Source in most stuff.

dart/frog/leg/scanner/scanner_task.dart

 // Copyright (c) 2012, 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 ScannerTask extends CompilerTask {
   ScannerTask(Compiler compiler) : super(compiler);
   String get name() => 'Scanner';
 
   void scan(CompilationUnitElement compilationUnit) {
     measure(() {
       scanElements(compilationUnit);
       if (compilationUnit.kind === ElementKind.LIBRARY) {
         processScriptTags(compilationUnit);
       }
     });
   }
 
   void processScriptTags(LibraryElement library) {
+    LinkBuilder<ScriptTag> imports = new LinkBuilder<ScriptTag>();
+    Uri cwd = new Uri(scheme: 'file', path: compiler.currentDirectory);
+    Uri base = cwd.resolve(library.script.name.toString());
     for (ScriptTag tag in library.tags.reverse()) {
       SourceString argument = tag.argument.value.copyWithoutQuotes(1, 1);
-      Uri cwd = new Uri(scheme: 'file', path: compiler.currentDirectory);
-      Uri base = cwd.resolve(library.script.name.toString());
       Uri resolved = base.resolve(argument.toString());
       if (tag.isImport()) {
-        importLibrary(library, loadLibrary(resolved, tag), tag.prefix);
+        // It is not safe to import other libraries at this point as
+        // another library could then observe the current library
+        // before it fully declares all the members that are sourced
+        // in.
+        imports.addLast(tag);
       } else if (tag.isLibrary()) {
         if (library.libraryTag !== null) {
           compiler.cancel("duplicated library declaration", node: tag);
         } else {
           library.libraryTag = tag;
         }
       } else if (tag.isSource()) {
         Script script = compiler.readScript(resolved, tag);
         CompilationUnitElement unit =
           new CompilationUnitElement(script, library);
         compiler.withCurrentElement(unit, () => scan(unit));
       } else {
         compiler.cancel("illegal script tag: ${tag.tag}", node: tag);
       }
     }
+    for (ScriptTag tag in imports.toLink()) {
+      // Now that we have processed all the source tags, it is safe to
+      // start loading other libraries.
+      SourceString argument = tag.argument.value.copyWithoutQuotes(1, 1);
+      Uri resolved = base.resolve(argument.toString());
+      importLibrary(library, loadLibrary(resolved, tag), tag.prefix);
+    }
     if (compiler.coreLibrary !== null) {
       importLibrary(library, compiler.coreLibrary, null);
     }
   }
 
   void scanElements(CompilationUnitElement compilationUnit) {
     compiler.log("scanning $compilationUnit");
     Script script = compilationUnit.script;
     Token tokens;
     try {
@@ skipping 35 matching lines @@
     } else {
       for (Link<Element> link = imported.topLevelElements; !link.isEmpty();
            link = link.tail) {
         compiler.withCurrentElement(link.head, () {
             library.define(link.head, compiler);
           });
       }
     }
   }
 }