OCaml Changelog

Fixed

• Fix crashes when expanding module artifact pforms (%{cmi:...} etc.) with (include_subdirs qualified). Qualified modules can now be referenced by dotted logical paths such as %{cmi:Sub_a.Foo}. (#14498, #16214, fixes #14496, @Alizter, @anmonteiro)
• dune show targets now accepts build-only directories such as _build/default/.simple.objs. (#14664, fixes #13782, @Alizter)
• Reword the error raised when %{target} is used in a rule that omits the (target ...) (or (targets ...)) field, so it points at the missing field instead of mentioning "inferred rules". (#14668, fixes #12439, @Alizter)
• Fix watch mode on Windows by creating the file-watcher sync directory before using it, avoiding open(_build/.sync\0): No such file or directory when an RPC client requests a build. (#14678, fixes #14632, @rgrinberg)
• Add file watcher trace events for the Mac and Windows backends (#14722, @rgrinberg)
• Fix decoding coalesced MacOS file notification events. (#14725, @rgrinberg)
• Handle directory invalidations correctly in watch mode on MacOS (#14756, @rgrinberg)
• Update ctime when restoring from the shared cache in copy mode. This prevents the trimmer from deleting the file. (#14777, @rgrinberg)
• Allow the use of all the available variables in the (enabled_if) field in (executable ...) and (install ...) stanzas, similar to other stanzas like (library ...). (#14860, fixes #14789, @punchagan)
• Linux: dune will now wait for the process group to be dead after the group leader is dead. This tightens dune's policy for what constitutes a successful action. Actions for which dune cannot be clean up the process group will now fail. (@rgrinberg, #14868)
• Fix caching of package sources with symlinks by resolving symlinks after fetching the sources, similar to the directory symlinks resolution introduced in #13792 (#14871, fixes #14509, @punchagan)
• Fixed wrong suggestion for duplicate entries in conflicts field (#14956, fixes #14903, @Leonidas-from-XIV)
• Fix building Dune on Solaris/illumos by handling its wait4 semantics and retrying interrupted reads when spawning processes. (#14980, fixes #14182, @jperkin)
• Fix dune-rpc-lwt clients so disconnecting shuts down socket output without invalidating pending input reads, avoiding EBADF errors. (#14983, fixes #7624, @rgrinberg)
• Dune now restores dependency cutoffs concurrently when they were originally computed in parallel, instead of recomputing them one at a time. The cutoffs_that_reduce_concurrency_in_watch_mode setting, which existed to avoid this serialisation, is no longer needed and has been removed. (#15012, @snowleopard)
• Validate project module names before creating the project directory in dune init project, so aborted initializations no longer leave empty directories behind. (#15014, fixes #9963, @rgrinberg)
• Fix cram test output sanitization when the project path contains a space. Absolute paths are now rewritten to $TESTCASE_ROOT even when the path contains spaces, and lines with multiple paths have every path sanitized. (#15017, fixes #14943, @yussypu)
• Improve the error message for private libraries that cannot be dependencies of public libraries by mentioning the (package ...) field as an alternative to giving the private library a public name (#15070, fixes #10230, @rgrinberg).
• Clarify the module conflict error shown when a module is used in multiple stanzas. The message now explains implicit module ownership and lists all relevant stanza kinds (#15072, fixes #6598, @rgrinberg).
• Emit relative artifact references in installed dune-package files when using an absolute external DUNE_BUILD_DIR, avoiding build-directory-dependent archive and module paths (#15077, fixes #11774, @rgrinberg).
• Simplify away (when false _) expressions (encoded Nils) that previously survived inside concat and when forms, producing cleaner generated lock directories. (#15092, fixes #15090, @chizy7)
• Drop (when false _) arguments from run actions in generated lock directories instead of keeping them as no-op entries that were re-encoded as (when false ""). (#15128, fixes #15099, @chizy7)
• Make dune-configurator pass --personality to pkgconf only for version 1.7.0 and later. (#15142, fixes #11536, @dra27)
• dune utop now accepts an absolute path to a workspace directory instead of crashing with an internal error. (#15272, fixes #15108, @chizy7)
• Fix watch-mode status lines after source changes interrupt a build. Dune now shows the restart status while cancelling the current build and resumes the normal progress counter when the next build starts. (#15289, fixes #11134, @rgrinberg)
• Short-circuit AND and OR expressions in blang. This makes their evaluation lazy by default. (#15291, @Sudha247)
• Fix the %{ppx:ppx1+..+ppxn} form. Previously, it was just broken and pointed at the wrong binary (#15361, @rgrinberg)
• Remove ppx runtime dependencies from the list of dependencies provided via the root_module field. If such a runtime dependency is needed, it should be written in the libraries field. (#15419, @rgrinberg)
• Avoid rebuilding js_of_ocaml library archives on every invocation for interface-only and empty libraries. (#15427, @anmonteiro)
• Do not crash when ~/.config/dune is a file instead of a directory. Just pretend it doesn't exist (#15475, fixes #15406, @rgrinberg)
• Dune will now terminate all launched sub-processes even if it received SIGKILL itself (#15483, @rgrinberg)
• Account for ctime in stat based digest cache (#15495, @rgrinberg)
• $ dune install --dry-run now checks for non empty directories as part of its validation (#15501, @rgrinberg)
• Fix a target-less rule attached to multiple aliases ((rule (aliases a b) ...)) leaking unrelated contributions between those aliases. Building one alias no longer pulls in actions or dependencies that were added only to another of the rule's aliases. (#15581, @NatKarmios)
• Make dune pkg enabled query a running Dune RPC server, so it observes transient server-side --pkg enabled and --pkg disabled settings without trying to acquire the build lock (#15589, fixes #15587, @Alizter)
• Make generated MDX executables inherit link_flags from env stanzas. (#15614, fixes #15613, @Alizter)
• Return Unix errors from Fs_io.read_file rather than raising them. (#15641, @rgrinberg)
• Correct filesystem trace metrics for file writes and directory scans. (#15686, @rgrinberg)
• Preserve runtime-event ring IDs in Dune traces so consumers can distinguish interleaved event streams. (#15687, @rgrinberg)
• BREAKING CHANGE: in dune-project, (warnings (duplicate_deps ..)) requires a dune lang version of 3.22, instead of 3.18 (#15696, @v-gb).
• Preserve spaces in unquoted filenames when applying Git patches instead of truncating paths at the first space (#15781, @rgrinberg)
• Respect enabled_if on install stanzas when adding their files and directories to the @all alias. (#15895, fixes #15825, @aryemans)
• Fix Melange emission with installed libraries whose .cmj and .cmi files are stored in the melange object directory (#15949, fixes #14820, @anmonteiro)
• Reject package dependencies in named dependency bindings while decoding dependency fields, including for disabled stanzas. (#15966, @rgrinberg)
• Fix Merlin definition lookup for libraries with private modules (#15977, fixes #4892, @anmonteiro)
• Fix a crash when generating install rules for a Melange-only implementation of an installed virtual library (#16033, @anmonteiro)
• Prevent build cancellation from crashing Dune when macOS reports EPERM while signaling a process group (#16059, fixes #16053, @rgrinberg)
• Fix dune pkg outdated so it fails early with a clear user message if it is run when package management is not enabled. (#16065, @shonfeder)
• Fix watch mode builds remaining stale after the file watcher event queue overflows (#16068, fixes #16052, @rgrinberg)
• Reject Windows path separators in validated filename components (#16076, @rgrinberg)
• Preserve output following malformed ANSI escape sequences and erase-line controls (#16116, @rgrinberg).
• Resolve relative paths passed to dune ocaml top-module from the directory where Dune was started, allowing use from workspace subdirectories. (#16135, @rgrinberg)
• Allow dune ocaml top to accept absolute directory paths inside the workspace. (#16142, @rgrinberg)
• Allow Dune promotion commands to accept absolute source paths inside the workspace. (#16143, @rgrinberg)
• Allow dune describe workspace to accept absolute directory filters inside the workspace. (#16144, @rgrinberg)
• Reject empty module_systems fields in melange.emit stanzas instead of silently producing no JavaScript files (#16162, @anmonteiro)
• Sandbox PPX lint actions starting with Dune language 3.25 so linters cannot observe undeclared build targets. (#16176, @rgrinberg)
• Prevent diagnostic source locations at compact-position field boundaries from being truncated (#16180, @rgrinberg)
• Sandbox ocaml-mdx deps when using MDX extension 0.6 so dependency discovery cannot observe undeclared workspace inputs. (#16183, @rgrinberg)
• Fix missing Odoc generation of OxCaml parameter implementations (#16200, @art-w)
• Make Dune_rpc_lwt.V1.Action_plugin.read_directory_with_glob return an empty listing for absent directories (#16207, fixes #4445, @rgrinberg)
• Fix compiling Melange implementations of installed virtual libraries, both with and without binary annotations, including transitive private module dependencies (#16211, #16212, #16272, @anmonteiro)
• Run Ctypes stub generation in a sandbox and honor its declared dependencies. (#16223, @rgrinberg)
• Fix @opam failing to promote a generated opam file after it is deleted (#16234, fixes #16233, @Alizter)
• Rebuild generated Ctypes helpers when headers from Ctypes' implicit include directories change (#16243, @rgrinberg)
• Collect action-provided trace events when an action fails instead of dropping them during result validation. (#16250, @rgrinberg)
• Report the usual program-not-found error when a dynamic-run executable is missing instead of failing with an assertion. (#16251, @rgrinberg)
• Prevent rules with duplicate lock declarations from deadlocking by acquiring each lock only once. (#16252, @rgrinberg)
• Prevent concurrent action children from closing shared redirections before their siblings use them (#16257, @rgrinberg)
• Resolve relative paths in forwarded build, runtest, and exec commands from the client's directory instead of the RPC server's directory (#16267, @rgrinberg)
• (env (env-vars ...)) in a (context ...) stanza of dune-workspace now takes precedence over the root env stanza, as documented. This affects commands such as dune exec; rules already used the documented order. (#16290, @punchagan)
• Fix a crash when an opam filter is not a boolean (#16313, @art-w)
• Correct module paths for generated interfaces of nested qualified module groups. (#16322, @anmonteiro)
• Resolve %{cmi:...}, %{cmt:...}, and %{cmti:...} against Melange module sets when no OCaml module is selected, while preferring OCaml for modules selected in both modes. (#16339, @anmonteiro)
• Reject . and .. as melange.emit targets instead of raising an internal error (#16371, @anmonteiro)
• Validate custom toplevel names as filenames, reporting an error for empty names and avoiding crashes for names containing paths (#16373, @anmonteiro)
• Fix Menhir type inference with package-managed relocatable compilers on macOS by making the compiler standard library available in the sandbox (#16374, fixes #15642, @Alizter, @shonfeder)
• Reject invalid Menhir merge_into names during parsing to prevent internal errors (#16387, @anmonteiro)
• Reject conflicting module sources in unqualified directory groups, including generated sources, instead of silently discarding one (#16414, @anmonteiro)
• fix copying of directory targets on windows (#16434, @kentookura)
• Track local module dependencies used by Menhir's type inference so generated parsers and dependent modules build and rebuild correctly (#16447, fixes #14450, @anmonteiro)
• Fix Menhir type inference for qualified module group interfaces while keeping dependency lookup in terms of logical module names (#16464, #16489, #16497, fixes #8989, @anmonteiro)
• Fix intermittent crashes on Windows caused by unstable file descriptor hashing (#16476, fixes #16459, @Alizter)
• Explain that forwarded build requests require a watch-mode Dune server instead of reporting an internal RPC error. (#16486, fixes #16219, @Alizter)
• (deps (package ...)) now tracks installed files of lock-built packages and their package dependencies, rebuilding actions when they change. (#16507, @Alizter)
• Share Rocq plugin layout dependencies between discovery and compilation rules, reducing repeated dependency processing in unchanged builds. (#16622, @Alizter)
• Support directory dependencies in hardlink sandboxes by linking their files rather than the directories themselves (#16675, @Alizter).
• Fix recursive copy actions rejecting symbolic links, including file links created by symlink sandboxes (#16686, @rgrinberg).
• Fix copy sandbox failures caused by overlapping directory and file dependencies (#16806, fixes #16547, @Alizter)
• Fix Menhir inference producing invalid module paths for types imported from other modules (#16952, @anmonteiro)

Added

• Add (dirs ...) to (include_subdirs (mode qualified) ...), allowing qualified source directories to be renamed in the module path, including when bootstrapping. Mappings can use variables, including reads from generated files outside the qualified group (#13691, #16418, #16420, fixes #7605, @anmonteiro).
• Add opt-in action runners via --action-runner, and add --sandbox-actions to run eligible process-spawning actions in a bubblewrap-wrapped worker. (#14240, @rgrinberg)
• Add platform support for DragonFly BSD (#14774, fixes same issue with lev as seen on NetBSD in #14484, @mneumann).
• Added command, subcommand, and flag completion in the command line. Supported shells are bash, zsh, and pwsh. See dune completion [shell] --help. (#14779, @ElectreAAS)
• Add %{git-sha} variable that expands to the short git SHA of the current HEAD commit, or the empty string when git is unavailable or the workspace is not inside a git repository (#14810, @toots).
• Add a ?static optional argumentin Configurator.V1.Pkg_config.get to instruct pkg-config to get static linking options. (#14947, @raphael-proust)
• Only generate Melange rule for multi-mode libraries if melc is installed (#15021, @anmonteiro)
• Add Configurator.V1.Pkg_config.query_variable to query package variables through pkg-config --variable (#15078, fixes #3332, @rgrinberg).
• Add env_vars as an alias for the env-vars field in env stanzas (#15187, fixes #11424, @rgrinberg).
• Add @rocqproject alias to generate all `_RocqProject files (#15221, @rlepigre-skylabs-ai).
• Tab completion for dune promote now lists pending promotion files. (#15338, fixes #7254, @Alizter).
• Add build time information to watch mode (#15384, @rgrinberg)
• Added the missing dune tools exec utop and dune tools exec odoc options. (#15388, @Leonidas-from-XIV)
• Display build parallelism in watch mode. (#15390, @rgrinberg)
• Add process counts, system cpu, user cpu, and wall clock cpu times to trace events (#15401, @rgrinberg)
• Support --sandbox-actions on macOS using sandbox-exec. (#15500, @rgrinberg)
• Add fish to the shells supported by dune completion, enabling command, subcommand, and flag completion in the fish shell (#15515, fixes #15334, @chizy7)
• Display build duration and average process parallelism in the status line for batch builds. (#15564, @rgrinberg)
• Add a --split-public-names flag to dune describe workspace and dune describe external-lib-deps. When enabled, the name/names fields report only private names and a new public_name/public_names field reports the public names. (#15582, @natkarmios)
• Add a --include-empty flag to dune describe external-lib-deps to also print libraries that have no internal or external dependencies (#15585, @NatKarmios)
• Support qualified module references in fields such as per_module when using (include_subdirs qualified) (#15633, fixes #15578, @anmonteiro)
• Display the current build run at the end of watch-mode status lines. (#15673, @rgrinberg)
• Record per-build Memo compute, restore, and cycle-detection metrics in Dune traces. (#15698, @rgrinberg)
• Record discovered, validated, and failed rule counts in Dune traces. (#15701, @rgrinberg)
• Add %{melange.emit:...} to reference a Melange output directory and depend on its emitted files (#15751, @anmonteiro)
• Add (flags ...) to the ocamllex and ocamlyacc stanzas to pass custom options to parser generators. (#15907, @rgrinberg)
• Added an opt-in sat trace category emitting a sat/solve event with the SAT solver's stats (variables, clauses, decisions, conflicts) and duration. Enable with DUNE_TRACE=+sat. (#15923, @Alizter)
• Add dune ocaml inferred-mli to infer an interface with a module's build configuration and register it for promotion. (#16111, fixes #12727, @rgrinberg)
• Add --no-actions and --only-actions to dune trace cat to filter events collected from actions. (#16245, @rgrinberg)

Changed

• BREAKING CHANGE: Actions no longer see the shared install staging area (_build/install/<context>/{bin,lib,lib/stublibs}) on PATH, OCAMLPATH and CAML_LD_LIBRARY_PATH. An action's environment only contains the packages it declares with (deps (package <pkg>)) (and their library closure, see below). Actions that rely on packages being visible (such as tests that #require the package under test from an mdx block, steps that run ocamlfind, a nested dune build, or load a bytecode stub library) must now declare the package dependency explicitly. (#14373, #16617, @Alizter)
• (package <pkg>) now also includes the packages owning the library closures of libraries in workspace and installed packages. Installed packages reached through those closures also work with Dune language versions older than 2.9. (#14373, #16362, #16529, @Alizter, @anmonteiro)
• Extract the structural-hash accumulator into a new Stdune.Hash module and route Stdune.Tuple.T2.hash, Stdune.Tuple.T3.hash, Stdune.List.hash, Stdune.Result.hash, and Resolve.error_hash through it. Hashing these structural shapes no longer allocates per call. (#14542, @robinbb)
• Remove (using melange 0.1) in Dune 3.25 in favor of version 1.0 of the extension. (#14574, @anmonteiro)
• $ dune rpc build invocations no longer queue. All build requests are built in parallel. Watch servers started by $ dune exec --watch can now also handle forwarded build and runtest requests (#14954, @rgrinberg)
• Report rule build progress as the number of rules built against the total number of live rules, rather than rules executed against rules discovered during the current run. This affects both the status line and the progress reported over RPC. (#14985, @snowleopard, @pwhite)
• With --error-reporting=twice, print an ==== Error Summary ==== separator before the deterministic list of errors reported at the end of the build. The separator is omitted when there are no errors to report. (#15016, fixes #14757, @yussypu)
• Enable fuzzy patch application by default for Dune. This is similar to OPAM's behaviour, and this makes it easier for packages like OxCaml to build. (#15146, fixes #15145, @Sudha247)
• Odoc rules are now sandboxed (#15190, @rgrinberg)
• In watch mode, $ dune rpc build requests now complete as soon as their requested build finishes, instead of waiting for unrelated concurrent RPC build requests in the same build iteration. (#15191, fixes #13788, @rgrinberg)
• Cleanup all build processes spawned by dune before starting a fresh build on Linux. (#15239, #15274, @rgrinberg)
• Show partial output timed out cram tests (#15269, @rgrinberg)
• In watch mode, $ dune rpc build now exits with status 1 when the requested build fails. (#15341, @rgrinberg)
• Debounce file change events in watch mode (#15344, @rgrinberg)
• Align dune's C compiler vendor detection with the OCaml compiler's own identifiers (msvc, icc, mingw, clang, gcc, xlc, sunc), so more C compilers are recognized without emitting a spurious warning. (#15423, fixes #14870, @chizy7)
• Never use $ lsof for counting file descriptors, as it is not allowed to reap processes outside of the scheduler. We have better mechanisms on MacOS and Linux for counting file descriptors. So this is only an issue on other Unices. (#15477, @rgrinberg)
• dune describe workspace now reports an origin field for every module, indicating whether its source was written by hand (source), generated by a rule stanza (dune, with the generating dune file), produced by ocamllex, ocamlyacc, or menhir, or synthesised by dune itself for wrapping (wrapper). Generated modules point at the responsible file. The --with-origin-deps and --with-origin-deps-expanded flags additionally report the dependencies of a rule-generated module, as declared and expanded to concrete files respectively. (#15478, @nat-karmios)
• Numbers with unit now allow dropping the unit if the number is zero ("0"). For example, dune cache trim --trimmed-size 0 and dune cache trim --trimmed-size 0TiB are now both accepted and equivalent. (#15498, @reynir)
• Run artifact substitution in background workers. (#15559, @anmonteiro)
• dune describe now reports the public name of an executable (from public_name/public_names) instead of its private name when one is available, falling back to the private name otherwise. (#15582, @natkarmios)
• Calculate status-line build parallelism from process CPU time rather than wall-clock action time; Windows continues to use wall-clock time. (#15685, @rgrinberg)
• Use sha256 instead of md5 for source archives that lack a checksum (#15824, @shunueda)
• Starting with Dune language 3.25, restrict sandboxed actions on Linux systems with Landlock ABI 3 or newer from writing outside their sandbox, temporary directory, action-trace directory, and /dev. Set DUNE_CONFIG__LANDLOCK=disabled to opt out. (#15858, @rgrinberg)
• dune pkg lock now fails without writing a lock directory when any platform requested by solve_for_platforms cannot be solved, instead of producing a partial lock directory containing only the successful platforms. (#15981, @Alizter)
• Portable lock directories now select one package version across all requested platforms, and fail when no common version exists. (#15982, fixes #13645, fixes #13647, @Alizter)
• BREAKING CHANGE: Reject : in context names so they remain portable path components (#16085, @rgrinberg)
• Keep .t suffixes in cram test names, including aliases and applies_to, starting with Dune language 3.25 (#16146, @rgrinberg)
• Sandbox ocaml-mdx dune-gen when using MDX extension 0.6, available from Dune 3.25. (#16177, @rgrinberg)
• Sandbox pkg-config queries starting with Dune language 3.25 so they cannot observe undeclared workspace inputs. (#16178, @rgrinberg)
• Remove the experimental OCamlFDO integration, including the (fdo ...) workspace field (#16198, @rgrinberg)
• BREAKING CHANGE: Generated files are now read-only even with Dune language versions before 2.4, regardless of whether the shared cache is enabled. Executable permissions are preserved. (#16388, @rgrinberg)
• Make newly written shared-cache metadata files read-only to guard against accidental modification. (#16393, @rgrinberg)

Bug fixes

• #15045: Atomic loads whose results are unused should not be removed during dead-code elimination. (Xavier Clerc, review by Steven Dolan and KC Sivaramakrishnan)

• #15067, #15071: Fix detection of functions available in the future on macOS. (Antonin Décimo, review by Nicolás Ojeda Bär and Damien Doligez)

• #15112, OSEC-2026-22: Unix.map_file: protect against overflow when computing the data size. (Xavier Leroy and Nicolás Ojeda Bär, review by Nicolás Ojeda Bär and Edwin Török)

• #15113, OSEC-2026-21: Str.string_partial_match: make sure captured groups are valid. (Xavier Leroy, review by Nicolás Ojeda Bär and Edwin Török)

• #15115, OSEC-2026-23: Fix multiple issues in demarshaling (Marshal.from_{channel,string,bytes}) (Xavier Leroy, review by Nicolás Ojeda Bär)

• #15133, OSEC 2026-24: Multiple issues in command quoting on Windows (Xavier Leroy and Nicolás Ojeda Bär, review by Nicolás Ojeda Bär)

• #15119, OSEC-2026-25: Harden decoding of runtime events messages from ring buffers. (Sadiq Jaffer, report by Hannes Mehnert, review by Olivier Nicole and Edwin Török)

• #15177, OSEC-2026-26: Maintain custom events cache integrity. (Sadiq Jaffer, report by Hannes Mehnert, review by Edwin Török)

• #15043, #15076: runtime events library, fix an infinite loop when a user event is larger than half the ring buffer. (Tim McGilchrist, review by Sadiq Jaffer)

• #15185, #15187: fix a pattern-matching miscompilation on certain combinations of immediate ranges and redundant patterns (Gabriel Scherer, report by Alperer Keleş, review by Vincent Laviron and Florian Angeletti)

Bug fixes

Type system

• 14891, 14982: fix scope error leading to an erroneous typechecking for non-dependent application of module-dependent function in presence of dependent first-class module types:

  module type T = sig module type S end
  let f (module M:T) (m: (module M.S)) = m
  module type P = sig type 'a t end
  let error =
    f (module struct module type S = P end) (module List)
  

  (Florian Angeletti, report by Hazem ElMasry, review by Gabriel Scherer)

Runtime

• 14872: harden loading of bytecode executable files against corrupted or malicious files having 2^29 TOC entries or more. (Xavier Leroy, review by Nicolás Ojeda Bär)

• 15019, 15030, OSEC-2026-18: Marshal.from_{string,bytes}: guard against overflow in the computation of the total data length. (Xavier Leroy, report by Akshay Singh, review by Nicolás Ojeda Bär and Antonin Décimo)

• 14933: Respect sysconf(_SC_SIGSTKSZ) when choosing the size for the alternate signal stack, avoiding fatal errors when linked against musl libc on some Intel CPUs. (Nat Mote, review by Florian Angeletti and Miod Vallat)

• 14940, fix a memory leak in the OCaml runtime by bounding the size of the internal cache of stacks. (Vesa Karvonen, Florian Angeletti, review by Gabriel Scherer)

• 15029: Fix a regression on Windows where an OCaml thread that never yielded voluntarily would keep the runtime lock forever, so that the other threads of its domain never ran. Preemptive switching between systhreads had no effect; only explicit calls to Thread.yield or blocking sections would let other threads run. (Nicolás Ojeda Bär, report by Daniel Larraz, review by Antonin Décimo)

Build system

• 14883, 14884: fix Windows cross-compilation with older mingw32-gcc versions (Brian Ward, review by Antonin Décimo and Stefan Muenzel)

• 14871, 14914: Ignore OCAMLTOP_INCLUDE_PATH during the build. (David Allsopp, report by Andreas Rossberg, review by Florian Angeletti)

• 14901, 14923: Fix the generated installation script to cope with macOS's geriatric version of bash when executing in opam's sandbox. (David Allsopp, report by Julian Fondren and Sacha-Élie Ayoun, investigation and initial fix by Kate Deplaix, review by Florian Angeletti)

• 14989: Improve build reproducibility by letting only otherlibs/{str,unix} build their own .cmi and .cmx. The generic %.cmi/%.cmx rules of the root Makefile were racing with them under make -j and recorded a different source path, which changed the interface digest (and, through it, most other compiled artefacts) as well as the debug info packed into str.a and unix.a. (Bernhard M. Wiedemann, review by David Allsopp and Stefan Muenzel)

User interface

• 14881, 14882: fix printing of external types that are subject to module constraints. (Stefan Muenzel, review by Florian Angeletti)

Runtime events library

• 14966: add the missing EV_MINOR_EPHE_CLEAN constructor to Runtime_events.runtime_phase, introduced in 13643. The runtime has emitted this phase since 5.4, when a minor collection has to clean locked ephemerons, but the OCaml type had no constructor for it, so consumers were handed an out-of-range value and crashed when matching on it. (Tim McGilchrist, review by Florian Angeletti)

• 14969: Fix the units of the runtime events counter EV_C_MINOR_ALLOCATED_WORDS to report as the number of words of minor heap consumed, including headers. (Tim McGilchrist, review by Nicolás Ojeda Bär)

Fixed

• Fix an internal error (modules_and_obj_dir: failed lookup) when generating js_of_ocaml archive rules for a dune file that defines two libraries with the same name distinguished by mutually exclusive enabled_if clauses, as ocaml-re does for ppx_expect_common (#14904, fixes #14775, @vouillon)
• Fix passing environment variables to formatter actions (#15386, @anmonteiro)
• Fix missing source dependency in the sandbox when preprocessing Melange sources (#15395, @anmonteiro)
• Treat OCaml compiler packages version 5.5 or newer as relocatable so their installations do not use the toolchain cache (#15444, fixes #15443, @Alizter)
• Fix build_runtime_flags given in a js_of_ocaml/wasm_of_ocaml field of an executable being silently ignored in separate compilation mode: such executables were given the workspace-shared standalone runtime, which is built with the default flags. Executables customizing build_runtime_flags now get their own standalone runtime again. (#15455, @hhugo)
• Use installed filenames for local package binaries in %{bin:...} PATH layouts on Windows (#15518, fixes #15512, @Alizter)

Changed

• Revert sandboxing Melange rules by default in the (library ..) and (melange.emit ..) stanzas. In Melange libraries with many modules, sandbox creation / destruction dominates build time and adds significant overhead to build time (#15418, @anmonteiro)

Fixed

• Fix promotion failure when a target changes from a directory to a file between builds, causing "Is a directory" errors. (#14371, fixes #5647, fixes #6575, @Alizter)
• Make dune build @doc pick up an odoc installed via dune tools install odoc even without DUNE_CONFIG__LOCK_DEV_TOOL=enabled, mirroring how dune fmt consumes a locked ocamlformat (#14426, fixes #14235, @mt-caret)
• Reject (package ...) inside a named dependency binding ((deps (:name (package foo)))). Previously this was silently accepted but %{name} would resolve to an empty path list. (#14499, @Alizter)
• Fix incorrect dependency in the .cmxs build for libraries with mode-dependent foreign stubs: the rule depended on the byte stubs archive instead of the native one, so parallel builds could fail to find -l<lib>_stubs_native. (#14500, fixes #12964, @Alizter)
• Fix dune build failing with "No rule found" when lock_dir paths in dune-workspace contain a subdirectory (e.g. (path sub/dune.lock)). (#14524, fixes #14523, @Alizter)
• Artifact substitution repairs executable bit if it's not set correctly in the workspace (#14556, @rgrinberg)
• Ignore EINVAL when accepting sockets on MacOS (#14612, fixes #12660, @rgrinberg)
• Validate profile names. Profile names must be non-empty and can only contain letters, digits, _ and -. The name _ is reserved as a wildcard in (env ...) stanzas. (#14657, fixes #14630, @rlepigre)

Added

• Add %{pkg:<package>:<section>:<path>} pform for resolving package install files. Works with workspace packages, lock-file packages, and installed packages. (#14200, fixes #14193, fixes #3378, @Alizter)
• Enable the relocatable compiler by default for package management (#14357, fixes #14012, @Alizter)
• Add changed source files to the build-start trace event for watch-mode restarts, showing the paths that triggered the rebuild (#14396, @rgrinberg)
• Add dune's rusage information in start/finish build trace events (#14402, @rgrinberg)
• Add a status message for RPC clients that manage to connect (#14424, @rgrinberg)
• Allow blang expressions in the runtest_alias field in the cram stanza (#14425, @rgrinberg)
• Extend the stat based cache to cache the contents of directories and not just source files (#14469, @rgrinberg).
• Show the number of connected RPC clients in the watch mode status line (#14489, @rgrinberg)
• Promote directory targets from experimental to generally available in 3.24 (#14579, @rgrinberg)

Changed

• Use / as directory separator when appending local paths to external paths, making path construction consistent across platforms. (#14278, @Alizter)
• On Windows, normalise process paths to \ before passing them to CreateProcessW so that programs which scan argv[0] (notably cmd.exe) do not misparse mixed separators. (#14278, @Alizter)
• %{bin:NAME} now resolves to the build artifact path rather than the install staging path. Rules with %{bin:NAME} deps additionally get a per-rule .binaries directory prepended to the action's PATH, containing correctly-named symlinks for each declared bin pform dep. (#14432, fixes #3324, @Alizter)
• Replace the Rocq language field (stdlib ...) with the presence-only field (no_corelib) in Rocq language 0.14. (#14452, fixes #14358, @Durbatuluk1701)
• Throttle sandbox creation to 250 concurrent sandboxes. (#14464, @rgrinberg)
• The package solver now uses cached revision store lookups for improved performance. (#14494, fixes #12637, @Alizter, @rgrinberg)
• Remove the deprecated (lang coq) Coq Build Language. Use the Rocq Build Language ((using rocq <version>)) instead. Projects that still declare (using coq <version>) now get an error pointing them at Rocq. (#14525, fixes #12788, @Alizter)
• Path-valued pforms (%{bin:...}, %{dep:...}, %{path:...}, and friends) now expand same-directory paths with a leading ./, so that shells like bash in (bash ...) and (system ...) actions execute them directly instead of looking them up in PATH. (#15156, fixes #15147, @Alizter)

Language features:

• (breaking change) #13681, #13682, #13683, #13684, #13275 : Introduce a new type (module M : S) -> t[M] that corresponds to module-dependent functions (also called: modular explicits). val mapM: (module M : Monad) (f : 'a -> 'b M.t) : 'a list -> 'b list M.t (Samuel Vivien review by Leo White, Gabriel Scherer, Florian Angeletti, Jacques Garrigue and Stephen Dolan)

• #14040: generalize the constructs let module, let exception and let open to most other structure items, for example: let type t = ... in ... let type Effect.t += Yield in ... (Nicolás Ojeda Bär, review by Valentin Gatien-Baron)

• #13806: Enable the use of function parameters with polymorphic types. let extract (getter : 'a . 'a t -> 'a) = ... let runST (m : 's . ('s, 'a) ST.t) : 'a = ... (Ulysse Gérard, Leo White, review by Florian Angeletti, Samuel Vivien, Gabriel Scherer and Jacques Garrigue)

• (breaking change) #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)

• (breaking change) #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)

Standard library:

• #13372: New Format and Printf printf-like functions that accept a heterogeneous list as arguments. Format.lprintf "@[%s@ %d@]@." [ "x ="; 1 ] (Leonardo Santos, review by Florian Angeletti and Gabriel Scherer)

• #14437: Add String.split_{first,last,all} and String.rsplit_all split_first: sep:string -> string -> (string * string) option split_all: sep:string -> drop:(string -> bool) -> string -> string list (Daniel Bünzli, review by Nicolás Ojeda Bär and Florian Angeletti)

• #14436: Add String.replace_{first,last,all} replace_first: sub:string -> by:string -> ?start:int -> string -> string (Daniel Bünzli, review by Nicolás Ojeda Bär, Ali Caglayan and Florian Angeletti)

• #14439: Add String.includes, to complete the trio: starts_with: prefix:string -> string -> bool ends_with: suffix:string -> string -> bool includes: affix:string -> string -> bool (Daniel Bünzli, review by Nicolás Ojeda Bär and Olivier Nicole)

• #14381: Add String.find_{first,last}index, String.find{first,last}, String.[r]find_all. find_first_index: (char -> bool) -> ?start:int -> string -> int option (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)

• #14352: Add String.{drop,take,cut}_{first,last}. take_first: int -> string -> string cut_first: int -> string -> string * string (Daniel Bünzli, review by David Allsopp, Nicolás Ojeda Bär and Vincent Laviron)

• #14362: Add String.{drop,take,cut}_{first,last}_while drop_first_while: (char -> bool) -> string -> string (Daniel Bünzli, review by Nicolás Ojeda Bär and David Allsopp)

• #13916: Add Option.product and Option.Syntax. (Nicolás Ojeda Bär, review by Daniel Bünzli, Gabriel Scherer and David Allsopp)

• #13995: Option.blend: ('a -> 'a -> 'a) -> 'a option -> 'a option -> 'a option (Kate Deplaix, review by Daniel Bünzli, Gabriel Scherer, Nicolás Ojeda Bär, Florian Angeletti and Josh Berdine)

• #13920: add Option.{for_all, exists} (Gabriel Scherer, review by Kate Deplaix, Nicolás Ojeda Bär, Richard Eisenberg and Jeremy Yallop)

• #14185: List.split_map: ('a -> 'b * 'c) -> 'a list -> 'b list * 'c list (Jeremy Yallop, review by Daniel Bünzli, Nicolás Ojeda Bär and Damien Doligez)

• #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)

• #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. find_and_replace: ('k, 'a) Hashtbl.t -> 'k -> 'a -> 'a option find_and_remove: ('k, 'a) Hashtbl.t -> 'k -> 'a option (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)

• #14432: Add floor division, ceil division, Euclidean division and remainder to the Int, Int32, Int64 and Nativeint modules: fdiv, cdiv, ediv. (Xavier Leroy, review by Ali Caglayan, Nicolás Ojeda Bär, 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)

• #10177: Seq.(delay : (unit -> 'a t) -> 'a t) (Gabriel Scherer, review by Jeremy Yallop and François Pottier)

• #13343: Add Array.stable_sort_sub (François Pottier, review by Gabriel Scherer, Corentin Leruth and Nicolás Ojeda Bär)

• #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)

• #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)

• #14086: Add Domain.count. (Nicolás Ojeda Bär, review by David Allsopp, Gabriel Scherer, Daniel Bünzli and KC Sivaramakrishnan)

• #12877: Dynarray.rev_iter, Dynarray.rev_iteri (Gabriel Scherer, review by Léo Andrès, Jeremy Yallop and Nicolás Ojeda Bär)

• #14084: Future-proof Dynarray implementation against a smarter compiler (Basile Clément, review by Gabriel Scherer)

Tools:

• #13728, #14014, #14243, #14244, #14245 : The compiler is now relocatable: it can be copied/moved to a different directory and everything still works. (David Allsopp, review by Nicolás Ojeda Bär, Jonah Beckford, Daniel Bünzli, Antonin Décimo, Damien Doligez, Hugo Heuzard, Samuel Hym, and Vincent Laviron)

• #14055: Invert BUILD_PATH_PREFIX_MAP in directories loaded at startup by the debugger. (Pierre Boutillier, review by Gabriel Scherer and Daniel Bünzli)

• (breaking change) #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)

Runtime system:

• #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)

• #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)

• #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)

• #14416: Spawned domains will record backtraces if the parent domain has enabled it. (Nathan Taylor, review by Gabriel Scherer)

• #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)

• #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)

• #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)

• (breaking change) #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)

• #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)

• #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)

• #14820: caml_ba_alloc must account for memory it allocated itself. CAML_BA_SUBARRAY (introduced in 5.2) with data=NULL would result in the Gc accounting for the allocation as 0 bytes, which can eventually lead to OOM. This condition never occurs in the compiler itself, but occurs in external C bindings that attempt to create a new bigarray in the shape of an existing one. For backwards compatibility ignore CAML_BA_SUBARRAY when data is NULL. (Edwin Török, review by Damien Doligez)

Type system:

• #13781: Set scope of internal type nodes during abbreviation expansion rather than recursing during unification. (Jacques Garrigue, review by Gabriel Scherer)

• (breaking change) #14066: catch invalid aliases introduced by signature constraints during merging rather than in subtyping:

    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)

• (breaking change) #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:

  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)

• #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)

Compiler user-interface and warnings:

• #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)

• #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)

• #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 and the manual (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)

Other libraries:

• #13700, #14454, #14715: 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 Florian Angeletti, David Allsopp, Stefan Muenzel, Gabriel Scherer, 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)

• (breaking change) #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)

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)

Manual and documentation:

• #14684, #14782, #14838: Improve ocamlc's and ocamlopt's manual pages and fix small issues in the manual (Samuel Hym, review by Florian Angeletti, Antonin Décimo, Gabriel Scherer and Nicolás Ojeda Bär)

• #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)

• (breaking change) #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)

• #13994: document external types (Gabriel Scherer, review by Jan Midtgaard, Jacques Garrigue and Florian Angeletti)

• #14077: Add missing item-attribute rule for let-bindings 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)

Internal/compiler-libs changes:

• #13913: Use Blake128 as the hash function for the compiler's CRCs (Vincent Laviron, review by Xavier Leroy and Gabriel Scherer)

• #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)

• #14120, #14474, #14476: Associate Uids to items that don't have a concrete definition; improves Merlin's renaming for functors. (Ulysse Gérard, review by Florian Angeletti and Gabriel Scherer)

• #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)

• #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)

• #14297, #14299: Avoid iterating on hash tables to produce types or terms (Vincent Laviron, review by Nicolás Ojeda Bär and Gabriel Scherer)

• (breaking change) #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)

• (breaking change) #14388: Remove support for let rec (module M : S) = e1 in e2. (Alistair O'Brien, review by Vincent Laviron and Gabriel Scherer)

• #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)

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:

• #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)

• #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)

• #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)

• #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, CVE-2026-28364, OSEC-2026-01: 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)

• #14557, #12150, #14696: ensure that the self type of class cannot escape through type constraints. (Leo White, review by Florian Angeletti)

• #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, #14675: take in account module-dependent functions when determining if an optional argument is non-erasable. (Alistair O'Brien and Florian Angeletti, review by Gabriel Scherer)

• #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)

• #14655, #14691: check for size overflow in caml_ba_reshape (Stephen Dolan, review by Xavier Leroy)

• #14667: enable application related warnings for module-dependent functions (Florian Angeletti, 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, review by Florian Angeletti)

• #14349, #14718, #14722: runtime, fix in the orphaning of ephemerons (Gabriel Scherer, review by Olivier Nicole and Damien Doligez, report by Jan Midtgaard)

• #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)

• #14719, #14721: compute arity correctly for module-dependent function (Florian Angeletti, report by Jeremy Yallop, review by Stefan Muenzel)

• #14760, #14802, #14846: Correct the detection of argument defaults in configure, fixing an incorrect error message when installing OCaml through opam on OpenSUSE with the site-config package installed. (David Allsopp, report and review by Edwin Török)

• #14797: avoid dropping attributes attached to package types when pretty printing in surface syntax. (Chet Murthy, review by Nicolás Ojeda Bär)

• #14853, CVE-2026-41083, OSEC-2026-05: fix quoting of filenames passed to Filename.quote_command on Windows. (David Allsopp, report by Andrew Nesbitt, review by Florian Angeletti)

Changes in OCaml 4.14.4 (15 June 2026)

Build system:

• #12372, #14572: Pass option -no-execute-only to the linker for OpenBSD >= 7.3 so that code sections remain readable, as needed for closure marshaling. Originally backported in 4.14.2, but the flag was accidentally not passed when linking the .so versions of the OCaml runtime libraries or when linking .cmxs files. (Xavier Leroy and Anil Madhavapeddy, review by Anil Madhavapeddy and Sébastien Hinderer)

Bug fixes:

• #14599, #14606: on ARM64 platforms, ocamlopt was under-estimating the sizes of some instructions. This could lead to overflows in relative branch offsets, reported as errors by the assembler. (Xavier Leroy, review by Vincent Laviron, report by Raphaël Proust)

• #14607: Fix linking with libasmrun_shared.so on Risc-V (undefined symbol declared riscv.o) (David Allsopp, review by Nicolás Ojeda Bär)

• #14661: Build dllthreads.so with pthreads flags (removed in #13018). For normal programs there's no semantic difference, because ocamlrun and ocamlc.opt are always linked with pthreads, but it was a regression to require programs wishing to dlopen dllthreads.so to have already linked with pthreads themselves. (David Allsopp, review by Gabriel Scherer)

• #14655, #14691, CVE-2026-34353, OSEC-2026-04: check for size overflow in caml_ba_reshape (Stephen Dolan, review by Xavier Leroy)

• #14853, CVE-2026-41083, OSEC-2026-05: fix quoting of filenames passed to Filename.quote_command on Windows. (David Allsopp, report by Andrew Nesbitt, review by Florian Angeletti)

Fixed

• Fix the menhir opam dependency injection introduced in 3.23. Dune now only fills in the lower bound {>= "20180523"} on an existing user-declared menhir dependency; it no longer adds menhir as a new dependency to packages that did not declare it themselves. (#14434, fixes #14428, @robinbb)
• Gate the dune version-bound deduplication in generated opam files (introduced in 3.23) on (lang dune 3.23). Projects at earlier lang versions get the prior And [...] shape — e.g. {>= "3.17" & >= "3.20"} — restoring 3.22 behaviour and avoiding a silent change to opam output on dune-binary upgrade. (#14436, @robinbb)
• Preserve library order when building a shared jsoo standalone runtime. (#14438, @vouillon)
• Fix the fallback to the secondary compiler, allowing recovering of support for packages with upper bounds on OCaml less than 4.14. Packages depending on dune 3.23.1 or later and with an upper bound on the OCaml compiler that is less than 4.14, will now be able to use the latest dune, but dune will be built with the secondary compiler at version 4.14. (#14443, @Alizter)
• Fix the bootstrap on NetBSD by including <sys/wait.h> in lev_stubs.c, matching the existing FreeBSD/OpenBSD guard. (#14512, fixes #14484, @0-wiz-0)

Fixed

• Auto-inject "menhir" {>= "20180523"} into generated opam files when the menhir extension is used. Dune's menhir rules rely on --infer-write-query and --infer-read-reply, which require at least this version; without the lower bound, builds fail with older menhir installations. (#10707, @robinbb)
• Fix --display=quiet not suppressing "Entering directory" and "Leaving directory" messages when using --root. These messages are now deferred until there is actual output, so silent builds produce no noise. (#12974, fixes #12854, @Alizter)
• Fix an internal error when a module is shared between a rocq.theory and rocq.extraction stanza. The error now includes a hint pointing to the conflicting stanza. (#13733, @Durbatuluk1701)
• Fix cookies defined on ppx_rewriter being lost when that rewriter was used as a dependency of another ppx_rewriter. (#13737, fixes #3426, @Alizter)
• Improve opam file generation for packages that set (dir ..). Such packages will now have a test target that is limited to this directory. (#13778, @rgrinberg)
• Stop duplicating dune diagnostics to subscribers over RPC (#13816, @rgrinberg)
• Fix dependency cycle when using the package with a library conditionally enabled via enabled_if. (#13833, @toots)
• Fix underspecification of dependencies in the sandbox for modules with interfaces. (#13842, @anmonteiro)
• Honor sandbox settings specified inside (:include ..) expressions in the deps field (#13898, @rgrinberg)
• Fix dune pkg lock failing when a pin stanza contains a file:// URL with a relative path outside the workspace (#13915, fixes #10254, @shunueda)
• Use all stat attributes to detect patch back source tree changes (#13986, @rgrinberg)
• Use device and inode number for invalidating cached digests (#13991, @rgrinberg)
• Stop trying to set SO_REUSEADDR on unix sockets when setting up dune rpc (#14056, @rgrinberg)
• Fix autolocking to correctly detect changes to (depends) in watch mode (#14066, fixes #13234, @Alizter)
• Fix incremental builds for libraries using (wrapped (transition ...)). The compat shim modules were never recompiled when the inner module's interface changed, causing "inconsistent assumptions" errors. (#14090, fixes #14089, @Alizter)
• Fix Rocq configuration detection to use rocq c --config subcommand instead of rocq --config (#14093, fixes #13774, @Durbatuluk1701)
• Bump dune rpc's request pending request limit 10 to 100 (#14094, @rginberg)
• Invalidate stale cached digests in all build commands (#14126, @rgrinberg)
• Fix root_module generating duplicate module definitions when a findlib sub-package shares a directory with its parent (e.g., logs.lwt alongside logs). (#14135, fixes #6148, @robinbb)
• Fix dune subst prepending a duplicate version: field to opam files that already contain one, instead of replacing it in place. (#14136, fixes #878, @robinbb)
• Fix @ocaml-index alias being generated for all contexts, causing build errors in multi-context workspaces where some libraries are disabled in non-default contexts. The alias is now only generated for the merlin context. (#14137, fixes #12007, @robinbb)
• Remove the warning about the deprecation of the coq stanza for dune lang before 3.21 since it has been introduced in this version (#14187, @bobot)
• $ dune init now generates projects with correct .opam files (#14192, @rgrinberg)
• Send SIGTERM before SIGKILL when cancelling child processes in watch mode, giving cleanup handlers a chance to run before escalating. (#14224, #14170, fixes #2445, @robinbb)
• Correctly specify dependencies for generate_runner in inline tests (#14276, @rgrinberg)
• Fix duplicate dune version bounds in generated opam files. When users declare (dune (>= X.Y)) matching or exceeding the (lang dune X.Y) version, the generated opam depends no longer contains redundant constraints like {>= "2.7" & >= "2.7"}. (#3916, #11106, @robinbb)
• Fix inline tests not being executed for byte-only libraries. When a library has (modes byte), the inline test runner is now linked in byte mode so the library's test code is included. (#9757, @robinbb)

Added

• Add support for c_library_flags in foreign_stubs (#13484, @madroach)
• Move the management of Jsoo config details out of dune (#13613, @vouillon)
• Js_of_ocaml: share standalone runtimes (#13621, @vouillon)
• Allow multiple (dirs ..) stanzas in the same Dune file. Starting with (lang dune 3.23), Dune takes the union of the specified directories (#13734, fixes #6249, @anmonteiro)
• Sandboxed rules are now allowed to produce diff promotions when (corrections produce) is set on the rules. Whenever such an action produces foo.corrected, it will be automatically registered as a promotion for foo (#13813, @rgrinberg)
• $ dune clean now accepts arguments to only remove certain targets from the _build directory (#13875, @rgrinberg)
• $ dune promote now promotes all paths that are a prefix of the path provided. For example, $ dune promote foo will promote foo, foo/bar, foo/bar/baz (but not foobar). (#13876, @rgrinberg)
• Allow for the diff action to diff entire directories (#13880, fixes #3567, @rgrinberg)
• A hint is now emitted when trying to build a target inside a directory that was excluded by a (dirs ...) stanza (#13919, @mefyl).
• Add --debug-backtraces to $ dune {promote,trace,cache} (#13933, @rgrinberg)
• Actions are now able to observe their project directory via DUNE_PROJECT_ROOT (#13934, @rgrinberg)
• Support hardlink sandboxing on Windows. (#13987, addresses part of #4362, @Alizter)
• rocq.extraction: Add extracted_files field in (rocq 0.13), replacing extracted_modules, supporting extraction to languages other than OCaml (#13997, @Durbatuluk1701).
• Infer source directories as dependencies when they're as reference directories in diff actions.
• Add trace events for build start/stop/restarts (#14163, #14166, @rgrinberg)
• Generate compile_commands.json for C/C++ foreign stubs when building @check with (lang dune 3.23). This enables clangd, ccls, and other tools that consume compilation databases. (#14185, fixes #3531, @Alizter)
• Add trace events for accepting clients and shutting down RPC (#14232, @rgrinberg)
• Back up the default trace file as trace.csexp.old before each build, preserving the previous trace for comparison. This does not apply when --trace-file is used. (#14269, @Alizter)

Changed

• Dune digests target files and directories in background threads (#13341, @rgrinbreg)
• Dyn.pp now prints valid OCaml literals for more constructors:
  • Char is quoted (e.g., 'a')
  • Int32/Int64/Nativeint include literal suffixes (l/L/n)
  • Float handles infinity, neg_infinity, and nan (#13394, grants #13378, @Alizter)
• Bump the minimal OCaml version required to build Dune from 4.08 to 4.14. (#13533, @Alizter)
• Starting from 3.23, user rules are sandboxed by default (#13805, @rgrinberg)
• Dune will no longer stat paths in the _build directory. This was done as protection from user rules accidentally touching things in the _build directory. This is forbidden, and dune offers rule sandboxing to prevent this (#13875, @rgrinberg)
• Improve mtime precision by no longer approximating them with floats (#13962, @rgrinberg).
• Remove --makefile (or -m) in $ dune rules. The sexp output is the only supported way of reflecting dune rules (#14069, @rgrinberg)
• Do not automatically promote files. Now, opam files must be manually promoted with $ dune promote. Their generation is triggered by @install, @runtest, and @opam. In release mode, .opam files aren't generated at all and whatever is in the source is used (#14108, @rgrinberg)
• Inline test runner generation is now sandboxed (#14257, @rgrinberg)

Added

• Allow persistent latex macros in HTML/KaTeX backend (@dlesbre, #1391)
• markdown-generate command now accepts multiple .odocl files in a single invocation, eliminating the need for shell scripting (@davesnx, #1388)
• Support for OxCaml (@lukemaurer, @art-w, #1399)
• OCaml 5.5.0 support (@panglesd, @xvw, #1406)

Fixed

• Fix compile-time crashing bugs #930 and #1385 (@jonludlam, #1400)
• Markdown backend assumes ocaml as langId on declarations
• Markdown backend collects all code snippets and render a single code block with comments, rather than split the variants/records per constructor/field
• Fix URL remapping for page references (@jonludlam, #1395)
• Fix #1396, which broke incrememntal builds (@jonludlam, #1402)
• Ensure all warnings turn into errors with --warn-error (@jonludlam, #1402)
• Fix missing parentheses for polymorphic arguments (@art-w, #1404)

Thu Apr 30 14:15:42 CEST 2026

• merlin library
  • Fix a cache invalidation issue due to the introduction of hidden deps in OCaml 5.2. (#2062)
• index format
  • Merged indexes now point to each-others. This results in smaller index files. The index of a project is now defined by all its index files, not only the final aggregation. (#2051)

Fixed

• Revert the change in behavior of --diff-command back to 3.21. Non-existent files are now passed to this command instead of being replaced with /dev/null (#14098, fixes 13891, @rgrinberg)

Features

• Add custom ocamllsp/refactorExtract request (#1545)
• Add destruct custom request (#1583)
• Add locate_types custom request (#1584)
• Add support for the textDocument/rangeFormatting request (#1591)
• Allow to configure merlin using build systems other than dune. If $OCAMLLSP_PROJECT_BUILD_SYSTEM environment variable is set then OCaml LSP will execute $OCAMLLSP_PROJECT_BUILD_SYSTEM ocaml-merlin command to get merlin configuration for a module. It is expected the command to communicate using merlin-dot-protocol. If $OCAMLLSP_PROJECT_ROOT environment variable is set then OCaml LSP will use it as a project root directory.

Fixes

• Enable "hover" on more locations, notably class and object related (#1599)

• merlin library
  • Implement new refactor-extract-region command for extracting region to a fresh let binding (warning: this feature is still experimental) (#1948)
  • Add "Other" variant to locate-types result (#2025)
  • Don't include option in locate-types result for optional parameters (#2027)
  • Fix record field autocompletion (#2028)
  • Signature help should not loop over the parameters once it is finished (#2023)
  • Fix bugs on signature help about labelled and optional parameters (#2032)
  • Add -end-position parameter for enclosing (#2029)
  • Signature help should appear even if the 'in' is not written (#2036)
  • Improve type enclosing behavior on various class and object related items (#2053)
• merlin binary
  • Define PATH_MAX to 4096 if undefined (eg. hurd) (#2039)
• test suite
  • Add a reproduction case for #1214, the issue has been resolved before (#2022)
  • Add reproduction case for #1763 but it is not failing anymore (#2021)
  • Add a test to reproduce Locate command fails on multi-line type definitions (#2020)
  • Add a regression test for issue #2019 (#2030)

Fixed

• Restore compatibility with Windows 7 (#13905, @nojb)

• dune test now runs tests in the default context only. When there is a single context, it is treated as the default. This fixes a crash when the workspace has no context named "default". (#13930, fixes #13904, @Alizter)

• Fix dune trace cat --chrome-trace to adhere to the Chrome Trace Event Format by providing timestamps and durations at microsecond granularity (#13911, fixes #13906, @Alizter)

• Add support for OCaml 5.5 (#510 @anmonteiro)
• Add support for neocaml or other major modes in utop.el (#511, @bbatsov)

Added

• Add support for marking a release as a prerelease. (#517, @Sudha247)

Added

• Support OCaml 5.5 (#475, @anmonteiro)

• Add support for OCaml 5.5 (#622, @patricoferris, @NathanReb)

• Add support for OCaml 5.4 bivariant type parameters, they can now be used alongside ppx-es. (#629, @NathanReb)

• Add Attribute.Floating.declare_with_attr_loc and .declare_with_name_loc, by analogy to the same functions at top level of Attribute. (#631, @ceastlund)

• Migrate Ptyp_open nodes using an extension point (#625, @patricoferris)

• Add Ast_builder and Ast_pattern utilities to manipulate encoded effect patterns (#624, @NathanReb)

• Fix a bug where ppat_effects would be encoded/decoded instead of copied by the 5.4 <-> 5.3 migrations (#624, @NathanReb)

• Fix infinite loop when duplicate attributes are present, raising an error instead (#613, @ceastlund, @patricoferris)

• Ignore extensions inside attributes for the unused extension check (#616, @Skepfyr)

• Fix a bug that inserted Location.none into Longidents when using OCaml 5.4 and above (#619, @patricoferris)

• Add support for OCaml 5.4 labeled tuples, they can now be used alongside ppx-es. Also adds Ast_builder and Ast_pattern utilities to manipulate them. (#607, @NathanReb)

Fixed

• Dyn.to_string now uses a smarter way to convert floats. This ensures that floats are printed with enough precision to round-trip and are valid OCaml lexemes. (#12982, fixes #12980, @Alizter)

• Fix dune install --prefix failing with relative paths outside the workspace like ../foo (#12993, fixes #12241, @benodiwal)

• Place the default trace file inside the build directory at the workspace root, rather than relative to the current directory. (#13735, @vouillon)

• Fixed interpreting relative paths in %{bin:..} and %{bin-available:..}. These are now interpreted correctly, relative to the dune file they're in. (#13712, fixes #9564, @anmonteiro)

• Delete sandboxes with broken permissions (#13511, @rgrinberg)

• Fix compiling Menhir parsers that refer to sibling modules within a subdirectory of (include_subdirs qualified). (#13118, fixes #11119, @anmonteiro)

• Fixed the dependency specification of C stubs, which could result in C stubs not getting rebuilt when needed (which could in turn lead to segmentation faults and other hard-to-track bugs). (#13652, fixes #13651, @nojb)

• Fix the Dune cache on Windows by correctly handling renames onto read-only files. Before this change, the Dune cache would be filled but the stored artifacts would not generally be usable by Dune. (#13713, @Nevor)

• Fix rpc not transferring promotion warnings to the client (#12604, fixes #12578, @ElectreAAS)

• Fix issue where dune exec -w was unable to kill running programs on rebuild. (#12360, fixes #12323, @Alizter)

• Resolve context and workspace binaries introduced by the respective (env (binaries ..)) stanzas. (#12952, fixes #6220, @anmonteiro)

• Fix diff promotions originating from sandboxed rules. Previously, they would be completely ignored as the sandbox with the promoted file would be destroyed if the promotion fired (#13520, @rgrinberg)

• Fix failure to digest installed directory targets, allowing them to be used as dependencies to other rules. (#13045, @anmonteiro)

• Fix handling of (select ..) field when used with (include_subdirs ..). (select <path> from ..) modules now parse path as a relative path starting from the module group root (#13175, fixes #4383, #12450, @anmonteiro)

• Fix dune trying to kill processes that were already reaped due to race conditions (#13245, @rgrinberg)

• Add O_CLOEXEC to all files used for stdin/stdout/stderr (#13385, @rgrinberg)

• Fix $ dune promote dir/foo when dir does not exist (#13493, @rgrinberg)

• Fix (select ..) field evaluation when a transitive library has optional dependencies (fixes #13299, #13389, @anmonteiro)

• Fix sandboxed builds of library stanzas that set (stdlib (modules_before_stdlib ..)) (#13624, @anmonteiro)

• Dune cache: use of hard links under Windows. (#13714, @Nevor)

• Fixed non-build caches not following $DUNE_CACHE_ROOT and instead only relying on $XDG_CACHE_HOME. This means the normal build cache moves: $DUNE_CACHE_ROOT -> $DUNE_CACHE_ROOT/db (no changes if that variable was unset). Affected users can prevent a full cache invalidation by moving previous contents: cd $DUNE_CACHE_ROOT; mkdir db; mv <contents of directory> db. (#11612, fixes #11584, @ElectreAAS)

• $ dune promotion list writes output to stdout rather than stderr (#13462)

• Improve handling of empty files in the diff action. These are now correctly distinguished from empty files. (#13696, @rgrinberg)

• Pass /dev/null to --diff-command instead of non-existent files (#13696, @rgrinberg)

• Fix failure when multiple rocq.extraction stanzas existing in a directory (#13531, fixes #8042, @rlepigre-skylabs-ai)

• Print $ dune promotion show output to stdout rather than stderr (#13481, @rgrinberg)

• Fix deadlock in the memo library in the presence of dependency cycles (#13625, @anmonteiro)

• Fix promotions that modify a directory into a file (#13516, fixes #4067, @rgrinberg)

• Fix installation of implementations of virtual libraries. This failed when the implementation had no private modules, but the virtual library did (#10635, @rgrinberg)

• Respect the (dir ..) field on packages when setting up cram tests (#13581, @rgrinberg)

Added

• Add support for generating .cms files using oxcaml and adding .cms or .cmt files as compilation dependencies (#13397, @spiessimon)

• Add trace events for custom actions (#13265, @rgrinberg)

• Allow enabling extensions with (using ..) in dune-workspace files (#13395, @spiessimon)

• Add sandbox extraction trace event (#13544, @rgrinberg)

• Add the initial cwd to the first config event (#13026, @rgrinberg)

• Dune dune produces trace events in DUNE_ACTION_TRACE_DIR if this variable is set. (#13302, @rgrinberg)

• Add file watching events to the trace file (#13038, @rgrinberg)

• Introduce the $ dune trace cat subcommand to view the trace file. (#13055, @rgrinberg)

• Add diagnostic events to the trace. (#13041, @rgrinberg)

• Add DUNE_JOBS environment variable for controlling concurrency of Dune from environment. The INSIDE_DUNE variable also now no longer controls concurrency (#12800, @Alizter)

• Support for Rocq expected output tests (#13632, @rlepigre-skylabs-ai)

• Add rusage information to completed processes in the trace (@rgrinberg, #13241)

• Add process start events to the trace (#13261, rgrinberg)

• Generate odoc documentation in markdown using the @doc-markdown alias (#12581, @davesnx)

• Add timing information for every command executed by cram (#13092, @rgrinberg)

• Add the workspace root to the config trace event (#12922, @rgrinberg)

• Introduce the dune-action-trace library. This public library is to be used by custom actions to emit trace events while executed as part of a dune build. The trace events emitted through this library will be incorporated into dune's own trace (#13348, @rgrinberg)

• Add dune-find-dominating to dune.el, a command to find the dominating dune file. (#12696, @arvidj)

• Add a --no-recursive flag to $ dune describe workspace (#13590, @rgrinberg)

• Trace events for files written directly by dune (#13618, @rgrinberg)

• Allow expansion of special forms like (:include ..) and %{read-lines:..} in the modules specification for the ocamllex, ocamlyacc and menhir stanzas. (#13105, #13135, #13157, @anmonteiro)

• Add a trace event for snapshotting the sandbox (#13541, @rgrinberg)

• Add signal send and receive events to the trace (#13193, @rgrinberg)

• Emit final trace event before exiting. (#13018, @rgrinberg)

• dune runtest can now run individual test executables from (tests) stanzas and inline tests from (library (inline_tests)) stanzas by providing their source files as arguments. (#13064, fixes #870, @Alizter)

• Add a shell field to the cram stanza. This field allows customizing the shell to be bash rather than sh (#13083, @haochenx)

Changed

• Start sandboxing the execution of tests defined with the test and tests stanzas (#13510, #13617, @rgrinberg)

• Disabled cram tests can now be run explicitly with dune runtest disabled.t. The enabled_if field now only controls whether a test is included in the @runtest alias. (#13081, @Alizter)

• Process categories in trace events are moved to their own field in args (#13024, @rgrinberg)

• Sandbox running ocamllex and ocamlyacc actions. (#13098, @anmonteiro)

• Sandboxing mdx test actions is now the default starting from 0.5 (#13504, @rgrinberg)

• Start sandboxing Melange rules by default in the (library ..) and (melange.emit ..) stanzas (#13619, @anmonteiro)

• Introduce a promotion trace event and remove the corresponding verbose log message. (#12949, #13444, @rgrinberg)

• Change dune's trace format to emit canonical s-expressions. This improves performance and is better aligned with dune's usage of the format elsewhere. $ dune trace cat can also emit the trace in --chrome-trace for perfetto, or --sexp for regular s-expressions for interactive usage. (#13059, @rgrinberg)

• Move all logging statements to the trace file. All log statements now contain structured payloads (#13015, fixes #12904, @rgrinberg)

• Add a target resolution event to replace the equivalent log message (#12955, @rgrinberg)

• No longer allow option names to be specified by a prefix if the prefix is unambiguous [#202 @kit-ty-kate]
• Query upstream repo for default branch instead of defaulting to master [#201 @mbarbin]
• Query fork name from GitHub to support users whose fork of opam-repository isn't named opam-repository [#199 @mbarbin]
• Fix an infinit loop if the user repeatedly provided an invalid token [#186 @filipeom]
• Remove the deprecated --split option [#194 @kit-ty-kate]
• Remove the github-unix dependency [#196 @kit-ty-kate]
• Upgrade to cmdliner 2.0 [#202 @kit-ty-kate]