rb_io_wait is declared but not implemented

[larskanis]

Truffleruby on the master branch declares rb_io_wait but doesn't implement it. It also defines RUBY_IO_READABLE without using it.

This issue leads to a build error in ruby-pg here. The extconf.rb tests for rb_io_wait and doesn't detect it, so that it enables a polyfill instead. This polyfill usually works on truffleruby, but conflicts on the definition of the function and the enum.

Truffleruby-head is currently disabled in ruby-pg, but the latest truffleruby release runs successfully.

[eregon]

@aardvark179 is working on implementing rb_io_wait.

The current conflict is unfortunate but expected: we import headers from CRuby, changed as little as possible to keep it maintainable.
have_func correctly detects it's not implemented, so the only issue here is those conflicts.

[larskanis]

OK, so the next release will implement rb_io_wait and the current inconsistent state is just temporary.

The polyfill in ruby-pg is here, just in case it's interesting. But sure, a complete implementation needs proper integration into Fiber.scheduler, far beyond the simple polyfill.

[eregon]

Maybe a simple workaround here is to do some renames/prefix for the polyfill?
I think that would be the fastest to solve this specific issue.

(We're also working on the Fiber scheduler, not merged yet)

[larskanis]

OK, I prefixed the function and enums in commit ged/ruby-pg@ec09240 so that the build and all non-scheduler tests succeed.

[larskanis]

rb_io_wait has been implemented in commit 58aea01