Deferred (aka lazy) loading of static functions.

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

+// Copyright (c) 2013, 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.
+
+class DeferredLoadTask extends CompilerTask {
+  DeferredLoadTask(Compiler compiler) : super(compiler);
+  String get name => 'Lazy';
+  final Set<LibraryElement> deferredLibraries = new Set<LibraryElement>();
+
+  bool isDeferred(Element element) {
+    // TODO(ahe): This is really a graph coloring problem. We should
+    // make sure that libraries and elements only used by a deferred
+    // library are also deferred.
+    // Also, if something is deferred depends on your
+    // perspective. Inside a deferred library, other elements of the
+    // same library are not deferred. We should add an extra parameter
+    // to this method to indicate "from where".
+    return deferredLibraries.contains(element.getLibrary());
+  }
+
+  void registerMainApp(LibraryElement mainApp) {
+    if (mainApp == null) return;
+    compiler.withCurrentElement(mainApp, () {
+      deferredLibraries.addAll(new List.from(findDeferredLibraries(mainApp)));
+    });
+  }
+
+  Link<Element> findDeferredLibraries(LibraryElement library) {
+    Link<Element> link = const Link<Element>();
+    for (LibraryTag tag in library.tags) {
+      for (MetadataAnnotation metadata in tag.metadata) {
+        metadata.ensureResolved(compiler);
+        if (metadata.value.type.element == compiler.deferLoadClass) {
+          ConstructedConstant value = metadata.value;
+          SourceString expectedName = value.fields[0].toDartString().source;
+          LibraryElement deferredLibrary = library.getDependency(tag);
+          link = link.prepend(deferredLibrary);
+          note(tag, 'Defer loading of $deferredLibrary');
+          SourceString actualName =
+              new SourceString(deferredLibrary.getLibraryOrScriptName());
+          if (expectedName != actualName) {
+            compiler.reportErrorCode(
+                metadata,
+                MessageKind.GENERIC, // DO NOT SUBMIT (add proper error code).
+                {'text':
+                  'Library name mismatch "${expectedName.slowToString()}" != '
+                    '"${actualName.slowToString()}"'});
+          } else {
+            // DO NOT SUBMIT (this is for debugging).
+            note(metadata,
+                 '${actualName.slowToString()} matches $deferredLibrary');
+          }
+        }
+      }
+    }
+    return link;
+  }
+
+  void note(Spannable node, message) {
+    compiler.reportMessage(compiler.spanFromSpannable(node),
+                           MessageKind.GENERIC.error({'text': message}),
+                           api.Diagnostic.INFO);
+  }
+}