mcs/mcs/assign.cs

   1 //
   2 // assign.cs: Assignments.
   3 //
   4 // Author:
   5 //   Miguel de Icaza (miguel@ximian.com)
   6 //   Martin Baulig (martin@ximian.com)
   7 //   Marek Safar (marek.safar@gmail.com)
   8 //
   9 // Dual licensed under the terms of the MIT X11 or GNU GPL
  10 //
  11 // Copyright 2001, 2002, 2003 Ximian, Inc.
  12 // Copyright 2004-2008 Novell, Inc
  13 // Copyright 2011 Xamarin Inc
  14 //
  15 using System;
  16
  17 #if STATIC
  18 using IKVM.Reflection.Emit;
  19 #else
  20 using System.Reflection.Emit;
  21 #endif
  22
  23 namespace Mono.CSharp {
  24
  25         /// <summary>
  26         ///   This interface is implemented by expressions that can be assigned to.
  27         /// </summary>
  28         /// <remarks>
  29         ///   This interface is implemented by Expressions whose values can not
  30         ///   store the result on the top of the stack.
  31         ///
  32         ///   Expressions implementing this (Properties, Indexers and Arrays) would
  33         ///   perform an assignment of the Expression "source" into its final
  34         ///   location.
  35         ///
  36         ///   No values on the top of the stack are expected to be left by
  37         ///   invoking this method.
  38         /// </remarks>
  39         public interface IAssignMethod {
  40                 //
  41                 // This is an extra version of Emit. If leave_copy is `true'
  42                 // A copy of the expression will be left on the stack at the
  43                 // end of the code generated for EmitAssign
  44                 //
  45                 void Emit (EmitContext ec, bool leave_copy);
  46
  47                 //
  48                 // This method does the assignment
  49                 // `source' will be stored into the location specified by `this'
  50                 // if `leave_copy' is true, a copy of `source' will be left on the stack
  51                 // if `prepare_for_load' is true, when `source' is emitted, there will
  52                 // be data on the stack that it can use to compuatate its value. This is
  53                 // for expressions like a [f ()] ++, where you can't call `f ()' twice.
  54                 //
  55                 void EmitAssign (EmitContext ec, Expression source, bool leave_copy, bool isCompound);
  56
  57                 /*
  58                 For simple assignments, this interface is very simple, EmitAssign is called with source
  59                 as the source expression and leave_copy and prepare_for_load false.
  60
  61                 For compound assignments it gets complicated.
  62
  63                 EmitAssign will be called as before, however, prepare_for_load will be
  64                 true. The @source expression will contain an expression
  65                 which calls Emit. So, the calls look like:
  66
  67                 this.EmitAssign (ec, source, false, true) ->
  68                         source.Emit (ec); ->
  69                                 [...] ->
  70                                         this.Emit (ec, false); ->
  71                                         end this.Emit (ec, false); ->
  72                                 end [...]
  73                         end source.Emit (ec);
  74                 end this.EmitAssign (ec, source, false, true)
  75
  76
  77                 When prepare_for_load is true, EmitAssign emits a `token' on the stack that
  78                 Emit will use for its state.
  79
  80                 Let's take FieldExpr as an example. assume we are emitting f ().y += 1;
  81
  82                 Here is the call tree again. This time, each call is annotated with the IL
  83                 it produces:
  84
  85                 this.EmitAssign (ec, source, false, true)
  86                         call f
  87                         dup
  88
  89                         Binary.Emit ()
  90                                 this.Emit (ec, false);
  91                                 ldfld y
  92                                 end this.Emit (ec, false);
  93
  94                                 IntConstant.Emit ()
  95                                 ldc.i4.1
  96                                 end IntConstant.Emit
  97
  98                                 add
  99                         end Binary.Emit ()
 100
 101                         stfld
 102                 end this.EmitAssign (ec, source, false, true)
 103
 104                 Observe two things:
 105                         1) EmitAssign left a token on the stack. It was the result of f ().
 106                         2) This token was used by Emit
 107
 108                 leave_copy (in both EmitAssign and Emit) tells the compiler to leave a copy
 109                 of the expression at that point in evaluation. This is used for pre/post inc/dec
 110                 and for a = x += y. Let's do the above example with leave_copy true in EmitAssign
 111
 112                 this.EmitAssign (ec, source, true, true)
 113                         call f
 114                         dup
 115
 116                         Binary.Emit ()
 117                                 this.Emit (ec, false);
 118                                 ldfld y
 119                                 end this.Emit (ec, false);
 120
 121                                 IntConstant.Emit ()
 122                                 ldc.i4.1
 123                                 end IntConstant.Emit
 124
 125                                 add
 126                         end Binary.Emit ()
 127
 128                         dup
 129                         stloc temp
 130                         stfld
 131                         ldloc temp
 132                 end this.EmitAssign (ec, source, true, true)
 133
 134                 And with it true in Emit
 135
 136                 this.EmitAssign (ec, source, false, true)
 137                         call f
 138                         dup
 139
 140                         Binary.Emit ()
 141                                 this.Emit (ec, true);
 142                                 ldfld y
 143                                 dup
 144                                 stloc temp
 145                                 end this.Emit (ec, true);
 146
 147                                 IntConstant.Emit ()
 148                                 ldc.i4.1
 149                                 end IntConstant.Emit
 150
 151                                 add
 152                         end Binary.Emit ()
 153
 154                         stfld
 155                         ldloc temp
 156                 end this.EmitAssign (ec, source, false, true)
 157
 158                 Note that these two examples are what happens for ++x and x++, respectively.
 159                 */
 160         }
 161
 162         /// <summary>
 163         ///   An Expression to hold a temporary value.
 164         /// </summary>
 165         /// <remarks>
 166         ///   The LocalTemporary class is used to hold temporary values of a given
 167         ///   type to "simulate" the expression semantics. The local variable is
 168         ///   never captured.
 169         ///
 170         ///   The local temporary is used to alter the normal flow of code generation
 171         ///   basically it creates a local variable, and its emit instruction generates
 172         ///   code to access this value, return its address or save its value.
 173         ///
 174         ///   If `is_address' is true, then the value that we store is the address to the
 175         ///   real value, and not the value itself.
 176         ///
 177         ///   This is needed for a value type, because otherwise you just end up making a
 178         ///   copy of the value on the stack and modifying it. You really need a pointer
 179         ///   to the origional value so that you can modify it in that location. This
 180         ///   Does not happen with a class because a class is a pointer -- so you always
 181         ///   get the indirection.
 182         ///
 183         /// </remarks>
 184         public class LocalTemporary : Expression, IMemoryLocation, IAssignMethod {
 185                 LocalBuilder builder;
 186
 187                 public LocalTemporary (TypeSpec t)
 188                 {
 189                         type = t;
 190                         eclass = ExprClass.Value;
 191                 }
 192
 193                 public LocalTemporary (LocalBuilder b, TypeSpec t)
 194                         : this (t)
 195                 {
 196                         builder = b;
 197                 }
 198
 199                 public void Release (EmitContext ec)
 200                 {
 201                         ec.FreeTemporaryLocal (builder, type);
 202                         builder = null;
 203                 }
 204
 205                 public override bool ContainsEmitWithAwait ()
 206                 {
 207                         return false;
 208                 }
 209
 210                 public override Expression CreateExpressionTree (ResolveContext ec)
 211                 {
 212                         Arguments args = new Arguments (1);
 213                         args.Add (new Argument (this));
 214                         return CreateExpressionFactoryCall (ec, "Constant", args);
 215                 }
 216
 217                 protected override Expression DoResolve (ResolveContext ec)
 218                 {
 219                         return this;
 220                 }
 221
 222                 public override Expression DoResolveLValue (ResolveContext ec, Expression right_side)
 223                 {
 224                         return this;
 225                 }
 226
 227                 public override void Emit (EmitContext ec)
 228                 {
 229                         if (builder == null)
 230                                 throw new InternalErrorException ("Emit without Store, or after Release");
 231
 232                         ec.Emit (OpCodes.Ldloc, builder);
 233                 }
 234
 235                 #region IAssignMethod Members
 236
 237                 public void Emit (EmitContext ec, bool leave_copy)
 238                 {
 239                         Emit (ec);
 240
 241                         if (leave_copy)
 242                                 Emit (ec);
 243                 }
 244
 245                 public void EmitAssign (EmitContext ec, Expression source, bool leave_copy, bool isCompound)
 246                 {
 247                         if (isCompound)
 248                                 throw new NotImplementedException ();
 249
 250                         source.Emit (ec);
 251
 252                         Store (ec);
 253
 254                         if (leave_copy)
 255                                 Emit (ec);
 256                 }
 257
 258                 #endregion
 259
 260                 public LocalBuilder Builder {
 261                         get { return builder; }
 262                 }
 263
 264                 public void Store (EmitContext ec)
 265                 {
 266                         if (builder == null)
 267                                 builder = ec.GetTemporaryLocal (type);
 268
 269                         ec.Emit (OpCodes.Stloc, builder);
 270                 }
 271
 272                 public void AddressOf (EmitContext ec, AddressOp mode)
 273                 {
 274                         if (builder == null)
 275                                 builder = ec.GetTemporaryLocal (type);
 276
 277                         if (builder.LocalType.IsByRef) {
 278                                 //
 279                                 // if is_address, than this is just the address anyways,
 280                                 // so we just return this.
 281                                 //
 282                                 ec.Emit (OpCodes.Ldloc, builder);
 283                         } else {
 284                                 ec.Emit (OpCodes.Ldloca, builder);
 285                         }
 286                 }
 287         }
 288
 289         /// <summary>
 290         ///   The Assign node takes care of assigning the value of source into
 291         ///   the expression represented by target.
 292         /// </summary>
 293         public abstract class Assign : ExpressionStatement {
 294                 protected Expression target, source;
 295
 296                 protected Assign (Expression target, Expression source, Location loc)
 297                 {
 298                         this.target = target;
 299                         this.source = source;
 300                         this.loc = loc;
 301                 }
 302
 303                 public Expression Target {
 304                         get { return target; }
 305                 }
 306
 307                 public Expression Source {
 308                         get {
 309                                 return source;
 310                         }
 311                 }
 312
 313                 public override Location StartLocation {
 314                         get {
 315                                 return target.StartLocation;
 316                         }
 317                 }
 318
 319                 public override bool ContainsEmitWithAwait ()
 320                 {
 321                         return target.ContainsEmitWithAwait () || source.ContainsEmitWithAwait ();
 322                 }
 323
 324                 public override Expression CreateExpressionTree (ResolveContext ec)
 325                 {
 326                         ec.Report.Error (832, loc, "An expression tree cannot contain an assignment operator");
 327                         return null;
 328                 }
 329
 330                 protected override Expression DoResolve (ResolveContext ec)
 331                 {
 332                         bool ok = true;
 333                         source = source.Resolve (ec);
 334
 335                         if (source == null) {
 336                                 ok = false;
 337                                 source = ErrorExpression.Instance;
 338                         }
 339
 340                         target = target.ResolveLValue (ec, source);
 341
 342                         if (target == null || !ok)
 343                                 return null;
 344
 345                         TypeSpec target_type = target.Type;
 346                         TypeSpec source_type = source.Type;
 347
 348                         eclass = ExprClass.Value;
 349                         type = target_type;
 350
 351                         if (!(target is IAssignMethod)) {
 352                                 target.Error_ValueAssignment (ec, source);
 353                                 return null;
 354                         }
 355
 356                         if (target_type != source_type) {
 357                                 Expression resolved = ResolveConversions (ec);
 358
 359                                 if (resolved != this)
 360                                         return resolved;
 361                         }
 362
 363                         return this;
 364                 }
 365
 366                 public override System.Linq.Expressions.Expression MakeExpression (BuilderContext ctx)
 367                 {
 368                         var tassign = target as IDynamicAssign;
 369                         if (tassign == null)
 370                                 throw new InternalErrorException (target.GetType () + " does not support dynamic assignment");
 371
 372                         var target_object = tassign.MakeAssignExpression (ctx, source);
 373
 374                         //
 375                         // Some hacking is needed as DLR does not support void type and requires
 376                         // always have object convertible return type to support caching and chaining
 377                         //
 378                         // We do this by introducing an explicit block which returns RHS value when
 379                         // available or null
 380                         //
 381                         if (target_object.NodeType == System.Linq.Expressions.ExpressionType.Block)
 382                                 return target_object;
 383
 384                         System.Linq.Expressions.UnaryExpression source_object;
 385                         if (ctx.HasSet (BuilderContext.Options.CheckedScope)) {
 386                                 source_object = System.Linq.Expressions.Expression.ConvertChecked (source.MakeExpression (ctx), target_object.Type);
 387                         } else {
 388                                 source_object = System.Linq.Expressions.Expression.Convert (source.MakeExpression (ctx), target_object.Type);
 389                         }
 390
 391                         return System.Linq.Expressions.Expression.Assign (target_object, source_object);
 392                 }
 393
 394                 protected virtual Expression ResolveConversions (ResolveContext ec)
 395                 {
 396                         source = Convert.ImplicitConversionRequired (ec, source, target.Type, source.Location);
 397                         if (source == null)
 398                                 return null;
 399
 400                         return this;
 401                 }
 402
 403                 void Emit (EmitContext ec, bool is_statement)
 404                 {
 405                         IAssignMethod t = (IAssignMethod) target;
 406                         t.EmitAssign (ec, source, !is_statement, this is CompoundAssign);
 407                 }
 408
 409                 public override void Emit (EmitContext ec)
 410                 {
 411                         Emit (ec, false);
 412                 }
 413
 414                 public override void EmitStatement (EmitContext ec)
 415                 {
 416                         Emit (ec, true);
 417                 }
 418
 419                 public override void FlowAnalysis (FlowAnalysisContext fc)
 420                 {
 421                         source.FlowAnalysis (fc);
 422
 423                         if (target is ArrayAccess || target is IndexerExpr) {
 424                                 target.FlowAnalysis (fc);
 425                                 return;
 426                         }
 427
 428                         var pe = target as PropertyExpr;
 429                         if (pe != null && !pe.IsAutoPropertyAccess)
 430                                 target.FlowAnalysis (fc);
 431                 }
 432
 433                 protected override void CloneTo (CloneContext clonectx, Expression t)
 434                 {
 435                         Assign _target = (Assign) t;
 436
 437                         _target.target = target.Clone (clonectx);
 438                         _target.source = source.Clone (clonectx);
 439                 }
 440
 441                 public override object Accept (StructuralVisitor visitor)
 442                 {
 443                         return visitor.Visit (this);
 444                 }
 445         }
 446
 447         public class SimpleAssign : Assign
 448         {
 449                 public SimpleAssign (Expression target, Expression source)
 450                         : this (target, source, target.Location)
 451                 {
 452                 }
 453
 454                 public SimpleAssign (Expression target, Expression source, Location loc)
 455                         : base (target, source, loc)
 456                 {
 457                 }
 458
 459                 bool CheckEqualAssign (Expression t)
 460                 {
 461                         if (source is Assign) {
 462                                 Assign a = (Assign) source;
 463                                 if (t.Equals (a.Target))
 464                                         return true;
 465                                 return a is SimpleAssign && ((SimpleAssign) a).CheckEqualAssign (t);
 466                         }
 467                         return t.Equals (source);
 468                 }
 469
 470                 protected override Expression DoResolve (ResolveContext ec)
 471                 {
 472                         Expression e = base.DoResolve (ec);
 473                         if (e == null || e != this)
 474                                 return e;
 475
 476                         if (CheckEqualAssign (target))
 477                                 ec.Report.Warning (1717, 3, loc, "Assignment made to same variable; did you mean to assign something else?");
 478
 479                         return this;
 480                 }
 481
 482                 public override void FlowAnalysis (FlowAnalysisContext fc)
 483                 {
 484                         base.FlowAnalysis (fc);
 485
 486                         var vr = target as VariableReference;
 487                         if (vr != null) {
 488                                 if (vr.VariableInfo != null)
 489                                         fc.SetVariableAssigned (vr.VariableInfo);
 490
 491                                 return;
 492                         }
 493
 494                         var fe = target as FieldExpr;
 495                         if (fe != null) {
 496                                 fe.SetFieldAssigned (fc);
 497                                 return;
 498                         }
 499
 500                         var pe = target as PropertyExpr;
 501                         if (pe != null) {
 502                                 pe.SetBackingFieldAssigned (fc);
 503                                 return;
 504                         }
 505
 506                         var td = target as TupleDeconstruct;
 507                         if (td != null) {
 508                                 td.SetGeneratedFieldAssigned (fc);
 509                                 return;
 510                         }
 511                 }
 512
 513                 public override Reachability MarkReachable (Reachability rc)
 514                 {
 515                         return source.MarkReachable (rc);
 516                 }
 517         }
 518
 519         public class RuntimeExplicitAssign : Assign
 520         {
 521                 public RuntimeExplicitAssign (Expression target, Expression source)
 522                         : base (target, source, target.Location)
 523                 {
 524                 }
 525
 526                 protected override Expression ResolveConversions (ResolveContext ec)
 527                 {
 528                         source = EmptyCast.Create (source, target.Type);
 529                         return this;
 530                 }
 531         }
 532
 533         //
 534         // Compiler generated assign
 535         //
 536         class CompilerAssign : Assign
 537         {
 538                 public CompilerAssign (Expression target, Expression source, Location loc)
 539                         : base (target, source, loc)
 540                 {
 541                         if (target.Type != null) {
 542                                 type = target.Type;
 543                                 eclass = ExprClass.Value;
 544                         }
 545                 }
 546
 547                 protected override Expression DoResolve (ResolveContext ec)
 548                 {
 549                         var expr = base.DoResolve (ec);
 550                         var vr = target as VariableReference;
 551                         if (vr != null && vr.VariableInfo != null)
 552                                 vr.VariableInfo.IsEverAssigned = false;
 553
 554                         return expr;
 555                 }
 556
 557                 public void UpdateSource (Expression source)
 558                 {
 559                         base.source = source;
 560                 }
 561         }
 562
 563         //
 564         // Implements fields and events class initializers
 565         //
 566         public class FieldInitializer : Assign
 567         {
 568                 //
 569                 // Field initializers are tricky for partial classes. They have to
 570                 // share same constructor (block) for expression trees resolve but
 571                 // they have they own resolve scope
 572                 //
 573                 sealed class FieldInitializerContext : BlockContext
 574                 {
 575                         readonly ExplicitBlock ctor_block;
 576
 577                         public FieldInitializerContext (IMemberContext mc, BlockContext constructorContext)
 578                                 : base (mc, null, constructorContext.ReturnType)
 579                         {
 580                                 flags |= Options.FieldInitializerScope | Options.ConstructorScope;
 581                                 this.ctor_block = constructorContext.CurrentBlock.Explicit;
 582
 583                                 if (ctor_block.IsCompilerGenerated)
 584                                         CurrentBlock = ctor_block;
 585                         }
 586
 587                         public override ExplicitBlock ConstructorBlock {
 588                             get {
 589                                 return ctor_block;
 590                             }
 591                         }
 592                 }
 593
 594                 //
 595                 // Keep resolved value because field initializers have their own rules
 596                 //
 597                 ExpressionStatement resolved;
 598                 FieldBase mc;
 599
 600                 public FieldInitializer (FieldBase mc, Expression expression, Location loc)
 601                         : base (new FieldExpr (mc.Spec, expression.Location), expression, loc)
 602                 {
 603                         this.mc = mc;
 604                         if (!mc.IsStatic)
 605                                 ((FieldExpr)target).InstanceExpression = new CompilerGeneratedThis (mc.CurrentType, expression.Location);
 606                 }
 607
 608                 public int AssignmentOffset { get; private set; }
 609
 610                 public FieldBase Field {
 611                         get {
 612                                 return mc;
 613                         }
 614                 }
 615
 616                 public override Location StartLocation {
 617                         get {
 618                                 return loc;
 619                         }
 620                 }
 621
 622                 protected override Expression DoResolve (ResolveContext rc)
 623                 {
 624                         // Field initializer can be resolved (fail) many times
 625                         if (source == null)
 626                                 return null;
 627
 628                         if (resolved == null) {
 629                                 var bc = (BlockContext) rc;
 630                                 var ctx = new FieldInitializerContext (mc, bc);
 631                                 resolved = base.DoResolve (ctx) as ExpressionStatement;
 632                                 AssignmentOffset = ctx.AssignmentInfoOffset - bc.AssignmentInfoOffset;
 633                         }
 634
 635                         return resolved;
 636                 }
 637
 638                 public override void EmitStatement (EmitContext ec)
 639                 {
 640                         if (resolved == null)
 641                                 return;
 642
 643                         //
 644                         // Emit sequence symbol info even if we are in compiler generated
 645                         // block to allow debugging field initializers when constructor is
 646                         // compiler generated
 647                         //
 648                         if (ec.HasSet (BuilderContext.Options.OmitDebugInfo) && ec.HasMethodSymbolBuilder) {
 649                                 using (ec.With (BuilderContext.Options.OmitDebugInfo, false)) {
 650                                         ec.Mark (loc);
 651                                 }
 652                         }
 653
 654                         if (resolved != this)
 655                                 resolved.EmitStatement (ec);
 656                         else
 657                                 base.EmitStatement (ec);
 658                 }
 659
 660                 public override void FlowAnalysis (FlowAnalysisContext fc)
 661                 {
 662                         source.FlowAnalysis (fc);
 663                         ((FieldExpr) target).SetFieldAssigned (fc);
 664                 }
 665
 666                 public bool IsDefaultInitializer {
 667                         get {
 668                                 Constant c = source as Constant;
 669                                 if (c == null)
 670                                         return false;
 671
 672                                 FieldExpr fe = (FieldExpr)target;
 673                                 return c.IsDefaultInitializer (fe.Type);
 674                         }
 675                 }
 676
 677                 public override bool IsSideEffectFree {
 678                         get {
 679                                 return source.IsSideEffectFree;
 680                         }
 681                 }
 682         }
 683
 684         class PrimaryConstructorAssign : SimpleAssign
 685         {
 686                 readonly Field field;
 687                 readonly Parameter parameter;
 688
 689                 public PrimaryConstructorAssign (Field field, Parameter parameter)
 690                         : base (null, null, parameter.Location)
 691                 {
 692                         this.field = field;
 693                         this.parameter = parameter;
 694                 }
 695
 696                 protected override Expression DoResolve (ResolveContext rc)
 697                 {
 698                         target = new FieldExpr (field, loc);
 699                         source = rc.CurrentBlock.ParametersBlock.GetParameterInfo (parameter).CreateReferenceExpression (rc, loc);
 700                         return base.DoResolve (rc);
 701                 }
 702
 703                 public override void EmitStatement (EmitContext ec)
 704                 {
 705                         using (ec.With (BuilderContext.Options.OmitDebugInfo, true)) {
 706                                 base.EmitStatement (ec);
 707                         }
 708                 }
 709         }
 710
 711         //
 712         // This class is used for compound assignments.
 713         //
 714         public class CompoundAssign : Assign
 715         {
 716                 // This is just a hack implemented for arrays only
 717                 public sealed class TargetExpression : Expression
 718                 {
 719                         readonly Expression child;
 720
 721                         public TargetExpression (Expression child)
 722                         {
 723                                 this.child = child;
 724                                 this.loc = child.Location;
 725                         }
 726
 727                         public bool RequiresEmitWithAwait { get; set; }
 728
 729                         public override bool ContainsEmitWithAwait ()
 730                         {
 731                                 return RequiresEmitWithAwait || child.ContainsEmitWithAwait ();
 732                         }
 733
 734                         public override Expression CreateExpressionTree (ResolveContext ec)
 735                         {
 736                                 throw new NotSupportedException ("ET");
 737                         }
 738
 739                         protected override Expression DoResolve (ResolveContext ec)
 740                         {
 741                                 type = child.Type;
 742                                 eclass = ExprClass.Value;
 743                                 return this;
 744                         }
 745
 746                         public override void Emit (EmitContext ec)
 747                         {
 748                                 child.Emit (ec);
 749                         }
 750
 751                         public override Expression EmitToField (EmitContext ec)
 752                         {
 753                                 return child.EmitToField (ec);
 754                         }
 755                 }
 756
 757                 // Used for underlying binary operator
 758                 readonly Binary.Operator op;
 759                 Expression right;
 760                 Expression left;
 761
 762                 public CompoundAssign (Binary.Operator op, Expression target, Expression source)
 763                         : base (target, source, target.Location)
 764                 {
 765                         right = source;
 766                         this.op = op;
 767                 }
 768
 769                 public CompoundAssign (Binary.Operator op, Expression target, Expression source, Expression left)
 770                         : this (op, target, source)
 771                 {
 772                         this.left = left;
 773                 }
 774
 775                 public Binary.Operator Operator {
 776                         get {
 777                                 return op;
 778                         }
 779                 }
 780
 781                 protected override Expression DoResolve (ResolveContext ec)
 782                 {
 783                         right = right.Resolve (ec);
 784                         if (right == null)
 785                                 return null;
 786
 787                         MemberAccess ma = target as MemberAccess;
 788                         using (ec.Set (ResolveContext.Options.CompoundAssignmentScope)) {
 789                                 target = target.Resolve (ec);
 790                         }
 791
 792                         if (target == null)
 793                                 return null;
 794
 795                         if (target is MethodGroupExpr){
 796                                 ec.Report.Error (1656, loc,
 797                                         "Cannot assign to `{0}' because it is a `{1}'",
 798                                         ((MethodGroupExpr)target).Name, target.ExprClassName);
 799                                 return null;
 800                         }
 801
 802                         var event_expr = target as EventExpr;
 803                         if (event_expr != null) {
 804                                 source = Convert.ImplicitConversionRequired (ec, right, target.Type, loc);
 805                                 if (source == null)
 806                                         return null;
 807
 808                                 Expression rside;
 809                                 if (op == Binary.Operator.Addition)
 810                                         rside = EmptyExpression.EventAddition;
 811                                 else if (op == Binary.Operator.Subtraction)
 812                                         rside = EmptyExpression.EventSubtraction;
 813                                 else
 814                                         rside = null;
 815
 816                                 target = target.ResolveLValue (ec, rside);
 817                                 if (target == null)
 818                                         return null;
 819
 820                                 eclass = ExprClass.Value;
 821                                 type = event_expr.Operator.ReturnType;
 822                                 return this;
 823                         }
 824
 825                         //
 826                         // Only now we can decouple the original source/target
 827                         // into a tree, to guarantee that we do not have side
 828                         // effects.
 829                         //
 830                         if (left == null)
 831                                 left = new TargetExpression (target);
 832
 833                         source = new Binary (op, left, right, true);
 834
 835                         if (target is DynamicMemberAssignable) {
 836                                 Arguments targs = ((DynamicMemberAssignable) target).Arguments;
 837                                 source = source.Resolve (ec);
 838
 839                                 Arguments args = new Arguments (targs.Count + 1);
 840                                 args.AddRange (targs);
 841                                 args.Add (new Argument (source));
 842
 843                                 var binder_flags = CSharpBinderFlags.ValueFromCompoundAssignment;
 844
 845                                 //
 846                                 // Compound assignment does target conversion using additional method
 847                                 // call, set checked context as the binary operation can overflow
 848                                 //
 849                                 if (ec.HasSet (ResolveContext.Options.CheckedScope))
 850                                         binder_flags |= CSharpBinderFlags.CheckedContext;
 851
 852                                 if (target is DynamicMemberBinder) {
 853                                         source = new DynamicMemberBinder (ma.Name, binder_flags, args, loc).Resolve (ec);
 854
 855                                         // Handles possible event addition/subtraction
 856                                         if (op == Binary.Operator.Addition || op == Binary.Operator.Subtraction) {
 857                                                 args = new Arguments (targs.Count + 1);
 858                                                 args.AddRange (targs);
 859                                                 args.Add (new Argument (right));
 860                                                 string method_prefix = op == Binary.Operator.Addition ?
 861                                                         Event.AEventAccessor.AddPrefix : Event.AEventAccessor.RemovePrefix;
 862
 863                                                 var invoke = DynamicInvocation.CreateSpecialNameInvoke (
 864                                                         new MemberAccess (right, method_prefix + ma.Name, loc), args, loc).Resolve (ec);
 865
 866                                                 args = new Arguments (targs.Count);
 867                                                 args.AddRange (targs);
 868                                                 source = new DynamicEventCompoundAssign (ma.Name, args,
 869                                                         (ExpressionStatement) source, (ExpressionStatement) invoke, loc).Resolve (ec);
 870                                         }
 871                                 } else {
 872                                         source = new DynamicIndexBinder (binder_flags, args, loc).Resolve (ec);
 873                                 }
 874
 875                                 return source;
 876                         }
 877
 878                         return base.DoResolve (ec);
 879                 }
 880
 881                 public override void FlowAnalysis (FlowAnalysisContext fc)
 882                 {
 883                         target.FlowAnalysis (fc);
 884                         source.FlowAnalysis (fc);
 885                 }
 886
 887                 protected override Expression ResolveConversions (ResolveContext ec)
 888                 {
 889                         //
 890                         // LAMESPEC: Under dynamic context no target conversion is happening
 891                         // This allows more natual dynamic behaviour but breaks compatibility
 892                         // with static binding
 893                         //
 894                         if (target is RuntimeValueExpression)
 895                                 return this;
 896
 897                         TypeSpec target_type = target.Type;
 898
 899                         //
 900                         // 1. the return type is implicitly convertible to the type of target
 901                         //
 902                         if (Convert.ImplicitConversionExists (ec, source, target_type)) {
 903                                 source = Convert.ImplicitConversion (ec, source, target_type, loc);
 904                                 return this;
 905                         }
 906
 907                         //
 908                         // Otherwise, if the selected operator is a predefined operator
 909                         //
 910                         Binary b = source as Binary;
 911                         if (b == null) {
 912                                 if (source is ReducedExpression)
 913                                         b = ((ReducedExpression) source).OriginalExpression as Binary;
 914                                 else if (source is ReducedExpression.ReducedConstantExpression) {
 915                                         b = ((ReducedExpression.ReducedConstantExpression) source).OriginalExpression as Binary;
 916                                 } else if (source is Nullable.LiftedBinaryOperator) {
 917                                         var po = ((Nullable.LiftedBinaryOperator) source);
 918                                         if (po.UserOperator == null)
 919                                                 b = po.Binary;
 920                                 } else if (source is TypeCast) {
 921                                         b = ((TypeCast) source).Child as Binary;
 922                                 }
 923                         }
 924
 925                         if (b != null) {
 926                                 //
 927                                 // 2a. the operator is a shift operator
 928                                 //
 929                                 // 2b. the return type is explicitly convertible to the type of x, and
 930                                 // y is implicitly convertible to the type of x
 931                                 //
 932                                 if ((b.Oper & Binary.Operator.ShiftMask) != 0 ||
 933                                         Convert.ImplicitConversionExists (ec, right, target_type)) {
 934                                         source = Convert.ExplicitConversion (ec, source, target_type, loc);
 935                                         return this;
 936                                 }
 937                         }
 938
 939                         if (source.Type.BuiltinType == BuiltinTypeSpec.Type.Dynamic) {
 940                                 Arguments arg = new Arguments (1);
 941                                 arg.Add (new Argument (source));
 942                                 return new SimpleAssign (target, new DynamicConversion (target_type, CSharpBinderFlags.ConvertExplicit, arg, loc), loc).Resolve (ec);
 943                         }
 944
 945                         right.Error_ValueCannotBeConverted (ec, target_type, false);
 946                         return null;
 947                 }
 948
 949                 protected override void CloneTo (CloneContext clonectx, Expression t)
 950                 {
 951                         CompoundAssign ctarget = (CompoundAssign) t;
 952
 953                         ctarget.right = ctarget.source = source.Clone (clonectx);
 954                         ctarget.target = target.Clone (clonectx);
 955                 }
 956
 957                 public override object Accept (StructuralVisitor visitor)
 958                 {
 959                         return visitor.Visit (this);
 960                 }
 961         }
 962 }