Dune 3.8.0

The dune team is pleased to announce the release of Dune 3.8.0.

It is now available in opam-repository. As usual, it should always be safe to upgrade your dune package: new features and deprecations are only available if you upgrade the language version in your dune-project files.

🌟 Spotlight Features

  1. Dune concurrent action

Dune 3.8.0 introduced the new concurrent action. You can now use it instead of the progn action to execute actions concurrently.

For instance:

  (write-file A "I am file A.\n")
  (write-file B "I am certainly file B.\n")
  (write-file C "I am most certainly file C.\n"))))

will write to files A, B and C concurrently.

  1. Support for .mld files

In Dune 3.7.0, we introduced version 0.3 of the mdx stanza, which came with support for .mld files.

In Dune 3.8.0, .mld files are now supported by default with version 0.4 of the mdx stanza!

Have a look at this diff to see how to migrate your code to the new stanza version.

See full changelog


  • Introduce mdx stanza 0.4 requiring mdx >= 2.3.0 which updates the default list of files to include *.mld files (#7582, @Leonidas-from-XIV)

  • Allow (stdlib ...) to be used with (wrapped false) in library stanzas (#7139, @anmonteiro).

  • Allow the main module of a library with (stdlib ...) to depend on other libraries (#7154, @anmonteiro).

  • Support (link_flags ...) in (cinaps ...) stanza. (#7423, fixes #7416, @nojb)

  • Allow (package ...) in any position within (rule ...) stanza (#7445, @Leonidas-from-XIV)

  • Added a new user action (concurrent ) which is like (progn ) but runs the actions concurrently. (#6933, @Alizter)

  • Accept the Ordered Set Language for the modes field in library stanzas (#6611, @anmonteiro).

  • Allow parallel execution of inline tests partitions (#7012, @hhugo)

  • Add the --display-separate-messages flag to separate the error messages produced by commands with a blank line. (#6823, fixes #6158, @esope)

  • Add --watch-exclusions to Dune build options (#7216, @jonahbeckford)

  • Adds support for loading plugins in toplevels (#6082, fixes #6081, @ivg, @richardlford)

  • Introduce a public_headers field on libraries. This field is like install_c_headers, but it allows to choose the extension and choose the paths for the installed headers. (#7512, @rgrinberg)

  • Dune can now detect Coq theories from outside the workspace. This allows for composition with installed theories (not necessarily installed with Dune). (#7047, @Alizter, @ejgallego)

  • Added a --no-build option to dune coq top for avoiding rebuilds (#7380, fixes #7355, @Alizter)

  • Add a coqdoc_flags field to the coq.theory stanza allowing the user to pass extra arguments to coqdoc. (#7676, fixes #7954 @Alizter)

  • Preliminary support for Coq compiled intefaces (.vos files) enabled via (mode vos) in coq.theory stanzas. This can be used in combination with dune coq top to obtain fast re-building of dependencies (with no checking of proofs) prior to stepping into a file. (#7406, @rlepigre)

  • Read pkg-config arguments from the PKG_CONFIG_ARGN environment variable (#1492, #7734, @anmonteiro)

  • Use $PKG_CONFIG, when set, to find the pkg-config binary (#7469, fixes #2572, @anmonteiro)


  • Bootstrap: remove reliance on shell. Previously, we'd use the shell to get the number of processors. (#7274, @rgrinberg)

  • Non-user proccesses such as version control or config checking are now run silently. (#6994, fixes #4066, @Alizter)

  • Bytecode executables built for JSOO are linked with -noautolink and no longer depend on the shared stubs of their dependent libraries (#7156, @nojb)

  • Always include opam files in the generated .install file. Previously, it would not be included whenever (generate_opam_files true) was set and the .install file wasn't yet generated. (#7547, @rgrinberg)


  • Modules that were declared in (modules_without_implementation), (private_modules) or (virtual_modules) but not declared in (modules) will cause Dune to emit a warning which will become an error in 3.9. (#7608, fixes #7026, @Alizter)

  • Coq language versions less 0.8 are deprecated, and will be removed in an upcoming Dune version. All users are required to migrate to (coq lang 0.8) which provides the right semantics for theories that have been globally installed, such as those coming from opam (@ejgallego, @Alizter)


  • Find pps dependencies in the host context when cross-compiling, (#7415, fixes #4156, @anmonteiro)

  • Fix plugin loading with findlib. The functionality was broken in 3.7.0. (#7556, @anmonteiro)

  • Load the host context findlib.conf when cross-compiling (#7428, fixes #1701, @rgrinberg, @anmonteiro)

  • Allow overriding the ocaml binary with findlib configuration (#7648, @rgrinberg)

  • Resolve ppx_runtime_libraries in the target context when cross compiling (#7450, fixes #2794, @anmonteiro)

  • Fix dune install when cross compiling (#7410, fixes #6191, @anmonteiro, @rizo)

  • Fix string quoting in the json file written by --trace-file (#7773, @rleshchinskiy)

  • Correctly set MANPATH in dune exec. Previously, we would use the bin/ directory of the context. (#7655, @rgrinberg)

  • merlin: ignore instrumentation settings for preprocessing. (#7606, fixes #7465, @Alizter)

  • When a rule's action is interrupted, delete any leftover directory targets. This is consistent with how we treat file targets. (#7564, @rgrinberg)

  • Fix dune crashing on MacOS in watch mode whenever $PATH contains $PWD (#7441, fixes #6907, @rgrinberg)

  • Dune in watch mode no longer builds concurrent rules in serial (#7395 @rgrinberg, @jchavarri)

  • dune coq top now correctly respects the project root when called from a subdirectory. However, absolute filenames passed to dune coq top are no longer supported (due to being buggy) (#7357, fixes #7344, @rlepigre and @Alizter)

  • RPC: Ignore SIGPIPE when clients suddenly disconnect (#7299, #7319, fixes #6879, @rgrinberg)

  • Always clean up the UI on exit. (#7271, fixes #7142 @rgrinberg)

  • Bootstrap: correctly detect the number of processors by allowing nproc to be looked up in $PATH (#7272, @Alizter)

  • Speed up file copying on macos by using clonefile when available (@rgrinberg, #7210)

  • Support commands that output 8-bit and 24-bit colors in the terminal (#7188, @Alizter)

  • Speed up rule generation for libraries and executables with many modules (#7187, @jchavarri)

  • Do not re-render UI on every frame if the UI doesn't change (#7186, fix #7184, @rgrinberg)

  • Make coq_db creation in scope lazy (@ejgallego, #7133)

  • dune install now respects --display quiet mode (#7116, fixes #4573, fixes #7106, @Alizter)

  • Stub shared libraries (dllXXX_stubs.so) in Dune-installed libraries could not be used as dependencies of libraries in the workspace (eg when compiling to bytecode and/or Javascript). This is now fixed. (#7151, @nojb)

  • Fix regression where Merlin was unable to handle filenames with uppercase letters under Windows. (#7577, @nojb)

  • On nix+macos, pass -f to the codesign hook to avoid errors when the binary is already signed (#7183, fixes #6265, @greedy)

  • Fix bug where RPC clients built with dune-rpc-lwt would crash when closing their connection to the server (#7581, @gridbugs)

  • Fix RPC server on Windows (used for OCaml-LSP). (#7666, @nojb)