Working version

--------------

(Changes that can break existing programs are marked with a "*")

### Language features:

### Runtime system:

- #14486, #14530: Add FreeBSD frame pointers support for AMD64 and ARM64.

Document the usage of pmcstat and dtrace for generating profiling

information.

(Tim McGilchrist, review by Gabriel Scherer)

- #14494: Consistently use macro to test header promotion.

(Nick Barnes, review by Gabriel Scherer)

- #14493: Use Scannable_* macros instead of comparisons to No_scan_tag, for

legibility and correctness (fixes one bug, in weak.c).

(Nick Barnes, review by Gabriel Scherer)

* #14559: Remove `caml_fatal_error_arg` and `caml_fatal_error_arg2`

symbols from the runtime. The declarations were removed in 5.0.

(Antonin Décimo, review by Nicolás Ojeda Bär)

- #14642: Ignore cleanup-at-exit / caml_shutdown when other domains remain

running

(Gabriel Scherer and Olivier Nicole, report by Olivier Nicole, review by Miod

Vallat and Damien Doligez)

- #14570, #14616, #14665: Distinguish between prefetching for read and write

access in the runtime. Significant performance benefit for some multi-domain

programs.

(Nick Barnes, review by Gabriel Scherer, Damien Doligez, and Antonin Décimo)

- #14651: Remove S390x TSan (Thread Sanitizer) support.

(Tim McGilchrist, review by Olivier Nicole)

- #14292: The value returned by `Hashtbl.is_randomized` is now reflected in the

`R` parameter of `Sys.runtime_parameters`.

(Antonin Décimo, David Allsopp, Hannes Mehnert, review by

Nicolás Ojeda Bär)

- #14482: Add DWARF CFI support to POWER backend.

(Tim McGilchrist, review by Xavier Leroy)

### Type system:

- #14512: Improve check for warning 16 (unerasable-optional-argument)

(Alistair O'Brien, review by Florian Angeletti, Gabriel Scherer)

- #12150: class type system improvements: self type constraints, virtual method

inheritance in mutually recursive definition, immediate object inheritance.

(Leo White, review by Florian Angeletti)

### Code generation and optimizations:

* #13919: optimize `lazy v` when `v` is a structured constant

(below a size threshold), so that `Lazy.from_val v` should not be

necessary anymore in most cases.

This may in theory break certain recursive value declarations,

in that case switching to `lazy ((); v)` should be enough to

disable the change in a backward-compatible way.

(Gabriel Scherer, review by Vincent Laviron)

- #13438: keep some optimization hints from lambda in bytecode modules

and executables (to be used by Js_of_ocaml / Wasm_of_ocaml)

(Jérôme Vouillon)

- #13588: propagate physical comparison operators to lambda

(to be used by Js_of_ocaml / Wasm_of_ocaml)

(Hugo Heuzard, review by Olivier Nicole)

- #14534: Fix bytecode peehole optimization for PUSHENVACC4

(Hugo heuzard, David Allsopp review by Nicolás Ojeda Bär, Vincent Laviron

and Gabriel Scherer)

### Standard library:

- #13554: Add `List.append_map` and `List.rev_append_map`.

(Sylvain Boilard and Hugo Heuzard, review by Nicolás Ojeda Bär, Daniel Bünzli,

Damien Doligez and Jeremy Yallop)

- #14121: Add Set.S.singleton_to_elt and Map.S.singleton_to_binding

(Vincent Laviron, review by Daniel Bünzli, Nicolás Ojeda Bär

and Gabriel Scherer)

- #14380: Add Atomic.Array.

(Clément Allain and Gabriel Scherer, review by Olivier Nicole

and Léo Andrès for the stdlib team)

- #14487: Add String.drop_{prefix,suffix}

(Michael Neumann, review by Léo Andrès, Nicolás Ojeda Bär and Gabriel Scherer)

- #14693: Add Dynarray.{of,to}_iarray

(Olivier Nicole, review by Gabriel Scherer and Nicolás Ojeda Bär, suggestion

by Andreas Rossberg)

- #14553: Add Array.fold_{left,right}2

(Clément Pottier, review by Nicolás Ojeda Bär and Vincent Laviron)

### Other libraries:

### Tools:

- #14499: in ocamltest, remove support for the legacy

test syntax (with '***') and the '-translate' option

to convert from this syntax.

(Gabriel Scherer, review by Nicolás Ojeda Bär)

- #14502: in ocamltest, `not <action>` negates a

predicate-like action.

(Gabriel Scherer, review by Olivier Nicole)

- #14532: in ocamltest, support `<action> && <action>`,

`<action> || <action>`

and `if <action> then <action> [else <action>]`.

(Gabriel Scherer, review by Olivier Nicole)

- #14545: in ocamltest, support `system` variable that uses

the configure-time @System@ value. Rename the `macos` variable to

`macosx` to match the configure-time choice.

(Tim McGilchrist, review by Gabriel Scherer and Antonin Décimo)

### Manual and documentation:

- #14598: Add `@since` annotations to `Runtime_events`. (Raphaël Proust)

### Compiler user-interface and warnings:

- #14205: Make inclusion check error message reference the user-written file

when operating on a ppx-generated file.

(Liam Stevenson, review by Florian Angeletti)

- #14142: print GADT equations in error messages when they introduce a type

(Stefan Muenzel, review by Florian Angeletti)

- #14359, #14600: when reporting unbound type variables in a type declaration,

avoid a possible confusion between type parameters and unbound variables.

(Florian Angeletti, report by Florian Weimer, review by Gabriel Scherer)

- #14690: Fix `Name_type_mismatch` error message when the expected type is an

alias: print the expanded path on the right-hand side of the equality, not

the alias twice.

(Weixie Cui)

### Internal/compiler-libs changes:

- #14620: optimize utf8 normalization and (un)capitalization functions

(Gabriel Scherer, review by Stefan Muenzel and Florian Angeletti,

report by Stefan Muenzel)

- #14618: optimize utf8 normalization outside of the ASCII range

(Stefan Muenzel, review by Gabriel Scherer, Daniel Bünzli, and

Florian Angeletti)

- #14601, remove an unreachable path for unbound type variables in extension

constructor declarations.

(Florian Angeletti, review by Gabriel Scherer)

- #14641: Move `Opnames` into `ocamlbytecomp`.

(David Allsopp, review by Nicolás Ojeda Bär)

- #14654: Fix non-exhaustive directive rule in lexer.

(Antonin Décimo, review by Martin Jambon and Gabriel Scherer)

### Build system:

### Bug fixes:

- #14492: Fix Obj.dup on closures.

(Mark Shinwell and Nick Barnes, review by Gabriel Scherer and Damien Doligez)

- #14500: Fix CFI information emitted for s390x architecture. This helps

debuggers to unwind the stack correctly and print accurate backtraces

for OCaml code.

(Tim McGilchrist, review by Miod Vallat, Zane Hambly and Olivier Nicole)

OCaml 5.5.0

-----------

(Changes that can break existing programs are marked with a "*")

### Language features:

* #14009: infix extension points/attributes appearing in local structure items,

eg `let module%foo[@bar] ... in ...` are attached to the AST node of the

corresponding structure item (similar to their global counterparts) and no

longer to the enclosing `let` expression. Extension points/attributes that

are to be attached to the enclosing `let` expression are to be written next to

the `let` keyword, eg `let%foo[@bar] module ... in ...`. The same holds for

`let exception` and `let open`.

(Nicolás Ojeda Bär, review by Gabriel Scherer)

- #14029: Recognize `%identity` as nonexpansive

(Stephen Dolan and Olivier Nicole, review by Hugo Heuzard, Jacques Garrigue,

Jeremy Yallop, and Gabriel Scherer)

* #13712: Introduce a new kind `Type_external` and syntax

`type t = external "name"` to discriminate external types from other types

and each other. This PR turns primitive types into external and removes the

past behavior of discriminating abstract types defined in the current module.

(Takafumi Saikawa, Jacques Garrigue, review by Richard Eisenberg)

- #13806: Enable the use of function parameters with polymorphic types.

(Ulysse Gérard, Leo White, review by Florian Angeletti, Samuel Vivien, Gabriel

Scherer and Jacques Garrigue)

- #14040: generalize the constructs `let module`, `let exception` and `let open`

to most other structure items, eg `let type t = ... in ...`, `let type t +=

... in ...`, etc.

(Nicolás Ojeda Bär, review by Valentin Gatien-Baron)

- #14692: Allow unparenthesized application expressions in record update syntax

(Stephen Dolan, review by Damien Doligez)

### Runtime system:

- #14469: Make continuation objects have one field instead of two.

(KC Sivaramakrishnan, review by Olivier Nicole, Tim McGilchrist, Zane Hambly

and Ali Caglayan)

- #14416: Spawned domains will record backtraces if the parent domain has

enabled it.

(Nathan Taylor, review by Gabriel Scherer)

- #13616: Change free list representation in shared heap

(Sadiq Jaffer, review by Damien Doligez)

- #13580: Introduce sweep-only phase at start of major GC cycle,

to reduce latent-garbage delay and therefore improve GC performance.

(Stephen Dolan and Nick Barnes, review by KC Sivaramakrishnan)

- #14123: Fix integer-overflow problems in heap compaction.

(Nick Barnes, review by Antonin Décimo).

- #14035: Fix the alignment of _Atomic long long unsigned int fields

before GCC 11.1 on i686. Silence GCC note on newer versions.

(Antonin Décimo, review by Sadiq Jaffer)

- #13574, #13594: Generational scanning of stack frames for ARM 64 bits, POWER,

and RISC-V. This reduces minor GC work in the presence of deep call stacks.

(Xavier Leroy, review by Miod Vallat, Gabriel Scherer and Olivier Nicole)

- #14053: Statmemprof: it is now possible to replace a profile in the

current domain without stopping it in all domains.

Added the function [Gc.Memprof.is_sampling].

(Guillaume Munch-Maccagnoni, review by Gabriel Scherer)

- #14168: restore the stack size statistic in `Gc.stat` and adds a new

`live_stacks_words` field tracking the total size in words of live stacks.

(Florian Angeletti, review by Gabriel Scherer)

- #14189: Add runtime counters EV_C_MINOR_PROMOTED_WORDS and

EV_C_MINOR_ALLOCATED_WORDS. EV_C_MINOR_PROMOTED_WORDS reports words promoted

by minor GC and EV_C_MINOR_ALLOCATED_WORDS reports words allocated by minor

GC. Both have equivalent bytes counters. Also updated the documentation for

EV_C_MINOR_PROMOTED and EV_C_MINOR_ALLOCATED to qualify scope of the values

reported as being per-domain.

(Tim McGilchrist, review by Nick Barnes, Sadiq Jaffer and

Gabriel Scherer)

* #14243: Explicit relative paths in ld.conf (".", "..", "./<path...>",

"../<path...>") are interpreted as being relative to the directory ld.conf

was loaded from, and the default ld.conf now uses relative paths, rather than

embedding the absolute path to the Standard Library. The brave may continue to

put implicit paths in ld.conf. The interpretation of CAML_LD_LIBRARY_PATH is

unaltered. Additionally, ld.conf is loaded from all of $OCAMLLIB/ld.conf,

$CAMLLIB/ld.conf and standard_library_default/ld.conf rather than just the

first one found. ld.conf files with CRLF line endings are now consistently

normalised on both Windows and Unix.

(David Allsopp, review by Jonah Beckford, Damien Doligez and Hugo Heuzard)

- #14244: Added --with-relative-libdir which allows the runtime and the

compilers to locate the Standard Library relative to where the binaries

themselves are installed, removing the absolute path previously embedded in

caml_standard_library_default. Executables linked with `ocamlc -custom` now

always attempt to load bytecode from the executable itself, rather than first

trying `argv[0]`.

(David Allsopp, review by Jonah Beckford, Antonin Décimo, Damien Doligez,

Samuel Hym and Vincent Laviron)

- #14245: Introduce Runtime IDs for use in filename mangling to allow different

configurations and different versions of the runtime system to coexist

harmoniously on a single system. The IDs are used, along with the host

triplet, to provide mangled names for the ocamlrun executable and its variants

and the DLL versions of both the bytecode and native runtimes, with symlinks

created for the original names. They are also used to mangle the names of stub

libraries so that stub libraries compiled for a given configuration of the

runtime will only be sought by that runtime. The behaviour is disabled by

configuring with --disable-suffixing.

(David Allsopp, review by Damien Doligez and Samuel Hym)

- #12269, #12410, #13063: Fix unsafety, deadlocks, and/or leaks should

rare errors happen during domain creation and thread

creation/registration.

(Guillaume Munch-Maccagnoni, review by Gabriel Scherer, B. Szilvasy,

Miod Vallat)

- #14275: Add function caml_c_thread_register_in_domain, which makes it

possible to register "C threads" in another domain than 0 (which is

what caml_c_thread_register does). The function takes a domain unique

ID in which to register the thread. The domain must be running

when the function is called.

(Jack Nørskov Jørgensen, review by Gabriel Scherer,

Guillaume Munch-Maccagnoni)

- #14337: Fix potential segfault due to the C callback mechanism dropping

continuations without calling `caml_continuation_use`.

(Max Slater, review by Nick Barnes and Stephen Dolan)

- #13416: Implement concurrency primitives using WinAPI instead of

winpthreads on Windows.

(Antonin Décimo, review by Samuel Hym, Gabriel Scherer, Miod Vallat,

B. Szilvasy, and Nicolás Ojeda Bär)

- #14367: Gc.Tweak mechanism to allow named GC parameters

(Stephen Dolan and Nick Barnes, review by Gabriel Scherer, David Allsopp and

Antonin Décimo)

- #14461: Fix racy socketpair on Windows. Address-in-use errors would sometimes

occur when concurrent threads or processes were trying to create socketpairs.

(Jessie Grosen, review by Antonin Décimo and Nicolás Ojeda Bär)

- #14365: Add an Idle phase to the GC for better performance on small

heaps and for a smooth start at program launch and after a forced major GC.

(Damien Doligez, review by Stephen Dolan and Nick Barnes)

### Code generation and optimizations:

- #14583: fix bug in linear scan spilling heuristic that in certain situations

could lead to miscompilations.

(Nicolás Ojeda Bär, review by Vincent Laviron)

### Standard library:

- #14437: Add String.split_{first,last,all} and String.rsplit_all

(Daniel Bünzli, review by Nicolás Ojeda Bär and Florian Angeletti)

- #14436: Add String.replace_{first,last,all}

(Daniel Bünzli, review by Nicolás Ojeda Bär, Ali Caglayan and

Florian Angeletti)

- #13343: Add Array.stable_sort_sub

(François Pottier, review by Gabriel Scherer, Corentin Leruth and Nicolás

Ojeda Bär)

- #14439: Add String.includes

(Daniel Bünzli, review by Nicolás Ojeda Bär and Olivier Nicole)

- #10177: Seq.(delay : (unit -> 'a t) -> 'a t)

(Gabriel Scherer, review by Jeremy Yallop and François Pottier)

- #14381: Add String.find_{first,last}_index, String.find_{first,last},

String.[r]find_all.

(Daniel Bünzli, review by Nicolás Ojeda Bär, Ali Caglayan and

Florian Angeletti)

- #14438: Add String.is_empty

(Daniel Bünzli, review by Nicolás Ojeda Bär and Gabriel Scherer)

- #14440: Add String.of_char

(Daniel Bünzli, review by Nicolás Ojeda Bär and Gabriel Scherer)

- #14362: Add String.{drop,take,cut}_{first,last}_while

(Daniel Bünzli, review by Nicolás Ojeda Bär and David Allsopp)

- #14363: Preserve the backtrace at exceptional domain termination. Domain.join

on an exceptionally terminated domain re-raises the exception with the

backtrace.

(KC Sivaramakrishnan, report by Nathan Taylor, review by Gabriel Scherer,

David Allsopp)

- #13372: New Format and Printf printf-like functions that accept a

heterogeneous list as arguments.

(Leonardo Santos, review by Florian Angeletti and Gabriel Scherer)

- #14352: Add String.{drop,take,cut}_{first,last}.

(Daniel Bünzli, review by David Allsopp, Nicolás Ojeda Bär and

Vincent Laviron)

- #14185: List.split_map

(Jeremy Yallop, review by Daniel Bünzli, Nicolás Ojeda Bär and Damien Doligez)

- #13728: Add Sys.runtime_executable containing the full path (if available) to

the currently executing runtime.

(David Allsopp, review by Nicolás Ojeda Bär and Daniel Bünzli)

- #13916: Add Option.product and Option.Syntax.

(Nicolás Ojeda Bär, review by Daniel Bünzli, Gabriel Scherer and David

Allsopp)

- #13995: Add Option.blend.

(Kate Deplaix, review by Daniel Bünzli, Gabriel Scherer,

Nicolás Ojeda Bär, Florian Angeletti and Josh Berdine)

- #14043, #14393: Lazy.Mutexed: simple mutex-protected lazy thunks,

that may block the entire domain/thread on initialization races.

(Gabriel Scherer, suggestion by Kate Deplaix and Pierre Chambart,

review by KC Sivaramakrishnan, Florian Angeletti, Kate Deplaix

and Daniel Bünzli)

- #14086: Add Domain.count.

(Nicolás Ojeda Bär, review by David Allsopp, Gabriel Scherer, Daniel Bünzli

and KC Sivaramakrishnan)

- #13920: add Option.{for_all, exists}

(Gabriel Scherer, review by Kate Deplaix, Nicolás Ojeda Bär, Richard Eisenberg

and Jeremy Yallop)

- #12877: Dynarray.rev_iter, Dynarray.rev_iteri

(Gabriel Scherer, review by Léo Andrès, Jeremy Yallop and Nicolás Ojeda Bär)

- #14118: Add {Set,Map}.S.is_singleton

(Kate Deplaix, review by Daniel Bünzli, Vincent Laviron, Nicolás Ojeda Bär

and Stephen Dolan)

- #14060: Add Hashtbl.find_and_replace and Hashtbl.find_and_remove.

(Sacha-Élie Ayoun, review by Nicolás Ojeda Bär and Gabriel Scherer)

- #14227: Add List.filter_mapi.

(Émile Trotignon, review by Nicolás Ojeda Bär, Jan Midtgaard and

Damien Doligez)

- #14084: Future-proof Dynarray implementation against a smarter compiler

(Basile Clément, review by Gabriel Scherer)

- #14432: Add floor division, ceil division, Euclidean division and remainder

to the Int, Int32, Int64 and Nativeint modules.

(Xavier Leroy, review by Ali Caglayan, Nicolás Ojeda Bär, Gabriel Scherer)

- #13101: Add `Fun.todo ()` to signal that a piece of code is not yet

implemented.

(Pavlo Khrystenko and Olivier Nicole, review by Daniel Bünzli, Yawar Amin,

Gabriel Scherer)

- #14433: Add bit-counting functions `leading_zeros`, `leading_sign_bits`,

`trailing_zeros`, `bit_count`, `unsigned_bitsize`, `signed_bitsize`

to Int, Int32, Int64, and Nativeint

(Xavier Leroy, review by Ali Caglayan and David Allsopp)

### Type system:

* #13681, #13682, #13683, #13684, #13275 :

Introduce a new type `(module M : S) -> t[M]` that corresponds to

module-dependent functions (aka modular explicits).

(Samuel Vivien review by Leo White, Gabriel Scherer, Florian Angeletti,

Jacques Garrigue and Stephen Dolan)

- #13781: Set scope of internal type nodes during abbreviation expansion

rather than recursing during unification.

(Jacques Garrigue, review by Gabriel Scherer)

* #14066: catch invalid aliases introduced by signature constraints during

merging rather than in subtyping:

```ocaml

module X = struct end module F (_:sig end) = struct end

module type T = (sig module X0 : sig end module X1 = X0 end)

with module X0 := F(X)

```

Before, it failed with a subtyping error. Now, it fails with a proper error,

explaining that `X1` would keep an invalid alias to `F(X)`

(Clement Blaudeau, review by Florian Angeletti)

* #14100: Do not ignore type-constraints and module-constraints when building

the approximated signature of recursive modules. Ignoring those constraints

resulted in incorrect (wrong set of fields, wrong shadowing between fields)

approximated signatures, failing to typecheck, as in:

```ocaml

module X0 : sig type t end

module rec X : ((sig module A : sig end end) with module A := X0)

and Y : sig type t = X.A.t end (* Unbound type constructor X.A.t *)

```

Now, type and module constraints are properly merged during approximation ,

reusing the infrastructure for normal merging of constraints, but disabling

any wellformedness check.

(Clement Blaudeau and Ryan Tjoa, review by Florian Angeletti)

- #14327: Allow retyping as-patterns that contain existentials

(completing #14229)

(Jacques Garrigue and Takafumi Saikawa, reported by Olivier Nicole,

review by Gabriel Scherer)

- #14483: Reset type ID and level counters between compilations to restore

reproducibility of debug information between `ocamlc -c foo.mli foo.ml` versus

`ocamlc -c foo.mli; ocamlc -c foo.ml`. Also hashcons the identifiers used for

persistent structures across resets of the type checker. In particular, that

means the initialisation of globals in Matching do not become observable in

the marshalled output.

(David Allsopp, review by Gabriel Scherer)

- #14434, #14652: Protect check_counter_example_pat against polymorphic types,

restoring type soundness.

(Stephen Dolan and Jacques Garrigue, report and review by Alistair O'Brien)

### Other libraries:

- #13700, #14454: Use POSIX thread-safe getgrnam_r, getgrgid_r, getpwnam_r,

getpwuid_r, gmtime_r, localtime_r, getlogin_r, and fix mktime error checking.

(Antonin Décimo, review by David Allsopp, Stefan Muenzel, and Miod Vallat)

- #14406: Better handling of address length for unix sockets, improving Haiku

compatibility.

(Sylvain Kerjean, review by Antonin Décimo and Nicolás Ojeda Bär)

* #14046: On Windows, `Unix.kill pid Sys.sigkill` causes the receiving process

to exit with code ERROR_PROCESS_ABORTED (1067) instead of 0.

(Nicolás Ojeda Bär, review by Miod Vallat, Antonin Décimo and David Allsopp)

- #14020: Add Unix.unsetenv.

(Nicolás Ojeda Bär, review by Antonin Décimo and David Allsopp)

- #13447: Symmetrize shared `Sys` and `Unix` functions. Apply fixes

of #12072, #12184, #12320, and #13166, from `Sys.rename` to

`Unix.rename`. Make `caml_sys_close` raise on error, allowing

`Filename.temp_file` retries if close fails. Flush buffers when

calling `caml_sys_system_command` on Windows. Error with EINVAL

instead of ENOENT if the command string is not a valid C string.

(Antonin Décimo, review by Gabriel Scherer and Nicolás Ojeda Bär)

- #14310: Deprecate union sock_addr_union for struct sockaddr_storage

and socklen_param_type for socklen_t.

(Antonin Décimo, review by Nicolás Ojeda Bär, David Allsopp and Samuel Hym)

- #14391: unload native dynlinked objects when an error occurs and it is safe to

do so. (Fixes #14323)

(Nicolás Ojeda Bär, review by Vincent Laviron)

### Tools:

- #14055: Invert BUILD_PATH_PREFIX_MAP in directories loaded at startup

by the debugger.

(Pierre Boutillier, review by Gabriel Scherer and Daniel Bünzli)

* #13638: ocamlmklib exits with code 4 if passed an unrecognised option, as it

does with an unrecognised file.

(David Allsopp, review by Antonin Décimo and Sébastien Hinderer)

- #13941, #13961: Fix `ocamltest` variable handing.

(Damien Doligez, report by Olivier Nicole, review by Gabriel Scherer)

- #13962: Little ocamltest refactors. Fix error handling in C code,

leaking file descriptors, code style.

(Antonin Décimo, review by Gabriel Scherer)

- #14059: Fix flaky TSan tests

(Fabrice Buoro and Olivier Nicole, review by Gabriel Scherer)

- #13966, #13969: Enable "generalized polymorphic #install_printer"

in the debugger

(Pierre Boutillier and Gabriel Scherer, review by Florian Angeletti)

- #14063 : Debugger fallbacks to "looking for 'module_name'.ml in the

loadpath" when seeking source files. It improves hit rate for

sources of installed packages.

(Pierre Boutillier, review by Gabriel Scherer)

- #14032, #14034: Update to and require FlexDLL 0.44.

(Jan Midtgaard, Antonin Décimo, review by David Allsopp)

- #14239: Fix `#show_constructor` when printing non-GADT type parameters

(Takafumi Saikawa, Jacques Garrigue, review by Gabriel Scherer)

- #14245: ocamlobjinfo now displays the runtime invoked by a bytecode

executable (either from the RNTM section or by analysing the shebang lines)

(David Allsopp, review by Damien Doligez and Samuel Hym)

- #14448: ocamllex now prints a `missing-case` warning and shows an example

of nonmatching input if a rule is not exhaustive (Martin Jambon,

review by David Allsopp and Gabriel Scherer)

### Manual and documentation:

- #14684: Improve ocamlopt's manual page

(Samuel Hym, review by Florian Angeletti)

- #14397: Improve documentation of type-directed disambiguation of array

literals (Alicia Michael, review by Olivier Nicole and Florian Angeletti)

- #14293: Improve documentation of Runtime_events.Timestamp (Raphaël Proust,

review by Gabriel Scherer)

- #13747: Document support for native debugging with GDB and LLDB.

(Tim McGilchrist, review by Daniel Bünzli, Samuel Hym, Olivier Nicole

and Antonin Décimo)

* #13975: documented the `[@remove_aliases]` built-in attribute for signatures

(introduced by #1652 in 2018). Small refactor of the code that fetches the

attribute.

(Clement Blaudeau, review by Gabriel Scherer)

- #14002: Add anchors to items and headings of the web version of the API

documentation for easier linking.

(Nicolás Ojeda Bär, report by Louis Roché, review by Gabriel Scherer and

Florian Angeletti)

- #14023: Add documentation for the [row_more] function.

(Richard Eisenberg, review by Jacques Garrigue)

- #14038: Fall back immediately to user-agent-defined fonts when web fonts

fail to load.

(toastal)

- #14048: document modular explicits

(Gabriel Scherer, review by Samuel Vivien, Ali Caglayan,

Didier Remy and François Pottier)

- #14077: Add missing `item-attribute` rule for `let-binding`s in documentation

for attributes.

(Shon Feder)

- #14228: Trim leading spaces from first lines of LaTeX `ocamldoccode`

environments.

(Yukai Chou, review by Nicolás Ojeda Bär)

- #14248: Added documentation about the way `Domain.join` triggers a

`Thread.join` on the domain's systhreads.

(Raphaël Proust, review by Gabriel Scherer)

- #14392: Fix AsciiDoc files, add more markup, xrefs, documentation.

(Antonin Décimo, review by Gabriel Scherer and David Allsopp)

- #13590: Document automatic command-line expansion of `*` and `?` wildcards by

the runtime under Windows.

(Benjamin Sigonneau, review by Nicolás Ojeda Bär)

### Compiler user-interface and warnings:

- #12628: Improved error message for unsafe values: print out the full path for

the value that is unsafe when they are detected during the compilation of

recursive modules.

(Shivam Acharya, review by Gabriel Scherer and Florian Angeletti)

- #13994: documentation for external types

(Gabriel Scherer, review by Jan Midtgaard, Jacques Garrigue

and Florian Angeletti)

- #14076, 14111: error messages, add a short explanation for mismatched

universal variables and universal quantifications.

(Florian Angeletti, review by Gabriel Scherer)

- #14126: Document the `-i-variance` option and `+-`, `-+` variance indicators

in the reference manual.

(Takafumi Saikawa, review by Florian Angeletti)

- #14146: add an error message for external declaration with

a non-syntactic arity

```

external fail: (int -> int as 'a) -> 'a = "%identity"

```

rather than failing with an internal error.

(Florian Angeletti, review by Gabriel Scherer)

- #14147: print row types in error messages when they are a type constructor,

e.g. `< foo : int; .. as $0>` when $0 is introduced by a GADT constructor

(Stefan Muenzel, review by Jacques Garrigue and Florian Angeletti)

- #14190: `ocaml -e` now also processes `-init` (previously it was ignored).

(Emile Trotignon, review by David Allsopp and @ygrek)

- #14225: do not raise unused-constructor warning on private

constructor in type implementations, for example

`type safe = private Safe`, which are typically used to

create new fresh/generative types (here `safe`) to be used

as GADT indices.

(Gabriel Scherer, review by Nicolás Ojeda Bär and Florian Angeletti,

report by Kate Deplaix)

- #14244: Add -set-runtime-default option to the compiler, allowing the default

value of the Standard Library location used by the runtime to be overridden.

(Antonin Décimo, review by David Allsopp, Jonah Beckford, Damien Doligez and

Samuel Hym)

- #14245: New option -launch-method for ocamlc allows the method used by a

tendered bytecode executable to locate the interpreter to be given explicitly.

In particular, it makes it easier to specify the use of the executable

launcher on Unix. New option -runtime-search extends the bytecode executable

header to be able to search for the runtime interpreter in the directory

containing the executable and in PATH rather than relying on a single

hard-coded path.

(David Allsopp, review by Damien Doligez and Samuel Hym)

- #14315: enable -i-variance also for classes and extension constructors,

and add description of -i-variance in manpages

(Takafumi Saikawa, review by Florian Angeletti and Jacques Garrigue)

- #14373: remove the OCAML_BINANNOT_WITHENV environment variable, and

always strip typing environment in cmt files

(Florian Angeletti, review by David Allsopp)

- #14330: add suggestions when a signature mismatch is likely to be be caused by

spellchecking mistakes, for instance

```

module M: sig type albatross end = struct type albatros end

```

(Malo Monin, Florian Angeletti, review by Gabriel Scherer)

### Internal/compiler-libs changes:

- #13839, #14008: Reimplement `let open`, `let module` and `let exception` in

terms of a single construct.

(Nicolás Ojeda Bär, review by Gabriel Scherer, Samuel Vivien, Ulysse Gérard

and Vincent Laviron, temporary regression reported by Antonio Monteiro)

- #13911, #14117, #14127: Refactor the merging of signature constraints, by

splitting the monolithic merge function into separate, specialized functions

(for merging types, modules and module types) - sharing only the recursive

part for handling deep constraints.

(Clement Blaudeau, review by Florian Angeletti and Samuel Vivien, fix by Ryan

Tjoa)

- #13980 Refactor `type-approx` and improve some errors' locations.

(Leo White, Ulysse Gérard, review by Samuel Vivien and Florian Angeletti)

- #14024: Fix unterminated-string-initialization warnings from the C compiler.

(Antonin Décimo, review by David Allsopp and Miod Vallat)

- #14094: toplevel, simplify check on installed printer types

(Florian Angeletti, review by Gabriel Scherer)

- #13656, #14114, #14308: Use C99 stdint.h/inttypes.h fixed-width

integer types and macros to define OCaml integers.

(Antonin Décimo, review by Nick Barnes and David Allsopp)

- #14148: Remove an unused field from package_type in typedtree

(Samuel Vivien, review by Gabriel Scherer)

- #14141: Rename cstrs to constraints when it refers to constraints to avoid

confusing it with constructors.

(Stefan Muenzel, review by Nicolás Ojeda Bär)

- #14149: Distinguish `(module M : S)` from `(module M) : (module S)` in

patterns.

(Samuel Vivien, review by Gabriel Scherer)

- #14161: refactor the STW-participants machinery to add an intermediate

category of 'parked' domain structures.

(Gabriel Scherer, review by Sivaramakrishnan)

- #14198 Constraints on module unpacking are not ghost

(Thomas Refis, review by Nicolás Ojeda Bär)

- #14243: ocamlc now uses the same code as the runtime to parse ld.conf (via a

C primitive), eliminating some highly obscure corner cases.

(David Allsopp, review by Jonah Beckford, Damien Doligez and Hugo Heuzard)

- #14260: Refactor Lambda.structured_constant to avoid duplicate

representations for string constants

(Vincent Laviron, review by Nicolás Ojeda Bär and Gabriel Scherer)

- #13913: Use Blake128 as the hash function for the compiler's CRCs

(Vincent Laviron, review by Xavier Leroy and Gabriel Scherer)

- #14297, #14299: Avoid iterating on hash tables to produce types or terms

(Vincent Laviron, review by Nicolás Ojeda Bär and Gabriel Scherer)

* #14322: Remove leftover hacks for handling pattern constraints

As a side effect, `let rec (_ as x) = ...` is now always rejected instead of

being treated as equivalent to `let rec x = ...`

(Vincent Laviron, review by Alistair O'Brien and Florian Angeletti)

- #14331: Enforce current_level <= generic_level, and explain create_scope

(Jacques Garrigue and Takafumi Saikawa, review by Gabriel Scherer)

* #14388: Remove support for `let rec (module M : S) = e1 in e2`.

(Alistair O'Brien, review by Vincent Laviron and Gabriel Scherer)

- #14413: Introduce and use the C2y countof operator.

(Antonin Décimo, review by David Allsopp)

- #14422: Refactoring an `if match e with p1 -> true | p2 -> false then ...`

into a match in typetexp.

(Samuel Vivien, review by Gabriel Scherer)

- #13224: Clarify barriers and spin macros with delayed expansion.

(Antonin Décimo, review by David Allsopp and Gabriel Scherer)

- #14435, #14455, #14550: Add the not-root builtin ocamltest action. This

allows to skip tests that fail if the current user is root (superuser).

(Kate Deplaix, review by Gabriel Scherer, Nicolás Ojeda Bär, and

Antonin Décimo)

- #14457: Handle qualified `M.{ x }` patterns in untypeast

(Basile Clément, review by Florian Angeletti)

- #14120, #14474, #14476: Associate Uids to items that don't have a concrete

definition

(Ulysse Gérard, review by Florian Angeletti and Gabriel Scherer)

- #14394: Refactor `type_let` into `type_let_nonrec` and `type_let_rec`.

(Alistair O'Brien, review by Samuel Vivien)

### Build system:

- #13705, #14444: Cache test results of custom Autoconf tests from aclocal.m4.

(Antonin Décimo, review by David Allsopp and Miod Vallat)

- #13810: Support build of cross compilers to native freestanding targets

(Samuel Hym, review by Antonin Décimo and Romain Calascibetta)

- #14243: New configure option --with-additional-stublibsdir allows an

additional directory to be added to the start of ld.conf. Additionally, the

stublibs subdirectory is no longer created, nor added to ld.conf, when

building OCaml with --disable-shared.

(David Allsopp, review by Jonah Beckford, Damien Doligez and Hugo Heuzard)

- #14244: When targeting native Windows on Cygwin or MSYS2, preserve

backslashes in the supplied `--prefix` (in particular, backslashes instead of

slashes will then be displayed by `ocamlopt -config-var standard_library`).

If the supplied prefix contains a slash, then it is normalised, as

previously.

(David Allsopp, review by Jonah Beckford, Antonin Décimo, Damien Doligez and

Samuel Hym)

- #14245: New --enable-runtime-search configure option controls the

-runtime-search option used to build the bytecode binaries in the compiler

distribution. --enable-runtime-search-target controls the default value of

-runtime-search used for bytecode executables produced by the compiler.

(David Allsopp, review by Damien Doligez and Samuel Hym)

- #14484: Set `_WIN32_WINNT` to require Windows 8/Server 2012 Windows header SDK

support.

(Antonin Décimo, review by David Allsopp)

### Bug fixes:

- #14010: Fix miscompilation / liveness errors for string operations

(Mark Shinwell, Xavier Clerc, review by Xavier Leroy and Gabriel Scherer)

- #14036: Fix nontermination of cycle printing in recursive modules with

`-short-paths`. Add error message for types considered abstract while

checking recursive modules.

(Brandon Stride, review by Florian Angeletti)

- #14065: Fix function signature mismatch of `__tsan_func_exit` with GCC 15.

Check in the configure step if the TSan provided internal builtins are the

same as what we expect, introduce `caml_tsan_*` wrappers for the `__tsan_*`

functions we use.

(Hari Hara Naveen S, report by Hari Hara Naveen S,

review by Gabriel Scherer, Antonin Décimo, Olivier Nicole)

- #14071: Fix exception name in Dynlink.Error printer.

(Etienne Millon, review by Nicolás Ojeda Bär)

- #13853: Format breaks some line too early when there

is a break hint at the end.

(Florian Angeletti, review by Gabriel Scherer)

- #10570: Fix handling of caml_sys_argv when exposed directly as an

external

(Keryan Didier, review by Vincent Laviron and Gabriel Scherer)

- #14155: Audit unexecuted phrases in compiler expect tests and

fix all occurrences

(Stefan Muenzel, review by Gabriel Scherer)

- #14163, #14176: add a filename location to the deprecation alert for implicit

uses of libraries bundled with the compiler (unix,re,threads,dynlink)

(Florian Angeletti, report by Ali Caglayan, review by Gabriel Scherer)

- #14210: fix TSan-reported data race in weak pointers runtime

(Gabriel Scherer and Damien Doligez, report by Olivier Nicole,

review by KC Sivaramakrishnan)

- #14213: Fix shadow-stack-related crashes with TSan

(Olivier Nicole, report by Nathan Taylor, review by Gabriel Scherer and

Stefan Muenzel)

- #13658, #14181: Fix handling of recursive function types that can result

in an unbounded number of labeled or optional arguments.

(Stefan Muenzel, report by Samuel Vivien, review by Florian Angeletti)

- #13777, #14347, #14348, #14421, #14498, #14526: Test that C++

compilers can link with the OCaml runtime and include its headers.

(Antonin Décimo, review by David Allsopp and Gabriel Scherer)

- #14255: Fix TSan bug with C calls that take many arguments

(Olivier Nicole and Miod Vallat, report by Nathan Taylor, review by Gabriel

Scherer)

- #14230 : ocamltest fails to link test program with -custom in some cases

(Damien Doligez, review by David Allsopp)

- #14279: -dsource, preserve (mod) and other escaped infix keyword operators in

the printed source wherever possible.

(Florian Angeletti, review by Gabriel Scherer)

- #14300, #14304: fix a race between memprof and the minor GC, detected by TSan

(Gabriel Scherer, review by Stephen Dolan and Nick Barnes,

report by Olivier Nicole)

- #14384: use the statmemprof status word, rather than a distinguished

value of a boxed float, to identify a "not really sampling"

profile.

(Nick Barnes, review by Gabriel Scherer)

- #14332: Fix missing TSan instrumentation in subexpressions

(Vincent Laviron, review by Gabriel Scherer and Olivier Nicole)

- #14370, #14429: Fix headers for C++ inclusion.

(Antonin Décimo, review by Gabriel Scherer)

- #14417: Fix issue with nested packs on macOS.

(Vincent Laviron, report by Kate Deplaix, review by Gabriel Scherer)

- #14423: Fix detection of SetThreadDescription on 32-bit builds, meaning that

Thread.set_current_thread_name now works on 32-bit MSVC and uses the correct

mechanism on 32-bit mingw-w64.

(David Allsopp, review by Antonin Décimo)

- #14431: Enable native backend for DragonFly BSD. This builds ocamlopt on

DragonFly.

(Michael Neumann, review by Gabriel Scherer and Kate Deplaix)

- #14495: Fix infix-tag bug in the minor collector which could cause SEGVs

in multi-domain programs.

(Nick Barnes, review by Gabriel Scherer)

- #14519: Fix segfault when using `Runtime_events` under certain

circumstances due to bad error checking when calling `mmap()`.

(Mark Elvers, review by Nicolás Ojeda Bär)

- private: robustify intern.c

(Xavier Leroy and Nicolás Ojeda Bär, review by Olivier Nicole, Mindy Preston,

Edwin Török, and Gabriel Scherer)

- #13693, #14514: s390x: fix heap corruption with libasmrun_shared.so caused

by PLT lazy binding trampoline saving FPRs into OCaml's fiber stack.

Replace @PLT calls with GOT-indirect calls in the s390x code emitter.

(Zane Hambly, review by David Allsopp and Xavier Leroy)

- #14603, #14604: avoid Ctype.apply failures when mixing

polymorphic types and unboxed constructors.

(Gabriel Scherer and Stefan Muenzel, report by Brandon Stride,

review by Florian Angeletti)

- #14626: Handle module-dependent functions in warning 16 (Reported in #14622).

(Alistair O'Brien, review by Gabriel Scherer, report by Kate Deplaix)

- #14635: Fix a bug in `caml_floatarray_gather` that would cause

the result of `Float.Array.sub`, `Float.Array.append`, `Float.Array.concat`

(when empty) not to be equal to `[||]`.

(Marc Lasson, review by Gabriel Scherer)

- #14644, #14647: Fix a bug related to unhandled effects in bytecode.

(Vincent Laviron, report by Thibaut Mattio,

review by Nicolás Ojeda Bär, Stephen Dolan and Olivier Nicole)

- #14667: enable application related warnings for module-dependent functions

(Florian Angeletti, review by Gabriel Scherer)

- #14702: Fix hidden directory files leaking into the visible load path table.

When a hidden directory contained a file whose basename was already present,

the file could be incorrectly added to the visible table.

(Hugo Heuzard, review by Florian Angeletti)

OCaml 5.4.0 (9 October 2025)

----------------------------

(Changes that can break existing programs are marked with a "*")

### Language features:

- #13097: added immutable arrays (`'a iarray` type, Iarray stdlib module)

(Antal Spector-Zabusky and Olivier Nicole, review by Gabriel Scherer,

Jeremy Yallop and Vincent Laviron)

- #13340: Array literal syntax [| e1; ...; en |] can now be used to

denote values of type `'a array` and `'a iarray` and `floatarray`,

both in expressions and patterns. The compiler disambiguates each

case by using contextual type information (assuming `'a array`

by default).

(Nicolás Ojeda Bär, review by Richard Eisenberg, Jeremy Yallop, Jacques

Garrigue, and Gabriel Scherer)

- #13498: Tuple fields are now optionally labeled:

`(x:42, y:0)` and `let (~x, ~y) = ... in ...`.

(Ryan Tjoa and Chris Casinghino, review by Gabriel Scherer, Chris Casinghino,

and Leo White)

- RFCs#39, #13404: atomic record fields

`{ ...; mutable readers : int [@atomic]; ... }`

`Atomic.Loc.fetch_and_add [%atomic.loc data.readers] 1`

(Clément Allain and Gabriel Scherer, review by KC Sivaramakrishnan,

Basile Clément and Olivier Nicole)

### Standard library:

* #14124: Do not raise Invalid_argument on negative List.{drop,take}.

(Daniel Bünzli, review by Gabriel Scherer, Nicolás Ojeda Bär)

- #13696: Add Result.product and Result.Syntax:

`let open Result.Syntax in let* x = ... in ...`

(Daniel Bünzli, review by Gabriel Scherer, Nicolás Ojeda Bär)

- #12871: Add the Pqueue module to the stdlib. It implements priority queues.

(Jean-Christophe Filliâtre, review by Daniel Bünzli, Léo Andrès and

Gabriel Scherer)

- #13760: Add String.{edit_distance,spellcheck}