Include only changed or affected libraries into delta.

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/incremental_resolved_ast_generator.dart';
@@ skipping 45 matching lines @@
 
   /// The current file system state.
   final FileSystemState _fsState;
 
   /// The byte storage to get and put serialized data.
   final ByteStore _byteStore;
 
   /// The URI of the program entry point.
   final Uri _entryPoint;
 
+  /// Latest compilation signatures produced by [computeDelta] for libraries.
+  final Map<Uri, String> _uriToLatestSignature = {};

[Siggi Cherem (dart-lang), 2017/05/17 18:15:10]

optional style nit: consider dropping "_uriTo" from the name, I think that's
implied given the type. Maybe simply "_lastSignature"?

[scheglov, 2017/05/17 22:04:05]

OK
Will do in https://codereview.chromium.org/2893453005.

+
   /// The set of absolute file URIs that were reported through [invalidate]
   /// and not checked for actual changes yet.
   final Set<Uri> _invalidatedFiles = new Set<Uri>();
 
   IncrementalKernelGeneratorImpl(
       this._options, this._uriTranslator, this._entryPoint)
       : _logger = _options.logger,
         _fsState = new FileSystemState(_options.fileSystem, _uriTranslator),
         _byteStore = _options.byteStore;
 
@@ skipping 19 matching lines @@
       List<_LibraryCycleResult> results = [];
       await _logger.runAsync('Compute results for cycles', () async {
         for (LibraryCycle cycle in cycles) {
           _LibraryCycleResult result =
               await _compileCycle(nameRoot, dillTarget, cycle);
           results.add(result);
         }
       });
 
       Program program = new Program(nameRoot: nameRoot);
+
+      // Add affected libraries (with different signatures).
       for (_LibraryCycleResult result in results) {
-        program.libraries.addAll(result.kernelLibraries);
+        for (Library library in result.kernelLibraries) {
+          Uri uri = library.importUri;
+          if (_uriToLatestSignature[uri] != result.signature) {
+            _uriToLatestSignature[uri] = result.signature;
+            program.libraries.add(library);
+          }
+        }
       }
 
+      // TODO(scheglov) Add libraries which import changed libraries.
+
       return new DeltaProgram(program);
     });
   }
 
   @override
   void invalidate(Uri uri) {
     _invalidatedFiles.add(uri);
   }
 
   @override
@@ skipping 111 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].  Dependencies are not
   /// included, they were returned as results for preceding cycles.
   final List<Library> kernelLibraries;
 
   _LibraryCycleResult(this.cycle, this.signature, this.kernelLibraries);
 }