src/pickProcess: show error when the process picker is hidden

If a user accidentally hides the UI for the process picker, the
debugging setup process will hang, and it is unclear how to stop
or restart the process. This makes sure to dispose of the ui
element when we are finished with it and rejects the input if the
ui is hidden.

Change-Id: I32516ffbde7f2a48c59439769b44806c969a642e
Reviewed-on: https://go-review.googlesource.com/c/vscode-go/+/499601
Run-TryBot: Suzy Mueller <suzmue@golang.org>
TryBot-Result: kokoro <noreply+kokoro@google.com>
Reviewed-by: Jamal Carvalho <jamal@golang.org>

src/pickProcess.ts

@@ -37,29 +37,34 @@ export async function pickGoProcess(): Promise<string> {
 }
 
 async function processPicker(processes: AttachItem[], name?: string): Promise<string> {
+	// We need to use createQuickPick instead of showQuickPick
+	// to set the starting value for the menu.
+	const menu = vscode.window.createQuickPick<AttachItem>();
+	if (name) {
+		menu.value = name;
+	}
+	menu.items = processes;
+	menu.placeholder = 'Choose a process to attach to';
+	menu.matchOnDescription = true;
+	menu.matchOnDetail = true;
 	return new Promise<string>(async (resolve, reject) => {
-		const menu = vscode.window.createQuickPick<AttachItem>();
-		if (name) {
-			menu.value = name;
-		}
-		menu.items = processes;
-		menu.placeholder = 'Choose a process to attach to';
-		menu.matchOnDescription = true;
-		menu.matchOnDetail = true;
-
 		menu.onDidAccept(() => {
 			if (menu.selectedItems.length !== 1) {
 				reject(new Error('No process selected.'));
 			}
 			const selectedId = menu.selectedItems[0].id;
-
-			menu.dispose();
-
 			resolve(selectedId);
 		});
+		// The quickpick menu can be hidden either explicitly or
+		// through other UI interactions. When the quick pick menu is
+		// missing we want to keep the debugging setup process from
+		// hanging, so we reject the selection.
+		menu.onDidHide(() => {
+			reject(new Error('No process selected.'));
+		});
 
 		menu.show();
-	});
+	}).finally(() => menu.dispose());
 }
 
 // Modified from: