public CommonConversion ClassifyConversion(TypeSymbol from, TypeSymbol to, ConversionKind kinds)
{
if (from == to)
{
return(IdentityConversion);
}
// implicit conversions handled by 'EmitConversion':
if (to.SpecialType == SpecialType.System_Void)
{
return(IdentityConversion);
}
// object cast possible implicitly:
if ((kinds & ConversionKind.Reference) == ConversionKind.Reference)
{
if (from.IsReferenceType && to.IsReferenceType && from.IsOfType(to))
{
// (PHP) string, resource, array, alias -> object: NoConversion
if (to.SpecialType != SpecialType.System_Object || !IsSpecialReferenceType(from))
{
return(ReferenceConversion);
}
}
if (to.SpecialType == SpecialType.System_Object && (from.IsInterfaceType() || (from.IsReferenceType && from.IsTypeParameter())))
{
return(ReferenceConversion);
}
}
// resolve conversion operator method:
if ((kinds & ConversionKind.Numeric) == ConversionKind.Numeric)
{
var conv = ClassifyNumericConversion(from, to);
if (conv.Exists)
{
return(conv);
}
}
// strict:
if ((kinds & ConversionKind.Strict) == ConversionKind.Strict)
{
var op = ResolveOperator(from, false, ImplicitConversionOpNames(to), new[] { _compilation.CoreTypes.StrictConvert.Symbol }, target: to);
if (op != null)
{
return(new CommonConversion(true, false, false, false, true, op));
}
}
// implicit
if ((kinds & ConversionKind.Implicit) == ConversionKind.Implicit)
{
var op = TryWellKnownImplicitConversion(from, to) ?? ResolveOperator(from, false, ImplicitConversionOpNames(to), new[] { to, _compilation.CoreTypes.Convert.Symbol }, target: to);
if (op != null)
{
return(new CommonConversion(true, false, false, false, true, op));
}
}
// explicit:
if ((kinds & ConversionKind.Explicit) == ConversionKind.Explicit)
{
var op = ResolveOperator(from, false, ExplicitConversionOpNames(to), new[] { to, _compilation.CoreTypes.Convert.Symbol }, target: to);
if (op != null)
{
return(new CommonConversion(true, false, false, false, false, op));
}
// explicit reference conversion (reference type -> reference type)
else if (
from.IsReferenceType && to.IsReferenceType &&
!IsSpecialReferenceType(from) && !IsSpecialReferenceType(to) &&
!from.IsArray() && !to.IsArray())
{
return(ExplicitReferenceConversion);
}
}
//
return(NoConversion);
}
// Although III.1.8.1.3 seems to imply that verifier understands variance casts.
// It appears that verifier/JIT gets easily confused.
// So to not rely on whether that should work or not we will flag potentially
// "complicated" casts and make them static casts to ensure we are all on
// the same page with what type should be tracked.
private static bool IsVarianceCast(TypeSymbol to, TypeSymbol from)
{
if (to == from)
{
return false;
}
if ((object)from == null)
{
// from unknown type - this could be a variance conversion.
return true;
}
// while technically variance casts, array conversions do not seem to be a problem
// unless the element types are converted via variance.
if (to.IsArray())
{
return IsVarianceCast(((ArrayTypeSymbol)to).ElementType, ((ArrayTypeSymbol)from).ElementType);
}
return (to.IsDelegateType() && to != from) ||
(to.IsInterfaceType() && from.IsInterfaceType() && !from.InterfacesAndTheirBaseInterfacesNoUseSiteDiagnostics.Contains((NamedTypeSymbol)to));
}
private static Symbol FindExplicitlyImplementedMember(
Symbol implementingMember,
TypeSymbol explicitInterfaceType,
string interfaceMemberName,
ExplicitInterfaceSpecifierSyntax explicitInterfaceSpecifierSyntax,
DiagnosticBag diagnostics)
{
if ((object)explicitInterfaceType == null)
{
return(null);
}
var memberLocation = implementingMember.Locations[0];
var containingType = implementingMember.ContainingType;
var containingTypeKind = containingType.TypeKind;
if (containingTypeKind != TypeKind.Class && containingTypeKind != TypeKind.Struct)
{
diagnostics.Add(ErrorCode.ERR_ExplicitInterfaceImplementationInNonClassOrStruct, memberLocation, implementingMember);
return(null);
}
if (!explicitInterfaceType.IsInterfaceType())
{
//we'd like to highlight just the type part of the name
var explictInterfaceSyntax = explicitInterfaceSpecifierSyntax.Name;
var location = new SourceLocation(explictInterfaceSyntax);
diagnostics.Add(ErrorCode.ERR_ExplicitInterfaceImplementationNotInterface, location, explicitInterfaceType);
return(null);
}
var explicitInterfaceNamedType = (NamedTypeSymbol)explicitInterfaceType;
// 13.4.1: "For an explicit interface member implementation to be valid, the class or struct must name an
// interface in its base class list that contains a member ..."
if (!containingType.InterfacesAndTheirBaseInterfacesNoUseSiteDiagnostics.Contains(explicitInterfaceNamedType))
{
//we'd like to highlight just the type part of the name
var explictInterfaceSyntax = explicitInterfaceSpecifierSyntax.Name;
var location = new SourceLocation(explictInterfaceSyntax);
diagnostics.Add(ErrorCode.ERR_ClassDoesntImplementInterface, location, implementingMember, explicitInterfaceNamedType);
//do a lookup anyway
}
var hasParamsParam = implementingMember.HasParamsParameter();
// Setting this flag to true does not imply that an interface member has been successfully implemented.
// It just indicates that a corresponding interface member has been found (there may still be errors).
var foundMatchingMember = false;
Symbol implementedMember = null;
foreach (Symbol interfaceMember in explicitInterfaceNamedType.GetMembers(interfaceMemberName))
{
// At this point, we know that explicitInterfaceNamedType is an interface, so candidate must be public
// and, therefore, accessible. So we don't need to check that.
// However, metadata interface members can be static - we ignore them, as does Dev10.
if (interfaceMember.Kind != implementingMember.Kind || interfaceMember.IsStatic)
{
continue;
}
if (MemberSignatureComparer.ExplicitImplementationComparer.Equals(implementingMember, interfaceMember))
{
foundMatchingMember = true;
// Cannot implement accessor directly unless
// the accessor is from an indexed property.
if (interfaceMember.IsAccessor() && !((MethodSymbol)interfaceMember).IsIndexedPropertyAccessor())
{
diagnostics.Add(ErrorCode.ERR_ExplicitMethodImplAccessor, memberLocation, implementingMember, interfaceMember);
}
else
{
if (interfaceMember.MustCallMethodsDirectly())
{
diagnostics.Add(ErrorCode.ERR_BogusExplicitImpl, memberLocation, implementingMember, interfaceMember);
}
else if (hasParamsParam && !interfaceMember.HasParamsParameter())
{
// Note: no error for !hasParamsParam && interfaceMethod.HasParamsParameter()
// Still counts as an implementation.
diagnostics.Add(ErrorCode.ERR_ExplicitImplParams, memberLocation, implementingMember, interfaceMember);
}
implementedMember = interfaceMember;
break;
}
}
}
if (!foundMatchingMember)
{
// CONSIDER: we may wish to suppress this error in the event that another error
// has been reported about the signature.
diagnostics.Add(ErrorCode.ERR_InterfaceMemberNotFound, memberLocation, implementingMember);
}
// In constructed types, it is possible that two method signatures could differ by only ref/out
// after substitution. We look for this as part of explicit implementation because, if someone
// tried to implement the ambiguous interface implicitly, we would separately raise an error about
// the implicit implementation methods differing by only ref/out.
FindExplicitImplementationCollisions(implementingMember, implementedMember, diagnostics);
return(implementedMember);
}
/// <summary>
/// This method find the set of applicable user-defined and lifted conversion operators, u.
/// The set consists of the user-defined and lifted implicit conversion operators declared by
/// the classes and structs in d that convert from a type encompassing source to a type encompassed by target.
/// However if allowAnyTarget is true, then it considers all operators that convert from a type encompassing source
/// to any target. This flag must be set only if we are computing user defined conversions from a given source
/// type to any target type.
/// </summary>
/// <remarks>
/// Currently allowAnyTarget flag is only set to true by <see cref="AnalyzeImplicitUserDefinedConversionForV6SwitchGoverningType"/>,
/// where we must consider user defined implicit conversions from the type of the switch expression to
/// any of the possible switch governing types.
/// </remarks>
private void ComputeApplicableUserDefinedImplicitConversionSet(
BoundExpression sourceExpression,
TypeSymbol source,
TypeSymbol target,
ArrayBuilder <NamedTypeSymbol> d,
ArrayBuilder <UserDefinedConversionAnalysis> u,
ref HashSet <DiagnosticInfo> useSiteDiagnostics,
bool allowAnyTarget = false)
{
Debug.Assert(sourceExpression != null || (object)source != null);
Debug.Assert(((object)target != null) == !allowAnyTarget);
Debug.Assert(d != null);
Debug.Assert(u != null);
// SPEC: Find the set of applicable user-defined and lifted conversion operators, U.
// SPEC: The set consists of the user-defined and lifted implicit conversion operators
// SPEC: declared by the classes and structs in D that convert from a type encompassing
// SPEC: E to a type encompassed by T. If U is empty, the conversion is undefined and
// SPEC: a compile-time error occurs.
// SPEC: Give a user-defined conversion operator that converts from a non-nullable
// SPEC: value type S to a non-nullable value type T, a lifted conversion operator
// SPEC: exists that converts from S? to T?.
// DELIBERATE SPEC VIOLATION:
//
// The spec here essentially says that we add an applicable "regular" conversion and
// an applicable lifted conversion, if there is one, to the candidate set, and then
// let them duke it out to determine which one is "best".
//
// This is not at all what the native compiler does, and attempting to implement
// the specification, or slight variations on it, produces too many backwards-compatibility
// breaking changes.
//
// The native compiler deviates from the specification in two major ways here.
// First, it does not add *both* the regular and lifted forms to the candidate set.
// Second, the way it characterizes a "lifted" form is very, very different from
// how the specification characterizes a lifted form.
//
// An operation, in this case, X-->Y, is properly said to be "lifted" to X?-->Y? via
// the rule that X?-->Y? matches the behavior of X-->Y for non-null X, and converts
// null X to null Y otherwise.
//
// The native compiler, by contrast, takes the existing operator and "lifts" either
// the operator's parameter type or the operator's return type to nullable. For
// example, a conversion from X?-->Y would be "lifted" to X?-->Y? by making the
// conversion from X? to Y, and then from Y to Y?. No "lifting" semantics
// are imposed; we do not check to see if the X? is null. This operator is not
// actually "lifted" at all; rather, an implicit conversion is applied to the
// output. **The native compiler considers the result type Y? of that standard implicit
// conversion to be the result type of the "lifted" conversion**, rather than
// properly considering Y to be the result type of the conversion for the purposes
// of computing the best output type.
//
// MOREOVER: the native compiler actually *does* implement nullable lifting semantics
// in the case where the input type of the user-defined conversion is a non-nullable
// value type and the output type is a nullable value type **or pointer type, or
// reference type**. This is an enormous departure from the specification; the
// native compiler will take a user-defined conversion from X-->Y? or X-->C and "lift"
// it to a conversion from X?-->Y? or X?-->C that has nullable semantics.
//
// This is quite confusing. In this code we will classify the conversion as either
// "normal" or "lifted" on the basis of *whether or not special lifting semantics
// are to be applied*. That is, whether or not a later rewriting pass is going to
// need to insert a check to see if the source expression is null, and decide
// whether or not to call the underlying unlifted conversion or produce a null
// value without calling the unlifted conversion.
// DELIBERATE SPEC VIOLATION (See bug 17021)
// The specification defines a type U as "encompassing" a type V
// if there is a standard implicit conversion from U to V, and
// neither are interface types.
//
// The intention of this language is to ensure that we do not allow user-defined
// conversions that involve interfaces. We have a reasonable expectation that a
// conversion that involves an interface is one that preserves referential identity,
// and user-defined conversions usually do not.
//
// Now, suppose we have a standard conversion from Alpha to Beta, a user-defined
// conversion from Beta to Gamma, and a standard conversion from Gamma to Delta.
// The specification allows the implicit conversion from Alpha to Delta only if
// Beta encompasses Alpha and Delta encompasses Gamma. And therefore, none of them
// can be interface types, de jure.
//
// However, the dev10 compiler only checks Alpha and Delta to see if they are interfaces,
// and allows Beta and Gamma to be interfaces.
//
// So what's the big deal there? It's not legal to define a user-defined conversion where
// the input or output types are interfaces, right?
//
// It is not legal to define such a conversion, no, but it is legal to create one via generic
// construction. If we have a conversion from T to C<T>, then C<I> has a conversion from I to C<I>.
//
// The dev10 compiler fails to check for this situation. This means that,
// you can convert from int to C<IComparable> because int implements IComparable, but cannot
// convert from IComparable to C<IComparable>!
//
// Unfortunately, we know of several real programs that rely upon this bug, so we are going
// to reproduce it here.
if ((object)source != null && source.IsInterfaceType() || (object)target != null && target.IsInterfaceType())
{
return;
}
foreach (NamedTypeSymbol declaringType in d)
{
foreach (MethodSymbol op in declaringType.GetOperators(WellKnownMemberNames.ImplicitConversionName))
{
// We might have a bad operator and be in an error recovery situation. Ignore it.
if (op.ReturnsVoid || op.ParameterCount != 1)
{
continue;
}
TypeSymbol convertsFrom = op.ParameterTypes[0];
TypeSymbol convertsTo = op.ReturnType;
Conversion fromConversion = EncompassingImplicitConversion(sourceExpression, source, convertsFrom, ref useSiteDiagnostics);
Conversion toConversion = allowAnyTarget ? Conversion.Identity :
EncompassingImplicitConversion(null, convertsTo, target, ref useSiteDiagnostics);
if (fromConversion.Exists && toConversion.Exists)
{
// There is an additional spec violation in the native compiler. Suppose
// we have a conversion from X-->Y and are asked to do "Y? y = new X();" Clearly
// the intention is to convert from X-->Y via the implicit conversion, and then
// stick a standard implicit conversion from Y-->Y? on the back end. **In this
// situation, the native compiler treats the conversion as though it were
// actually X-->Y? in source for the purposes of determining the best target
// type of an operator.
//
// We perpetuate this fiction here.
if ((object)target != null && target.IsNullableType() && convertsTo.IsNonNullableValueType())
{
convertsTo = MakeNullableType(convertsTo);
toConversion = allowAnyTarget ? Conversion.Identity :
EncompassingImplicitConversion(null, convertsTo, target, ref useSiteDiagnostics);
}
u.Add(UserDefinedConversionAnalysis.Normal(op, fromConversion, toConversion, convertsFrom, convertsTo));
}
else if ((object)source != null && source.IsNullableType() && convertsFrom.IsNonNullableValueType() &&
(allowAnyTarget || target.CanBeAssignedNull()))
{
// As mentioned above, here we diverge from the specification, in two ways.
// First, we only check for the lifted form if the normal form was inapplicable.
// Second, we are supposed to apply lifting semantics only if the conversion
// parameter and return types are *both* non-nullable value types.
//
// In fact the native compiler determines whether to check for a lifted form on
// the basis of:
//
// * Is the type we are ultimately converting from a nullable value type?
// * Is the parameter type of the conversion a non-nullable value type?
// * Is the type we are ultimately converting to a nullable value type,
// pointer type, or reference type?
//
// If the answer to all those questions is "yes" then we lift to nullable
// and see if the resulting operator is applicable.
TypeSymbol nullableFrom = MakeNullableType(convertsFrom);
TypeSymbol nullableTo = convertsTo.IsNonNullableValueType() ? MakeNullableType(convertsTo) : convertsTo;
Conversion liftedFromConversion = EncompassingImplicitConversion(sourceExpression, source, nullableFrom, ref useSiteDiagnostics);
Conversion liftedToConversion = !allowAnyTarget?
EncompassingImplicitConversion(null, nullableTo, target, ref useSiteDiagnostics) :
Conversion.Identity;
if (liftedFromConversion.Exists && liftedToConversion.Exists)
{
u.Add(UserDefinedConversionAnalysis.Lifted(op, liftedFromConversion, liftedToConversion, nullableFrom, nullableTo));
}
}
}
}
}
private static Symbol FindExplicitlyImplementedMember(
Symbol implementingMember,
TypeSymbol explicitInterfaceType,
string interfaceMemberName,
ExplicitInterfaceSpecifierSyntax explicitInterfaceSpecifierSyntax,
DiagnosticBag diagnostics)
{
if ((object)explicitInterfaceType == null)
{
return(null);
}
var memberLocation = implementingMember.Locations[0];
var containingType = implementingMember.ContainingType;
switch (containingType.TypeKind)
{
case TypeKind.Class:
case TypeKind.Struct:
case TypeKind.Interface:
break;
default:
diagnostics.Add(ErrorCode.ERR_ExplicitInterfaceImplementationInNonClassOrStruct, memberLocation, implementingMember);
return(null);
}
if (!explicitInterfaceType.IsInterfaceType())
{
//we'd like to highlight just the type part of the name
var explicitInterfaceSyntax = explicitInterfaceSpecifierSyntax.Name;
var location = new SourceLocation(explicitInterfaceSyntax);
diagnostics.Add(ErrorCode.ERR_ExplicitInterfaceImplementationNotInterface, location, explicitInterfaceType);
return(null);
}
var explicitInterfaceNamedType = (NamedTypeSymbol)explicitInterfaceType;
// 13.4.1: "For an explicit interface member implementation to be valid, the class or struct must name an
// interface in its base class list that contains a member ..."
MultiDictionary <NamedTypeSymbol, NamedTypeSymbol> .ValueSet set = containingType.InterfacesAndTheirBaseInterfacesNoUseSiteDiagnostics[explicitInterfaceNamedType];
int setCount = set.Count;
if (setCount == 0 || !set.Contains(explicitInterfaceNamedType, Symbols.SymbolEqualityComparer.ObliviousNullableModifierMatchesAny))
{
//we'd like to highlight just the type part of the name
var explicitInterfaceSyntax = explicitInterfaceSpecifierSyntax.Name;
var location = new SourceLocation(explicitInterfaceSyntax);
if (setCount > 0 && set.Contains(explicitInterfaceNamedType, Symbols.SymbolEqualityComparer.IgnoringNullable))
{
diagnostics.Add(ErrorCode.WRN_NullabilityMismatchInExplicitlyImplementedInterface, location);
}
else
{
diagnostics.Add(ErrorCode.ERR_ClassDoesntImplementInterface, location, implementingMember, explicitInterfaceNamedType);
}
//do a lookup anyway
}
// Do not look in itself
if (containingType == (object)explicitInterfaceNamedType.OriginalDefinition)
{
// An error will be reported elsewhere.
// Either the interface is not implemented, or it causes a cycle in the interface hierarchy.
return(null);
}
var hasParamsParam = implementingMember.HasParamsParameter();
// Setting this flag to true does not imply that an interface member has been successfully implemented.
// It just indicates that a corresponding interface member has been found (there may still be errors).
var foundMatchingMember = false;
Symbol implementedMember = null;
foreach (Symbol interfaceMember in explicitInterfaceNamedType.GetMembers(interfaceMemberName))
{
// At this point, we know that explicitInterfaceNamedType is an interface.
// However, metadata interface members can be static - we ignore them, as does Dev10.
if (interfaceMember.Kind != implementingMember.Kind || !interfaceMember.IsImplementableInterfaceMember())
{
continue;
}
if (MemberSignatureComparer.ExplicitImplementationComparer.Equals(implementingMember, interfaceMember))
{
foundMatchingMember = true;
// Cannot implement accessor directly unless
// the accessor is from an indexed property.
if (interfaceMember.IsAccessor() && !((MethodSymbol)interfaceMember).IsIndexedPropertyAccessor())
{
diagnostics.Add(ErrorCode.ERR_ExplicitMethodImplAccessor, memberLocation, implementingMember, interfaceMember);
}
else
{
if (interfaceMember.MustCallMethodsDirectly())
{
diagnostics.Add(ErrorCode.ERR_BogusExplicitImpl, memberLocation, implementingMember, interfaceMember);
}
else if (hasParamsParam && !interfaceMember.HasParamsParameter())
{
// Note: no error for !hasParamsParam && interfaceMethod.HasParamsParameter()
// Still counts as an implementation.
diagnostics.Add(ErrorCode.ERR_ExplicitImplParams, memberLocation, implementingMember, interfaceMember);
}
implementedMember = interfaceMember;
break;
}
}
}
if (!foundMatchingMember)
{
// CONSIDER: we may wish to suppress this error in the event that another error
// has been reported about the signature.
diagnostics.Add(ErrorCode.ERR_InterfaceMemberNotFound, memberLocation, implementingMember);
}
// Make sure implemented member is accessible
if ((object)implementedMember != null)
{
HashSet <DiagnosticInfo> useSiteDiagnostics = null;
if (!AccessCheck.IsSymbolAccessible(implementedMember, implementingMember.ContainingType, ref useSiteDiagnostics, throughTypeOpt: null))
{
diagnostics.Add(ErrorCode.ERR_BadAccess, memberLocation, implementedMember);
}
else
{
switch (implementedMember.Kind)
{
case SymbolKind.Property:
var propertySymbol = (PropertySymbol)implementedMember;
checkAccessorIsAccessibleIfImplementable(propertySymbol.GetMethod);
checkAccessorIsAccessibleIfImplementable(propertySymbol.SetMethod);
break;
case SymbolKind.Event:
var eventSymbol = (EventSymbol)implementedMember;
checkAccessorIsAccessibleIfImplementable(eventSymbol.AddMethod);
checkAccessorIsAccessibleIfImplementable(eventSymbol.RemoveMethod);
break;
}
void checkAccessorIsAccessibleIfImplementable(MethodSymbol accessor)
{
if (accessor.IsImplementable() &&
!AccessCheck.IsSymbolAccessible(accessor, implementingMember.ContainingType, ref useSiteDiagnostics, throughTypeOpt: null))
{
diagnostics.Add(ErrorCode.ERR_BadAccess, memberLocation, accessor);
}
}
}
diagnostics.Add(memberLocation, useSiteDiagnostics);
}
return(implementedMember);
}
private void AddUserDefinedConversionsToExplicitCandidateSet(
BoundExpression sourceExpression,
TypeSymbol source,
TypeSymbol target,
ArrayBuilder <UserDefinedConversionAnalysis> u,
NamedTypeSymbol declaringType,
string operatorName,
ref HashSet <DiagnosticInfo> useSiteDiagnostics)
{
Debug.Assert(sourceExpression != null || (object)source != null);
Debug.Assert((object)target != null);
Debug.Assert(u != null);
Debug.Assert((object)declaringType != null);
Debug.Assert(operatorName != null);
// SPEC: Find the set of applicable user-defined and lifted conversion operators, U.
// SPEC: The set consists of the user-defined and lifted implicit or explicit
// SPEC: conversion operators declared by the classes and structs in D that convert
// SPEC: from a type encompassing E or encompassed by S (if it exists) to a type
// SPEC: encompassing or encompassed by T.
// DELIBERATE SPEC VIOLATION:
//
// The spec here essentially says that we add an applicable "regular" conversion and
// an applicable lifted conversion, if there is one, to the candidate set, and then
// let them duke it out to determine which one is "best".
//
// This is not at all what the native compiler does, and attempting to implement
// the specification, or slight variations on it, produces too many backwards-compatibility
// breaking changes.
//
// The native compiler deviates from the specification in two major ways here.
// First, it does not add *both* the regular and lifted forms to the candidate set.
// Second, the way it characterizes a "lifted" form is very, very different from
// how the specification characterizes a lifted form.
//
// An operation, in this case, X-->Y, is properly said to be "lifted" to X?-->Y? via
// the rule that X?-->Y? matches the behavior of X-->Y for non-null X, and converts
// null X to null Y otherwise.
//
// The native compiler, by contrast, takes the existing operator and "lifts" either
// the operator's parameter type or the operator's return type to nullable. For
// example, a conversion from X?-->Y would be "lifted" to X?-->Y? by making the
// conversion from X? to Y, and then from Y to Y?. No "lifting" semantics
// are imposed; we do not check to see if the X? is null. This operator is not
// actually "lifted" at all; rather, an implicit conversion is applied to the
// output. **The native compiler considers the result type Y? of that standard implicit
// conversion to be the result type of the "lifted" conversion**, rather than
// properly considering Y to be the result type of the conversion for the purposes
// of computing the best output type.
//
// Moreover: the native compiler actually *does* implement nullable lifting semantics
// in the case where the input type of the user-defined conversion is a non-nullable
// value type and the output type is a nullable value type **or pointer type, or
// reference type**. This is an enormous departure from the specification; the
// native compiler will take a user-defined conversion from X-->Y? or X-->C and "lift"
// it to a conversion from X?-->Y? or X?-->C that has nullable semantics.
//
// This is quite confusing. In this code we will classify the conversion as either
// "normal" or "lifted" on the basis of *whether or not special lifting semantics
// are to be applied*. That is, whether or not a later rewriting pass is going to
// need to insert a check to see if the source expression is null, and decide
// whether or not to call the underlying unlifted conversion or produce a null
// value without calling the unlifted conversion.
// DELIBERATE SPEC VIOLATION: See the comment regarding bug 17021 in
// UserDefinedImplicitConversions.cs.
if ((object)source != null && source.IsInterfaceType() || target.IsInterfaceType())
{
return;
}
foreach (MethodSymbol op in declaringType.GetOperators(operatorName))
{
// We might have a bad operator and be in an error recovery situation. Ignore it.
if (op.ReturnsVoid || op.ParameterCount != 1 || op.ReturnType.TypeKind == TypeKind.Error)
{
continue;
}
TypeSymbol convertsFrom = op.GetParameterType(0);
TypeSymbol convertsTo = op.ReturnType;
Conversion fromConversion = EncompassingExplicitConversion(sourceExpression, source, convertsFrom, ref useSiteDiagnostics);
Conversion toConversion = EncompassingExplicitConversion(null, convertsTo, target, ref useSiteDiagnostics);
// We accept candidates for which the parameter type encompasses the *underlying* source type.
if (!fromConversion.Exists &&
(object)source != null &&
source.IsNullableType() &&
EncompassingExplicitConversion(null, source.GetNullableUnderlyingType(), convertsFrom, ref useSiteDiagnostics).Exists)
{
fromConversion = ClassifyBuiltInConversion(source, convertsFrom, ref useSiteDiagnostics);
}
// As in dev11 (and the revised spec), we also accept candidates for which the return type is encompassed by the *stripped* target type.
if (!toConversion.Exists &&
(object)target != null &&
target.IsNullableType() &&
EncompassingExplicitConversion(null, convertsTo, target.GetNullableUnderlyingType(), ref useSiteDiagnostics).Exists)
{
toConversion = ClassifyBuiltInConversion(convertsTo, target, ref useSiteDiagnostics);
}
// In the corresponding implicit conversion code we can get away with first
// checking to see if standard implicit conversions exist from the source type
// to the parameter type, and from the return type to the target type. If not,
// then we can check for a lifted operator.
//
// That's not going to cut it in the explicit conversion code. Suppose we have
// a conversion X-->Y and have source type X? and target type Y?. There *are*
// standard explicit conversions from X?-->X and Y?-->Y, but we do not want
// to bind this as an *unlifted* conversion from X? to Y?; we want such a thing
// to be a *lifted* conversion from X? to Y?, that checks for null on the source
// and decides to not call the underlying user-defined conversion if it is null.
//
// We therefore cannot do what we do in the implicit conversions, where we check
// to see if the unlifted conversion works, and if it does, then don't add the lifted
// conversion at all. Rather, we have to see if what we're building here is a
// lifted conversion or not.
//
// Under what circumstances is this conversion a lifted conversion? (In the
// "spec" sense of a lifted conversion; that is, that we check for null
// and skip the user-defined conversion if necessary).
//
// * The source type must be a nullable value type.
// * The parameter type must be a non-nullable value type.
// * The target type must be able to take on a null value.
if (fromConversion.Exists && toConversion.Exists)
{
if ((object)source != null && source.IsNullableType() && convertsFrom.IsNonNullableValueType() && target.CanBeAssignedNull())
{
TypeSymbol nullableFrom = MakeNullableType(convertsFrom);
TypeSymbol nullableTo = convertsTo.IsNonNullableValueType() ? MakeNullableType(convertsTo) : convertsTo;
Conversion liftedFromConversion = EncompassingExplicitConversion(sourceExpression, source, nullableFrom, ref useSiteDiagnostics);
Conversion liftedToConversion = EncompassingExplicitConversion(null, nullableTo, target, ref useSiteDiagnostics);
Debug.Assert(liftedFromConversion.Exists);
Debug.Assert(liftedToConversion.Exists);
u.Add(UserDefinedConversionAnalysis.Lifted(op, liftedFromConversion, liftedToConversion, nullableFrom, nullableTo));
}
else
{
// There is an additional spec violation in the native compiler. Suppose
// we have a conversion from X-->Y and are asked to do "Y? y = new X();" Clearly
// the intention is to convert from X-->Y via the implicit conversion, and then
// stick a standard implicit conversion from Y-->Y? on the back end. **In this
// situation, the native compiler treats the conversion as though it were
// actually X-->Y? in source for the purposes of determining the best target
// type of a set of operators.
//
// Similarly, if we have a conversion from X-->Y and are asked to do
// an explicit conversion from X? to Y then we treat the conversion as
// though it really were X?-->Y for the purposes of determining the best
// source type of a set of operators.
//
// We perpetuate these fictions here.
if (target.IsNullableType() && convertsTo.IsNonNullableValueType())
{
convertsTo = MakeNullableType(convertsTo);
toConversion = EncompassingExplicitConversion(null, convertsTo, target, ref useSiteDiagnostics);
}
if ((object)source != null && source.IsNullableType() && convertsFrom.IsNonNullableValueType())
{
convertsFrom = MakeNullableType(convertsFrom);
fromConversion = EncompassingExplicitConversion(null, convertsFrom, source, ref useSiteDiagnostics);
}
u.Add(UserDefinedConversionAnalysis.Normal(op, fromConversion, toConversion, convertsFrom, convertsTo));
}
}
}
}
public CommonConversion ClassifyConversion(TypeSymbol from, TypeSymbol to, bool checkimplicit = true, bool checkexplicit = true)
{
if (from == to)
{
return(IdentityConversion);
}
if (from.IsReferenceType && to.IsReferenceType && from.IsOfType(to))
{
// (PHP) string, resource, array, alias -> object: NoConversion
if (to.SpecialType != SpecialType.System_Object || !IsSpecialReferenceType(from))
{
return(ReferenceConversion);
}
}
if (to.SpecialType == SpecialType.System_Object && (from.IsInterfaceType() || (from.IsReferenceType && from.IsTypeParameter())))
{
return(ReferenceConversion);
}
// implicit conversions handled by 'EmitConversion':
if (to.SpecialType == SpecialType.System_Void)
{
return(IdentityConversion);
}
// resolve conversion operator method:
var conv = ClassifyNumericConversion(from, to);
if (!conv.Exists)
{
// TODO: cache result
var op = checkimplicit
? TryWellKnownImplicitConversion(from, to) ?? ResolveOperator(from, false, ImplicitConversionOpNames(to), new[] { to, _compilation.CoreTypes.Convert.Symbol }, target: to)
: null;
if (op != null)
{
conv = new CommonConversion(true, false, false, false, true, op);
}
else if (checkexplicit)
{
op = ResolveOperator(from, false, ExplicitConversionOpNames(to), new[] { to, _compilation.CoreTypes.Convert.Symbol }, target: to);
if (op != null)
{
conv = new CommonConversion(true, false, false, false, false, op);
}
// explicit reference conversion (reference type -> reference type)
else if (
from.IsReferenceType && to.IsReferenceType &&
!IsSpecialReferenceType(from) && !IsSpecialReferenceType(to) &&
!from.IsArray() && !to.IsArray())
{
conv = ExplicitReferenceConversion;
}
}
}
return(conv);
}
private bool GetUserDefinedOperators(UnaryOperatorKind kind, BoundExpression operand, ArrayBuilder <UnaryOperatorAnalysisResult> results, ref HashSet <DiagnosticInfo> useSiteDiagnostics)
{
Debug.Assert(operand != null);
if ((object)operand.Type == null)
{
// If the operand has no type -- because it is a null reference or a lambda or a method group --
// there is no way we can determine what type to search for user-defined operators.
return(false);
}
// Spec 7.3.5 Candidate user-defined operators
// SPEC: Given a type T and an operation op(A) ... the set of candidate user-defined
// SPEC: operators provided by T for op(A) is determined as follows:
// SPEC: If T is a nullable type then T0 is its underlying type; otherwise T0 is T.
// SPEC: For all operator declarations in T0 and all lifted forms of such operators, if
// SPEC: at least one operator is applicable with respect to A then the set of candidate
// SPEC: operators consists of all such applicable operators. Otherwise, if T0 is object
// SPEC: then the set of candidate operators is empty. Otherwise, the set of candidate
// SPEC: operators is the set provided by the direct base class of T0, or the effective
// SPEC: base class of T0 if T0 is a type parameter.
// https://github.com/dotnet/roslyn/issues/34451: The spec quote should be adjusted to cover operators from interfaces as well.
// From https://github.com/dotnet/csharplang/blob/master/meetings/2017/LDM-2017-06-27.md:
// - We only even look for operator implementations in interfaces if one of the operands has a type that is an interface or
// a type parameter with a non-empty effective base interface list.
// - The applicable operators from classes / structs shadow those in interfaces.This matters for constrained type parameters:
// the effective base class can shadow operators from effective base interfaces.
// - If we find an applicable candidate in an interface, that candidate shadows all applicable operators in base interfaces:
// we stop looking.
TypeSymbol type0 = operand.Type.StrippedType();
// Searching for user-defined operators is expensive; let's take an early out if we can.
if (OperatorFacts.DefinitelyHasNoUserDefinedOperators(type0))
{
return(false);
}
string name = OperatorFacts.UnaryOperatorNameFromOperatorKind(kind);
var operators = ArrayBuilder <UnaryOperatorSignature> .GetInstance();
bool hadApplicableCandidates = false;
NamedTypeSymbol current = type0 as NamedTypeSymbol;
if ((object)current == null)
{
current = type0.BaseTypeWithDefinitionUseSiteDiagnostics(ref useSiteDiagnostics);
}
if ((object)current == null && type0.IsTypeParameter())
{
current = ((TypeParameterSymbol)type0).EffectiveBaseClass(ref useSiteDiagnostics);
}
for (; (object)current != null; current = current.BaseTypeWithDefinitionUseSiteDiagnostics(ref useSiteDiagnostics))
{
operators.Clear();
GetUserDefinedUnaryOperatorsFromType(current, kind, name, operators);
results.Clear();
if (CandidateOperators(operators, operand, results, ref useSiteDiagnostics))
{
hadApplicableCandidates = true;
break;
}
}
// Look in base interfaces, or effective interfaces for type parameters
if (!hadApplicableCandidates)
{
ImmutableArray <NamedTypeSymbol> interfaces = default;
if (type0.IsInterfaceType())
{
interfaces = type0.AllInterfacesWithDefinitionUseSiteDiagnostics(ref useSiteDiagnostics);
}
else if (type0.IsTypeParameter())
{
interfaces = ((TypeParameterSymbol)type0).AllEffectiveInterfacesWithDefinitionUseSiteDiagnostics(ref useSiteDiagnostics);
}
if (!interfaces.IsDefaultOrEmpty)
{
var shadowedInterfaces = PooledHashSet <NamedTypeSymbol> .GetInstance();
var resultsFromInterface = ArrayBuilder <UnaryOperatorAnalysisResult> .GetInstance();
results.Clear();
foreach (NamedTypeSymbol @interface in interfaces)
{
if ([email protected])
{
// this code could be reachable in error situations
continue;
}
if (shadowedInterfaces.Contains(@interface))
{
// this interface is "shadowed" by a derived interface
continue;
}
operators.Clear();
resultsFromInterface.Clear();
GetUserDefinedUnaryOperatorsFromType(@interface, kind, name, operators);
if (CandidateOperators(operators, operand, resultsFromInterface, ref useSiteDiagnostics))
{
hadApplicableCandidates = true;
results.AddRange(resultsFromInterface);
// this interface "shadows" all its base interfaces
shadowedInterfaces.AddAll(@interface.AllInterfacesWithDefinitionUseSiteDiagnostics(ref useSiteDiagnostics));
}
}
shadowedInterfaces.Free();
resultsFromInterface.Free();
}
}
operators.Free();
return(hadApplicableCandidates);
}
internal static bool IsIFormatProvider(this TypeSymbol source)
{
return(source.IsInterfaceType() && source.Name == "IFormatProvider");
}
private ConversionKind UnBoxXSharpType(ref BoundExpression rewrittenOperand, ConversionKind conversionKind, TypeSymbol rewrittenType)
{
var nts = rewrittenOperand?.Type as NamedTypeSymbol;
if (_compilation.Options.HasRuntime)
{
var usualType = _compilation.UsualType();
if (nts != null)
{
nts = nts.ConstructedFrom;
}
// Ticket C575: Assign Interface to USUAL
// Marked as Boxing in Conversions.cs
// Implementation here
if (nts != null && nts.IsInterface && rewrittenType == usualType)
{
var members = usualType.GetMembers("op_Implicit");
foreach (var m in members)
{
var pt = m.GetParameterTypes()[0] as TypeSymbol;
if (pt == _compilation.GetSpecialType(SpecialType.System_Object))
{
rewrittenOperand = _factory.StaticCall(rewrittenType, (MethodSymbol)m, rewrittenOperand);
rewrittenOperand.WasCompilerGenerated = true;
return(ConversionKind.Identity);
}
}
}
if (nts == usualType)
{
// USUAL -> WINBOOL, use LOGIC as intermediate type
if (rewrittenType == _compilation.WinBoolType())
{
MethodSymbol m = null;
m = getImplicitOperator(usualType, _compilation.GetSpecialType(SpecialType.System_Boolean));
rewrittenOperand = _factory.StaticCall(rewrittenType, m, rewrittenOperand);
rewrittenOperand.WasCompilerGenerated = true;
return(ConversionKind.Identity);
}
if (rewrittenType.IsPointerType())
{
// Pointer types are not really boxed
// we call the appropriate implicit operator here
MethodSymbol m = null;
m = getImplicitOperator(usualType, rewrittenType);
if (m == null)
{
m = getImplicitOperator(usualType, _compilation.GetSpecialType(SpecialType.System_IntPtr));
}
if (m != null)
{
rewrittenOperand = _factory.StaticCall(rewrittenType, m, rewrittenOperand);
rewrittenOperand.WasCompilerGenerated = true;
return(ConversionKind.PointerToPointer);
}
}
else if (rewrittenType.SpecialType == SpecialType.System_DateTime)
{
rewrittenOperand = _factory.StaticCall(usualType, ReservedNames.ToObject, rewrittenOperand);
return(ConversionKind.Unboxing);
}
else // System.Decimals, Objects and reference types, but not String
{
// check to see if we are casting to an interface that the usualtype supports
if (rewrittenType.IsInterfaceType())
{
foreach (var interf in usualType.AllInterfacesNoUseSiteDiagnostics)
{
if (interf == rewrittenType)
{
return(ConversionKind.ImplicitReference);
}
}
}
// special case for __CastClass
var xnode = rewrittenOperand.Syntax.Parent?.XNode as LanguageService.CodeAnalysis.XSharp.SyntaxParser.XSharpParserRuleContext;
if (xnode != null && xnode.IsCastClass())
{
conversionKind = ConversionKind.Boxing;
}
else
{
rewrittenOperand = _factory.StaticCall(usualType, ReservedNames.ToObject, rewrittenOperand);
if (rewrittenType.IsObjectType())
{
conversionKind = ConversionKind.Identity;
}
else if (rewrittenType.IsReferenceType)
{
rewrittenOperand = MakeConversionNode(rewrittenOperand, rewrittenType, @checked: true, acceptFailingConversion: false);
conversionKind = ConversionKind.ImplicitReference;
}
else
{
conversionKind = ConversionKind.Unboxing;
}
}
}
}
var floatType = _compilation.FloatType();
if (nts == floatType && rewrittenType is NamedTypeSymbol)
{
MethodSymbol m = getExplicitOperator(floatType, rewrittenType as NamedTypeSymbol);
if (m != null)
{
rewrittenOperand = _factory.StaticCall(rewrittenType, m, rewrittenOperand);
rewrittenOperand.WasCompilerGenerated = true;
return(ConversionKind.Identity);
}
m = getImplicitOperator(floatType, rewrittenType as NamedTypeSymbol);
if (m != null)
{
rewrittenOperand = _factory.StaticCall(rewrittenType, m, rewrittenOperand);
rewrittenOperand.WasCompilerGenerated = true;
return(ConversionKind.Identity);
}
if (rewrittenType == _compilation.GetSpecialType(SpecialType.System_Object) ||
rewrittenType == _compilation.UsualType())
{
return(ConversionKind.Boxing);
}
// what else, any other numeric type Convert to Double first and then to destination type
m = getImplicitOperator(floatType, _compilation.GetSpecialType(SpecialType.System_Double));
if (m != null) // this should never happen. This is an implicit converter
{
rewrittenOperand = _factory.StaticCall(rewrittenType, m, rewrittenOperand);
rewrittenOperand.WasCompilerGenerated = true;
rewrittenOperand = MakeConversionNode(rewrittenOperand.Syntax,
rewrittenOperand: rewrittenOperand,
rewrittenType: rewrittenType,
conversion: Conversion.ImplicitNumeric,
@checked: true,
explicitCastInCode: false
);
rewrittenOperand.WasCompilerGenerated = true;
return(ConversionKind.Identity);
}
}
}
return(conversionKind);
}
private void AddUserDefinedConversionsToExplicitCandidateSet(
BoundExpression sourceExpression,
TypeSymbol source,
TypeSymbol target,
ArrayBuilder<UserDefinedConversionAnalysis> u,
NamedTypeSymbol declaringType,
string operatorName,
ref HashSet<DiagnosticInfo> useSiteDiagnostics)
{
Debug.Assert(sourceExpression != null || (object)source != null);
Debug.Assert((object)target != null);
Debug.Assert(u != null);
Debug.Assert((object)declaringType != null);
Debug.Assert(operatorName != null);
// SPEC: Find the set of applicable user-defined and lifted conversion operators, U.
// SPEC: The set consists of the user-defined and lifted implicit or explicit
// SPEC: conversion operators declared by the classes and structs in D that convert
// SPEC: from a type encompassing E or encompassed by S (if it exists) to a type
// SPEC: encompassing or encompassed by T.
// DELIBERATE SPEC VIOLATION:
//
// The spec here essentially says that we add an applicable "regular" conversion and
// an applicable lifted conversion, if there is one, to the candidate set, and then
// let them duke it out to determine which one is "best".
//
// This is not at all what the native compiler does, and attempting to implement
// the specification, or slight variations on it, produces too many backwards-compatibility
// breaking changes.
//
// The native compiler deviates from the specification in two major ways here.
// First, it does not add *both* the regular and lifted forms to the candidate set.
// Second, the way it characterizes a "lifted" form is very, very different from
// how the specification characterizes a lifted form.
//
// An operation, in this case, X-->Y, is properly said to be "lifted" to X?-->Y? via
// the rule that X?-->Y? matches the behavior of X-->Y for non-null X, and converts
// null X to null Y otherwise.
//
// The native compiler, by contrast, takes the existing operator and "lifts" either
// the operator's parameter type or the operator's return type to nullable. For
// example, a conversion from X?-->Y would be "lifted" to X?-->Y? by making the
// conversion from X? to Y, and then from Y to Y?. No "lifting" semantics
// are imposed; we do not check to see if the X? is null. This operator is not
// actually "lifted" at all; rather, an implicit conversion is applied to the
// output. **The native compiler considers the result type Y? of that standard implicit
// conversion to be the result type of the "lifted" conversion**, rather than
// properly considering Y to be the result type of the conversion for the purposes
// of computing the best output type.
//
// Moreover: the native compiler actually *does* implement nullable lifting semantics
// in the case where the input type of the user-defined conversion is a non-nullable
// value type and the output type is a nullable value type **or pointer type, or
// reference type**. This is an enormous departure from the specification; the
// native compiler will take a user-defined conversion from X-->Y? or X-->C and "lift"
// it to a conversion from X?-->Y? or X?-->C that has nullable semantics.
//
// This is quite confusing. In this code we will classify the conversion as either
// "normal" or "lifted" on the basis of *whether or not special lifting semantics
// are to be applied*. That is, whether or not a later rewriting pass is going to
// need to insert a check to see if the source expression is null, and decide
// whether or not to call the underlying unlifted conversion or produce a null
// value without calling the unlifted conversion.
// DELIBERATE SPEC VIOLATION: See the comment regarding bug 17021 in
// UserDefinedImplicitConversions.cs.
if ((object)source != null && source.IsInterfaceType() || target.IsInterfaceType())
{
return;
}
foreach (MethodSymbol op in declaringType.GetOperators(operatorName))
{
// We might have a bad operator and be in an error recovery situation. Ignore it.
if (op.ReturnsVoid || op.ParameterCount != 1 || op.ReturnType.TypeKind == TypeKind.Error)
{
continue;
}
TypeSymbol convertsFrom = op.ParameterTypes[0];
TypeSymbol convertsTo = op.ReturnType;
Conversion fromConversion = EncompassingExplicitConversion(sourceExpression, source, convertsFrom, ref useSiteDiagnostics);
Conversion toConversion = EncompassingExplicitConversion(null, convertsTo, target, ref useSiteDiagnostics);
// We accept candidates for which the parameter type encompasses the *underlying* source type.
if (!fromConversion.Exists &&
(object)source != null &&
source.IsNullableType() &&
EncompassingExplicitConversion(null, source.GetNullableUnderlyingType(), convertsFrom, ref useSiteDiagnostics).Exists)
{
fromConversion = ClassifyConversion(source, convertsFrom, ref useSiteDiagnostics, builtinOnly: true);
}
// As in dev11 (and the revised spec), we also accept candidates for which the return type is encompassed by the *stripped* target type.
if (!toConversion.Exists &&
(object)target != null &&
target.IsNullableType() &&
EncompassingExplicitConversion(null, convertsTo, target.GetNullableUnderlyingType(), ref useSiteDiagnostics).Exists)
{
toConversion = ClassifyConversion(convertsTo, target, ref useSiteDiagnostics, builtinOnly: true);
}
// In the corresponding implicit conversion code we can get away with first
// checking to see if standard implicit conversions exist from the source type
// to the parameter type, and from the return type to the target type. If not,
// then we can check for a lifted operator.
//
// That's not going to cut it in the explicit conversion code. Suppose we have
// a conversion X-->Y and have source type X? and target type Y?. There *are*
// standard explicit conversions from X?-->X and Y?-->Y, but we do not want
// to bind this as an *unlifted* conversion from X? to Y?; we want such a thing
// to be a *lifted* conversion from X? to Y?, that checks for null on the source
// and decides to not call the underlying user-defined conversion if it is null.
//
// We therefore cannot do what we do in the implicit conversions, where we check
// to see if the unlifted conversion works, and if it does, then don't add the lifted
// conversion at all. Rather, we have to see if what we're building here is a
// lifted conversion or not.
//
// Under what circumstances is this conversion a lifted conversion? (In the
// "spec" sense of a lifted conversion; that is, that we check for null
// and skip the user-defined conversion if necessary).
//
// * The source type must be a nullable value type.
// * The parameter type must be a non-nullable value type.
// * The target type must be able to take on a null value.
if (fromConversion.Exists && toConversion.Exists)
{
if ((object)source != null && source.IsNullableType() && convertsFrom.IsNonNullableValueType() && target.CanBeAssignedNull())
{
TypeSymbol nullableFrom = MakeNullableType(convertsFrom);
TypeSymbol nullableTo = convertsTo.IsNonNullableValueType() ? MakeNullableType(convertsTo) : convertsTo;
Conversion liftedFromConversion = EncompassingExplicitConversion(sourceExpression, source, nullableFrom, ref useSiteDiagnostics);
Conversion liftedToConversion = EncompassingExplicitConversion(null, nullableTo, target, ref useSiteDiagnostics);
Debug.Assert(liftedFromConversion.Exists);
Debug.Assert(liftedToConversion.Exists);
u.Add(UserDefinedConversionAnalysis.Lifted(op, liftedFromConversion, liftedToConversion, nullableFrom, nullableTo));
}
else
{
// There is an additional spec violation in the native compiler. Suppose
// we have a conversion from X-->Y and are asked to do "Y? y = new X();" Clearly
// the intention is to convert from X-->Y via the implicit conversion, and then
// stick a standard implicit conversion from Y-->Y? on the back end. **In this
// situation, the native compiler treats the conversion as though it were
// actually X-->Y? in source for the purposes of determining the best target
// type of a set of operators.
//
// Similarly, if we have a conversion from X-->Y and are asked to do
// an explicit conversion from X? to Y then we treat the conversion as
// though it really were X?-->Y for the purposes of determining the best
// source type of a set of operators.
//
// We perpetuate these fictions here.
if (target.IsNullableType() && convertsTo.IsNonNullableValueType())
{
convertsTo = MakeNullableType(convertsTo);
toConversion = EncompassingExplicitConversion(null, convertsTo, target, ref useSiteDiagnostics);
}
if ((object)source != null && source.IsNullableType() && convertsFrom.IsNonNullableValueType())
{
convertsFrom = MakeNullableType(convertsFrom);
fromConversion = EncompassingExplicitConversion(null, convertsFrom, source, ref useSiteDiagnostics);
}
u.Add(UserDefinedConversionAnalysis.Normal(op, fromConversion, toConversion, convertsFrom, convertsTo));
}
}
}
}
