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Misc. Union changes #82448

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12 changes: 12 additions & 0 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 @@ -650,6 +650,7 @@ internal BoundPattern BindConstantPatternWithFallbackToTypePattern(
BindingDiagnosticBag diagnostics,
out bool hasUnionMatching)
{
NamedTypeSymbol? unionTypeOnEntry = unionType;
NamedTypeSymbol? unionTypeOverride = PrepareForUnionMatchingIfAppropriateAndReturnUnionType(node, ref inputType, diagnostics);
hasUnionMatching = false;

Expand All @@ -676,6 +677,17 @@ internal BoundPattern BindConstantPatternWithFallbackToTypePattern(
diagnostics.Add(ErrorCode.ERR_CannotMatchOnINumberBase, node.Location, inputType);
}

if (constantValueOpt == ConstantValue.Null && unionTypeOverride?.IsValueType == false)
{
Debug.Assert(hasUnionMatching);

// Special case of a null test for a class Union. Its meaning is equivalent to: (<union instance> is null or <union instance>.Value is null)
// Therefore, the type isn't narrowed by this pattern and the following pattern, if any, will do union matching from scratch.
unionType = unionTypeOnEntry;
return new BoundConstantPattern(
node, convertedExpression, constantValueOpt, isUnionMatching: true, inputType: unionTypeOverride, narrowedType: unionTypeOverride, hasErrors);
}

return new BoundConstantPattern(
node, convertedExpression, constantValueOpt ?? ConstantValue.Bad, isUnionMatching: hasUnionMatching, inputType: unionTypeOverride ?? inputType, convertedType, hasErrors || constantValueOpt is null);
}
Expand Down
18 changes: 18 additions & 0 deletions src/Compilers/CSharp/Portable/Binder/UnionMatchingRewriter.cs
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Expand Up @@ -76,6 +76,24 @@ private static BoundPatternWithUnionMatching CreatePatternWithUnionMatching(Name
node = (BoundConstantPattern)base.VisitConstantPattern(node)!;
if (node.IsUnionMatching)
{
Debug.Assert(node.InputType is NamedTypeSymbol { IsUnionType: true });

if (node.ConstantValue == ConstantValue.Null && !node.InputType.IsValueType && node.NarrowedType.Equals(node.InputType, TypeCompareKind.AllIgnoreOptions))
{
// Special case of a null test for a class Union. Its meaning is equivalent to: (<union instance> is null or <union instance>.Value is null)
BoundPatternWithUnionMatching underlyingValueMatching = CreatePatternWithUnionMatching(
(NamedTypeSymbol)node.InputType,
node.Update(node.Value, node.ConstantValue, isUnionMatching: false, inputType: ObjectType, narrowedType: ObjectType));

return new BoundBinaryPattern(
node.Syntax, disjunction: true,
left: node.Update(node.Value, node.ConstantValue, isUnionMatching: false, node.InputType, node.InputType),
right: RewritePatternWithUnionMatchingToPropertyPattern(underlyingValueMatching),
inputType: node.InputType,
narrowedType: node.InputType)
{ WasCompilerGenerated = true };
}

return CreatePatternWithUnionMatching(
(NamedTypeSymbol)node.InputType,
node.Update(node.Value, node.ConstantValue, isUnionMatching: false, inputType: ObjectType, narrowedType: node.NarrowedType));
Expand Down
3 changes: 2 additions & 1 deletion src/Compilers/CSharp/Portable/BoundTree/BoundConstantPattern.cs
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Expand Up @@ -14,7 +14,8 @@ private partial void Validate()
if (IsUnionMatching)
{
Debug.Assert(NarrowedType.IsObjectType() ||
NarrowedType.Equals(Value.Type, TypeCompareKind.AllIgnoreOptions));
NarrowedType.Equals(Value.Type, TypeCompareKind.AllIgnoreOptions) ||
(ConstantValue == ConstantValue.Null && !InputType.IsValueType && NarrowedType.Equals(InputType, TypeCompareKind.AllIgnoreOptions)));
}
else
{
Expand Down
90 changes: 70 additions & 20 deletions src/Compilers/CSharp/Portable/FlowAnalysis/NullableWalker.cs
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Expand Up @@ -7928,12 +7928,30 @@ private void ApplyMemberPostConditions(int receiverSlot, MethodSymbol method)
applyMemberPostConditions(receiverSlot, type, notNullMembers, ref State);
}

if (method.ReturnType.SpecialType == SpecialType.System_Boolean
&& !(notNullWhenTrueMembers.IsEmpty && notNullWhenFalseMembers.IsEmpty))
if (method.ReturnType.SpecialType == SpecialType.System_Boolean)
{
Split();
applyMemberPostConditions(receiverSlot, type, notNullWhenTrueMembers, ref StateWhenTrue);
applyMemberPostConditions(receiverSlot, type, notNullWhenFalseMembers, ref StateWhenFalse);
if (!(notNullWhenTrueMembers.IsEmpty && notNullWhenFalseMembers.IsEmpty))
{
Split();
applyMemberPostConditions(receiverSlot, type, notNullWhenTrueMembers, ref StateWhenTrue);
applyMemberPostConditions(receiverSlot, type, notNullWhenFalseMembers, ref StateWhenFalse);
}

if (method is MethodSymbol
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@RikkiGibson RikkiGibson Feb 18, 2026

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It might be reasonable to share the isTryGetValueSignature helper from GetUnionTypeTryGetValueMethod here.

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@AlekseyTs AlekseyTs Feb 18, 2026

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It might be reasonable to share the isTryGetValueSignature helper from GetUnionTypeTryGetValueMethod here.

If I remember correctly the logic doesn't match exactly.

{
Name: WellKnownMemberNames.TryGetValueMethodName,
ReturnType.SpecialType: SpecialType.System_Boolean,
DeclaredAccessibility: Accessibility.Public,
RefKind: RefKind.None,
Parameters: [{ RefKind: RefKind.Out, Type: var parameterType }]
} tryGetValue &&
tryGetValue.ContainingType is { IsUnionType: true } unionType &&
(object)tryGetValue.OriginalDefinition == Binder.GetUnionTypeTryGetValueMethod(unionType, parameterType)?.OriginalDefinition && // Looking for TryGetValue with exact type match at this call site
Binder.GetUnionTypeValuePropertyNoUseSiteDiagnostics(unionType) is { } unionValue)
{
Split();
markMemberAsNotNull(receiverSlot, ref StateWhenTrue, unionValue);
}
}

method = method.OverriddenMethod;
Expand Down Expand Up @@ -7972,18 +7990,25 @@ void markMembersAsNotNull(int receiverSlot, TypeSymbol type, string memberName,
{
case SymbolKind.Field:
case SymbolKind.Property:
if (GetOrCreateSlot(member, receiverSlot) is int memberSlot &&
memberSlot > 0)
{
SetState(ref state, memberSlot, NullableFlowState.NotNull);
}
state = markMemberAsNotNull(receiverSlot, ref state, member);
break;
case SymbolKind.Event:
case SymbolKind.Method:
break;
}
}
}

LocalState markMemberAsNotNull(int receiverSlot, ref LocalState state, Symbol member)
{
if (GetOrCreateSlot(member, receiverSlot) is int memberSlot &&
memberSlot > 0)
{
SetState(ref state, memberSlot, NullableFlowState.NotNull);
}

return state;
}
}

private ImmutableArray<VisitResult> VisitArgumentsEvaluate(
Expand Down Expand Up @@ -8286,7 +8311,7 @@ private void VisitArgumentOutboundAssignmentsAndPostConditions(

var parameterValue = new BoundParameter(argument.Syntax, parameter);
var lValueType = result.LValueType;
trackNullableStateForAssignment(parameterValue, lValueType, MakeSlot(argument), parameterWithState, argument.IsSuppressed, parameterAnnotations);
trackNullableStateForAssignment(parameterValue, lValueType, MakeSlot(argument), parameterWithState, argument.IsSuppressed, parameterAnnotations, refKind, parameter);

// check whether parameter would unsafely let a null out in the worse case
if (!argument.IsSuppressed)
Expand Down Expand Up @@ -8330,7 +8355,7 @@ private void VisitArgumentOutboundAssignmentsAndPostConditions(
CheckDisallowedNullAssignment(parameterWithState, leftAnnotations, argument.Syntax);

AdjustSetValue(argument, ref parameterWithState);
trackNullableStateForAssignment(parameterValue, lValueType, MakeSlot(argument), parameterWithState, argument.IsSuppressed, parameterAnnotations);
trackNullableStateForAssignment(parameterValue, lValueType, MakeSlot(argument), parameterWithState, argument.IsSuppressed, parameterAnnotations, refKind, parameter);

// report warnings if parameter would unsafely let a null out in the worst case
if (!argument.IsSuppressed)
Expand Down Expand Up @@ -8368,9 +8393,9 @@ FlowAnalysisAnnotations notNullBasedOnParameters(FlowAnalysisAnnotations paramet
return parameterAnnotations;
}

void trackNullableStateForAssignment(BoundExpression parameterValue, TypeWithAnnotations lValueType, int targetSlot, TypeWithState parameterWithState, bool isSuppressed, FlowAnalysisAnnotations parameterAnnotations)
void trackNullableStateForAssignment(BoundExpression parameterValue, TypeWithAnnotations lValueType, int targetSlot, TypeWithState parameterWithState, bool isSuppressed, FlowAnalysisAnnotations parameterAnnotations, RefKind refKind, ParameterSymbol parameter)
{
if (!IsConditionalState && !hasConditionalPostCondition(parameterAnnotations))
if (!IsConditionalState && !hasConditionalPostCondition(parameterAnnotations, refKind, parameter))
{
TrackNullableStateForAssignment(parameterValue, lValueType, targetSlot, parameterWithState.WithSuppression(isSuppressed));
}
Expand All @@ -8381,7 +8406,7 @@ void trackNullableStateForAssignment(BoundExpression parameterValue, TypeWithAnn

SetState(StateWhenTrue);
// Note: the suppression applies over the post-condition attributes
TrackNullableStateForAssignment(parameterValue, lValueType, targetSlot, applyPostConditionsWhenTrue(parameterWithState, parameterAnnotations).WithSuppression(isSuppressed));
TrackNullableStateForAssignment(parameterValue, lValueType, targetSlot, applyPostConditionsWhenTrue(parameterWithState, parameterAnnotations, refKind, parameter).WithSuppression(isSuppressed));
Debug.Assert(!IsConditionalState);
var newWhenTrue = State.Clone();

Expand All @@ -8393,10 +8418,35 @@ void trackNullableStateForAssignment(BoundExpression parameterValue, TypeWithAnn
}
}

static bool hasConditionalPostCondition(FlowAnalysisAnnotations annotations)
static bool hasConditionalPostCondition(FlowAnalysisAnnotations annotations, RefKind refKind, ParameterSymbol parameter)
{
if ((((annotations & FlowAnalysisAnnotations.MaybeNullWhenTrue) != 0) ^ ((annotations & FlowAnalysisAnnotations.MaybeNullWhenFalse) != 0)) ||
(((annotations & FlowAnalysisAnnotations.NotNullWhenTrue) != 0) ^ ((annotations & FlowAnalysisAnnotations.NotNullWhenFalse) != 0)))
{
return true;
}

return isUnionTryGetValueValue(refKind, parameter);
}

static bool isUnionTryGetValueValue(RefKind refKind, ParameterSymbol parameter)
{
return (((annotations & FlowAnalysisAnnotations.MaybeNullWhenTrue) != 0) ^ ((annotations & FlowAnalysisAnnotations.MaybeNullWhenFalse) != 0)) ||
(((annotations & FlowAnalysisAnnotations.NotNullWhenTrue) != 0) ^ ((annotations & FlowAnalysisAnnotations.NotNullWhenFalse) != 0));
if (refKind == RefKind.Out &&
parameter.ContainingSymbol is MethodSymbol
{
Name: WellKnownMemberNames.TryGetValueMethodName,
ReturnType.SpecialType: SpecialType.System_Boolean,
DeclaredAccessibility: Accessibility.Public,
RefKind: RefKind.None,
ParameterCount: 1
} tryGetValue &&
tryGetValue.ContainingType is { IsUnionType: true } unionType &&
(object)tryGetValue.OriginalDefinition == Binder.GetUnionTypeTryGetValueMethod(unionType, parameter.Type)?.OriginalDefinition) // Looking for TryGetValue with exact type match at this call site
{
return true;
}

return false;
}

static TypeWithState applyPostConditionsUnconditionally(TypeWithState typeWithState, FlowAnalysisAnnotations annotations)
Expand All @@ -8416,7 +8466,7 @@ static TypeWithState applyPostConditionsUnconditionally(TypeWithState typeWithSt
return typeWithState;
}

static TypeWithState applyPostConditionsWhenTrue(TypeWithState typeWithState, FlowAnalysisAnnotations annotations)
static TypeWithState applyPostConditionsWhenTrue(TypeWithState typeWithState, FlowAnalysisAnnotations annotations, RefKind refKind, ParameterSymbol parameter)
{
bool notNullWhenTrue = (annotations & FlowAnalysisAnnotations.NotNullWhenTrue) != 0;
bool maybeNullWhenTrue = (annotations & FlowAnalysisAnnotations.MaybeNullWhenTrue) != 0;
Expand All @@ -8427,7 +8477,7 @@ static TypeWithState applyPostConditionsWhenTrue(TypeWithState typeWithState, Fl
// [MaybeNull, NotNullWhen(true)] means [MaybeNullWhen(false)]
return TypeWithState.Create(typeWithState.Type, NullableFlowState.MaybeDefault);
}
else if (notNullWhenTrue)
else if (notNullWhenTrue || isUnionTryGetValueValue(refKind, parameter))
{
return TypeWithState.Create(typeWithState.Type, NullableFlowState.NotNull);
}
Expand Down
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