fix: move platform check from start builder to run-ios builder (closes #8)

Author: jaysoo

packages/react-native/src/builders/run-ios/run-ios.impl.ts

@@ -6,6 +6,7 @@ import { join } from 'path';
 import { getProjectRoot } from '../../utils/get-project-root';
 import { fork } from 'child_process';
 import { ensureNodeModulesSymlink } from '../../utils/ensure-node-modules-symlink';
+import { platform } from 'os';
 
 export interface ReactNativeRunIOsOptions extends JsonObject {
   configuration: string;
@@ -25,14 +26,17 @@ function run(
   options: ReactNativeRunIOsOptions,
   context: BuilderContext
 ): Observable<ReactNativeRunIOsOutput> {
+  if (platform() !== 'darwin') {
+    throw new Error(`The run-ios build requires OSX to run`);
+  }
   return from(getProjectRoot(context)).pipe(
     tap((root) => ensureNodeModulesSymlink(context.workspaceRoot, root)),
     switchMap((root) =>
       from(runCliRunIOS(context.workspaceRoot, root, options))
     ),
     map(() => {
       return {
-        success: true
+        success: true,
       };
     })
   );

packages/react-native/src/builders/start/start.impl.ts

@@ -25,9 +25,6 @@ function run(
   options: ReactNativeDevServerOptions,
   context: BuilderContext
 ): Observable<ReactNativeDevServerBuildOutput> {
-  if (platform() !== 'darwin') {
-    throw new Error(`The run-ios build requires OSX to run`);
-  }
   return from(getProjectRoot(context)).pipe(
     tap((root) => ensureNodeModulesSymlink(context.workspaceRoot, root)),
     switchMap((root) =>