FS3356 Extension members

[pezipink]

The following code used to work

module Test =
    type Holding.Position with 
        member this.X = ""
        member this.Y = ""

    type Reporting.Position with 
        member this.A = ""
        member this.B = ""

Where these types are declared somewhere else. In the new compiler I now get:

Extension members extending types with the same simple name 'Position' but different fully qualified names cannot be defined in the same module. Consider defining these extensions in separate modules.

I have reported this is a bug since this has always worked over many versions. The error is very specific though, is this a new behaviour and breaking change?

[T-Gro]

This is already fixed, but not yet part of the release VS product.
93c31cb

CheckForDuplicateExtensionMemberNames (added by #18821) was flagging all extension members on types with the same simple name from different namespaces. However, the underlying IL collision problem only affects static extension members — instance extension members compile with the extended type as the first IL parameter, which differentiates their signatures.

[pezipink]

Excellent, thanks! Apologies if this issue already existed - I couldn't find it.

[T-Gro]

I think it surfaced when adding "try build IcedTasks projects" regression test, I guess separate issue was never created - good to have this one as a reference point for anyone else.