Breaking

These changes were announced in Lwt 3.1.0 and Lwt 3.2.0. See #453 about smooth upgrade paths.

• Delete package lwt.ppx. The PPX syntax is in package lwt_ppx since Lwt 3.2.0 (#338).
• Remove >> syntax from the PPX (#495).
• Delete modules Lwt_log, Lwt_daemon, Lwt_log_core, and package lwt.log. These are in package lwt_log since Lwt 3.2.0, but it is recommended to use Logs_lwt from the logs library instead (#484, initiated Hannes Mehnert).
• Delete package lwt.preemptive. It is an alias for lwt.unix since Lwt 3.2.0 (#487).
• Delete package lwt.syntax. The Camlp4 syntax is in package lwt_camlp4 since Lwt 3.2.0 (#370).
• Delete module Lwt_chan, a predecessor of Lwt_io (#441).
• Delete package lwt.simple-top, a predecessor of utop (#371).
• Make resolvers (Lwt.u) contravariant (#458).

Planned to break in 5.0.0

• 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 (#562, Tim Reinke, prompted Hezekiah Carty).
• Remove translation of [%lwt ...] to Lwt.catch from the PPX (#527).
• Remove -no-debug option from the PPX (#528).
• Remove Lwt_log support from the PPX (#520).

Bugs fixed

• Lwt_io.file_length now fails with EISDIR when used on a directory (#563, requested Cedric Cellier).
• Lwt_react.E.limit and Lwt_react.S.limit now working more correctly (#566, @Freyr666).

Miscellaneous

• Documentation improvements (#561, Jason Evans).