Skip directly to the last library to set the entry point and check importUri

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 39930073fdf8a50070e64340bbb26d9eb9c59f9c..477c07b61dae337d7f3c4272924039f7f07ab828 100644
--- a/pkg/front_end/lib/src/incremental_kernel_generator_impl.dart
+++ b/pkg/front_end/lib/src/incremental_kernel_generator_impl.dart
@@ -136,13 +136,12 @@ class IncrementalKernelGeneratorImpl implements IncrementalKernelGenerator {
       // that imports a changed one, is affected.
 
       // Set the main method.
-      for (var library in program.libraries) {
-        if (library.fileUri == _entryPoint.toString()) {
-          program.mainMethod = library.procedures.firstWhere(
-              (procedure) => procedure.name.name == 'main',
-              orElse: () => null);
-          break;
-        }
+      if (program.libraries.isNotEmpty) {
+        var entryLibrary = program.libraries.last;

[scheglov, 2017/06/07 21:31:16]

I thought about doing this, but decided that this is not perfectly safe. What if
the last strongly connected component (with the entry point) consists of two
libraries, and it happens that the entry point library is not the last one in
this component? Topological sorting does not guarantee this to us.

[Siggi Cherem (dart-lang), 2017/06/07 21:36:10]

Good point, what do you think of either of these two ideas:
 - go backwards with program.libraries.reversed (it's likely closer to the end)
 - only visit libraries in results.last.kernelLibraries?

[scheglov, 2017/06/07 21:38:42]

Yeah, we know for sure that it is in the last result.

+        assert(entryLibrary.importUri == _entryPoint);
+        program.mainMethod = entryLibrary.procedures.firstWhere(
+            (procedure) => procedure.name.name == 'main',
+            orElse: () => null);
       }
 
       return new DeltaProgram(program);