You can simply contribute to https://github.com/dotnet/fsharp/, the maintainers are very friendly to new contributors in my experience (though the codebase is old and often quite hard to understand).
> though the codebase is old and often quite hard to understand
Even some new stuff is like that - and partially my fault, depending on the area :)
That said, some stuff that was REALLY tough to understand was ripped out recently, the "reactor queue" and incremental build system. They were central to how editor tooling works and utterly incomprehensible since they were working around the lack of a free-threaded compiler service. Now the entire compiler is free-threaded, so all the complex machinery to coordinate work is mostly deleted and/or reduced to like 50 lines of straightforward code.
As a note, the codebase is also huge because contains lot of code:
- FSharp.Core library, who contains most of the types and functions you want to use
- the fsc F# compiler
- the FSharp.Compiler.Service, who is the compiler as a library used by all editors/ide, written to be performant and support the logic of IDE functionalities (find references, etc)
- The Microsoft Visual F# code, who is the F# extension for Visual Studio
So is complicated repo, but for a reason.
But nice to work with given the features there
