Move dart2js from sdk/lib/_internal/compiler to pkg/compiler

sdk/lib/_internal/compiler/implementation/deferred_load.dart

Index: sdk/lib/_internal/compiler/implementation/deferred_load.dart
diff --git a/sdk/lib/_internal/compiler/implementation/deferred_load.dart b/sdk/lib/_internal/compiler/implementation/deferred_load.dart
deleted file mode 100644
index ae262b7764f8f59e467b5ca0755d744d3678155e..0000000000000000000000000000000000000000
--- a/sdk/lib/_internal/compiler/implementation/deferred_load.dart
+++ /dev/null
@@ -1,767 +0,0 @@
-// 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 deferred_load;
-
-import 'constants/expressions.dart';
-import 'constants/values.dart' show
-    ConstantValue,
-    ConstructedConstantValue,
-    DeferredConstantValue,
-    StringConstantValue;
-
-import 'dart2jslib.dart' show
-    Backend,
-    Compiler,
-    CompilerTask,
-    invariant,
-    MessageKind;
-
-import 'dart_backend/dart_backend.dart' show
-    DartBackend;
-
-import 'js_backend/js_backend.dart' show
-    JavaScriptBackend;
-
-import 'elements/elements.dart' show
-    AstElement,
-    ClassElement,
-    Element,
-    ElementKind,
-    Elements,
-    FunctionElement,
-    LibraryElement,
-    MetadataAnnotation,
-    PrefixElement,
-    ScopeContainerElement,
-    TypedefElement,
-    VoidElement;
-
-import 'util/util.dart' show
-    Link, makeUnique;
-
-import 'util/setlet.dart' show
-    Setlet;
-
-import 'tree/tree.dart' show
-    Import,
-    LibraryTag,
-    LibraryDependency,
-    LiteralDartString,
-    LiteralString,
-    NewExpression,
-    Node;
-
-import 'tree/tree.dart' as ast;
-
-import 'resolution/resolution.dart' show
-    AnalyzableElementX,
-    TreeElements;
-
-/// A "hunk" of the program that will be loaded whenever one of its [imports]
-/// are loaded.
-///
-/// Elements that are only used in one deferred import, is in an OutputUnit with
-/// the deferred import as single element in the [imports] set.
-///
-/// Whenever a deferred Element is shared between several deferred imports it is
-/// in an output unit with those imports in the [imports] Set.
-///
-/// OutputUnits are equal if their [imports] are equal.
-class OutputUnit {
-  /// The deferred imports that will load this output unit when one of them is
-  /// loaded.
-  final Setlet<Import> imports = new Setlet<Import>();
-
-  /// A unique name representing this [OutputUnit].
-  /// Based on the set of [imports].
-  String name;
-
-  String toString() => "OutputUnit($name)";
-
-  bool operator==(OutputUnit other) {
-    return imports.length == other.imports.length &&
-        imports.containsAll(other.imports);
-  }
-
-  int get hashCode {
-    int sum = 0;
-    for (Import import in imports) {
-      sum = (sum + import.hashCode) & 0x3FFFFFFF;  // Stay in 30 bit range.
-    }
-    return sum;
-  }
-}
-
-/// For each deferred import, find elements and constants to be loaded when that
-/// import is loaded. Elements that are used by several deferred imports are in
-/// shared OutputUnits.
-class DeferredLoadTask extends CompilerTask {
-  /// The name of this task.
-  String get name => 'Deferred Loading';
-
-  /// DeferredLibrary from dart:async
-  ClassElement get deferredLibraryClass => compiler.deferredLibraryClass;
-
-  /// A synthetic [Import] representing the loading of the main
-  /// program.
-  final Import _fakeMainImport = new Import(null, new LiteralString(null,
-      new LiteralDartString("main")), null, null, null);
-
-  /// The OutputUnit that will be loaded when the program starts.
-  final OutputUnit mainOutputUnit = new OutputUnit();
-
-  /// A set containing (eventually) all output units that will result from the
-  /// program.
-  final Set<OutputUnit> allOutputUnits = new Set<OutputUnit>();
-
-  /// Will be `true` if the program contains deferred libraries.
-  bool isProgramSplit = false;
-
-  /// A mapping from the name of a defer import to all the output units it
-  /// depends on in a list of lists to be loaded in the order they appear.
-  ///
-  /// For example {"lib1": [[lib1_lib2_lib3], [lib1_lib2, lib1_lib3],
-  /// [lib1]]} would mean that in order to load "lib1" first the hunk
-  /// lib1_lib2_lib2 should be loaded, then the hunks lib1_lib2 and lib1_lib3
-  /// can be loaded in parallel. And finally lib1 can be loaded.
-  final Map<String, List<OutputUnit>> hunksToLoad =
-      new Map<String, List<OutputUnit>>();
-  final Map<Import, String> importDeferName = new Map<Import, String>();
-
-  /// A mapping from elements and constants to their output unit. Query this via
-  /// [outputUnitForElement]
-  final Map<Element, OutputUnit> _elementToOutputUnit =
-      new Map<Element, OutputUnit>();
-
-  /// A mapping from constants to their output unit. Query this via
-  /// [outputUnitForConstant]
-  final Map<ConstantValue, OutputUnit> _constantToOutputUnit =
-      new Map<ConstantValue, OutputUnit>();
-
-  /// All the imports with a [DeferredLibrary] annotation, mapped to the
-  /// [LibraryElement] they import.
-  /// The main library is included in this set for convenience.
-  final Map<Import, LibraryElement> _allDeferredImports =
-      new Map<Import, LibraryElement>();
-
-  // For each deferred import we want to know exactly what elements have to
-  // be loaded.
-  Map<Import, Set<Element>> _importedDeferredBy = null;
-  Map<Import, Set<ConstantValue>> _constantsDeferredBy = null;
-
-  Set<Element> _mainElements = new Set<Element>();
-
-  DeferredLoadTask(Compiler compiler) : super(compiler) {
-    mainOutputUnit.imports.add(_fakeMainImport);
-  }
-
-  Backend get backend => compiler.backend;
-
-  /// Returns the [OutputUnit] where [element] belongs.
-  OutputUnit outputUnitForElement(Element element) {
-    if (!isProgramSplit) return mainOutputUnit;
-
-    element = element.implementation;
-    while (!_elementToOutputUnit.containsKey(element)) {
-      // TODO(21051): workaround: it looks like we output annotation constants
-      // for classes that we don't include in the output. This seems to happen
-      // when we have reflection but can see that some classes are not needed.
-      // We still add the annotation but don't run through it below (where we
-      // assign every element to its output unit).
-      if (element.enclosingElement == null) {
-        _elementToOutputUnit[element] = mainOutputUnit;
-        break;
-      }
-      element = element.enclosingElement.implementation;
-    }
-    return _elementToOutputUnit[element];
-  }
-
-  /// Returns the [OutputUnit] where [constant] belongs.
-  OutputUnit outputUnitForConstant(ConstantValue constant) {
-    if (!isProgramSplit) return mainOutputUnit;
-
-    return _constantToOutputUnit[constant];
-  }
-
-  bool isDeferred(Element element) {
-    return outputUnitForElement(element) != mainOutputUnit;
-  }
-
-  /// Returns true if e1 and e2 are in the same output unit.
-  bool inSameOutputUnit(Element e1, Element e2) {
-    return outputUnitForElement(e1) == outputUnitForElement(e2);
-  }
-
-  void registerConstantDeferredUse(DeferredConstantValue constant,
-                                   PrefixElement prefix) {
-    OutputUnit outputUnit = new OutputUnit();
-    outputUnit.imports.add(prefix.deferredImport);
-    _constantToOutputUnit[constant] = outputUnit;
-  }
-
-  /// Answers whether [element] is explicitly deferred when referred to from
-  /// [library].
-  bool _isExplicitlyDeferred(Element element, LibraryElement library) {
-    Link<Import> imports = _getImports(element, library);
-    // If the element is not imported explicitly, it is implicitly imported
-    // not deferred.
-    if (imports.isEmpty) return false;
-    // An element could potentially be loaded by several imports. If all of them
-    // is explicitly deferred, we say the element is explicitly deferred.
-    // TODO(sigurdm): We might want to give a warning if the imports do not
-    // agree.
-    return imports.every((Import import) => import.isDeferred);
-  }
-
-  /// Returns a [Link] of every [Import] that imports [element] into [library].
-  Link<Import> _getImports(Element element, LibraryElement library) {
-    if (element.isClassMember) {
-      element = element.enclosingClass;
-    }
-    if (element.isAccessor) {
-      element = (element as FunctionElement).abstractField;
-    }
-    return library.getImportsFor(element);
-  }
-
-  /// Finds all elements and constants that [element] depends directly on.
-  /// (not the transitive closure.)
-  ///
-  /// Adds the results to [elements] and [constants].
-  void _collectAllElementsAndConstantsResolvedFrom(
-      Element element,
-      Set<Element> elements,
-      Set<ConstantValue> constants,
-      isMirrorUsage) {
-
-    /// Recursively add the constant and its dependencies to [constants].
-    void addConstants(ConstantValue constant) {
-      if (constants.contains(constant)) return;
-      constants.add(constant);
-      if (constant is ConstructedConstantValue) {
-        elements.add(constant.type.element);
-      }
-      constant.getDependencies().forEach(addConstants);
-    }
-
-    /// Collects all direct dependencies of [element].
-    ///
-    /// The collected dependent elements and constants are are added to
-    /// [elements] and [constants] respectively.
-    void collectDependencies(Element element) {
-      // TODO(johnniwinther): Remove this when [AbstractFieldElement] has been
-      // removed.
-      if (element is! AstElement) return;
-      AstElement astElement = element;
-
-      // TODO(sigurdm): We want to be more specific about this - need a better
-      // way to query "liveness".
-      if (astElement is! TypedefElement &&
-          !compiler.enqueuer.resolution.hasBeenResolved(astElement)) {
-        return;
-      }
-
-      TreeElements treeElements = astElement.resolvedAst.elements;
-
-      assert(treeElements != null);
-
-      for (Element dependency in treeElements.allElements) {
-        if (dependency.isLocal && !dependency.isFunction) continue;
-        if (dependency.isErroneous) continue;
-        if (dependency.isTypeVariable) continue;
-
-        elements.add(dependency);
-      }
-      treeElements.forEachConstantNode((Node node, _) {
-        // Explicitly depend on the backend constants.
-        addConstants(
-            backend.constants.getConstantForNode(node, treeElements).value);
-      });
-      elements.addAll(treeElements.otherDependencies);
-    }
-
-    // TODO(sigurdm): How is metadata on a patch-class handled?
-    for (MetadataAnnotation metadata in element.metadata) {
-      ConstantExpression constant =
-          backend.constants.getConstantForMetadata(metadata);
-      if (constant != null) {
-        addConstants(constant.value);
-      }
-    }
-    if (element.isClass) {
-      // If we see a class, add everything its live instance members refer
-      // to.  Static members are not relevant, unless we are processing
-      // extra dependencies due to mirrors.
-      void addLiveInstanceMember(Element element) {
-        if (!compiler.enqueuer.resolution.hasBeenResolved(element)) return;
-        if (!isMirrorUsage && !element.isInstanceMember) return;
-        collectDependencies(element.implementation);
-      }
-      ClassElement cls = element.declaration;
-      cls.forEachLocalMember(addLiveInstanceMember);
-      if (cls.implementation != cls) {
-        // TODO(ahe): Why doesn't ClassElement.forEachLocalMember do this?
-        cls.implementation.forEachLocalMember(addLiveInstanceMember);
-      }
-      for (var type in cls.implementation.allSupertypes) {
-        elements.add(type.element.implementation);
-      }
-      elements.add(cls.implementation);
-    } else if (Elements.isStaticOrTopLevel(element) ||
-               element.isConstructor) {
-      collectDependencies(element);
-    }
-    if (element.isGenerativeConstructor) {
-      // When instantiating a class, we record a reference to the
-      // constructor, not the class itself.  We must add all the
-      // instance members of the constructor's class.
-      ClassElement implementation =
-          element.enclosingClass.implementation;
-      _collectAllElementsAndConstantsResolvedFrom(
-          implementation, elements, constants, isMirrorUsage);
-    }
-
-    // Other elements, in particular instance members, are ignored as
-    // they are processed as part of the class.
-  }
-
-  /// Returns the transitive closure of all libraries that are imported
-  /// from root without DeferredLibrary annotations.
-  Set<LibraryElement> _nonDeferredReachableLibraries(LibraryElement root) {
-    Set<LibraryElement> result = new Set<LibraryElement>();
-
-    void traverseLibrary(LibraryElement library) {
-      if (result.contains(library)) return;
-      result.add(library);
-
-      iterateTags(LibraryElement library) {
-        // TODO(sigurdm): Make helper getLibraryDependencyTags when tags is
-        // changed to be a List instead of a Link.
-        for (LibraryTag tag in library.tags) {
-          if (tag is! LibraryDependency) continue;
-          LibraryDependency libraryDependency = tag;
-          if (!(libraryDependency is Import && libraryDependency.isDeferred)) {
-            LibraryElement importedLibrary = library.getLibraryFromTag(tag);
-            traverseLibrary(importedLibrary);
-          }
-        }
-      }
-
-      iterateTags(library);
-      if (library.isPatched) {
-        iterateTags(library.implementation);
-      }
-    }
-    traverseLibrary(root);
-    result.add(compiler.coreLibrary);
-    return result;
-  }
-
-  /// Recursively traverses the graph of dependencies from [element], mapping
-  /// deferred imports to each dependency it needs in the sets
-  /// [_importedDeferredBy] and [_constantsDeferredBy].
-  void _mapDependencies(Element element, Import import,
-                        {isMirrorUsage: false}) {
-    Set<Element> elements = _importedDeferredBy.putIfAbsent(import,
-        () => new Set<Element>());
-    Set<ConstantValue> constants = _constantsDeferredBy.putIfAbsent(import,
-        () => new Set<ConstantValue>());
-
-    // Only process elements once, unless we are doing dependencies due to
-    // mirrors, which are added in additional traversals.
-    if (!isMirrorUsage && elements.contains(element)) return;
-    // Anything used directly by main will be loaded from the start
-    // We do not need to traverse it again.
-    if (import != _fakeMainImport && _mainElements.contains(element)) return;
-
-    // Here we modify [_importedDeferredBy].
-    elements.add(element);
-
-    Set<Element> dependentElements = new Set<Element>();
-
-    // This call can modify [_importedDeferredBy] and [_constantsDeferredBy].
-    _collectAllElementsAndConstantsResolvedFrom(
-        element, dependentElements, constants, isMirrorUsage);
-
-    LibraryElement library = element.library;
-    for (Element dependency in dependentElements) {
-      if (_isExplicitlyDeferred(dependency, library)) {
-        for (Import deferredImport in _getImports(dependency, library)) {
-          _mapDependencies(dependency, deferredImport);
-        };
-      } else {
-        _mapDependencies(dependency, import);
-      }
-    }
-  }
-
-  /// Adds extra dependencies coming from mirror usage.
-  ///
-  /// The elements are added with [_mapDependencies].
-  void _addMirrorElements() {
-    void mapDependenciesIfResolved(Element element, Import deferredImport) {
-      // If an element is the target of a MirrorsUsed annotation but never used
-      // It will not be resolved, and we should not call isNeededForReflection.
-      // TODO(sigurdm): Unresolved elements should just answer false when
-      // asked isNeededForReflection. Instead an internal error is triggered.
-      // So we have to filter them out here.
-      if (element is AnalyzableElementX && !element.hasTreeElements) return;
-      if (compiler.backend.isAccessibleByReflection(element)) {
-        _mapDependencies(element, deferredImport, isMirrorUsage: true);
-      }
-    }
-
-    // For each deferred import we analyze all elements reachable from the
-    // imported library through non-deferred imports.
-    handleLibrary(LibraryElement library, Import deferredImport) {
-      library.implementation.forEachLocalMember((Element element) {
-        mapDependenciesIfResolved(element, deferredImport);
-      });
-
-      for (MetadataAnnotation metadata in library.metadata) {
-        ConstantExpression constant =
-            backend.constants.getConstantForMetadata(metadata);
-        if (constant != null) {
-          _mapDependencies(constant.value.computeType(compiler).element,
-              deferredImport);
-        }
-      }
-      for (LibraryTag tag in library.tags) {
-        for (MetadataAnnotation metadata in tag.metadata) {
-          ConstantExpression constant =
-              backend.constants.getConstantForMetadata(metadata);
-          if (constant != null) {
-            _mapDependencies(constant.value.computeType(compiler).element,
-                deferredImport);
-          }
-        }
-      }
-    }
-
-    for (Import deferredImport in _allDeferredImports.keys) {
-      LibraryElement deferredLibrary = _allDeferredImports[deferredImport];
-      for (LibraryElement library in
-          _nonDeferredReachableLibraries(deferredLibrary)) {
-        handleLibrary(library, deferredImport);
-      }
-    }
-  }
-
-  /// Computes a unique string for the name field for each outputUnit.
-  ///
-  /// Also sets up the [hunksToLoad] mapping.
-  void _assignNamesToOutputUnits(Set<OutputUnit> allOutputUnits) {
-    Set<String> usedImportNames = new Set<String>();
-
-    // Finds the first argument to the [DeferredLibrary] annotation
-    void computeImportDeferName(Import import) {
-      String result;
-      if (import == _fakeMainImport) {
-        result = "main";
-      } else if (import.isDeferred) {
-        result = import.prefix.toString();
-      } else {
-        Link<MetadataAnnotation> metadatas = import.metadata;
-        assert(metadatas != null);
-        for (MetadataAnnotation metadata in metadatas) {
-          metadata.ensureResolved(compiler);
-          Element element =
-              metadata.constant.value.computeType(compiler).element;
-          if (element == deferredLibraryClass) {
-            ConstructedConstantValue constant = metadata.constant.value;
-            StringConstantValue s = constant.fields[0];
-            result = s.primitiveValue.slowToString();
-            break;
-          }
-        }
-      }
-      assert(result != null);
-      importDeferName[import] = makeUnique(result, usedImportNames);;
-    }
-
-    int counter = 1;
-
-    for (Import import in _allDeferredImports.keys) {
-      computeImportDeferName(import);
-    }
-
-    for (OutputUnit outputUnit in allOutputUnits) {
-      if (outputUnit == mainOutputUnit) {
-        outputUnit.name = "main";
-      } else {
-        outputUnit.name = "$counter";
-        ++counter;
-      }
-    }
-
-    List sortedOutputUnits = new List.from(allOutputUnits);
-    // Sort the output units in descending order of the number of imports they
-    // include.
-
-    // The loading of the output units mut be ordered because a superclass needs
-    // to be initialized before its subclass.
-    // But a class can only depend on another class in an output unit shared by
-    // a strict superset of the imports:
-    // By contradiction: Assume a class C in output unit shared by imports in
-    // the set S1 = (lib1,.., lib_n) depends on a class D in an output unit
-    // shared by S2 such that S2 not a superset of S1. Let lib_s be a library in
-    // S1 not in S2. lib_s must depend on C, and then in turn on D therefore D
-    // is not in the right output unit.
-    sortedOutputUnits.sort((a, b) => b.imports.length - a.imports.length);
-
-    // For each deferred import we find out which outputUnits to load.
-    for (Import import in _allDeferredImports.keys) {
-      if (import == _fakeMainImport) continue;
-      hunksToLoad[importDeferName[import]] = new List<OutputUnit>();
-      for (OutputUnit outputUnit in sortedOutputUnits) {
-        if (outputUnit == mainOutputUnit) continue;
-        if (outputUnit.imports.contains(import)) {
-          hunksToLoad[importDeferName[import]].add(outputUnit);
-        }
-      }
-    }
-  }
-
-  void onResolutionComplete(FunctionElement main) {
-    if (!isProgramSplit) {
-      allOutputUnits.add(mainOutputUnit);
-      return;
-    }
-    if (main == null) return;
-    LibraryElement mainLibrary = main.library;
-    _importedDeferredBy = new Map<Import, Set<Element>>();
-    _constantsDeferredBy = new Map<Import, Set<ConstantValue>>();
-    _importedDeferredBy[_fakeMainImport] = _mainElements;
-
-    measureElement(mainLibrary, () {
-
-      // Starting from main, traverse the program and find all dependencies.
-      _mapDependencies(compiler.mainFunction, _fakeMainImport);
-
-      // Also add "global" dependencies to the main OutputUnit.  These are
-      // things that the backend need but cannot associate with a particular
-      // element, for example, startRootIsolate.  This set also contains
-      // elements for which we lack precise information.
-      for (Element element in compiler.globalDependencies.otherDependencies) {
-        _mapDependencies(element, _fakeMainImport);
-      }
-
-      // Now check to see if we have to add more elements due to mirrors.
-      if (compiler.mirrorsLibrary != null) {
-        _addMirrorElements();
-      }
-
-      // Build the OutputUnits using these two maps.
-      Map<Element, OutputUnit> elementToOutputUnitBuilder =
-          new Map<Element, OutputUnit>();
-      Map<ConstantValue, OutputUnit> constantToOutputUnitBuilder =
-          new Map<ConstantValue, OutputUnit>();
-
-      // Reverse the mappings. For each element record an OutputUnit collecting
-      // all deferred imports mapped to this element. Same for constants.
-      for (Import import in _importedDeferredBy.keys) {
-        for (Element element in _importedDeferredBy[import]) {
-          // Only one file should be loaded when the program starts, so make
-          // sure that only one OutputUnit is created for [fakeMainImport].
-          if (import == _fakeMainImport) {
-            elementToOutputUnitBuilder[element] = mainOutputUnit;
-          } else {
-            elementToOutputUnitBuilder
-                .putIfAbsent(element, () => new OutputUnit())
-                .imports.add(import);
-          }
-        }
-        for (ConstantValue constant in _constantsDeferredBy[import]) {
-          // Only one file should be loaded when the program starts, so make
-          // sure that only one OutputUnit is created for [fakeMainImport].
-          if (import == _fakeMainImport) {
-            constantToOutputUnitBuilder[constant] = mainOutputUnit;
-          } else {
-            constantToOutputUnitBuilder
-                .putIfAbsent(constant, () => new OutputUnit())
-                .imports.add(import);
-          }
-        }
-      }
-
-      // Release maps;
-      _importedDeferredBy = null;
-      _constantsDeferredBy = null;
-
-      // Find all the output units elements/constants have been mapped to, and
-      // canonicalize them.
-      elementToOutputUnitBuilder.forEach(
-          (Element element, OutputUnit outputUnit) {
-        OutputUnit representative = allOutputUnits.lookup(outputUnit);
-        if (representative == null) {
-          representative = outputUnit;
-          allOutputUnits.add(representative);
-        }
-        _elementToOutputUnit[element] = representative;
-      });
-      constantToOutputUnitBuilder.forEach(
-          (ConstantValue constant, OutputUnit outputUnit) {
-        OutputUnit representative = allOutputUnits.lookup(outputUnit);
-        if (representative == null) {
-          representative = outputUnit;
-          allOutputUnits.add(representative);
-        }
-        _constantToOutputUnit[constant] = representative;
-      });
-
-      // Generate a unique name for each OutputUnit.
-      _assignNamesToOutputUnits(allOutputUnits);
-    });
-  }
-
-  void ensureMetadataResolved(Compiler compiler) {
-    if (compiler.mainApp == null) return;
-    _allDeferredImports[_fakeMainImport] = compiler.mainApp;
-    var lastDeferred;
-    // When detecting duplicate prefixes of deferred libraries there are 4
-    // cases of duplicate prefixes:
-    // 1.
-    // import "lib.dart" deferred as a;
-    // import "lib2.dart" deferred as a;
-    // 2.
-    // import "lib.dart" deferred as a;
-    // import "lib2.dart" as a;
-    // 3.
-    // import "lib.dart" as a;
-    // import "lib2.dart" deferred as a;
-    // 4.
-    // import "lib.dart" as a;
-    // import "lib2.dart" as a;
-    // We must be able to signal error for case 1, 2, 3, but accept case 4.
-
-    // The prefixes that have been used by any imports in this library.
-    Setlet<String> usedPrefixes = new Setlet<String>();
-    // The last deferred import we saw with a given prefix (if any).
-    Map<String, Import> prefixDeferredImport = new Map<String, Import>();
-    for (LibraryElement library in compiler.libraryLoader.libraries) {
-      compiler.withCurrentElement(library, () {
-        prefixDeferredImport.clear();
-        usedPrefixes.clear();
-        // TODO(sigurdm): Make helper getLibraryImportTags when tags is a List
-        // instead of a Link.
-        for (LibraryTag tag in library.tags) {
-          if (tag is! Import) continue;
-          Import import = tag;
-
-          /// Give an error if the old annotation-based syntax has been used.
-          Link<MetadataAnnotation> metadataList = import.metadata;
-          if (metadataList != null) {
-            for (MetadataAnnotation metadata in metadataList) {
-              metadata.ensureResolved(compiler);
-              Element element =
-                  metadata.constant.value.computeType(compiler).element;
-              if (element == deferredLibraryClass) {
-                 compiler.reportFatalError(
-                     import, MessageKind.DEFERRED_OLD_SYNTAX);
-              }
-            }
-          }
-
-          String prefix = (import.prefix != null)
-              ? import.prefix.toString()
-              : null;
-          // The last import we saw with the same prefix.
-          Import previousDeferredImport = prefixDeferredImport[prefix];
-          if (import.isDeferred) {
-            _allDeferredImports[import] = library.getLibraryFromTag(import);
-
-            if (prefix == null) {
-              compiler.reportError(import,
-                  MessageKind.DEFERRED_LIBRARY_WITHOUT_PREFIX);
-            } else {
-              prefixDeferredImport[prefix] = import;
-            }
-            isProgramSplit = true;
-            lastDeferred = import;
-          }
-          if (prefix != null) {
-            if (previousDeferredImport != null ||
-                (import.isDeferred && usedPrefixes.contains(prefix))) {
-              Import failingImport = (previousDeferredImport != null)
-                  ? previousDeferredImport
-                  : import;
-              compiler.reportError(failingImport.prefix,
-                  MessageKind.DEFERRED_LIBRARY_DUPLICATE_PREFIX);
-            }
-            usedPrefixes.add(prefix);
-          }
-        }
-      });
-    }
-    Backend backend = compiler.backend;
-    if (isProgramSplit && backend is JavaScriptBackend) {
-      backend.registerCheckDeferredIsLoaded(compiler.globalDependencies);
-    }
-    if (isProgramSplit && backend is DartBackend) {
-      // TODO(sigurdm): Implement deferred loading for dart2dart.
-      compiler.reportWarning(
-          lastDeferred,
-          MessageKind.DEFERRED_LIBRARY_DART_2_DART);
-      isProgramSplit = false;
-    }
-  }
-
-  /// If [send] is a static send with a deferred element, returns the
-  /// [PrefixElement] that the first prefix of the send resolves to.
-  /// Otherwise returns null.
-  ///
-  /// Precondition: send must be static.
-  ///
-  /// Example:
-  ///
-  /// import "a.dart" deferred as a;
-  ///
-  /// main() {
-  ///   print(a.loadLibrary.toString());
-  ///   a.loadLibrary().then((_) {
-  ///     a.run();
-  ///     a.foo.method();
-  ///   });
-  /// }
-  ///
-  /// Returns null for a.loadLibrary() (the special
-  /// function loadLibrary is not deferred). And returns the PrefixElement for
-  /// a.run() and a.foo.
-  /// a.loadLibrary.toString() and a.foo.method() are dynamic sends - and
-  /// this functions should not be called on them.
-  PrefixElement deferredPrefixElement(ast.Send send, TreeElements elements) {
-    Element element = elements[send];
-    // The DeferredLoaderGetter is not deferred, therefore we do not return the
-    // prefix.
-    if (element != null && element.isDeferredLoaderGetter) return null;
-
-    ast.Node firstNode(ast.Node node) {
-      if (node is! ast.Send) {
-        return node;
-      } else {
-        ast.Send send = node;
-        ast.Node receiver = send.receiver;
-        ast.Node receiverFirst = firstNode(receiver);
-        if (receiverFirst != null) {
-          return receiverFirst;
-        } else {
-          return firstNode(send.selector);
-        }
-      }
-    }
-    ast.Node first = firstNode(send);
-    ast.Node identifier = first.asIdentifier();
-    if (identifier == null) return null;
-    Element maybePrefix = elements[identifier];
-    if (maybePrefix != null && maybePrefix.isPrefix) {
-      PrefixElement prefixElement = maybePrefix;
-      if (prefixElement.isDeferred) {
-        return prefixElement;
-      }
-    }
-    return null;
-  }
-}