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Cannot assign maybe-null value to TNotNull variable #41445

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Jul 30, 2020
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Cannot assign maybe-null value to TNotNull variable #41445

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Cannot assign maybe-null value to TNotNull variable
jcouv Feb 5, 2020
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Address feedback
jcouv Jul 24, 2020
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Address feedback from Chuck
jcouv Jul 30, 2020
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2 changes: 1 addition & 1 deletion src/Compilers/CSharp/Portable/FlowAnalysis/NullableWalker.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -1425,7 +1425,7 @@ private static bool ShouldReportNullableAssignment(TypeWithAnnotations type, Nul
return false;
case NullableFlowState.MaybeNull:
// https://github.com/dotnet/roslyn/issues/46044: Skip the following check if /langversion > 8?
if (type.Type.IsTypeParameterDisallowingAnnotationInCSharp8())
if (type.Type.IsTypeParameterDisallowingAnnotationInCSharp8() && !(type.Type is TypeParameterSymbol { IsNotNullable: true }))
{
return false;
}
Expand Down
1 change: 1 addition & 0 deletions src/Compilers/CSharp/Portable/Symbols/TypeSymbolExtensions.cs
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Expand Up @@ -52,6 +52,7 @@ public static bool CanBeConst(this TypeSymbol typeSymbol)
/// T where T : class? => true
/// T where T : IComparable => true
/// T where T : IComparable? => true
/// T where T : notnull => true
/// </summary>
/// <remarks>
/// In C#9, annotations are allowed regardless of constraints.
Expand Down
123 changes: 91 additions & 32 deletions src/Compilers/CSharp/Test/Semantic/Semantics/NullableReferenceTypesTests.cs
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Expand Up @@ -34738,96 +34738,97 @@ class C<T>
comp.VerifyDiagnostics();
}

[Theory]
[InlineData("T")]
[InlineData("TNotNull")]
[Fact]
[WorkItem(39922, "https://github.com/dotnet/roslyn/issues/39922")]
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@cston cston Jul 24, 2020 •
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The test no longer needs parameters. #Closed

public void EnforcedInMethodBody_MaybeNullWhen(string type)
public void EnforcedInMethodBody_MaybeNullWhen()
{
var source = @"
#nullable enable
using System.Diagnostics.CodeAnalysis;

class C<T, TNotNull>
where TNotNull : notnull
class C<T>
{
static void GetValue(TYPE x, [MaybeNull] out TYPE y)
static void GetValue(T x, [MaybeNull] out T y)
{
y = x;
}

static bool TryGetValue(TYPE x, [MaybeNullWhen(true)] out TYPE y)
static bool TryGetValue(T x, [MaybeNullWhen(true)] out T y)
{
y = x;
return y == null;
}

static bool TryGetValue2(TYPE x, [MaybeNullWhen(true)] out TYPE y)
static bool TryGetValue2(T x, [MaybeNullWhen(true)] out T y)
{
y = x;
return y != null;
}

static bool TryGetValue3(TYPE x, [MaybeNullWhen(false)] out TYPE y)
static bool TryGetValue3(T x, [MaybeNullWhen(false)] out T y)
{
y = x;
return y == null;
}

static bool TryGetValue4(TYPE x, [MaybeNullWhen(false)] out TYPE y)
static bool TryGetValue4(T x, [MaybeNullWhen(false)] out T y)
{
y = x;
return y != null;
}
}
";
var comp = CreateNullableCompilation(new[] { MaybeNullAttributeDefinition, MaybeNullWhenAttributeDefinition, source.Replace("TYPE", type) });
var comp = CreateNullableCompilation(new[] { MaybeNullAttributeDefinition, MaybeNullWhenAttributeDefinition, source });
comp.VerifyDiagnostics();
}

[Fact, WorkItem(39922, "https://github.com/dotnet/roslyn/issues/39922")]
public void EnforcedInMethodBody_MaybeNullWhen_ReferenceType()
[Theory]
[InlineData("TClass")]
[InlineData("TNotNull")]
[WorkItem(39922, "https://github.com/dotnet/roslyn/issues/39922")]
public void EnforcedInMethodBody_MaybeNullWhen_NotNullableTypes(string type)
{
var source = @"
#nullable enable
using System.Diagnostics.CodeAnalysis;

class C<TClass>
class C<TClass, TNotNull>
where TClass : class
where TNotNull : notnull
{
static bool TryGetValue(TClass x, [MaybeNullWhen(true)] out TClass y)
static bool TryGetValue(TYPE x, [MaybeNullWhen(true)] out TYPE y)
{
y = x;
return y == null;
}

static bool TryGetValue2(TClass x, [MaybeNullWhen(true)] out TClass y)
static bool TryGetValue2(TYPE x, [MaybeNullWhen(true)] out TYPE y)
{
y = x;
return y != null; // 1
}

static bool TryGetValue3(TClass x, [MaybeNullWhen(false)] out TClass y)
static bool TryGetValue3(TYPE x, [MaybeNullWhen(false)] out TYPE y)
{
y = x;
return y == null; // 2
}

static bool TryGetValue4(TClass x, [MaybeNullWhen(false)] out TClass y)
static bool TryGetValue4(TYPE x, [MaybeNullWhen(false)] out TYPE y)
{
y = x;
return y != null;
}
}
";
var comp = CreateNullableCompilation(new[] { MaybeNullWhenAttributeDefinition, source });
var comp = CreateNullableCompilation(new[] { MaybeNullWhenAttributeDefinition, source.Replace("TYPE", type) });
comp.VerifyDiagnostics(
// (17,9): error CS8762: Parameter 'y' must have a non-null value when exiting with 'false'.
// (18,9): warning CS8762: Parameter 'y' must have a non-null value when exiting with 'false'.
// return y != null; // 1
Diagnostic(ErrorCode.WRN_ParameterConditionallyDisallowsNull, "return y != null;").WithArguments("y", "false").WithLocation(17, 9),
// (23,9): error CS8762: Parameter 'y' must have a non-null value when exiting with 'true'.
Diagnostic(ErrorCode.WRN_ParameterConditionallyDisallowsNull, "return y != null;").WithArguments("y", "false").WithLocation(18, 9),
// (24,9): warning CS8762: Parameter 'y' must have a non-null value when exiting with 'true'.
// return y == null; // 2
Diagnostic(ErrorCode.WRN_ParameterConditionallyDisallowsNull, "return y == null;").WithArguments("y", "true").WithLocation(23, 9)
Diagnostic(ErrorCode.WRN_ParameterConditionallyDisallowsNull, "return y == null;").WithArguments("y", "true").WithLocation(24, 9)
);
}

Expand Down Expand Up @@ -35734,11 +35735,8 @@ public class Derived : Base
}
";
var comp = CreateNullableCompilation(new[] { MaybeNullWhenAttributeDefinition, source });
// Note: we're missing warnings on F1 because the overridden method with substituted T from Derived has an oblivious T
// Note: we're missing warnings on F1 and F6 because the overridden method with substituted T from Derived has an oblivious T
// https://github.com/dotnet/roslyn/issues/41368

// Note: assignment of `[MaybeNull] TNotNull` to `TNotNull` is currently not detected
// This is a known issue: https://github.com/dotnet/roslyn/issues/41437
comp.VerifyDiagnostics(
// (14,26): warning CS8765: Type of parameter 't2' doesn't match overridden member because of nullability attributes.
// public override bool F2<T>([MaybeNullWhen(false)]T t1, [MaybeNullWhen(false)] out T t2, [MaybeNullWhen(false)] ref T t3, [MaybeNullWhen(false)] in T t4) where T : class => throw null!; // t2, t3
Expand All @@ -35749,6 +35747,29 @@ public class Derived : Base
);
}

[Fact, WorkItem(41437, "https://github.com/dotnet/roslyn/issues/41437")]
public void AssigningMaybeNullTNotNullToTNotNullInOverride()
{
var source =
@"using System.Diagnostics.CodeAnalysis;
public class Base
{
public virtual bool F6<T>([AllowNull] in T t4) where T : notnull => throw null!;
}
public class Derived : Base
{
public override bool F6<T>(in T t4) => throw null!;
}
";
var comp = CreateNullableCompilation(new[] { AllowNullAttributeDefinition, source });

comp.VerifyDiagnostics(
// (8,26): warning CS8765: Nullability of type of parameter 't4' doesn't match overridden member (possibly because of nullability attributes).
// public override bool F6<T>(in T t4) => throw null!;
Diagnostic(ErrorCode.WRN_TopLevelNullabilityMismatchInParameterTypeOnOverride, "F6").WithArguments("t4").WithLocation(8, 26)
);
}

[Fact, WorkItem(41437, "https://github.com/dotnet/roslyn/issues/41437")]
public void MaybeNullWhenTrue_Parameter_Generic_OnOverrides_WithMaybeNull()
{
Expand All @@ -35773,11 +35794,8 @@ public class Derived : Base
public override bool F6<T>([MaybeNull]T t1, [MaybeNull] out T t2, [MaybeNull] ref T t3, [MaybeNull] in T t4) => throw null!;
}
";
// Note: we're missing warnings on F1 because the overridden method with substituted T from Derived has an oblivious T
// Note: we're missing warnings on F1 and F6 because the overridden method with substituted T from Derived has an oblivious T
// https://github.com/dotnet/roslyn/issues/41368

// Note: assignment of `[MaybeNull] TNotNull` to `TNotNull` is currently not detected
// This is a known issue: https://github.com/dotnet/roslyn/issues/41437
var comp = CreateNullableCompilation(new[] { MaybeNullWhenAttributeDefinition, MaybeNullAttributeDefinition, source });
comp.VerifyDiagnostics(
// (14,26): warning CS8765: Type of parameter 't2' doesn't match overridden member because of nullability attributes.
Expand Down Expand Up @@ -132859,6 +132877,47 @@ public static void Main()
CompileAndVerify(executeComp, expectedOutput: "ran");
}

[Fact, WorkItem(41437, "https://github.com/dotnet/roslyn/issues/41437")]
public void CannotAssignMaybeNullToTNotNull()
{
var source = @"
class C
{
TNotNull M<TNotNull>(TNotNull t) where TNotNull : notnull
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Sorry, I should have asked earlier, but do corresponding tests already exist for 'class' constraint? (I would be surprised if they didn't..)

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Yes, it's covered by NullCastToUnannotatableReferenceTypedTypeParameter I think

{
if (t is null) System.Console.WriteLine();

return t; // 1
}
}";
var comp = CreateNullableCompilation(source);
comp.VerifyDiagnostics(
// (8,16): warning CS8603: Possible null reference return.
// return t; // 1
Diagnostic(ErrorCode.WRN_NullReferenceReturn, "t").WithLocation(8, 16)
);
}
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@cston cston Jul 28, 2020 •
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} [](start = 8, length = 1)

Please test:

[return: MaybeNull] TNotNull M<TNotNull>(TNotNull t) where TNotNull : notnull
{
    ...
}
``` #Closed


[Fact]
public void TNotNullFieldMustBeAssigned()
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@cston cston Jul 28, 2020 •
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TNotNullFieldMustBeAssigned [](start = 20, length = 27)

Was the behavior of this method affected? This case and others are covered in UninitializedNonNullableFieldTests.GenericType_NotNullConstraint. #Closed

{
var source = @"
public class C<TNotNull> where TNotNull : notnull
{
public TNotNull field;

public C()
{
}
}";
var comp = CreateNullableCompilation(source);
comp.VerifyDiagnostics(
// (6,12): warning CS8618: Non-nullable field 'field' is uninitialized. Consider declaring the field as nullable.
// public C()
Diagnostic(ErrorCode.WRN_UninitializedNonNullableField, "C").WithArguments("field", "field").WithLocation(6, 12)
);
}

[Fact]
[WorkItem(35602, "https://github.com/dotnet/roslyn/issues/35602")]
public void PureNullTestOnUnconstrainedType()
Expand Down