source: trunk/HeuristicLab.ExtLibs/HeuristicLab.NRefactory/5.5.0/NRefactory.CSharp-5.5.0/Parser/mcs/generic.cs @ 15888

//
// generic.cs: Generics support
//
// Authors: Martin Baulig (martin@ximian.com)
//          Miguel de Icaza (miguel@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 (http://www.ximian.com)
// Copyright 2004-2008 Novell, Inc
// Copyright 2011 Xamarin, Inc (http://www.xamarin.com)
//

using System;
using System.Collections.Generic;
using System.Text;
using System.Linq;

#if STATIC
using MetaType = IKVM.Reflection.Type;
using IKVM.Reflection;
using IKVM.Reflection.Emit;
#else
using MetaType = System.Type;
using System.Reflection;
using System.Reflection.Emit;
#endif

namespace Mono.CSharp {
  public class VarianceDecl
  {
    public VarianceDecl (Variance variance, Location loc)
    {
      this.Variance = variance;
      this.Location = loc;
    }

    public Variance Variance { get; private set; }
    public Location Location { get; private set; }

    public static Variance CheckTypeVariance (TypeSpec t, Variance expected, IMemberContext member)
    {
      var tp = t as TypeParameterSpec;
      if (tp != null) {
        var v = tp.Variance;
        if (expected == Variance.None && v != expected ||
          expected == Variance.Covariant && v == Variance.Contravariant ||
          expected == Variance.Contravariant && v == Variance.Covariant) {
          ((TypeParameter) tp.MemberDefinition).ErrorInvalidVariance (member, expected);
        }

        return expected;
      }

      if (t.TypeArguments.Length > 0) {
        var targs_definition = t.MemberDefinition.TypeParameters;
        TypeSpec[] targs = TypeManager.GetTypeArguments (t);
        for (int i = 0; i < targs.Length; ++i) {
          var v = targs_definition[i].Variance;
          CheckTypeVariance (targs[i], (Variance) ((int) v * (int) expected), member);
        }

        return expected;
      }

      var ac = t as ArrayContainer;
      if (ac != null)
        return CheckTypeVariance (ac.Element, expected, member);

      return Variance.None;
    }
  }

  public enum Variance
  {
    //
    // Don't add or modify internal values, they are used as -/+ calculation signs
    //
    None      = 0,
    Covariant   = 1,
    Contravariant = -1
  }

  [Flags]
  public enum SpecialConstraint
  {
    None    = 0,
    Constructor = 1 << 2,
    Class   = 1 << 3,
    Struct    = 1 << 4
  }

  public class SpecialContraintExpr : FullNamedExpression
  {
    public SpecialContraintExpr (SpecialConstraint constraint, Location loc)
    {
      this.loc = loc;
      this.Constraint = constraint;
    }

    public SpecialConstraint Constraint { get; private set; }

    protected override Expression DoResolve (ResolveContext rc)
    {
      throw new NotImplementedException ();
    }

    public override FullNamedExpression ResolveAsTypeOrNamespace (IMemberContext mc, bool allowUnboundTypeArguments)
    {
      throw new NotImplementedException ();
    }
  }

  //
  // A set of parsed constraints for a type parameter
  //
  public class Constraints
  {
    readonly SimpleMemberName tparam;
    readonly List<FullNamedExpression> constraints;
    readonly Location loc;
    bool resolved;
    bool resolving;
    
    public IEnumerable<FullNamedExpression> ConstraintExpressions {
      get {
        return constraints;
      }
    }

    public Constraints (SimpleMemberName tparam, List<FullNamedExpression> constraints, Location loc)
    {
      this.tparam = tparam;
      this.constraints = constraints;
      this.loc = loc;
    }

    #region Properties

    public List<FullNamedExpression> TypeExpressions {
      get {
        return constraints;
      }
    }

    public Location Location {
      get {
        return loc;
      }
    }

    public SimpleMemberName TypeParameter {
      get {
        return tparam;
      }
    }

    #endregion

    public static bool CheckConflictingInheritedConstraint (TypeParameterSpec spec, TypeSpec bb, IMemberContext context, Location loc)
    {
      if (spec.HasSpecialClass && bb.IsStruct) {
        context.Module.Compiler.Report.Error (455, loc,
          "Type parameter `{0}' inherits conflicting constraints `{1}' and `{2}'",
          spec.Name, "class", bb.GetSignatureForError ());

        return false;
      }

      return CheckConflictingInheritedConstraint (spec, spec.BaseType, bb, context, loc);
    }

    static bool CheckConflictingInheritedConstraint (TypeParameterSpec spec, TypeSpec ba, TypeSpec bb, IMemberContext context, Location loc)
    {
      if (ba == bb)
        return true;

      if (TypeSpec.IsBaseClass (ba, bb, false) || TypeSpec.IsBaseClass (bb, ba, false))
        return true;

      Error_ConflictingConstraints (context, spec, ba, bb, loc);
      return false;
    }

    public static void Error_ConflictingConstraints (IMemberContext context, TypeParameterSpec tp, TypeSpec ba, TypeSpec bb, Location loc)
    {
      context.Module.Compiler.Report.Error (455, loc,
        "Type parameter `{0}' inherits conflicting constraints `{1}' and `{2}'",
        tp.Name, ba.GetSignatureForError (), bb.GetSignatureForError ());
    }

    public void CheckGenericConstraints (IMemberContext context, bool obsoleteCheck)
    {
      foreach (var c in constraints) {
        if (c == null)
          continue;

        var t = c.Type;
        if (t == null)
          continue;

        if (obsoleteCheck) {
          ObsoleteAttribute obsolete_attr = t.GetAttributeObsolete ();
          if (obsolete_attr != null)
            AttributeTester.Report_ObsoleteMessage (obsolete_attr, t.GetSignatureForError (), c.Location, context.Module.Compiler.Report);
        }

        ConstraintChecker.Check (context, t, c.Location);
      }
    }

    //
    // Resolve the constraints types with only possible early checks, return
    // value `false' is reserved for recursive failure
    //
    public bool Resolve (IMemberContext context, TypeParameter tp)
    {
      if (resolved)
        return true;

      if (resolving)
        return false;

      resolving = true;
      var spec = tp.Type;
      List<TypeParameterSpec> tparam_types = null;
      bool iface_found = false;

      spec.BaseType = context.Module.Compiler.BuiltinTypes.Object;

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

        if (constraint is SpecialContraintExpr) {
          spec.SpecialConstraint |= ((SpecialContraintExpr) constraint).Constraint;
          if (spec.HasSpecialStruct)
            spec.BaseType = context.Module.Compiler.BuiltinTypes.ValueType;

          // Set to null as it does not have a type
          constraints[i] = null;
          continue;
        }

        var type = constraint.ResolveAsType (context);
        if (type == null)
          continue;

        if (type.Arity > 0 && ((InflatedTypeSpec) type).HasDynamicArgument ()) {
          context.Module.Compiler.Report.Error (1968, constraint.Location,
            "A constraint cannot be the dynamic type `{0}'", type.GetSignatureForError ());
          continue;
        }

        if (!context.CurrentMemberDefinition.IsAccessibleAs (type)) {
          context.Module.Compiler.Report.SymbolRelatedToPreviousError (type);
          context.Module.Compiler.Report.Error (703, loc,
            "Inconsistent accessibility: constraint type `{0}' is less accessible than `{1}'",
            type.GetSignatureForError (), context.GetSignatureForError ());
        }

        if (type.IsInterface) {
          if (!spec.AddInterface (type)) {
            context.Module.Compiler.Report.Error (405, constraint.Location,
              "Duplicate constraint `{0}' for type parameter `{1}'", type.GetSignatureForError (), tparam.Value);
          }

          iface_found = true;
          continue;
        }
          
        var constraint_tp = type as TypeParameterSpec;
        if (constraint_tp != null) {
          if (tparam_types == null) {
            tparam_types = new List<TypeParameterSpec> (2);
          } else if (tparam_types.Contains (constraint_tp)) {
            context.Module.Compiler.Report.Error (405, constraint.Location,
              "Duplicate constraint `{0}' for type parameter `{1}'", type.GetSignatureForError (), tparam.Value);
            continue;
          }

          //
          // Checks whether each generic method parameter constraint type
          // is valid with respect to T
          //
          if (tp.IsMethodTypeParameter) {
            VarianceDecl.CheckTypeVariance (type, Variance.Contravariant, context);
          }

          var tp_def = constraint_tp.MemberDefinition as TypeParameter;
          if (tp_def != null && !tp_def.ResolveConstraints (context)) {
            context.Module.Compiler.Report.Error (454, constraint.Location,
              "Circular constraint dependency involving `{0}' and `{1}'",
              constraint_tp.GetSignatureForError (), tp.GetSignatureForError ());
            continue;
          }

          //
          // Checks whether there are no conflicts between type parameter constraints
          //
          // class Foo<T, U>
          //      where T : A
          //      where U : B, T
          //
          // A and B are not convertible and only 1 class constraint is allowed
          //
          if (constraint_tp.HasTypeConstraint) {
            if (spec.HasTypeConstraint || spec.HasSpecialStruct) {
              if (!CheckConflictingInheritedConstraint (spec, constraint_tp.BaseType, context, constraint.Location))
                continue;
            } else {
              for (int ii = 0; ii < tparam_types.Count; ++ii) {
                if (!tparam_types[ii].HasTypeConstraint)
                  continue;

                if (!CheckConflictingInheritedConstraint (spec, tparam_types[ii].BaseType, constraint_tp.BaseType, context, constraint.Location))
                  break;
              }
            }
          }

          if (constraint_tp.TypeArguments != null) {
            var eb = constraint_tp.GetEffectiveBase ();
            if (eb != null && !CheckConflictingInheritedConstraint (spec, eb, spec.BaseType, context, constraint.Location))
              break;
          }

          if (constraint_tp.HasSpecialStruct) {
            context.Module.Compiler.Report.Error (456, constraint.Location,
              "Type parameter `{0}' has the `struct' constraint, so it cannot be used as a constraint for `{1}'",
              constraint_tp.GetSignatureForError (), tp.GetSignatureForError ());
            continue;
          }

          tparam_types.Add (constraint_tp);
          continue;
        }

        if (iface_found || spec.HasTypeConstraint) {
          context.Module.Compiler.Report.Error (406, constraint.Location,
            "The class type constraint `{0}' must be listed before any other constraints. Consider moving type constraint to the beginning of the constraint list",
            type.GetSignatureForError ());
        }

        if (spec.HasSpecialStruct || spec.HasSpecialClass) {
          context.Module.Compiler.Report.Error (450, constraint.Location,
            "`{0}': cannot specify both a constraint class and the `class' or `struct' constraint",
            type.GetSignatureForError ());
        }

        switch (type.BuiltinType) {
        case BuiltinTypeSpec.Type.Array:
        case BuiltinTypeSpec.Type.Delegate:
        case BuiltinTypeSpec.Type.MulticastDelegate:
        case BuiltinTypeSpec.Type.Enum:
        case BuiltinTypeSpec.Type.ValueType:
        case BuiltinTypeSpec.Type.Object:
          context.Module.Compiler.Report.Error (702, constraint.Location,
            "A constraint cannot be special class `{0}'", type.GetSignatureForError ());
          continue;
        case BuiltinTypeSpec.Type.Dynamic:
          context.Module.Compiler.Report.Error (1967, constraint.Location,
            "A constraint cannot be the dynamic type");
          continue;
        }

        if (type.IsSealed || !type.IsClass) {
          context.Module.Compiler.Report.Error (701, loc,
            "`{0}' is not a valid constraint. A constraint must be an interface, a non-sealed class or a type parameter",
            type.GetSignatureForError ());
          continue;
        }

        if (type.IsStatic) {
          context.Module.Compiler.Report.Error (717, constraint.Location,
            "`{0}' is not a valid constraint. Static classes cannot be used as constraints",
            type.GetSignatureForError ());
        }

        spec.BaseType = type;
      }

      if (tparam_types != null)
        spec.TypeArguments = tparam_types.ToArray ();

      resolving = false;
      resolved = true;
      return true;
    }

    public void VerifyClsCompliance (Report report)
    {
      foreach (var c in constraints)
      {
        if (c == null)
          continue;

        if (!c.Type.IsCLSCompliant ()) {
          report.SymbolRelatedToPreviousError (c.Type);
          report.Warning (3024, 1, loc, "Constraint type `{0}' is not CLS-compliant",
            c.Type.GetSignatureForError ());
        }
      }
    }
  }

  //
  // A type parameter for a generic type or generic method definition
  //
  public class TypeParameter : MemberCore, ITypeDefinition
  {
    static readonly string[] attribute_target = { "type parameter" };
    
    Constraints constraints;
    GenericTypeParameterBuilder builder;
    readonly TypeParameterSpec spec;

    public TypeParameter (int index, MemberName name, Constraints constraints, Attributes attrs, Variance Variance)
      : base (null, name, attrs)
    {
      this.constraints = constraints;
      this.spec = new TypeParameterSpec (null, index, this, SpecialConstraint.None, Variance, null);
    }

    //
    // Used by parser
    //
    public TypeParameter (MemberName name, Attributes attrs, VarianceDecl variance)
      : base (null, name, attrs)
    {
      var var = variance == null ? Variance.None : variance.Variance;
      this.spec = new TypeParameterSpec (null, -1, this, SpecialConstraint.None, var, null);
      this.VarianceDecl = variance;
    }
    
    public TypeParameter (TypeParameterSpec spec, TypeSpec parentSpec, MemberName name, Attributes attrs)
      : base (null, name, attrs)
    {
      this.spec = new TypeParameterSpec (parentSpec, spec.DeclaredPosition, spec.MemberDefinition, spec.SpecialConstraint, spec.Variance, null) {
        BaseType = spec.BaseType,
        InterfacesDefined = spec.InterfacesDefined,
        TypeArguments = spec.TypeArguments
      };
    }
    
    #region Properties

    public override AttributeTargets AttributeTargets {
      get {
        return AttributeTargets.GenericParameter;
      }
    }

    public Constraints Constraints {
      get {
        return constraints;
      }
      set {
        constraints = value;
      }
    }

    public IAssemblyDefinition DeclaringAssembly {
      get {
        return Module.DeclaringAssembly;
      }
    }

    public override string DocCommentHeader {
      get {
        throw new InvalidOperationException (
          "Unexpected attempt to get doc comment from " + this.GetType ());
      }
    }

    bool ITypeDefinition.IsComImport {
      get {
        return false;
      }
    }

    bool ITypeDefinition.IsPartial {
      get {
        return false;
      }
    }

    public bool IsMethodTypeParameter {
      get {
        return spec.IsMethodOwned;
      }
    }

    bool ITypeDefinition.IsTypeForwarder {
      get {
        return false;
      }
    }

    bool ITypeDefinition.IsCyclicTypeForwarder {
      get {
        return false;
      }
    }

    public string Name {
      get {
        return MemberName.Name;
      }
    }

    public string Namespace {
      get {
        return null;
      }
    }

    public TypeParameterSpec Type {
      get {
        return spec;
      }
    }

    public int TypeParametersCount {
      get {
        return 0;
      }
    }

    public TypeParameterSpec[] TypeParameters {
      get {
        return null;
      }
    }

    public override string[] ValidAttributeTargets {
      get {
        return attribute_target;
      }
    }

    public Variance Variance {
      get {
        return spec.Variance;
      }
    }

    public VarianceDecl VarianceDecl { get; private set; }

    #endregion

    //
    // This is called for each part of a partial generic type definition.
    //
    // If partial type parameters constraints are not null and we don't
    // already have constraints they become our constraints. If we already
    // have constraints, we must check that they're same.
    //
    public bool AddPartialConstraints (TypeDefinition part, TypeParameter tp)
    {
      if (builder == null)
        throw new InvalidOperationException ();

      var new_constraints = tp.constraints;
      if (new_constraints == null)
        return true;

      // TODO: could create spec only
      //tp.Define (null, -1, part.Definition);
      tp.spec.DeclaringType = part.Definition;
      if (!tp.ResolveConstraints (part))
        return false;

      if (constraints != null)
        return spec.HasSameConstraintsDefinition (tp.Type);

      // Copy constraint from resolved part to partial container
      spec.SpecialConstraint = tp.spec.SpecialConstraint;
      spec.InterfacesDefined = tp.spec.InterfacesDefined;
      spec.TypeArguments = tp.spec.TypeArguments;
      spec.BaseType = tp.spec.BaseType;
      
      return true;
    }

    public override void ApplyAttributeBuilder (Attribute a, MethodSpec ctor, byte[] cdata, PredefinedAttributes pa)
    {
      builder.SetCustomAttribute ((ConstructorInfo) ctor.GetMetaInfo (), cdata);
    }

    public void CheckGenericConstraints (bool obsoleteCheck)
    {
      if (constraints != null)
        constraints.CheckGenericConstraints (this, obsoleteCheck);
    }

    public TypeParameter CreateHoistedCopy (TypeSpec declaringSpec)
    {
      return new TypeParameter (spec, declaringSpec, MemberName, null);
    }

    public override bool Define ()
    {
      return true;
    }

    //
    // This is the first method which is called during the resolving
    // process; we're called immediately after creating the type parameters
    // with SRE (by calling `DefineGenericParameters()' on the TypeBuilder /
    // MethodBuilder).
    //
    public void Create (TypeSpec declaringType, TypeContainer parent)
    {
      if (builder != null)
        throw new InternalErrorException ();

      // Needed to get compiler reference
      this.Parent = parent;
      spec.DeclaringType = declaringType;
    }

    public void Define (GenericTypeParameterBuilder type)
    {
      this.builder = type;
      spec.SetMetaInfo (type);
    }

    public void Define (TypeParameter tp)
    {
      builder = tp.builder;
    }

    public void EmitConstraints (GenericTypeParameterBuilder builder)
    {
      var attr = GenericParameterAttributes.None;
      if (spec.Variance == Variance.Contravariant)
        attr |= GenericParameterAttributes.Contravariant;
      else if (spec.Variance == Variance.Covariant)
        attr |= GenericParameterAttributes.Covariant;

      if (spec.HasSpecialClass)
        attr |= GenericParameterAttributes.ReferenceTypeConstraint;
      else if (spec.HasSpecialStruct)
        attr |= GenericParameterAttributes.NotNullableValueTypeConstraint | GenericParameterAttributes.DefaultConstructorConstraint;

      if (spec.HasSpecialConstructor)
        attr |= GenericParameterAttributes.DefaultConstructorConstraint;

      if (spec.BaseType.BuiltinType != BuiltinTypeSpec.Type.Object)
        builder.SetBaseTypeConstraint (spec.BaseType.GetMetaInfo ());

      if (spec.InterfacesDefined != null)
        builder.SetInterfaceConstraints (spec.InterfacesDefined.Select (l => l.GetMetaInfo ()).ToArray ());

      if (spec.TypeArguments != null) {
        var meta_constraints = new List<MetaType> (spec.TypeArguments.Length);
        foreach (var c in spec.TypeArguments) {
          //
          // Inflated type parameters can collide with special constraint types, don't
          // emit any such type parameter.
          //
          if (c.BuiltinType == BuiltinTypeSpec.Type.Object || c.BuiltinType == BuiltinTypeSpec.Type.ValueType)
            continue;

          meta_constraints.Add (c.GetMetaInfo ());
        }

        builder.SetInterfaceConstraints (meta_constraints.ToArray ());
      }

      builder.SetGenericParameterAttributes (attr);
    }

    public override void Emit ()
    {
      EmitConstraints (builder);

      if (OptAttributes != null)
        OptAttributes.Emit ();

      base.Emit ();
    }

    public void ErrorInvalidVariance (IMemberContext mc, Variance expected)
    {
      Report.SymbolRelatedToPreviousError (mc.CurrentMemberDefinition);
      string input_variance = Variance == Variance.Contravariant ? "contravariant" : "covariant";
      string gtype_variance;
      switch (expected) {
      case Variance.Contravariant: gtype_variance = "contravariantly"; break;
      case Variance.Covariant: gtype_variance = "covariantly"; break;
      default: gtype_variance = "invariantly"; break;
      }

      Delegate d = mc as Delegate;
      string parameters = d != null ? d.Parameters.GetSignatureForError () : "";

      Report.Error (1961, Location,
        "The {2} type parameter `{0}' must be {3} valid on `{1}{4}'",
          GetSignatureForError (), mc.GetSignatureForError (), input_variance, gtype_variance, parameters);
    }

    public TypeSpec GetAttributeCoClass ()
    {
      return null;
    }

    public string GetAttributeDefaultMember ()
    {
      throw new NotSupportedException ();
    }

    public AttributeUsageAttribute GetAttributeUsage (PredefinedAttribute pa)
    {
      throw new NotSupportedException ();
    }

    public override string GetSignatureForDocumentation ()
    {
      throw new NotImplementedException ();
    }

    public override string GetSignatureForError ()
    {
      return MemberName.Name;
    }

    bool ITypeDefinition.IsInternalAsPublic (IAssemblyDefinition assembly)
    {
      return spec.MemberDefinition.DeclaringAssembly == assembly;
    }

    public void LoadMembers (TypeSpec declaringType, bool onlyTypes, ref MemberCache cache)
    {
      throw new NotSupportedException ("Not supported for compiled definition");
    }

    //
    // Resolves all type parameter constraints
    //
    public bool ResolveConstraints (IMemberContext context)
    {
      if (constraints != null)
        return constraints.Resolve (context, this);

      if (spec.BaseType == null)
        spec.BaseType = context.Module.Compiler.BuiltinTypes.Object;

      return true;
    }

    public override bool IsClsComplianceRequired ()
    {
      return false;
    }

    public new void VerifyClsCompliance ()
    {
      if (constraints != null)
        constraints.VerifyClsCompliance (Report);
    }

    public void WarningParentNameConflict (TypeParameter conflict)
    {
      conflict.Report.SymbolRelatedToPreviousError (conflict.Location, null);
      conflict.Report.Warning (693, 3, Location,
        "Type parameter `{0}' has the same name as the type parameter from outer type `{1}'",
        GetSignatureForError (), conflict.CurrentType.GetSignatureForError ());
    }
  }

  [System.Diagnostics.DebuggerDisplay ("{DisplayDebugInfo()}")]
  public class TypeParameterSpec : TypeSpec
  {
    public static readonly new TypeParameterSpec[] EmptyTypes = new TypeParameterSpec[0];

    Variance variance;
    SpecialConstraint spec;
    int tp_pos;
    TypeSpec[] targs;
    TypeSpec[] ifaces_defined;
    TypeSpec effective_base;

    //
    // Creates type owned type parameter
    //
    public TypeParameterSpec (TypeSpec declaringType, int index, ITypeDefinition definition, SpecialConstraint spec, Variance variance, MetaType info)
      : base (MemberKind.TypeParameter, declaringType, definition, info, Modifiers.PUBLIC)
    {
      this.variance = variance;
      this.spec = spec;
      state &= ~StateFlags.Obsolete_Undetected;
      tp_pos = index;
    }

    //
    // Creates method owned type parameter
    //
    public TypeParameterSpec (int index, ITypeDefinition definition, SpecialConstraint spec, Variance variance, MetaType info)
      : this (null, index, definition, spec, variance, info)
    {
    }

    #region Properties

    public int DeclaredPosition {
      get {
        return tp_pos;
      }
      set {
        tp_pos = value;
      }
    }

    public bool HasSpecialConstructor {
      get {
        return (spec & SpecialConstraint.Constructor) != 0;
      }
    }

    public bool HasSpecialClass {
      get {
        return (spec & SpecialConstraint.Class) != 0;
      }
    }

    public bool HasSpecialStruct {
      get {
        return (spec & SpecialConstraint.Struct) != 0;
      }
    }

    public bool HasAnyTypeConstraint {
      get {
        return (spec & (SpecialConstraint.Class | SpecialConstraint.Struct)) != 0 || ifaces != null || targs != null || HasTypeConstraint;
      }
    }

    public bool HasTypeConstraint {
      get {
        var bt = BaseType.BuiltinType;
        return bt != BuiltinTypeSpec.Type.Object && bt != BuiltinTypeSpec.Type.ValueType;
      }
    }

    public override IList<TypeSpec> Interfaces {
      get {
        if ((state & StateFlags.InterfacesExpanded) == 0) {
          if (ifaces != null) {
            if (ifaces_defined == null)
              ifaces_defined = ifaces.ToArray ();

            for (int i = 0; i < ifaces_defined.Length; ++i ) {
              var iface_type = ifaces_defined[i];
              var td = iface_type.MemberDefinition as TypeDefinition;
              if (td != null)
                td.DoExpandBaseInterfaces ();

              if (iface_type.Interfaces != null) {
                for (int ii = 0; ii < iface_type.Interfaces.Count; ++ii) {
                  var ii_iface_type = iface_type.Interfaces [ii];
                  AddInterface (ii_iface_type);
                }
              }
            }
          } else if (ifaces_defined == null) {
            ifaces_defined = ifaces == null ? TypeSpec.EmptyTypes : ifaces.ToArray ();
          }

          //
          // Include all base type interfaces too, see ImportTypeBase for details
          //
          if (BaseType != null) {
            var td = BaseType.MemberDefinition as TypeDefinition;
            if (td != null)
              td.DoExpandBaseInterfaces ();

            if (BaseType.Interfaces != null) {
              foreach (var iface in BaseType.Interfaces) {
                AddInterface (iface);
              }
            }
          }

          state |= StateFlags.InterfacesExpanded;
        }

        return ifaces;
      }
    }

    //
    // Unexpanded interfaces list
    //
    public TypeSpec[] InterfacesDefined {
      get {
        if (ifaces_defined == null) {
          ifaces_defined = ifaces == null ? TypeSpec.EmptyTypes : ifaces.ToArray ();
        }

        return ifaces_defined.Length == 0 ? null : ifaces_defined;
      }
      set {
        ifaces_defined = value;
        if (value != null && value.Length != 0)
          ifaces = new List<TypeSpec> (value);
      }
    }

    public bool IsConstrained {
      get {
        return spec != SpecialConstraint.None || ifaces != null || targs != null || HasTypeConstraint;
      }
    }

    //
    // Returns whether the type parameter is known to be a reference type
    //
    public new bool IsReferenceType {
      get {
        if ((spec & (SpecialConstraint.Class | SpecialConstraint.Struct)) != 0)
          return (spec & SpecialConstraint.Class) != 0;

        //
        // Full check is needed (see IsValueType for details)
        //
        if (HasTypeConstraint && TypeSpec.IsReferenceType (BaseType))
          return true;

        if (targs != null) {
          foreach (var ta in targs) {
            //
            // Secondary special constraints are ignored (I am not sure why)
            //
            var tp = ta as TypeParameterSpec;
            if (tp != null && (tp.spec & (SpecialConstraint.Class | SpecialConstraint.Struct)) != 0)
              continue;

            if (TypeSpec.IsReferenceType (ta))
              return true;
          }
        }

        return false;
      }
    }

    //
    // Returns whether the type parameter is known to be a value type
    //
    public new bool IsValueType {
      get {
        //
        // Even if structs/enums cannot be used directly as constraints
        // they can apear as constraint type when inheriting base constraint
        // which has dependant type parameter constraint which has been
        // inflated using value type
        //
        // class A : B<int> { override void Foo<U> () {} }
        // class B<T> { virtual void Foo<U> () where U : T {} }
        //
        if (HasSpecialStruct)
          return true;

        if (targs != null) {
          foreach (var ta in targs) {
            if (TypeSpec.IsValueType (ta))
              return true;
          }
        }

        return false;
      }
    }

    public override string Name {
      get {
        return definition.Name;
      }
    }

    public bool IsMethodOwned {
      get {
        return DeclaringType == null;
      }
    }

    public SpecialConstraint SpecialConstraint {
      get {
        return spec;
      }
      set {
        spec = value;
      }
    }

    //
    // Types used to inflate the generic type
    //
    public new TypeSpec[] TypeArguments {
      get {
        return targs;
      }
      set {
        targs = value;
      }
    }

    public Variance Variance {
      get {
        return variance;
      }
    }

    #endregion

    public string DisplayDebugInfo ()
    {
      var s = GetSignatureForError ();
      return IsMethodOwned ? s + "!!" : s + "!";
    }

    //
    // Finds effective base class. The effective base class is always a class-type
    //
    public TypeSpec GetEffectiveBase ()
    {
      if (HasSpecialStruct)
        return BaseType;

      //
      // If T has a class-type constraint C but no type-parameter constraints, its effective base class is C
      //
      if (BaseType != null && targs == null) {
        //
        // If T has a constraint V that is a value-type, use instead the most specific base type of V that is a class-type.
        // 
        // LAMESPEC: Is System.ValueType always the most specific base type in this case?
        //
        // Note: This can never happen in an explicitly given constraint, but may occur when the constraints of a generic method
        // are implicitly inherited by an overriding method declaration or an explicit implementation of an interface method.
        //
        return BaseType.IsStruct ? BaseType.BaseType : BaseType;
      }

      if (effective_base != null)
        return effective_base;

      var types = new TypeSpec [HasTypeConstraint ? targs.Length + 1 : targs.Length];

      for (int i = 0; i < targs.Length; ++i) {
        var t = targs [i];

        // Same issue as above, inherited constraints can be of struct type
        if (t.IsStruct) {
          types [i] = t.BaseType;
          continue;
        }

        var tps = t as TypeParameterSpec;
        types [i] = tps != null ? tps.GetEffectiveBase () : t;
      }

      if (HasTypeConstraint)
        types [types.Length - 1] = BaseType;

      return effective_base = Convert.FindMostEncompassedType (types);
    }

    public override string GetSignatureForDocumentation ()
    {
      var prefix = IsMethodOwned ? "``" : "`";
      return prefix + DeclaredPosition;
    }

    public override string GetSignatureForError ()
    {
      return Name;
    }

    //
    // Constraints have to match by definition but not position, used by
    // partial classes or methods
    //
    public bool HasSameConstraintsDefinition (TypeParameterSpec other)
    {
      if (spec != other.spec)
        return false;

      if (BaseType != other.BaseType)
        return false;

      if (!TypeSpecComparer.Override.IsSame (InterfacesDefined, other.InterfacesDefined))
        return false;

      if (!TypeSpecComparer.Override.IsSame (targs, other.targs))
        return false;

      return true;
    }

    //
    // Constraints have to match by using same set of types, used by
    // implicit interface implementation
    //
    public bool HasSameConstraintsImplementation (TypeParameterSpec other)
    {
      if (spec != other.spec)
        return false;

      //
      // It can be same base type or inflated type parameter
      //
      // interface I<T> { void Foo<U> where U : T; }
      // class A : I<int> { void Foo<X> where X : int {} }
      //
      bool found;
      if (!TypeSpecComparer.Override.IsEqual (BaseType, other.BaseType)) {
        if (other.targs == null)
          return false;

        found = false;
        foreach (var otarg in other.targs) {
          if (TypeSpecComparer.Override.IsEqual (BaseType, otarg)) {
            found = true;
            break;
          }
        }

        if (!found)
          return false;
      }

      // Check interfaces implementation -> definition
      if (InterfacesDefined != null) {
        //
        // Iterate over inflated interfaces
        //
        foreach (var iface in Interfaces) {
          found = false;
          if (other.InterfacesDefined != null) {
            foreach (var oiface in other.Interfaces) {
              if (TypeSpecComparer.Override.IsEqual (iface, oiface)) {
                found = true;
                break;
              }
            }
          }

          if (found)
            continue;

          if (other.targs != null) {
            foreach (var otarg in other.targs) {
              if (TypeSpecComparer.Override.IsEqual (iface, otarg)) {
                found = true;
                break;
              }
            }
          }

          if (!found)
            return false;
        }
      }

      // Check interfaces implementation <- definition
      if (other.InterfacesDefined != null) {
        if (InterfacesDefined == null)
          return false;

        //
        // Iterate over inflated interfaces
        //
        foreach (var oiface in other.Interfaces) {
          found = false;
          foreach (var iface in Interfaces) {
            if (TypeSpecComparer.Override.IsEqual (iface, oiface)) {
              found = true;
              break;
            }
          }

          if (!found)
            return false;
        }
      }

      // Check type parameters implementation -> definition
      if (targs != null) {
        if (other.targs == null)
          return false;

        foreach (var targ in targs) {
          found = false;
          foreach (var otarg in other.targs) {
            if (TypeSpecComparer.Override.IsEqual (targ, otarg)) {
              found = true;
              break;
            }
          }

          if (!found)
            return false;
        }
      }

      // Check type parameters implementation <- definition
      if (other.targs != null) {
        foreach (var otarg in other.targs) {
          // Ignore inflated type arguments, were checked above
          if (!otarg.IsGenericParameter)
            continue;

          if (targs == null)
            return false;

          found = false;
          foreach (var targ in targs) {
            if (TypeSpecComparer.Override.IsEqual (targ, otarg)) {
              found = true;
              break;
            }
          }

          if (!found)
            return false;
        }       
      }

      return true;
    }

    public static TypeParameterSpec[] InflateConstraints (TypeParameterInflator inflator, TypeParameterSpec[] tparams)
    {
      return InflateConstraints (tparams, l => l, inflator);
    }

    public static TypeParameterSpec[] InflateConstraints<T> (TypeParameterSpec[] tparams, Func<T, TypeParameterInflator> inflatorFactory, T arg)
    {
      TypeParameterSpec[] constraints = null;
      TypeParameterInflator? inflator = null;

      for (int i = 0; i < tparams.Length; ++i) {
        var tp = tparams[i];
        if (tp.HasTypeConstraint || tp.InterfacesDefined != null || tp.TypeArguments != null) {
          if (constraints == null) {
            constraints = new TypeParameterSpec[tparams.Length];
            Array.Copy (tparams, constraints, constraints.Length);
          }

          //
          // Using a factory to avoid possibly expensive inflator build up
          //
          if (inflator == null)
            inflator = inflatorFactory (arg);

          constraints[i] = (TypeParameterSpec) constraints[i].InflateMember (inflator.Value);
        }
      }

      if (constraints == null)
        constraints = tparams;

      return constraints;
    }

    public void InflateConstraints (TypeParameterInflator inflator, TypeParameterSpec tps)
    {
      tps.BaseType = inflator.Inflate (BaseType);

      var defined = InterfacesDefined;
      if (defined != null) {
        tps.ifaces_defined = new TypeSpec[defined.Length];
        for (int i = 0; i < defined.Length; ++i)
          tps.ifaces_defined [i] = inflator.Inflate (defined[i]);
      } else if (ifaces_defined == TypeSpec.EmptyTypes) {
        tps.ifaces_defined = TypeSpec.EmptyTypes;
      }

      var ifaces = Interfaces;
      if (ifaces != null) {
        tps.ifaces = new List<TypeSpec> (ifaces.Count);
        for (int i = 0; i < ifaces.Count; ++i)
          tps.ifaces.Add (inflator.Inflate (ifaces[i]));
        tps.state |= StateFlags.InterfacesExpanded;
      }

      if (targs != null) {
        tps.targs = new TypeSpec[targs.Length];
        for (int i = 0; i < targs.Length; ++i)
          tps.targs[i] = inflator.Inflate (targs[i]);
      }
    }

    public override MemberSpec InflateMember (TypeParameterInflator inflator)
    {
      var tps = (TypeParameterSpec) MemberwiseClone ();
#if DEBUG
      tps.ID += 1000000;
#endif

      InflateConstraints (inflator, tps);
      return tps;
    }

    //
    // Populates type parameter members using type parameter constraints
    // The trick here is to be called late enough but not too late to
    // populate member cache with all members from other types
    //
    protected override void InitializeMemberCache (bool onlyTypes)
    {
      cache = new MemberCache ();

      //
      // For a type parameter the membercache is the union of the sets of members of the types
      // specified as a primary constraint or secondary constraint
      //
      if (BaseType.BuiltinType != BuiltinTypeSpec.Type.Object && BaseType.BuiltinType != BuiltinTypeSpec.Type.ValueType)
        cache.AddBaseType (BaseType);

      if (InterfacesDefined != null) {
        foreach (var iface_type in InterfacesDefined) {
          cache.AddInterface (iface_type);
        }
      }

      if (targs != null) {
        foreach (var ta in targs) {
          var tps = ta as TypeParameterSpec;
          IList<TypeSpec> ifaces;
          if (tps != null) {
            var b_type = tps.GetEffectiveBase ();
            if (b_type != null && b_type.BuiltinType != BuiltinTypeSpec.Type.Object && b_type.BuiltinType != BuiltinTypeSpec.Type.ValueType)
              cache.AddBaseType (b_type);

            ifaces = tps.InterfacesDefined;
          } else {
            ifaces = ta.Interfaces;
          }

          if (ifaces != null) {
            foreach (var iface_type in ifaces) {
              cache.AddInterface (iface_type);
            }
          }
        }
      }
    }

    public bool IsConvertibleToInterface (TypeSpec iface)
    {
      if (Interfaces != null) {
        foreach (var t in Interfaces) {
          if (t == iface)
            return true;
        }
      }

      if (TypeArguments != null) {
        foreach (var t in TypeArguments) {
          var tps = t as TypeParameterSpec;
          if (tps != null) {
            if (tps.IsConvertibleToInterface (iface))
              return true;

            continue;
          }

          if (t.ImplementsInterface (iface, false))
            return true;
        }
      }

      return false;
    }

    public static bool HasAnyTypeParameterTypeConstrained (IGenericMethodDefinition md)
    {
      var tps = md.TypeParameters;
      for (int i = 0; i < md.TypeParametersCount; ++i) {
        if (tps[i].HasAnyTypeConstraint) {
          return true;
        }
      }

      return false;
    }

    public static bool HasAnyTypeParameterConstrained (IGenericMethodDefinition md)
    {
      var tps = md.TypeParameters;
      for (int i = 0; i < md.TypeParametersCount; ++i) {
        if (tps[i].IsConstrained) {
          return true;
        }
      }

      return false;
    }

    public bool HasDependencyOn (TypeSpec type)
    {
      if (TypeArguments != null) {
        foreach (var targ in TypeArguments) {
          if (TypeSpecComparer.Override.IsEqual (targ, type))
            return true;

          var tps = targ as TypeParameterSpec;
          if (tps != null && tps.HasDependencyOn (type))
            return true;
        }
      }

      return false;
    }

    public override TypeSpec Mutate (TypeParameterMutator mutator)
    {
      return mutator.Mutate (this);
    }
  }

  public struct TypeParameterInflator
  {
    readonly TypeSpec type;
    readonly TypeParameterSpec[] tparams;
    readonly TypeSpec[] targs;
    readonly IModuleContext context;

    public TypeParameterInflator (TypeParameterInflator nested, TypeSpec type)
      : this (nested.context, type, nested.tparams, nested.targs)
    {
    }

    public TypeParameterInflator (IModuleContext context, TypeSpec type, TypeParameterSpec[] tparams, TypeSpec[] targs)
    {
      if (tparams.Length != targs.Length)
        throw new ArgumentException ("Invalid arguments");

      this.context = context;
      this.tparams = tparams;
      this.targs = targs;
      this.type = type;
    }

    #region Properties

    public IModuleContext Context {
      get {
        return context;
      }
    }

    public TypeSpec TypeInstance {
      get {
        return type;
      }
    }

    //
    // Type parameters to inflate
    //
    public TypeParameterSpec[] TypeParameters {
      get {
        return tparams;
      }
    }

    #endregion

    public TypeSpec Inflate (TypeSpec type)
    {
      var tp = type as TypeParameterSpec;
      if (tp != null)
        return Inflate (tp);

      var ec = type as ElementTypeSpec;
      if (ec != null) {
        var et = Inflate (ec.Element);
        if (et != ec.Element) {
          var ac = ec as ArrayContainer;
          if (ac != null)
            return ArrayContainer.MakeType (context.Module, et, ac.Rank);

          if (ec is PointerContainer)
            return PointerContainer.MakeType (context.Module, et);

          throw new NotImplementedException ();
        }

        return ec;
      }

      if (type.Kind == MemberKind.MissingType)
        return type;

      //
      // When inflating a nested type, inflate its parent first
      // in case it's using same type parameters (was inflated within the type)
      //
      TypeSpec[] targs;
      int i = 0;
      if (type.IsNested) {
        var parent = Inflate (type.DeclaringType);

        //
        // Keep the inflated type arguments
        // 
        targs = type.TypeArguments;

        //
        // When inflating imported nested type used inside same declaring type, we get TypeSpec
        // because the import cache helps us to catch it. However, that means we have to look at
        // type definition to get type argument (they are in fact type parameter in this case)
        //
        if (targs.Length == 0 && type.Arity > 0)
          targs = type.MemberDefinition.TypeParameters;

        //
        // Parent was inflated, find the same type on inflated type
        // to use same cache for nested types on same generic parent
        //
        type = MemberCache.FindNestedType (parent, type.Name, type.Arity);

        //
        // Handle the tricky case where parent shares local type arguments
        // which means inflating inflated type
        //
        // class Test<T> {
        //    public static Nested<T> Foo () { return null; }
        //
        //    public class Nested<U> {}
        //  }
        //
        //  return type of Test<string>.Foo() has to be Test<string>.Nested<string> 
        //
        if (targs.Length > 0) {
          var inflated_targs = new TypeSpec[targs.Length];
          for (; i < targs.Length; ++i)
            inflated_targs[i] = Inflate (targs[i]);

          type = type.MakeGenericType (context, inflated_targs);
        }

        return type;
      }

      // Nothing to do for non-generic type
      if (type.Arity == 0)
        return type;

      targs = new TypeSpec[type.Arity];

      //
      // Inflating using outside type arguments, var v = new Foo<int> (), class Foo<T> {}
      //
      if (type is InflatedTypeSpec) {
        for (; i < targs.Length; ++i)
          targs[i] = Inflate (type.TypeArguments[i]);

        type = type.GetDefinition ();
      } else {
        //
        // Inflating parent using inside type arguments, class Foo<T> { ITest<T> foo; }
        //
        var args = type.MemberDefinition.TypeParameters;
        foreach (var ds_tp in args)
          targs[i++] = Inflate (ds_tp);
      }

      return type.MakeGenericType (context, targs);
    }

    public TypeSpec Inflate (TypeParameterSpec tp)
    {
      for (int i = 0; i < tparams.Length; ++i)
        if (tparams [i] == tp)
          return targs[i];

      // This can happen when inflating nested types
      // without type arguments specified
      return tp;
    }
  }

  //
  // Before emitting any code we have to change all MVAR references to VAR
  // when the method is of generic type and has hoisted variables
  //
  public class TypeParameterMutator
  {
    readonly TypeParameters mvar;
    readonly TypeParameters var;
    readonly TypeParameterSpec[] src;
    Dictionary<TypeSpec, TypeSpec> mutated_typespec;

    public TypeParameterMutator (TypeParameters mvar, TypeParameters var)
    {
      if (mvar.Count != var.Count)
        throw new ArgumentException ();

      this.mvar = mvar;
      this.var = var;
    }

    public TypeParameterMutator (TypeParameterSpec[] srcVar, TypeParameters destVar)
    {
      if (srcVar.Length != destVar.Count)
        throw new ArgumentException ();

      this.src = srcVar;
      this.var = destVar;
    }

    #region Properties

    public TypeParameters MethodTypeParameters {
      get {
        return mvar;
      }
    }

    #endregion

    public static TypeSpec GetMemberDeclaringType (TypeSpec type)
    {
      if (type is InflatedTypeSpec) {
        if (type.DeclaringType == null)
          return type.GetDefinition ();

        var parent = GetMemberDeclaringType (type.DeclaringType);
        type = MemberCache.GetMember<TypeSpec> (parent, type);
      }

      return type;
    }

    public TypeSpec Mutate (TypeSpec ts)
    {
      TypeSpec value;
      if (mutated_typespec != null && mutated_typespec.TryGetValue (ts, out value))
        return value;

      value = ts.Mutate (this);
      if (mutated_typespec == null)
        mutated_typespec = new Dictionary<TypeSpec, TypeSpec> ();

      mutated_typespec.Add (ts, value);
      return value;
    }

    public TypeParameterSpec Mutate (TypeParameterSpec tp)
    {
      if (mvar != null) {
        for (int i = 0; i < mvar.Count; ++i) {
          if (mvar[i].Type == tp)
            return var[i].Type;
        }
      } else {
        for (int i = 0; i < src.Length; ++i) {
          if (src[i] == tp)
            return var[i].Type;
        }
      }

      return tp;
    }

    public TypeSpec[] Mutate (TypeSpec[] targs)
    {
      TypeSpec[] mutated = new TypeSpec[targs.Length];
      bool changed = false;
      for (int i = 0; i < targs.Length; ++i) {
        mutated[i] = Mutate (targs[i]);
        changed |= targs[i] != mutated[i];
      }

      return changed ? mutated : targs;
    }
  }

  /// <summary>
  ///   A TypeExpr which already resolved to a type parameter.
  /// </summary>
  public class TypeParameterExpr : TypeExpression
  {
    public TypeParameterExpr (TypeParameter type_parameter, Location loc)
      : base (type_parameter.Type, loc)
    {
      this.eclass = ExprClass.TypeParameter;
    }
  }

  public class InflatedTypeSpec : TypeSpec
  {
    TypeSpec[] targs;
    TypeParameterSpec[] constraints;
    readonly TypeSpec open_type;
    readonly IModuleContext context;

    public InflatedTypeSpec (IModuleContext context, TypeSpec openType, TypeSpec declaringType, TypeSpec[] targs)
      : base (openType.Kind, declaringType, openType.MemberDefinition, null, openType.Modifiers)
    {
      if (targs == null)
        throw new ArgumentNullException ("targs");

      this.state &= ~SharedStateFlags;
      this.state |= (openType.state & SharedStateFlags);

      this.context = context;
      this.open_type = openType;
      this.targs = targs;

      foreach (var arg in targs) {
        if (arg.HasDynamicElement || arg.BuiltinType == BuiltinTypeSpec.Type.Dynamic) {
          state |= StateFlags.HasDynamicElement;
          break;
        }
      }

      if (open_type.Kind == MemberKind.MissingType)
        MemberCache = MemberCache.Empty;

      if ((open_type.Modifiers & Modifiers.COMPILER_GENERATED) != 0)
        state |= StateFlags.ConstraintsChecked;
    }

    #region Properties

    public override TypeSpec BaseType {
      get {
        if (cache == null || (state & StateFlags.PendingBaseTypeInflate) != 0)
          InitializeMemberCache (true);

        return base.BaseType;
      }
    }

    //
    // Inflated type parameters with constraints array, mapping with type arguments is based on index
    //
    public TypeParameterSpec[] Constraints {
      get {
        if (constraints == null) {
          constraints = TypeParameterSpec.InflateConstraints (MemberDefinition.TypeParameters, l => l.CreateLocalInflator (context), this);
        }

        return constraints;
      }
    }

    //
    // Used to cache expensive constraints validation on constructed types
    //
    public bool HasConstraintsChecked {
      get {
        return (state & StateFlags.ConstraintsChecked) != 0;
      }
      set {
        state = value ? state | StateFlags.ConstraintsChecked : state & ~StateFlags.ConstraintsChecked;
      }
    }

    public override IList<TypeSpec> Interfaces {
      get {
        if (cache == null)
          InitializeMemberCache (true);

        return base.Interfaces;
      }
    }

    public override bool IsExpressionTreeType {
      get {
        return (open_type.state & StateFlags.InflatedExpressionType) != 0;
      }
    }

    public override bool IsArrayGenericInterface {
      get {
        return (open_type.state & StateFlags.GenericIterateInterface) != 0;
      }
    }

    public override bool IsGenericTask {
      get {
        return (open_type.state & StateFlags.GenericTask) != 0;
      }
    }

    public override bool IsNullableType {
      get {
        return (open_type.state & StateFlags.InflatedNullableType) != 0;
      }
    }

    //
    // Types used to inflate the generic  type
    //
    public override TypeSpec[] TypeArguments {
      get {
        return targs;
      }
    }

    #endregion

    public override bool AddInterface (TypeSpec iface)
    {
      var inflator = CreateLocalInflator (context);
      iface = inflator.Inflate (iface);
      if (iface == null)
        return false;

      return base.AddInterface (iface);
    }

    public static bool ContainsTypeParameter (TypeSpec type)
    {
      if (type.Kind == MemberKind.TypeParameter)
        return true;

      var element_container = type as ElementTypeSpec;
      if (element_container != null)
        return ContainsTypeParameter (element_container.Element);

      foreach (var t in type.TypeArguments) {
        if (ContainsTypeParameter (t)) {
          return true;
        }
      }

      return false;
    }

    public TypeParameterInflator CreateLocalInflator (IModuleContext context)
    {
      TypeParameterSpec[] tparams_full;
      TypeSpec[] targs_full = targs;
      if (IsNested) {
        //
        // Special case is needed when we are inflating an open type (nested type definition)
        // on inflated parent. Consider following case
        //
        // Foo<T>.Bar<U> => Foo<string>.Bar<U>
        //
        // Any later inflation of Foo<string>.Bar<U> has to also inflate T if used inside Bar<U>
        //
        List<TypeSpec> merged_targs = null;
        List<TypeParameterSpec> merged_tparams = null;

        var type = DeclaringType;

        do {
          if (type.TypeArguments.Length > 0) {
            if (merged_targs == null) {
              merged_targs = new List<TypeSpec> ();
              merged_tparams = new List<TypeParameterSpec> ();
              if (targs.Length > 0) {
                merged_targs.AddRange (targs);
                merged_tparams.AddRange (open_type.MemberDefinition.TypeParameters);
              }
            }
            merged_tparams.AddRange (type.MemberDefinition.TypeParameters);
            merged_targs.AddRange (type.TypeArguments);
          }
          type = type.DeclaringType;
        } while (type != null);

        if (merged_targs != null) {
          // Type arguments are not in the right order but it should not matter in this case
          targs_full = merged_targs.ToArray ();
          tparams_full = merged_tparams.ToArray ();
        } else if (targs.Length == 0) {
          tparams_full = TypeParameterSpec.EmptyTypes;
        } else {
          tparams_full = open_type.MemberDefinition.TypeParameters;
        }
      } else if (targs.Length == 0) {
        tparams_full = TypeParameterSpec.EmptyTypes;
      } else {
        tparams_full = open_type.MemberDefinition.TypeParameters;
      }

      return new TypeParameterInflator (context, this, tparams_full, targs_full);
    }

    MetaType CreateMetaInfo ()
    {
      //
      // Converts nested type arguments into right order
      // Foo<string, bool>.Bar<int> => string, bool, int
      //
      var all = new List<MetaType> ();
      TypeSpec type = this;
      TypeSpec definition = type;
      do {
        if (type.GetDefinition().IsGeneric) {
          all.InsertRange (0,
            type.TypeArguments != TypeSpec.EmptyTypes ?
            type.TypeArguments.Select (l => l.GetMetaInfo ()) :
            type.MemberDefinition.TypeParameters.Select (l => l.GetMetaInfo ()));
        }

        definition = definition.GetDefinition ();
        type = type.DeclaringType;
      } while (type != null);

      return definition.GetMetaInfo ().MakeGenericType (all.ToArray ());
    }

    public override ObsoleteAttribute GetAttributeObsolete ()
    {
      return open_type.GetAttributeObsolete ();
    }

    protected override bool IsNotCLSCompliant (out bool attrValue)
    {
      if (base.IsNotCLSCompliant (out attrValue))
        return true;

      foreach (var ta in TypeArguments) {
        if (ta.MemberDefinition.CLSAttributeValue == false)
          return true;
      }

      return false;
    }

    public override TypeSpec GetDefinition ()
    {
      return open_type;
    }

    public override MetaType GetMetaInfo ()
    {
      if (info == null)
        info = CreateMetaInfo ();

      return info;
    }

    public override string GetSignatureForError ()
    {
      if (IsNullableType)
        return targs[0].GetSignatureForError () + "?";

      return base.GetSignatureForError ();
    }

    protected override string GetTypeNameSignature ()
    {
      if (targs.Length == 0 || MemberDefinition is AnonymousTypeClass)
        return null;

      return "<" + TypeManager.CSharpName (targs) + ">";
    }

    public bool HasDynamicArgument ()
    {
      for (int i = 0; i < targs.Length; ++i) {
        var item = targs[i];

        if (item.BuiltinType == BuiltinTypeSpec.Type.Dynamic)
          return true;

        if (item is InflatedTypeSpec) {
          if (((InflatedTypeSpec) item).HasDynamicArgument ())
            return true;

          continue;
        }

        if (item.IsArray) {
          while (item.IsArray) {
            item = ((ArrayContainer) item).Element;
          }

          if (item.BuiltinType == BuiltinTypeSpec.Type.Dynamic)
            return true;
        }
      }

      return false;
    }

    protected override void InitializeMemberCache (bool onlyTypes)
    {
      if (cache == null) {
        var open_cache = onlyTypes ? open_type.MemberCacheTypes : open_type.MemberCache;

        // Surprisingly, calling MemberCache on open type could meantime create cache on this type
        // for imported type parameter constraints referencing nested type of this declaration
        if (cache == null)
          cache = new MemberCache (open_cache);
      }

      var inflator = CreateLocalInflator (context);

      //
      // Two stage inflate due to possible nested types recursive
      // references
      //
      // class A<T> {
      //    B b;
      //    class B {
      //      T Value;
      //    }
      // }
      //
      // When resolving type of `b' members of `B' cannot be 
      // inflated because are not yet available in membercache
      //
      if ((state & StateFlags.PendingMemberCacheMembers) == 0) {
        open_type.MemberCacheTypes.InflateTypes (cache, inflator);

        //
        // Inflate any implemented interfaces
        //
        if (open_type.Interfaces != null) {
          ifaces = new List<TypeSpec> (open_type.Interfaces.Count);
          foreach (var iface in open_type.Interfaces) {
            var iface_inflated = inflator.Inflate (iface);
            if (iface_inflated == null)
              continue;

            base.AddInterface (iface_inflated);
          }
        }

        //
        // Handles the tricky case of recursive nested base generic type
        //
        // class A<T> : Base<A<T>.Nested> {
        //    class Nested {}
        // }
        //
        // When inflating A<T>. base type is not yet known, secondary
        // inflation is required (not common case) once base scope
        // is known
        //
        if (open_type.BaseType == null) {
          if (IsClass)
            state |= StateFlags.PendingBaseTypeInflate;
        } else {
          BaseType = inflator.Inflate (open_type.BaseType);
        }
      } else if ((state & StateFlags.PendingBaseTypeInflate) != 0) {
        //
        // It can happen when resolving base type without being defined
        // which is not allowed to happen and will always lead to an error
        //
        // class B { class N {} }
        // class A<T> : A<B.N> {}
        //
        if (open_type.BaseType == null)
          return;

        BaseType = inflator.Inflate (open_type.BaseType);
        state &= ~StateFlags.PendingBaseTypeInflate;
      }

      if (onlyTypes) {
        state |= StateFlags.PendingMemberCacheMembers;
        return;
      }

      var tc = open_type.MemberDefinition as TypeDefinition;
      if (tc != null && !tc.HasMembersDefined) {
        //
        // Inflating MemberCache with undefined members
        //
        return;
      }

      if ((state & StateFlags.PendingBaseTypeInflate) != 0) {
        BaseType = inflator.Inflate (open_type.BaseType);
        state &= ~StateFlags.PendingBaseTypeInflate;
      }

      state &= ~StateFlags.PendingMemberCacheMembers;
      open_type.MemberCache.InflateMembers (cache, open_type, inflator);
    }

    public override TypeSpec Mutate (TypeParameterMutator mutator)
    {
      var targs = TypeArguments;
      if (targs != null)
        targs = mutator.Mutate (targs);

      var decl = DeclaringType;
      if (IsNested && DeclaringType.IsGenericOrParentIsGeneric)
        decl = mutator.Mutate (decl);

      if (targs == TypeArguments && decl == DeclaringType)
        return this;

      var mutated = (InflatedTypeSpec) MemberwiseClone ();
      if (decl != DeclaringType) {
        // Gets back MethodInfo in case of metaInfo was inflated
        //mutated.info = MemberCache.GetMember<TypeSpec> (DeclaringType.GetDefinition (), this).info;

        mutated.declaringType = decl;
        mutated.state |= StateFlags.PendingMetaInflate;
      }

      if (targs != null) {
        mutated.targs = targs;
        mutated.info = null;
      }

      return mutated;
    }
  }


  //
  // Tracks the type arguments when instantiating a generic type. It's used
  // by both type arguments and type parameters
  //
  public class TypeArguments
  {
    List<FullNamedExpression> args;
    TypeSpec[] atypes;

    public List<FullNamedExpression> Args {
      get { return this.args; }
    }

    public TypeArguments (params FullNamedExpression[] types)
    {
      this.args = new List<FullNamedExpression> (types);
    }

    public void Add (FullNamedExpression type)
    {
      args.Add (type);
    }

    /// <summary>
    ///   We may only be used after Resolve() is called and return the fully
    ///   resolved types.
    /// </summary>
    // TODO: Not needed, just return type from resolve
    public TypeSpec[] Arguments {
      get {
        return atypes;
      }
      set {
        atypes = value;
      }
    }

    public int Count {
      get {
        return args.Count;
      }
    }

    public virtual bool IsEmpty {
      get {
        return false;
      }
    }

    public List<FullNamedExpression> TypeExpressions {
      get {
        return this.args;
      }
    }

    public string GetSignatureForError()
    {
      StringBuilder sb = new StringBuilder ();
      for (int i = 0; i < Count; ++i) {
        var expr = args[i];
        if (expr != null)
          sb.Append (expr.GetSignatureForError ());

        if (i + 1 < Count)
          sb.Append (',');
      }

      return sb.ToString ();
    }

    /// <summary>
    ///   Resolve the type arguments.
    /// </summary>
    public virtual bool Resolve (IMemberContext ec)
    {
      if (atypes != null)
          return true;

      int count = args.Count;
      bool ok = true;

      atypes = new TypeSpec [count];

      var errors = ec.Module.Compiler.Report.Errors;

      for (int i = 0; i < count; i++){
        var te = args[i].ResolveAsType (ec);
        if (te == null) {
          ok = false;
          continue;
        }

        atypes[i] = te;

        if (te.IsStatic) {
          ec.Module.Compiler.Report.Error (718, args[i].Location, "`{0}': static classes cannot be used as generic arguments",
            te.GetSignatureForError ());
          ok = false;
        }

        if (te.IsPointer || te.IsSpecialRuntimeType) {
          ec.Module.Compiler.Report.Error (306, args[i].Location,
            "The type `{0}' may not be used as a type argument",
            te.GetSignatureForError ());
          ok = false;
        }
      }

      if (!ok || errors != ec.Module.Compiler.Report.Errors)
        atypes = null;

      return ok;
    }

    public TypeArguments Clone ()
    {
      TypeArguments copy = new TypeArguments ();
      foreach (var ta in args)
        copy.args.Add (ta);

      return copy;
    }
  }

  public class UnboundTypeArguments : TypeArguments
  {
    public UnboundTypeArguments (int arity)
      : base (new FullNamedExpression[arity])
    {
    }

    public override bool IsEmpty {
      get {
        return true;
      }
    }

    public override bool Resolve (IMemberContext ec)
    {
      // Nothing to be resolved
      return true;
    }
  }

  public class TypeParameters
  {
    List<TypeParameter> names;
    TypeParameterSpec[] types;

    public TypeParameters ()
    {
      names = new List<TypeParameter> ();
    }

    public TypeParameters (int count)
    {
      names = new List<TypeParameter> (count);
    }

    #region Properties

    public int Count {
      get {
        return names.Count;
      }
    }

    public TypeParameterSpec[] Types {
      get {
        return types;
      }
    }

    #endregion

    public void Add (TypeParameter tparam)
    {
      names.Add (tparam);
    }

    public void Add (TypeParameters tparams)
    {
      names.AddRange (tparams.names);
    }

    public void Create (TypeSpec declaringType, int parentOffset, TypeContainer parent)
    {
      types = new TypeParameterSpec[Count];
      for (int i = 0; i < types.Length; ++i) {
        var tp = names[i];

        tp.Create (declaringType, parent);
        types[i] = tp.Type;
        types[i].DeclaredPosition = i + parentOffset;

        if (tp.Variance != Variance.None && !(declaringType != null && (declaringType.Kind == MemberKind.Interface || declaringType.Kind == MemberKind.Delegate))) {
          parent.Compiler.Report.Error (1960, tp.Location, "Variant type parameters can only be used with interfaces and delegates");
        }
      }
    }

    public void Define (GenericTypeParameterBuilder[] builders)
    {
      for (int i = 0; i < types.Length; ++i) {
        var tp = names[i];
        tp.Define (builders [types [i].DeclaredPosition]);
      }
    }

    public TypeParameter this[int index] {
      get {
        return names [index];
      }
      set {
        names[index] = value;
      }
    }

    public TypeParameter Find (string name)
    {
      foreach (var tp in names) {
        if (tp.Name == name)
          return tp;
      }

      return null;
    }

    public string[] GetAllNames ()
    {
      return names.Select (l => l.Name).ToArray ();
    }

    public string GetSignatureForError ()
    {
      StringBuilder sb = new StringBuilder ();
      for (int i = 0; i < Count; ++i) {
        if (i > 0)
          sb.Append (',');

        var name = names[i];
        if (name != null)
          sb.Append (name.GetSignatureForError ());
      }

      return sb.ToString ();
    }


    public void CheckPartialConstraints (Method part)
    {
      var partTypeParameters = part.CurrentTypeParameters;

      for (int i = 0; i < Count; i++) {
        var tp_a = names[i];
        var tp_b = partTypeParameters [i];
        if (tp_a.Constraints == null) {
          if (tp_b.Constraints == null)
            continue;
        } else if (tp_b.Constraints != null && tp_a.Type.HasSameConstraintsDefinition (tp_b.Type)) {
          continue;
        }

        part.Compiler.Report.SymbolRelatedToPreviousError (this[i].CurrentMemberDefinition.Location, "");
        part.Compiler.Report.Error (761, part.Location,
          "Partial method declarations of `{0}' have inconsistent constraints for type parameter `{1}'",
          part.GetSignatureForError (), partTypeParameters[i].GetSignatureForError ());
      }
    }

    public void UpdateConstraints (TypeDefinition part)
    {
      var partTypeParameters = part.MemberName.TypeParameters;

      for (int i = 0; i < Count; i++) {
        var tp = names [i];
        if (tp.AddPartialConstraints (part, partTypeParameters [i]))
          continue;

        part.Compiler.Report.SymbolRelatedToPreviousError (this[i].CurrentMemberDefinition);
        part.Compiler.Report.Error (265, part.Location,
          "Partial declarations of `{0}' have inconsistent constraints for type parameter `{1}'",
          part.GetSignatureForError (), tp.GetSignatureForError ());
      }
    }

    public void VerifyClsCompliance ()
    {
      foreach (var tp in names) {
        tp.VerifyClsCompliance ();
      }
    }
  }

  //
  // A type expression of generic type with type arguments
  //
  class GenericTypeExpr : TypeExpr
  {
    TypeArguments args;
    TypeSpec open_type;

    /// <summary>
    ///   Instantiate the generic type `t' with the type arguments `args'.
    ///   Use this constructor if you already know the fully resolved
    ///   generic type.
    /// </summary>    
    public GenericTypeExpr (TypeSpec open_type, TypeArguments args, Location l)
    {
      this.open_type = open_type;
      loc = l;
      this.args = args;
    }

    public override string GetSignatureForError ()
    {
      return type.GetSignatureForError ();
    }

    public override TypeSpec ResolveAsType (IMemberContext mc, bool allowUnboundTypeArguments = false)
    {
      if (eclass != ExprClass.Unresolved)
        return type;

      if (!args.Resolve (mc))
        return null;

      TypeSpec[] atypes = args.Arguments;
      if (atypes == null)
        return null;

      //
      // Now bind the parameters
      //
      var inflated = open_type.MakeGenericType (mc, atypes);
      type = inflated;
      eclass = ExprClass.Type;

      //
      // The constraints can be checked only when full type hierarchy is known
      //
      if (!inflated.HasConstraintsChecked && mc.Module.HasTypesFullyDefined) {
        var constraints = inflated.Constraints;
        if (constraints != null) {
          var cc = new ConstraintChecker (mc);
          if (cc.CheckAll (open_type, atypes, constraints, loc)) {
            inflated.HasConstraintsChecked = true;
          }
        }
      }

      return type;
    }

    public override bool Equals (object obj)
    {
      GenericTypeExpr cobj = obj as GenericTypeExpr;
      if (cobj == null)
        return false;

      if ((type == null) || (cobj.type == null))
        return false;

      return type == cobj.type;
    }

    public override int GetHashCode ()
    {
      return base.GetHashCode ();
    }
  }

  //
  // Generic type with unbound type arguments, used for typeof (G<,,>)
  //
  class GenericOpenTypeExpr : TypeExpression
  {
    public GenericOpenTypeExpr (TypeSpec type, /*UnboundTypeArguments args,*/ Location loc)
      : base (type.GetDefinition (), loc)
    {
    }
  }

  struct ConstraintChecker
  {
    IMemberContext mc;
    bool recursive_checks;

    public ConstraintChecker (IMemberContext ctx)
    {
      this.mc = ctx;
      recursive_checks = false;
    }

    //
    // Checks the constraints of open generic type against type
    // arguments. This version is used for types which could not be
    // checked immediatelly during construction because the type
    // hierarchy was not yet fully setup (before Emit phase)
    //
    public static bool Check (IMemberContext mc, TypeSpec type, Location loc)
    {
      //
      // Check declaring type first if there is any
      //
      if (type.DeclaringType != null && !Check (mc, type.DeclaringType, loc))
        return false;

      while (type is ElementTypeSpec)
        type = ((ElementTypeSpec) type).Element;

      if (type.Arity == 0)
        return true;

      var gtype = type as InflatedTypeSpec;
      if (gtype == null)
        return true;

      var constraints = gtype.Constraints;
      if (constraints == null)
        return true;

      if (gtype.HasConstraintsChecked)
        return true;

      var cc = new ConstraintChecker (mc);
      cc.recursive_checks = true;

      if (cc.CheckAll (gtype.GetDefinition (), type.TypeArguments, constraints, loc)) {
        gtype.HasConstraintsChecked = true;
        return true;
      }

      return false;
    }

    //
    // Checks all type arguments againts type parameters constraints
    // NOTE: It can run in probing mode when `this.mc' is null
    //
    public bool CheckAll (MemberSpec context, TypeSpec[] targs, TypeParameterSpec[] tparams, Location loc)
    {
      for (int i = 0; i < tparams.Length; i++) {
        var targ = targs[i];
        if (!CheckConstraint (context, targ, tparams [i], loc))
          return false;

        if (!recursive_checks)
          continue;

        if (!Check (mc, targ, loc))
          return false;
      }

      return true;
    }

    bool CheckConstraint (MemberSpec context, TypeSpec atype, TypeParameterSpec tparam, Location loc)
    {
      //
      // First, check the `class' and `struct' constraints.
      //
      if (tparam.HasSpecialClass && !TypeSpec.IsReferenceType (atype)) {
        if (mc != null) {
          mc.Module.Compiler.Report.Error (452, loc,
            "The type `{0}' must be a reference type in order to use it as type parameter `{1}' in the generic type or method `{2}'",
            atype.GetSignatureForError (), tparam.GetSignatureForError (), context.GetSignatureForError ());
        }

        return false;
      }

      if (tparam.HasSpecialStruct && (!TypeSpec.IsValueType (atype) || atype.IsNullableType)) {
        if (mc != null) {
          mc.Module.Compiler.Report.Error (453, loc,
            "The type `{0}' must be a non-nullable value type in order to use it as type parameter `{1}' in the generic type or method `{2}'",
            atype.GetSignatureForError (), tparam.GetSignatureForError (), context.GetSignatureForError ());
        }

        return false;
      }

      bool ok = true;

      //
      // Check the class constraint
      //
      if (tparam.HasTypeConstraint) {
        if (!CheckConversion (mc, context, atype, tparam, tparam.BaseType, loc)) {
          if (mc == null)
            return false;

          ok = false;
        }
      }

      //
      // Check the interfaces constraints
      //
      if (tparam.InterfacesDefined != null) {
        foreach (TypeSpec iface in tparam.InterfacesDefined) {
          if (!CheckConversion (mc, context, atype, tparam, iface, loc)) {
            if (mc == null)
              return false;

            ok = false;
            break;
          }
        }
      }

      //
      // Check the type parameter constraint
      //
      if (tparam.TypeArguments != null) {
        foreach (var ta in tparam.TypeArguments) {
          if (!CheckConversion (mc, context, atype, tparam, ta, loc)) {
            if (mc == null)
              return false;

            ok = false;
            break;
          }
        }
      }

      //
      // Finally, check the constructor constraint.
      //
      if (!tparam.HasSpecialConstructor)
        return ok;

      if (!HasDefaultConstructor (atype)) {
        if (mc != null) {
          mc.Module.Compiler.Report.SymbolRelatedToPreviousError (atype);
          mc.Module.Compiler.Report.Error (310, loc,
            "The type `{0}' must have a public parameterless constructor in order to use it as parameter `{1}' in the generic type or method `{2}'",
            atype.GetSignatureForError (), tparam.GetSignatureForError (), context.GetSignatureForError ());
        }
        return false;
      }

      return ok;
    }

    static bool HasDynamicTypeArgument (TypeSpec[] targs)
    {
      for (int i = 0; i < targs.Length; ++i) {
        var targ = targs [i];
        if (targ.BuiltinType == BuiltinTypeSpec.Type.Dynamic)
          return true;

        if (HasDynamicTypeArgument (targ.TypeArguments))
          return true;
      }

      return false;
    }

    bool CheckConversion (IMemberContext mc, MemberSpec context, TypeSpec atype, TypeParameterSpec tparam, TypeSpec ttype, Location loc)
    {
      if (atype == ttype)
        return true;

      if (atype.IsGenericParameter) {
        var tps = (TypeParameterSpec) atype;
        if (tps.HasDependencyOn (ttype))
          return true;

        if (Convert.ImplicitTypeParameterConversion (null, tps, ttype) != null)
          return true;

      } else if (TypeSpec.IsValueType (atype)) {
        if (atype.IsNullableType) {
          //
          // LAMESPEC: Only identity or base type ValueType or Object satisfy nullable type
          //
          if (TypeSpec.IsBaseClass (atype, ttype, false))
            return true;
        } else {
          if (Convert.ImplicitBoxingConversion (null, atype, ttype) != null)
            return true;
        }
      } else {
        if (Convert.ImplicitReferenceConversionExists (atype, ttype) || Convert.ImplicitBoxingConversion (null, atype, ttype) != null)
          return true;
      }

      if (mc != null) {
        mc.Module.Compiler.Report.SymbolRelatedToPreviousError (tparam);
        if (atype.IsGenericParameter) {
          mc.Module.Compiler.Report.Error (314, loc,
            "The type `{0}' cannot be used as type parameter `{1}' in the generic type or method `{2}'. There is no boxing or type parameter conversion from `{0}' to `{3}'",
            atype.GetSignatureForError (), tparam.GetSignatureForError (), context.GetSignatureForError (), ttype.GetSignatureForError ());
        } else if (TypeSpec.IsValueType (atype)) {
          if (atype.IsNullableType) {
            if (ttype.IsInterface) {
              mc.Module.Compiler.Report.Error (313, loc,
                "The type `{0}' cannot be used as type parameter `{1}' in the generic type or method `{2}'. The nullable type `{0}' never satisfies interface constraint `{3}'",
                atype.GetSignatureForError (), tparam.GetSignatureForError (), context.GetSignatureForError (), ttype.GetSignatureForError ());
            } else {
              mc.Module.Compiler.Report.Error (312, loc,
                "The type `{0}' cannot be used as type parameter `{1}' in the generic type or method `{2}'. The nullable type `{0}' does not satisfy constraint `{3}'",
                atype.GetSignatureForError (), tparam.GetSignatureForError (), context.GetSignatureForError (), ttype.GetSignatureForError ());
            }
          } else {
            mc.Module.Compiler.Report.Error (315, loc,
              "The type `{0}' cannot be used as type parameter `{1}' in the generic type or method `{2}'. There is no boxing conversion from `{0}' to `{3}'",
              atype.GetSignatureForError (), tparam.GetSignatureForError (), context.GetSignatureForError (), ttype.GetSignatureForError ());
          }
        } else {
          mc.Module.Compiler.Report.Error (311, loc,
            "The type `{0}' cannot be used as type parameter `{1}' in the generic type or method `{2}'. There is no implicit reference conversion from `{0}' to `{3}'",
            atype.GetSignatureForError (), tparam.GetSignatureForError (), context.GetSignatureForError (), ttype.GetSignatureForError ());
        }
      }

      return false;
    }

    static bool HasDefaultConstructor (TypeSpec atype)
    {
      var tp = atype as TypeParameterSpec;
      if (tp != null) {
        return tp.HasSpecialConstructor || tp.HasSpecialStruct;
      }

      if (atype.IsStruct || atype.IsEnum)
        return true;

      if (atype.IsAbstract)
        return false;

      var tdef = atype.GetDefinition ();

      var found = MemberCache.FindMember (tdef,
        MemberFilter.Constructor (ParametersCompiled.EmptyReadOnlyParameters),
        BindingRestriction.DeclaredOnly | BindingRestriction.InstanceOnly);

      return found != null && (found.Modifiers & Modifiers.PUBLIC) != 0;
    }
  }

  //
  // Implements C# type inference
  //
  class TypeInference
  {
    //
    // Tracks successful rate of type inference
    //
    int score = int.MaxValue;
    readonly Arguments arguments;
    readonly int arg_count;

    public TypeInference (Arguments arguments)
    {
      this.arguments = arguments;
      if (arguments != null)
        arg_count = arguments.Count;
    }

    public int InferenceScore {
      get {
        return score;
      }
    }

    public TypeSpec[] InferMethodArguments (ResolveContext ec, MethodSpec method)
    {
      var method_generic_args = method.GenericDefinition.TypeParameters;
      TypeInferenceContext context = new TypeInferenceContext (method_generic_args);
      if (!context.UnfixedVariableExists)
        return TypeSpec.EmptyTypes;

      AParametersCollection pd = method.Parameters;
      if (!InferInPhases (ec, context, pd))
        return null;

      return context.InferredTypeArguments;
    }

    //
    // Implements method type arguments inference
    //
    bool InferInPhases (ResolveContext ec, TypeInferenceContext tic, AParametersCollection methodParameters)
    {
      int params_arguments_start;
      if (methodParameters.HasParams) {
        params_arguments_start = methodParameters.Count - 1;
      } else {
        params_arguments_start = arg_count;
      }

      TypeSpec [] ptypes = methodParameters.Types;
      
      //
      // The first inference phase
      //
      TypeSpec method_parameter = null;
      for (int i = 0; i < arg_count; i++) {
        Argument a = arguments [i];
        if (a == null)
          continue;
        
        if (i < params_arguments_start) {
          method_parameter = methodParameters.Types [i];
        } else if (i == params_arguments_start) {
          if (arg_count == params_arguments_start + 1 && TypeManager.HasElementType (a.Type))
            method_parameter = methodParameters.Types [params_arguments_start];
          else
            method_parameter = TypeManager.GetElementType (methodParameters.Types [params_arguments_start]);

          ptypes = (TypeSpec[]) ptypes.Clone ();
          ptypes [i] = method_parameter;
        }

        //
        // When a lambda expression, an anonymous method
        // is used an explicit argument type inference takes a place
        //
        AnonymousMethodExpression am = a.Expr as AnonymousMethodExpression;
        if (am != null) {
          if (am.ExplicitTypeInference (tic, method_parameter))
            --score; 
          continue;
        }

        if (a.IsByRef) {
          score -= tic.ExactInference (a.Type, method_parameter);
          continue;
        }

        if (a.Expr.Type == InternalType.NullLiteral)
          continue;

        if (TypeSpec.IsValueType (method_parameter)) {
          score -= tic.LowerBoundInference (a.Type, method_parameter);
          continue;
        }

        //
        // Otherwise an output type inference is made
        //
        score -= tic.OutputTypeInference (ec, a.Expr, method_parameter);
      }

      //
      // Part of the second phase but because it happens only once
      // we don't need to call it in cycle
      //
      bool fixed_any = false;
      if (!tic.FixIndependentTypeArguments (ec, ptypes, ref fixed_any))
        return false;

      return DoSecondPhase (ec, tic, ptypes, !fixed_any);
    }

    bool DoSecondPhase (ResolveContext ec, TypeInferenceContext tic, TypeSpec[] methodParameters, bool fixDependent)
    {
      bool fixed_any = false;
      if (fixDependent && !tic.FixDependentTypes (ec, ref fixed_any))
        return false;

      // If no further unfixed type variables exist, type inference succeeds
      if (!tic.UnfixedVariableExists)
        return true;

      if (!fixed_any && fixDependent)
        return false;
      
      // For all arguments where the corresponding argument output types
      // contain unfixed type variables but the input types do not,
      // an output type inference is made
      for (int i = 0; i < arg_count; i++) {
        
        // Align params arguments
        TypeSpec t_i = methodParameters [i >= methodParameters.Length ? methodParameters.Length - 1: i];
        
        if (!t_i.IsDelegate) {
          if (!t_i.IsExpressionTreeType)
            continue;

          t_i = TypeManager.GetTypeArguments (t_i) [0];
        }

        var mi = Delegate.GetInvokeMethod (t_i);
        TypeSpec rtype = mi.ReturnType;

        if (tic.IsReturnTypeNonDependent (mi, rtype)) {
          // It can be null for default arguments
          if (arguments[i] == null)
            continue;

          score -= tic.OutputTypeInference (ec, arguments[i].Expr, t_i);
        }
      }


      return DoSecondPhase (ec, tic, methodParameters, true);
    }
  }

  public class TypeInferenceContext
  {
    protected enum BoundKind
    {
      Exact = 0,
      Lower = 1,
      Upper = 2
    }

    struct BoundInfo : IEquatable<BoundInfo>
    {
      public readonly TypeSpec Type;
      public readonly BoundKind Kind;

      public BoundInfo (TypeSpec type, BoundKind kind)
      {
        this.Type = type;
        this.Kind = kind;
      }
      
      public override int GetHashCode ()
      {
        return Type.GetHashCode ();
      }

      public Expression GetTypeExpression ()
      {
        return new TypeExpression (Type, Location.Null);
      }

      #region IEquatable<BoundInfo> Members

      public bool Equals (BoundInfo other)
      {
        return Type == other.Type && Kind == other.Kind;
      }

      #endregion
    }

    readonly TypeSpec[] tp_args;
    readonly TypeSpec[] fixed_types;
    readonly List<BoundInfo>[] bounds;

    // TODO MemberCache: Could it be TypeParameterSpec[] ??
    public TypeInferenceContext (TypeSpec[] typeArguments)
    {
      if (typeArguments.Length == 0)
        throw new ArgumentException ("Empty generic arguments");

      fixed_types = new TypeSpec [typeArguments.Length];
      for (int i = 0; i < typeArguments.Length; ++i) {
        if (typeArguments [i].IsGenericParameter) {
          if (bounds == null) {
            bounds = new List<BoundInfo> [typeArguments.Length];
            tp_args = new TypeSpec [typeArguments.Length];
          }
          tp_args [i] = typeArguments [i];
        } else {
          fixed_types [i] = typeArguments [i];
        }
      }
    }

    // 
    // Used together with AddCommonTypeBound fo implement
    // 7.4.2.13 Finding the best common type of a set of expressions
    //
    public TypeInferenceContext ()
    {
      fixed_types = new TypeSpec [1];
      tp_args = new TypeSpec [1];
      tp_args[0] = InternalType.Arglist; // it can be any internal type
      bounds = new List<BoundInfo> [1];
    }

    public TypeSpec[] InferredTypeArguments {
      get {
        return fixed_types;
      }
    }

    public void AddCommonTypeBound (TypeSpec type)
    {
      AddToBounds (new BoundInfo (type, BoundKind.Lower), 0, false);
    }

    public void AddCommonTypeBoundAsync (TypeSpec type)
    {
      AddToBounds (new BoundInfo (type, BoundKind.Lower), 0, true);
    }

    void AddToBounds (BoundInfo bound, int index, bool voidAllowed)
    {
      //
      // Some types cannot be used as type arguments
      //
      if ((bound.Type.Kind == MemberKind.Void && !voidAllowed) || bound.Type.IsPointer || bound.Type.IsSpecialRuntimeType ||
        bound.Type == InternalType.MethodGroup || bound.Type == InternalType.AnonymousMethod)
        return;

      var a = bounds [index];
      if (a == null) {
        a = new List<BoundInfo> (2);
        a.Add (bound);
        bounds [index] = a;
        return;
      }

      if (a.Contains (bound))
        return;

      a.Add (bound);
    }
    
    bool AllTypesAreFixed (TypeSpec[] types)
    {
      foreach (TypeSpec t in types) {
        if (t.IsGenericParameter) {
          if (!IsFixed (t))
            return false;
          continue;
        }

        if (TypeManager.IsGenericType (t))
          return AllTypesAreFixed (TypeManager.GetTypeArguments (t));
      }
      
      return true;
    }   

    //
    // 26.3.3.8 Exact Inference
    //
    public int ExactInference (TypeSpec u, TypeSpec v)
    {
      // If V is an array type
      if (v.IsArray) {
        if (!u.IsArray)
          return 0;

        var ac_u = (ArrayContainer) u;
        var ac_v = (ArrayContainer) v;
        if (ac_u.Rank != ac_v.Rank)
          return 0;

        return ExactInference (ac_u.Element, ac_v.Element);
      }

      // If V is constructed type and U is constructed type
      if (TypeManager.IsGenericType (v)) {
        if (!TypeManager.IsGenericType (u) || v.MemberDefinition != u.MemberDefinition)
          return 0;

        TypeSpec [] ga_u = TypeManager.GetTypeArguments (u);
        TypeSpec [] ga_v = TypeManager.GetTypeArguments (v);
        if (ga_u.Length != ga_v.Length)
          return 0;

        int score = 0;
        for (int i = 0; i < ga_u.Length; ++i)
          score += ExactInference (ga_u [i], ga_v [i]);

        return System.Math.Min (1, score);
      }

      // If V is one of the unfixed type arguments
      int pos = IsUnfixed (v);
      if (pos == -1)
        return 0;

      AddToBounds (new BoundInfo (u, BoundKind.Exact), pos, false);
      return 1;
    }

    public bool FixAllTypes (ResolveContext ec)
    {
      for (int i = 0; i < tp_args.Length; ++i) {
        if (!FixType (ec, i))
          return false;
      }
      return true;
    }

    //
    // All unfixed type variables Xi are fixed for which all of the following hold:
    // a, There is at least one type variable Xj that depends on Xi
    // b, Xi has a non-empty set of bounds
    // 
    public bool FixDependentTypes (ResolveContext ec, ref bool fixed_any)
    {
      for (int i = 0; i < tp_args.Length; ++i) {
        if (fixed_types[i] != null)
          continue;

        if (bounds[i] == null)
          continue;

        if (!FixType (ec, i))
          return false;
        
        fixed_any = true;
      }

      return true;
    }

    //
    // All unfixed type variables Xi which depend on no Xj are fixed
    //
    public bool FixIndependentTypeArguments (ResolveContext ec, TypeSpec[] methodParameters, ref bool fixed_any)
    {
      var types_to_fix = new List<TypeSpec> (tp_args);
      for (int i = 0; i < methodParameters.Length; ++i) {
        TypeSpec t = methodParameters[i];

        if (!t.IsDelegate) {
          if (!t.IsExpressionTreeType)
            continue;

          t =  TypeManager.GetTypeArguments (t) [0];
        }

        if (t.IsGenericParameter)
          continue;

        var invoke = Delegate.GetInvokeMethod (t);
        TypeSpec rtype = invoke.ReturnType;
        while (rtype.IsArray)
          rtype = ((ArrayContainer) rtype).Element;

        if (!rtype.IsGenericParameter && !TypeManager.IsGenericType (rtype))
          continue;

        // Remove dependent types, they cannot be fixed yet
        RemoveDependentTypes (types_to_fix, rtype);
      }

      foreach (TypeSpec t in types_to_fix) {
        if (t == null)
          continue;

        int idx = IsUnfixed (t);
        if (idx >= 0 && !FixType (ec, idx)) {
          return false;
        }
      }

      fixed_any = types_to_fix.Count > 0;
      return true;
    }

    //
    // 26.3.3.10 Fixing
    //
    public bool FixType (ResolveContext ec, int i)
    {
      // It's already fixed
      if (fixed_types[i] != null)
        throw new InternalErrorException ("Type argument has been already fixed");

      var candidates = bounds [i];
      if (candidates == null)
        return false;

      if (candidates.Count == 1) {
        TypeSpec t = candidates[0].Type;
        if (t == InternalType.NullLiteral)
          return false;

        fixed_types [i] = t;
        return true;
      }

      //
      // The set of candidate types Uj starts out as the set of
      // all types in the set of bounds for Xi
      //
      var applicable = new bool [candidates.Count];
      for (int ci = 0; ci < applicable.Length; ++ci)
        applicable [ci] = true;

      for (int ci = 0; ci < applicable.Length; ++ci) {
        var bound = candidates [ci];
        int cii = 0;

        switch (bound.Kind) {
        case BoundKind.Exact:
          for (; cii != applicable.Length; ++cii) {
            if (ci == cii)
              continue;

            if (!applicable[cii])
              break;

            //
            // For each exact bound U of Xi all types Uj which are not identical
            // to U are removed from the candidate set
            //
            if (candidates [cii].Type != bound.Type)
              applicable[cii] = false;
          }

          break;
        case BoundKind.Lower:
          for (; cii != applicable.Length; ++cii) {
            if (ci == cii)
              continue;

            if (!applicable[cii])
              break;

            //
            // For each lower bound U of Xi all types Uj to which there is not an implicit conversion
            // from U are removed from the candidate set
            //
            if (!Convert.ImplicitConversionExists (ec, bound.GetTypeExpression (), candidates [cii].Type)) {
              applicable[cii] = false;
            }
          }

          break;

        case BoundKind.Upper:
          for (; cii != applicable.Length; ++cii) {
            if (ci == cii)
              continue;

            if (!applicable[cii])
              break;

            //
            // For each upper bound U of Xi all types Uj from which there is not an implicit conversion
            // to U are removed from the candidate set
            //
            if (!Convert.ImplicitConversionExists (ec, candidates[cii].GetTypeExpression (), bound.Type))
              applicable[cii] = false;
          }

          break;
        }
      }

      TypeSpec best_candidate = null;
      for (int ci = 0; ci < applicable.Length; ++ci) {
        if (!applicable[ci])
          continue;

        var bound = candidates [ci];
        if (bound.Type == best_candidate)
          continue;

        int cii = 0;
        for (; cii < applicable.Length; ++cii) {
          if (ci == cii)
            continue;

          if (!applicable[cii])
            continue;

          if (!Convert.ImplicitConversionExists (ec, candidates[cii].GetTypeExpression (), bound.Type))
            break;
        }

        if (cii != applicable.Length)
          continue;

        //
        // We already have the best candidate, break if it's different (non-unique)
        //
        // Dynamic is never ambiguous as we prefer dynamic over other best candidate types
        //
        if (best_candidate != null) {

          if (best_candidate.BuiltinType == BuiltinTypeSpec.Type.Dynamic)
            continue;

          if (bound.Type.BuiltinType != BuiltinTypeSpec.Type.Dynamic && best_candidate != bound.Type)
            return false;
        }

        best_candidate = bound.Type;
      }

      if (best_candidate == null)
        return false;

      fixed_types[i] = best_candidate;
      return true;
    }

    public bool HasBounds (int pos)
    {
      return bounds[pos] != null;
    }
    
    //
    // Uses inferred or partially infered types to inflate delegate type argument. Returns
    // null when type parameter has not been fixed
    //
    public TypeSpec InflateGenericArgument (IModuleContext context, TypeSpec parameter)
    {
      var tp = parameter as TypeParameterSpec;
      if (tp != null) {
        //
        // Type inference works on generic arguments (MVAR) only
        //
        if (!tp.IsMethodOwned)
          return parameter;

        //
        // Ensure the type parameter belongs to same container
        //
        if (tp.DeclaredPosition < tp_args.Length && tp_args[tp.DeclaredPosition] == parameter)
          return fixed_types[tp.DeclaredPosition] ?? parameter;

        return parameter;
      }

      var gt = parameter as InflatedTypeSpec;
      if (gt != null) {
        var inflated_targs = new TypeSpec [gt.TypeArguments.Length];
        for (int ii = 0; ii < inflated_targs.Length; ++ii) {
          var inflated = InflateGenericArgument (context, gt.TypeArguments [ii]);
          if (inflated == null)
            return null;

          inflated_targs[ii] = inflated;
        }

        return gt.GetDefinition ().MakeGenericType (context, inflated_targs);
      }

      var ac = parameter as ArrayContainer;
      if (ac != null) {
        var inflated = InflateGenericArgument (context, ac.Element);
        if (inflated != ac.Element)
          return ArrayContainer.MakeType (context.Module, inflated);
      }

      return parameter;
    }
    
    //
    // Tests whether all delegate input arguments are fixed and generic output type
    // requires output type inference 
    //
    public bool IsReturnTypeNonDependent (MethodSpec invoke, TypeSpec returnType)
    {
      AParametersCollection d_parameters = invoke.Parameters;

      if (d_parameters.IsEmpty)
        return true;

      while (returnType.IsArray)
        returnType = ((ArrayContainer) returnType).Element;

      if (returnType.IsGenericParameter) {
        if (IsFixed (returnType))
            return false;
      } else if (TypeManager.IsGenericType (returnType)) {
        TypeSpec[] g_args = TypeManager.GetTypeArguments (returnType);
        
        // At least one unfixed return type has to exist 
        if (AllTypesAreFixed (g_args))
          return false;
      } else {
        return false;
      }

      // All generic input arguments have to be fixed
      return AllTypesAreFixed (d_parameters.Types);
    }

    bool IsFixed (TypeSpec type)
    {
      return IsUnfixed (type) == -1;
    }   

    int IsUnfixed (TypeSpec type)
    {
      if (!type.IsGenericParameter)
        return -1;

      for (int i = 0; i < tp_args.Length; ++i) {
        if (tp_args[i] == type) {
          if (fixed_types[i] != null)
            break;

          return i;
        }
      }

      return -1;
    }

    //
    // 26.3.3.9 Lower-bound Inference
    //
    public int LowerBoundInference (TypeSpec u, TypeSpec v)
    {
      return LowerBoundInference (u, v, false);
    }

    //
    // Lower-bound (false) or Upper-bound (true) inference based on inversed argument
    //
    int LowerBoundInference (TypeSpec u, TypeSpec v, bool inversed)
    {
      // If V is one of the unfixed type arguments
      int pos = IsUnfixed (v);
      if (pos != -1) {
        AddToBounds (new BoundInfo (u, inversed ? BoundKind.Upper : BoundKind.Lower), pos, false);
        return 1;
      }     

      // If U is an array type
      var u_ac = u as ArrayContainer;
      if (u_ac != null) {
        var v_ac = v as ArrayContainer;
        if (v_ac != null) {
          if (u_ac.Rank != v_ac.Rank)
            return 0;

          if (TypeSpec.IsValueType (u_ac.Element))
            return ExactInference (u_ac.Element, v_ac.Element);

          return LowerBoundInference (u_ac.Element, v_ac.Element, inversed);
        }

        if (u_ac.Rank != 1 || !v.IsArrayGenericInterface)
          return 0;

        var v_i = TypeManager.GetTypeArguments (v) [0];
        if (TypeSpec.IsValueType (u_ac.Element))
          return ExactInference (u_ac.Element, v_i);

        return LowerBoundInference (u_ac.Element, v_i);
      }
      
      if (v.IsGenericOrParentIsGeneric) {
        //
        // if V is a constructed type C<V1..Vk> and there is a unique type C<U1..Uk>
        // such that U is identical to, inherits from (directly or indirectly),
        // or implements (directly or indirectly) C<U1..Uk>
        //
        var u_candidates = new List<TypeSpec> ();
        var open_v = v.MemberDefinition;

        for (TypeSpec t = u; t != null; t = t.BaseType) {
          if (open_v == t.MemberDefinition)
            u_candidates.Add (t);

          //
          // Using this trick for dynamic type inference, the spec says the type arguments are "unknown" but
          // that would complicate the process a lot, instead I treat them as dynamic
          //
          if (t.BuiltinType == BuiltinTypeSpec.Type.Dynamic)
            u_candidates.Add (t);
        }

        if (u.Interfaces != null) {
          foreach (var iface in u.Interfaces) {
            if (open_v == iface.MemberDefinition)
              u_candidates.Add (iface);
          }
        }

        TypeSpec[] unique_candidate_targs = null;
        var ga_v = TypeSpec.GetAllTypeArguments (v);
        foreach (TypeSpec u_candidate in u_candidates) {
          //
          // The unique set of types U1..Uk means that if we have an interface I<T>,
          // class U : I<int>, I<long> then no type inference is made when inferring
          // type I<T> by applying type U because T could be int or long
          //
          if (unique_candidate_targs != null) {
            TypeSpec[] second_unique_candidate_targs = TypeSpec.GetAllTypeArguments (u_candidate);
            if (TypeSpecComparer.Equals (unique_candidate_targs, second_unique_candidate_targs)) {
              unique_candidate_targs = second_unique_candidate_targs;
              continue;
            }

            //
            // Break when candidate arguments are ambiguous
            //
            return 0;
          }

          //
          // A candidate is dynamic type expression, to simplify things use dynamic
          // for all type parameter of this type. For methods like this one
          // 
          // void M<T, U> (IList<T>, IList<U[]>)
          //
          // dynamic becomes both T and U when the arguments are of dynamic type
          //
          if (u_candidate.BuiltinType == BuiltinTypeSpec.Type.Dynamic) {
            unique_candidate_targs = new TypeSpec[ga_v.Length];
            for (int i = 0; i < unique_candidate_targs.Length; ++i)
              unique_candidate_targs[i] = u_candidate;
          } else {
            unique_candidate_targs = TypeSpec.GetAllTypeArguments (u_candidate);
          }
        }

        if (unique_candidate_targs != null) {
          int score = 0;
          int tp_index = -1;
          TypeParameterSpec[] tps = null;

          for (int i = 0; i < unique_candidate_targs.Length; ++i) {
            if (tp_index < 0) {
              while (v.Arity == 0)
                v = v.DeclaringType;

              tps = v.MemberDefinition.TypeParameters;
              tp_index = tps.Length - 1;
            }

            Variance variance = tps [tp_index--].Variance;

            TypeSpec u_i = unique_candidate_targs [i];
            if (variance == Variance.None || TypeSpec.IsValueType (u_i)) {
              if (ExactInference (u_i, ga_v [i]) == 0)
                ++score;
            } else {
              bool upper_bound = (variance == Variance.Contravariant && !inversed) ||
                (variance == Variance.Covariant && inversed);

              if (LowerBoundInference (u_i, ga_v [i], upper_bound) == 0)
                ++score;
            }
          }

          return score;
        }
      }

      return 0;
    }

    //
    // 26.3.3.6 Output Type Inference
    //
    public int OutputTypeInference (ResolveContext ec, Expression e, TypeSpec t)
    {
      // If e is a lambda or anonymous method with inferred return type
      AnonymousMethodExpression ame = e as AnonymousMethodExpression;
      if (ame != null) {
        TypeSpec rt = ame.InferReturnType (ec, this, t);
        var invoke = Delegate.GetInvokeMethod (t);

        if (rt == null) {
          AParametersCollection pd = invoke.Parameters;
          return ame.Parameters.Count == pd.Count ? 1 : 0;
        }

        TypeSpec rtype = invoke.ReturnType;
        return LowerBoundInference (rt, rtype) + 1;
      }

      //
      // if E is a method group and T is a delegate type or expression tree type
      // return type Tb with parameter types T1..Tk and return type Tb, and overload
      // resolution of E with the types T1..Tk yields a single method with return type U,
      // then a lower-bound inference is made from U for Tb.
      //
      if (e is MethodGroupExpr) {
        if (!t.IsDelegate) {
          if (!t.IsExpressionTreeType)
            return 0;

          t = TypeManager.GetTypeArguments (t)[0];
        }

        var invoke = Delegate.GetInvokeMethod (t);
        TypeSpec rtype = invoke.ReturnType;

        if (!IsReturnTypeNonDependent (invoke, rtype))
          return 0;

        // LAMESPEC: Standard does not specify that all methodgroup arguments
        // has to be fixed but it does not specify how to do recursive type inference
        // either. We choose the simple option and infer return type only
        // if all delegate generic arguments are fixed.
        TypeSpec[] param_types = new TypeSpec [invoke.Parameters.Count];
        for (int i = 0; i < param_types.Length; ++i) {
          var inflated = InflateGenericArgument (ec, invoke.Parameters.Types[i]);
          if (inflated == null)
            return 0;

          param_types[i] = inflated;
        }

        MethodGroupExpr mg = (MethodGroupExpr) e;
        Arguments args = DelegateCreation.CreateDelegateMethodArguments (ec, invoke.Parameters, param_types, e.Location);
        mg = mg.OverloadResolve (ec, ref args, null, OverloadResolver.Restrictions.CovariantDelegate | OverloadResolver.Restrictions.ProbingOnly);
        if (mg == null)
          return 0;

        return LowerBoundInference (mg.BestCandidateReturnType, rtype) + 1;
      }

      //
      // if e is an expression with type U, then
      // a lower-bound inference is made from U for T
      //
      return LowerBoundInference (e.Type, t) * 2;
    }

    void RemoveDependentTypes (List<TypeSpec> types, TypeSpec returnType)
    {
      int idx = IsUnfixed (returnType);
      if (idx >= 0) {
        types [idx] = null;
        return;
      }

      if (TypeManager.IsGenericType (returnType)) {
        foreach (TypeSpec t in TypeManager.GetTypeArguments (returnType)) {
          RemoveDependentTypes (types, t);
        }
      }
    }

    public bool UnfixedVariableExists {
      get {
        foreach (TypeSpec ut in fixed_types) {
          if (ut == null)
            return true;
        }

        return false;
      }
    }
  }
}