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fix: prevent generation for nullable delegate parameters #397

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fix: prevent generation for nullable delegate parameters #397

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16 changes: 14 additions & 2 deletions src/PolyType.SourceGenerator/SourceFormatter/SourceFormatter.Function.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -176,7 +176,7 @@ static string FormatFunctionParameterExpr(ParameterShapeModel parameter, bool is
}

string delegateSignature = string.Join(", ", functionShapeModel.Parameters
.Select(parameter => $"{FormatRefPrefix(parameter)}{parameter.ParameterType.FullyQualifiedName}{GetNullableSuffix(parameter)} {parameter.Name}"));
.Select(parameter => $"{FormatRefPrefix(parameter)}{FormatDelegateParameterType(parameter)} {parameter.Name}"));

@eiriktsarpalis eiriktsarpalis Feb 25, 2026

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Does the issue occur with constructor methods? I feel the underlying issue here is that nullable annotations isn't being stripped in delegate parameters, unlike what is happening with constructor or method shapes.

@teneko teneko Mar 12, 2026

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I do not understand. Is this a clarification question: "does this issue occur with constructor methods [too]"? If not I can only clarify: when using top-level statements, the delegate turns into a global non-Program-class owned delegate.

Ahh I think I understand what you mean. So you say, that nullable annotations are stripped for method parameters, but not for constructor parameters and method parameters.

I am not sure what you mean by "nullable annotation stripping". Am I right in the assumption, that you mean PolyType that does nullable annotation stripping?

I did not researched, how the nullable annotation (stripping) is handled by PolyType in case of constructor parameters or method parameters. If you want I can do that and report back.

@eiriktsarpalis eiriktsarpalis Mar 12, 2026

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There are many parts of the source generator that deal with method/constructor parameter. I was asking if this is the only location where the bug manifests. What happens if the same pattern occurs in a constructor annotated with [ConstructorShape]?

@teneko teneko Apr 13, 2026

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Thanks for clarification.. Sorry I have seen it.. my time.. I try to take a closer look this weekend. Sorry for the huge delay.


string argumentStateCtorExpr = functionShapeModel.Parameters switch
{
Expand All @@ -199,7 +199,19 @@ static string FormatFunctionParameterExpr(ParameterShapeModel parameter, bool is

return $$"""static {{innerFuncVar}} => ({{delegateSignature}}) => { {{functionArgumentStateFQN}} {{stateVar}} = {{argumentStateCtorExpr}}; {{tailExpr}}; }""";

static string GetNullableSuffix(ParameterShapeModel parameter) => parameter.NullableAnnotation is NullableAnnotation.Annotated ? "?" : "";
static string FormatDelegateParameterType(ParameterShapeModel parameter)
{
string parameterType = parameter.ParameterType.FullyQualifiedName;
if (parameter.NullableAnnotation is not NullableAnnotation.Annotated)
{
return parameterType;
}

return parameterType.Length > 0 && parameterType[^1] == '?'
? parameterType
: parameterType + "?";
}

static string GetSuppressionSuffix(ParameterShapeModel parameter) => parameter.ParameterTypeContainsNullabilityAnnotations ? "!" : "";
}

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17 changes: 17 additions & 0 deletions tests/PolyType.SourceGenerator.UnitTests/CompilationTests.FunctionShapes.cs
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Expand Up @@ -43,6 +43,23 @@ public partial class Witness { }
Assert.Empty(result.Diagnostics);
}

[Fact]
public static void DelegateShapes_NullableBoolParameter_NoErrors()
{
// Regression test for nullable bool delegate parameters being emitted as bool??.
Compilation compilation = CompilationHelpers.CreateCompilation("""
using PolyType;

public delegate void BrokenCommand(bool? skipDuplicate = null);

[GenerateShapeFor(typeof(BrokenCommand))]
public partial class Witness { }
""");

PolyTypeSourceGeneratorResult result = CompilationHelpers.RunPolyTypeSourceGenerator(compilation);
Assert.Empty(result.Diagnostics);
}

[Fact]
public static void EventShapes_PublicInstanceAndStatic_NoErrors()
{
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