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// 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.
#nullable disable
using System.Collections.Immutable;
using System.Diagnostics;
using System.Linq;
using Microsoft.CodeAnalysis.CSharp.Symbols;
using Microsoft.CodeAnalysis.CSharp.Syntax;
using Microsoft.CodeAnalysis.PooledObjects;
using Microsoft.CodeAnalysis.Text;
using System.Collections.Generic;
namespace Microsoft.CodeAnalysis.CSharp
{
internal partial class ConversionsBase
{
private UserDefinedConversionResult AnalyzeExplicitUserDefinedConversions(
BoundExpression sourceExpression,
TypeSymbol source,
TypeSymbol target,
bool isChecked,
ref CompoundUseSiteInfo<AssemblySymbol> useSiteInfo)
{
Debug.Assert(sourceExpression is null || Compilation is not null);
Debug.Assert(sourceExpression != null || (object)source != null);
Debug.Assert((object)target != null);
// SPEC: A user-defined explicit conversion from type S to type T is processed
// SPEC: as follows:
// SPEC: Find the set of types D from which user-defined conversion operators
// SPEC: will be considered...
var d = ArrayBuilder<(NamedTypeSymbol ParticipatingType, TypeParameterSymbol ConstrainedToTypeOpt)>.GetInstance();
ComputeUserDefinedExplicitConversionTypeSet(source, target, d, ref useSiteInfo);
// SPEC: Find the set of applicable user-defined and lifted conversion operators, U...
var ubuild = ArrayBuilder<UserDefinedConversionAnalysis>.GetInstance();
ComputeApplicableUserDefinedExplicitConversionSet(sourceExpression, source, target, isChecked: isChecked, d, ubuild, ref useSiteInfo);
d.Free();
ImmutableArray<UserDefinedConversionAnalysis> u = ubuild.ToImmutableAndFree();
// SPEC: If U is empty, the conversion is undefined and a compile-time error occurs.
if (u.Length == 0)
{
return UserDefinedConversionResult.NoApplicableOperators(u);
}
// SPEC: Find the most specific source type SX of the operators in U...
TypeSymbol sx = MostSpecificSourceTypeForExplicitUserDefinedConversion(u, sourceExpression, source, ref useSiteInfo);
if ((object)sx == null)
{
return UserDefinedConversionResult.NoBestSourceType(u);
}
// SPEC: Find the most specific target type TX of the operators in U...
TypeSymbol tx = MostSpecificTargetTypeForExplicitUserDefinedConversion(u, target, ref useSiteInfo);
if ((object)tx == null)
{
return UserDefinedConversionResult.NoBestTargetType(u);
}
int? best = MostSpecificConversionOperator(sx, tx, u);
if (best == null)
{
return UserDefinedConversionResult.Ambiguous(u);
}
return UserDefinedConversionResult.Valid(u, best.Value);
}
private static void ComputeUserDefinedExplicitConversionTypeSet(TypeSymbol source, TypeSymbol target, ArrayBuilder<(NamedTypeSymbol ParticipatingType, TypeParameterSymbol ConstrainedToTypeOpt)> d, ref CompoundUseSiteInfo<AssemblySymbol> useSiteInfo)
{
// Spec 6.4.5: User-defined explicit conversions
// Find the set of types, D, from which user-defined conversion operators will be considered.
// This set consists of S0 (if S0 is a class or struct), the base classes of S0 (if S0 is a class),
// T0 (if T0 is a class or struct), and the base classes of T0 (if T0 is a class).
AddTypesParticipatingInUserDefinedConversion(d, source, includeBaseTypes: true, useSiteInfo: ref useSiteInfo);
AddTypesParticipatingInUserDefinedConversion(d, target, includeBaseTypes: true, useSiteInfo: ref useSiteInfo);
}
private void ComputeApplicableUserDefinedExplicitConversionSet(
BoundExpression sourceExpression,
TypeSymbol source,
TypeSymbol target,
bool isChecked,
ArrayBuilder<(NamedTypeSymbol ParticipatingType, TypeParameterSymbol ConstrainedToTypeOpt)> d,
ArrayBuilder<UserDefinedConversionAnalysis> u,
ref CompoundUseSiteInfo<AssemblySymbol> useSiteInfo)
{
Debug.Assert(sourceExpression is null || Compilation is not null);
Debug.Assert(sourceExpression != null || (object)source != null);
Debug.Assert((object)target != null);
Debug.Assert(d != null);
Debug.Assert(u != null);
bool haveInterfaces = false;
foreach ((NamedTypeSymbol declaringType, TypeParameterSymbol constrainedToTypeOpt) in d)
{
if (declaringType.IsInterface)
{
Debug.Assert(constrainedToTypeOpt is not null);
haveInterfaces = true;
}
else
{
addCandidatesFromType(constrainedToTypeOpt: null, declaringType, sourceExpression, source, target, isChecked: isChecked, u, ref useSiteInfo);
}
}
if (u.Count == 0 && haveInterfaces)
{
foreach ((NamedTypeSymbol declaringType, TypeParameterSymbol constrainedToTypeOpt) in d)
{
if (declaringType.IsInterface)
{
addCandidatesFromType(constrainedToTypeOpt: constrainedToTypeOpt, declaringType, sourceExpression, source, target, isChecked: isChecked, u, ref useSiteInfo);
}
}
}
void addCandidatesFromType(
TypeParameterSymbol constrainedToTypeOpt,
NamedTypeSymbol declaringType,
BoundExpression sourceExpression,
TypeSymbol source,
TypeSymbol target,
bool isChecked,
ArrayBuilder<UserDefinedConversionAnalysis> u,
ref CompoundUseSiteInfo<AssemblySymbol> useSiteInfo)
{
AddUserDefinedConversionsToExplicitCandidateSet(sourceExpression, source, target, u, constrainedToTypeOpt, declaringType, isExplicit: true, isChecked: isChecked, ref useSiteInfo);
AddUserDefinedConversionsToExplicitCandidateSet(sourceExpression, source, target, u, constrainedToTypeOpt, declaringType, isExplicit: false, isChecked: isChecked, ref useSiteInfo);
}
}
private void AddUserDefinedConversionsToExplicitCandidateSet(
BoundExpression sourceExpression,
TypeSymbol source,
TypeSymbol target,
ArrayBuilder<UserDefinedConversionAnalysis> u,
TypeParameterSymbol constrainedToTypeOpt,
NamedTypeSymbol declaringType,
bool isExplicit,
bool isChecked,
ref CompoundUseSiteInfo<AssemblySymbol> useSiteInfo)
{
Debug.Assert(sourceExpression is null || Compilation is not null);
Debug.Assert(sourceExpression != null || (object)source != null);
Debug.Assert((object)target != null);
Debug.Assert(u != null);
Debug.Assert((object)declaringType != 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;
}
ImmutableArray<MethodSymbol> operators = declaringType.GetOperators(
isExplicit ? (isChecked ? WellKnownMemberNames.CheckedExplicitConversionName : WellKnownMemberNames.ExplicitConversionName) : WellKnownMemberNames.ImplicitConversionName);
var candidates = ArrayBuilder<MethodSymbol>.GetInstance(operators.Length);
candidates.AddRange(operators);
if (isExplicit && isChecked)
{
ImmutableArray<MethodSymbol> operators2 = declaringType.GetOperators(WellKnownMemberNames.ExplicitConversionName);
// Add regular operators as well.
if (operators.IsEmpty)
{
candidates.AddRange(operators2);
}
else
{
foreach (MethodSymbol op2 in operators2)
{
// Drop operators that have a match among the checked ones.
bool add = true;
foreach (MethodSymbol op in operators)
{
if (SourceMemberContainerTypeSymbol.DoOperatorsPair(op, op2))
{
add = false;
break;
}
}
if (add)
{
candidates.Add(op2);
}
}
}
}
foreach (MethodSymbol op in candidates)
{
// 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 useSiteInfo);
Conversion toConversion = EncompassingExplicitConversion(convertsTo, target, ref useSiteInfo);
// We accept candidates for which the parameter type encompasses the *underlying* source type.
if (!fromConversion.Exists &&
(object)source != null &&
source.IsNullableType() &&
EncompassingExplicitConversion(source.GetNullableUnderlyingType(), convertsFrom, ref useSiteInfo).Exists)
{
fromConversion = ClassifyBuiltInConversion(source, convertsFrom, isChecked: isChecked, ref useSiteInfo);
}
// 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(convertsTo, target.GetNullableUnderlyingType(), ref useSiteInfo).Exists)
{
toConversion = ClassifyBuiltInConversion(convertsTo, target, isChecked: isChecked, ref useSiteInfo);
}
// 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.IsValidNullableTypeArgument() && target.CanBeAssignedNull())
{
TypeSymbol nullableFrom = MakeNullableType(convertsFrom);
TypeSymbol nullableTo = convertsTo.IsValidNullableTypeArgument() ? MakeNullableType(convertsTo) : convertsTo;
Conversion liftedFromConversion = EncompassingExplicitConversion(sourceExpression, source, nullableFrom, ref useSiteInfo);
Conversion liftedToConversion = EncompassingExplicitConversion(nullableTo, target, ref useSiteInfo);
Debug.Assert(liftedFromConversion.Exists);
Debug.Assert(liftedToConversion.Exists);
u.Add(UserDefinedConversionAnalysis.Lifted(constrainedToTypeOpt, 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, except when X or Y is not a valid
// type argument to `Nullable<T>`.
if (target.IsNullableType() && convertsTo.IsValidNullableTypeArgument())
{
convertsTo = MakeNullableType(convertsTo);
toConversion = EncompassingExplicitConversion(convertsTo, target, ref useSiteInfo);
}
if ((object)source != null && source.IsNullableType() && convertsFrom.IsValidNullableTypeArgument())
{
convertsFrom = MakeNullableType(convertsFrom);
fromConversion = EncompassingExplicitConversion(convertsFrom, source, ref useSiteInfo);
}
u.Add(UserDefinedConversionAnalysis.Normal(constrainedToTypeOpt, op, fromConversion, toConversion, convertsFrom, convertsTo));
}
}
}
candidates.Free();
}
private TypeSymbol MostSpecificSourceTypeForExplicitUserDefinedConversion(
ImmutableArray<UserDefinedConversionAnalysis> u,
BoundExpression sourceExpression,
TypeSymbol source,
ref CompoundUseSiteInfo<AssemblySymbol> useSiteInfo)
{
// SPEC: If any of the operators in U convert from S then SX is S.
// SPEC: Otherwise, if any of the operators in U convert from types
// SPEC: that encompass E, then SX is the most encompassed type
// SPEC: in the combined set of the source types of these operators.
// SPEC: If no most encompassed type can be found then the
// SPEC: conversion is ambiguous and a compile-time error occurs.
// SPEC: Otherwise, SX is the most encompassing type in the combined
// SPEC: set of the source types of these operators. If exactly one
// SPEC: most encompassing type cannot be found then the conversion
// SPEC: is ambiguous and a compile-time error occurs.
// DELIBERATE SPEC VIOLATION:
// The native compiler deviates from the specification in the way it
// determines what the "converts from" type is. The specification is pretty
// clear that the "converts from" type is the actual parameter type of the
// conversion operator, or, in the case of a lifted operator, the lifted-to-
// nullable type. That is, if we have X-->Y then the converts-to type of
// the operator in its normal form is Y, and the converts-to type of the
// operator in its lifted form is Y?.
//
// The native compiler does not do this. Suppose we have a user-defined
// conversion X-->Y, and the cast (Y)(some_nullable_x). The native
// compiler will consider the converts-from type of X-->Y to be X?, surprisingly
// enough.
//
// We have already written the "FromType" into the conversion analysis to
// perpetuate this fiction.
if ((object)source != null)
{
if (u.Any(static (conv, source) => TypeSymbol.Equals(conv.FromType, source, TypeCompareKind.ConsiderEverything2), source))
{
return source;
}
CompoundUseSiteInfo<AssemblySymbol> inLambdaUseSiteInfo = useSiteInfo;
System.Func<UserDefinedConversionAnalysis, bool> isValid = conv => IsEncompassedBy(sourceExpression, source, conv.FromType, ref inLambdaUseSiteInfo);
if (u.Any(isValid))
{
var result = MostEncompassedType(u, isValid, conv => conv.FromType, ref inLambdaUseSiteInfo);
useSiteInfo = inLambdaUseSiteInfo;
return result;
}
useSiteInfo = inLambdaUseSiteInfo;
}
return MostEncompassingType(u, conv => conv.FromType, ref useSiteInfo);
}
private TypeSymbol MostSpecificTargetTypeForExplicitUserDefinedConversion(
ImmutableArray<UserDefinedConversionAnalysis> u,
TypeSymbol target,
ref CompoundUseSiteInfo<AssemblySymbol> useSiteInfo)
{
// SPEC: If any of the operators in U convert to T then TX is T.
// SPEC: Otherwise, if any of the operators in U convert to types that are
// SPEC: encompassed by T then TX is the most encompassing type in the combined
// SPEC: set of target types of those operators. If exactly one most encompassing
// SPEC: type cannot be found then the conversion is ambiguous and a compile-time
// SPEC: error occurs.
// SPEC: Otherwise, Tx is the most encompassed type in the combined set of target
// SPEC: types of the operators in U. If no most encompassed type can be found,
// SPEC: then the conversion is ambiguous and a compile-time error occurs.
// DELIBERATE SPEC VIOLATION:
// The native compiler deviates from the specification in the way it
// determines what the "converts to" type is. The specification is pretty
// clear that the "converts to" type is the actual return type of the
// conversion operator, or, in the case of a lifted operator, the lifted-to-
// nullable type. That is, if we have X-->Y then the converts-to type of
// the operator in its normal form is Y, and the converts-to type of the
// operator in its lifted form is Y?.
//
// The native compiler does not do this. Suppose we have a user-defined
// conversion X-->Y, and the assignment Y? y = new X(); -- the native
// compiler will consider the converts-to type of X-->Y to be Y?, surprisingly
// enough.
//
// We have already written the "ToType" into the conversion analysis to
// perpetuate this fiction.
if (u.Any(static (conv, target) => TypeSymbol.Equals(conv.ToType, target, TypeCompareKind.ConsiderEverything2), target))
{
return target;
}
CompoundUseSiteInfo<AssemblySymbol> inLambdaUseSiteInfo = useSiteInfo;
System.Func<UserDefinedConversionAnalysis, bool> isValid = conv => IsEncompassedBy(conv.ToType, target, ref inLambdaUseSiteInfo);
if (u.Any(isValid))
{
var result = MostEncompassingType(u, isValid, conv => conv.ToType, ref inLambdaUseSiteInfo);
useSiteInfo = inLambdaUseSiteInfo;
return result;
}
useSiteInfo = inLambdaUseSiteInfo;
return MostEncompassedType(u, conv => conv.ToType, ref useSiteInfo);
}
private Conversion EncompassingExplicitConversion(BoundExpression expr, TypeSymbol a, TypeSymbol b, ref CompoundUseSiteInfo<AssemblySymbol> useSiteInfo)
{
Debug.Assert(expr is null || Compilation is not null);
Debug.Assert(expr != null || (object)a != null);
Debug.Assert((object)b != null);
// SPEC: If a standard implicit conversion exists from a type A to a type B
// SPEC: and if neither A nor B is an interface type then A is said to be
// SPEC: encompassed by B, and B is said to encompass A.
// DELIBERATE SPEC VIOLATION: We should be checking to see if A and B are
// interface types here. See the comment regarding bug 17021 in
// UserDefinedImplicitConversions.cs
// DELIBERATE SPEC VIOLATION:
// We do not support an encompassing implicit conversion from a zero constant
// to an enum type, because the native compiler did not. It would be a breaking
// change.
var result = ClassifyStandardConversion(expr, a, b, ref useSiteInfo);
return result.IsEnumeration ? Conversion.NoConversion : result;
}
private Conversion EncompassingExplicitConversion(TypeSymbol a, TypeSymbol b, ref CompoundUseSiteInfo<AssemblySymbol> useSiteInfo)
{
return EncompassingExplicitConversion(expr: null, a, b, ref useSiteInfo);
}
}
}
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