First beta release for OCaml 5.3.0

Ecosystem
1

One month and half after the release of the first alpha for OCaml 5.3.0, the release of OCaml 5.3.0 is drawing near.

The internal API of the compiler libraries has been frozen, and most core developer tools support (or will support soon) the new version of the compiler.

We have thus released a first beta version of OCaml 5.3.0 to help you update your software and libraries ahead of the release (see below for the installation instructions). More information about the whole release process is now available in the compiler repository.

Compared to the first alpha release, this beta contains a few runtime or typechecker fixes, a handful of fixes for the runtime event library and other miscellaneous fixes.

Exceptionally, this beta release also introduces a new flag -keywords for the compiler. This backward compatibility flag aims to help compiling old code that are using effect as a normal identifier, now that effect is a keyword in the new effect handler syntax.

The progresses on stabilising the ecosystem are tracked on the opam readiness for 5.3.0 meta-issue.

The full release is expected in the end of November or beginning of December, see the new prospective calendar for more information.

If you find any bugs, please report them on OCaml’s issue tracker.

If you are interested in full list of features and bug fixes of the new OCaml version, the updated change log for OCaml 5.3.0 is available on GitHub and a short list of the changes since the last alpha is available below.

Installation Instructions

The base compiler can be installed as an opam switch with the following commands
on opam 2.1 and later:

opam update
opam switch create 5.3.0~beta1

The source code for the beta is also available at these addresses:

Fine-Tuned Compiler Configuration

If you want to tweak the configuration of the compiler, you can switch to the option variant with:

opam update
opam switch create <switch_name> ocaml-variants.5.3.0~beta1+options <option_list>

where option_list is a space separated list of ocaml-option-* packages. For instance, for a flambda and no-flat-float-array switch:

opam switch create 5.3.0~beta1+flambda+nffa ocaml-variants.5.3.0~beta1+options ocaml-option-flambda ocaml-option-no-flat-float-array

All available options can be listed with opam search ocaml-option.

Changes since the first alpha

Runtime fixes

  • #13502: Fix misindexing related to Gc.finalise_last that could prevent
    finalisers from being run.
    (Nick Roberts, review by Mark Shinwell)

  • #13402, #13512, #13549, #13553: Revise bytecode implementation of callbacks
    so that it no longer produces dangling registered bytecode fragments.
    (Xavier Leroy, report by Jan Midtgaard, analysis by Stephen Dolan,
    review by Miod Vallat)

  • #13520: Fix compilation of native-code version of systhreads. Bytecode fields
    were being included in the thread descriptors.
    (David Allsopp, review by SĂ©bastien Hinderer and Miod Vallat)

Typechecker fixes

  • #13579, #13583: Unsoundness involving non-injective types + gadts
    (Jacques Garrigue, report by @v-gb,
    review by Richard Eisenberg and Florian Angeletti)

  • #13388, #13540: raises an error message (and not an internal compiler error)
    when two local substitutions are incompatible (for instance module type S:=sig end type t:=(module S))
    (Florian Angeletti, report by Nailen Matschke, review by Gabriel Scherer, and
    Leo White)

Compiler flag

  • #13471: add -keywords <version?+list> flag to define the list of keywords
    recognized by the lexer, for instance -keywords 5.2 disable the effect
    keyword.
    (Florian Angeletti, review by Gabriel Scherer)

Runtime event library fixes

  • #13419: Fix memory bugs in runtime events system.
    (B. Szilvasy and Nick Barnes, review by Miod Vallat, Nick Barnes,
    Tim McGilchrist, and Gabriel Scherer)

  • #13407: Add Runtime_events.EV_EMPTY_MINOR
    (Thomas Leonard)

  • #13522: Confirm runtime events ring is still active after callback.
    (KC Sivaramakrishnan, review by Sadiq Jaffer and Miod Vallat)

  • #13529: Do not write to event ring after going out of stw participant set.
    (KC Sivaramakrishnan, review by Sadiq Jaffer)

Documentation

  • #13424: Fix Gc.quick_stat documentation to clarify that returned fields
    live_words, live_blocks, free_words, and fragments are not zero.
    (Jan Midtgaard, review by Damien Doligez and KC Sivaramakrishnan)

  • #13440: Update documentation of Gc.{control,get,set} to reflect fields
    not currently supported on OCaml 5.
    (Jan Midtgaard, review by Gabriel Scherer)

  • #13469, #13474, #13535: Document that [Hashtbl.create n] creates a hash table
    with a default minimal size, even if [n] is very small or negative.
    (Antonin DĂ©cimo, Nick Bares, report by Nikolaus Huber and Jan Midtgaard,
    review by Florian Angeletti, Anil Madhavapeddy, Gabriel Scherer,
    and Miod Vallat)

Standard library internal fix

  • #13543: Remove some String-Bytes conversion from the stdlib to behave better
    with js_of_ocaml
    (Hugo Heuzard, review by Gabriel Scherer)

Toplevel fix

  • #13263, #13560: fix printing true and false in toplevel and error
    messages (no more unexpected #true)
    (Florian Angeletti, report by Samuel Vivien, review by Gabriel Scherer)

Compiler internals

  • #13391, #13551: fix a printing bug with -dsource when using
    raw literal inside a locally abstract type constraint
    (i.e. let f: type \#for. ... )
    (Florian Angeletti, report by Nick Roberts, review by Richard Eisenberg)
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