dune/doc/project-layout-specification.rst

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Project Layout and Metadata Specification
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A typical jbuilder project will have one or more ``<package>.opam`` file
at toplevel as well as ``jbuild`` files wherever interesting things are:
libraries, executables, tests, documents to install, etc...

It is recommended to organize your project so that you have exactly one
library per directory. You can have several executables in the same
directory, as long as they share the same build configuration. If you'd
like to have multiple executables with different configurations in the
same directory, you will have to make an explicit module list for every
executable using ``modules``.

The next sections describe the format of Jbuilder metadata files.

Note that the Jbuilder metadata format is versioned in order to ensure
forward compatibility. There is currently only one version available,
but to be future proof, you should still specify it in your ``jbuild``
files. If no version is specified, the latest one will be used.

.. _metadata-format:

Metadata format
===============

Most configuration files read by Jbuilder are using the S-expression
syntax, which is very simple. Everything is either an atom or a list.
The exact specification of S-expressions is described in the
documentation of the `parsexp <https://github.com/janestreet/parsexp>`__
library.

In a nutshell, the syntax is as follows:

- atoms that do no contain special characters are simply written as
  is. For instance: ``foo``, ``bar`` are valid atomic S-expressions

- atoms containing special characters or spaces must be quoted using
  the syntax ``"..."``: ``"foo bar\n"``

- lists are formed by surrounding a sequence of S-expressions separated
  by spaces with parentheses: ``(a b (c d))``

- single-line comments are introduced with the ``;`` character and may
  appear anywhere except in the middle of a quoted atom

- block comment are enclosed by ``#|`` and ``|#`` and can be nested

Note that the format is completely static. However you can do
meta-programming on jbuilds files by writing them in :ref:`ocaml-syntax`.

.. _opam-files:

<package>.opam files
====================

When a ``<package>.opam`` file is present, Jbuilder will know that the
package named ``<package>`` exists. It will know how to construct a
``<package>.install`` file in the same directory to handle installation
via `opam <https://opam.ocaml.org/>`__. Jbuilder also defines the
recursive ``install`` alias, which depends on all the buildable
``<package>.install`` files in the workspace. So for instance to build
everything that is installable in a workspace, run at the root:

::

    $ jbuilder build @install

Declaring a package this way will allow you to add elements such as
libraries, executables, documentation, ... to your package by declaring
them in ``jbuild`` files.

Such elements can only be declared in the scope defined by the
corresponding ``<package>.opam`` file. Typically, your
``<package>.opam`` files should be at the root of your project, since
this is where ``opam pin ...`` will look for them.

Note that ``<package>`` must be non-empty, so in particular ``.opam``
files are ignored.

.. _scopes:

Scopes
------

Any directory containing at least one ``<package>.opam`` file defines
a scope. This scope is the sub-tree starting from this directory,
excluding any other scopes rooted in sub-direcotries.

Typically, any given project will define a single scope. Libraries and
executables that are not meant to be installed will be visible inside
this scope only.

Because scopes are exclusive, if you whish to include the dependencies
of the project you are currently working on into your workspace, you
may copy them in a ``vendor`` directory, or any other name of your
choice. Jbuilder will look for them there rather than in the installed
world and there will be no overlap between the various scopes.

Package version
---------------

Note that Jbuilder will try to determine the version number of packages
defined in the workspace. While Jbuilder itself makes no use of version
numbers, it can be use by external tools such as
`ocamlfind <http://projects.camlcity.org/projects/findlib.html>`__.

Jbuilder determines the version of a package by first looking in the
``<package>.opam`` for a ``version`` variable. If not found, it will try
to read the first line of a version file in the same directory as the
``<package>.opam`` file. The version file is any file whose name is, in
order in which they are looked for:

-  ``<package>.version``
-  ``version``
-  ``VERSION``

The version file can be generated by a user rule.

If the version can't be determined, Jbuilder just won't assign one.

Note that if you are using `Topkg <https://github.com/dbuenzli/topkg>`__
as well in your project, you shouldn't manually set a version in your
``<package>.opam`` file or write/generate on of the file listed above.
See the section about :ref:`using-topkg` for more details.

Odig conventions
----------------

Jbuilder follows the `odig <http://erratique.ch/software/odig>`__
conventions and automatically installs any README\*, CHANGE\*, HISTORY\*
and LICENSE\* files in the same directory as the ``<package>.opam`` file
to a location where odig will find them.

Note that this includes files present in the source tree as well as
generated files. So for instance a changelog generated by a user rule
will be automatically installed as well.

jbuild-ignore
=============

By default Jbuilder traverses the whole source tree, ignoring the
following files and directories:

- any file that start with ``.#``
- any directory that start with either ``.`` or ``_``

To ignore a subtree, simply write a ``jbuild-ignore`` file in the
parent directory containing the name of the sub-directories to ignore.

So for instance, if you write ``foo`` in ``src/jbuild-ignore``, then
``src/foo`` won't be traversed and any ``jbuild`` file it contains will
be ignored.

``jbuild-ignore`` files contain a list of directory names, one per line.