File: Symbols\TypeSymbol.vb
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Project: src\src\Compilers\VisualBasic\Portable\Microsoft.CodeAnalysis.VisualBasic.vbproj (Microsoft.CodeAnalysis.VisualBasic)
' Licensed to the .NET Foundation under one or more agreements.
' The .NET Foundation licenses this file to you under the MIT license.
' See the LICENSE file in the project root for more information.
 
Imports System.Collections.Concurrent
Imports System.Collections.Generic
Imports System.Collections.Immutable
Imports System.Runtime.InteropServices
Imports System.Threading
Imports Microsoft.CodeAnalysis.PooledObjects
Imports Microsoft.CodeAnalysis.Text
Imports Microsoft.CodeAnalysis.Symbols
Imports Microsoft.CodeAnalysis.VisualBasic.Symbols
Imports Microsoft.CodeAnalysis.VisualBasic.Syntax
 
Namespace Microsoft.CodeAnalysis.VisualBasic.Symbols
    ''' <summary>
    ''' A TypeSymbol is a base class for all the symbols that represent a type
    ''' in Visual Basic.
    ''' </summary>
    Friend MustInherit Class TypeSymbol
        Inherits NamespaceOrTypeSymbol
        Implements ITypeSymbol, ITypeSymbolInternal
 
        ' !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
        ' Changes to the public interface of this class should remain synchronized with the C# version of Symbol.
        ' Do not make any changes to the public interface without making the corresponding change
        ' to the C# version.
        ' !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
 
        ' TODO (tomat): Consider changing this to an empty name. This name shouldn't ever leak to the user in error messages.
        Friend Const ImplicitTypeName As String = "<invalid-global-code>"
 
        Private Shared ReadOnly s_EmptyTypeSymbols() As TypeSymbol = Array.Empty(Of TypeSymbol)
 
        Private _lazyAllInterfaces As ImmutableArray(Of NamedTypeSymbol)
 
        ''' <summary>
        ''' <see cref="InterfacesAndTheirBaseInterfacesNoUseSiteDiagnostics"/>
        ''' </summary>
        Private _lazyInterfacesAndTheirBaseInterfaces As MultiDictionary(Of NamedTypeSymbol, NamedTypeSymbol)
 
        Private Shared ReadOnly EmptyInterfacesAndTheirBaseInterfaces As New MultiDictionary(Of NamedTypeSymbol, NamedTypeSymbol)(0, EqualsIgnoringComparer.InstanceCLRSignatureCompare)
 
        ' Map with the interface member implementations for this type.
        ' Key is implemented method, value is implementing method (from the perspective of this type)
        ' Don't allocate until someone needs it.
        Private _lazyImplementationForInterfaceMemberMap As ConcurrentDictionary(Of Symbol, Symbol)
 
        ''' <summary>
        ''' Map with all the explicitly implemented interface symbols declared on this type.
        ''' key = interface method/property/event compared using <see cref="ExplicitInterfaceImplementationTargetMemberEqualityComparer"/>,
        ''' value = explicitly implementing methods/properties/events declared on this type (normally a single value, multiple in case of
        ''' an error).
        ''' Access through <see cref="ExplicitInterfaceImplementationMap"/> property ONLY!
        ''' </summary>
        Protected m_lazyExplicitInterfaceImplementationMap As MultiDictionary(Of Symbol, Symbol)
 
        Public Shared ReadOnly Property EmptyTypeSymbolsList As IList(Of TypeSymbol)
            Get
                Return s_EmptyTypeSymbols
            End Get
        End Property
 
        ''' <summary>
        ''' Get the original definition of this symbol. If this symbol is derived from another
        ''' symbol by (say) type substitution, this gets the original symbol, as it was defined
        ''' in source or metadata.
        ''' </summary>
        Public Shadows ReadOnly Property OriginalDefinition As TypeSymbol
            Get
                Return OriginalTypeSymbolDefinition
            End Get
        End Property
 
        Protected Overridable ReadOnly Property OriginalTypeSymbolDefinition As TypeSymbol
            Get
                ' Default implements returns Me.
                Return Me
            End Get
        End Property
 
        Protected NotOverridable Overrides ReadOnly Property OriginalSymbolDefinition As Symbol
            Get
                Return OriginalTypeSymbolDefinition
            End Get
        End Property
 
        ''' <summary>
        ''' Gets the BaseType of this type. If the base type could not be determined, then 
        ''' an instance of ErrorType is returned. If this kind of type does not have a base type
        ''' (for example, interfaces), Nothing is returned. Also the special class System.Object
        ''' always has a BaseType of Nothing.
        ''' </summary>
        Friend MustOverride ReadOnly Property BaseTypeNoUseSiteDiagnostics As NamedTypeSymbol
 
        Friend Function BaseTypeWithDefinitionUseSiteDiagnostics(<[In], Out> ByRef useSiteInfo As CompoundUseSiteInfo(Of AssemblySymbol)) As NamedTypeSymbol
            Dim result = BaseTypeNoUseSiteDiagnostics
 
            If result IsNot Nothing Then
                result.OriginalDefinition.AddUseSiteInfo(useSiteInfo)
            End If
 
            Return result
        End Function
 
        Friend Function BaseTypeOriginalDefinition(<[In], Out> ByRef useSiteInfo As CompoundUseSiteInfo(Of AssemblySymbol)) As NamedTypeSymbol
            Dim result = BaseTypeNoUseSiteDiagnostics
 
            If result IsNot Nothing Then
                result = result.OriginalDefinition
                result.AddUseSiteInfo(useSiteInfo)
            End If
 
            Return result
        End Function
 
        ''' <summary>
        ''' Gets the set of interfaces that this type directly implements. This set does not
        ''' include interfaces that are base interfaces of directly implemented interfaces.
        ''' </summary>
        Friend MustOverride ReadOnly Property InterfacesNoUseSiteDiagnostics As ImmutableArray(Of NamedTypeSymbol)
 
        ''' <summary>
        ''' The list of all interfaces of which this type is a declared subtype, excluding this type
        ''' itself. This includes all declared base interfaces, all declared base interfaces of base
        ''' types, and all declared base interfaces of those results (recursively).  Each result
        ''' appears exactly once in the list. This list is topologically sorted by the inheritance
        ''' relationship: if interface type A extends interface type B, then A precedes B in the
        ''' list. This is not quite the same as "all interfaces of which this type is a proper
        ''' subtype" because it does not take into account variance: AllInterfaces for
        ''' IEnumerable(Of String) will not include IEnumerable(Of Object).
        ''' </summary>
        Friend ReadOnly Property AllInterfacesNoUseSiteDiagnostics As ImmutableArray(Of NamedTypeSymbol)
            Get
                If (_lazyAllInterfaces.IsDefault) Then
                    ImmutableInterlocked.InterlockedInitialize(_lazyAllInterfaces, MakeAllInterfaces())
                End If
 
                Return _lazyAllInterfaces
            End Get
        End Property
 
        Friend Function AllInterfacesWithDefinitionUseSiteDiagnostics(<[In], Out> ByRef useSiteInfo As CompoundUseSiteInfo(Of AssemblySymbol)) As ImmutableArray(Of NamedTypeSymbol)
            Dim result = AllInterfacesNoUseSiteDiagnostics
 
            ' Since bases affect content of AllInterfaces set, we need to make sure they all are good.
            Me.AddUseSiteDiagnosticsForBaseDefinitions(useSiteInfo)
 
            For Each iface In result
                iface.OriginalDefinition.AddUseSiteInfo(useSiteInfo)
            Next
 
            Return result
        End Function
 
        ''' Produce all implemented interfaces in topologically sorted order. We use
        ''' TypeSymbol.Interfaces as the source of edge data, which has had cycles and infinitely
        ''' long dependency cycles removed. Consequently, it is possible (and we do) use the
        ''' simplest version of Tarjan's topological sorting algorithm.
        Protected Overridable Function MakeAllInterfaces() As ImmutableArray(Of NamedTypeSymbol)
            Dim result = ArrayBuilder(Of NamedTypeSymbol).GetInstance()
            Dim visited = New HashSet(Of NamedTypeSymbol)()
 
            Dim baseType = Me
 
            While baseType IsNot Nothing
                Dim baseInterfaces As ImmutableArray(Of NamedTypeSymbol) = baseType.InterfacesNoUseSiteDiagnostics
                For n = baseInterfaces.Length - 1 To 0 Step -1
                    MakeAllInterfacesInternal(baseInterfaces(n), visited, result)
                Next
 
                baseType = baseType.BaseTypeNoUseSiteDiagnostics
            End While
 
            result.ReverseContents()
            Return result.ToImmutableAndFree()
        End Function
 
        Private Shared Sub MakeAllInterfacesInternal(i As NamedTypeSymbol, visited As HashSet(Of NamedTypeSymbol), result As ArrayBuilder(Of NamedTypeSymbol))
            If visited.Add(i) Then
                Dim baseInterfaces As ImmutableArray(Of NamedTypeSymbol) = i.InterfacesNoUseSiteDiagnostics
                For n = baseInterfaces.Length - 1 To 0 Step -1
                    MakeAllInterfacesInternal(baseInterfaces(n), visited, result)
                Next
 
                result.Add(i)
            End If
        End Sub
 
        ''' <summary>
        ''' Gets the set of interfaces that this type directly implements, plus the base interfaces
        ''' of all such types.
        ''' Keys are compared using <see cref="EqualsIgnoringComparer.InstanceCLRSignatureCompare"/>,
        ''' values are distinct interfaces corresponding to the key, according to <see cref="TypeCompareKind.ConsiderEverything"/> rules.
        ''' </summary>
        ''' <remarks>
        ''' CONSIDER: it probably isn't truly necessary to cache this.  If space gets tight, consider
        ''' alternative approaches (recompute every time, cache on the side, only store on some types,
        ''' etc).
        ''' </remarks>
        Friend ReadOnly Property InterfacesAndTheirBaseInterfacesNoUseSiteDiagnostics As MultiDictionary(Of NamedTypeSymbol, NamedTypeSymbol)
            Get
                If _lazyInterfacesAndTheirBaseInterfaces Is Nothing Then
                    Interlocked.CompareExchange(_lazyInterfacesAndTheirBaseInterfaces, MakeInterfacesAndTheirBaseInterfaces(Me.InterfacesNoUseSiteDiagnostics), Nothing)
                End If
 
                Return _lazyInterfacesAndTheirBaseInterfaces
            End Get
 
        End Property
 
        ' Note: Unlike MakeAllInterfaces, this doesn't need to be virtual. It depends on
        ' AllInterfaces for its implementation, so it will pick up all changes to MakeAllInterfaces
        ' indirectly.
        Private Shared Function MakeInterfacesAndTheirBaseInterfaces(declaredInterfaces As ImmutableArray(Of NamedTypeSymbol)) As MultiDictionary(Of NamedTypeSymbol, NamedTypeSymbol)
            If declaredInterfaces.IsEmpty Then
                Return EmptyInterfacesAndTheirBaseInterfaces
            End If
 
            Dim result As New MultiDictionary(Of NamedTypeSymbol, NamedTypeSymbol)(declaredInterfaces.Length, EqualsIgnoringComparer.InstanceCLRSignatureCompare)
 
            For Each [interface] In declaredInterfaces
                If result.Add([interface], [interface]) Then
                    For Each baseInterface In [interface].AllInterfacesNoUseSiteDiagnostics
                        result.Add(baseInterface, baseInterface)
                    Next
                End If
            Next
 
            Return result
        End Function
 
        ''' <summary>
        ''' Returns true if this type is known to be a reference type. It is never the case
        ''' that <see cref="IsReferenceType"/> and <see cref="IsValueType"/> both return true. However, for an unconstrained
        ''' type parameter, <see cref="IsReferenceType"/> and <see cref="IsValueType"/> will both return false.
        ''' </summary>
        Public MustOverride ReadOnly Property IsReferenceType As Boolean Implements ITypeSymbol.IsReferenceType, ITypeSymbolInternal.IsReferenceType
 
        ''' <summary>
        ''' Returns true if this type is known to be a value type. It is never the case
        ''' that <see cref="IsReferenceType"/> and <see cref="IsValueType"/> both return true. However, for an unconstrained
        ''' type parameter, <see cref="IsReferenceType"/> and <see cref="IsValueType"/> will both return false.
        ''' </summary>
        Public MustOverride ReadOnly Property IsValueType As Boolean Implements ITypeSymbol.IsValueType, ITypeSymbolInternal.IsValueType
 
        ''' <summary>
        ''' Is this a symbol for an anonymous type (including delegate).
        ''' </summary>
        Public Overridable ReadOnly Property IsAnonymousType As Boolean Implements ITypeSymbol.IsAnonymousType
            Get
                Return False
            End Get
        End Property
 
        Public NotOverridable Overrides ReadOnly Property IsShared As Boolean
            Get
                ' VB doesn't have a concept of shared types.
                Return False
            End Get
        End Property
 
        ' <summary>
        ' Indicates whether a type is managed or not in C# terms (i.e. you can take a pointer to it).
        ' </summary>
        Friend MustOverride Function GetManagedKind(ByRef useSiteInfo As CompoundUseSiteInfo(Of AssemblySymbol)) As ManagedKind
 
        ' Only the compiler can create TypeSymbols.
        Friend Sub New()
        End Sub
 
        ''' <summary>
        ''' Gets the kind of this type.
        ''' </summary>
        Public MustOverride ReadOnly Property TypeKind As TYPEKIND
 
        ''' <summary>
        ''' Gets corresponding special TypeId of this type.
        ''' </summary>
        Public Overridable ReadOnly Property ExtendedSpecialType As ExtendedSpecialType
            Get
                Return Nothing
            End Get
        End Property
 
        Public ReadOnly Property SpecialType As SpecialType Implements ITypeSymbol.SpecialType, ITypeSymbolInternal.SpecialType
            Get
                Return CType(ExtendedSpecialType, SpecialType)
            End Get
        End Property
 
        ''' <summary>
        ''' Gets corresponding primitive type code for this type declaration.
        ''' </summary>
        Friend ReadOnly Property PrimitiveTypeCode As Microsoft.Cci.PrimitiveTypeCode
            Get
                Return SpecialTypes.GetTypeCode(SpecialType)
            End Get
        End Property
 
        ''' <summary>
        ''' Substitute the given type substitution within this type, returning a new type. If the
        ''' substitution had no effect, return Me. 
        ''' !!! Only code implementing construction of generic types is allowed to call this method !!!
        ''' !!! All other code should use Construct methods.                                        !!! 
        ''' </summary>
        Friend MustOverride Function InternalSubstituteTypeParameters(substitution As TypeSubstitution) As TypeWithModifiers
 
        <Obsolete("Use TypeWithModifiers.Is method.", True)>
        Friend Overloads Function Equals(other As TypeWithModifiers) As Boolean
            Return other.Is(Me)
        End Function
 
        <Obsolete("Use TypeSymbol.Equals(TypeSymbol, TypeSymbol, TypeCompareKind) method.", True)>
        Public Overloads Shared Operator =(left As TypeSymbol, right As TypeSymbol) As Boolean
            Throw ExceptionUtilities.Unreachable
        End Operator
 
        <Obsolete("Use TypeSymbol.Equals(TypeSymbol, TypeSymbol, TypeCompareKind) method.", True)>
        Public Overloads Shared Operator <>(left As TypeSymbol, right As TypeSymbol) As Boolean
            Throw ExceptionUtilities.Unreachable
        End Operator
 
        <Obsolete("Use TypeSymbol.Equals(TypeSymbol, TypeSymbol, TypeCompareKind) method.", True)>
        Public Overloads Shared Operator =(left As Symbol, right As TypeSymbol) As Boolean
            Throw ExceptionUtilities.Unreachable
        End Operator
 
        <Obsolete("Use TypeSymbol.Equals(TypeSymbol, TypeSymbol, TypeCompareKind) method.", True)>
        Public Overloads Shared Operator <>(left As Symbol, right As TypeSymbol) As Boolean
            Throw ExceptionUtilities.Unreachable
        End Operator
 
        <Obsolete("Use TypeSymbol.Equals(TypeSymbol, TypeSymbol, TypeCompareKind) method.", True)>
        Public Overloads Shared Operator =(left As TypeSymbol, right As Symbol) As Boolean
            Throw ExceptionUtilities.Unreachable
        End Operator
 
        <Obsolete("Use TypeSymbol.Equals(TypeSymbol, TypeSymbol, TypeCompareKind) method.", True)>
        Public Overloads Shared Operator <>(left As TypeSymbol, right As Symbol) As Boolean
            Throw ExceptionUtilities.Unreachable
        End Operator
 
        Public Overloads Shared Function Equals(left As TypeSymbol, right As TypeSymbol, comparison As TypeCompareKind) As Boolean
            Return If(left?.Equals(right, comparison), right Is Nothing)
        End Function
 
        Public NotOverridable Overrides Function Equals(obj As Object) As Boolean
            Return Equals(TryCast(obj, TypeSymbol), TypeCompareKind.ConsiderEverything)
        End Function
 
        Public NotOverridable Overrides Function Equals(other As Symbol, compareKind As TypeCompareKind) As Boolean
            Return Equals(TryCast(other, TypeSymbol), compareKind)
        End Function
 
        Public MustOverride Overrides Function GetHashCode() As Integer
 
        Public MustOverride Overloads Function Equals(other As TypeSymbol, comparison As TypeCompareKind) As Boolean
 
        ''' <summary>
        ''' Lookup an immediately nested type referenced from metadata, names should be
        ''' compared case-sensitively.
        ''' </summary>
        ''' <param name="emittedTypeName">
        ''' Type name.
        ''' </param>
        ''' <returns>
        ''' Symbol for the type, or Nothing if the type isn't found.
        ''' </returns>
        ''' <remarks></remarks>
        Friend Overridable Function LookupMetadataType(ByRef emittedTypeName As MetadataTypeName) As NamedTypeSymbol
            Debug.Assert(Not emittedTypeName.IsNull)
            Debug.Assert(TypeOf Me Is NamedTypeSymbol)
 
            Dim namedType As NamedTypeSymbol = Nothing
 
            If Me.Kind <> SymbolKind.ErrorType Then
                Dim typeMembers As ImmutableArray(Of NamedTypeSymbol)
 
                If emittedTypeName.IsMangled Then
                    Debug.Assert(Not emittedTypeName.UnmangledTypeName.Equals(emittedTypeName.TypeName) AndAlso emittedTypeName.InferredArity > 0)
 
                    If emittedTypeName.ForcedArity = -1 OrElse emittedTypeName.ForcedArity = emittedTypeName.InferredArity Then
                        ' Let's handle mangling case first.
                        typeMembers = Me.GetTypeMembers(emittedTypeName.UnmangledTypeName)
 
                        For Each named In typeMembers
                            If emittedTypeName.InferredArity = named.Arity AndAlso named.MangleName AndAlso String.Equals(named.Name, emittedTypeName.UnmangledTypeName, StringComparison.Ordinal) Then
                                If namedType IsNot Nothing Then
                                    ' ambiguity
                                    namedType = Nothing
                                    Exit For
                                End If
 
                                namedType = named
                            End If
                        Next
                    End If
                Else
                    Debug.Assert(emittedTypeName.UnmangledTypeName Is emittedTypeName.TypeName AndAlso emittedTypeName.InferredArity = 0)
                End If
 
                ' Now try lookup without removing generic arity mangling.
                Dim forcedArity As Integer = emittedTypeName.ForcedArity
 
                If emittedTypeName.UseCLSCompliantNameArityEncoding Then
                    ' Only types with arity 0 are acceptable, we already examined types with mangled names.
                    If emittedTypeName.InferredArity > 0 Then
                        GoTo Done
                    ElseIf forcedArity = -1 Then
                        forcedArity = 0
                    ElseIf forcedArity <> 0 Then
                        GoTo Done
                    Else
                        Debug.Assert(forcedArity = emittedTypeName.InferredArity)
                    End If
                End If
 
                typeMembers = Me.GetTypeMembers(emittedTypeName.TypeName)
 
                For Each named In typeMembers
                    ' If the name of the type must include generic mangling, it cannot be our match.
                    If Not named.MangleName AndAlso (forcedArity = -1 OrElse forcedArity = named.Arity) AndAlso
                       String.Equals(named.Name, emittedTypeName.TypeName, StringComparison.Ordinal) Then
 
                        If namedType IsNot Nothing Then
                            ' ambiguity
                            namedType = Nothing
                            Exit For
                        End If
 
                        namedType = named
                    End If
                Next
            End If
 
Done:
            Return namedType
        End Function
 
        Friend Overridable Function GetDirectBaseTypeNoUseSiteDiagnostics(basesBeingResolved As BasesBeingResolved) As NamedTypeSymbol
            Return BaseTypeNoUseSiteDiagnostics
        End Function
 
        Friend Overridable Function GetDirectBaseTypeWithDefinitionUseSiteDiagnostics(basesBeingResolved As BasesBeingResolved, <[In], Out> ByRef useSiteInfo As CompoundUseSiteInfo(Of AssemblySymbol)) As NamedTypeSymbol
            Dim result = GetDirectBaseTypeNoUseSiteDiagnostics(basesBeingResolved)
 
            If result IsNot Nothing Then
                result.OriginalDefinition.AddUseSiteInfo(useSiteInfo)
            End If
 
            Return result
        End Function
 
        Public Overridable ReadOnly Property IsTupleType() As Boolean
            Get
                Return False
            End Get
        End Property
 
        Public Overridable ReadOnly Property TupleUnderlyingType() As NamedTypeSymbol
            Get
                Return Nothing
            End Get
        End Property
 
        Public Overridable ReadOnly Property TupleElements As ImmutableArray(Of FieldSymbol)
            Get
                Return Nothing
            End Get
        End Property
 
        Public Overridable ReadOnly Property TupleElementTypes() As ImmutableArray(Of TypeSymbol)
            Get
                Return Nothing
            End Get
        End Property
 
        Public Overridable ReadOnly Property TupleElementNames() As ImmutableArray(Of String)
            Get
                Return Nothing
            End Get
        End Property
 
        ''' <summary>
        ''' Verify if the given type can be used to back a tuple type 
        ''' and return cardinality of that tuple type in <paramref name="tupleCardinality"/>. 
        ''' </summary>
        ''' <param name="tupleCardinality">If method returns true, contains cardinality of the compatible tuple type.</param>
        ''' <returns></returns>
        Public Overridable Function IsTupleCompatible(<Out> ByRef tupleCardinality As Integer) As Boolean
            tupleCardinality = 0
            Return False
        End Function
 
        ''' <summary>
        ''' Verify if the given type can be used to back a tuple type. 
        ''' </summary>
        Public Function IsTupleCompatible() As Boolean
            Dim countOfItems As Integer
            Return IsTupleCompatible(countOfItems)
        End Function
 
        ''' <summary>
        ''' Verify if the given type is a tuple of a given cardinality, or can be used to back a tuple type 
        ''' with the given cardinality. 
        ''' </summary>
        Public Function IsTupleOrCompatibleWithTupleOfCardinality(targetCardinality As Integer) As Boolean
            If (IsTupleType) Then
                Return TupleElementTypes.Length = targetCardinality
            End If
 
            Dim countOfItems As Integer
            Return IsTupleCompatible(countOfItems) AndAlso countOfItems = targetCardinality
        End Function
 
#Region "Use-Site Diagnostics"
 
        ''' <summary>
        ''' Return error code that has highest priority while calculating use site error for this symbol. 
        ''' </summary>
        Protected Overrides Function IsHighestPriorityUseSiteError(code As Integer) As Boolean
            Return code = ERRID.ERR_UnsupportedType1 OrElse code = ERRID.ERR_UnsupportedCompilerFeature
        End Function
 
        Public Overrides ReadOnly Property HasUnsupportedMetadata As Boolean
            Get
                Dim info As DiagnosticInfo = GetUseSiteInfo().DiagnosticInfo
                Return info IsNot Nothing AndAlso (info.Code = ERRID.ERR_UnsupportedType1 OrElse info.Code = ERRID.ERR_UnsupportedCompilerFeature)
            End Get
        End Property
 
        Friend MustOverride Overloads Function GetUnificationUseSiteDiagnosticRecursive(owner As Symbol, ByRef checkedTypes As HashSet(Of TypeSymbol)) As DiagnosticInfo
#End Region
 
#Region "ITypeSymbol"
 
        Private Function ITypeSymbol_FindImplementationForInterfaceMember(interfaceMember As ISymbol) As ISymbol Implements ITypeSymbol.FindImplementationForInterfaceMember
            Return If(TypeOf interfaceMember Is Symbol,
                FindImplementationForInterfaceMember(DirectCast(interfaceMember, Symbol)),
                Nothing)
        End Function
 
        Private ReadOnly Property ITypeSymbol_AllInterfaces As ImmutableArray(Of INamedTypeSymbol) Implements ITypeSymbol.AllInterfaces
            Get
                Return StaticCast(Of INamedTypeSymbol).From(Me.AllInterfacesNoUseSiteDiagnostics)
            End Get
        End Property
 
        Private ReadOnly Property ITypeSymbol_BaseType As INamedTypeSymbol Implements ITypeSymbol.BaseType
            Get
                Return Me.BaseTypeNoUseSiteDiagnostics
            End Get
        End Property
 
        Private ReadOnly Property ITypeSymbol_Interfaces As ImmutableArray(Of INamedTypeSymbol) Implements ITypeSymbol.Interfaces
            Get
                Return StaticCast(Of INamedTypeSymbol).From(Me.InterfacesNoUseSiteDiagnostics)
            End Get
        End Property
 
        Private ReadOnly Property ITypeSymbol_OriginalDefinition As ITypeSymbol Implements ITypeSymbol.OriginalDefinition
            Get
                Return Me.OriginalDefinition
            End Get
        End Property
 
        Private ReadOnly Property ITypeSymbol_IsTupleSymbol As Boolean Implements ITypeSymbol.IsTupleType
            Get
                Return Me.IsTupleType
            End Get
        End Property
 
        Private ReadOnly Property ITypeSymbol_IsNativeIntegerType As Boolean Implements ITypeSymbol.IsNativeIntegerType
            Get
                Return False
            End Get
        End Property
 
        Private ReadOnly Property ITypeSymbol_TypeKind As TypeKind Implements ITypeSymbol.TypeKind, ITypeSymbolInternal.TypeKind
            Get
                Return Me.TypeKind
            End Get
        End Property
 
        Private ReadOnly Property ITypeSymbol_IsRefLikeType As Boolean Implements ITypeSymbol.IsRefLikeType
            Get
                ' VB has no concept of ref-like types
                Return False
            End Get
        End Property
 
        Private ReadOnly Property ITypeSymbol_IsUnmanagedType As Boolean Implements ITypeSymbol.IsUnmanagedType
            Get
                Return GetManagedKind(CompoundUseSiteInfo(Of AssemblySymbol).Discarded) <> ManagedKind.Managed
            End Get
        End Property
 
        Private ReadOnly Property ITypeSymbol_IsReadOnly As Boolean Implements ITypeSymbol.IsReadOnly
            Get
                ' VB does not have readonly structures
                Return False
            End Get
        End Property
 
        Private ReadOnly Property ITypeSymbol_IsRecord As Boolean Implements ITypeSymbol.IsRecord
            Get
                ' VB does not have records
                Return False
            End Get
        End Property
 
        Private Function ITypeSymbol_ToDisplayString(topLevelNullability As NullableFlowState, Optional format As SymbolDisplayFormat = Nothing) As String Implements ITypeSymbol.ToDisplayString
            Return ToDisplayString(format)
        End Function
 
        Private Function ITypeSymbol_ToDisplayParts(topLevelNullability As NullableFlowState, Optional format As SymbolDisplayFormat = Nothing) As ImmutableArray(Of SymbolDisplayPart) Implements ITypeSymbol.ToDisplayParts
            Return ToDisplayParts(format)
        End Function
 
        Private Function ITypeSymbol_ToMinimalDisplayString(semanticModel As SemanticModel, topLevelNullability As NullableFlowState, position As Integer, Optional format As SymbolDisplayFormat = Nothing) As String Implements ITypeSymbol.ToMinimalDisplayString
            Return ToMinimalDisplayString(semanticModel, position, format)
        End Function
 
        Private Function ITypeSymbol_ToMinimalDisplayParts(semanticModel As SemanticModel, topLevelNullability As NullableFlowState, position As Integer, Optional format As SymbolDisplayFormat = Nothing) As ImmutableArray(Of SymbolDisplayPart) Implements ITypeSymbol.ToMinimalDisplayParts
            Return ToMinimalDisplayParts(semanticModel, position, format)
        End Function
 
#End Region
 
#Region "Interface checks"
        ''' <summary>
        ''' Returns the corresponding symbol in this type or a base type that implements 
        ''' interfaceMember (either implicitly or explicitly), or null if no such symbol 
        ''' exists (which might be either because this type doesn't implement the container 
        ''' of interfaceMember, or this type doesn't supply a member that successfully 
        ''' implements interfaceMember).
        ''' </summary>
        ''' <param name="interfaceMember">
        ''' Must be a non-null interface property, method, or event.
        ''' </param>
        ''' <returns>The implementing member.</returns>
        Public Function FindImplementationForInterfaceMember(interfaceMember As Symbol) As Symbol
            ' This layer handles caching, ComputeImplementationForInterfaceMember does the work.
            If interfaceMember Is Nothing Then
                Throw New ArgumentNullException(NameOf(interfaceMember))
            End If
 
            If Not interfaceMember.RequiresImplementation() OrElse
               Me.IsInterfaceType() OrElse ' In VB interfaces do not implement anything
               Not Me.ImplementsInterface(interfaceMember.ContainingType, comparer:=EqualsIgnoringComparer.InstanceCLRSignatureCompare, useSiteInfo:=CompoundUseSiteInfo(Of AssemblySymbol).Discarded) Then
                Return Nothing
            End If
 
            ' PERF: Avoid delegate allocation by splitting GetOrAdd into TryGetValue+TryAdd
            Dim map = ImplementationForInterfaceMemberMap
            Dim result As Symbol = Nothing
            If map.TryGetValue(interfaceMember, result) Then
                Return result
            End If
 
            result = ComputeImplementationForInterfaceMember(interfaceMember)
            map.TryAdd(interfaceMember, result)
            Return result
        End Function
 
        Private ReadOnly Property ImplementationForInterfaceMemberMap As ConcurrentDictionary(Of Symbol, Symbol)
            Get
                Dim map = _lazyImplementationForInterfaceMemberMap
                If map IsNot Nothing Then
                    Return map
                End If
 
                ' PERF: Avoid over-allocation. In many cases, there's only 1 entry and we don't expect concurrent updates.
                map = New ConcurrentDictionary(Of Symbol, Symbol)(concurrencyLevel:=1, capacity:=1)
                Return If(Interlocked.CompareExchange(_lazyImplementationForInterfaceMemberMap, map, Nothing), map)
            End Get
        End Property
 
        ''' <summary>
        ''' Compute the implementation for an interface member in this type, or Nothing if none.
        ''' </summary>
        Private Function ComputeImplementationForInterfaceMember(interfaceMember As Symbol) As Symbol
            Select Case interfaceMember.Kind
                Case SymbolKind.Method
                    Return ImplementsHelper.ComputeImplementationForInterfaceMember(Of MethodSymbol)(
                        DirectCast(interfaceMember, MethodSymbol),
                        Me,
                        MethodSignatureComparer.RuntimeMethodSignatureComparer)
 
                Case SymbolKind.Property
                    Return ImplementsHelper.ComputeImplementationForInterfaceMember(Of PropertySymbol)(
                        DirectCast(interfaceMember, PropertySymbol),
                        Me,
                        PropertySignatureComparer.RuntimePropertySignatureComparer)
 
                Case SymbolKind.Event
                    Return ImplementsHelper.ComputeImplementationForInterfaceMember(Of EventSymbol)(
                        DirectCast(interfaceMember, EventSymbol),
                        Me,
                        EventSignatureComparer.RuntimeEventSignatureComparer)
 
                Case Else
                    Return Nothing
            End Select
        End Function
 
        ''' <summary>
        ''' Get a dictionary with all the explicitly implemented interface symbols declared on this type.
        ''' 
        ''' key = interface method/property/event compared using <see cref="ExplicitInterfaceImplementationTargetMemberEqualityComparer"/>,
        ''' value = explicitly implementing methods/properties/events declared on this type (normally a single value, multiple in case of
        ''' an error).
        ''' 
        ''' Note: This implementation is overridden by source symbols, because they diagnose errors also.
        ''' </summary>
        Friend Overridable ReadOnly Property ExplicitInterfaceImplementationMap As MultiDictionary(Of Symbol, Symbol)
            Get
                If m_lazyExplicitInterfaceImplementationMap Is Nothing Then
                    Interlocked.CompareExchange(Me.m_lazyExplicitInterfaceImplementationMap, MakeExplicitInterfaceImplementationMap(), Nothing)
                End If
 
                Return m_lazyExplicitInterfaceImplementationMap
            End Get
        End Property
 
        ' An empty dictionary to use if there are no members in the explicit interface map.
        Protected Shared ReadOnly EmptyExplicitImplementationMap As MultiDictionary(Of Symbol, Symbol) = New MultiDictionary(Of Symbol, Symbol)
 
        ' Build the explicit interface map for this type. 
        ' This implementation is not used by source symbols, which additionally diagnose errors.
        Private Function MakeExplicitInterfaceImplementationMap() As MultiDictionary(Of Symbol, Symbol)
            If Me.IsClassType() OrElse Me.IsStructureType() Then
                Dim map = New MultiDictionary(Of Symbol, Symbol)(ExplicitInterfaceImplementationTargetMemberEqualityComparer.Instance)
                For Each implementingMember In Me.GetMembersUnordered()
                    For Each interfaceMember In GetExplicitInterfaceImplementations(implementingMember)
                        map.Add(interfaceMember, implementingMember)
                    Next
                Next
 
                If map.Count > 0 Then
                    Return map
                Else
                    Return EmptyExplicitImplementationMap  ' Better to use singleton and garbage collection the empty dictionary we just created.
                End If
            Else
                Return EmptyExplicitImplementationMap
            End If
        End Function
 
        Protected Class ExplicitInterfaceImplementationTargetMemberEqualityComparer
            Implements IEqualityComparer(Of Symbol)
 
            Public Shared ReadOnly Instance As New ExplicitInterfaceImplementationTargetMemberEqualityComparer()
 
            Private Sub New()
            End Sub
 
            Public Overloads Function Equals(x As Symbol, y As Symbol) As Boolean Implements IEqualityComparer(Of Symbol).Equals
                Return x.OriginalDefinition = y.OriginalDefinition AndAlso
                       EqualsIgnoringComparer.InstanceCLRSignatureCompare.Equals(x.ContainingType, y.ContainingType)
            End Function
 
            Public Overloads Function GetHashCode(obj As Symbol) As Integer Implements IEqualityComparer(Of Symbol).GetHashCode
                Return obj.OriginalDefinition.GetHashCode()
            End Function
        End Class
 
#End Region
 
        Private ReadOnly Property ITypeSymbol_NullableAnnotation As NullableAnnotation Implements ITypeSymbol.NullableAnnotation
            Get
                Return NullableAnnotation.None
            End Get
        End Property
 
        Private Function ITypeSymbol_WithNullability(nullableAnnotation As NullableAnnotation) As ITypeSymbol Implements ITypeSymbol.WithNullableAnnotation
            Return Me
        End Function
 
        Private Function ITypeSymbolInternal_GetITypeSymbol() As ITypeSymbol Implements ITypeSymbolInternal.GetITypeSymbol
            Return Me
        End Function
 
    End Class
End Namespace