dune/doc/manual.org

• Intro
• Terminology
• Jbuilder project layout and metadata specification
  • Metadata format
  • <package>.opam files
    • Package version
    • Odig conventions
  • jbuild
    • Specification
      • jbuilder_version
      • library
      • executables
      • rule
      • ocamllex
      • ocamlyacc
      • alias
      • provides
      • install
      • Common items
        • Ordered set language
        • Variables expansion
        • Alternative dependencies
        • Preprocessing specification
          • Per module pre-processing specification
        • Dependency specification
          • Glob
        • OCaml flags
        • User actions
• Usage
• Advanced topics
  • META file generation

This document describe the usage of Jbuilder and specifies its metadata format. It is written using the org syntax and the best way to read it is either using the Emacs org-mode or on github.

If you want quick usage example, read the quick start document instead.

Intro

Jbuilder is a build system for OCaml. It is not intended as a completely generic build system that is able to build any given project in any language. On the contrary, it makes lots of choices in order to encourage a consistent development style.

This scheme is inspired from the one used inside Jane Street and adapted to the opam world. It has matured over a long time and is used daily by hundred of developpers, which means that it is highly tested and productive.

When using Jbuilder, you give very little and high-level information to the build system, which in turns takes care of all the low-level details, from the compilation of your libraries, executables and documentation to the installation, setting up of tests, setting up of the devepment tools such as merlin, etc…

In addition to the normal features one would expect from a build system for OCaml, Jbuilder provides a few additional ones that detach it from the crowd:

• you never need to tell Jbuilder where things such as libraries are. Jbuilder will always discover it automatically. In particular this mean that when you want to re-organize your project you need to do no more than rename your directories, Jbuilder will do the rest
• things always work the same whether your dependencies are local or installed on the system. In particular this mean that you can always drop in the source for a dependency of your project in your working copy and Jbuilder will start using immediately. This makes Jbuilder a great choice for multi-project development
• cross-platform: as long as your code is portable, Jbuilder will be able to cross-compile it automatically
• release directly from any revision: Jbuilder needs no setup stage. To release your project, you can simply point to a specific tag. You can of course add some release steps if you want to, but it is not necessary

The first section of this document defines some terms used in the rest of this manual. The second section specifies the Jbuilder metadata format and the third one describes how to use the jbuilder command.

Terminology

• package: a package is a set of libraries, executables, … that are built and installed as one by opam
• project: project is a source tree, maybe containing one or more packages
• root: the root is the directory from where Jbuilder can build things. Jbuilder knows how to build target that are descendant of the root. Anything outside of the tree starting from the root is considered part of the installed world
• workspace: a workspace is the sub-tree starting from the root. It can contain any number of projects that will be built simultaneously by jbuilder
• installed world: anything outside of the workspace, that Jbuilder takes for granted and doesn't know how to build
• build context: a build context is a subdirectory of the <root>/_build directory. It contains all the build artifacts of the workspace built against a specific configuration. The is always a default build context, which correspond to the environemnt in which Jbuilder is executed. Unless a workspace.sexp file exists in a parent directory and defines more build contexts, default is the only build context available
• alias: an alias is a build target that doesn't produce any file and has configurable dependencies. Alias are per-directory and some are recursive; asking an alias to be built in a given directrory will trigger the construction of the alias in all children directories recursively. The most interesting one is runtest, which will run user defined tests

Jbuilder project layout and metadata specification

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

It is recommemded 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.

The rest of these section describe the format of Jbuilder metadata files.

Note that the Jbuilder metadata format is versionned in order to ensure forward compatibilty. Jane Street packages use a special jane_street version which correspond to a rolling and unstable version that follows the internal Jane Street development. You shouldn't use this in your project, it is only intended to make the publication of Jane Street packages easier.

Except for the special jane_street version, there is currently only one version available, but to be future proof, you should still specify it in your toplevel jbuild file. If no version is specified, the latest one will be used. Specifying a version in a jbuild file will affect the current file as well as the sub-tree where it is defined. As a result it is recommended to specify the version in the toplevel jbuild file of your project.

Metadata format

All configuration files read by Jbuilder are using 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 library.

Note that the format is completely static. If you have a pattern that's repeated a lot, you can use cinaps to generate the boilerplate.

<package>.opam files

Jbuilder doesn't read <package>.opam files, however when a <package>.opam is present, Jbuilder will knows 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. In addition, Jbuilder will also know how to build <package>.install at the root of the workspace, for convenience. Jbuilder also defines the install alias, which depends on all the buildable <package>.install at the root of the workspace. So for instance to build everything that is installable in a workspace, run:

$ jbuilder build @install

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

Jbuilder will only register the existence of <package> in the subtree starting where the <package>.opam file lives, so you can only declare parts of the packages in this subtree. Typically your <package>.opam files should be at the root of your project, since this is where opam pin ... will look for them.

Package version

Note that when installing a package, Jbuilder will write down the version of the package in the installation directory. While Jbuilder makes no use of it at the moment, it can be use by external tools such as ocamlfind.

Jbuilder determines the version of a package by looking for a version file in the same directory as the <package>.opam file and by reading its first line. The version file is any file whose name is, in order in which they are looked for:

• <package>.version
• version
• VERSION

Note that it is not mandatory to specify a version number and if Jbuilder cannot determine the package version, then it just won't assign one. Managing versions should be left to package managers anyway.

Odig conventions

Jbuilder follows the 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 include files present in the source tree as well as generated files. So for instance a changelog generated by a rule will be automatically installed as well.

jbuild

jbuild files are the main part of Jbuilder, and are the origin of its name. They are used to describe libraries, executables, tests, and everything Jbuilder needs to know about.

Specification

jbuild files are composed of stanzas. For instance a typical jbuild looks like:

(library
 ((name mylib)
  (libraries (base lwt))))

(rule
 ((targets (foo.ml))
  (deps    (generator/gen.exe))
  (action  (run ${<} -o ${@}))))

The following sections describe the available stanzas and their meaning.

jbuilder_version

(jbuilder_version 1) specifies that we are using the version 1 of the Jbuilder metadata format in this jbuild file and the sub-tree starting from this directory.

library

The library stanza must be used to describe OCaml libraries. The format of library stanzas is as follow:

(library
  ((name <library-name>)
   <optional-fields>
  ))

<library-name> is the real name of the library. It determines the names of the archive files generated for the library as well as the module name under which the library will be available, unless (wrapped false) is used (see below). It must be a valid OCaml module name but doesn't need to start with a uppercase letter.

For instance, the modules of a library named foo will be available as Foo.XXX outside of foo itself. It is however allowed to write an explicit Foo module, in which case this will be the interface of the library and you are free to expose only the modules you want.

<optional-fields> are:

• (public_name <name>) this is the name under which the library can be refered as a dependency when it is not part of the current workspace, i.e. when it is installed. Without a (public_name ...) field, the library will not be installed by Jbuilder. The public name must start by the package name it is part of and optionally followed by a dot and anything else you want. The package name must be one of the package that Jbuilder knows about, as determined by the <package>.opam files
• (synopsis <string>) should give a one-line description of the library. This is used by tools that list installed libraries
• (modules <modules>) specifies what modules are part of the library. By default Jbuilder will use all the .ml files in the same directory as the jbuild file. This include ones that are present in the file system as well as ones generated by user rules. You can restrict this list by using a (modules <modules>) field. <modules> uses the ordered set language where elements are module names and don't need to start with a uppercase letter. For instance to exclude module Foo: (modules (:standard \ foo))
• (libraries (<library-dependencies>)) is used to specifiy the dependencies of the library. In here you should put library names. For library that are present in the workspace, you can use either the real name or the public name. For libraries that are part of the installed world, you need to use the public name. For instance: (libraries (base re)). In addition to direct dependencies you can specify alternative dependencies. This is described in the alternative dependencies section
• (wrapped <boolean>) specifies whether the modules of the library should be available only through of the toplevel library module, or should all be exposed at toplevel. The default is true and it is highly recommed to keep it this way. Because OCaml toplevel modules must all be unique when linking an executables, polluting the toplevel namespace will make your library unusable with other libraries if there is a module name clash. This option is only intended for libraries that manually prefix all their modules by the library name
• (preprocess <preprocess-spec>) specifies how to pre-process files if needed. The default is no_processing. Other options are described in the preprocessing specification section
• (preprocessor_deps (<deps-conf list>)) specifies extra dependencies of the preprocessor, for instance if the preprocessor reads a generated file. The specification of dependencies is described in the dependency specification section
• (optional), if present it indicates that the library should only be built and installed if all the dependencies are available, either in the workspace or in the installed world. You can use this to provide extra features without adding hard dependencies to your project
• (c_names (<names>)), if your library has stubs, you must list the C files in this field, without the .c extension
• (cxx_names (<names>)) is the same as c_names but for C++ stubs
• (install_c_headers (<names>)) if your libraries has public C header files that must be installed, you must list them in this field, with the .h extension
• (modes (<modes>)) modes (byte and native) which should be built by default. This is only useful when writing libraries for the OCaml toplevel
• (kind <kind>) is the kind of the library. The default is normal, other available choices are ppx_rewriter and ppx_type_conv_plugin and must be set when the library is intended to be used as a ppx rewriter or a [@@deriving ...] plugin
• (ppx_runtime_libraries (<library-names>)) when the library is a ppx rewriter or a [@@deriving ...] plugin and has runtime dependencies, you can specify them here
• (virtual_deps (<opam-packages>). Sometimes opam packages enable a specific feature only if another package is installed. This is for instance the case of ctypes which will only install ctypes.foreign if the dummy ctypes-forein package is installed. You can specify such virtual dependencies here. You don't need to do so unless you use Jbuilder to synthesize the depends and depopts sections of your opam file
• flags, ocamlc_flags and ocamlopt_flags. See the section about specifying OCaml flags
• (library_flags (<flags>)) is a list of flags that are passed as it to ocamlc and ocamlopt when building the library archive files. You can use this to specify -linkall for instance. <flags> is a list of strings supporting variables expansion.
• (c_flags <flags>) specifies the compilation flags for C stubs, using the ordered set language. This field supports (:include ...) forms
• (cxx_flags <flags>) is the same as c_flags but for C++ stubs
• (c_library_flags <flags>) specifies the flags to pass to the C compiler when constructing the library archive file for the C stubs. <flags> uses the ordered set language and supports (:include ...) forms. When you are writing bindings for a C library named bar, you should typically write -lbar here, or whatever flags are necessary to to link against this library.

Note that when binding C libraries, Jbuilder doesn't provide special support for tools such as pkg-config, however it integrates easily with configurator by using (c_flags (:include ...)) and (c_library_flags (:include ...)).

executables

The executables stanza must be used to describe sets of executables. The format of executables stanzas is as follow:

(executables
  ((names (<entry point names>))
   <optional-fields>
  ))

<entry point names> is a list of module names that contain the main entry point of each executables. There can be additional modules in the current directory, you only need to list the entry point in (names ...). For every <name>, Jbuilder will know how to build <name>.exe and <name>.bc. <name>.exe is a native code executable and <name>.bc is a bytecode executable which requires ocamlrun to run.

Note that in case native compilation is not available, <name>.exe will in fact be a custom byte-code executable. Custom in the sense of ocamlc -custom, meaning that it is a native executable that embeds the ocamlrun virtual machine as well as the byte code. As such you can always rely on <name>.exe begin available.

<optional-fields> are:

• (libraries (<library-dependencies>)) is the same as the (libraries ...) field of libraries
• (modules <modules>) specifies which modules in the current directory Jbuilder should consider when building executables. Modules not listed here will be ignored and cannot be used inside executables described by the current stanza. It is interpreted in the same way as the (modules ...) field of libraries
• (preprocess <preprocess-spec>) is the same as the (preprocess ...) field of libraries
• (preprocessor_deps (<deps-conf list>)) is the same as the (preprocessor_deps ...) field of libraries
• flags, ocamlc_flags and ocamlopt_flags. See the section about specifying OCaml flags

rule

The rule stanza is used to create custom rules. It tells Jbuilder how to generate a specific set of files from a specific set of dependencies.

The syntax is as follow:

(rule
  ((targets (<filenames>))
   (deps    (<deps-conf list>))
   (action  <action>)))

<filenames> is a list of file names. Note that currently Jbuilder only support user rules with targets in the current directory.

<deps-conf list> specifies the dependencies of the rule. See the [[Dependency specification][dependency specification section]] for more details.

<action> is the action to run to produce the targets from the dependencies. See the actions section for more details.

ocamllex

(ocamllex (<names>)) is essentially a short-hand for:

(rule
  ((targets (<name>.ml))
   (deps    (<name>.mll))
   (action  (run ocamllex ${<}))))

ocamlyacc

(ocamlyacc (<names>)) is essentially a short-hand for:

(rule
  ((targets (<name>.ml <name>.mli))
   (deps    (<name>.mly))
   (action  (run ocamlyacc ${<}))))

alias

The alias stanza lets you add dependencies to an alias, or specify an action to run to construct the alias.

The syntax is as follow:

(rule
  ((name    <alias-name>)
   (deps    (<deps-conf list>))
   <optional-fields>
   ))

<name> is an alias name such as runtest.

<deps-conf list> specifies the dependencies of the rule. See the [[Dependency specification][dependency specification section]] for more details.

<optional-fields> are:

• <action>, an action to run when constructing the alias. See the actions section for more details.

The typical use of the alias stanza is to define tests:

(rule
  ((name   runtest)
   (deps   (my-test-program.exe))
   (action "./${<} blah")))

See the section about running tests for details.

provides

The provides stanza allows you to globally name a file, either a source file or a target. This is especially important for build tools; by using the provides mechanism, you don't need to know whether the binary is in the tree or installed.

The syntax is as follow:

(provides (<name> (file <filename>)))

<name> is the name under which the artefact can be refered and <filename> is the file it resolves to. When <filename> can be guessed from the <name>, you can use the following shorter syntax:

(provides <name>)

In this case, the file name is guessed as follow:

• if <name> contains a :, the file name is anything that comes after the first :
• otherwise it is the same as <name>

Once you have written a provides stanza, you can refer to the file in points to using the special forms ${bin:<name>} or ${findlib:<library>:<file>} inside (action ...) fields. See the section about variables expansion for details.

Note that any file referred by a provides stanza should probably be installed as well, using an /gitea/matthieu/dune/install stanza. If the file is meant to be installed in a library directory, then its name should be of the form <public-library-name>:<file>. It is meant to be installed in the bin directory, then its name should be the program name.

install

The install stanza is what lets you describe what Jbuilder should install, either when running jbuilder install or through opam.

Libraries don't need an install stanza to be installed, just a public_name field. Everything else needs an install stanza.

The syntax is as follow:

(install
  ((section <section>)
   (files   (<filenames>))
   <optional-fields>
  ))

<section> is the installation section, as described in the opam manual. The following sections are available:

• lib
• libexec
• bin
• sbin
• toplevel
• share
• share_root
• etc
• doc
• stublibs
• man
• misc

<files> is the list of files to install.

<optional-fields> are:

• (package <name>). If there are no ambiguities, you can omit this field. Otherwise you need it to specify which package these files are part of. The package is not ambiguous when the first parent directory to contain a <package>.opam file contains exactly one <package>.opam file

Common items

Ordered set language

A few fields takes as argument a ordered set and can be specified using a small DSL.

This DSL is interpreted by jbuilder into an ordered set of strings using the following rules:

• :standard denotes to the standard value of the field when it is absent
• an atom not starting with a : is a singleton containing only this atom
• a list of sets is the concatenation of its inner sets
• (<sets1> \ <sets2>) is the set composed of elements of <sets1> that do not appear in <sets2>

In addition, some fields support the inclusion of an external file using the syntax (:include <filename>). This is useful for instance when you need to run a script to figure out some compilation flags. <filename> is expected to contain a single S-expression and cannot contain (:include ...) forms.

Most fields using the ordered set language also support variables expansion. Variables are expanded after the set language is interpreted.

Variables expansion

Some fields can contains variables of the form $(var) or ${var} that are expanded by Jbuilder.

Jbuilder supports the following variables:

• ROOT is the relative path to the root of the workspace
• CC is the C compiler command line being used in the current build context
• CXX is the C++ compiler command line being used in the current build context
• ocaml_bin is the path where ocamlc lives
• OCAML is the ocaml binary
• OCAMLC is the ocamlc binary
• OCAMLOPT is the ocamlopt binary
• ocaml_version is the version of the compiler used in the current build context
• ocaml_where is the output of ocamlc -where
• ARCH_SIXTYFOUR is true if using a compiler targetting a 64 bit architecture and false otherwise

In addition, (action ...) fields support the following special variables:

• @ expands to the list of target, separated by spaces
• < expands to the first dependency, or the empty string if there are no dependencies
• ^ expands to the list of dependencies, separated by spaces
• exe:<path> expands to <path>, except when cross-compiling, in which case it will expand to <path> from the host build context
• bin:<program> expands to a path to program. If program is provided by a jbuild in the workspace (see provide stanzas), the locally built binarry will be used, otherwise it will be searched in the PATH of the current build context
• findlib:<public-library-name>:<file> expands to a path to file <file> of library <public-library-name>. If <public-library-name> is available in the current workspace, the local file will be used, otherwise the one from the installed world will be used

The last two forms of variable are what allows you to write custom rules that work transparently whether things are installed or not.

Alternative dependencies

It is sometimes the case that one wants to not depend on a specific library, but instead on whatever is already installed. For instance to use a different backend depending on the target.

Jbuilder allows this by using a (select ... from ...) form inside the list of library dependencies.

Select forms are specified as follow:

(select <target-filename> from
  ((<literals> -> <filename>)
   (<literals> -> <filename>)
   ...))

<literals> are list of literals, where each literal is one of:

• <library-name>, which will evaluate to true if <library-name> is available, either in the worksapce either in the installed world
• !<library-name>, which will evaluate to true if <library-name> is not availale in the workspace or in the installed world

When evaluating a select form, Jbuilder will create <target-filename> by copying the file given by the first (<literals> -> <filename>) case where all the literals evaluate to true. It is an error if none of the clauses are selectable. You can add a fallback by adding a clause of the form (-> <file>) at the end of the list.

Preprocessing specification

Jbuilder accept three kinds of pre-processing:

• no_preprocessing, meaning that files are given as it to the compiler, this is the default
• (command <shell-command>) to pre-process files using the given shell command. The input file is given as an extra argument and the command is expected to output the result on its standard output
• (pps (<ppx-rewriters-and-flags>)) to pre-process files using the given list of ppx rewriters

Note that in any cases, files are pre-processed only once. Jbuilder doesn't use the -pp or -ppx of the various OCaml tools.

<ppx-rewriters-and-flags> is expected to be a list where each element is either a command line flag if starting with a - or the name of a library implementing an OCaml AST rewriter. These must be libraries as Jbuilder always build a single ppx driver in order to speed up compilation.

Currently Jbuilder only knows how to buid ppx_driver based drivers, so using (pps (...)) will force a dependency on ppx_driver. You are however free to use ppx rewriters that are not based on ppx_driver in this list, since ppx_driver is able to import rewriters that where not designed for ppx_driver.

Per module pre-processing specification

By default a preprocessing specification will apply to all modules in the library/set of executables. It is possible to select the preprocessing on a module-by-module basis by using the following syntax:

(preprocess (per_file
               (<spec1> (<module-list1))
               (<spec2> (<module-list2))
               ...))

Where <spec1>, <spec2>, … are preprocessing specifications and <module-list1>, <module-list2>, … are list of module names. It is currently not possible to distinguish between .ml/.mli files, however it wouldn't be hard to support if needed.

For instance:

(preprocess (per_file
               ((command "./pp.sh X=1" (foo bar)))
               ((command "./pp.sh X=2" (baz)))))

Dependency specification

Dependecies in jbuild files can be specified using one of the following syntax:

• (file <filename>) or simply <filename>: depend on this file
• (alias <alias-name>): depend on the construction of this alias, for instance: (alias src/runtest)
• (glob_files <glob>): depend on all files matched by <glob>, see the glob section for details

In all these cases, the argument supports variables expansion.

Glob

You can use globs to declare dependencies on a set of files. Note that globs will match files that exist in the source tree as well as buildable targets, so for instance you can depend on *.cmi.

Currently jbuilder only support globbing files in a single directory. And in particular the glob is interpreted as follow:

• anything before the last / is taken as a literal path
• anything after the last /, or everything if the glob contains no /, is interpreted using the glob syntax

The glob syntax is interpreted as follow:

• \<char> matches exactly <char>, even if it is a special character (*, ?, …)
• * matches any sequence of characters, except if it comes first in which case it matches any character that is not . followed by anything
• ** matches any character that is not . followed by anything, except if it comes first in which case it matches anything
• ? matches any single character
• [<set>] matches any character that is part of <set>
• [!<set>] matches any character that is not part of <set>
• {<glob1>,<glob2>,...,<globn>} matches any string that is matched by one of <glob1>, <glob2>, …

OCaml flags

In library and executables stanzas, you can specify OCaml compilation flags using the following fields:

• (flags <flags>) to specify flags passed to both ocamlc and ocamlopt
• (ocamlc_flags <flags>) to specify flags passed to ocamlc only
• (ocamlopt_flags <flags>) to specify flags passed to ocamlopt only

For all these fields, <flags> is specified in the ordered set language.

User actions

(action ...) fields describe user actions. The argument can use one of these two forms:

• a simple string, in which case it is passed to bash
• using a small DSL, that is interpreted by jbuilder directly and doesn't require an external shell

In both case, each atom in the argument supports variables expansion. Moreover, you don't need to specify dependencies explicitely for the special ${exe:...}, ${bin:...} or ${findlib:...} forms, these are recognized automatically by Jbuilder.

The DSL is preferable in general as it will make your package more portable. It is currently quite limited, so the recommendation is to write a small OCaml program and use the DSL to invoke it. You can use shexp to write portable scripts or configurator for configuration related tasks.

The following constructions are available:

• (run <prog> <args>) to execute a program
• (chdir <dir> <DSL>) to change the current directory
• (setenv <var> <value> <DSL>) to set an environment variable
• (with-stdout-to <file> <DSL>) to redirect the output to a file

Usage

TODO

Advanced topics

This section describes some details of Jbuilder for advanced users.

META file generation

Jbuilder uses META files from the findlib library manager in order to inter-operate with the rest of the world when installing libraries. It is able to generate them automatically. However, for the rare cases where you would need a specific META file, or to ease the transition of a project to Jbuilder, it is allowed to write/generate a specific one.

In order to do that, write or setup a rule to generate a META.<package> file in the same directory as the <package>.opam file. If you do that, Jbuilder will still generate a META file but it will be called META.<package>.from-jbuilder. So for instance if you want to extend the META file generated by Jbuilder you can write:

(rule
 ((targets (META.foo))
  (deps    (META.foo.from-jbuilder))
  (action  "{ cat ${<}; echo blah } > ${@}")))

Additionally, Jbuilder provides a simpler mechanism for this scheme: just write or generate a META.<package>.template file containing a line of the form # JBUILDER_GEN. Jbuilder will automatically insert its generated META contents in place of this line.