Release 2.7.0 on 3 January

[aantron]

Draft changelog

General

• Values of types 'a Lwt.t are now referred to as promises rather than threads (Refer to 'a Lwt.t as promises rather than threads (proposal) #300). The manual has not yet been updated.

Breaking

• After this release, Lwt will switch to semantic versioning. Future breaking changes will first require deprecation, then a major version number increase (Semantic versioning; safely breaking Lwt (proposal) #293).
• Lwt no longer supports OCaml 4.01 (Drop support for 4.01 #272).
• Lwt_unix.fdatasync is no longer available on macOS. It was calling an undocumented system call on that system (no fdatasync prototype on OS X #285, Jeremy Yallop).

Planned to break in 3.0.0

• APIs in this category have deprecation messages attached.
• Lwt_engine.libev will have an argument for selecting the libev back end (Add support for selecting the libev backend #269, Add support for selecting the libev backend (more gently) #294, Jeremy Yallop).
• Lwt_io.establish_server will be replaced by a version that makes it difficult to leak file descriptors (Safer alternative to Lwt_io.establish_server #258, Replace establish_server by establish_server_safe #260).
• Lwt_io.shutdown_server will evaluate to a promise, which indicates when the close operation completes (Lwt_io.shutdown_server should evaluate to a thread #259).
• Lwt_unix.bind will evaluate to a promise, since bind can block for Unix domain sockets (Cooperative Lwt_unix.bind (sockets) #296, requested David Sheets).
• ocamlfind packages lwt.react, lwt.ssl, and lwt.glib will be replaced by the new lwt_react, lwt_ssl, and lwt_glib. These are are distributed in new OPAM packages with the same names, separately from OPAM package lwt (Begin factoring out Lwt_ssl, Lwt_glib, Lwt_react #301).

Additions

• Lwt_unix.readv and Lwt_unix.writev – zero-copy scatter/gather I/O (writev – zero-copy gather output #291, readv – zero-copy scatter input #299).
• ?fail_on_error argument for Lwt_log.load_rules (Add ?fail_on_error argument to Lwt_log_core.load_rules, also expose new level_of_string function in the interface #306, Daniil Baturin).
• Lwt_log.level_of_string (Add ?fail_on_error argument to Lwt_log_core.load_rules, also expose new level_of_string function in the interface #306, Daniil Baturin).

Changes

• Lwt_stream.of_list, Lwt_stream.of_array, Lwt_stream.of_string now immediately push all elements into the created streams (change close semantics for fixed-length sources #239, Spiros Eliopoulos).

Deprecations

• Lwt_stream.map_exn in favor of Lwt_stream.wrap_exn, which uses OCaml's standard result type (Deprecate Lwt_stream.result #295).

Bugs fixed

• Ungraceful failure if directory handle used after Lwt_unix.closedir (Some improvements to readdir, readdir_n #292).
• Buffer overflow in Lwt_unix.readdir and Lwt_unix.readdir_n (Some improvements to readdir, readdir_n #292).
• Unnecessary allocations in Lwt_unix.readdir_n (Some improvements to readdir, readdir_n #292, found Jeremly Yallop).

Miscellaneous

• Annotate existing deprecations with [@@ocaml.deprecated ...] (5737f5b).
• Improvements to the examples (Convert 'Let.return ()' to 'Lwt.return_unit'. #288, Rich Neswold).
• Documentation fixes, including by Rich Neswold.
• New tests and various minor internal improvements.
• Run tests in CI with all OCaml warnings enabled (dadb926).
• Much cleaner build output.
• Add scratch/ directory for local use by developers.

[aantron]

Final changelog.

Now installable from OPAM (after opam update; discussed/merged in ocaml/opam-repository#8195, ocaml/opam-repository#8196).