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Null coalescing assignment for nullable value type should set state of nullable type not underlying type #67468

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merged 7 commits into from
Apr 17, 2023
Merged

Null coalescing assignment for nullable value type should set state of nullable type not underlying type #67468

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9db9155
Null coalescing assignment for nullable value type should set state o…
cston Mar 22, 2023
e6766e4
Add test
cston Mar 24, 2023
f227740
Fix tests
cston Mar 24, 2023
29cf664
Fix build
cston Mar 24, 2023
aa642aa
Update src/Compilers/CSharp/Portable/FlowAnalysis/NullableWalker.cs
cston Mar 24, 2023
2d689b6
Merge remote-tracking branch 'upstream/main' into 67040
cston Apr 7, 2023
5750193
Address feedback
cston Apr 15, 2023
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58 changes: 58 additions & 0 deletions src/Compilers/CSharp/Portable/FlowAnalysis/NullableWalker.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -2641,6 +2641,13 @@ protected override void JoinTryBlockState(ref LocalState self, ref LocalState ot
private void InheritDefaultState(TypeSymbol targetType, int targetSlot)
{
Debug.Assert(targetSlot > 0);
#if DEBUG
var actualType = _variables[targetSlot].Symbol.GetTypeOrReturnType().Type;
Debug.Assert(actualType is { });
Debug.Assert(actualType.ContainsErrorType() ||
targetType.ContainsErrorType() ||
isOfTypeOrBaseOrInterface(actualType, targetType));
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@RikkiGibson RikkiGibson Apr 7, 2023 •
edited by cston
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Should we use some "classify conversion" API instead? e.g. if it's identity or implicit reference conversion, maybe that's good enough? #Resolved

#endif

// Reset the state of any members of the target.
var members = ArrayBuilder<(VariableIdentifier, int)>.GetInstance();
Expand All @@ -2652,6 +2659,43 @@ private void InheritDefaultState(TypeSymbol targetType, int targetSlot)
InheritDefaultState(symbol.GetTypeOrReturnType().Type, slot);
}
members.Free();

#if DEBUG
static bool isOfTypeOrBaseOrInterface(TypeSymbol actualType, TypeSymbol expectedType)
{
if (isType(actualType, expectedType))
{
return true;
}
if (actualType is NamedTypeSymbol namedType)
{
if (namedType.IsInterface)
{
return namedType.AllInterfacesNoUseSiteDiagnostics.Contains(expectedType);
}
else
{
while (true)
{
var baseType = namedType.BaseTypeNoUseSiteDiagnostics;
if (baseType is null)
{
return false;
}
if (isType(baseType, expectedType))
{
return true;
}
namedType = baseType;
}
}
}
return false;
}

static bool isType(TypeSymbol a, TypeSymbol b)
=> a.Equals(b, TypeCompareKind.AllIgnoreOptions);
#endif
}

private NullableFlowState GetDefaultState(Symbol symbol)
Expand Down Expand Up @@ -5105,12 +5149,26 @@ private static BoundExpression SkipReferenceConversions(BoundExpression possibly
var leftState = this.State.Clone();
LearnFromNonNullTest(leftOperand, ref leftState);
LearnFromNullTest(leftOperand, ref this.State);

// If we are assigning the underlying value type to a nullable value type variable,
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@RikkiGibson RikkiGibson Apr 7, 2023 •
edited by cston
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I found this comment a little unclear. I think it should say that we do a special step to set the nullable variable's top level state within this block, then change the slot to later simulate an assignment from the RHS to the LHS's Value property, to update nullable states within the underlying value type. #Resolved

// set the state of the .Value property of the variable.
if (node.IsNullableValueTypeAssignment)
{
Debug.Assert(targetType.Type.ContainsErrorType() ||
node.Type?.ContainsErrorType() == true ||
TypeSymbol.Equals(targetType.Type.GetNullableUnderlyingType(), node.Type, TypeCompareKind.AllIgnoreOptions));
if (leftSlot > 0)
{
SetState(ref this.State, leftSlot, NullableFlowState.NotNull);
leftSlot = GetNullableOfTValueSlot(targetType.Type, leftSlot, out _);
}
targetType = TypeWithAnnotations.Create(node.Type, NullableAnnotation.NotAnnotated);
}

TypeWithState rightResult = VisitOptionalImplicitConversion(rightOperand, targetType, useLegacyWarnings: UseLegacyWarnings(leftOperand), trackMembers: false, AssignmentKind.Assignment);
Debug.Assert(TypeSymbol.Equals(targetType.Type, rightResult.Type, TypeCompareKind.AllIgnoreOptions));
TrackNullableStateForAssignment(rightOperand, targetType, leftSlot, rightResult, MakeSlot(rightOperand));

Join(ref this.State, ref leftState);
TypeWithState resultType = TypeWithState.Create(targetType.Type, rightResult.State);
SetResultType(node, resultType);
Expand Down
108 changes: 108 additions & 0 deletions src/Compilers/CSharp/Test/Semantic/Semantics/NullableReferenceTypesTests.cs
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Expand Up @@ -156945,5 +156945,113 @@ public void Repro66960_2()
Diagnostic(ErrorCode.WRN_UnreferencedVar, "e").WithArguments("e").WithLocation(5, 54)
);
}

[WorkItem(67040, "https://github.com/dotnet/roslyn/issues/67040")]
[Fact]
public void NullCoalescingAssignment_NullableValueTypeWithValue_01()
{
var source = """
#pragma warning disable 649
#nullable enable
readonly struct S<T>
{
public readonly T Item;
}
class Program
{
static void M(S<object> x, bool b)
{
S<object>? y;
y = x;
y ??= b ? default : default;
}
}
""";
var comp = CreateCompilation(source);
comp.VerifyDiagnostics();
}

[Fact]
public void NullCoalescingAssignment_NullableValueTypeWithValue_02()
{
var source = """
#pragma warning disable 649
#nullable enable
readonly struct S<T>
{
public readonly T Item;
}
class Program
{
static void M(S<object> x)
{
S<object>? y = x;
S<object>? z = null;
z ??= y;
z.Value.Item.ToString();
}
}
""";
var comp = CreateCompilation(source);
comp.VerifyDiagnostics();
}

[Fact]
public void NullCoalescingAssignment_NullableValueTypeWithValue_03()
{
var source = """
#nullable enable
struct S
{
public object? Item;
}
class Program
{
static void M()
{
S x = new S();
x.Item = 1;
S? y;
y = x;
y ??= new S();
y.Value.Item.ToString();
}
}
""";
var comp = CreateCompilation(source);
comp.VerifyDiagnostics(
// (15,9): warning CS8602: Dereference of a possibly null reference.
// y.Value.Item.ToString();
Diagnostic(ErrorCode.WRN_NullReferenceReceiver, "y.Value.Item").WithLocation(15, 9));
}

[Fact]
public void NullCoalescingAssignment_NullableValueTypeWithValue_04()
{
var source = """
#nullable enable
interface I
{
object? Item { get; set; }
}
class Program
{
static void M<T>() where T : struct, I
{
T x = new T();
x.Item = 1;
T? y;
y = x;
y ??= new T();
y.Value.Item.ToString();
}
}
""";
var comp = CreateCompilation(source);
comp.VerifyDiagnostics(
// (15,9): warning CS8602: Dereference of a possibly null reference.
// y.Value.Item.ToString();
Diagnostic(ErrorCode.WRN_NullReferenceReceiver, "y.Value.Item").WithLocation(15, 9));
}
}
}