Enforce single computeDelta() invocation.

pkg/front_end/test/incremental_kernel_generator_test.dart

 // Copyright (c) 2017, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 import 'dart:async';
 
 import 'package:front_end/compiler_options.dart';
 import 'package:front_end/incremental_kernel_generator.dart';
 import 'package:front_end/memory_file_system.dart';
 import 'package:front_end/src/byte_store/byte_store.dart';
@@ skipping 42 matching lines @@
       compilerOptions.packagesFileUri = Uri.parse('file:///test/.packages');
     }
     incrementalKernelGenerator = await IncrementalKernelGenerator
         .newInstance(compilerOptions, entryPoint, watch: watchFn);
     return (await incrementalKernelGenerator.computeDelta()).newProgram;
   }
 
   test_acceptLastDelta() async {
     writeFile('/test/.packages', 'test:lib/');
     String path = '/test/lib/test.dart';
-    Uri uri = writeFile(path, 'var v = 1;');
+    Uri uri = writeFile(path, '');
 
     await getInitialState(uri);
     incrementalKernelGenerator.acceptLastDelta();
 
     // Attempt to accept the second time.
-    expect(() {
+    _assertStateError(() {
       incrementalKernelGenerator.acceptLastDelta();
-    }, throwsStateError);
+    }, IncrementalKernelGeneratorImpl.MSG_NO_LAST_DELTA);
   }
 
   test_compile_chain() async {
     writeFile('/test/.packages', 'test:lib/');
     String aPath = '/test/lib/a.dart';
     String bPath = '/test/lib/b.dart';
     String cPath = '/test/lib/c.dart';
     Uri aUri = writeFile(aPath, 'var a = 1;');
     Uri bUri = writeFile(bPath, r'''
 import 'a.dart';
@@ skipping 134 matching lines @@
     expect(_getLibraryText(library), r'''library;
 import self as self;
 import "dart:core" as core;
 import "dart:async" as asy;
 
 static field core::int a = 1;
 static field asy::Future<core::String> b;
 ''');
   }
 
+  test_computeDelta_hasAnotherRunning() async {
+    writeFile('/test/.packages', 'test:lib/');
+    String path = '/test/lib/test.dart';
+    Uri uri = writeFile(path, '');
+
+    await getInitialState(uri);
+    incrementalKernelGenerator.acceptLastDelta();
+
+    // Run, but don't wait.
+    var future = incrementalKernelGenerator.computeDelta();
+
+    // acceptLastDelta() is failing while the future is pending.
+    _assertStateError(() {
+      incrementalKernelGenerator.acceptLastDelta();
+    }, IncrementalKernelGeneratorImpl.MSG_PENDING_COMPUTE);
+
+    // rejectLastDelta() is failing while the future is pending.
+    _assertStateError(() {
+      incrementalKernelGenerator.rejectLastDelta();
+    }, IncrementalKernelGeneratorImpl.MSG_PENDING_COMPUTE);
+
+    // Run another, this causes StateError.
+    _assertStateError(() {
+      incrementalKernelGenerator.computeDelta();
+    }, IncrementalKernelGeneratorImpl.MSG_PENDING_COMPUTE);
+
+    // Wait for the pending future.
+    await future;
+  }
+
   test_inferPackagesFile() async {
     writeFile('/test/.packages', 'test:lib/');
     String aPath = '/test/lib/a.dart';
     String bPath = '/test/lib/b.dart';
     writeFile(aPath, 'var a = 1;');
     Uri bUri = writeFile(bPath, r'''
 import "package:test/a.dart";
 var b = a;
 ''');
 
@@ skipping 27 matching lines @@
     // Reject the last delta, so the test library is included again.
     incrementalKernelGenerator.rejectLastDelta();
     {
       var delta = await incrementalKernelGenerator.computeDelta();
       Program program = delta.newProgram;
       _assertLibraryUris(program, includes: [uri]);
     }
 
     // Attempt to reject the last delta twice.
     incrementalKernelGenerator.rejectLastDelta();
-    expect(() {
+    _assertStateError(() {
       incrementalKernelGenerator.rejectLastDelta();
-    }, throwsStateError);
+    }, IncrementalKernelGeneratorImpl.MSG_NO_LAST_DELTA);
   }
 
   test_updateEntryPoint() async {
     writeFile('/test/.packages', 'test:lib/');
     String path = '/test/lib/test.dart';
     Uri uri = writeFile(path, r'''
 main() {
   var v = 1;
 }
 ''');
@@ skipping 162 matching lines @@
     List<Uri> libraryUris =
         program.libraries.map((library) => library.importUri).toList();
     for (var shouldInclude in includes) {
       expect(libraryUris, contains(shouldInclude));
     }
     for (var shouldExclude in excludes) {
       expect(libraryUris, isNot(contains(shouldExclude)));
     }
   }
 
+  /// Assert that invocation of [f] throws a [StateError] with the given [msg].
+  void _assertStateError(f(), String msg) {
+    try {
+      f();
+      fail('StateError expected.');
+    } on StateError catch (e) {
+      expect(e.message, msg);
+    }
+  }
+
   Future<List<int>> _computeSdkOutlineBytes() async {
     var options = new CompilerOptions()
       ..fileSystem = fileSystem
       ..sdkRoot = Uri.parse('file:///sdk/')
       ..compileSdk = true
       ..chaseDependencies = true
       ..strongMode = true;
     var inputs = [Uri.parse('dart:core')];
     return summaryFor(inputs, options);
   }
 
   Library _getLibrary(Program program, Uri uri) {
     for (var library in program.libraries) {
       if (library.importUri == uri) return library;
     }
     throw fail('No library found with URI "$uri"');
   }
 
   String _getLibraryText(Library library) {
     StringBuffer buffer = new StringBuffer();
     new Printer(buffer, syntheticNames: new NameSystem())
         .writeLibraryFile(library);
     return buffer.toString();
   }
 }