Lwt 5.0.0 breaking changes notice

[aantron]

Lwt 5.0.0 will be released in November 2019 or later, with some minor breaking changes. All breaking changes are announced at least three months ahead of time by Lwt, and this issue includes details on the ones scheduled for 5.0.0.

---

Lwt.pick will raise Invalid_argument on the empty list, instead of returning a forever-pending promise. This also applies to Lwt.choose, Lwt.npick, Lwt.nchoose, and Lwt.nchoose_split (#562).

We found only one usage in opam that could be affected by this, in package eliom. This is fixed by checking for the empty list before calling Lwt.pick, or otherwise reasoning that the argument cannot be the empty list.

cc @vasilisp @vouillon

---

[%lwt ...] will no longer be translated to Lwt.catch by the PPX (#527). The replacement is to use Lwt.catch directly, or try%lwt.

[%lwt ...] is found in opam packages sqlexpr and eliom.

cc @vasilisp @vouillon @mfp

---

The -no-debug option will be removed from the PPX (#528). It has no users in opam.

---

Support for Lwt_log will be removed from the PPX (#520). It has no users in opam.

[aantron]

Additional breaking changes were announced by Lwt 4.3.0:

• The signature of Lwt.async will change to (unit -> unit Lwt.t) -> unit (Lwt.async not demanding unit Lwt.t #603 (comment)). Maintainers have been notified in that issue.

• Lwt_unix.send_msg and Lwt_unix.recv_msg will take Lwt_io.IO_vectors.t instead of io_vector lists (string/bytes (apparent?) inconsistency in Lwt_unix.io_vector and Lwt_unix.recv_msg #594 (comment), string/bytes (apparent?) inconsistency in Lwt_unix.io_vector and Lwt_unix.recv_msg #594 (comment)). Maintainers have been notified in that issue.

• Nested calls to Lwt_main.run will raise Failure (Forbid nesting calls to Lwt_main.run #609). We don't expect anyone to be affected.

• configure.ml will be removed, and replaced by direct use of discover.ml (Remove configure.ml #700 (comment)). Maintainers have been notified in that issue.

• Lwt_unix.async_method will have no effect (Deprecate the Lwt_unix.async_method machinery and eventually remove it #572). We don't expect anyone to be affected.

[aantron]

Lwt 5.0.0 is now installable from opam!