Lwt 4.3.0 - concurrency library

[aantron]

Changelog:

Planned to break in 5.0.0

For general discussion of breakage in Lwt 5.0.0, see ocsigen/lwt#584. See ocsigen/lwt#293 about how Lwt announces and does breaking changes.

• The signature of Lwt.async will change from (unit -> 'a Lwt.t) -> unit to (unit -> unit Lwt.t) -> unit (Lwt.async not demanding unit Lwt.t ocsigen/lwt#603, prompted @cfcs).
• Lwt_unix.send_msg and Lwt_unix.recv_msg will be changed to take Lwt_unix.IO_vectors.t instead of Lwt_unix.io_vectors (Prepare to use new IO_vectors in Lwt_unix.recv_msg, send_msg ocsigen/lwt#702, prompted Marcello Seri).
• Nesting calls to Lwt_main.run will be forbidden, and will raise an Failure. Most programs don't do this (Forbid nesting calls to Lwt_main.run ocsigen/lwt#609, prompted François-René Rideau).
• configure.ml will be removed in favor of an improved discover.ml This affects only users who are configuring Lwt as part of a manual installation (i.e., not users of opam or esy). See discover.ml for usage (Remove configure.ml ocsigen/lwt#700).
• Lwt_unix.async_method will have no effect. In practice, it already does nothing, and has almost no users (Deprecate the Lwt_unix.async_method machinery and eventually remove it ocsigen/lwt#572).

The following planned breaking changes have already been announced:

• Lwt.pick will raise Invalid_argument on the empty list, instead of returning a forever-pending promise. Also applies to Lwt.choose, Lwt.npick, Lwt.nchoose, and Lwt.nchoose_split ([5.0.0] Lwt.pick, etc raise Invalid_argument on empty list ocsigen/lwt#562, Tim Reinke, prompted Hezekiah Carty).
• Remove translation of [%lwt ...] to Lwt.catch from the PPX ([easy-ish] PPX: replace [%lwt ...] by [%lwt.catch ...] or remove it ocsigen/lwt#527).
• Remove -no-debug option from the PPX (PPX: remove -no-debug option ocsigen/lwt#528).
• Remove Lwt_log support from the PPX (Delete logging support from the PPX ocsigen/lwt#520).

Additions

• Lwt_process: allow setting working directory for new processes (Allow setting the cwd when spawning a process ocsigen/lwt#694, Thomas Leonard).
• PPX: use OCaml 4.08 ASTs to support latest features (Update the PPX to use the 4.08 ASTs ocsigen/lwt#697).
• Lwt_io.NumberIO: use compiler intrinsics for better performance (Inefficient Lwt_io.NumberIO implementations (int32, int64, float read/write). ocsigen/lwt#178, requested Mauricio Fernandez).

Bugs fixed

• Race condition in Lwt_react.S.limit (ocsigen/lwt@4e592eb).
• Use fallback rule during configuration (Better custom configuration ocsigen/lwt#693, Hongchang Wu).
• Fix typos (Fixing typos ocsigen/lwt#688, Added argot #692, @Fourchaux).

[aantron]

None of the revdeps failures have to do with this release. However, I found that some old releases of ocurl need Lwt < 4.0.0 because they expect package lwt.ppx ([1] [2]), so I added constraints.

[mseri]

Thanks for triaging the failures

[aantron]

Thanks!