Emit API-only summaries

pkg/dev_compiler/lib/src/compiler/command.dart

 // Copyright (c) 2016, 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:io';
 import 'package:analyzer/src/generated/source.dart' show Source;
 import 'package:analyzer/src/summary/package_bundle_reader.dart'
     show InSummarySource;
 import 'package:args/args.dart' show ArgParser, ArgResults;
 import 'package:args/command_runner.dart' show UsageException;
@@ skipping 63 matching lines @@
     dartdevc arguments: ${args.join(' ')}
     dart --version: ${Platform.version}
 ```
 $error
 $stackTrace
 ```''');
     return 70;
   }
 }
 
+bool _changed(List<int> list1, List<int> list2) {
+  var length = list1.length;
+  if (length != list2.length) return true;
+  for (var i = 0; i < length; ++i) {
+    if (list1[i] != list2[i]) return true;
+  }
+  return false;
+}
+
 void _compile(ArgResults argResults, void printFn(Object obj)) {
   var compiler =
       new ModuleCompiler(new AnalyzerOptions.fromArguments(argResults));
   var compilerOpts = new CompilerOptions.fromArguments(argResults);
   if (argResults['help']) {
     printFn(_usageMessage);
     return;
   }
   var outPaths = argResults['out'] as List<String>;
   var moduleFormats = parseModuleFormatOption(argResults);
@@ skipping 49 matching lines @@
 
   if (!module.isValid) throw new CompileErrorException();
 
   // Write JS file, as well as source map and summary (if requested).
   for (var i = 0; i < outPaths.length; i++) {
     var outPath = outPaths[i];
     module.writeCodeSync(moduleFormats[i], singleOutFile, outPath);
     if (module.summaryBytes != null) {
       var summaryPath =
           path.withoutExtension(outPath) + '.${compilerOpts.summaryExtension}';
-      new File(summaryPath).writeAsBytesSync(module.summaryBytes);
+      // Only overwrite if summary changed.  This plays better with timestamp
+      // based build systems.
+      var file = new File(summaryPath);
+      if (!file.existsSync() ||
+          _changed(file.readAsBytesSync(), module.summaryBytes)) {
+        file.writeAsBytesSync(module.summaryBytes);
+      }
     }
   }
 }
 
 String _moduleForLibrary(
     String moduleRoot, Source source, CompilerOptions compilerOpts) {
   if (source is InSummarySource) {
     var summaryPath = source.summaryPath;
     var ext = '.${compilerOpts.summaryExtension}';
     if (path.isWithin(moduleRoot, summaryPath) && summaryPath.endsWith(ext)) {
@@ skipping 18 matching lines @@
     '\n\n${_argParser.usage}';
 
 void _usageException(String message) {
   throw new UsageException(message, _usageMessage);
 }
 
 /// Thrown when the input source code has errors.
 class CompileErrorException implements Exception {
   toString() => '\nPlease fix all errors before compiling (warnings are okay).';
 }