[vm/frontend-server] Fix frontend_server so that it can be tested.

With explicit exit() invocation, frontend_server_test only gets through first two tests before exiting.

Change-Id: Ica0b6f4f09baa8262b6097779be772877ca6f8d8
Reviewed-on: https://dart-review.googlesource.com/69220
Commit-Queue: Alexander Aprelev <aam@google.com>
Reviewed-by: Ryan Macnak <rmacnak@google.com>

pkg/vm/bin/frontend_server_starter.dart

@@ -1,9 +1,13 @@
 library frontend_server;
 
 import 'dart:async';
+import 'dart:io';
 
 import '../lib/frontend_server.dart';
 
 Future<Null> main(List<String> args) async {
-  starter(args);
+  final int exitCode = await starter(args);
+  if (exitCode != 0) {
+    exit(exitCode);
+  }
 }

pkg/vm/lib/frontend_server.dart

@@ -390,8 +390,13 @@ class FrontendCompiler implements CompilerInterface {
       if (uri == null || '$uri' == '') continue nextUri;
 
       final List<int> oldBytes = component.uriToSource[uri].source;
-      final FileSystemEntity entity =
-          _compilerOptions.fileSystem.entityForUri(uri);
+      FileSystemEntity entity;
+      try {
+        entity = _compilerOptions.fileSystem.entityForUri(uri);
+      } catch (_) {
+        // Ignore errors that might be caused by non-file uris.
+        continue nextUri;
+      }
       if (!await entity.exists()) {
         _generator.invalidate(uri);
         continue nextUri;
@@ -554,7 +559,7 @@ class _CompileExpressionRequest {
 /// Listens for the compilation commands on [input] stream.
 /// This supports "interactive" recompilation mode of execution.
 void listenAndCompile(CompilerInterface compiler, Stream<List<int>> input,
-    ArgResults options, void quit(),
+    ArgResults options, Completer<int> completer,
     {IncrementalCompiler generator}) {
   _State state = _State.READY_FOR_INSTRUCTION;
   _CompileExpressionRequest compileExpressionRequest;
@@ -608,7 +613,7 @@ void listenAndCompile(CompilerInterface compiler, Stream<List<int>> input,
         } else if (string == 'reset') {
           compiler.resetIncrementalCompiler();
         } else if (string == 'quit') {
-          quit();
+          completer.complete(0);
         }
         break;
       case _State.RECOMPILE_LIST:
@@ -668,7 +673,7 @@ void listenAndCompile(CompilerInterface compiler, Stream<List<int>> input,
 /// processes user input.
 /// `compiler` is an optional parameter so it can be replaced with mocked
 /// version for testing.
-Future<void> starter(
+Future<int> starter(
   List<String> args, {
   CompilerInterface compiler,
   Stream<List<int>> input,
@@ -682,7 +687,7 @@ Future<void> starter(
   } catch (error) {
     print('ERROR: $error\n');
     print(usage);
-    exit(1);
+    return 1;
   }
 
   if (options['train']) {
@@ -714,7 +719,7 @@ Future<void> starter(
       compiler.acceptLastDelta();
       await compiler.recompileDelta();
       compiler.acceptLastDelta();
-      return;
+      return 0;
     } finally {
       temp.deleteSync(recursive: true);
     }
@@ -726,12 +731,14 @@ Future<void> starter(
   );
 
   if (options.rest.isNotEmpty) {
-    exit(await compiler.compile(options.rest[0], options, generator: generator)
+    return await compiler.compile(options.rest[0], options,
+            generator: generator)
         ? 0
-        : 254);
+        : 254;
   }
 
-  listenAndCompile(compiler, input ?? stdin, options, () {
-    exit(0);
-  }, generator: generator);
+  Completer<int> completer = new Completer<int>();
+  listenAndCompile(compiler, input ?? stdin, options, completer,
+      generator: generator);
+  return completer.future;
 }