source: trunk/HeuristicLab.ExtLibs/HeuristicLab.NRefactory/5.5.0/NRefactory.CSharp-5.5.0/Parser/mcs/namespace.cs @ 17197

//
// namespace.cs: Tracks namespaces
//
// Author:
//   Miguel de Icaza (miguel@ximian.com)
//   Marek Safar (marek.safar@seznam.cz)
//
// Copyright 2001 Ximian, Inc.
// Copyright 2003-2008 Novell, Inc.
// Copyright 2011 Xamarin Inc
//
using System;
using System.Collections.Generic;
using System.Linq;
using Mono.CompilerServices.SymbolWriter;

namespace Mono.CSharp {

  public class RootNamespace : Namespace {

    readonly string alias_name;
    readonly Dictionary<string, Namespace> all_namespaces;

    public RootNamespace (string alias_name)
      : base ()
    {
      this.alias_name = alias_name;
      RegisterNamespace (this);

      all_namespaces = new Dictionary<string, Namespace> ();
      all_namespaces.Add ("", this);
    }

    public string Alias {
      get {
        return alias_name;
      }
    }

    public static void Error_GlobalNamespaceRedefined (Report report, Location loc)
    {
      report.Error (1681, loc, "The global extern alias cannot be redefined");
    }

    //
    // For better error reporting where we try to guess missing using directive
    //
    public List<string> FindTypeNamespaces (IMemberContext ctx, string name, int arity)
    {
      List<string> res = null;

      foreach (var ns in all_namespaces) {
        var type = ns.Value.LookupType (ctx, name, arity, LookupMode.Normal, Location.Null);
        if (type != null) {
          if (res == null)
            res = new List<string> ();

          res.Add (ns.Key);
        }
      }

      return res;
    }

    //
    // For better error reporting where compiler tries to guess missing using directive
    //
    public List<string> FindExtensionMethodNamespaces (IMemberContext ctx, string name, int arity)
    {
      List<string> res = null;

      foreach (var ns in all_namespaces) {
        var methods = ns.Value.LookupExtensionMethod (ctx, name, arity);
        if (methods != null) {
          if (res == null)
            res = new List<string> ();

          res.Add (ns.Key);
        }
      }

      return res;
    }

    public void RegisterNamespace (Namespace child)
    {
      if (child != this)
        all_namespaces.Add (child.Name, child);
    }

    public override string GetSignatureForError ()
    {
      return alias_name + "::";
    }
  }

  public sealed class GlobalRootNamespace : RootNamespace
  {
    public GlobalRootNamespace ()
      : base ("global")
    {
    }
  }

  //
  // Namespace cache for imported and compiled namespaces
  //
  public class Namespace
  {
    readonly Namespace parent;
    string fullname;
    protected Dictionary<string, Namespace> namespaces;
    protected Dictionary<string, IList<TypeSpec>> types;
    List<TypeSpec> extension_method_types;
    Dictionary<string, TypeSpec> cached_types;
    bool cls_checked;

    /// <summary>
    ///   Constructor Takes the current namespace and the
    ///   name.  This is bootstrapped with parent == null
    ///   and name = ""
    /// </summary>
    public Namespace (Namespace parent, string name)
      : this ()
    {
      if (name == null)
        throw new ArgumentNullException ("name");

      this.parent = parent;

      string pname = parent != null ? parent.fullname : null;
        
      if (pname == null)
        fullname = name;
      else
        fullname = pname + "." + name;

      while (parent.parent != null)
        parent = parent.parent;

      var root = parent as RootNamespace;
      if (root == null)
        throw new InternalErrorException ("Root namespaces must be created using RootNamespace");

      root.RegisterNamespace (this);
    }

    protected Namespace ()
    {
      namespaces = new Dictionary<string, Namespace> ();
      cached_types = new Dictionary<string, TypeSpec> ();
    }

    #region Properties

    /// <summary>
    ///   The qualified name of the current namespace
    /// </summary>
    public string Name {
      get { return fullname; }
    }

    /// <summary>
    ///   The parent of this namespace, used by the parser to "Pop"
    ///   the current namespace declaration
    /// </summary>
    public Namespace Parent {
      get { return parent; }
    }

    #endregion

    public Namespace AddNamespace (MemberName name)
    {
      var ns_parent = name.Left == null ? this : AddNamespace (name.Left);
      return ns_parent.TryAddNamespace (name.Basename);
    }

    Namespace TryAddNamespace (string name)
    {
      Namespace ns;

      if (!namespaces.TryGetValue (name, out ns)) {
        ns = new Namespace (this, name);
        namespaces.Add (name, ns);
      }

      return ns;
    }

    public bool TryGetNamespace (string name, out Namespace ns)
    {
      return namespaces.TryGetValue (name, out ns);
    }

    // TODO: Replace with CreateNamespace where MemberName is created for the method call
    public Namespace GetNamespace (string name, bool create)
    {
      int pos = name.IndexOf ('.');

      Namespace ns;
      string first;
      if (pos >= 0)
        first = name.Substring (0, pos);
      else
        first = name;

      if (!namespaces.TryGetValue (first, out ns)) {
        if (!create)
          return null;

        ns = new Namespace (this, first);
        namespaces.Add (first, ns);
      }

      if (pos >= 0)
        ns = ns.GetNamespace (name.Substring (pos + 1), create);

      return ns;
    }

    public IList<TypeSpec> GetAllTypes (string name)
    {
      IList<TypeSpec> found;
      if (types == null || !types.TryGetValue (name, out found))
        return null;

      return found;
    }

    public virtual string GetSignatureForError ()
    {
      return fullname;
    }

    public TypeSpec LookupType (IMemberContext ctx, string name, int arity, LookupMode mode, Location loc)
    {
      if (types == null)
        return null;

      TypeSpec best = null;
      if (arity == 0 && cached_types.TryGetValue (name, out best)) {
        if (best != null || mode != LookupMode.IgnoreAccessibility)
          return best;
      }

      IList<TypeSpec> found;
      if (!types.TryGetValue (name, out found))
        return null;

      foreach (var ts in found) {
        if (ts.Arity == arity || mode == LookupMode.NameOf) {
          if (best == null) {
            if ((ts.Modifiers & Modifiers.INTERNAL) != 0 && !ts.MemberDefinition.IsInternalAsPublic (ctx.Module.DeclaringAssembly) && mode != LookupMode.IgnoreAccessibility)
              continue;

            best = ts;
            continue;
          }

          if (best.MemberDefinition.IsImported && ts.MemberDefinition.IsImported) {
            if (ts.Kind == MemberKind.MissingType)
              continue;

            if (best.Kind == MemberKind.MissingType) {
              best = ts;
              continue;
            }

            if (mode == LookupMode.Normal) {
              ctx.Module.Compiler.Report.SymbolRelatedToPreviousError (best);
              ctx.Module.Compiler.Report.SymbolRelatedToPreviousError (ts);
              ctx.Module.Compiler.Report.Error (433, loc, "The imported type `{0}' is defined multiple times", ts.GetSignatureForError ());
            }

            break;
          }

          if (best.MemberDefinition.IsImported)
            best = ts;

          if ((best.Modifiers & Modifiers.INTERNAL) != 0 && !best.MemberDefinition.IsInternalAsPublic (ctx.Module.DeclaringAssembly))
            continue;

          if (mode != LookupMode.Normal)
            continue;

          if (ts.MemberDefinition.IsImported) {
            ctx.Module.Compiler.Report.SymbolRelatedToPreviousError (best);
            ctx.Module.Compiler.Report.SymbolRelatedToPreviousError (ts);
          }

          ctx.Module.Compiler.Report.Warning (436, 2, loc,
            "The type `{0}' conflicts with the imported type of same name'. Ignoring the imported type definition",
            best.GetSignatureForError ());
        }

        //
        // Lookup for the best candidate with the closest arity match
        //
        if (arity < 0) {
          if (best == null) {
            best = ts;
          } else if (System.Math.Abs (ts.Arity + arity) < System.Math.Abs (best.Arity + arity)) {
            best = ts;
          }
        }
      }

      // TODO MemberCache: Cache more
      if (arity == 0 && mode == LookupMode.Normal)
        cached_types.Add (name, best);

      if (best != null) {
        var dep = best.GetMissingDependencies ();
        if (dep != null)
          ImportedTypeDefinition.Error_MissingDependency (ctx, dep, loc);
      }

      return best;
    }

    public FullNamedExpression LookupTypeOrNamespace (IMemberContext ctx, string name, int arity, LookupMode mode, Location loc)
    {
      var texpr = LookupType (ctx, name, arity, mode, loc);

      Namespace ns;
      if (arity == 0 && namespaces.TryGetValue (name, out ns)) {
        if (texpr == null)
          return new NamespaceExpression (ns, loc);

        if (mode != LookupMode.Probing) {
          //ctx.Module.Compiler.Report.SymbolRelatedToPreviousError (texpr.Type);
          // ctx.Module.Compiler.Report.SymbolRelatedToPreviousError (ns.loc, "");
          ctx.Module.Compiler.Report.Warning (437, 2, loc,
            "The type `{0}' conflicts with the imported namespace `{1}'. Using the definition found in the source file",
            texpr.GetSignatureForError (), ns.GetSignatureForError ());
        }

        if (texpr.MemberDefinition.IsImported)
          return new NamespaceExpression (ns, loc);
      }

      if (texpr == null)
        return null;

      return new TypeExpression (texpr, loc);
    }

    //
    // Completes types with the given `prefix'
    //
    public IEnumerable<string> CompletionGetTypesStartingWith (string prefix)
    {
      if (types == null)
        return Enumerable.Empty<string> ();

      var res = from item in types
            where item.Key.StartsWith (prefix) && item.Value.Any (l => (l.Modifiers & Modifiers.PUBLIC) != 0)
            select item.Key;

      if (namespaces != null)
        res = res.Concat (from item in namespaces where item.Key.StartsWith (prefix) select item.Key);

      return res;
    }

    // 
    // Looks for extension method in this namespace
    //
    public List<MethodSpec> LookupExtensionMethod (IMemberContext invocationContext, string name, int arity)
    {
      if (extension_method_types == null)
        return null;

      List<MethodSpec> found = null;
      for (int i = 0; i < extension_method_types.Count; ++i) {
        var ts = extension_method_types[i];

        //
        // When the list was built we didn't know what members the type
        // contains
        //
        if ((ts.Modifiers & Modifiers.METHOD_EXTENSION) == 0) {
          if (extension_method_types.Count == 1) {
            extension_method_types = null;
            return found;
          }

          extension_method_types.RemoveAt (i--);
          continue;
        }

        var res = ts.MemberCache.FindExtensionMethods (invocationContext, name, arity);
        if (res == null)
          continue;

        if (found == null) {
          found = res;
        } else {
          found.AddRange (res);
        }
      }

      return found;
    }

    public void AddType (ModuleContainer module, TypeSpec ts)
    {
      if (types == null) {
        types = new Dictionary<string, IList<TypeSpec>> (64);
      }

      if (ts.IsClass && ts.Arity == 0) {
        var extension_method_allowed = ts.MemberDefinition.IsImported ? (ts.Modifiers & Modifiers.METHOD_EXTENSION) != 0 : (ts.IsStatic || ts.MemberDefinition.IsPartial);
        if (extension_method_allowed) {
          if (extension_method_types == null)
            extension_method_types = new List<TypeSpec> ();

          extension_method_types.Add (ts);
        }
      }

      var name = ts.Name;
      IList<TypeSpec> existing;
      if (types.TryGetValue (name, out existing)) {
        TypeSpec better_type;
        TypeSpec found;
        if (existing.Count == 1) {
          found = existing[0];
          if (ts.Arity == found.Arity) {
            better_type = IsImportedTypeOverride (module, ts, found);
            if (better_type == found)
              return;

            if (better_type != null) {
              existing [0] = better_type;
              return;
            }
          }

          existing = new List<TypeSpec> ();
          existing.Add (found);
          types[name] = existing;
        } else {
          for (int i = 0; i < existing.Count; ++i) {
            found = existing[i];
            if (ts.Arity != found.Arity)
              continue;

            better_type = IsImportedTypeOverride (module, ts, found);
            if (better_type == found)
              return;

            if (better_type != null) {
              existing.RemoveAt (i);
              --i;
              continue;
            }
          }
        }

        existing.Add (ts);
      } else {
        types.Add (name, new TypeSpec[] { ts });
      }
    }

    //
    // We import any types but in the situation there are same types
    // but one has better visibility (either public or internal with friend)
    // the less visible type is removed from the namespace cache
    //
    public static TypeSpec IsImportedTypeOverride (ModuleContainer module, TypeSpec ts, TypeSpec found)
    {
      var ts_accessible = (ts.Modifiers & Modifiers.PUBLIC) != 0 || ts.MemberDefinition.IsInternalAsPublic (module.DeclaringAssembly);
      var found_accessible = (found.Modifiers & Modifiers.PUBLIC) != 0 || found.MemberDefinition.IsInternalAsPublic (module.DeclaringAssembly);

      if (ts_accessible && !found_accessible)
        return ts;

      // found is better always better for accessible or inaccessible ts
      if (!ts_accessible)
        return found;

      return null;
    }

    public void RemoveContainer (TypeContainer tc)
    {
      types.Remove (tc.Basename);
      cached_types.Remove (tc.Basename);
    }

    public void SetBuiltinType (BuiltinTypeSpec pts)
    {
      var found = types[pts.Name];
      cached_types.Remove (pts.Name);
      if (found.Count == 1) {
        types[pts.Name][0] = pts;
      } else {
        throw new NotImplementedException ();
      }
    }

    public void VerifyClsCompliance ()
    {
      if (types == null || cls_checked)
        return;

      cls_checked = true;

      // TODO: This is quite ugly way to check for CLS compliance at namespace level

      var locase_types = new Dictionary<string, List<TypeSpec>> (StringComparer.OrdinalIgnoreCase);
      foreach (var tgroup in types.Values) {
        foreach (var tm in tgroup) {
          if ((tm.Modifiers & Modifiers.PUBLIC) == 0 || !tm.IsCLSCompliant ())
            continue;

          List<TypeSpec> found;
          if (!locase_types.TryGetValue (tm.Name, out found)) {
            found = new List<TypeSpec> ();
            locase_types.Add (tm.Name, found);
          }

          found.Add (tm);
        }
      }

      foreach (var locase in locase_types.Values) {
        if (locase.Count < 2)
          continue;

        bool all_same = true;
        foreach (var notcompliant in locase) {
          all_same = notcompliant.Name == locase[0].Name;
          if (!all_same)
            break;
        }

        if (all_same)
          continue;

        TypeContainer compiled = null;
        foreach (var notcompliant in locase) {
          if (!notcompliant.MemberDefinition.IsImported) {
            if (compiled != null)
              compiled.Compiler.Report.SymbolRelatedToPreviousError (compiled);

            compiled = notcompliant.MemberDefinition as TypeContainer;
          } else {
            compiled.Compiler.Report.SymbolRelatedToPreviousError (notcompliant);
          }
        }

        compiled.Compiler.Report.Warning (3005, 1, compiled.Location,
          "Identifier `{0}' differing only in case is not CLS-compliant", compiled.GetSignatureForError ());
      }
    }
  }

  public class CompilationSourceFile : NamespaceContainer
  {
    readonly SourceFile file;
    CompileUnitEntry comp_unit;
    Dictionary<string, SourceFile> include_files;
    Dictionary<string, bool> conditionals;

    public CompilationSourceFile (ModuleContainer parent, SourceFile sourceFile)
      : this (parent)
    {
      this.file = sourceFile;
    }

    public CompilationSourceFile (ModuleContainer parent)
      : base (parent)
    {
    }

    public CompileUnitEntry SymbolUnitEntry {
      get {
        return comp_unit;
      }
    }

    public IDictionary<string, bool> Conditionals {
      get {
        return conditionals ?? new Dictionary<string, bool> ();
      }
    }

    public string FileName {
      get {
        return file.Name;
      }
    }

    public SourceFile SourceFile {
      get {
        return file;
      }
    }

    public void AddIncludeFile (SourceFile file)
    {
      if (file == this.file)
        return;

      if (include_files == null)
        include_files = new Dictionary<string, SourceFile> ();

      if (!include_files.ContainsKey (file.FullPathName))
        include_files.Add (file.FullPathName, file);
    }

    public void AddDefine (string value)
    {
      if (conditionals == null)
        conditionals = new Dictionary<string, bool> (2);

      conditionals[value] = true;
    }

    public void AddUndefine (string value)
    {
      if (conditionals == null)
        conditionals = new Dictionary<string, bool> (2);

      conditionals[value] = false;
    }

    public override void PrepareEmit ()
    {
      var sw = Module.DeclaringAssembly.SymbolWriter;
      if (sw != null) {
        CreateUnitSymbolInfo (sw);
      }

      base.PrepareEmit ();
    }

    //
    // Creates symbol file index in debug symbol file
    //
    void CreateUnitSymbolInfo (MonoSymbolFile symwriter)
    {
      var si = file.CreateSymbolInfo (symwriter);
      comp_unit = new CompileUnitEntry (symwriter, si);

      if (include_files != null) {
        foreach (SourceFile include in include_files.Values) {
          si = include.CreateSymbolInfo (symwriter);
          comp_unit.AddFile (si);
        }
      }
    }

    public bool IsConditionalDefined (string value)
    {
      if (conditionals != null) {
        bool res;
        if (conditionals.TryGetValue (value, out res))
          return res;

        // When conditional was undefined
        if (conditionals.ContainsKey (value))
          return false;
      }

      return Compiler.Settings.IsConditionalSymbolDefined (value);
    }

    public override void Accept (StructuralVisitor visitor)
    {
      visitor.Visit (this);
    }
  }


  //
  // Namespace block as created by the parser
  //
  public class NamespaceContainer : TypeContainer, IMemberContext
  {
    static readonly Namespace[] empty_namespaces = new Namespace[0];

    readonly Namespace ns;

    public new readonly NamespaceContainer Parent;

    List<UsingNamespace> clauses;

    // Used by parsed to check for parser errors
    public bool DeclarationFound;

    Namespace[] namespace_using_table;
    TypeSpec[] types_using_table;
    Dictionary<string, UsingAliasNamespace> aliases;
    public readonly MemberName RealMemberName;

    public NamespaceContainer (MemberName name, NamespaceContainer parent)
      : base (parent, name, null, MemberKind.Namespace)
    {
      this.RealMemberName = name;
      this.Parent = parent;
      this.ns = parent.NS.AddNamespace (name);

      containers = new List<TypeContainer> ();
    }

    protected NamespaceContainer (ModuleContainer parent)
      : base (parent, null, null, MemberKind.Namespace)
    {
      ns = parent.GlobalRootNamespace;
      containers = new List<TypeContainer> (2);
    }

    #region Properties

    public override AttributeTargets AttributeTargets {
      get {
        throw new NotSupportedException ();
      }
    }

    public override string DocCommentHeader {
      get {
        throw new NotSupportedException ();
      }
    }

    public Namespace NS {
      get {
        return ns;
      }
    }

    public List<UsingNamespace> Usings {
      get {
        return clauses;
      }
    }

    public override string[] ValidAttributeTargets {
      get {
        throw new NotSupportedException ();
      }
    }

    #endregion

    public void AddUsing (UsingNamespace un)
    {
      if (DeclarationFound){
        Compiler.Report.Error (1529, un.Location, "A using clause must precede all other namespace elements except extern alias declarations");
      }

      if (clauses == null)
        clauses = new List<UsingNamespace> ();

      clauses.Add (un);
    }

    public void AddUsing (UsingAliasNamespace un)
    {
      if (DeclarationFound){
        Compiler.Report.Error (1529, un.Location, "A using clause must precede all other namespace elements except extern alias declarations");
      }

      AddAlias (un);
    }

    void AddAlias (UsingAliasNamespace un)
    {
      if (clauses == null) {
        clauses = new List<UsingNamespace> ();
      } else {
        foreach (var entry in clauses) {
          var a = entry as UsingAliasNamespace;
          if (a != null && a.Alias.Value == un.Alias.Value) {
            Compiler.Report.SymbolRelatedToPreviousError (a.Location, "");
            Compiler.Report.Error (1537, un.Location,
              "The using alias `{0}' appeared previously in this namespace", un.Alias.Value);
          }
        }
      }

      clauses.Add (un);
    }

    public override void AddPartial (TypeDefinition next_part)
    {
      var existing = ns.LookupType (this, next_part.MemberName.Name, next_part.MemberName.Arity, LookupMode.Probing, Location.Null);
      var td = existing != null ? existing.MemberDefinition as TypeDefinition : null;
      AddPartial (next_part, td);
    }

    public override void AddTypeContainer (TypeContainer tc)
    {
      string name = tc.Basename;

      var mn = tc.MemberName;
      while (mn.Left != null) {
        mn = mn.Left;
        name = mn.Name;
      }

      var names_container = Parent == null ? Module : (TypeContainer) this;

      MemberCore mc;
      if (names_container.DefinedNames.TryGetValue (name, out mc)) {
        if (tc is NamespaceContainer && mc is NamespaceContainer) {
          AddTypeContainerMember (tc);
          return;
        }

        Report.SymbolRelatedToPreviousError (mc);
        if ((mc.ModFlags & Modifiers.PARTIAL) != 0 && (tc is ClassOrStruct || tc is Interface)) {
          Error_MissingPartialModifier (tc);
        } else {
          Report.Error (101, tc.Location, "The namespace `{0}' already contains a definition for `{1}'",
            GetSignatureForError (), mn.GetSignatureForError ());
        }
      } else {
        names_container.DefinedNames.Add (name, tc);

        var tdef = tc.PartialContainer;
        if (tdef != null) {
          //
          // Same name conflict in different namespace containers
          //
          var conflict = ns.GetAllTypes (name);
          if (conflict != null) {
            foreach (var e in conflict) {
              if (e.Arity == mn.Arity) {
                mc = (MemberCore) e.MemberDefinition;
                break;
              }
            }
          }

          if (mc != null) {
            Report.SymbolRelatedToPreviousError (mc);
            Report.Error (101, tc.Location, "The namespace `{0}' already contains a definition for `{1}'",
              GetSignatureForError (), mn.GetSignatureForError ());
          } else {
            ns.AddType (Module, tdef.Definition);
          }
        }
      }

      base.AddTypeContainer (tc);
    }

    public override void ApplyAttributeBuilder (Attribute a, MethodSpec ctor, byte[] cdata, PredefinedAttributes pa)
    {
      throw new NotSupportedException ();
    }

    public override void EmitContainer ()
    {
      VerifyClsCompliance ();

      base.EmitContainer ();
    }

    public ExtensionMethodCandidates LookupExtensionMethod (IMemberContext invocationContext, TypeSpec extensionType, string name, int arity, int position)
    {
      //
      // Here we try to resume the search for extension method at the point
      // where the last bunch of candidates was found. It's more tricky than
      // it seems as we have to check both namespace containers and namespace
      // in correct order.
      //
      // Consider:
      // 
      // namespace A {
      //  using N1;
      //  namespace B.C.D {
      //    <our first search found candidates in A.B.C.D
      //  }
      // }
      //
      // In the example above namespace A.B.C.D, A.B.C and A.B have to be
      // checked before we hit A.N1 using
      //
      ExtensionMethodCandidates candidates;
      var container = this;
      do {
        candidates = container.LookupExtensionMethodCandidates (invocationContext, name, arity, ref position);
        if (candidates != null || container.MemberName == null)
          return candidates;

        var container_ns = container.ns.Parent;
        var mn = container.MemberName.Left;
        int already_checked = position - 2;
        while (already_checked-- > 0) {
          mn = mn.Left;
          container_ns = container_ns.Parent;
        }

        while (mn != null) {
          ++position;

          var methods = container_ns.LookupExtensionMethod (invocationContext, name, arity);
          if (methods != null) {
            return new ExtensionMethodCandidates (invocationContext, methods, container, position);
          }

          mn = mn.Left;
          container_ns = container_ns.Parent;
        }

        position = 0;
        container = container.Parent;
      } while (container != null);

      return null;
    }

    ExtensionMethodCandidates LookupExtensionMethodCandidates (IMemberContext invocationContext, string name, int arity, ref int position)
    {
      List<MethodSpec> candidates = null;

      if (position == 0) {
        ++position;

        candidates = ns.LookupExtensionMethod (invocationContext, name, arity);
        if (candidates != null) {
          return new ExtensionMethodCandidates (invocationContext, candidates, this, position);
        }
      }

      if (position == 1) {
        ++position;

        foreach (Namespace n in namespace_using_table) {
          var a = n.LookupExtensionMethod (invocationContext, name, arity);
          if (a == null)
            continue;

          if (candidates == null)
            candidates = a;
          else
            candidates.AddRange (a);
        }

        if (candidates != null)
          return new ExtensionMethodCandidates (invocationContext, candidates, this, position);
      }

      // LAMESPEC: TODO no spec about priority over normal extension methods yet
      if (types_using_table != null) {
        foreach (var t in types_using_table) {

          var res = t.MemberCache.FindExtensionMethods (invocationContext, name, arity);
          if (res == null)
            continue;

          if (candidates == null)
            candidates = res;
          else
            candidates.AddRange (res);
        }

        if (candidates != null)
          return new ExtensionMethodCandidates (invocationContext, candidates, this, position);
      }

      return null;
    }

    public override FullNamedExpression LookupNamespaceOrType (string name, int arity, LookupMode mode, Location loc)
    {
      //
      // Only simple names (no dots) will be looked up with this function
      //
      FullNamedExpression resolved;
      for (NamespaceContainer container = this; container != null; container = container.Parent) {
        resolved = container.Lookup (name, arity, mode, loc);
        if (resolved != null || container.MemberName == null)
          return resolved;

        var container_ns = container.ns.Parent;
        var mn = container.MemberName.Left;
        while (mn != null) {
          resolved = container_ns.LookupTypeOrNamespace (this, name, arity, mode, loc);
          if (resolved != null)
            return resolved;

          mn = mn.Left;
          container_ns = container_ns.Parent;
        }
      }

      return null;
    }

    public override void GetCompletionStartingWith (string prefix, List<string> results)
    {
      if (Usings == null)
        return;

      foreach (var un in Usings) {
        if (un.Alias != null)
          continue;

        var name = un.NamespaceExpression.Name;
        if (name.StartsWith (prefix))
          results.Add (name);
      }


      IEnumerable<string> all = Enumerable.Empty<string> ();

      foreach (Namespace using_ns in namespace_using_table) {
        if (prefix.StartsWith (using_ns.Name)) {
          int ld = prefix.LastIndexOf ('.');
          if (ld != -1) {
            string rest = prefix.Substring (ld + 1);

            all = all.Concat (using_ns.CompletionGetTypesStartingWith (rest));
          }
        }
        all = all.Concat (using_ns.CompletionGetTypesStartingWith (prefix));
      }

      results.AddRange (all);

      base.GetCompletionStartingWith (prefix, results);
    }

    
    //
    // Looks-up a alias named @name in this and surrounding namespace declarations
    //
    public FullNamedExpression LookupExternAlias (string name)
    {
      if (aliases == null)
        return null;

      UsingAliasNamespace uan;
      if (aliases.TryGetValue (name, out uan) && uan is UsingExternAlias)
        return uan.ResolvedExpression;

      return null;
    }
    
    //
    // Looks-up a alias named @name in this and surrounding namespace declarations
    //
    public override FullNamedExpression LookupNamespaceAlias (string name)
    {
      for (NamespaceContainer n = this; n != null; n = n.Parent) {
        if (n.aliases == null)
          continue;

        UsingAliasNamespace uan;
        if (n.aliases.TryGetValue (name, out uan))
          return uan.ResolvedExpression;
      }

      return null;
    }

    FullNamedExpression Lookup (string name, int arity, LookupMode mode, Location loc)
    {
      //
      // Check whether it's in the namespace.
      //
      FullNamedExpression fne = ns.LookupTypeOrNamespace (this, name, arity, mode, loc);

      //
      // Check aliases. 
      //
      if (aliases != null && arity == 0) {
        UsingAliasNamespace uan;
        if (aliases.TryGetValue (name, out uan)) {
          if (fne != null && mode != LookupMode.Probing) {
            // TODO: Namespace has broken location
            //Report.SymbolRelatedToPreviousError (fne.Location, null);
            Compiler.Report.SymbolRelatedToPreviousError (uan.Location, null);
            Compiler.Report.Error (576, loc,
              "Namespace `{0}' contains a definition with same name as alias `{1}'",
              GetSignatureForError (), name);
          }

          return uan.ResolvedExpression;
        }
      }

      if (fne != null)
        return fne;

      //
      // Lookup can be called before the namespace is defined from different namespace using alias clause
      //
      if (namespace_using_table == null) {
        DoDefineNamespace ();
      }

      //
      // Check using entries.
      //
      FullNamedExpression match = null;
      foreach (Namespace using_ns in namespace_using_table) {
        //
        // A using directive imports only types contained in the namespace, it
        // does not import any nested namespaces
        //
        var t = using_ns.LookupType (this, name, arity, mode, loc);
        if (t == null)
          continue;

        fne = new TypeExpression (t, loc);
        if (match == null) {
          match = fne;
          continue;
        }

        // Prefer types over namespaces
        var texpr_fne = fne as TypeExpr;
        var texpr_match = match as TypeExpr;
        if (texpr_fne != null && texpr_match == null) {
          match = fne;
          continue;
        } else if (texpr_fne == null) {
          continue;
        }

        // It can be top level accessibility only
        var better = Namespace.IsImportedTypeOverride (Module, texpr_match.Type, texpr_fne.Type);
        if (better == null) {
          if (mode == LookupMode.Normal) {
            Compiler.Report.SymbolRelatedToPreviousError (texpr_match.Type);
            Compiler.Report.SymbolRelatedToPreviousError (texpr_fne.Type);
            Compiler.Report.Error (104, loc, "`{0}' is an ambiguous reference between `{1}' and `{2}'",
              name, texpr_match.GetSignatureForError (), texpr_fne.GetSignatureForError ());
          }

          return match;
        }

        if (better == texpr_fne.Type)
          match = texpr_fne;
      }

      return match;
    }

    public static MethodGroupExpr LookupStaticUsings (IMemberContext mc, string name, int arity, Location loc)
    {
      for (var m = mc.CurrentMemberDefinition; m != null; m = m.Parent) {

        var nc = m as NamespaceContainer;
        if (nc == null)
          continue;

        List<MemberSpec> candidates = null;
        if (nc.types_using_table != null) {
          foreach (var using_type in nc.types_using_table) {
            var members = MemberCache.FindMembers (using_type, name, true);
            if (members != null) {
              foreach (var member in members) {
                if ((member.Modifiers & Modifiers.METHOD_EXTENSION) != 0)
                  continue;

                if (arity > 0 && member.Arity != arity)
                  continue;

                if (candidates == null)
                  candidates = new List<MemberSpec> ();

                candidates.Add (member);
              }
            }
          }
        }

        if (candidates != null)
          return new MethodGroupExpr (candidates, null, loc);
      }

      return null;
    }

    protected override void DefineNamespace ()
    {
      if (namespace_using_table == null)
        DoDefineNamespace ();

      base.DefineNamespace ();
    }

    void DoDefineNamespace ()
    {
      namespace_using_table = empty_namespaces;

      if (clauses != null) {
        List<Namespace> namespaces = null;
        List<TypeSpec> types = null;

        bool post_process_using_aliases = false;

        for (int i = 0; i < clauses.Count; ++i) {
          var entry = clauses[i];

          if (entry.Alias != null) {
            if (aliases == null)
              aliases = new Dictionary<string, UsingAliasNamespace> ();

            //
            // Aliases are not available when resolving using section
            // except extern aliases
            //
            if (entry is UsingExternAlias) {
              entry.Define (this);
              if (entry.ResolvedExpression != null)
                aliases.Add (entry.Alias.Value, (UsingExternAlias) entry);

              clauses.RemoveAt (i--);
            } else {
              post_process_using_aliases = true;
            }

            continue;
          }

          entry.Define (this);

          //
          // It's needed for repl only, when using clause cannot be resolved don't hold it in
          // global list which is resolved for each evaluation
          //
          if (entry.ResolvedExpression == null) {
            clauses.RemoveAt (i--);
            continue;
          }

          var using_ns = entry.ResolvedExpression as NamespaceExpression;
          if (using_ns == null) {

            var type = ((TypeExpr)entry.ResolvedExpression).Type;

            if (types == null)
              types = new List<TypeSpec> ();

            if (types.Contains (type)) {
              Warning_DuplicateEntry (entry);
            } else {
              types.Add (type);
            }
          } else {
            if (namespaces == null)
              namespaces = new List<Namespace> ();

            if (namespaces.Contains (using_ns.Namespace)) {
              // Ensure we don't report the warning multiple times in repl
              clauses.RemoveAt (i--);

              Warning_DuplicateEntry (entry);
            } else {
              namespaces.Add (using_ns.Namespace);
            }
          }
        }

        namespace_using_table = namespaces == null ? new Namespace [0] : namespaces.ToArray ();
        if (types != null)
          types_using_table = types.ToArray ();

        if (post_process_using_aliases) {
          for (int i = 0; i < clauses.Count; ++i) {
            var entry = clauses[i];
            if (entry.Alias != null) {
              entry.Define (this);
              if (entry.ResolvedExpression != null) {
                aliases.Add (entry.Alias.Value, (UsingAliasNamespace) entry);
              }

              clauses.RemoveAt (i--);
            }
          }
        }
      }
    }

    public void EnableRedefinition ()
    {
      is_defined = false;
      namespace_using_table = null;
    }

    internal override void GenerateDocComment (DocumentationBuilder builder)
    {
      if (containers != null) {
        foreach (var tc in containers)
          tc.GenerateDocComment (builder);
      }
    }

    public override string GetSignatureForError ()
    {
      return MemberName == null ? "global::" : base.GetSignatureForError ();
    }

    public override void RemoveContainer (TypeContainer cont)
    {
      base.RemoveContainer (cont);
      NS.RemoveContainer (cont);
    }

    protected override bool VerifyClsCompliance ()
    {
      if (Module.IsClsComplianceRequired ()) {
        if (MemberName != null && MemberName.Name[0] == '_') {
          Warning_IdentifierNotCompliant ();
        }

        ns.VerifyClsCompliance ();
        return true;
      }

      return false;
    }

    void Warning_DuplicateEntry (UsingNamespace entry)
    {
      Compiler.Report.Warning (105, 3, entry.Location,
        "The using directive for `{0}' appeared previously in this namespace",
        entry.ResolvedExpression.GetSignatureForError ());
    }

    public override void Accept (StructuralVisitor visitor)
    {
      visitor.Visit (this);
    }
  }

  public class UsingNamespace
  {
    readonly ATypeNameExpression expr;
    readonly Location loc;
    protected FullNamedExpression resolved;

    public UsingNamespace (ATypeNameExpression expr, Location loc)
    {
      this.expr = expr;
      this.loc = loc;
    }

    #region Properties

    public virtual SimpleMemberName Alias {
      get {
        return null;
      }
    }

    public Location Location {
      get {
        return loc;
      }
    }

    public ATypeNameExpression NamespaceExpression  {
      get {
        return expr;
      }
    }

    public FullNamedExpression ResolvedExpression {
      get {
        return resolved;
      }
    }

    #endregion

    public string GetSignatureForError ()
    {
      return expr.GetSignatureForError ();
    }

    public virtual void Define (NamespaceContainer ctx)
    {
      resolved = expr.ResolveAsTypeOrNamespace (ctx, false);
      var ns = resolved as NamespaceExpression;
      if (ns != null)
        return;

      if (resolved != null) {
        var compiler = ctx.Module.Compiler;
        var type = resolved.Type;
        if (compiler.Settings.Version >= LanguageVersion.V_6) {
          if (!type.IsClass || !type.IsStatic) {
            compiler.Report.SymbolRelatedToPreviousError (type);
            compiler.Report.Error (7007, Location,
              "`{0}' is not a static class. A using namespace directive can only be applied to static classes or namespace",
              GetSignatureForError ());
          }

          return;
        }

        compiler.Report.SymbolRelatedToPreviousError (type);
        compiler.Report.Error (138, Location,
          "`{0}' is a type not a namespace. A using namespace directive can only be applied to namespaces",
          GetSignatureForError ());
      }
    }
    
    public virtual void Accept (StructuralVisitor visitor)
    {
      visitor.Visit (this);
    }

    public override string ToString()
    {
      return resolved.ToString();
    }
  }

  public class UsingExternAlias : UsingAliasNamespace
  {
    public UsingExternAlias (SimpleMemberName alias, Location loc)
      : base (alias, null, loc)
    {
    }

    public override void Define (NamespaceContainer ctx)
    {
      var ns = ctx.Module.GetRootNamespace (Alias.Value);
      if (ns == null) {
        ctx.Module.Compiler.Report.Error (430, Location,
          "The extern alias `{0}' was not specified in -reference option",
          Alias.Value);
        return;
      }

      resolved = new NamespaceExpression (ns, Location);
    }
    
    public override void Accept (StructuralVisitor visitor)
    {
      visitor.Visit (this);
    }
  }

  public class UsingAliasNamespace : UsingNamespace
  {
    readonly SimpleMemberName alias;

    public struct AliasContext : IMemberContext
    {
      readonly NamespaceContainer ns;

      public AliasContext (NamespaceContainer ns)
      {
        this.ns = ns;
      }

      public TypeSpec CurrentType {
        get {
          return null;
        }
      }

      public TypeParameters CurrentTypeParameters {
        get {
          return null;
        }
      }

      public MemberCore CurrentMemberDefinition {
        get {
          return null;
        }
      }

      public bool IsObsolete {
        get {
          return false;
        }
      }

      public bool IsUnsafe {
        get {
          throw new NotImplementedException ();
        }
      }

      public bool IsStatic {
        get {
          throw new NotImplementedException ();
        }
      }

      public ModuleContainer Module {
        get {
          return ns.Module;
        }
      }

      public string GetSignatureForError ()
      {
        throw new NotImplementedException ();
      }

      public ExtensionMethodCandidates LookupExtensionMethod (TypeSpec extensionType, string name, int arity)
      {
        return null;
      }

      public FullNamedExpression LookupNamespaceOrType (string name, int arity, LookupMode mode, Location loc)
      {
        var fne = ns.NS.LookupTypeOrNamespace (ns, name, arity, mode, loc);
        if (fne != null)
          return fne;

        //
        // Only extern aliases are allowed in this context
        //
        fne = ns.LookupExternAlias (name);
        if (fne != null || ns.MemberName == null)
          return fne;

        var container_ns = ns.NS.Parent;
        var mn = ns.MemberName.Left;
        while (mn != null) {
          fne = container_ns.LookupTypeOrNamespace (this, name, arity, mode, loc);
          if (fne != null)
            return fne;

          mn = mn.Left;
          container_ns = container_ns.Parent;
        }

        if (ns.Parent != null)
          return ns.Parent.LookupNamespaceOrType (name, arity, mode, loc);

        return null;
      }

      public FullNamedExpression LookupNamespaceAlias (string name)
      {
        return ns.LookupNamespaceAlias (name);
      }
    }

    public UsingAliasNamespace (SimpleMemberName alias, ATypeNameExpression expr, Location loc)
      : base (expr, loc)
    {
      this.alias = alias;
    }

    public override SimpleMemberName Alias {
      get {
        return alias;
      }
    }

    public override void Define (NamespaceContainer ctx)
    {
      //
      // The namespace-or-type-name of a using-alias-directive is resolved as if
      // the immediately containing compilation unit or namespace body had no
      // using-directives. A using-alias-directive may however be affected
      // by extern-alias-directives in the immediately containing compilation
      // unit or namespace body
      //
      // We achieve that by introducing alias-context which redirect any local
      // namespace or type resolve calls to parent namespace
      //
      resolved = NamespaceExpression.ResolveAsTypeOrNamespace (new AliasContext (ctx), false);
    }
    
    public override void Accept (StructuralVisitor visitor)
    {
      visitor.Visit (this);
    }
  }
}