Mix salt into result signatures.

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 43c016a0cae0bad16cfeb8a40d1e64bded16e650..c81a6f8bec89fc787f6bb9df4332214e4eeb2c18 100644
--- a/pkg/front_end/lib/src/incremental_kernel_generator_impl.dart
+++ b/pkg/front_end/lib/src/incremental_kernel_generator_impl.dart
@@ -4,6 +4,7 @@
 
 import 'dart:async';
 import 'dart:io';
+import 'dart:typed_data';
 
 import 'package:front_end/file_system.dart';
 import 'package:front_end/incremental_kernel_generator.dart';
@@ -45,6 +46,9 @@ class ByteSink implements Sink<List<int>> {
 /// used to obtain resolved ASTs, and these are fed into kernel code generation
 /// logic.
 class IncrementalKernelGeneratorImpl implements IncrementalKernelGenerator {
+  /// The version of data format, should be incremented on every format change.
+  static const int DATA_VERSION = 1;
+
   /// The compiler options, such as the [FileSystem], the SDK dill location,
   /// etc.
   final ProcessedOptions _options;
@@ -64,8 +68,11 @@ class IncrementalKernelGeneratorImpl implements IncrementalKernelGenerator {
   /// The URI of the program entry point.
   final Uri _entryPoint;
 
+  /// The salt to mix into all hashes used as keys for serialized data.
+  final Uint8List _salt = new Uint8List(16);
+
   /// Latest compilation signatures produced by [computeDelta] for libraries.
-  final Map<Uri, String> _uriToLatestSignature = {};
+  final Map<Uri, String> _latestSignature = {};
 
   /// The set of absolute file URIs that were reported through [invalidate]
   /// and not checked for actual changes yet.
@@ -75,7 +82,9 @@ class IncrementalKernelGeneratorImpl implements IncrementalKernelGenerator {
       this._options, this._uriTranslator, this._entryPoint)
       : _logger = _options.logger,
         _fsState = new FileSystemState(_options.fileSystem, _uriTranslator),
-        _byteStore = _options.byteStore;
+        _byteStore = _options.byteStore {
+    _fillSalt();
+  }
 
   @override
   Future<DeltaProgram> computeDelta(
@@ -111,8 +120,8 @@ class IncrementalKernelGeneratorImpl implements IncrementalKernelGenerator {
       for (_LibraryCycleResult result in results) {
         for (Library library in result.kernelLibraries) {
           Uri uri = library.importUri;
-          if (_uriToLatestSignature[uri] != result.signature) {
-            _uriToLatestSignature[uri] = result.signature;
+          if (_latestSignature[uri] != result.signature) {
+            _latestSignature[uri] = result.signature;
             program.libraries.add(library);
           }
         }
@@ -141,8 +150,7 @@ class IncrementalKernelGeneratorImpl implements IncrementalKernelGenerator {
       String signature;
       {
         var signatureBuilder = new ApiSignature();
-        // TODO(scheglov) add salt
-        //    signature.addUint32List(_fsState._salt);
+        signatureBuilder.addBytes(_salt);
         Set<FileState> transitiveFiles = cycle.libraries
             .map((library) => library.transitiveFiles)
             .expand((files) => files)
@@ -253,6 +261,15 @@ class IncrementalKernelGeneratorImpl implements IncrementalKernelGenerator {
     } while (wasChanged);
   }
 
+  /// Fill [_salt] with data.
+  void _fillSalt() {
+    var saltBuilder = new ApiSignature();
+    saltBuilder.addInt(DATA_VERSION);
+    saltBuilder.addBool(_options.strongMode);
+    var saltBytes = saltBuilder.toByteList();
+    _salt.setRange(0, 16, saltBytes);

[Paul Berry, 2017/05/17 22:25:06]

This doesn't seem safe.  If saltBytes has fewer than 16 bytes, then the behavior
of setRange is undefined (setRange docs say "The [iterable] must have enough
objects to fill the range from `start` to `end` after skipping [skipCount]
objects).  If saltBytes has more than 16 bytes, then some of the salt bytes
won't get copied.

[scheglov, 2017/05/17 22:38:09]

Hm... I think toByteList() returns exactly 16 bytes of md5 signature.

[Paul Berry, 2017/05/18 02:57:15]

Oops, you're right.  I forgot about that.

+  }
+
   /// Refresh all the invalidated files and update dependencies.
   Future<Null> _refreshInvalidatedFiles() async {
     await _logger.runAsync('Refresh invalidated files', () async {