[fpc-pascal] Issue #39746 fpwidestring case conversion string too long

[Michael Van Canneyt]

On Mon, 25 Sep 2023, Tony Whyman via fpc-pascal wrote:

> This issue seems to be still open after one year. There was a proposed fix: 
> https://gitlab.com/freepascal.org/fpc/source/-/merge_requests/158. However 
> the discussion seems to tail off without an obvious resolution.
>
> This is a clear bug in fpwidestring and needs to be fixed. What is the 
> status?

Unresolved, someone needs to take a deep dive into this; 
The comments by Florian and Jonas are still unresolved:

- As far as I can see, no testcases are provided.
   (a requirement for the compiler)
- I don't see a clear resolution to Jonas' remark that the len is already taking
   into account the null terminator.

- Unfortunately the branch can no longer be merged as-is, since trunk has evolved too much :/

The patch also mixes various issues: some things in the compiler, some
things in the RTL. These should be separated out. I think that is easily
doable. I'll look at applying the RTL patches separately next week if no-one
did it before. It would help if there was a testcase for the compiler.

Michael.