 				{
@@ -151,16 +153,19 @@ class InputEditorDecorations extends Disposable {
 					},
 					renderOptions: {
 						after: {
-							contentText: viewModel.inputPlaceholder || placeholder,
+							contentText: displayPlaceholder,
 							color: this.getPlaceholderColor()
 						}
 					}
 				}
 			];
+			this.updateAriaPlaceholder(displayPlaceholder || undefined);
 			this.widget.inputEditor.setDecorationsByType(decorationDescription, placeholderDecorationType, decoration);
 			return;
 		}
 
+		this.updateAriaPlaceholder(undefined);
+
 		const parsedRequest = this.widget.parsedInput.parts;
 
 		let placeholderDecoration: IDecorationOptions[] | undefined;
@@ -295,6 +300,19 @@ class InputEditorDecorations extends Disposable {
 
 		this.widget.inputEditor.setDecorationsByType(decorationDescription, variableTextDecorationType, varDecorations);
 	}
+
+	private updateAriaPlaceholder(value: string | undefined): void {
+		// eslint-disable-next-line no-restricted-syntax
+		const nativeEditContext = this.widget.inputEditor.getDomNode()?.querySelector<HTMLElement>('.native-edit-context');
+		if (!nativeEditContext) {
+			return;
+		}
+		if (value && value.trim().length) {
+			nativeEditContext.setAttribute('aria-placeholder', value);
+		} else {
+			nativeEditContext.removeAttribute('aria-placeholder');
+		}
+	}
 }
 
 class InputEditorSlashCommandMode extends Disposable {