2010-05-27 Jb Evain <jbevain@novell.com>

[mcs.git] / mcs / assign.cs

//
// assign.cs: Assignments.
//
// Author:
//   Miguel de Icaza (miguel@ximian.com)
//   Martin Baulig (martin@ximian.com)
//   Marek Safar (marek.safar@gmail.com)        
//
// Dual licensed under the terms of the MIT X11 or GNU GPL
//
// Copyright 2001, 2002, 2003 Ximian, Inc.
// Copyright 2004-2008 Novell, Inc
//
using System;
using System.Reflection;
using System.Reflection.Emit;

namespace Mono.CSharp {

        /// <summary>
        ///   This interface is implemented by expressions that can be assigned to.
        /// </summary>
        /// <remarks>
        ///   This interface is implemented by Expressions whose values can not
        ///   store the result on the top of the stack.
        ///
        ///   Expressions implementing this (Properties, Indexers and Arrays) would
        ///   perform an assignment of the Expression "source" into its final
        ///   location.
        ///
        ///   No values on the top of the stack are expected to be left by
        ///   invoking this method.
        /// </remarks>
        public interface IAssignMethod {
                //
                // This is an extra version of Emit. If leave_copy is `true'
                // A copy of the expression will be left on the stack at the
                // end of the code generated for EmitAssign
                //
                void Emit (EmitContext ec, bool leave_copy);

                //
                // This method does the assignment
                // `source' will be stored into the location specified by `this'
                // if `leave_copy' is true, a copy of `source' will be left on the stack
                // if `prepare_for_load' is true, when `source' is emitted, there will
                // be data on the stack that it can use to compuatate its value. This is
                // for expressions like a [f ()] ++, where you can't call `f ()' twice.
                //
                void EmitAssign (EmitContext ec, Expression source, bool leave_copy, bool prepare_for_load);

                /*
                For simple assignments, this interface is very simple, EmitAssign is called with source
                as the source expression and leave_copy and prepare_for_load false.

                For compound assignments it gets complicated.

                EmitAssign will be called as before, however, prepare_for_load will be
                true. The @source expression will contain an expression
                which calls Emit. So, the calls look like:

                this.EmitAssign (ec, source, false, true) ->
                        source.Emit (ec); ->
                                [...] ->
                                        this.Emit (ec, false); ->
                                        end this.Emit (ec, false); ->
                                end [...]
                        end source.Emit (ec);
                end this.EmitAssign (ec, source, false, true)


                When prepare_for_load is true, EmitAssign emits a `token' on the stack that
                Emit will use for its state.

                Let's take FieldExpr as an example. assume we are emitting f ().y += 1;

                Here is the call tree again. This time, each call is annotated with the IL
                it produces:

                this.EmitAssign (ec, source, false, true)
                        call f
                        dup

                        Binary.Emit ()
                                this.Emit (ec, false);
                                ldfld y
                                end this.Emit (ec, false);

                                IntConstant.Emit ()
                                ldc.i4.1
                                end IntConstant.Emit

                                add
                        end Binary.Emit ()

                        stfld
                end this.EmitAssign (ec, source, false, true)

                Observe two things:
                        1) EmitAssign left a token on the stack. It was the result of f ().
                        2) This token was used by Emit

                leave_copy (in both EmitAssign and Emit) tells the compiler to leave a copy
                of the expression at that point in evaluation. This is used for pre/post inc/dec
                and for a = x += y. Let's do the above example with leave_copy true in EmitAssign

                this.EmitAssign (ec, source, true, true)
                        call f
                        dup

                        Binary.Emit ()
                                this.Emit (ec, false);
                                ldfld y
                                end this.Emit (ec, false);

                                IntConstant.Emit ()
                                ldc.i4.1
                                end IntConstant.Emit

                                add
                        end Binary.Emit ()

                        dup
                        stloc temp
                        stfld
                        ldloc temp
                end this.EmitAssign (ec, source, true, true)

                And with it true in Emit

                this.EmitAssign (ec, source, false, true)
                        call f
                        dup

                        Binary.Emit ()
                                this.Emit (ec, true);
                                ldfld y
                                dup
                                stloc temp
                                end this.Emit (ec, true);

                                IntConstant.Emit ()
                                ldc.i4.1
                                end IntConstant.Emit

                                add
                        end Binary.Emit ()

                        stfld
                        ldloc temp
                end this.EmitAssign (ec, source, false, true)

                Note that these two examples are what happens for ++x and x++, respectively.
                */
        }

        /// <summary>
        ///   An Expression to hold a temporary value.
        /// </summary>
        /// <remarks>
        ///   The LocalTemporary class is used to hold temporary values of a given
        ///   type to "simulate" the expression semantics on property and indexer
        ///   access whose return values are void.
        ///
        ///   The local temporary is used to alter the normal flow of code generation
        ///   basically it creates a local variable, and its emit instruction generates
        ///   code to access this value, return its address or save its value.
        ///
        ///   If `is_address' is true, then the value that we store is the address to the
        ///   real value, and not the value itself.
        ///
        ///   This is needed for a value type, because otherwise you just end up making a
        ///   copy of the value on the stack and modifying it. You really need a pointer
        ///   to the origional value so that you can modify it in that location. This
        ///   Does not happen with a class because a class is a pointer -- so you always
        ///   get the indirection.
        ///
        /// </remarks>
        public class LocalTemporary : Expression, IMemoryLocation, IAssignMethod {
                LocalBuilder builder;

                public LocalTemporary (TypeSpec t)
                {
                        type = t;
                        eclass = ExprClass.Value;
                }

                public LocalTemporary (LocalBuilder b, TypeSpec t)
                        : this (t)
                {
                        builder = b;
                }

                public void Release (EmitContext ec)
                {
                        ec.FreeTemporaryLocal (builder, type);
                        builder = null;
                }

                public override Expression CreateExpressionTree (ResolveContext ec)
                {
                        Arguments args = new Arguments (1);
                        args.Add (new Argument (this));
                        return CreateExpressionFactoryCall (ec, "Constant", args);
                }

                protected override Expression DoResolve (ResolveContext ec)
                {
                        return this;
                }

                public override Expression DoResolveLValue (ResolveContext ec, Expression right_side)
                {
                        return this;
                }

                public override void Emit (EmitContext ec)
                {
                        if (builder == null)
                                throw new InternalErrorException ("Emit without Store, or after Release");

                        ec.Emit (OpCodes.Ldloc, builder);
                }

                #region IAssignMethod Members

                public void Emit (EmitContext ec, bool leave_copy)
                {
                        Emit (ec);

                        if (leave_copy)
                                Emit (ec);
                }

                public void EmitAssign (EmitContext ec, Expression source, bool leave_copy, bool prepare_for_load)
                {
                        if (prepare_for_load)
                                throw new NotImplementedException ();

                        source.Emit (ec);

                        Store (ec);

                        if (leave_copy)
                                Emit (ec);
                }

                #endregion

                public LocalBuilder Builder {
                        get { return builder; }
                }

                public void Store (EmitContext ec)
                {
                        if (builder == null)
                                builder = ec.GetTemporaryLocal (type);

                        ec.Emit (OpCodes.Stloc, builder);
                }

                public void AddressOf (EmitContext ec, AddressOp mode)
                {
                        if (builder == null)
                                builder = ec.GetTemporaryLocal (type);

                        if (builder.LocalType.IsByRef) {
                                //
                                // if is_address, than this is just the address anyways,
                                // so we just return this.
                                //
                                ec.Emit (OpCodes.Ldloc, builder);
                        } else {
                                ec.Emit (OpCodes.Ldloca, builder);
                        }
                }
        }

        /// <summary>
        ///   The Assign node takes care of assigning the value of source into
        ///   the expression represented by target.
        /// </summary>
        public abstract class Assign : ExpressionStatement {
                protected Expression target, source;

                protected Assign (Expression target, Expression source, Location loc)
                {
                        this.target = target;
                        this.source = source;
                        this.loc = loc;
                }
                
                public override Expression CreateExpressionTree (ResolveContext ec)
                {
                        ec.Report.Error (832, loc, "An expression tree cannot contain an assignment operator");
                        return null;
                }

                public Expression Target {
                        get { return target; }
                }

                public Expression Source {
                        get { return source; }
                }

                protected override Expression DoResolve (ResolveContext ec)
                {
                        bool ok = true;
                        source = source.Resolve (ec);
                                                
                        if (source == null) {
                                ok = false;
                                source = EmptyExpression.Null;
                        }

                        target = target.ResolveLValue (ec, source);

                        if (target == null || !ok)
                                return null;

                        TypeSpec target_type = target.Type;
                        TypeSpec source_type = source.Type;

                        eclass = ExprClass.Value;
                        type = target_type;

                        if (!(target is IAssignMethod)) {
                                Error_ValueAssignment (ec, loc);
                                return null;
                        }

                        if ((RootContext.Version == LanguageVersion.ISO_1) && (source is MethodGroupExpr)){
                                ((MethodGroupExpr) source).ReportUsageError (ec);
                                return null;
                        }

                        if (!TypeManager.IsEqual (target_type, source_type)) {
                                Expression resolved = ResolveConversions (ec);

                                if (resolved != this)
                                        return resolved;
                        }

                        return this;
                }

#if NET_4_0
                public override System.Linq.Expressions.Expression MakeExpression (BuilderContext ctx)
                {
                        var tassign = target as IDynamicAssign;
                        if (tassign == null)
                                throw new InternalErrorException (target.GetType () + " does not support dynamic assignment");

                        var target_object = tassign.MakeAssignExpression (ctx);

                        //
                        // Some hacking is needed as DLR does not support void type and requires
                        // always have object convertible return type to support caching and chaining
                        //
                        // We do this by introducing an explicit block which returns RHS value when
                        // available or null
                        //
                        if (target_object.NodeType == System.Linq.Expressions.ExpressionType.Block)
                                return target_object;

                        var source_object = System.Linq.Expressions.Expression.Convert (source.MakeExpression (ctx), target_object.Type);
                        return System.Linq.Expressions.Expression.Assign (target_object, source_object);
                }
#endif
                protected virtual Expression ResolveConversions (ResolveContext ec)
                {
                        source = Convert.ImplicitConversionRequired (ec, source, target.Type, loc);
                        if (source == null)
                                return null;

                        return this;
                }

                void Emit (EmitContext ec, bool is_statement)
                {
                        IAssignMethod t = (IAssignMethod) target;
                        t.EmitAssign (ec, source, !is_statement, this is CompoundAssign);
                }

                public override void Emit (EmitContext ec)
                {
                        Emit (ec, false);
                }

                public override void EmitStatement (EmitContext ec)
                {
                        Emit (ec, true);
                }

                protected override void CloneTo (CloneContext clonectx, Expression t)
                {
                        Assign _target = (Assign) t;

                        _target.target = target.Clone (clonectx);
                        _target.source = source.Clone (clonectx);
                }
        }

        public class SimpleAssign : Assign {
                public SimpleAssign (Expression target, Expression source)
                        : this (target, source, target.Location)
                {
                }

                public SimpleAssign (Expression target, Expression source, Location loc)
                        : base (target, source, loc)
                {
                }

                bool CheckEqualAssign (Expression t)
                {
                        if (source is Assign) {
                                Assign a = (Assign) source;
                                if (t.Equals (a.Target))
                                        return true;
                                return a is SimpleAssign && ((SimpleAssign) a).CheckEqualAssign (t);
                        }
                        return t.Equals (source);
                }

                protected override Expression DoResolve (ResolveContext ec)
                {
                        Expression e = base.DoResolve (ec);
                        if (e == null || e != this)
                                return e;

                        if (CheckEqualAssign (target))
                                ec.Report.Warning (1717, 3, loc, "Assignment made to same variable; did you mean to assign something else?");

                        return this;
                }
        }

        // This class implements fields and events class initializers
        public class FieldInitializer : Assign
        {
                //
                // Keep resolved value because field initializers have their own rules
                //
                ExpressionStatement resolved;
                IMemberContext rc;

                public FieldInitializer (FieldBase field, Expression expression, IMemberContext rc)
                        : base (new FieldExpr (field, expression.Location), expression, expression.Location)
                {
                        this.rc = rc;
                        if (!field.IsStatic)
                                ((FieldExpr)target).InstanceExpression = CompilerGeneratedThis.Instance;
                }

                protected override Expression DoResolve (ResolveContext ec)
                {
                        // Field initializer can be resolved (fail) many times
                        if (source == null)
                                return null;

                        if (resolved == null) {
                                //
                                // Field initializers are tricky for partial classes. They have to
                                // share same constructor (block) but they have they own resolve scope.
                                //

                                IMemberContext old = ec.MemberContext;
                                ec.MemberContext = rc;

                                using (ec.Set (ResolveContext.Options.FieldInitializerScope)) {
                                        resolved = base.DoResolve (ec) as ExpressionStatement;
                                }

                                ec.MemberContext = old;
                        }

                        return resolved;
                }

                public override void EmitStatement (EmitContext ec)
                {
                        if (resolved == null)
                                return;
                        
                        if (resolved != this)
                                resolved.EmitStatement (ec);
                        else
                                base.EmitStatement (ec);
                }
                
                public bool IsComplexInitializer {
                        get { return !(source is Constant); }
                }

                public bool IsDefaultInitializer {
                        get {
                                Constant c = source as Constant;
                                if (c == null)
                                        return false;
                                
                                FieldExpr fe = (FieldExpr)target;
                                return c.IsDefaultInitializer (fe.Type);
                        }
                }
        }

        class EventAddOrRemove : ExpressionStatement {
                EventExpr target;
                Binary.Operator op;
                Expression source;

                public EventAddOrRemove (Expression target, Binary.Operator op, Expression source, Location loc)
                {
                        this.target = target as EventExpr;
                        this.op = op;
                        this.source = source;
                        this.loc = loc;
                }

                public override Expression CreateExpressionTree (ResolveContext ec)
                {
                        return new SimpleAssign (target, source).CreateExpressionTree (ec);
                }

                protected override Expression DoResolve (ResolveContext ec)
                {
                        if (op != Binary.Operator.Addition && op != Binary.Operator.Subtraction)
                                target.Error_AssignmentEventOnly (ec);

                        source = source.Resolve (ec);
                        if (source == null)
                                return null;

                        source = Convert.ImplicitConversionRequired (ec, source, target.Type, loc);
                        if (source == null)
                                return null;

                        eclass = ExprClass.Value;
                        type = TypeManager.void_type;
                        return this;
                }

                public override void Emit (EmitContext ec)
                {
                        if (RootContext.EvalMode)
                                EmitStatement (ec);
                        else
                                throw new InternalErrorException ("don't know what to emit");                           
                }

                public override void EmitStatement (EmitContext ec)
                {
                        target.EmitAddOrRemove (ec, op == Binary.Operator.Addition, source);
                }
        }

        //
        // This class is used for compound assignments.
        //
        public class CompoundAssign : Assign
        {
                // This is just a hack implemented for arrays only
                public sealed class TargetExpression : Expression
                {
                        Expression child;
                        public TargetExpression (Expression child)
                        {
                                this.child = child;
                                this.loc = child.Location;
                        }

                        public override Expression CreateExpressionTree (ResolveContext ec)
                        {
                                throw new NotSupportedException ("ET");
                        }

                        protected override Expression DoResolve (ResolveContext ec)
                        {
                                type = child.Type;
                                eclass = ExprClass.Value;
                                return this;
                        }

                        public override void Emit (EmitContext ec)
                        {
                                child.Emit (ec);
                        }
                }

                // Used for underlying binary operator
                readonly Binary.Operator op;
                Expression right;
                Expression left;

                public CompoundAssign (Binary.Operator op, Expression target, Expression source)
                        : base (target, source, target.Location)
                {
                        right = source;
                        this.op = op;
                }

                public CompoundAssign (Binary.Operator op, Expression target, Expression source, Expression left)
                        : this (op, target, source)
                {
                        this.left = left;
                }

                protected override Expression DoResolve (ResolveContext ec)
                {
                        right = right.Resolve (ec);
                        if (right == null)
                                return null;

                        MemberAccess ma = target as MemberAccess;
                        using (ec.Set (ResolveContext.Options.CompoundAssignmentScope)) {
                                target = target.Resolve (ec);
                        }
                        
                        if (target == null)
                                return null;

                        if (target is MethodGroupExpr){
                                ec.Report.Error (1656, loc,
                                        "Cannot assign to `{0}' because it is a `{1}'",
                                        ((MethodGroupExpr)target).Name, target.ExprClassName);
                                return null;
                        }

                        if (target is EventExpr)
                                return new EventAddOrRemove (target, op, right, loc).Resolve (ec);

                        //
                        // Only now we can decouple the original source/target
                        // into a tree, to guarantee that we do not have side
                        // effects.
                        //
                        if (left == null)
                                left = new TargetExpression (target);

                        source = new Binary (op, left, right, true, loc);

                        if (target is DynamicMemberBinder) {
                                Arguments targs = ((DynamicMemberBinder) target).Arguments;
                                source = source.Resolve (ec);

                                Arguments args = new Arguments (2);
                                args.AddRange (targs);
                                args.Add (new Argument (source));
                                source = new DynamicMemberBinder (ma.Name, args, loc).ResolveLValue (ec, right);

                                // Handles possible event addition/subtraction
                                if (op == Binary.Operator.Addition || op == Binary.Operator.Subtraction) {
                                        args = new Arguments (2);
                                        args.AddRange (targs);
                                        args.Add (new Argument (right));
                                        string method_prefix = op == Binary.Operator.Addition ?
                                                Event.AEventAccessor.AddPrefix : Event.AEventAccessor.RemovePrefix;

                                        var invoke = DynamicInvocation.CreateSpecialNameInvoke (
                                                new MemberAccess (right, method_prefix + ma.Name, loc), args, loc).Resolve (ec);

                                        args = new Arguments (1);
                                        args.AddRange (targs);
                                        source = new DynamicEventCompoundAssign (ma.Name, args,
                                                (ExpressionStatement) source, (ExpressionStatement) invoke, loc).Resolve (ec);
                                }

                                return source;
                        }

                        return base.DoResolve (ec);
                }

                protected override Expression ResolveConversions (ResolveContext ec)
                {
                        TypeSpec target_type = target.Type;

                        //
                        // 1. the return type is implicitly convertible to the type of target
                        //
                        if (Convert.ImplicitConversionExists (ec, source, target_type)) {
                                source = Convert.ImplicitConversion (ec, source, target_type, loc);
                                return this;
                        }

                        //
                        // Otherwise, if the selected operator is a predefined operator
                        //
                        Binary b = source as Binary;
                        if (b != null) {
                                //
                                // 2a. the operator is a shift operator
                                //
                                // 2b. the return type is explicitly convertible to the type of x, and
                                // y is implicitly convertible to the type of x
                                //
                                if ((b.Oper & Binary.Operator.ShiftMask) != 0 ||
                                        Convert.ImplicitConversionExists (ec, right, target_type)) {
                                        source = Convert.ExplicitConversion (ec, source, target_type, loc);
                                        return this;
                                }
                        }

                        if (source.Type == InternalType.Dynamic) {
                                Arguments arg = new Arguments (1);
                                arg.Add (new Argument (source));
                                return new SimpleAssign (target, new DynamicConversion (target_type, CSharpBinderFlags.ConvertExplicit, arg, loc), loc).Resolve (ec);
                        }

                        right.Error_ValueCannotBeConverted (ec, loc, target_type, false);
                        return null;
                }

                protected override void CloneTo (CloneContext clonectx, Expression t)
                {
                        CompoundAssign ctarget = (CompoundAssign) t;

                        ctarget.right = ctarget.source = source.Clone (clonectx);
                        ctarget.target = target.Clone (clonectx);
                }
        }
}