DEV Community: Sabine Schmaltz

OCaml Platform Newsletter: May to August 2025

Sabine Schmaltz — Thu, 04 Sep 2025 13:33:29 +0000

Welcome to the fifteenth edition of the OCaml Platform newsletter!

In this May to August 2025 edition, we are excited to bring you the latest on the OCaml Platform, continuing our tradition of highlighting recent developments as seen in previous editions. To understand the direction we're headed, especially regarding development workflows and user experience improvements, check out our roadmap.

You can comment on this newsletter on the OCaml Discuss Forums!

You can subscribe to this newsletter on LinkedIn!

Highlights:

Enhanced Editor Integration: OCaml-LSP 1.23.0 and Merlin 5.5 provide improved project navigation and error reporting. New ocaml-eglot brings modern LSP support to Emacs users. Continued work on project-wide features brings OCaml's development experience closer to modern IDEs.
Enhanced Package Management: opam 2.4.0 stable release eliminates GNU patch/diff dependencies, improves newcomer experience by avoiding problematic system compilers by default, and provides better handling of deprecated packages. This addresses common setup issues that previously complicated OCaml adoption.
Improved Testing Workflows: Dune 3.20 introduces concurrent watch mode operations, named test aliases for running specific tests (@runtest-testname), and timeout support for cram tests.
Documentation and Tooling Maturity: Odoc 3.1.0 refines cross-package linking capabilities.
OCaml 5.4.0-beta1: you can help test upcoming compiler improvements!

Announcements:

Emacs Integration for OCaml LSP Server: Introducing ocaml-eglot (August 26, 2025)
Dune Developer Preview: Portable External Dependencies for Dune Package Management (June 5, 2025)
Dune Developer Preview: Portable Lock Directories for Dune Package Management (May 19, 2025)

Stable Releases:

Dune 3.20.1 (August 26, 2025)
Dune 3.20.0 (August 21, 2025)
Utop 2.16.0 (July 25, 2025)
opam 2.4.1 (July 23, 2025)
opam 2.4.0 (July 18, 2025)
Odoc 3.1.0 (July 15, 2025)
Ppxlib 0.36.1 (July 10, 2025)
OCaml-LSP 1.23.0 (June 24, 2025)
Merlin 5.5-503 (June 24, 2025)
OCaml-LSP 1.21.0-4.14 for OCaml 4.14 (June 23, 2025)
Merlin 4.19-414 (June 23, 2025)
Dune 3.19.1 (June 11, 2025)
Dune 3.19.0 (May 23, 2025)

Unstable Releases:

Dune 3.20.0~alpha4 (August 12, 2025)
Dune 3.20.0~alpha3 (August 6, 2025)
Dune 3.20.0~alpha2 (August 5, 2025)
Dune 3.20.0~alpha1 (July 30, 2025)
Dune 3.20.0~alpha0 (July 28, 2025)
OCaml 5.4.0-beta1 (July 22, 2025)
opam 2.4.0~rc1 (July 4, 2025)
opam 2.4.0~beta1 (June 19, 2025)
OCaml 5.4.0-alpha1 (May 22, 2025)
Dune 3.19.0~alpha0 (May 20, 2025)
opam 2.4.0~alpha2 (May 5, 2025)

Dune

Roadmap: Develop / (W4) Build a Project

The release introduces the dune describe location command for printing the path to executables.

dune runtest now understands absolute paths and can run tests in specific build contexts. Improvements to cram test handling fix issues where tests attached to multiple aliases would run multiple times.

Testing Workflow Improvements

Dune 3.20 significantly improves testing workflows with named test aliases. Tests declared with (test (name a)) can now be run individually using dune build @runtest-a. Inline test libraries produce aliases like @runtest-name_of_lib, allowing targeted execution of specific test suites without running the entire test battery.

The new (timeout <float>) field for cram tests prevents runaway tests from blocking CI pipelines. Combined with the ability to run dune promote while watch mode is active, these features remove common friction points in test-driven development workflows.

Performance and Watch Mode Enhancements

Dune's watch mode now supports concurrent dune exec operations and file promotion without requiring restarts, maintaining development flow during iterative changes.

The introduction of the 'empty' alias containing no targets provides more flexible build target management. New --alias and --alias-rec flags offer alternatives to the @@ and @ command-line syntax.

Dune 3.20 switches from MD5 to BLAKE3 for digesting targets and rules, providing both performance improvements and better cryptographic properties.

Activities:

Enhanced implicit transitive dependency handling for OCaml 5.2+ compatibility (#11866)
Improved alias system with new 'empty' alias support (#11556, #11952, #11955, #11956)
Better integration between promotion workflows and watch mode (#12010)
Fixed cram test duplicate execution issues (#11547)
Added timeout support for cram tests (#12041)
Added dune describe location command (#11905)
Named test aliases for targeted test execution (#11558, #11109)
BLAKE3 migration for improved performance (#11735)

Maintained by: Rudi Grinberg (@rgrinberg, Jane Street), Nicolás Ojeda Bär (@nojb, LexiFi), Marek Kubica (@Leonidas-from-XIV, Tarides), Ali Caglayan (@Alizter), Etienne Millon (@emillon), Stephen Sherratt (@gridbugs, Tarides), Antonio Nuno Monteiro (@anmonteiro), Etienne Marais (@maiste, Tarides)

Dune Package Management

Portable lock directories appear as an experimental feature. This is a major prospective enhancement for teams working across different platforms. Lockfile naming in the experimental feature now includes version numbers (e.g., ocaml-compiler.5.3.0.pkg instead of ocaml-compiler.pkg) to handle cases where different platforms require different package versions in the same project.

The portable external dependencies feature extends this capability to system-level dependencies, ensuring consistent build environments across development, testing, and production systems. Combined with the existing binary cache system, this could reduce the complexity of managing OCaml projects in diverse environments.

Note however, that the outcome of these experiments, and whether they mature into features on the stable version of Dune is still open. If you would like to help test and give feedback: run dune pkg lock and, if you encounter issues, please report them!

At dune.check.ci.dev, continuous monitoring shows ecosystem compatibility progress, with a large part of Dune-based packages in opam-repository now building successfully with Dune package management.

Activities:

Enhanced ecosystem compatibility testing and monitoring at dune.check.ci.dev
"Opam Health Check: or How we Got to 90+% of Packages Building with Dune Package Management" - detailed analysis of ecosystem compatibility progress

Dune Developer Preview

Dune Developer Preview continues to serve as an experimental channel for cutting-edge OCaml development features. The tooling includes built-in LSP support, formatting capabilities, and a shared cache that improves build performance.

The team has expanded testing beyond initial projects to include broader ecosystem validation. The binary repository provides static Linux binaries (built with musl) that work across distributions, along with native binaries for macOS on both x86_64 and aarch64 architectures.

Activities:

Enhanced LSP integration through automated tool management
Expanded ecosystem compatibility testing as documented in the Opam Health Check blog post

Package Management

Opam

The stable release of opam 2.4.0 represents a significant improvement in cross-platform reliability and user experience. The elimination of GNU patch and diff as runtime dependencies removes a major source of configuration issues that previously complicated deployment and CI/CD pipelines. The package manager now uses the native OCaml patch library instead.

The default compiler selection during opam init no longer uses ocaml-system, which was a common source of setup problems across different development environments. This change provides a more consistent onboarding experience for newcomers to OCaml.

Package lifecycle management receives clearer visibility through enhanced handling of deprecated packages. The opam show command displays deprecated packages in gray, while opam upgrade removes confusing "not up-to-date" messages for packages being phased out.

Development workflows benefit from the new OPAMSOLVERTOLERANCE environment variable, which addresses persistent solver timeout issues. The enhanced pinning system now displays current revisions of pinned repositories, providing better transparency in development workflows that rely on unreleased versions.

For Windows users, the prebuilt binaries now include Cygwin's setup executable as a fallback when cygwin.com is inaccessible, improving reliability in restricted network environments.

Notable Activity:

opam 2.4.0 stable release with comprehensive improvements
Use patch OCaml library instead of the patch command (#5892)
UX improvements: remove ocaml-system from default compiler at init (#6307)
Provide a way to avoid solver timeouts (#5510)
Add opam lock <pkg> --keep-local (#6411)

Maintained by: Raja Boujbel (@rjbou, OCamlPro), Kate Deplaix (@kit-ty-kate, Ahrefs), David Allsopp (@dra27, Tarides)

Editor Tools

Roadmap: Edit / (W19) Navigate Code, Edit / (W20) Refactor Code

OCaml LSP Server and Merlin

The release of OCaml-LSP 1.23.0 and Merlin 5.5 brings enhanced project navigation and error reporting capabilities. The release addresses several long-standing issues with jump-to-definition, occurrences reporting, and inlay hints while adding new utilities for working with typed holes.

Project-wide features continue to evolve, with cross-project symbol search and refactoring capabilities bringing OCaml's editor support in line with other modern programming languages. The features work by building an index with dune build @build-index -w and provide comprehensive symbol searching across entire codebases.

By the way: we are currently working on a refactor feature that enables automatically extracting and inlining function parameters!

Support for OCaml 4.14 continues with dedicated releases (OCaml-LSP 1.21.0-4.14 and Merlin 4.19-414).

Activities:

Enhanced project navigation and symbol search capabilities
Better integration with Dune package management workflows
"Internship Report: Refactoring Tools Coming to Merlin" - new extract command for refactoring

Notable Activity:

Release of OCaml-LSP 1.23.0
Release of Merlin 5.5-503
OCaml 4.14 support with OCaml-LSP 1.21.0-4.14 and Merlin 4.19-414

OCaml LSP Server maintained by: Ulysse Gérard (@voodoos, Tarides), Xavier Van de Woestyne (@xvw, Tarides), Rudi Grinberg (@rgrinberg, Jane Street)

Merlin maintained by: Ulysse Gérard (@voodoos, Tarides), Xavier Van de Woestyne (@xvw, Tarides)

Emacs Integration

The introduction of ocaml-eglot provides Emacs users with modern LSP-based OCaml support as an alternative to the traditional merlin.el. This package leverages Emacs 29's built-in eglot LSP client, offering simplified configuration and access to project-wide features previously unavailable in Emacs.

ocaml-eglot provides feature parity with other editors through ocaml-lsp-server, including project-wide search and rename capabilities. For users migrating from merlin.el, existing keybindings work immediately. The package is actively maintained, while merlin.el enters maintenance-only mode.

The integration works with any OCaml major mode (tuareg, caml-mode, or neocaml) and provides error navigation, type information display, code generation through the "destruct" feature, and enhanced navigation between language constructs.

Notable Activity:

ocaml-eglot 1.0.0 release bringing LSP to Emacs
Subsequent releases 1.1.0 and 1.2.0 adding flycheck support and Emacs 30.1 compatibility
Active development replacing maintenance-only merlin.el

Visual Studio Code Plugin

We're happy to announce that the Visual Studio Code editor plugin now integrates seamlessly with Dune package management! This is an important milestone for Dune package management, and if you haven't tried it, or have been waiting for it to mature, now is a great time to get started!

Development continues on improving the OCaml VSCode editor plugin experience. For example, when using opam to manage your project's dependencies and ocaml-lsp-server is not found in the opam switch, the plugin will now prompt users to install it.

Notable Activity:

Automatically installing/updating ocaml-lsp-server (#1725)
Automatically configuring dune package management (#1791)

Documentation Tools

Roadmap: Share / (W25) Generate Documentation

Odoc

Odoc 3.1.0 continues to refine the modern documentation experience introduced with Odoc 3.0. The cross-package linking system and multimedia support capabilities help teams create comprehensive and discoverable documentation for complex systems.

The improved documentation tooling addresses ecosystem discoverability and maintainability. The ability to generate interconnected documentation across multiple packages makes large OCaml codebases more accessible for new team members and external collaborators.

Work continues on integrating Odoc 3.x with the OCaml.org documentation pipeline to provide a unified documentation experience across the ecosystem. As of July 2025, Odoc 3 is now live on OCaml.org, bringing the new features to the entire package ecosystem. The improved pipeline addresses dependency complexities by using new tooling that archives and restores opam packages, eliminating redundant builds that previously occurred thousands of times.

Notable Activity:

Release of Odoc 3.1.0
"Odoc 3 is now live on OCaml.org!" - Jon Ludlam's blog post about the deployment of Odoc 3 to ocaml.org
"Odoc 3: So what?" - in-depth explanation of Odoc 3's manual-focused features
Continued work on OCaml.org documentation pipeline integration through new package archiving tools

Maintained by: Jon Ludlam (@jonludlam, Tarides), Daniel Bünzli (@dbuenzli), Jules Aguillon (@julow, Tarides), Paul-Elliot Anglès d'Auriac (@panglesd, Tarides), Emile Trotignon (@EmileTrotignon, Tarides, then Ahrefs)

Ppxlib

Ppxlib 0.36.1 refines the improvements introduced in version 0.36.0, which updated the internal AST to target OCaml 5.2. This enables ppx authors to leverage features from OCaml 5.2 while maintaining compatibility with OCaml 4.08.0 and newer.

The update includes changes to the representation of functions, and package authors are encouraged to consult the upgrade guide as some ppxes may require updates.

Notable Activity:

Release of Ppxlib 0.36.1
Enhanced support for OCaml 5.2 AST features and compatibility improvements

Maintained by: Patrick Ferris (@patricoferris)

OCaml 5.4.0

OCaml 5.4.0-beta1 provides early access to upcoming compiler improvements and serves as a validation point for the ecosystem. The beta release allows forward-looking projects to begin testing compatibility with the new version while the broader ecosystem prepares for the eventual stable release.

The continued parallel maintenance of OCaml 4.14 LTS ensures that projects with longer upgrade cycles maintain access to critical updates without forced compiler upgrades. This dual-track approach provides flexibility for organizations with different risk tolerance levels.

Notable Activity:

OCaml 5.4.0-beta1 release for early testing
OCaml 5.4.0-alpha1 provided initial preview
Continued LTS support for OCaml 4.14 users

Utop

Utop 2.16.0 adds OCaml 5.4 support, restores backtrace functionality, improves preprocessor and Emacs integration, and relocates configuration files to a dedicated utop subdirectory.

Notable Activity:

Release of Utop 2.16.0

We are seeing continued progress toward making OCaml development more accessible and productive. The maturation of Dune package management, stability improvements in opam 2.4.0, and enhanced editor support provide a solid foundation for teams adopting OCaml or expanding their existing OCaml usage.

OCaml Platform Newsletter: February to April 2025

Sabine Schmaltz — Mon, 12 May 2025 09:58:05 +0000

Welcome to the fourteenth edition of the OCaml Platform newsletter!

In this February to April 2025 edition, we are excited to bring you the latest on the OCaml Platform, continuing our tradition of highlighting recent developments as seen in previous editions. To understand the direction we're headed, especially regarding development workflows and user experience improvements, check out our roadmap.

You can comment on this newsletter on the OCaml Discuss Forums, or subscribe to the OCaml Platform Newsletter on LinkedIn!

Highlights:

Dune Package Management is now Compatible with Large Parts of the Ecosystem: The majority of Dune-based packages in opam-repository now build successfully with Dune package management. Continuous monitoring is available at dune.check.ci.dev. Technical barriers are being systematically addressed while maintaining compatibility with both opam and Dune workflows to ensure teams can transition at their own pace.
Odoc 3.0 Release: A major upgrade, introducing powerful features like type-based search through Sherlodoc, global sidebar navigation, integrated source code display, multimedia support, hierarchical documentation pages, and cross-package linking that creates truly connected documentation.
New minor Emacs Mode: OCaml-eglot replaces the venerable "merlin-mode", providing modern editor features through ocaml-lsp-server.
First alpha of opam 2.4.0: Significant improvements including removal of GNU patch/diff dependencies, better Nix integration, improved pinned repository visibility, UI enhancements for deprecated packages, and new version comparison tools and lock file management features.

Announcements:

Calls for Feedback:

Releases:

Dune

Roadmap: Develop / (W4) Build a Project

Dune 3.18 brings various quality-of-life improvements, bug fixes, and new features. It introduces support for the new x-maintenance-intent field in opam packages, allowing maintainers to better communicate project status. The release also includes the new (format-dune-file ...) stanza, formalizing the dune format-dune-file command as an inside rule, and adds support for the not operator in package dependencies constraints. Several improvements to cache handling of file permissions have been implemented, and users can now utilize the --prefix flag when configuring dune with ocaml configure.ml, providing greater installation flexibility.

From 3.18.0, Dune now uses shorter paths for inline-test artifacts, allows dash characters in project names created with dune init, and displays negative error codes on Windows in hexadecimal format — the customary way to display NTSTATUS codes. The release also enhances stability with improved retry mechanisms for file delete operations on Windows under heavy load and provides better warning behavior when failing to discover the project root due to read failures, replacing the previous abort behavior.

Shortly after, Dune 3.18.1 was released with a hotfix that corrects an issue where pkg-config would fail to find certain libraries in specific contexts, while Dune 3.18.2 provides support for the upcoming OCaml 5.4 release.

Activities:

Maintained by: Rudi Grinberg (@rgrinberg, Jane Street), Nicolás Ojeda Bär (@nojb, LexiFi), Marek Kubica (@Leonidas-from-XIV, Tarides), Ali Caglayan (@Alizter), Etienne Millon (@emillon, Tarides), Stephen Sherratt (@gridbugs, Tarides), Antonio Nuno Monteiro (@anmonteiro), Etienne Marais (@maiste)

Dune Package Management

As of May 9, a large part of Dune-based packages on opam-repository now build successfully with Dune package management. At dune.check.ci.dev, we provide continuous monitoring of build success across the ecosystem, giving visibility into compatibility before migration.

The effort of making Dune package management compatible with the wider OCaml ecosystem is ongoing and aims to assess when Dune package management is ready for adoption in production settings. We are committed to maintain compatibility with both opam and Dune workflows, ensuring teams can transition at their own pace with minimal disruption to existing projects

Technical barriers have been and are being systematically addressed, e.g. improved handling of ZIP archives, better dependency conflict resolution, and enhanced support for pinned packages that don't use Dune's build system.

Activities:

"Expanding Dune Package Management to the Rest of the Ecosystem" on the Tarides Blog

Dune Developer Preview

Dune Developer Preview is an experimental channel that introduces cutting-edge features to streamline OCaml development workflows. Building upon Dune's foundation as OCaml's official build system, this initiative allows us to iterate quickly on ideas and experiment with improving the developer experience and with experimental features. For example, one feature that came out of Dune Developer Preview and made it into the upstream codebase is package management: by enabling Dune to deal with project dependencies, we eliminate the need to juggle multiple tools.

The tooling includes built-in LSP support, formatting capabilities, and a shared cache that dramatically improves build performance. Early adopters are encouraged to provide feedback as these experimental features mature toward stable releases.

We are in the process of adopting Dune Developer Preview for the OCaml Platform Tools and other projects. This is to ensure that (1) Dune Developer Preview keeps providing a good developer experience on production codebases and (2) to catch bugs and issues as early as we can. At the moment, we are making a concerted effort to fix issues and add necessary features that block adoption of Dune Developer Preview on the OCaml Platform Tools projects.

We're always interested in and addressing community feedback and bug reports, as well. In March, we conducted a public survey to better understand the reach, adoption, and experience of/with Dune Developer Preview in the OCaml community.

Activities:

Dune Developer Preview Adoption Survey

Editor Tools

Roadmap: Edit / (W19) Navigate Code, Edit / (W20) Refactor Code

To better understand how the OCaml community uses the different editor plugins available for OCaml, and to get an idea which features are most anticipated, we ran a survey on the OCaml Editors Plugins.

Notable Activity

OCaml Editor Plugins Survey
April 2025 Editors Dev Meeting Focus: Project-wide occurrences demo
February 2025 Editors Dev Meeting Focus: Introduction of ocaml-eglot Emacs mode

OCaml LSP Server maintained by: Ulysse Gérard (@voodoos, Tarides), Xavier Van de Woestyne (@xvw, Tarides), Rudi Grinberg (@rgrinberg, Jane Street)

Merlin maintained by: Ulysse Gérard (@voodoos, Tarides), Xavier Van de Woestyne (@xvw, Tarides)

Merlin and OCaml LSP Server

Project-wide occurrences are available in both Merlin and OCaml-LSP, allowing developers to find all instances of a symbol across their codebase by running dune build @build-index -w. The feature has basic editor support via merlin-project-occurrences in Emacs and :MerlinOccurrencesProjectWide in Vim. Additionally, users of OCaml 5.3 and LSP-based plugins can experiment with the first iteration on project-wide renaming.

Visual Studio Code plugin

Behind the scenes, some work is happening on improving the developer experience for the OCaml VSCode editor plugin: When ocaml-lsp-server is not found in the opam switch, the plugin will prompt the user to offer installing it, and we are working on making the editor plugin work seamlessly with the recent dune package management features.

Notable Activity

WIP on opam: Automatically installing/updating ocaml-lsp-server https://github.com/ocamllabs/vscode-ocaml-platform/pull/1725
WIP on Dune: Automatically configuring dune package management: https://github.com/ocamllabs/vscode-ocaml-platform/pull/1791

Emacs support

On January 17, OCaml-eglot version 1.0.0 was released, providing a new
minor emacs mode to enable the editor features provided by ocaml-lsp-server.
This replaces the venerable “merlin-mode”, after many years of loyal service.

Subsequent releases 1.1.0 and 1.2.0 enable support for
flycheck as a configurable alternative to flymake (1.0.0 release),
Emacs 30.1 support, better user experience and error handling, as
well as support for new features.

All these features have enabled OCaml-eglot to support client commands, making it possible to extend OCaml-eglot more easily and to integrate features much more rapidly. Since version 1.2.0, OCaml-eglot has all the functions of Merlin mode (and more)!

We encourage you to try ocaml-eglot (refer to the updated documentation on editor setup on OCaml.org) and to give feedback / report bugs by raising an issue on the ocaml-eglot repository!

Besides this, we have updated the documentation on Editor Setup on OCaml.org to reflect the new situation for Emacs!

Notable Activity

Documentation Tools

Roadmap: Share / (W25) Generate Documentation

Odoc

Odoc 3.0 has arrived after more than a year of development since the previous 2.4 release, bringing significant enhancements to OCaml's documentation tooling. The update introduces powerful new features including type-based search functionality through Sherlodoc, a global sidebar for improved navigation across documentation pages, and integrated source code display that allows developers to jump directly from documentation to rendered source regardless of module system complexity. Additional highlights include support for multimedia content (images, video, and audio), hierarchical documentation pages for better structure, and cross-package linking capabilities that create truly connected documentation, as well as support for incremental documentation builds.

It's worth noting that Dune does not yet support Odoc 3 as its rules need rewriting to accommodate the new CLI and incremental build capabilities. In the interim, developers can use the standalone odoc_driver command to generate documentation for their packages as shown in the "Remapping dependencies" documentation.

The Odoc team encourages all OCaml developers to test their documentation with the new release before publishing packages, which can help avoid post-release fixes like this example. For a practical introduction to the new features, developers can install the package via opam install odoc-driver and explore the comprehensive documentation available for the Odoc toolchain.

Notable Activity

Release of odoc 3.0.0
"Odoc 3: So what?" on Jon Ludlam's blog - blog post that touches on how odoc 3's cross-package linking capabilities enable writing better manuals

Maintained by: Jon Ludlam (@jonludlam, Tarides), Daniel Bünzli (@dbuenzli), Jules Aguillon (@julow, Tarides), Paul-Elliot Anglès d'Auriac (@panglesd, Tarides), Emile Trotignon (@EmileTrotignon, Tarides, then Ahrefs)

Package Management

Opam

The first alpha of opam 2.4.0 has been released, bringing significant improvements.

The removal of GNU patch and diff as runtime dependencies reduces cross-platform inconsistencies, as the manager now uses the native OCaml patch library instead. Nix users will appreciate Nix support for external dependencies, facilitating more consistent environments across development and production systems.

Notable for daily development work: pinned VCS repositories now display their current revision for better traceability, and several UI improvements provide clearer visibility into deprecated packages. The enhanced command set includes version comparison tools and better lock file management with opam lock --keep-local, particularly useful for maintaining consistent dependency states across team environments.

Teams running NixOS will benefit from fixed sandboxing support, while the new OPAMSOLVERTOLERANCE environment variable helps resolve persistent solver timeouts that previously was unsolvable by MCCS.

Early testing and feedback from development teams is encouraged to ensure a stable final release. Please report any issues to the bug-tracker.

Notable Activity

"opam 2.4.0 alpha1 release" on the Opam Blog
opam upgrade fixes #6373
Use patch OCaml library instead of the patch command #5892
Add some lints #6317, #6438
Pinning system fixes #5471, #6343, #6309, #6375, #6256, #5471
Add opam admin migrate-extrafiles command #5960, change opam admin check options #6335
Depext system: better performance #6324, enhance OpenBSD #6362
Some UI improvments #6376, #6401, #6358, #6273
UX improvments: remove ocaml-system from default compiler at init #6307
Provide a way to avoid solver timeouts #5510
Add opam lock <pkg> --keep-local #6411

Maintained by: Raja Boujbel (@rjbou - OCamlPro), Kate Deplaix (@kit-ty-kate, Ahrefs), David Allsopp (@dra27, Tarides)

Dune-release

Roadmap: Share / (W26) Package Publication

Dune-release 2.1.0, has been released, providing a new command dune-release delegate-info version, which makes it easier to identify the current version of a package as inferred by the tool. Additionally, the release introduces more flexibility with the --dev-repo flag for dune-release and dune-release publish commands, allowing users to override the dev-repo field specified in the .opam file during the release process.

Dune-release no longer publishes documentation to GitHub Pages by default. This decision reflects the OCaml ecosystem's consolidation around centralized documentation, as package documentation is now automatically built and served by ocaml.org/packages following publication to the opam repository.

The update also improves compatibility and resolves several issues, including a fix for decoding GitHub URLs and ensuring dune-release works with the experimental package management feature from Dune. The tool now handles the presence of ~/.dune/bin/dune without failing, making it more robust for developers exploring Dune's newer features.

Notable Activity

Release of dune-release 2.1.0

Maintained by: Thomas Gazagnaire (@samoht, Tarides), Etienne Millon (@emillon, Tarides), Marek Kubica (@Leonidas-from-XIV, Tarides)

Ppxlib

The ppxlib team has released versions 0.35.0 and 0.36.0!

Ppxlib 0.35.0, released in February 2025, brings significant improvements for OCaml 5.3 compatibility by allowing ppx rewriters to operate on files containing the new effect syntax. While ppx extensions and effect syntax can coexist, developers should note that rewriters might encounter errors when processing effect syntax nodes in extension payloads or generated code. The release introduces a new --use-compiler-pp driver flag, useful for preserving effect syntax when outputting source code instead of marshalled AST. This update also removes support for compilers older than 4.08.

The latest ppxlib 0.36.0, released in March 2025, updates the internal AST to target OCaml 5.2, enabling ppx authors to leverage features from this version while maintaining compatibility with OCaml 4.08.0 and newer. This release includes notable changes to the representation of functions. Thus, package authors are strongly encouraged to consult the upgrade guide as many ppxes may break.

Other improvements include fixing a bug in loc_of_attribute, adding support for the [@@@expand_inline] transformation and floating attribute context-free transformations, and introducing a -raise-embedded-errors flag to the driver.

Notable Activity

Maintained by: Patrick Ferris (@patricoferris)

OCaml Infrastructure

The OCaml infrastructure team has upgraded their OBuilder workers for FreeBSD from version 14.1 to 14.2, which directly impacts two key continuous integration services:

OCaml-CI (ocaml.ci.dev) - This service automatically tests OCaml projects hosted on GitHub, and will now test against FreeBSD 14.2 instead of 14.1. Projects using this CI service will automatically be tested against the newer FreeBSD version.
opam-repo-CI (opam.ci.ocaml.org) - This service tests pull requests to the opam package repository, and will also now test against FreeBSD 14.2 rather than 14.1.

With the release of ocaml-version 4.0.0, the OCaml version considered "recent" has been raised from 4.02 to 4.08. This change affects multiple services that use this definition to determine which OCaml versions to test against:

OCaml-CI - Will adjust which OCaml compiler versions are tested by default for projects
opam-repo-CI - Will modify its testing matrix for packages in the opam repository
Docker base image builder - Will only build images for OCaml 4.08 and newer

As these services update, testing on older OCaml releases (versions 4.02 through 4.07) will be gradually removed. Package maintainers should consider upgrading projects still using pre-4.08 OCaml versions to OCaml 4.08 or higher.

Apart from this, at the end of April 2025, registry.ci.dev, opam-repo-ci, OCaml-CI and get.dune.build were moved from Equinix Hosting to hosting at the Cambridge University Computer Lab, because of the sunset of the Equinix Metal platform.

Notable Activity

WIP: Odoc 3 on OCaml-Docs-CI

The OCaml documentation pages provided through the OCaml.org package area are scheduled to receive significant updates with the release of odoc 3. To enable odoc 3 and all of its new features on OCaml.org, we are overhauling the docs-ci pipeline that powers documentation on ocaml.org. The improved pipeline addresses dependency complexities by using a new tool (https://github.com/jonludlam/opamh) that archives and restores opam packages, eliminating redundant builds of packages like dune that previously occurred thousands of times. The underlying infrastructure is also being upgraded, with plans to migrate docs-ci to a new blade server.

Notable Activity

"OCaml-Docs-CI and Odoc 3" on Jon Ludlam's blog