fix: enrich DEVICE_NOT_FOUND error for empty scoped iOS simulator sets (#168)

When selectDevice finds no candidates and a simulatorSetPath context is
provided for iOS, throw a detailed error including the set path and a
suggested xcrun simctl --set ... create command to provision the first
simulator.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Author: thymikee

src/core/dispatch.ts

@@ -72,7 +72,7 @@ export async function resolveTargetDevice(flags: CommandFlags): Promise<DeviceIn
 
       if (selector.platform === 'ios') {
         const devices = await listIosDevices({ simulatorSetPath: iosSimulatorSetPath });
-        return await selectDevice(devices, selector);
+        return await selectDevice(devices, selector, { simulatorSetPath: iosSimulatorSetPath });
       }
 
       const devices: DeviceInfo[] = [];
@@ -86,7 +86,7 @@ export async function resolveTargetDevice(flags: CommandFlags): Promise<DeviceIn
       } catch {
         // ignore
       }
-      return await selectDevice(devices, selector);
+      return await selectDevice(devices, selector, { simulatorSetPath: iosSimulatorSetPath });
     },
     {
       platform: normalizedPlatform,

src/utils/__tests__/device.test.ts

@@ -1,6 +1,8 @@
 import test from 'node:test';
 import assert from 'node:assert/strict';
-import { normalizePlatformSelector, resolveApplePlatformName } from '../device.ts';
+import { normalizePlatformSelector, resolveApplePlatformName, selectDevice } from '../device.ts';
+import type { DeviceInfo } from '../device.ts';
+import { AppError } from '../errors.ts';
 
 test('normalizePlatformSelector resolves apple alias to ios', () => {
   assert.equal(normalizePlatformSelector('apple'), 'ios');
@@ -14,3 +16,47 @@ test('resolveApplePlatformName resolves tv targets to tvOS', () => {
   assert.equal(resolveApplePlatformName('mobile'), 'iOS');
   assert.equal(resolveApplePlatformName(undefined), 'iOS');
 });
+
+test('selectDevice throws DEVICE_NOT_FOUND with scoped set guidance when simulatorSetPath is set and no devices found', async () => {
+  const setPath = '/path/to/sessions/abc/Simulators';
+  const err = await selectDevice([], { platform: 'ios' }, { simulatorSetPath: setPath }).catch((e) => e);
+  assert.ok(err instanceof AppError);
+  assert.equal(err.code, 'DEVICE_NOT_FOUND');
+  assert.match(err.message, /scoped simulator set/);
+  assert.equal(err.details?.simulatorSetPath, setPath);
+  assert.ok(typeof err.details?.hint === 'string');
+  assert.match(err.details.hint as string, /simctl --set/);
+  assert.match(err.details.hint as string, /create/);
+});
+
+test('selectDevice throws generic DEVICE_NOT_FOUND when no simulatorSetPath and no devices found', async () => {
+  const err = await selectDevice([], { platform: 'ios' }).catch((e) => e);
+  assert.ok(err instanceof AppError);
+  assert.equal(err.code, 'DEVICE_NOT_FOUND');
+  assert.equal(err.message, 'No devices found');
+  assert.equal(err.details?.simulatorSetPath, undefined);
+});
+
+test('selectDevice does not apply scoped set guidance for non-iOS platform with simulatorSetPath', async () => {
+  const setPath = '/path/to/sessions/abc/Simulators';
+  const err = await selectDevice([], { platform: 'android' }, { simulatorSetPath: setPath }).catch((e) => e);
+  assert.ok(err instanceof AppError);
+  assert.equal(err.code, 'DEVICE_NOT_FOUND');
+  assert.equal(err.message, 'No devices found');
+  assert.equal(err.details?.simulatorSetPath, undefined);
+});
+
+test('selectDevice applies scoped set guidance when no platform selector specified and simulatorSetPath is set', async () => {
+  const setPath = '/path/to/sessions/abc/Simulators';
+  const err = await selectDevice([], {}, { simulatorSetPath: setPath }).catch((e) => e);
+  assert.ok(err instanceof AppError);
+  assert.equal(err.code, 'DEVICE_NOT_FOUND');
+  assert.match(err.message, /scoped simulator set/);
+  assert.equal(err.details?.simulatorSetPath, setPath);
+});
+
+test('selectDevice returns a device when candidates are available', async () => {
+  const device: DeviceInfo = { platform: 'ios', id: 'abc123', name: 'iPhone 16', kind: 'simulator', booted: true };
+  const result = await selectDevice([device], { platform: 'ios' });
+  assert.equal(result.id, 'abc123');
+});

src/utils/device.ts

@@ -25,6 +25,10 @@ type DeviceSelector = {
   serial?: string;
 };
 
+type DeviceSelectionContext = {
+  simulatorSetPath?: string;
+};
+
 export function normalizePlatformSelector(
   platform: PlatformSelector | undefined,
 ): Platform | undefined {
@@ -39,6 +43,7 @@ export function resolveApplePlatformName(target: DeviceTarget | undefined): 'iOS
 export async function selectDevice(
   devices: DeviceInfo[],
   selector: DeviceSelector,
+  context: DeviceSelectionContext = {},
 ): Promise<DeviceInfo> {
   let candidates = devices;
   const normalize = (value: string): string =>
@@ -76,6 +81,14 @@ export async function selectDevice(
   if (candidates.length === 1) return candidates[0];
 
   if (candidates.length === 0) {
+    const simulatorSetPath = context.simulatorSetPath;
+    if (simulatorSetPath && (!selector.platform || selector.platform === 'ios')) {
+      throw new AppError('DEVICE_NOT_FOUND', 'No devices found in the scoped simulator set', {
+        simulatorSetPath,
+        hint: `The simulator set at "${simulatorSetPath}" appears to be empty. Create a simulator first:\n  xcrun simctl --set "${simulatorSetPath}" create "iPhone 16" com.apple.CoreSimulator.SimDeviceType.iPhone-16 com.apple.CoreSimulator.SimRuntime.iOS-18-0`,
+        selector,
+      });
+    }
     throw new AppError('DEVICE_NOT_FOUND', 'No devices found', { selector });
   }