default adb path

Summary:
As I was setting up a new mac I had to change this setting in flipper settings.

From a few android people that I've spoken to no one could answer me if the old one is still used.

Ideally we should infer this during the first time flipper starts

- `/opt/android_sdk` current default
- `$HOME/Library/Android/sdk` adb from Android Studio
- `$HOME/fbsource/third-party/toolchains/android-sdk` adb that is always available in fbsource

Reviewed By: lblasa

Differential Revision: D51120929

fbshipit-source-id: edb2a58b9c9f37465ea2fc5493975dd427d5523b

desktop/flipper-server-core/src/utils/settings.tsx

@@ -8,6 +8,7 @@
  */
 
 import os from 'os';
+import fs from 'fs-extra';
 import {resolve} from 'path';
 import {Settings, Tristate} from 'flipper-common';
 import {readFile, writeFile, pathExists, mkdirp} from 'fs-extra';
@@ -18,7 +19,7 @@ export async function loadSettings(
 ): Promise<Settings> {
   if (settingsString !== '') {
     try {
-      return replaceDefaultSettings(JSON.parse(settingsString));
+      return await replaceDefaultSettings(JSON.parse(settingsString));
     } catch (e) {
       throw new Error("couldn't read the user settingsString");
     }
@@ -48,9 +49,9 @@ function getSettingsFile() {
 
 export const DEFAULT_ANDROID_SDK_PATH = getDefaultAndroidSdkPath();
 
-function getDefaultSettings(): Settings {
+async function getDefaultSettings(): Promise<Settings> {
   return {
-    androidHome: getDefaultAndroidSdkPath(),
+    androidHome: await getDefaultAndroidSdkPath(),
     enableAndroid: true,
     enableIOS: os.platform() === 'darwin',
     enablePhysicalIOS: os.platform() === 'darwin',
@@ -69,14 +70,24 @@ function getDefaultSettings(): Settings {
   };
 }
 
-function getDefaultAndroidSdkPath() {
+async function getDefaultAndroidSdkPath() {
-  return os.platform() === 'win32' ? getWindowsSdkPath() : '/opt/android_sdk';
+  if (os.platform() === 'win32') {
+    return `${os.homedir()}\\AppData\\Local\\android\\sdk`;
+  }
+
+  // non windows platforms
+
+  // created when created a project in Android Studio
+  const androidStudioSdkPath = `${os.homedir()}/Library/Android/sdk`;
+  if (await fs.exists(androidStudioSdkPath)) {
+    return androidStudioSdkPath;
+  }
+
+  return '/opt/android_sdk';
 }
 
-function getWindowsSdkPath() {
+async function replaceDefaultSettings(
-  return `${os.homedir()}\\AppData\\Local\\android\\sdk`;
+  userSettings: Partial<Settings>,
-}
+): Promise<Settings> {
-
+  return {...(await getDefaultSettings()), ...userSettings};
-function replaceDefaultSettings(userSettings: Partial<Settings>): Settings {
-  return {...getDefaultSettings(), ...userSettings};
 }