Don't return symbolic columns for webview panels

Fixes #56097

When a symbolic column is used while creating a webview panel, instead set the `viewColum` as `undefined` and then resolve it once we know the real (non-symbolic) column

extensions/vscode-api-tests/src/singlefolder-tests/webview.test.ts

@@ -307,6 +307,38 @@ suite('Webview tests', () => {
 			assert.strictEqual((await response).value, false);
 		}
 	});
+
+	test('webviews should have real view column after they are created, #56097', async () => {
+		const webview = _register(vscode.window.createWebviewPanel(webviewId, 'title', { viewColumn: vscode.ViewColumn.Active }, { enableScripts: true }));
+
+		// Since we used a symbolic column, we don't know what view column the webview will actually show in at first
+		assert.strictEqual(webview.viewColumn, undefined);
+
+		let changed = false;
+		const viewStateChanged = new Promise<vscode.WebviewPanelOnDidChangeViewStateEvent>((resolve) => {
+			webview.onDidChangeViewState(e => {
+				if (changed) {
+					throw new Error('Only expected a single view state change');
+				}
+				changed = true;
+				resolve(e);
+			}, undefined, disposables);
+		});
+
+		assert.strictEqual((await viewStateChanged).webviewPanel.viewColumn, vscode.ViewColumn.One);
+
+		const firstResponse = getMesssage(webview);
+		webview.webview.html = createHtmlDocumentWithBody(/*html*/`
+			<script>
+				const vscode = acquireVsCodeApi();
+				vscode.postMessage({  });
+			</script>`);
+
+		webview.webview.postMessage({ value: 1 });
+		await firstResponse;
+		assert.strictEqual(webview.viewColumn, vscode.ViewColumn.One);
+
+	});
 });
 
 function createHtmlDocumentWithBody(body: string): string {

src/vs/workbench/api/node/extHostWebview.ts

@@ -171,8 +171,13 @@ export class ExtHostWebviewPanel implements vscode.WebviewPanel {
 		return this._options;
 	}
 
-	get viewColumn(): vscode.ViewColumn {
+	get viewColumn(): vscode.ViewColumn | undefined {
 		this.assertNotDisposed();
+		if (this._viewColumn < 0) {
+			// We are using a symbolic view column
+			// Return undefined instead to indicate that the real view column is currently unknown but will be resolved.
+			return undefined;
+		}
 		return this._viewColumn;
 	}