Gracefully handle isolate exceptions

Author: kevmoo

webdev/CHANGELOG.md

@@ -2,6 +2,8 @@
 
 - Checks for a dependency on `build_web_compilers`.
 
+- Gracefully handle exceptions.
+
 ## 0.1.0
 
 - Initial release. Supports basic invocation of `build` and `serve` with

webdev/bin/webdev.dart

@@ -4,6 +4,7 @@
 
 import 'dart:async';
 import 'dart:io';
+import 'dart:isolate';
 
 import 'package:args/command_runner.dart';
 import 'package:io/ansi.dart';
@@ -35,5 +36,9 @@ Future main(List<String> args) async {
       print('  ${e.path}');
     }
     exitCode = ExitCode.config.code;
+  } on IsolateSpawnException catch (e) {
+    print(red.wrap('An unexpected exception has occurred.'));
+    print(e.message);
+    exitCode = ExitCode.software.code;
   }
 }

webdev/lib/src/command/build_runner_command_base.dart

@@ -53,10 +53,18 @@ abstract class BuildRunnerCommandBase extends Command<int> {
       stderr.writeln(new Trace.parse(trace).terse);
       if (exitCode == 0) exitCode = 1;
     });
-    await Isolate.spawnUri(buildRunnerScript, arguments, messagePort.sendPort,
-        onExit: exitPort.sendPort,
-        onError: errorPort.sendPort,
-        automaticPackageResolution: true);
+
+    try {
+      await Isolate.spawnUri(buildRunnerScript, arguments, messagePort.sendPort,
+          onExit: exitPort.sendPort,
+          onError: errorPort.sendPort,
+          automaticPackageResolution: true);
+    } on IsolateSpawnException {
+      exitPort.close();
+      errorPort.close();
+      messagePort.close();
+      rethrow;
+    }
     StreamSubscription exitCodeListener;
     exitCodeListener = messagePort.listen((isolateExitCode) {
       if (isolateExitCode is! int) {
@@ -90,11 +98,18 @@ Future<Uri> _buildRunnerScript() async {
   var exitPort = new ReceivePort();
   var errorPort = new ReceivePort();
 
-  await Isolate.spawnUri(dataUri, [], messagePort.sendPort,
-      onExit: exitPort.sendPort,
-      onError: errorPort.sendPort,
-      errorsAreFatal: true,
-      packageConfig: new Uri.file(_packagesFileName));
+  try {
+    await Isolate.spawnUri(dataUri, [], messagePort.sendPort,
+        onExit: exitPort.sendPort,
+        onError: errorPort.sendPort,
+        errorsAreFatal: true,
+        packageConfig: new Uri.file(_packagesFileName));
+  } on IsolateSpawnException {
+    messagePort.close();
+    exitPort.close();
+    errorPort.close();
+    rethrow;
+  }
 
   var allErrorsFuture = errorPort.forEach((error) {
     var errorList = error as List;

webdev/test/integration_test.dart

@@ -127,4 +127,34 @@ packages:
         contains('A `.packages` file does not exist in the target directory.'));
     await process.shouldExit(78);
   });
+
+  test('should fail gracefully if there is an isolate error', () async {
+    await d.file('pubspec.lock', '''
+# Copy-pasted from a valid run
+packages:
+  build_runner:
+    dependency: "direct main"
+    description:
+      name: build_runner
+      url: "https://pub.dartlang.org"
+    source: hosted
+    version: "0.8.0"
+  build_web_compilers:
+    dependency: "direct main"
+    description:
+      name: build_web_compilers
+      url: "https://pub.dartlang.org"
+    source: hosted
+    version: "0.3.4+2"
+''').create();
+
+    await d.file('.packages', '').create();
+
+    var process = await TestProcess.start('dart', [_webdevBin, 'build'],
+        workingDirectory: d.sandbox);
+    var output = (await process.stdoutStream().join('\n')).trim();
+
+    expect(output, contains('An unexpected exception has occurred.'));
+    await process.shouldExit(70);
+  });
 }