dart2js: build metadata-types lazily in the new emitter.

pkg/compiler/lib/src/js_emitter/new_emitter/model_emitter.dart

 // Copyright (c) 2014, 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.
 
 library dart2js.new_js_emitter.model_emitter;
 
 import '../../constants/values.dart' show ConstantValue, FunctionConstantValue;
 import '../../dart2jslib.dart' show Compiler;
 import '../../dart_types.dart' show DartType;
 import '../../elements/elements.dart' show ClassElement, FunctionElement;
@@ skipping 182 matching lines @@
        'parseFunctionDescriptor':
            js.js.statement(parseFunctionDescriptorBoilerplate,
                {'argumentCount': js.string(namer.requiredParameterField),
                 'defaultArgumentValues': js.string(namer.defaultValuesField),
                 'callName': js.string(namer.callNameField)}),
 
        'cyclicThrow':
            backend.emitter.staticFunctionAccess(backend.getCyclicThrowHelper()),
        'outputContainsConstantList': program.outputContainsConstantList,
        'embeddedGlobals': emitEmbeddedGlobals(program),
+       'readMetadataTypeFunction': readMetadataTypeFunction,
        'staticNonFinals':
             emitStaticNonFinalFields(fragment.staticNonFinalFields),
        'operatorIsPrefix': js.string(namer.operatorIsPrefix),
        'callName': js.string(namer.callNameField),
        'argumentCount': js.string(namer.requiredParameterField),
        'defaultArgumentValues': js.string(namer.defaultValuesField),
        'eagerClasses': emitEagerClassInitializations(fragment.libraries),
        'invokeMain': fragment.invokeMain,
        'code': code};
 
@@ skipping 200 matching lines @@
   }
 
   js.Property emitGetTypeFromName() {
     js.Expression function =
         js.js( """function(name) {
                     return holdersMap[name][name].ensureResolved();
                   }""");
     return new js.Property(js.string(GET_TYPE_FROM_NAME), function);
   }
 
+  static final metadataTypeComment =
+      "Types are non-evaluated and must be compiled at first use. "
+      "Compiled strings are guaranteed not to be strings, and it's thus safe "
+      "to use a type-test to determine if a type has already been compiled.";
+
+  static final String readMetadataTypeName = "readMetadataType";
+
+  js.Statement get readMetadataTypeFunction {
+    return js.js.statement('''function $readMetadataTypeName(index) {
+      // $metadataTypeComment.

[sra1, 2015/05/07 03:39:30]

Just put the comment here.

[floitsch, 2015/05/07 04:08:59]

Done.

+      var type = #typesAccess[index];
+      if (typeof type == 'string') {
+        type = expressionCompile(type);
+        #typesAccess[index] = type;
+      }
+      return type;
+    }''', {"typesAccess": generateEmbeddedGlobalAccess(TYPES)});
+  }
+
+  js.Template get templateForReadType {
+    // TODO(floitsch): make sure that no local variable shadows the access to
+    // the readMetadataType function.
+    return js.js.expressionTemplateFor('$readMetadataTypeName(#)');
+  }
+
   List<js.Property> emitMetadata(Program program) {
 
     List<js.Property> metadataGlobals = <js.Property>[];
 
     js.Property createGlobal(List<String> list, String global) {
       String listAsString = "[${list.join(",")}]";
       js.Expression metadata =
                 js.js.uncachedExpressionTemplate(listAsString).instantiate([]);
       return new js.Property(js.string(global), metadata);
     }
 
     metadataGlobals.add(createGlobal(program.metadata, METADATA));
     List<String> types =
         program.metadataTypes[program.fragments.first.outputUnit];
     if (types == null) types = <String>[];
-    metadataGlobals.add(createGlobal(types, TYPES));
+    // The strings in the array are already pretty-printed JS expressions.
+    js.Expression unparsedTypes = js.stringArray(types);
+    metadataGlobals.add(new js.Property(js.string(TYPES), unparsedTypes));
 
     return metadataGlobals;
   }
 
   js.Expression emitDeferredFragment(List<String> types,
                                      DeferredFragment fragment,
                                      List<Holder> holders) {
     // TODO(floitsch): initialize eager classes.
     // TODO(floitsch): the hash must depend on the output.
     int hash = fragment.hashCode;
 
     List<js.Expression> deferredCode =
         fragment.libraries.map(emitLibrary).toList();
 
     deferredCode.add(
         emitLazilyInitializedStatics(fragment.staticLazilyInitializedFields));
 
     deferredCode.add(emitConstants(fragment.constants));
 
     js.ArrayInitializer deferredArray = new js.ArrayInitializer(deferredCode);
 
     // This is the code that must be evaluated after all deferred classes have
     // been setup.
     js.Statement immediateCode =
         emitEagerClassInitializations(fragment.libraries);
 
     js.LiteralString immediateString = unparse(compiler, immediateCode);
 
-    js.Expression deferredTypes = types == null
+    js.Expression deferredTypes = (types == null)
         ? js.string("[]")
         : js.string("[${types.join(",")}]");
 
     js.ArrayInitializer hunk =
         new js.ArrayInitializer([deferredArray, immediateString,
                                  deferredTypes]);
 
     return js.js("$deferredInitializersGlobal[$hash] = #", hunk);
   }
 
@@ skipping 677 matching lines @@
         #nativeInfoHandler;
       }
     }
   }
 
   $setupProgramName(program, 0);
 
   // Initialize globals.
   #embeddedGlobals;
 
+  function expressionCompile(__s__) {
+    'use strict';
+    return eval('(' + __s__ + ')');
+  }
+
+  #readMetadataTypeFunction;
+
   // TODO(floitsch): this order means that native classes may not be
   // referenced from constants. I'm mostly afraid of things like using them as
   // generic arguments (which should be fine, but maybe there are other
   // similar things).
   // Initialize natives.
   if (#needsNativeSupport) handleNativeClassInfos();
 
   // Initialize static non-final fields.
   #staticNonFinals;
 
   // Add native boilerplate code.
   #nativeIsolateAffinityTagInitialization;
 
   // Initialize eager classes.
   #eagerClasses;
 
   var end = Date.now();
   // print('Setup: ' + (end - start) + ' ms.');
 
   #invokeMain;  // Start main.
 
 }(Date.now(), #code)
 }""";
 
 }