2007-03-21 Mike Kestner <mkestner@novell.com>
[mono.git] / mcs / mcs / namespace.cs
index c113217e5d867da28e4e3e94b86b22882893e174..b3cdc33336b1489799d3ba976ba5894a5dc08820 100644 (file)
 //
 // Author:
 //   Miguel de Icaza (miguel@ximian.com)
+//   Marek Safar (marek.safar@seznam.cz)
 //
 // (C) 2001 Ximian, Inc.
 //
 using System;
 using System.Collections;
 using System.Collections.Specialized;
+using System.Reflection;
 
 namespace Mono.CSharp {
 
+       public class RootNamespace : Namespace {
+               static MethodInfo get_namespaces_method;
+
+               string alias_name;
+               Assembly referenced_assembly;
+
+               Hashtable all_namespaces;
+
+               static Hashtable root_namespaces;
+               public static GlobalRootNamespace Global;
+               
+               static RootNamespace ()
+               {
+                       get_namespaces_method = typeof (Assembly).GetMethod ("GetNamespaces", BindingFlags.Instance | BindingFlags.NonPublic);
+
+                       Reset ();
+               }
+
+               public static void Reset ()
+               {
+                       root_namespaces = new Hashtable ();
+                       Global = new GlobalRootNamespace ();
+                       root_namespaces ["global"] = Global;
+               }
+
+               protected RootNamespace (string alias_name, Assembly assembly)
+                       : base (null, String.Empty)
+               {
+                       this.alias_name = alias_name;
+                       referenced_assembly = assembly;
+
+                       all_namespaces = new Hashtable ();
+                       all_namespaces.Add ("", this);
+
+                       if (referenced_assembly != null)
+                               ComputeNamespaces (this.referenced_assembly);
+               }
+
+               public static void DefineRootNamespace (string name, Assembly assembly)
+               {
+                       if (name == "global") {
+                               NamespaceEntry.Error_GlobalNamespaceRedefined (Location.Null);
+                               return;
+                       }
+                       RootNamespace retval = GetRootNamespace (name);
+                       if (retval == null || retval.referenced_assembly != assembly)
+                               root_namespaces [name] = new RootNamespace (name, assembly);
+               }
+
+               public static RootNamespace GetRootNamespace (string name)
+               {
+                       return (RootNamespace) root_namespaces [name];
+               }
+
+               public virtual Type LookupTypeReflection (string name, Location loc)
+               {
+                       return GetTypeInAssembly (referenced_assembly, name);
+               }
+
+               public void RegisterNamespace (Namespace child)
+               {
+                       if (child != this)
+                               all_namespaces.Add (child.Name, child);
+               }
+
+               public bool IsNamespace (string name)
+               {
+                       return all_namespaces.Contains (name);
+               }
+
+               protected void RegisterNamespace (string dotted_name)
+               {
+                       if (dotted_name != null && dotted_name.Length != 0 && ! IsNamespace (dotted_name))
+                               GetNamespace (dotted_name, true);
+               }
+
+               void RegisterExtensionMethodClass (Type t)
+               {
+                       string n = t.Namespace;
+                       Namespace ns = n == null ? Global : (Namespace)all_namespaces [n];
+                       if (ns == null)
+                               ns = GetNamespace (n, true);
+                       ns.RegisterExternalExtensionMethodClass (t);
+               }
+
+               protected void ComputeNamespaces (Assembly assembly)
+               {
+                       // How to test whether attribute exists without loading the assembly :-(
+                       const string SystemCore = "System.Core, Version=2.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089"; 
+                       if (TypeManager.extension_attribute_type == null &&
+                               assembly.FullName == SystemCore) {
+                               TypeManager.extension_attribute_type = assembly.GetType("System.Runtime.CompilerServices.ExtensionAttribute");
+                       }
+                       bool contains_extension_methods = TypeManager.extension_attribute_type != null &&
+                                       assembly.IsDefined(TypeManager.extension_attribute_type, false);
+                       if (get_namespaces_method != null && !contains_extension_methods) {
+                               string [] namespaces = (string []) get_namespaces_method.Invoke (assembly, null);
+                               foreach (string ns in namespaces)
+                                       RegisterNamespace (ns);
+                               return;
+                       }
+  
+                       foreach (Type t in assembly.GetExportedTypes ()) {
+                               if ((t.Attributes & Class.StaticClassAttribute) == Class.StaticClassAttribute &&
+                                       contains_extension_methods && t.IsDefined (TypeManager.extension_attribute_type, false))
+                                       RegisterExtensionMethodClass (t);
+                               else
+                                       RegisterNamespace (t.Namespace);
+                       }
+               }
+
+               protected static Type GetTypeInAssembly (Assembly assembly, string name)
+               {
+                       Type t = assembly.GetType (name);
+                       if (t == null)
+                               return null;
+
+                       if (t.IsPointer)
+                               throw new InternalErrorException ("Use GetPointerType() to get a pointer");
+
+                       TypeAttributes ta = t.Attributes & TypeAttributes.VisibilityMask;
+                       if (ta == TypeAttributes.NestedPrivate)
+                               return null;
+
+                       if ((ta == TypeAttributes.NotPublic ||
+                            ta == TypeAttributes.NestedAssembly ||
+                            ta == TypeAttributes.NestedFamANDAssem) &&
+                           !TypeManager.IsFriendAssembly (t.Assembly))
+                               return null;
+
+                       return t;
+               }
+
+               public override string ToString ()
+               {
+                       return String.Format ("RootNamespace ({0}::)", alias_name);
+               }
+
+               public override string GetSignatureForError ()
+               {
+                       return alias_name + "::";
+               }
+       }
+
+       public class GlobalRootNamespace : RootNamespace {
+               Assembly [] assemblies;
+               Module [] modules;
+
+               public GlobalRootNamespace ()
+                       : base ("global", null)
+               {
+                       assemblies = new Assembly [0];
+               }
+
+               public Assembly [] Assemblies {
+                       get { return assemblies; }
+               }
+
+               public Module [] Modules {
+                       get { return modules; }
+               }
+
+               public void AddAssemblyReference (Assembly a)
+               {
+                       foreach (Assembly assembly in assemblies) {
+                               if (a == assembly)
+                                       return;
+                       }
+
+                       int top = assemblies.Length;
+                       Assembly [] n = new Assembly [top + 1];
+                       assemblies.CopyTo (n, 0);
+                       n [top] = a;
+                       assemblies = n;
+
+                       ComputeNamespaces (a);
+               }
+
+               public void AddModuleReference (Module m)
+               {
+                       int top = modules != null ? modules.Length : 0;
+                       Module [] n = new Module [top + 1];
+                       if (modules != null)
+                               modules.CopyTo (n, 0);
+                       n [top] = m;
+                       modules = n;
+
+                       if (m == CodeGen.Module.Builder)
+                               return;
+
+                       foreach (Type t in m.GetTypes ())
+                               RegisterNamespace (t.Namespace);
+               }
+
+               public override void Error_NamespaceDoesNotExist(DeclSpace ds, Location loc, string name)
+               {
+                       Report.Error (400, loc, "The type or namespace name `{0}' could not be found in the global namespace (are you missing an assembly reference?)",
+                               name);
+               }
+
+               public override Type LookupTypeReflection (string name, Location loc)
+               {
+                       Type found_type = null;
+               
+                       foreach (Assembly a in assemblies) {
+                               Type t = GetTypeInAssembly (a, name);
+                               if (t == null)
+                                       continue;
+                                       
+                               if (found_type == null) {
+                                       found_type = t;
+                                       continue;
+                               }
+
+                               Report.SymbolRelatedToPreviousError (found_type);
+                               Report.SymbolRelatedToPreviousError (t);
+                               Report.Error (433, loc, "The imported type `{0}' is defined multiple times", name);
+                                       
+                               return found_type;
+                       }
+
+                       if (modules != null) {
+                               foreach (Module module in modules) {
+                                       Type t = module.GetType (name);
+                                       if (t == null)
+                                               continue;
+
+                                       if (found_type == null) {
+                                               found_type = t;
+                                               continue;
+                                       }
+
+                                       Report.SymbolRelatedToPreviousError (found_type);
+                                       if (loc.IsNull) {
+                                               DeclSpace ds = TypeManager.LookupDeclSpace (t);
+                                               Report.Warning (1685, 1, ds.Location, "The type `{0}' conflicts with the predefined type `{1}' and will be ignored",
+                                                       ds.GetSignatureForError (), TypeManager.CSharpName (found_type));
+                                               return found_type;
+                                       }
+                                       Report.SymbolRelatedToPreviousError (t);
+                                       Report.Warning (436, 2, loc, "The type `{0}' conflicts with the imported type `{1}'. Ignoring the imported type definition",
+                                               TypeManager.CSharpName (t), TypeManager.CSharpName (found_type));
+                                       return t;
+                               }
+                       }
+
+                       return found_type;
+               }
+       }
+
        /// <summary>
        ///   Keeps track of the namespaces defined in the C# code.
        ///
@@ -19,33 +274,17 @@ namespace Mono.CSharp {
        ///   compiler parse/intermediate tree during name resolution.
        /// </summary>
        public class Namespace : FullNamedExpression {
-               static ArrayList all_namespaces;
-               static Hashtable namespaces_map;
                
                Namespace parent;
                string fullname;
-               ArrayList entries;
-               Hashtable namespaces;
+               IDictionary namespaces;
                IDictionary declspaces;
                Hashtable cached_types;
+               RootNamespace root;
+               ArrayList external_exmethod_classes;
 
                public readonly MemberName MemberName;
 
-               public static Namespace Root;
-
-               static Namespace ()
-               {
-                       Reset ();
-               }
-
-               public static void Reset ()
-               {
-                       all_namespaces = new ArrayList ();
-                       namespaces_map = new Hashtable ();
-
-                       Root = new Namespace (null, "");
-               }
-
                /// <summary>
                ///   Constructor Takes the current namespace and the
                ///   name.  This is bootstrapped with parent == null
@@ -55,11 +294,19 @@ namespace Mono.CSharp {
                {
                        // Expression members.
                        this.eclass = ExprClass.Namespace;
-                       this.Type = null;
+                       this.Type = typeof (Namespace);
                        this.loc = Location.Null;
 
                        this.parent = parent;
 
+                       if (parent != null)
+                               this.root = parent.root;
+                       else
+                               this.root = this as RootNamespace;
+
+                       if (this.root == null)
+                               throw new InternalErrorException ("Root namespaces must be created using RootNamespace");
+                       
                        string pname = parent != null ? parent.Name : "";
                                
                        if (pname == "")
@@ -72,19 +319,15 @@ namespace Mono.CSharp {
 
                        if (parent != null && parent.MemberName != MemberName.Null)
                                MemberName = new MemberName (parent.MemberName, name);
-                       else if (name == "")
+                       else if (name.Length == 0)
                                MemberName = MemberName.Null;
                        else
                                MemberName = new MemberName (name);
 
-                       entries = new ArrayList ();
-                       namespaces = new Hashtable ();
+                       namespaces = new HybridDictionary ();
                        cached_types = new Hashtable ();
 
-                       all_namespaces.Add (this);
-                       if (namespaces_map.Contains (fullname))
-                               return;
-                       namespaces_map [fullname] = true;
+                       root.RegisterNamespace (this);
                }
 
                public override Expression DoResolve (EmitContext ec)
@@ -92,19 +335,48 @@ namespace Mono.CSharp {
                        return this;
                }
 
-               public override void Emit (EmitContext ec)
+               public virtual void Error_NamespaceDoesNotExist (DeclSpace ds, Location loc, string name)
                {
-                       throw new InternalErrorException ("Expression tree referenced namespace " + fullname + " during Emit ()");
+                       if (name.IndexOf ('`') > 0) {
+                               FullNamedExpression retval = Lookup (ds, SimpleName.RemoveGenericArity (name), loc);
+                               if (retval != null) {
+                                       Error_TypeArgumentsCannotBeUsed (retval.Type, loc, "type");
+                                       return;
+                               }
+                       } else {
+                               Type t = LookForAnyGenericType (name);
+                               if (t != null) {
+                                       Error_InvalidNumberOfTypeArguments (t, loc);
+                                       return;
+                               }
+                       }
+
+                       Report.Error (234, loc, "The type or namespace name `{0}' does not exist in the namespace `{1}'. Are you missing an assembly reference?",
+                               name, FullName);
+               }
+
+               public static void Error_InvalidNumberOfTypeArguments (Type t, Location loc)
+               {
+                       Report.SymbolRelatedToPreviousError (t);
+                       Report.Error (305, loc, "Using the generic type `{0}' requires `{1}' type argument(s)",
+                               TypeManager.CSharpName(t), TypeManager.GetNumberOfTypeArguments(t).ToString());
                }
 
-               public static bool IsNamespace (string name)
+               public static void Error_TypeArgumentsCannotBeUsed(Type t, Location loc, string symbol)
                {
-                       return namespaces_map [name] != null;
+                       Report.SymbolRelatedToPreviousError(t);
+                       Report.Error(308, loc, "The non-generic {0} `{1}' cannot be used with the type argument(s)",
+                               symbol, TypeManager.CSharpName(t));
+               }
+
+               public override void Emit (EmitContext ec)
+               {
+                       throw new InternalErrorException ("Expression tree referenced namespace " + fullname + " during Emit ()");
                }
 
                public override string GetSignatureForError ()
                {
-                       return Name.Length == 0 ? "::global" : Name;
+                       return Name;
                }
                
                public Namespace GetNamespace (string name, bool create)
@@ -133,11 +405,6 @@ namespace Mono.CSharp {
                        return ns;
                }
 
-               public static Namespace LookupNamespace (string name, bool create)
-               {
-                       return Root.GetNamespace (name, create);
-               }
-
                TypeExpr LookupType (string name, Location loc)
                {
                        if (cached_types.Contains (name))
@@ -160,9 +427,11 @@ namespace Mono.CSharp {
                                        t = tdecl.TypeBuilder;
                                }
                        }
-                       string lookup = t != null ? t.FullName : (fullname == "" ? name : fullname + "." + name);
-                       Type rt = TypeManager.LookupTypeReflection (lookup, loc);
-                       if (t == null)
+                       string lookup = t != null ? t.FullName : (fullname.Length == 0 ? name : fullname + "." + name);
+                       Type rt = root.LookupTypeReflection (lookup, loc);
+
+                       // HACK: loc.IsNull when the type is core type
+                       if (t == null || (rt != null && loc.IsNull))
                                t = rt;
 
                        TypeExpr te = t == null ? null : new TypeExpression (t, Location.Null);
@@ -170,11 +439,29 @@ namespace Mono.CSharp {
                        return te;
                }
 
+               ///
+               /// Used for better error reporting only
+               /// 
+               public Type LookForAnyGenericType (string typeName)
+               {
+                       if (declspaces == null)
+                               return null;
+
+                       typeName = SimpleName.RemoveGenericArity (typeName);
+
+                       foreach (DictionaryEntry de in declspaces) {
+                               string type_item = (string) de.Key;
+                               int pos = type_item.LastIndexOf ('`');
+                               if (pos == typeName.Length && String.Compare (typeName, 0, type_item, 0, pos) == 0)
+                                       return ((DeclSpace) de.Value).TypeBuilder;
+                       }
+                       return null;
+               }
+
                public FullNamedExpression Lookup (DeclSpace ds, string name, Location loc)
                {
-                       Namespace ns = GetNamespace (name, false);
-                       if (ns != null)
-                               return ns;
+                       if (namespaces.Contains (name))
+                               return (Namespace) namespaces [name];
 
                        TypeExpr te = LookupType (name, loc);
                        if (te == null || !ds.CheckAccessLevel (te.Type))
@@ -183,9 +470,56 @@ namespace Mono.CSharp {
                        return te;
                }
 
-               public void AddNamespaceEntry (NamespaceEntry entry)
+               public void RegisterExternalExtensionMethodClass (Type type)
+               {
+                       if (external_exmethod_classes == null)
+                               external_exmethod_classes = new ArrayList ();
+
+                       external_exmethod_classes.Add (type);
+               }
+
+               /// 
+               /// Looks for extension method in this namespace
+               /// 
+               public ArrayList LookupExtensionMethod (Type extensionType, string name, NamespaceEntry ns)
                {
-                       entries.Add (entry);
+                       if (declspaces == null)
+                               return null;
+
+                       ArrayList found = null;
+                       IEnumerator e = declspaces.Values.GetEnumerator ();
+                       e.Reset ();
+                       while (e.MoveNext ()) {
+                               Class c = e.Current as Class;
+                               if (c == null)
+                                       continue;
+
+                               if (!c.IsStaticClass)
+                                       continue;
+
+                               ArrayList res = c.MemberCache.FindExtensionMethods (extensionType, name);
+                               if (res == null)
+                                       continue;
+
+                               if (found == null)
+                                       found = res;
+                               else
+                                       found.AddRange (res);
+                       }
+
+                       if (external_exmethod_classes == null)
+                               return found;
+
+                       foreach (Type t in external_exmethod_classes) {
+                               MemberCache m = TypeHandle.GetMemberCache (t);
+                               ArrayList res = m.FindExtensionMethods (extensionType, name);
+                               if (found == null)
+                                       found = res;
+                               else
+                                       found.AddRange (res);
+                       }
+
+                       return found;
                }
 
                public void AddDeclSpace (string name, DeclSpace ds)
@@ -195,10 +529,6 @@ namespace Mono.CSharp {
                        declspaces.Add (name, ds);
                }
 
-               static public ArrayList UserDefinedNamespaces {
-                       get { return all_namespaces; }
-               }
-
                /// <summary>
                ///   The qualified name of the current namespace
                /// </summary>
@@ -218,37 +548,13 @@ namespace Mono.CSharp {
                        get { return parent; }
                }
 
-               public static void DefineNamespaces (SymbolWriter symwriter)
-               {
-                       foreach (Namespace ns in all_namespaces) {
-                               foreach (NamespaceEntry entry in ns.entries)
-                                       entry.DefineNamespace (symwriter);
-                       }
-               }
-
-               /// <summary>
-               ///   Used to validate that all the using clauses are correct
-               ///   after we are finished parsing all the files.  
-               /// </summary>
-               public static void VerifyUsing ()
-               {
-                       foreach (Namespace ns in all_namespaces) {
-                               foreach (NamespaceEntry entry in ns.entries)
-                                       entry.VerifyUsing ();
-                       }
-               }
-
                public override string ToString ()
                {
-                       if (this == Root)
-                               return "Namespace (<root>)";
-                       else
-                               return String.Format ("Namespace ({0})", Name);
+                       return String.Format ("Namespace ({0})", Name);
                }
        }
 
-       public class NamespaceEntry
-       {
+       public class NamespaceEntry {
                Namespace ns;
                NamespaceEntry parent, implicit_parent;
                SourceFile file;
@@ -256,6 +562,18 @@ namespace Mono.CSharp {
                Hashtable aliases;
                ArrayList using_clauses;
                public bool DeclarationFound = false;
+               bool UsingFound;
+
+               public readonly DeclSpace SlaveDeclSpace;
+
+               ListDictionary extern_aliases;
+
+               static ArrayList entries = new ArrayList ();
+
+               public static void Reset ()
+               {
+                       entries = new ArrayList ();
+               }
 
                //
                // This class holds the location where a using definition is
@@ -264,16 +582,14 @@ namespace Mono.CSharp {
                // We use this to flag using clauses for namespaces that do not
                // exist.
                //
-               public class UsingEntry {
+               public class UsingEntry : IResolveContext {
                        public readonly MemberName Name;
-                       readonly Expression Expr;
                        readonly NamespaceEntry NamespaceEntry;
                        readonly Location Location;
                        
                        public UsingEntry (NamespaceEntry entry, MemberName name, Location loc)
                        {
                                Name = name;
-                               Expr = name.GetTypeExpression ();
                                NamespaceEntry = entry;
                                Location = loc;
                        }
@@ -285,11 +601,7 @@ namespace Mono.CSharp {
                                if (resolved != null)
                                        return resolved;
 
-                               DeclSpace root = RootContext.Tree.Types;
-                               root.NamespaceEntry = NamespaceEntry;
-                               FullNamedExpression fne = Expr.ResolveAsTypeStep (root.EmitContext, false);
-                               root.NamespaceEntry = null;
-
+                               FullNamedExpression fne = Name.GetTypeExpression ().ResolveAsTypeStep (this, false);
                                if (fne == null) {
                                        Error_NamespaceNotFound (Location, Name.ToString ());
                                        return null;
@@ -297,67 +609,143 @@ namespace Mono.CSharp {
 
                                resolved = fne as Namespace;
                                if (resolved == null) {
+                                       Report.SymbolRelatedToPreviousError (fne.Type);
                                        Report.Error (138, Location,
-                                               "`{0} is a type not a namespace. A using namespace directive can only be applied to namespaces", Name.ToString ());
+                                               "`{0}' is a type not a namespace. A using namespace directive can only be applied to namespaces", Name.ToString ());
                                }
                                return resolved;
                        }
+
+                       DeclSpace IResolveContext.DeclContainer {
+                               get { return NamespaceEntry.SlaveDeclSpace; }
+                       }
+
+                       DeclSpace IResolveContext.GenericDeclContainer {
+                               get { return NamespaceEntry.SlaveDeclSpace; }
+                       }
+
+                       bool IResolveContext.IsInObsoleteScope {
+                               get { return false; }
+                       }
+                       bool IResolveContext.IsInUnsafeScope {
+                               get { return false; }
+                       }
                }
 
-               public class AliasEntry {
+               public abstract class AliasEntry {
                        public readonly string Name;
-                       public readonly Expression Alias;
                        public readonly NamespaceEntry NamespaceEntry;
                        public readonly Location Location;
                        
-                       public AliasEntry (NamespaceEntry entry, string name, MemberName alias, Location loc)
+                       protected AliasEntry (NamespaceEntry entry, string name, Location loc)
                        {
                                Name = name;
-                               Alias = alias.GetTypeExpression ();
                                NamespaceEntry = entry;
                                Location = loc;
                        }
-
-                       FullNamedExpression resolved;
+                       
+                       protected FullNamedExpression resolved;
+                       bool error;
 
                        public FullNamedExpression Resolve ()
                        {
-                               if (resolved != null)
+                               if (resolved != null || error)
                                        return resolved;
+                               resolved = DoResolve ();
+                               if (resolved == null)
+                                       error = true;
+                               return resolved;
+                       }
+
+                       protected abstract FullNamedExpression DoResolve ();
+               }
+
+               public class LocalAliasEntry : AliasEntry, IResolveContext {
+                       public readonly Expression Alias;
+                       
+                       public LocalAliasEntry (NamespaceEntry entry, string name, MemberName alias, Location loc) :
+                               base (entry, name, loc)
+                       {
+                               Alias = alias.GetTypeExpression ();
+                       }
+
+                       protected override FullNamedExpression DoResolve ()
+                       {
+                               resolved = Alias.ResolveAsTypeStep (this, false);
+                               if (resolved == null)
+                                       return null;
+
+                               if (resolved.Type != null) {
+                                       TypeAttributes attr = resolved.Type.Attributes & TypeAttributes.VisibilityMask;
+                                       if (attr == TypeAttributes.NestedPrivate || attr == TypeAttributes.NestedFamily ||
+                                               ((attr == TypeAttributes.NestedFamORAssem || attr == TypeAttributes.NestedAssembly) && 
+                                               TypeManager.LookupDeclSpace (resolved.Type) == null)) {
+                                               Expression.ErrorIsInaccesible (Alias.Location, Alias.ToString ());
+                                               return null;
+                                       }
+                               }
+
+                               return resolved;
+                       }
+
+                       DeclSpace IResolveContext.DeclContainer {
+                               get { return NamespaceEntry.SlaveDeclSpace; }
+                       }
+
+                       DeclSpace IResolveContext.GenericDeclContainer {
+                               get { return NamespaceEntry.SlaveDeclSpace; }
+                       }
+
+                       bool IResolveContext.IsInObsoleteScope {
+                               get { return false; }
+                       }
+                       bool IResolveContext.IsInUnsafeScope {
+                               get { return false; }
+                       }
+               }
+
+               public class ExternAliasEntry : AliasEntry {
+                       public ExternAliasEntry (NamespaceEntry entry, string name, Location loc) :
+                               base (entry, name, loc)
+                       {
+                       }
 
-                               DeclSpace root = RootContext.Tree.Types;
-                               root.NamespaceEntry = NamespaceEntry;
-                               resolved = Alias.ResolveAsTypeStep (root.EmitContext, false);
-                               root.NamespaceEntry = null;
+                       protected override FullNamedExpression DoResolve ()
+                       {
+                               resolved = RootNamespace.GetRootNamespace (Name);
+                               if (resolved == null)
+                                       Report.Error (430, Location, "The extern alias '" + Name +
+                                                                       "' was not specified in a /reference option");
 
                                return resolved;
                        }
                }
 
-               public NamespaceEntry (NamespaceEntry parent, SourceFile file, string name, Location loc)
+               public NamespaceEntry (NamespaceEntry parent, SourceFile file, string name)
                {
                        this.parent = parent;
                        this.file = file;
-                       this.IsImplicit = false;
-                       this.ID = ++next_id;
+                       entries.Add (this);
+                       this.ID = entries.Count;
 
                        if (parent != null)
                                ns = parent.NS.GetNamespace (name, true);
                        else if (name != null)
-                               ns = Namespace.LookupNamespace (name, true);
+                               ns = RootNamespace.Global.GetNamespace (name, true);
                        else
-                               ns = Namespace.Root;
-                       ns.AddNamespaceEntry (this);
+                               ns = RootNamespace.Global;
+                       SlaveDeclSpace = new RootDeclSpace (this);
                }
 
-
-               private NamespaceEntry (NamespaceEntry parent, SourceFile file, Namespace ns)
+               private NamespaceEntry (NamespaceEntry parent, SourceFile file, Namespace ns, bool slave)
                {
                        this.parent = parent;
                        this.file = file;
+                       // no need to add self to 'entries', since we don't have any aliases or using entries.
+                       this.ID = -1;
                        this.IsImplicit = true;
-                       this.ID = ++next_id;
                        this.ns = ns;
+                       this.SlaveDeclSpace = slave ? new RootDeclSpace (this) : null;
                }
 
                //
@@ -374,12 +762,11 @@ namespace Mono.CSharp {
                NamespaceEntry Doppelganger {
                        get {
                                if (!IsImplicit && doppelganger == null)
-                                       doppelganger = new NamespaceEntry (ImplicitParent, file, ns);
+                                       doppelganger = new NamespaceEntry (ImplicitParent, file, ns, true);
                                return doppelganger;
                        }
                }
 
-               static int next_id = 0;
                public readonly int ID;
                public readonly bool IsImplicit;
 
@@ -398,7 +785,7 @@ namespace Mono.CSharp {
                                if (implicit_parent == null) {
                                        implicit_parent = (parent.NS == ns.Parent)
                                                ? parent
-                                               : new NamespaceEntry (parent, file, ns.Parent);
+                                               : new NamespaceEntry (parent, file, ns.Parent, false);
                                }
                                return implicit_parent;
                        }
@@ -414,6 +801,8 @@ namespace Mono.CSharp {
                                return;
                        }
 
+                       UsingFound = true;
+
                        if (name.Equals (ns.MemberName))
                                return;
                        
@@ -422,13 +811,11 @@ namespace Mono.CSharp {
 
                        foreach (UsingEntry old_entry in using_clauses) {
                                if (name.Equals (old_entry.Name)) {
-                                       if (RootContext.WarningLevel >= 3)
-                                               Report.Warning (105, loc, "The using directive for `{0}' appeared previously in this namespace", name);
+                                       Report.Warning (105, 3, loc, "The using directive for `{0}' appeared previously in this namespace", name.GetName ());
                                        return;
                                }
                        }
 
-
                        UsingEntry ue = new UsingEntry (Doppelganger, name, loc);
                        using_clauses.Add (ue);
                }
@@ -440,23 +827,96 @@ namespace Mono.CSharp {
                                return;
                        }
 
+                       UsingFound = true;
+
                        if (aliases == null)
                                aliases = new Hashtable ();
 
                        if (aliases.Contains (name)) {
-                               AliasEntry ae = (AliasEntry)aliases [name];
+                               AliasEntry ae = (AliasEntry) aliases [name];
                                Report.SymbolRelatedToPreviousError (ae.Location, ae.Name);
-                               Report.Error (1537, loc, "The using alias `" + name +
-                                             "' appeared previously in this namespace");
+                               Report.Error (1537, loc, "The using alias `{0}' appeared previously in this namespace", name);
                                return;
                        }
 
                        if (RootContext.Version == LanguageVersion.Default &&
                            name == "global" && RootContext.WarningLevel >= 2)
-                               Report.Warning (440, loc, "An alias named `global' will not be used when resolving 'global::';" +
+                               Report.Warning (440, 2, loc, "An alias named `global' will not be used when resolving 'global::';" +
                                        " the global namespace will be used instead");
 
-                       aliases [name] = new AliasEntry (Doppelganger, name, alias, loc);
+                       // FIXME: get correct error number.  See if the above check can be merged
+                       if (extern_aliases != null && extern_aliases.Contains (name)) {
+                               AliasEntry ae = (AliasEntry) extern_aliases [name];
+                               Report.SymbolRelatedToPreviousError (ae.Location, ae.Name);
+                               Report.Error (1537, loc, "The using alias `{0}' appeared previously in this namespace", name);
+                               return;
+                       }
+
+                       aliases [name] = new LocalAliasEntry (Doppelganger, name, alias, loc);
+               }
+
+               public void UsingExternalAlias (string name, Location loc)
+               {
+                       if (UsingFound || DeclarationFound) {
+                               Report.Error (439, loc, "An extern alias declaration must precede all other elements");
+                               return;
+                       }
+                       
+                       // Share the extern_aliases field with the Doppelganger
+                       if (extern_aliases == null) {
+                               extern_aliases = new ListDictionary ();
+                               Doppelganger.extern_aliases = extern_aliases;
+                       }
+
+                       if (extern_aliases.Contains (name)) {
+                               AliasEntry ae = (AliasEntry) extern_aliases [name];
+                               Report.SymbolRelatedToPreviousError (ae.Location, ae.Name);
+                               Report.Error (1537, loc, "The using alias `{0}' appeared previously in this namespace", name);
+                               return;
+                       }
+
+                       if (name == "global") {
+                               Error_GlobalNamespaceRedefined (loc);
+                               return;
+                       }
+
+                       // Register the alias in aliases and extern_aliases, since we need both of them
+                       // to keep things simple (different resolution scenarios)
+                       ExternAliasEntry alias = new ExternAliasEntry (Doppelganger, name, loc);
+                       extern_aliases [name] = alias;
+               }
+
+               ///
+               /// Does extension methods look up to find a method which matches name and extensionType.
+               /// Search starts from this namespace and continues hierarchically up to top level.
+               ///
+               public ExtensionMethodGroupExpr LookupExtensionMethod (Type extensionType, bool fullLookup, string name)
+               {
+                       ArrayList candidates = null;
+                       if (fullLookup) {
+                               candidates = ns.LookupExtensionMethod (extensionType, name, this);
+                               if (candidates != null)
+                                       return new ExtensionMethodGroupExpr (candidates, this, false, extensionType, Location.Null);
+                       }
+
+                       foreach (Namespace n in GetUsingTable ()) {
+                               ArrayList a = n.LookupExtensionMethod (extensionType, name, this);
+                               if (a == null)
+                                       continue;
+
+                               if (candidates == null)
+                                       candidates = a;
+                               else
+                                       candidates.AddRange (a);
+                       }
+
+                       if (candidates != null)
+                               return new ExtensionMethodGroupExpr (candidates, parent, true, extensionType, Location.Null);
+
+                       if (parent == null)
+                               return null;
+
+                       return parent.LookupExtensionMethod (extensionType, true, name);
                }
 
                public FullNamedExpression LookupNamespaceOrType (DeclSpace ds, string name, Location loc, bool ignore_cs0104)
@@ -480,16 +940,13 @@ namespace Mono.CSharp {
                public FullNamedExpression LookupAlias (string name)
                {
                        AliasEntry entry = null;
-                       // We use Parent rather than ImplicitParent since we know implicit namespace declarations
-                       // cannot have using entries.
-                       for (NamespaceEntry n = this; n != null; n = n.Parent) {
-                               if (n.aliases == null)
-                                       continue;
-                               entry = n.aliases [name] as AliasEntry;
-                               if (entry != null)
-                                       return entry.Resolve ();
+                       for (NamespaceEntry n = this; n != null; n = n.ImplicitParent) {
+                               if (n.extern_aliases != null && (entry = n.extern_aliases [name] as AliasEntry) != null)
+                                       break;
+                               if (n.aliases != null && (entry = n.aliases [name] as AliasEntry) != null)
+                                       break;
                        }
-                       return null;
+                       return entry == null ? null : entry.Resolve ();
                }
 
                private FullNamedExpression Lookup (DeclSpace ds, string name, Location loc, bool ignore_cs0104)
@@ -497,15 +954,21 @@ namespace Mono.CSharp {
                        //
                        // Check whether it's in the namespace.
                        //
-                       FullNamedExpression fne = NS.Lookup (ds, name, loc);
+                       FullNamedExpression fne = ns.Lookup (ds, name, loc);
                        if (fne != null)
                                return fne;
 
+                       if (extern_aliases != null) {
+                               AliasEntry entry = extern_aliases [name] as AliasEntry;
+                               if (entry != null)
+                                       return entry.Resolve ();
+                       }
+                       
                        if (IsImplicit)
                                return null;
-
+                       
                        //
-                       // Check aliases.
+                       // Check aliases. 
                        //
                        if (aliases != null) {
                                AliasEntry entry = aliases [name] as AliasEntry;
@@ -533,7 +996,7 @@ namespace Mono.CSharp {
                }
 
                // Our cached computation.
-               readonly Namespace [] empty_namespaces = new Namespace [0];
+               static readonly Namespace [] empty_namespaces = new Namespace [0];
                Namespace [] namespace_using_table;
                Namespace [] GetUsingTable ()
                {
@@ -560,32 +1023,24 @@ namespace Mono.CSharp {
                        return namespace_using_table;
                }
 
-               readonly string [] empty_using_list = new string [0];
+               static readonly string [] empty_using_list = new string [0];
 
-               public void DefineNamespace (SymbolWriter symwriter)
-               {
-                       if (symfile_id != 0)
-                               return;
-                       if (parent != null)
-                               parent.DefineNamespace (symwriter);
-
-                       string [] using_list = empty_using_list;
-                       if (using_clauses != null) {
-                               using_list = new string [using_clauses.Count];
-                               for (int i = 0; i < using_clauses.Count; i++)
-                                       using_list [i] = ((UsingEntry) using_clauses [i]).Name.ToString ();
-                       } 
+               public int SymbolFileID {
+                       get {
+                               if (symfile_id == 0 && file.SourceFileEntry != null) {
+                                       int parent_id = parent == null ? 0 : parent.SymbolFileID;
 
-                       int parent_id = parent != null ? parent.symfile_id : 0;
-                       if (file.SourceFileEntry == null)
-                               return;
+                                       string [] using_list = empty_using_list;
+                                       if (using_clauses != null) {
+                                               using_list = new string [using_clauses.Count];
+                                               for (int i = 0; i < using_clauses.Count; i++)
+                                                       using_list [i] = ((UsingEntry) using_clauses [i]).Name.ToString ();
+                                       }
 
-                       symfile_id = symwriter.DefineNamespace (
-                               ns.Name, file.SourceFileEntry, using_list, parent_id);
-               }
-
-               public int SymbolFileID {
-                       get { return symfile_id; }
+                                       symfile_id = CodeGen.SymbolWriter.DefineNamespace (ns.Name, file.SourceFileEntry, using_list, parent_id);
+                               }
+                               return symfile_id;
+                       }
                }
 
                static void MsgtryRef (string s)
@@ -598,6 +1053,11 @@ namespace Mono.CSharp {
                        Console.WriteLine ("    Try using -pkg:" + s);
                }
 
+               public static void Error_GlobalNamespaceRedefined (Location loc)
+               {
+                       Report.Error (1681, loc, "You cannot redefine the global extern alias");
+               }
+
                public static void Error_NamespaceNotFound (Location loc, string name)
                {
                        Report.Error (246, loc, "The type or namespace name `{0}' could not be found. Are you missing a using directive or an assembly reference?",
@@ -630,36 +1090,42 @@ namespace Mono.CSharp {
                ///   Used to validate that all the using clauses are correct
                ///   after we are finished parsing all the files.  
                /// </summary>
-               public void VerifyUsing ()
+               void VerifyUsing ()
                {
+                       if (extern_aliases != null) {
+                               foreach (DictionaryEntry de in extern_aliases)
+                                       ((AliasEntry) de.Value).Resolve ();
+                       }               
+
                        if (using_clauses != null) {
                                foreach (UsingEntry ue in using_clauses)
                                        ue.Resolve ();
                        }
 
                        if (aliases != null) {
-                               foreach (DictionaryEntry de in aliases) {
-                                       AliasEntry alias = (AliasEntry) de.Value;
-                                       if (alias.Resolve () == null)
-                                               Error_NamespaceNotFound (alias.Location, alias.Alias.ToString ());
-                               }
+                               foreach (DictionaryEntry de in aliases)
+                                       ((AliasEntry) de.Value).Resolve ();
                        }
                }
 
+               /// <summary>
+               ///   Used to validate that all the using clauses are correct
+               ///   after we are finished parsing all the files.  
+               /// </summary>
+               static public void VerifyAllUsing ()
+               {
+                       foreach (NamespaceEntry entry in entries)
+                               entry.VerifyUsing ();
+               }
+
                public string GetSignatureForError ()
                {
-                       if (NS == Namespace.Root)
-                               return "::global";
-                       else
-                               return ns.Name;
+                       return ns.GetSignatureForError ();
                }
 
                public override string ToString ()
                {
-                       if (NS == Namespace.Root)
-                               return "NamespaceEntry (<root>)";
-                       else
-                               return String.Format ("NamespaceEntry ({0},{1},{2})", ns.Name, IsImplicit, ID);
+                       return ns.ToString ();
                }
        }
 }