mcs/mcs/namespace.cs

   1 //
   2 // namespace.cs: Tracks namespaces
   3 //
   4 // Author:
   5 //   Miguel de Icaza (miguel@ximian.com)
   6 //   Marek Safar (marek.safar@seznam.cz)
   7 //
   8 // (C) 2001 Ximian, Inc.
   9 //
  10 using System;
  11 using System.Collections;
  12 using System.Collections.Specialized;
  13 using System.Reflection;
  14
  15 namespace Mono.CSharp {
  16
  17         public class RootNamespace : Namespace {
  18                 static MethodInfo get_namespaces_method;
  19
  20                 string alias_name;
  21                 Assembly referenced_assembly;
  22
  23                 Hashtable all_namespaces;
  24
  25                 static Hashtable root_namespaces;
  26                 public static GlobalRootNamespace Global;
  27
  28                 static RootNamespace ()
  29                 {
  30                         get_namespaces_method = typeof (Assembly).GetMethod ("GetNamespaces", BindingFlags.Instance | BindingFlags.NonPublic);
  31
  32                         Reset ();
  33                 }
  34
  35                 public static void Reset ()
  36                 {
  37                         root_namespaces = new Hashtable ();
  38                         Global = new GlobalRootNamespace ();
  39                         root_namespaces ["global"] = Global;
  40                 }
  41
  42                 protected RootNamespace (string alias_name, Assembly assembly)
  43                         : base (null, String.Empty)
  44                 {
  45                         this.alias_name = alias_name;
  46                         referenced_assembly = assembly;
  47
  48                         all_namespaces = new Hashtable ();
  49                         all_namespaces.Add ("", this);
  50
  51                         if (referenced_assembly != null)
  52                                 ComputeNamespaces (this.referenced_assembly);
  53                 }
  54
  55                 public static void DefineRootNamespace (string name, Assembly assembly)
  56                 {
  57                         if (name == "global") {
  58                                 // FIXME: Add proper error number
  59                                 Report.Error (-42, "Cannot define an external alias named `global'");
  60                                 return;
  61                         }
  62                         RootNamespace retval = GetRootNamespace (name);
  63                         if (retval == null || retval.referenced_assembly != assembly)
  64                                 root_namespaces [name] = new RootNamespace (name, assembly);
  65                 }
  66
  67                 public static RootNamespace GetRootNamespace (string name)
  68                 {
  69                         return (RootNamespace) root_namespaces [name];
  70                 }
  71
  72                 public virtual Type LookupTypeReflection (string name, Location loc)
  73                 {
  74                         return GetTypeInAssembly (referenced_assembly, name);
  75                 }
  76
  77                 public void RegisterNamespace (Namespace child)
  78                 {
  79                         if (child != this)
  80                                 all_namespaces.Add (child.Name, child);
  81                 }
  82
  83                 public bool IsNamespace (string name)
  84                 {
  85                         return all_namespaces.Contains (name);
  86                 }
  87
  88                 protected void EnsureNamespace (string dotted_name)
  89                 {
  90                         if (dotted_name != null && dotted_name.Length != 0 && ! IsNamespace (dotted_name))
  91                                 GetNamespace (dotted_name, true);
  92                 }
  93
  94                 protected void ComputeNamespaces (Assembly assembly)
  95                 {
  96                         if (get_namespaces_method != null) {
  97                                 string [] namespaces = (string []) get_namespaces_method.Invoke (assembly, null);
  98                                 foreach (string ns in namespaces)
  99                                         EnsureNamespace (ns);
 100                                 return;
 101                         }
 102
 103                         foreach (Type t in assembly.GetExportedTypes ())
 104                                 EnsureNamespace (t.Namespace);
 105                 }
 106
 107                 protected static Type GetTypeInAssembly (Assembly assembly, string name)
 108                 {
 109                         Type t = assembly.GetType (name);
 110                         if (t == null)
 111                                 return null;
 112
 113                         if (t.IsPointer)
 114                                 throw new InternalErrorException ("Use GetPointerType() to get a pointer");
 115
 116                         TypeAttributes ta = t.Attributes & TypeAttributes.VisibilityMask;
 117                         if (ta == TypeAttributes.NotPublic ||
 118                             ta == TypeAttributes.NestedPrivate ||
 119                             ta == TypeAttributes.NestedAssembly ||
 120                             ta == TypeAttributes.NestedFamANDAssem)
 121                                 return null;
 122
 123                         return t;
 124                 }
 125
 126                 public override string ToString ()
 127                 {
 128                         return String.Format ("RootNamespace ({0}::)", alias_name);
 129                 }
 130
 131                 public override string GetSignatureForError ()
 132                 {
 133                         return alias_name + "::";
 134                 }
 135         }
 136
 137         public class GlobalRootNamespace : RootNamespace {
 138                 Assembly [] assemblies;
 139                 Module [] modules;
 140
 141                 public GlobalRootNamespace ()
 142                         : base ("global", null)
 143                 {
 144                         assemblies = new Assembly [0];
 145                 }
 146
 147                 public Assembly [] Assemblies {
 148                         get { return assemblies; }
 149                 }
 150
 151                 public Module [] Modules {
 152                         get { return modules; }
 153                 }
 154
 155                 public void AddAssemblyReference (Assembly a)
 156                 {
 157                         foreach (Assembly assembly in assemblies) {
 158                                 if (a == assembly)
 159                                         return;
 160                         }
 161
 162                         int top = assemblies.Length;
 163                         Assembly [] n = new Assembly [top + 1];
 164                         assemblies.CopyTo (n, 0);
 165                         n [top] = a;
 166                         assemblies = n;
 167
 168                         ComputeNamespaces (a);
 169                 }
 170
 171                 public void AddModuleReference (Module m)
 172                 {
 173                         int top = modules != null ? modules.Length : 0;
 174                         Module [] n = new Module [top + 1];
 175                         if (modules != null)
 176                                 modules.CopyTo (n, 0);
 177                         n [top] = m;
 178                         modules = n;
 179
 180                         if (m == CodeGen.Module.Builder)
 181                                 return;
 182
 183                         foreach (Type t in m.GetTypes ())
 184                                 EnsureNamespace (t.Namespace);
 185                 }
 186
 187                 public override void Error_NamespaceDoesNotExist(Location loc, string name)
 188                 {
 189                         Report.Error (400, loc, "The type or namespace name `{0}' could not be found in the global namespace (are you missing an assembly reference?)",
 190                                 name);
 191                 }
 192
 193                 public override Type LookupTypeReflection (string name, Location loc)
 194                 {
 195                         Type found_type = null;
 196
 197                         foreach (Assembly a in assemblies) {
 198                                 Type t = GetTypeInAssembly (a, name);
 199                                 if (t == null)
 200                                         continue;
 201
 202                                 if (found_type == null) {
 203                                         found_type = t;
 204                                         continue;
 205                                 }
 206
 207                                 Report.SymbolRelatedToPreviousError (found_type);
 208                                 Report.SymbolRelatedToPreviousError (t);
 209                                 Report.Error (433, loc, "The imported type `{0}' is defined multiple times", name);
 210
 211                                 return found_type;
 212                         }
 213
 214                         if (modules != null) {
 215                                 foreach (Module module in modules) {
 216                                         Type t = module.GetType (name);
 217                                         if (t == null)
 218                                                 continue;
 219
 220                                         if (found_type == null) {
 221                                                 found_type = t;
 222                                                 continue;
 223                                         }
 224
 225                                         Report.SymbolRelatedToPreviousError (t);
 226                                         Report.SymbolRelatedToPreviousError (found_type);
 227                                         Report.Warning (436, 2, loc, "Ignoring imported type `{0}' since the current assembly already has a declaration with the same name",
 228                                                 TypeManager.CSharpName (t));
 229                                         return t;
 230                                 }
 231                         }
 232
 233                         return found_type;
 234                 }
 235         }
 236
 237         /// <summary>
 238         ///   Keeps track of the namespaces defined in the C# code.
 239         ///
 240         ///   This is an Expression to allow it to be referenced in the
 241         ///   compiler parse/intermediate tree during name resolution.
 242         /// </summary>
 243         public class Namespace : FullNamedExpression {
 244
 245                 Namespace parent;
 246                 string fullname;
 247                 Hashtable namespaces;
 248                 IDictionary declspaces;
 249                 Hashtable cached_types;
 250                 RootNamespace root;
 251
 252                 public readonly MemberName MemberName;
 253
 254                 /// <summary>
 255                 ///   Constructor Takes the current namespace and the
 256                 ///   name.  This is bootstrapped with parent == null
 257                 ///   and name = ""
 258                 /// </summary>
 259                 public Namespace (Namespace parent, string name)
 260                 {
 261                         // Expression members.
 262                         this.eclass = ExprClass.Namespace;
 263                         this.Type = null;
 264                         this.loc = Location.Null;
 265
 266                         this.parent = parent;
 267
 268                         if (parent != null)
 269                                 this.root = parent.root;
 270                         else
 271                                 this.root = this as RootNamespace;
 272
 273                         if (this.root == null)
 274                                 throw new InternalErrorException ("Root namespaces must be created using RootNamespace");
 275
 276                         string pname = parent != null ? parent.Name : "";
 277
 278                         if (pname == "")
 279                                 fullname = name;
 280                         else
 281                                 fullname = parent.Name + "." + name;
 282
 283                         if (fullname == null)
 284                                 throw new InternalErrorException ("Namespace has a null fullname");
 285
 286                         if (parent != null && parent.MemberName != MemberName.Null)
 287                                 MemberName = new MemberName (parent.MemberName, name);
 288                         else if (name.Length == 0)
 289                                 MemberName = MemberName.Null;
 290                         else
 291                                 MemberName = new MemberName (name);
 292
 293                         namespaces = new Hashtable ();
 294                         cached_types = new Hashtable ();
 295
 296                         root.RegisterNamespace (this);
 297                 }
 298
 299                 public override Expression DoResolve (EmitContext ec)
 300                 {
 301                         return this;
 302                 }
 303
 304                 public virtual void Error_NamespaceDoesNotExist (Location loc, string name)
 305                 {
 306                         Report.Error (234, loc, "The type or namespace name `{0}' does not exist in the namespace `{1}'. Are you missing an assembly reference?",
 307                                 name, FullName);
 308                 }
 309
 310                 public override void Emit (EmitContext ec)
 311                 {
 312                         throw new InternalErrorException ("Expression tree referenced namespace " + fullname + " during Emit ()");
 313                 }
 314
 315                 public override string GetSignatureForError ()
 316                 {
 317                         return Name;
 318                 }
 319
 320                 public Namespace GetNamespace (string name, bool create)
 321                 {
 322                         int pos = name.IndexOf ('.');
 323
 324                         Namespace ns;
 325                         string first;
 326                         if (pos >= 0)
 327                                 first = name.Substring (0, pos);
 328                         else
 329                                 first = name;
 330
 331                         ns = (Namespace) namespaces [first];
 332                         if (ns == null) {
 333                                 if (!create)
 334                                         return null;
 335
 336                                 ns = new Namespace (this, first);
 337                                 namespaces.Add (first, ns);
 338                         }
 339
 340                         if (pos >= 0)
 341                                 ns = ns.GetNamespace (name.Substring (pos + 1), create);
 342
 343                         return ns;
 344                 }
 345
 346                 TypeExpr LookupType (string name, Location loc)
 347                 {
 348                         if (cached_types.Contains (name))
 349                                 return cached_types [name] as TypeExpr;
 350
 351                         Type t = null;
 352                         if (declspaces != null) {
 353                                 DeclSpace tdecl = declspaces [name] as DeclSpace;
 354                                 if (tdecl != null) {
 355                                         //
 356                                         // Note that this is not:
 357                                         //
 358                                         //   t = tdecl.DefineType ()
 359                                         //
 360                                         // This is to make it somewhat more useful when a DefineType
 361                                         // fails due to problems in nested types (more useful in the sense
 362                                         // of fewer misleading error messages)
 363                                         //
 364                                         tdecl.DefineType ();
 365                                         t = tdecl.TypeBuilder;
 366                                 }
 367                         }
 368                         string lookup = t != null ? t.FullName : (fullname.Length == 0 ? name : fullname + "." + name);
 369                         Type rt = root.LookupTypeReflection (lookup, loc);
 370                         if (t == null)
 371                                 t = rt;
 372
 373                         TypeExpr te = t == null ? null : new TypeExpression (t, Location.Null);
 374                         cached_types [name] = te;
 375                         return te;
 376                 }
 377
 378                 public FullNamedExpression Lookup (DeclSpace ds, string name, Location loc)
 379                 {
 380                         if (namespaces.Contains (name))
 381                                 return (Namespace) namespaces [name];
 382
 383                         TypeExpr te = LookupType (name, loc);
 384                         if (te == null || !ds.CheckAccessLevel (te.Type))
 385                                 return null;
 386
 387                         return te;
 388                 }
 389
 390                 public void AddDeclSpace (string name, DeclSpace ds)
 391                 {
 392                         if (declspaces == null)
 393                                 declspaces = new HybridDictionary ();
 394                         declspaces.Add (name, ds);
 395                 }
 396
 397                 /// <summary>
 398                 ///   The qualified name of the current namespace
 399                 /// </summary>
 400                 public string Name {
 401                         get { return fullname; }
 402                 }
 403
 404                 public override string FullName {
 405                         get { return fullname; }
 406                 }
 407
 408                 /// <summary>
 409                 ///   The parent of this namespace, used by the parser to "Pop"
 410                 ///   the current namespace declaration
 411                 /// </summary>
 412                 public Namespace Parent {
 413                         get { return parent; }
 414                 }
 415
 416                 public override string ToString ()
 417                 {
 418                         return String.Format ("Namespace ({0})", Name);
 419                 }
 420         }
 421
 422         public class NamespaceEntry {
 423                 Namespace ns;
 424                 NamespaceEntry parent, implicit_parent;
 425                 SourceFile file;
 426                 int symfile_id;
 427                 Hashtable aliases;
 428                 ArrayList using_clauses;
 429                 public bool DeclarationFound = false;
 430                 bool UsingFound;
 431
 432                 public readonly DeclSpace SlaveDeclSpace;
 433
 434                 ListDictionary extern_aliases;
 435
 436                 static ArrayList entries = new ArrayList ();
 437
 438                 public static void Reset ()
 439                 {
 440                         entries = new ArrayList ();
 441                 }
 442
 443                 //
 444                 // This class holds the location where a using definition is
 445                 // done, and whether it has been used by the program or not.
 446                 //
 447                 // We use this to flag using clauses for namespaces that do not
 448                 // exist.
 449                 //
 450                 public class UsingEntry {
 451                         public readonly MemberName Name;
 452                         readonly Expression Expr;
 453                         readonly NamespaceEntry NamespaceEntry;
 454                         readonly Location Location;
 455
 456                         public UsingEntry (NamespaceEntry entry, MemberName name, Location loc)
 457                         {
 458                                 Name = name;
 459                                 Expr = name.GetTypeExpression ();
 460                                 NamespaceEntry = entry;
 461                                 Location = loc;
 462                         }
 463
 464                         internal Namespace resolved;
 465
 466                         public Namespace Resolve ()
 467                         {
 468                                 if (resolved != null)
 469                                         return resolved;
 470
 471                                 DeclSpace root = RootContext.ToplevelTypes;
 472                                 root.NamespaceEntry = NamespaceEntry;
 473                                 FullNamedExpression fne = Expr.ResolveAsTypeStep (root, false);
 474                                 root.NamespaceEntry = null;
 475
 476                                 if (fne == null) {
 477                                         Error_NamespaceNotFound (Location, Name.ToString ());
 478                                         return null;
 479                                 }
 480
 481                                 resolved = fne as Namespace;
 482                                 if (resolved == null) {
 483                                         Report.Error (138, Location,
 484                                                 "`{0} is a type not a namespace. A using namespace directive can only be applied to namespaces", Name.ToString ());
 485                                 }
 486                                 return resolved;
 487                         }
 488                 }
 489
 490                 public abstract class AliasEntry {
 491                         public readonly string Name;
 492                         public readonly NamespaceEntry NamespaceEntry;
 493                         public readonly Location Location;
 494
 495                         protected AliasEntry (NamespaceEntry entry, string name, Location loc)
 496                         {
 497                                 Name = name;
 498                                 NamespaceEntry = entry;
 499                                 Location = loc;
 500                         }
 501
 502                         protected FullNamedExpression resolved;
 503                         bool error;
 504
 505                         public FullNamedExpression Resolve ()
 506                         {
 507                                 if (resolved != null || error)
 508                                         return resolved;
 509                                 resolved = DoResolve ();
 510                                 if (resolved == null)
 511                                         error = true;
 512                                 return resolved;
 513                         }
 514
 515                         protected abstract FullNamedExpression DoResolve ();
 516                 }
 517
 518                 public class LocalAliasEntry : AliasEntry
 519                 {
 520                         public readonly Expression Alias;
 521
 522                         public LocalAliasEntry (NamespaceEntry entry, string name, MemberName alias, Location loc) :
 523                                 base (entry, name, loc)
 524                         {
 525                                 Alias = alias.GetTypeExpression ();
 526                         }
 527
 528                         protected override FullNamedExpression DoResolve ()
 529                         {
 530                                 DeclSpace root = RootContext.ToplevelTypes;
 531                                 root.NamespaceEntry = NamespaceEntry;
 532                                 resolved = Alias.ResolveAsTypeStep (root, false);
 533                                 root.NamespaceEntry = null;
 534
 535                                 if (resolved == null)
 536                                         return null;
 537
 538                                 if (resolved.Type != null) {
 539                                         TypeAttributes attr = resolved.Type.Attributes & TypeAttributes.VisibilityMask;
 540                                         if (attr == TypeAttributes.NestedPrivate || attr == TypeAttributes.NestedFamily ||
 541                                                 ((attr == TypeAttributes.NestedFamORAssem || attr == TypeAttributes.NestedAssembly) &&
 542                                                 TypeManager.LookupDeclSpace (resolved.Type) == null)) {
 543                                                 Expression.ErrorIsInaccesible (Alias.Location, Alias.ToString ());
 544                                                 return null;
 545                                         }
 546                                 }
 547
 548                                 return resolved;
 549                         }
 550                 }
 551
 552                 public class ExternAliasEntry : AliasEntry
 553                 {
 554                         public ExternAliasEntry (NamespaceEntry entry, string name, Location loc) :
 555                                 base (entry, name, loc)
 556                         {
 557                         }
 558
 559                         protected override FullNamedExpression DoResolve ()
 560                         {
 561                                 resolved = RootNamespace.GetRootNamespace (Name);
 562                                 if (resolved == null)
 563                                         Report.Error (430, Location, "The extern alias '" + Name +
 564                                                                         "' was not specified in a /reference option");
 565
 566                                 return resolved;
 567                         }
 568                 }
 569
 570                 public NamespaceEntry (NamespaceEntry parent, SourceFile file, string name)
 571                 {
 572                         this.parent = parent;
 573                         this.file = file;
 574                         entries.Add (this);
 575                         this.ID = entries.Count;
 576
 577                         if (parent != null)
 578                                 ns = parent.NS.GetNamespace (name, true);
 579                         else if (name != null)
 580                                 ns = RootNamespace.Global.GetNamespace (name, true);
 581                         else
 582                                 ns = RootNamespace.Global;
 583                         SlaveDeclSpace = new RootDeclSpace (this);
 584                 }
 585
 586                 private NamespaceEntry (NamespaceEntry parent, SourceFile file, Namespace ns)
 587                 {
 588                         this.parent = parent;
 589                         this.file = file;
 590                         // no need to add self to 'entries', since we don't have any aliases or using entries.
 591                         this.ID = -1;
 592                         this.IsImplicit = true;
 593                         this.ns = ns;
 594                         this.SlaveDeclSpace = null;
 595                 }
 596
 597                 //
 598                 // According to section 16.3.1 (using-alias-directive), the namespace-or-type-name is
 599                 // resolved as if the immediately containing namespace body has no using-directives.
 600                 //
 601                 // Section 16.3.2 says that the same rule is applied when resolving the namespace-name
 602                 // in the using-namespace-directive.
 603                 //
 604                 // To implement these rules, the expressions in the using directives are resolved using
 605                 // the "doppelganger" (ghostly bodiless duplicate).
 606                 //
 607                 NamespaceEntry doppelganger;
 608                 NamespaceEntry Doppelganger {
 609                         get {
 610                                 if (!IsImplicit && doppelganger == null)
 611                                         doppelganger = new NamespaceEntry (ImplicitParent, file, ns);
 612                                 return doppelganger;
 613                         }
 614                 }
 615
 616                 public readonly int ID;
 617                 public readonly bool IsImplicit;
 618
 619                 public Namespace NS {
 620                         get { return ns; }
 621                 }
 622
 623                 public NamespaceEntry Parent {
 624                         get { return parent; }
 625                 }
 626
 627                 public NamespaceEntry ImplicitParent {
 628                         get {
 629                                 if (parent == null)
 630                                         return null;
 631                                 if (implicit_parent == null) {
 632                                         implicit_parent = (parent.NS == ns.Parent)
 633                                                 ? parent
 634                                                 : new NamespaceEntry (parent, file, ns.Parent);
 635                                 }
 636                                 return implicit_parent;
 637                         }
 638                 }
 639
 640                 /// <summary>
 641                 ///   Records a new namespace for resolving name references
 642                 /// </summary>
 643                 public void Using (MemberName name, Location loc)
 644                 {
 645                         if (DeclarationFound){
 646                                 Report.Error (1529, loc, "A using clause must precede all other namespace elements except extern alias declarations");
 647                                 return;
 648                         }
 649
 650                         UsingFound = true;
 651
 652                         if (name.Equals (ns.MemberName))
 653                                 return;
 654
 655                         if (using_clauses == null)
 656                                 using_clauses = new ArrayList ();
 657
 658                         foreach (UsingEntry old_entry in using_clauses) {
 659                                 if (name.Equals (old_entry.Name)) {
 660                                         Report.Warning (105, 3, loc, "The using directive for `{0}' appeared previously in this namespace", name.GetName ());
 661                                         return;
 662                                 }
 663                         }
 664
 665                         UsingEntry ue = new UsingEntry (Doppelganger, name, loc);
 666                         using_clauses.Add (ue);
 667                 }
 668
 669                 public void UsingAlias (string name, MemberName alias, Location loc)
 670                 {
 671                         if (DeclarationFound){
 672                                 Report.Error (1529, loc, "A using clause must precede all other namespace elements except extern alias declarations");
 673                                 return;
 674                         }
 675
 676                         UsingFound = true;
 677
 678                         if (aliases == null)
 679                                 aliases = new Hashtable ();
 680
 681                         if (aliases.Contains (name)) {
 682                                 AliasEntry ae = (AliasEntry) aliases [name];
 683                                 Report.SymbolRelatedToPreviousError (ae.Location, ae.Name);
 684                                 Report.Error (1537, loc, "The using alias `{0}' appeared previously in this namespace", name);
 685                                 return;
 686                         }
 687
 688                         if (RootContext.Version == LanguageVersion.Default &&
 689                             name == "global" && RootContext.WarningLevel >= 2)
 690                                 Report.Warning (440, 2, loc, "An alias named `global' will not be used when resolving 'global::';" +
 691                                         " the global namespace will be used instead");
 692
 693                         // FIXME: get correct error number.  See if the above check can be merged
 694                         if (extern_aliases != null && extern_aliases.Contains (name)) {
 695                                 AliasEntry ae = (AliasEntry) extern_aliases [name];
 696                                 Report.SymbolRelatedToPreviousError (ae.Location, ae.Name);
 697                                 Report.Error (1537, loc, "The using alias `{0}' appeared previously in this namespace", name);
 698                                 return;
 699                         }
 700
 701                         aliases [name] = new LocalAliasEntry (Doppelganger, name, alias, loc);
 702                 }
 703
 704                 public void UsingExternalAlias (string name, Location loc)
 705                 {
 706                         if (UsingFound || DeclarationFound) {
 707                                 Report.Error (439, loc, "An extern alias declaration must precede all other elements");
 708                                 return;
 709                         }
 710
 711                         // Share the extern_aliases field with the Doppelganger
 712                         if (extern_aliases == null) {
 713                                 extern_aliases = new ListDictionary ();
 714                                 Doppelganger.extern_aliases = extern_aliases;
 715                         }
 716
 717                         if (extern_aliases.Contains (name)) {
 718                                 AliasEntry ae = (AliasEntry) extern_aliases [name];
 719                                 Report.SymbolRelatedToPreviousError (ae.Location, ae.Name);
 720                                 Report.Error (1537, loc, "The using alias `{0}' appeared previously in this namespace", name);
 721                                 return;
 722                         }
 723
 724                         if (name == "global") {
 725                                 Report.Error (1681, loc, "You cannot redefine the global extern alias");
 726                                 return;
 727                         }
 728
 729                         // Register the alias in aliases and extern_aliases, since we need both of them
 730                         // to keep things simple (different resolution scenarios)
 731                         ExternAliasEntry alias = new ExternAliasEntry (Doppelganger, name, loc);
 732                         extern_aliases [name] = alias;
 733                 }
 734
 735                 public FullNamedExpression LookupNamespaceOrType (DeclSpace ds, string name, Location loc, bool ignore_cs0104)
 736                 {
 737                         // Precondition: Only simple names (no dots) will be looked up with this function.
 738                         FullNamedExpression resolved = null;
 739                         for (NamespaceEntry curr_ns = this; curr_ns != null; curr_ns = curr_ns.ImplicitParent) {
 740                                 if ((resolved = curr_ns.Lookup (ds, name, loc, ignore_cs0104)) != null)
 741                                         break;
 742                         }
 743                         return resolved;
 744                 }
 745
 746                 static void Error_AmbiguousTypeReference (Location loc, string name, FullNamedExpression t1, FullNamedExpression t2)
 747                 {
 748                         Report.Error (104, loc, "`{0}' is an ambiguous reference between `{1}' and `{2}'",
 749                                 name, t1.FullName, t2.FullName);
 750                 }
 751
 752                 // Looks-up a alias named @name in this and surrounding namespace declarations
 753                 public FullNamedExpression LookupAlias (string name)
 754                 {
 755                         AliasEntry entry = null;
 756                         for (NamespaceEntry n = this; n != null; n = n.ImplicitParent) {
 757                                 if (n.extern_aliases != null && (entry = n.extern_aliases [name] as AliasEntry) != null)
 758                                         break;
 759                                 if (n.aliases != null && (entry = n.aliases [name] as AliasEntry) != null)
 760                                         break;
 761                         }
 762                         return entry == null ? null : entry.Resolve ();
 763                 }
 764
 765                 private FullNamedExpression Lookup (DeclSpace ds, string name, Location loc, bool ignore_cs0104)
 766                 {
 767                         //
 768                         // Check whether it's in the namespace.
 769                         //
 770                         FullNamedExpression fne = NS.Lookup (ds, name, loc);
 771                         if (fne != null)
 772                                 return fne;
 773
 774                         if (extern_aliases != null) {
 775                                 AliasEntry entry = extern_aliases [name] as AliasEntry;
 776                                 if (entry != null)
 777                                         return entry.Resolve ();
 778                         }
 779
 780                         if (IsImplicit)
 781                                 return null;
 782
 783                         //
 784                         // Check aliases.
 785                         //
 786                         if (aliases != null) {
 787                                 AliasEntry entry = aliases [name] as AliasEntry;
 788                                 if (entry != null)
 789                                         return entry.Resolve ();
 790                         }
 791
 792                         //
 793                         // Check using entries.
 794                         //
 795                         FullNamedExpression match = null;
 796                         foreach (Namespace using_ns in GetUsingTable ()) {
 797                                 match = using_ns.Lookup (ds, name, loc);
 798                                 if (match == null || !(match is TypeExpr))
 799                                         continue;
 800                                 if (fne != null) {
 801                                         if (!ignore_cs0104)
 802                                                 Error_AmbiguousTypeReference (loc, name, fne, match);
 803                                         return null;
 804                                 }
 805                                 fne = match;
 806                         }
 807
 808                         return fne;
 809                 }
 810
 811                 // Our cached computation.
 812                 readonly Namespace [] empty_namespaces = new Namespace [0];
 813                 Namespace [] namespace_using_table;
 814                 Namespace [] GetUsingTable ()
 815                 {
 816                         if (namespace_using_table != null)
 817                                 return namespace_using_table;
 818
 819                         if (using_clauses == null) {
 820                                 namespace_using_table = empty_namespaces;
 821                                 return namespace_using_table;
 822                         }
 823
 824                         ArrayList list = new ArrayList (using_clauses.Count);
 825
 826                         foreach (UsingEntry ue in using_clauses) {
 827                                 Namespace using_ns = ue.Resolve ();
 828                                 if (using_ns == null)
 829                                         continue;
 830
 831                                 list.Add (using_ns);
 832                         }
 833
 834                         namespace_using_table = new Namespace [list.Count];
 835                         list.CopyTo (namespace_using_table, 0);
 836                         return namespace_using_table;
 837                 }
 838
 839                 readonly string [] empty_using_list = new string [0];
 840
 841                 public int SymbolFileID {
 842                         get {
 843                                 if (symfile_id == 0 && file.SourceFileEntry != null) {
 844                                         int parent_id = parent == null ? 0 : parent.SymbolFileID;
 845
 846                                         string [] using_list = empty_using_list;
 847                                         if (using_clauses != null) {
 848                                                 using_list = new string [using_clauses.Count];
 849                                                 for (int i = 0; i < using_clauses.Count; i++)
 850                                                         using_list [i] = ((UsingEntry) using_clauses [i]).Name.ToString ();
 851                                         }
 852
 853                                         symfile_id = CodeGen.SymbolWriter.DefineNamespace (ns.Name, file.SourceFileEntry, using_list, parent_id);
 854                                 }
 855                                 return symfile_id;
 856                         }
 857                 }
 858
 859                 static void MsgtryRef (string s)
 860                 {
 861                         Console.WriteLine ("    Try using -r:" + s);
 862                 }
 863
 864                 static void MsgtryPkg (string s)
 865                 {
 866                         Console.WriteLine ("    Try using -pkg:" + s);
 867                 }
 868
 869                 public static void Error_NamespaceNotFound (Location loc, string name)
 870                 {
 871                         Report.Error (246, loc, "The type or namespace name `{0}' could not be found. Are you missing a using directive or an assembly reference?",
 872                                 name);
 873
 874                         switch (name) {
 875                         case "Gtk": case "GtkSharp":
 876                                 MsgtryPkg ("gtk-sharp");
 877                                 break;
 878
 879                         case "Gdk": case "GdkSharp":
 880                                 MsgtryPkg ("gdk-sharp");
 881                                 break;
 882
 883                         case "Glade": case "GladeSharp":
 884                                 MsgtryPkg ("glade-sharp");
 885                                 break;
 886
 887                         case "System.Drawing":
 888                         case "System.Web.Services":
 889                         case "System.Web":
 890                         case "System.Data":
 891                         case "System.Windows.Forms":
 892                                 MsgtryRef (name);
 893                                 break;
 894                         }
 895                 }
 896
 897                 /// <summary>
 898                 ///   Used to validate that all the using clauses are correct
 899                 ///   after we are finished parsing all the files.
 900                 /// </summary>
 901                 void VerifyUsing ()
 902                 {
 903                         if (extern_aliases != null) {
 904                                 foreach (DictionaryEntry de in extern_aliases)
 905                                         ((AliasEntry) de.Value).Resolve ();
 906                         }
 907
 908                         if (using_clauses != null) {
 909                                 foreach (UsingEntry ue in using_clauses)
 910                                         ue.Resolve ();
 911                         }
 912
 913                         if (aliases != null) {
 914                                 foreach (DictionaryEntry de in aliases)
 915                                         ((AliasEntry) de.Value).Resolve ();
 916                         }
 917                 }
 918
 919                 /// <summary>
 920                 ///   Used to validate that all the using clauses are correct
 921                 ///   after we are finished parsing all the files.
 922                 /// </summary>
 923                 static public void VerifyAllUsing ()
 924                 {
 925                         foreach (NamespaceEntry entry in entries)
 926                                 entry.VerifyUsing ();
 927                 }
 928
 929                 public string GetSignatureForError ()
 930                 {
 931                         return ns.GetSignatureForError ();
 932                 }
 933
 934                 public override string ToString ()
 935                 {
 936                         return ns.ToString ();
 937                 }
 938         }
 939 }