Dune 1.2.0

by Etienne Millon on Sep 6th, 2018

After a tiny but important patch release as 1.1.1, the dune team is thrilled to announce the release of dune 1.2.0! Here are some highlights of the new features in that version. The full list of changes can be found in the dune repository.

Watch mode

When developing, it is common to edit a file, run a build, read the error message, and fix the error. Since this is a very tight loop and developers are doing this hundreds or thousands times a day, it is crucial to have the quickest feedback possible.

dune build and dune runtest now accept a -w flag that will watch the filesystem for changes, and trigger a new build. This feature is demonstrated here:

Better error messages

Inspired by the great work done in Elm and bucklescript, dune now displays the relevant file in error messages.

 % cat dune
(executable
 (name my_program)
 (librarys cmdliner)
)
 % dune build
File "dune", line 3, characters 2-10:
3 |  (librarys cmdliner)
      ^^^^^^^^
Error: Unknown field librarys
Hint: did you mean libraries?

Many messages have also been improved, in particular to help users switching from the jbuild format to the dune format.

dune unstable-fmt

Are you confused about how to format S-expressions? You are not alone. That is why we are gradually introducing a formatter for dune files. It can transform a valid but ugly dune into one that is consistently formatted.

 % cat dune
(executable( name ls) (libraries cmdliner)
(preprocess (pps ppx_deriving.std)))
 % dune unstable-fmt dune
(executable
 (name ls)
 (libraries cmdliner)
 (preprocess
  (pps ppx_deriving.std)
 )
)

This feature is not ready yet for the end user (hence the unstable part), and in particular the concrete syntax is not stable yet. But having it already in the code base will make it possible to build useful integrations with dune itself (to automatically reformat all dune files in a project, for example) and common editors, so that they format dune files on save.

First class support of findlib plugins

It is now easy to support findlib plugins by just adding the findlib.dynload library dependency. Then you can use Fl_dynload module in your code which will automatically do the right thing. A complete example can be found in the dune manual.

Promote only certain files

The dune promote command now accept a list of files. This is useful to promote just the file that is opened in a text editor for example. Some emacs bindings are provided to do this, which works particularly well with inline expectation tests.

Deprecation message for (wrapped) modes

By default, libraries are (wrapped true), which means that they expose a single OCaml module (source files are exposed as submodules of this main module). This is usually desired as it makes link-time name collisions less likely. However, a lot of libraries are using (wrapped false) (expose all source files as modules) to keep compatibility.

It can be challenging to transition from (wrapped false) to (wrapped true) because it breaks compatibility. That is why we have added (wrapped (transition "message")) which will generate wrapped modules but keep unwrapped modules with a deprecation message to help coordinate the change.

Credits

Special thanks to our contributors for this release: @aantron, @anuragsoni, @bobot, @ddickstein, @dra27, @drjdn, @hongchangwu, @khady, @kodek16, @prometheansacrifice and @ryyppy.