Fix for issue 20125 - improved error messages

pkg/analyzer/lib/src/generated/error_verifier.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 engine.resolver.error_verifier;
 
 import 'dart:collection';
 import "dart:math" as math;
 
 import 'java_engine.dart';
@@ skipping 2765 matching lines @@
    */
   bool _checkForExportDuplicateLibraryName(ExportDirective node, ExportElement exportElement, LibraryElement exportedLibrary) {
     if (exportedLibrary == null) {
       return false;
     }
     String name = exportedLibrary.name;
     // check if there is other exported library with the same name
     LibraryElement prevLibrary = _nameToExportElement[name];
     if (prevLibrary != null) {
       if (prevLibrary != exportedLibrary) {
-        _errorReporter.reportErrorForNode(StaticWarningCode.EXPORT_DUPLICATED_LIBRARY_NAME, node, [
-            prevLibrary.definingCompilationUnit.displayName,
-            exportedLibrary.definingCompilationUnit.displayName,
-            name]);
+        if (name.isEmpty) {
+          _errorReporter.reportErrorForNode(
+              StaticWarningCode.EXPORT_DUPLICATED_LIBRARY_UNNAMED,
+              node,
+              [prevLibrary.definingCompilationUnit.displayName,
+                  exportedLibrary.definingCompilationUnit.displayName]);
+        } else {
+          _errorReporter.reportErrorForNode(
+              StaticWarningCode.EXPORT_DUPLICATED_LIBRARY_NAMED,
+              node,
+              [prevLibrary.definingCompilationUnit.displayName,
+                  exportedLibrary.definingCompilationUnit.displayName,
+                  name]);
+        }
         return true;
       }
     } else {
       _nameToExportElement[name] = exportedLibrary;
     }
     // OK
     return false;
   }
 
   /**
@@ skipping 421 matching lines @@
    * @return `true` if and only if an error code is generated on the passed node
    * @see CompileTimeErrorCode#IMPORT_DUPLICATED_LIBRARY_NAME
    */
   bool _checkForImportDuplicateLibraryName(ImportDirective node, ImportElement importElement) {
     // prepare imported library
     LibraryElement nodeLibrary = importElement.importedLibrary;
     if (nodeLibrary == null) {
       return false;
     }
     String name = nodeLibrary.name;
-    // check if there is other imported library with the same name
+    // check if there is another imported library with the same name
     LibraryElement prevLibrary = _nameToImportElement[name];
     if (prevLibrary != null) {
       if (prevLibrary != nodeLibrary) {
-        _errorReporter.reportErrorForNode(StaticWarningCode.IMPORT_DUPLICATED_LIBRARY_NAME, node, [
-            prevLibrary.definingCompilationUnit.displayName,
-            nodeLibrary.definingCompilationUnit.displayName,
-            name]);
+        if (name.isEmpty) {
+          _errorReporter.reportErrorForNode(
+              StaticWarningCode.IMPORT_DUPLICATED_LIBRARY_UNNAMED,
+              node,
+              [prevLibrary.definingCompilationUnit.displayName,
+                  nodeLibrary.definingCompilationUnit.displayName]);
+        } else {
+          _errorReporter.reportErrorForNode(
+              StaticWarningCode.IMPORT_DUPLICATED_LIBRARY_NAMED,
+              node,
+              [prevLibrary.definingCompilationUnit.displayName,
+                  nodeLibrary.definingCompilationUnit.displayName,
+                  name]);
+        }
         return true;
       }
     } else {
       _nameToImportElement[name] = nodeLibrary;
     }
     // OK
     return false;
   }
 
   /**
@@ skipping 2218 matching lines @@
     toCheck.add(type.element);
     // type arguments
     if (type is InterfaceType) {
       InterfaceType interfaceType = type;
       for (DartType typeArgument in interfaceType.typeArguments) {
         _addTypeToCheck(typeArgument);
       }
     }
   }
 }