Warn if we're offering a Coalesce Expression inside an ExpressionOfT.

[CyrusNajmabadi]

Mitigation for #17028

[CyrusNajmabadi]

The change from x != null ? x : y into x ?? y can be observed inside an Expression<T> context. i.e. a different type of node is generated for ?? vs ? : . Some Expression<T> providers might not support the ?? node. As such, we warn that this may cause problems, but we do not prevent people from making this change if it is what they want to do.

[CyrusNajmabadi]

Tagging @dotnet/roslyn-ide

[CyrusNajmabadi]

Tagging @dotnet/roslyn-ide

[miloush]

I disagree with this fix. Why warning for the coalesce code fix only? Expression consumers can lack support for arbitrary set of expressions, and any fix potentially changes the behavior.

[miloush]

I mean it's not even about supporting the expressions or not. The consumer might support them all, but not be executing them. Could be serializing it or hashing it or whatever and things might break. EDIT: The code fixes work under the assumption of C# spec and execution equivalence. If this should be fixed on Roslyn side then I think all code fixes inside ExpressionOfT should be with warning at least.

[CyrusNajmabadi]

Why warning for the coalesce code fix only?

There is no claim that the warning would only be for coalesce expressions. We're just happening to start with that. I'm happy to add more warnings in the future for other features as well.

[CyrusNajmabadi]

If this should be fixed on Roslyn side then I think all code fixes inside ExpressionOfT should be with warning at least.

That's fine. We can do that.

[DustinCampbell]

If this should be fixed on Roslyn side then I think all code fixes inside ExpressionOfT should be with warning at least.

That's fine. We can do that.

That's fair.

[Pilchie]

👍