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

pkg/front_end/lib/src/incremental_kernel_generator_impl.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 'dart:io';
 
 import 'package:front_end/file_system.dart';
 import 'package:front_end/incremental_kernel_generator.dart';
 import 'package:front_end/src/base/api_signature.dart';
@@ skipping 118 matching lines @@
       }
 
       if (watch != null) _fsState.fileUris.forEach((f) => watch(f, true));
 
       // TODO(scheglov) Add libraries which import changed libraries.
       // For now the corresponding test works because we use full library
       // contents to compute signatures (not just API parts). So, every library
       // 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) {
+        for (Library library in results.last.kernelLibraries) {
+          if (library.importUri == _entryPoint) {
+            program.mainMethod = library.procedures.firstWhere(
+                (procedure) => procedure.name.name == 'main',
+                orElse: () => null);
+            break;
+          }
         }
       }
 
       return new DeltaProgram(program);
     });
   }
 
   @override
   void invalidate(Uri uri) {
     _invalidatedFiles.add(uri);
@@ skipping 170 matching lines @@
   /// TODO(scheglov) Use API signatures.
   /// TODO(scheglov) Or use tree shaking and compute signatures of outlines.
   final String signature;
 
   /// Kernel libraries for libraries in the [cycle].  Bodies of dependencies
   /// are not included, but but references to those dependencies are included.
   final List<Library> kernelLibraries;
 
   _LibraryCycleResult(this.cycle, this.signature, this.kernelLibraries);
 }