/// <summary>
/// Determine whether there is any substitution of type parameters that will
/// make two types identical.
/// </summary>
/// <param name="t1">LHS</param>
/// <param name="t2">RHS</param>
/// <param name="substitution">
/// Substitutions performed so far (or null for none).
/// Keys are type parameters, values are types (possibly type parameters).
/// Will be updated with new substitutions by the callee.
/// Should be ignored when false is returned.
/// </param>
/// <returns>True if there exists a type map such that Map(LHS) == Map(RHS).</returns>
/// <remarks>
/// Derived from Dev10's BSYMMGR::UnifyTypes.
/// Two types will not unify if they have different custom modifiers.
/// </remarks>
private static bool CanUnifyHelper(
TypeWithAnnotations t1,
TypeWithAnnotations t2,
ref MutableTypeMap?substitution
)
{
if (!t1.HasType || !t2.HasType)
{
return(t1.IsSameAs(t2));
}
if (substitution != null)
{
t1 = t1.SubstituteType(substitution);
t2 = t2.SubstituteType(substitution);
}
if (
TypeSymbol.Equals(t1.Type, t2.Type, TypeCompareKind.CLRSignatureCompareOptions) &&
t1.CustomModifiers.SequenceEqual(t2.CustomModifiers)
)
{
return(true);
}
// We can avoid a lot of redundant checks if we ensure that we only have to check
// for type parameters on the LHS
if (!t1.Type.IsTypeParameter() && t2.Type.IsTypeParameter())
{
TypeWithAnnotations tmp = t1;
t1 = t2;
t2 = tmp;
}
// If t1 is not a type parameter, then neither is t2
Debug.Assert(t1.Type.IsTypeParameter() || !t2.Type.IsTypeParameter());
switch (t1.Type.Kind)
{
case SymbolKind.ArrayType:
{
if (
t2.TypeKind != t1.TypeKind ||
!t2.CustomModifiers.SequenceEqual(t1.CustomModifiers)
)
{
return(false);
}
ArrayTypeSymbol at1 = (ArrayTypeSymbol)t1.Type;
ArrayTypeSymbol at2 = (ArrayTypeSymbol)t2.Type;
if (!at1.HasSameShapeAs(at2))
{
return(false);
}
return(CanUnifyHelper(
at1.ElementTypeWithAnnotations,
at2.ElementTypeWithAnnotations,
ref substitution
));
}
case SymbolKind.PointerType:
{
if (
t2.TypeKind != t1.TypeKind ||
!t2.CustomModifiers.SequenceEqual(t1.CustomModifiers)
)
{
return(false);
}
PointerTypeSymbol pt1 = (PointerTypeSymbol)t1.Type;
PointerTypeSymbol pt2 = (PointerTypeSymbol)t2.Type;
return(CanUnifyHelper(
pt1.PointedAtTypeWithAnnotations,
pt2.PointedAtTypeWithAnnotations,
ref substitution
));
}
case SymbolKind.NamedType:
case SymbolKind.ErrorType:
{
if (
t2.TypeKind != t1.TypeKind ||
!t2.CustomModifiers.SequenceEqual(t1.CustomModifiers)
)
{
return(false);
}
NamedTypeSymbol nt1 = (NamedTypeSymbol)t1.Type;
NamedTypeSymbol nt2 = (NamedTypeSymbol)t2.Type;
if (!nt1.IsGenericType || !nt2.IsGenericType)
{
// Initial TypeSymbol.Equals(...) && CustomModifiers.SequenceEqual(...) failed above,
// and custom modifiers compared equal in this case block, so the types must be distinct.
Debug.Assert(!nt1.Equals(nt2, TypeCompareKind.CLRSignatureCompareOptions));
return(false);
}
int arity = nt1.Arity;
if (
nt2.Arity != arity ||
!TypeSymbol.Equals(
nt2.OriginalDefinition,
nt1.OriginalDefinition,
TypeCompareKind.ConsiderEverything
)
)
{
return(false);
}
var nt1Arguments = nt1.TypeArgumentsWithAnnotationsNoUseSiteDiagnostics;
var nt2Arguments = nt2.TypeArgumentsWithAnnotationsNoUseSiteDiagnostics;
for (int i = 0; i < arity; i++)
{
if (!CanUnifyHelper(nt1Arguments[i], nt2Arguments[i], ref substitution))
{
return(false);
}
}
// Note: Dev10 folds this into the loop since GetTypeArgsAll includes type args for containing types
// TODO: Calling CanUnifyHelper for the containing type is an overkill, we simply need to go through type arguments for all containers.
return((object)nt1.ContainingType == null ||
CanUnifyHelper(nt1.ContainingType, nt2.ContainingType, ref substitution));
}
case SymbolKind.TypeParameter:
{
// These substitutions are not allowed in C#
if (t2.Type.IsPointerOrFunctionPointer() || t2.IsVoidType())
{
return(false);
}
TypeParameterSymbol tp1 = (TypeParameterSymbol)t1.Type;
// Perform the "occurs check" - i.e. ensure that t2 doesn't contain t1 to avoid recursive types
// Note: t2 can't be the same type param - we would have caught that with ReferenceEquals above
if (Contains(t2.Type, tp1))
{
return(false);
}
if (t1.CustomModifiers.IsDefaultOrEmpty)
{
AddSubstitution(ref substitution, tp1, t2);
return(true);
}
if (t1.CustomModifiers.SequenceEqual(t2.CustomModifiers))
{
AddSubstitution(ref substitution, tp1, TypeWithAnnotations.Create(t2.Type));
return(true);
}
if (
t1.CustomModifiers.Length < t2.CustomModifiers.Length &&
t1.CustomModifiers.SequenceEqual(
t2.CustomModifiers.Take(t1.CustomModifiers.Length)
)
)
{
AddSubstitution(
ref substitution,
tp1,
TypeWithAnnotations.Create(
t2.Type,
customModifiers: ImmutableArray.Create(
t2.CustomModifiers,
t1.CustomModifiers.Length,
t2.CustomModifiers.Length - t1.CustomModifiers.Length
)
)
);
return(true);
}
if (t2.Type.IsTypeParameter())
{
var tp2 = (TypeParameterSymbol)t2.Type;
if (t2.CustomModifiers.IsDefaultOrEmpty)
{
AddSubstitution(ref substitution, tp2, t1);
return(true);
}
if (
t2.CustomModifiers.Length < t1.CustomModifiers.Length &&
t2.CustomModifiers.SequenceEqual(
t1.CustomModifiers.Take(t2.CustomModifiers.Length)
)
)
{
AddSubstitution(
ref substitution,
tp2,
TypeWithAnnotations.Create(
t1.Type,
customModifiers: ImmutableArray.Create(
t1.CustomModifiers,
t2.CustomModifiers.Length,
t1.CustomModifiers.Length - t2.CustomModifiers.Length
)
)
);
return(true);
}
}
return(false);
}
default:
{
return(false);
}
}
}