Check xcode-select is set

Summary:
Basic check for some xcode-path

There'll be a separate connected device check that looks at the current simulators and sees if they are running the same xcode version.

Reviewed By: mweststrate

Differential Revision: D18427090

fbshipit-source-id: 5e202d8920cae1ffce444e81a0c138a97936f758

doctor/src/index.ts

@@ -9,6 +9,8 @@
 
 import {getEnvInfo, EnvironmentInfo} from './environmentInfo';
 export {getEnvInfo} from './environmentInfo';
+import {exec} from 'child_process';
+import {promisify} from 'util';
 
 type HealthcheckCategory = {
   label: string;
@@ -66,6 +68,15 @@ export function getHealthchecks(): Healthchecks {
                   hasProblem: e.IDEs == null || e.IDEs.Xcode == null,
                 }),
               },
+              {
+                label: 'Is xcode-select set',
+                isRequired: true,
+                run: async (e: EnvironmentInfo) => ({
+                  hasProblem:
+                    (await promisify(exec)('xcode-select -p')).stdout.trim()
+                      .length < 1,
+                }),
+              },
             ],
           },
         }