iOS CLI version mismatch detection

Summary:
Trying to detect version mismatches between the running Simulator and the version of Xcode's CLI tools.

What is done in this check:
- The running path of the running simulator is queries from `ps`
- The path of Xcode CLI tools is queried using `xcode-select -p`.
- The two paths are compared if they differ

Reviewed By: jknoxville, passy

Differential Revision: D15803238

fbshipit-source-id: 6638312505fc950ff7869fd55494984bfffb677b

src/dispatcher/iOSDevice.js

@@ -53,6 +53,7 @@ if (typeof window !== 'undefined') {
 }
 
 function queryDevices(store: Store, logger: Logger): Promise<void> {
+  checkXcodeVersionMismatch();
   const {connections} = store.getState();
   const currentDeviceIDs: Set<string> = new Set(
     connections.devices
@@ -143,6 +144,34 @@ function getActiveDevices(): Promise<Array<IOSDeviceParams>> {
   });
 }
 
+let xcodeVersionMismatchFound = false;
+async function checkXcodeVersionMismatch() {
+  if (xcodeVersionMismatchFound) {
+    return;
+  }
+  const exec = promisify(child_process.exec);
+  try {
+    let {stdout: xcodeCLIVersion} = await exec('xcode-select -p');
+    xcodeCLIVersion = xcodeCLIVersion.trim();
+    const {stdout} = await exec('ps aux | grep CoreSimulator');
+    for (let line of stdout.split('\n')) {
+      const match = line.match(
+        /\/Applications\/Xcode[^/]*\.app\/Contents\/Developer/,
+      );
+      const runningVersion = match && match.length > 0 ? match[0].trim() : null;
+      if (runningVersion && runningVersion !== xcodeCLIVersion) {
+        console.error(
+          `Xcode version mismatch: Simulator is running from "${runningVersion}" while Xcode CLI is "${xcodeCLIVersion}". Running "xcode-select --switch ${runningVersion}" can fix this.`,
+        );
+        xcodeVersionMismatchFound = true;
+        break;
+      }
+    }
+  } catch (e) {
+    console.error(e);
+  }
+}
+
 export async function getActiveDevicesAndSimulators(): Promise<
   Array<IOSDevice>,
 > {