IncrementalKernalGenerator watch source callback

pkg/front_end/lib/src/incremental_kernel_generator_impl.dart

Index: pkg/front_end/lib/src/incremental_kernel_generator_impl.dart
diff --git a/pkg/front_end/lib/src/incremental_kernel_generator_impl.dart b/pkg/front_end/lib/src/incremental_kernel_generator_impl.dart
index 4221ba8f2f2b21bc71a14ec2b54bff25c22deb5d..e26d19a967e0211a54ecd28ac85f5410e03a1caf 100644
--- a/pkg/front_end/lib/src/incremental_kernel_generator_impl.dart
+++ b/pkg/front_end/lib/src/incremental_kernel_generator_impl.dart
@@ -57,7 +57,8 @@ class IncrementalKernelGeneratorImpl implements IncrementalKernelGenerator {
         _options = options;
 
   @override
-  Future<DeltaProgram> computeDelta() async {
+  Future<DeltaProgram> computeDelta(
+      {Future<Null> watch(Uri uri, bool used)}) async {
     var deltaLibraries = await _resolvedAstGenerator.computeDelta();
     var kernelOptions = _convertOptions(_options);
     var packages = null; // TODO(paulberry)
@@ -76,7 +77,11 @@ class IncrementalKernelGeneratorImpl implements IncrementalKernelGenerator {
           new DartLoader(repository, kernelOptions, packages, context: context);
       loader.loadLibrary(uri);
       kernels[uri] = new Program(repository.libraries);
+      // TODO(danrubel) rework watch invocation to eliminate race condition

[Paul Berry, 2017/01/25 22:03:34]

Please add my name to this TODO as well.

[danrubel, 2017/01/25 22:40:41]

I replaced my name with yours both here and below as you will probably be
addressing these TODOs. PLMK if that is not correct and I'll change them to
include both our names.

+      // and include part source files
+      if (watch != null) watch(uri, true);

[Paul Berry, 2017/01/25 22:03:34]

Please change to:

if (watch != null) await watch(uri, true);

It doesn't address the race condition, but it at least ensures that all calls to
[watch] have completed by the time [computeDelta] returns (which I think would
be reasonably expected by client code).

[danrubel, 2017/01/25 22:40:41]

That seems reasonable. I had to restructure the loop somewhat to get await to
work as expected. There's probably a better way of doing this so that watch does
not become a bottleneck, but I'll leave that for when it's reworked to eliminate
the watch race condition.

     });
+    // TODO(danrubel) invoke watch with used=false for each unused source
     return new DeltaProgram(kernels);
   }