Handle abnormal termination of frontend compiler. (#13982)

* Check frontend_server exit code.

When frontend_server completes abnormally, flutter tools has to stop and let user know.

* Add tests

packages/flutter_tools/lib/src/commands/build_aot.dart

@@ -342,6 +342,10 @@ Future<String> _buildAotSnapshot(
       aot : true,
       strongMode: strongMode,
     );
+    if (mainPath == null) {
+      printError('Compiler terminated unexpectedly.');
+      return null;
+    }
   }
 
   genSnapshotCmd.add(mainPath);

packages/flutter_tools/lib/src/compile.dart

@@ -110,8 +110,8 @@ Future<String> compile(
     .transform(UTF8.decoder)
     .transform(const LineSplitter())
     .listen(stdoutHandler.handler);
-  await server.exitCode;
-  return stdoutHandler.outputFilename.future;
+  final int exitCode = await server.exitCode;
+  return exitCode == 0 ? stdoutHandler.outputFilename.future : null;
 }
 
 /// Wrapper around incremental frontend server compiler, that communicates with
@@ -175,7 +175,8 @@ class ResidentCompiler {
 
     _server.stdin.writeln('compile $scriptFilename');
 
-    return stdoutHandler.outputFilename.future;
+    final int exitCode = await _server.exitCode;
+    return exitCode == 0 ? stdoutHandler.outputFilename.future : null;
   }
 
 

packages/flutter_tools/lib/src/flx.dart

@@ -76,6 +76,9 @@ Future<Null> build({
       mainPath: fs.file(mainPath).absolute.path,
       strongMode: strongMode
     );
+    if (kernelBinaryFilename == null) {
+      throwToolExit('Compiler terminated unexpectedly on $mainPath');
+    }
     kernelContent = new DevFSFileContent(fs.file(kernelBinaryFilename));
   }
 

packages/flutter_tools/test/compile_test.dart

@@ -74,6 +74,28 @@ void main() {
     }, overrides: <Type, Generator>{
       ProcessManager: () => mockProcessManager,
     });
+
+    testUsingContext('single dart abnormal compiler termination', () async {
+      when(mockFrontendServer.exitCode).thenReturn(255);
+
+      final BufferLogger logger = context[Logger];
+
+      when(mockFrontendServer.stdout)
+          .thenAnswer((Invocation invocation) => new Stream<List<int>>.fromFuture(
+          new Future<List<int>>.value(UTF8.encode(
+              'result abc\nline1\nline2\nabc'
+          ))
+      ));
+
+      final String output = await compile(sdkRoot: '/path/to/sdkroot',
+          mainPath: '/path/to/main.dart'
+      );
+      expect(mockFrontendServerStdIn.getAndClear(), isEmpty);
+      expect(logger.errorText, equals('compiler message: line1\ncompiler message: line2\n'));
+      expect(output, equals(null));
+    }, overrides: <Type, Generator>{
+      ProcessManager: () => mockProcessManager,
+    });
   });
 
   group('incremental compile', () {
@@ -125,6 +147,27 @@ void main() {
       ProcessManager: () => mockProcessManager,
     });
 
+    testUsingContext('single dart compile abnormally terminates', () async {
+      when(mockFrontendServer.exitCode).thenReturn(255);
+
+      final BufferLogger logger = context[Logger];
+
+      when(mockFrontendServer.stdout)
+          .thenAnswer((Invocation invocation) => new Stream<List<int>>.fromFuture(
+          new Future<List<int>>.value(UTF8.encode(
+              'result abc\nline1\nline2\nabc /path/to/main.dart.dill'
+          ))
+      ));
+
+      final String output = await generator.recompile(
+          '/path/to/main.dart', null /* invalidatedFiles */
+      );
+      expect(logger.errorText, equals('compiler message: line1\ncompiler message: line2\n'));
+      expect(output, equals(null));
+    }, overrides: <Type, Generator>{
+      ProcessManager: () => mockProcessManager,
+    });
+
     testUsingContext('compile and recompile', () async {
       final BufferLogger logger = context[Logger];