CallerArgumentExpression attributes on partial method parameters look at the implemention rather than definition parameter names

[RikkiGibson]

CallerArgumentExpression attributes on partial method parameters look at the implemention rather than definition parameter names

[Youssef1313]

That's an interesting scenario 🤓

I think the current behavior is indeed not the correct one.

[Youssef1313]

This may need to be adjusted for VB as well.

(Guessing): The relevant code is:

roslyn/src/Compilers/CSharp/Portable/Symbols/Source/SourceComplexParameterSymbol.cs

Line 684 in 6f815fb

var parameters = ContainingSymbol.GetParameters();

roslyn/src/Compilers/VisualBasic/Portable/Symbols/Source/SourceParameterSymbol.vb

Line 185 in 6f815fb

Dim containingSymbol = Me.ContainingSymbol

Instead of using ContainingSymbol, This probably should be (ContainingSymbol as MethodSymbol)?.PartialDefinitionPart ?? ContainingSymbol.

Edit: Reading the code and thinking again, I think ContainingSymbol should actually have been the definition part. Needs a bit of debugging to see what ContainingSymbol is in this code path.

[jaredpar]

Agree the declaration name makes more sense but this is now 15 year old behavior. Changing it is very risky. Think this should be documented but not changed.

[Youssef1313]

@jaredpar That is 3 or 4 years only I think?

[jaredpar]

Partial members go back to C# 2.0. I cannot recall definitively if we allowed call info in partial but believe we did.

[Youssef1313]

This seems very specific to caller argument expression and not caller info attributes in general. Am I missing some scenario where a similar issue could be noticed with other caller infos?