Compiler codebase chore :: Hash directives around nullness syntax are not needed anymore

[T-Gro]

While the nullness feature was being developed, the previous compiler (LKG = Last Known Good) did not understand nullness syntax ("not null", | null).
Which lead to null-relevant code surrounded in "#if" directives, to make it compile both under the .NET8 compiler as well as the new .NET9 one.

With .NET being out, those should not be needed anymore.
The same would apply to wrapper types created in order to limit the number of "#if" directives, pretty much most of the NullnessShims.fs file and the broad usage of the "MaybeNull" wrapper.

This can be done incrementally.

[progressive-galib]

I can do it all i need is is a bit guidance on where these codes are from anyone familiar with the codebase.

[T-Gro]

Hello @progressive-galib , I will be happy to assist.

I would first recommend to start with the compiler (FSharp.Compiler.Service.fsproj and projects depending on it) itself, and do FSharp.Core separately later.

In VisualFsharp.sln solution, you search for usages of "NO_CHECKNULLS" directive.
Most of them will be in insolation and can be resolved directly.

There is a single file (which is being referenced from multiple projects) called NullnessShims.fs
https://github.com/dotnet/fsharp/blob/main/src/Compiler/Utilities/NullnessShims.fs

That file uses that directive as well to provide two alternate versions of types/functions.
Ideally, those should be deleted and the respective callsite adjusted.
For example, the type "MaybeNull" should not be needed anymore, as the callsite can move from (e.g.) MaybeNull<string> to vanilla string | null.

I definitely recommend to go with full-text search to find all the places and not rely on "Find references". Reason is, hash directives are branching the code even for tooling and some paths might not be found because of it.

[progressive-galib]

already started

[progressive-galib]

This can be done incrementally.

@T-Gro can i do one file per pr ?

also i am not building locally anymore, you guys have great CI/CD #18201