feat(cli): auto enable --dev-client in npx expo start (#22926)

# Why

- related #22924
#22925
#22890
- Use a basic heuristic to auto enable `--dev-client` when
`expo-dev-client` is in the project `package.json`. Users can swap to
Expo Go with `s` or pass `--go` to ensure Expo Go is the default target.

# Test Plan

- Added basic option tests.
- Updated the docs.

---------

Co-authored-by: Expo Bot <34669131+expo-bot@users.noreply.github.com>

docs/pages/more/expo-cli.mdx

@@ -68,19 +68,26 @@ The UI that shows up in the process is referred to as the **Terminal UI**. It co
 
 | Keyboard shortcut               | Description                                                                                                                                                                              |
 | ------------------------------- | ---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- |
-| <kbd>A</kbd>                    | Open the project in Expo Go on Android.                                                                                                                                                  |
+| <kbd>A</kbd>                    | Open the project on a connected Android device.                                                                                                                                          |
 | <kbd>Shift</kbd> + <kbd>A</kbd> | Select an Android device or emulator to open.                                                                                                                                            |
-| <kbd>I</kbd>                    | Open the project in Expo Go on iOS.                                                                                                                                                      |
+| <kbd>I</kbd>                    | Open the project in an iOS simulator.                                                                                                                                                    |
 | <kbd>Shift</kbd> + <kbd>I</kbd> | Select an iOS Simulator to open.                                                                                                                                                         |
 | <kbd>W</kbd>                    | Open the project in a web browser. This may require webpack to be installed in your project.                                                                                             |
 | <kbd>R</kbd>                    | Reload the app on any connected device.                                                                                                                                                  |
+| <kbd>S</kbd>                    | Switch the launch target between Expo Go and development builds.                                                                                                                         |
 | <kbd>M</kbd>                    | Open the dev menu on any connected native device (web not supported).                                                                                                                    |
 | <kbd>Shift</kbd> + <kbd>M</kbd> | Choose more commands to trigger on connected devices.<br/>This includes toggling the performance monitor, opening the element inspector, reloading the device, and opening the dev menu. |
 | <kbd>J</kbd>                    | Open Chrome Dev Tools for any connected device that is using Hermes as the JavaScript engine. [Learn more](/guides/using-hermes#javascript-inspector-for-hermes).                        |
 | <kbd>O</kbd>                    | Open project code in your editor. This can be configured with the `EXPO_EDITOR` and `EDITOR` [environment variables](#environment-variables).                                            |
 | <kbd>E</kbd>                    | Show the development server URL as a QR code in the terminal.                                                                                                                            |
 | <kbd>?</kbd>                    | Show all Terminal UI commands.                                                                                                                                                           |
 
+### Launch target
+
+The `npx expo start` command will automatically launch the app in Expo Go unless `expo-dev-client` in installed in the project, in which case it will open in the custom app. You can force the launch target by passing the `--dev-client` and `--go` flags. For example, running `npx expo start --go` will always launch the app in Expo Go, and `npx expo start --dev-client` will always attempt to launch the app in a development build.
+
+You can switch the launch target during runtime by pressing <kbd>S</kbd> in the **Terminal UI**. The run commands will also default to using `--dev-client` after compiling the development build.
+
 ### Server URL
 
 By default, the project is served over a LAN connection. You can change this behavior to localhost-only by using the flag `npx expo start --localhost`.

packages/@expo/cli/CHANGELOG.md

@@ -13,6 +13,7 @@
 - Add `-d` as an alias to `--dev-client`. ([#22925](https://github.com/expo/expo/pull/22925) by [@EvanBacon](https://github.com/EvanBacon))
 - Allow client-side device ids to reuse debugger sessions when restarting app. ([#22742](https://github.com/expo/expo/pull/22742) by [@byCedric](https://github.com/byCedric))
 - Enable inspector proxy with network support by default. ([#22936](https://github.com/expo/expo/pull/22936) by [@byCedric](https://github.com/byCedric))
+- Auto enable `--dev-client` in `expo start` if `--go` is not passed and `expo-dev-client` is in the `package.json`. ([#22926](https://github.com/expo/expo/pull/22926) by [@EvanBacon](https://github.com/EvanBacon))
 - Add `EXPO_OFFLINE` environment variable to disable network requests across the entire CLI. ([#22961](https://github.com/expo/expo/pull/22961) by [@EvanBacon](https://github.com/EvanBacon))
 
 ### 🐛 Bug fixes

packages/@expo/cli/src/start/__tests__/resolveOptions-test.ts

@@ -1,4 +1,5 @@
 import { asMock } from '../../__tests__/asMock';
+import { hasDirectDevClientDependency } from '../../utils/analytics/getDevClientProperties';
 import { resolvePortAsync } from '../../utils/port';
 import { resolveHostType, resolveOptionsAsync, resolvePortsAsync } from '../resolveOptions';
 
@@ -12,6 +13,11 @@ jest.mock('../../utils/scheme', () => {
     getOptionalDevClientSchemeAsync: jest.fn(async () => []),
   };
 });
+jest.mock('../../utils/analytics/getDevClientProperties', () => {
+  return {
+    hasDirectDevClientDependency: jest.fn(() => false),
+  };
+});
 
 describe(resolveOptionsAsync, () => {
   it(`prevents using --dev-client and --go together`, async () => {
@@ -39,6 +45,14 @@ describe(resolveOptionsAsync, () => {
   it(`sets devClient to true`, async () => {
     expect((await resolveOptionsAsync('/noop', { '--dev-client': true })).devClient).toBe(true);
   });
+  it(`infers that devClient should be true`, async () => {
+    jest.mocked(hasDirectDevClientDependency).mockReturnValueOnce(true);
+    expect((await resolveOptionsAsync('/noop', {})).devClient).toBe(true);
+  });
+  it(`--go forces devClient to false`, async () => {
+    jest.mocked(hasDirectDevClientDependency).mockReturnValueOnce(true);
+    expect((await resolveOptionsAsync('/noop', { '--go': true })).devClient).toBe(false);
+  });
 });
 
 describe(resolveHostType, () => {

packages/@expo/cli/src/start/resolveOptions.ts

@@ -1,5 +1,6 @@
 import assert from 'assert';
 
+import { hasDirectDevClientDependency } from '../utils/analytics/getDevClientProperties';
 import { AbortCommandError, CommandError } from '../utils/errors';
 import { resolvePortAsync } from '../utils/port';
 
@@ -38,8 +39,19 @@ export async function resolveOptionsAsync(projectRoot: string, args: any): Promi
     tunnel: args['--tunnel'],
   });
 
-  // TODO: Add a third option which is auto detecting if the user is using `expo-dev-client` or `expo-dev-launcher`.
-  const isDevClient = !!args['--dev-client'] || (args['--go'] == null ? false : !args['--go']);
+  // User can force the default target by passing either `--dev-client` or `--go`. They can also
+  // swap between them during development by pressing `s`.
+  const isUserDefinedDevClient =
+    !!args['--dev-client'] || (args['--go'] == null ? false : !args['--go']);
+
+  // If the user didn't specify `--dev-client` or `--go` we check if they have the dev client package
+  // in their package.json.
+  const isAutoDevClient =
+    args['--dev-client'] == null &&
+    args['--go'] == null &&
+    hasDirectDevClientDependency(projectRoot);
+
+  const isDevClient = isAutoDevClient || isUserDefinedDevClient;
 
   const scheme = await resolveSchemeAsync(projectRoot, {
     scheme: args['--scheme'],

packages/@expo/cli/src/utils/analytics/getDevClientProperties.ts

@@ -1,4 +1,4 @@
-import { ExpoConfig, getAccountUsername, getDefaultTarget } from '@expo/config';
+import { ExpoConfig, getAccountUsername, getDefaultTarget, getPackageJson } from '@expo/config';
 import JsonFile, { JSONValue } from '@expo/json-file';
 import resolveFrom from 'resolve-from';
 
@@ -8,6 +8,12 @@ const getAccountName = memoize((exp: Pick<ExpoConfig, 'owner'>) => {
   return getAccountUsername(exp);
 });
 
+/** @returns true if the expo-dev-client package is found in the project `package.json` file. */
+export function hasDirectDevClientDependency(projectRoot: string): boolean {
+  const pkg = getPackageJson(projectRoot);
+  return !!pkg.dependencies?.['expo-dev-client'] || !!pkg.devDependencies?.['expo-dev-client'];
+}
+
 const getDevClientVersion = memoize((projectRoot: string): JSONValue | undefined => {
   try {
     const devClientPackage = resolveFrom.silent(projectRoot, 'expo-dev-client/package.json');