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Fix #3821: keep ref-struct conditional as if/return, not ?. / ?? (CS8978) #3823

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Merged
siegfriedpammer merged 1 commit into from
Jun 29, 2026
+38 −2
Merged

Fix #3821: keep ref-struct conditional as if/return, not ?. / ?? (CS8978) #3823

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34 changes: 34 additions & 0 deletions ICSharpCode.Decompiler.Tests/TestCases/Correctness/NullPropagation.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -7,6 +7,9 @@ class NullPropagation
static void Main()
{
new NullPropagation().TestNotCoalescing();
#if CS72
new NullPropagation().TestRefStructNotCoalescing();
#endif
}

class MyClass
Expand All @@ -25,5 +28,36 @@ string NotCoalescing(MyClass c)
{
return c != null ? c.Text : "Hello";
}

#if CS72
ref struct ByRefLikeStruct
{
public int Value;
}

class RefStructHolder
{
public ByRefLikeStruct Get()
{
ByRefLikeStruct result = default(ByRefLikeStruct);
result.Value = 42;
return result;
}
}

void TestRefStructNotCoalescing()
{
Console.WriteLine("TestRefStructNotCoalescing:");
Console.WriteLine(RefStructNotCoalescing(null).Value);
Console.WriteLine(RefStructNotCoalescing(new RefStructHolder()).Value);
}

// A by-ref-like return type cannot be turned into a ?. / ?? null-propagation: a ref struct
// cannot be wrapped in Nullable<T>, so that form does not compile.
ByRefLikeStruct RefStructNotCoalescing(RefStructHolder holder)
{
return holder != null ? holder.Get() : default(ByRefLikeStruct);
}
#endif
}
}
6 changes: 4 additions & 2 deletions ICSharpCode.Decompiler/IL/Transforms/NullPropagationTransform.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -140,12 +140,14 @@ ILInstruction TryNullPropagation(ILVariable testedVar, ILInstruction nonNullInst
IntroduceUnwrap(testedVar, varLoad, mode);
return new NullableRewrap(nonNullInst);
}
else if (!removedRewrapOrNullableCtor && NullableType.IsNonNullableValueType(returnType))
else if (!removedRewrapOrNullableCtor && NullableType.IsNonNullableValueType(returnType)
&& !returnType.IsByRefLike)
{
context.Step($"Null propagation (mode={mode}, output=null coalescing)", nonNullInst);
// testedVar != null ? testedVar.AccessChain : nullInst
// => testedVar?.AccessChain ?? nullInst
// (only valid if AccessChain returns a non-nullable value)
// (only valid if AccessChain returns a non-nullable value; a by-ref-like type such as
// Span<T> is excluded because it cannot be wrapped in Nullable<T> for the ?. / ?? form)
IntroduceUnwrap(testedVar, varLoad, mode);
return new NullCoalescingInstruction(
NullCoalescingKind.NullableWithValueFallback,
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