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Initial support for nullable analysis for Unions #81721

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8766804
Initial support for nullable analysis for Unions
AlekseyTs Dec 16, 2025
462727f
PR feedback
AlekseyTs Dec 18, 2025
904354d
Add tests
AlekseyTs Dec 18, 2025
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34 changes: 20 additions & 14 deletions src/Compilers/CSharp/Portable/Binder/Binder_Patterns.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -41,7 +41,7 @@ partial class Binder
PropertySymbol? valueProperty = null;
foreach (var m in iUnion.GetMembers(WellKnownMemberNames.ValuePropertyName))
{
if (m is PropertySymbol prop && HasIUnionValueSignature(prop))
if (m is PropertySymbol prop && hasIUnionValueSignature(prop))
{
valueProperty = prop;
break;
Expand All @@ -59,22 +59,28 @@ partial class Binder
}

return valueProperty;

static bool hasIUnionValueSignature(PropertySymbol property)
{
// PROTOTYPE: Cover individual conditions with tests
return property is
{
IsStatic: false,
DeclaredAccessibility: Accessibility.Public,
IsAbstract: true,
GetMethod: not null,
SetMethod: null,
RefKind: RefKind.None,
ParameterCount: 0,
TypeWithAnnotations: { Type.SpecialType: SpecialType.System_Object, CustomModifiers: [] }
};
}
}

public static bool HasIUnionValueSignature(PropertySymbol property)
internal static PropertySymbol? GetUnionTypeValuePropertyNoUseSiteDiagnostics(NamedTypeSymbol inputUnionType)
{
// PROTOTYPE: Cover individual conditions with tests
return property is
{
IsStatic: false,
DeclaredAccessibility: Accessibility.Public,
IsAbstract: true,
GetMethod: not null,
SetMethod: null,
RefKind: RefKind.None,
ParameterCount: 0,
TypeWithAnnotations: { Type.SpecialType: SpecialType.System_Object, CustomModifiers: [] }
};
var useSiteInfo = CompoundUseSiteInfo<AssemblySymbol>.Discarded;
return GetUnionTypeValueProperty(inputUnionType, ref useSiteInfo);
}

private BoundExpression BindIsPatternExpression(IsPatternExpressionSyntax node, BindingDiagnosticBag diagnostics)
Expand Down
5 changes: 3 additions & 2 deletions src/Compilers/CSharp/Portable/Binder/PatternExplainer.cs
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Expand Up @@ -687,8 +687,9 @@ string tryHandleRecursivePattern(ref bool unnamedEnumValue)
var subInput = new BoundDagTemp(e.Syntax, e.Property.Type, e);
var subPattern = SamplePatternForTemp(subInput, constraintMap, evaluationMap, false, ref unnamedEnumValue);

if (evaluations.Length == 1 && e.Property is { Name: WellKnownMemberNames.ValuePropertyName } &&
Binder.HasIUnionValueSignature(e.Property) && e.Input.Type is NamedTypeSymbol { IsUnionTypeNoUseSiteDiagnostics: true })
if (evaluations.Length == 1 && e.Property is { Name: WellKnownMemberNames.ValuePropertyName } property &&
e.Input.Type is NamedTypeSymbol { IsUnionTypeNoUseSiteDiagnostics: true } unionType &&
Binder.GetUnionTypeValuePropertyNoUseSiteDiagnostics(unionType) == (object)property)
{
return subPattern;
}
Expand Down
19 changes: 13 additions & 6 deletions src/Compilers/CSharp/Portable/Binder/Semantics/Conversions/ConversionsBase.cs
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Expand Up @@ -1908,8 +1908,9 @@ public bool HasAnyNullabilityImplicitConversion(TypeWithAnnotations source, Type
{
Debug.Assert(IncludeNullability);
var discardedUseSiteInfo = CompoundUseSiteInfo<AssemblySymbol>.Discarded;
return HasTopLevelNullabilityImplicitConversion(source, destination) &&
ClassifyImplicitConversionFromType(source.Type, destination.Type, ref discardedUseSiteInfo).Kind != ConversionKind.NoConversion;
Conversion conversion = ClassifyImplicitConversionFromType(source.Type, destination.Type, ref discardedUseSiteInfo);
return conversion.Kind != ConversionKind.NoConversion &&
(conversion.IsUnion || conversion.IsUserDefined || HasTopLevelNullabilityImplicitConversion(source, destination));
}

private static bool HasIdentityConversionToAny(NamedTypeSymbol type, ArrayBuilder<(NamedTypeSymbol ParticipatingType, TypeParameterSymbol ConstrainedToTypeOpt)> targetTypes)
Expand Down Expand Up @@ -2382,11 +2383,14 @@ private Conversion ClassifyImplicitTupleConversion(TypeSymbol source, TypeSymbol
ConversionKind.ImplicitTuple,
(ConversionsBase conversions, TypeWithAnnotations s, TypeWithAnnotations d, bool _, ref CompoundUseSiteInfo<AssemblySymbol> u, bool _) =>
{
if (!conversions.HasTopLevelNullabilityImplicitConversion(s, d))
Conversion conversion = conversions.ClassifyImplicitConversionFromType(s.Type, d.Type, ref u);

if (!conversion.IsUserDefined && !conversion.IsUnion && !conversions.HasTopLevelNullabilityImplicitConversion(s, d))
{
return Conversion.NoConversion;
}
return conversions.ClassifyImplicitConversionFromType(s.Type, d.Type, ref u);

return conversion;
},
isChecked: false,
forCast: false);
Expand All @@ -2401,11 +2405,14 @@ private Conversion ClassifyExplicitTupleConversion(TypeSymbol source, TypeSymbol
ConversionKind.ExplicitTuple,
(ConversionsBase conversions, TypeWithAnnotations s, TypeWithAnnotations d, bool isChecked, ref CompoundUseSiteInfo<AssemblySymbol> u, bool forCast) =>
{
if (!conversions.HasTopLevelNullabilityImplicitConversion(s, d))
Conversion conversion = conversions.ClassifyConversionFromType(s.Type, d.Type, isChecked: isChecked, ref u, forCast);

if (!conversion.IsUserDefined && !conversion.IsUnion && !conversions.HasTopLevelNullabilityImplicitConversion(s, d))
{
return Conversion.NoConversion;
}
return conversions.ClassifyConversionFromType(s.Type, d.Type, isChecked: isChecked, ref u, forCast);

return conversion;
},
isChecked: isChecked,
forCast);
Expand Down
8 changes: 2 additions & 6 deletions src/Compilers/CSharp/Portable/Binder/Semantics/OverloadResolution/MethodTypeInference.cs
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Expand Up @@ -3048,12 +3048,8 @@ private static bool ImplicitConversionExists(TypeWithAnnotations sourceWithAnnot
return false;
}

if (!conversions.HasTopLevelNullabilityImplicitConversion(sourceWithAnnotations, destinationWithAnnotations))
{
return false;
}

return conversions.ClassifyImplicitConversionFromTypeWhenNeitherOrBothFunctionTypes(source, destination, ref useSiteInfo).Exists;
Conversion conversion = conversions.ClassifyImplicitConversionFromTypeWhenNeitherOrBothFunctionTypes(source, destination, ref useSiteInfo);
return conversion.Exists && (conversion.IsUnion || conversion.IsUserDefined || conversions.HasTopLevelNullabilityImplicitConversion(sourceWithAnnotations, destinationWithAnnotations));
}
#nullable disable

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3 changes: 1 addition & 2 deletions src/Compilers/CSharp/Portable/Binder/UnionMatchingRewriter.cs
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Expand Up @@ -59,8 +59,7 @@ private static BoundPatternWithUnionMatching CreatePatternWithUnionMatching(Name
Debug.Assert(inputUnionType.IsUnionTypeNoUseSiteDiagnostics);
Debug.Assert(innerPattern.InputType.IsObjectType());

var discardedUseSiteInfo = CompoundUseSiteInfo<AssemblySymbol>.Discarded;
PropertySymbol? valueProperty = Binder.GetUnionTypeValueProperty(inputUnionType, ref discardedUseSiteInfo);
PropertySymbol? valueProperty = Binder.GetUnionTypeValuePropertyNoUseSiteDiagnostics(inputUnionType);

var member = new BoundPropertySubpatternMember(innerPattern.Syntax, receiver: null, valueProperty, type: innerPattern.InputType, hasErrors: valueProperty is null).MakeCompilerGenerated();

Expand Down
3 changes: 2 additions & 1 deletion src/Compilers/CSharp/Portable/FlowAnalysis/AbstractFlowPass.cs
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Expand Up @@ -961,7 +961,8 @@ BoundDeclarationPattern or BoundConstantPattern or BoundNegatedPattern or BoundB
VariableAccess: null,
IsUnionMatching: false,
} rewritten &&
(possibleUnionValueSymbol is null || (Binder.HasIUnionValueSignature((PropertySymbol)possibleUnionValueSymbol) && possibleUnionValueSymbol.ContainingType.IsWellKnownTypeIUnion())))
(possibleUnionValueSymbol is null ||
(possibleUnionValueSymbol.ContainingType.IsWellKnownTypeIUnion() && Binder.GetUnionTypeValuePropertyNoUseSiteDiagnostics(inputType) == (object)possibleUnionValueSymbol)))
{
Debug.Assert(!inputType.IsNullableType());
Debug.Assert(!negated);
Expand Down
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