Stanza reference


These files are used to mark the root of projects as well as define project-wide parameters. The first line of dune-project must be a lang stanza with no extra whitespace or comments. The lang stanza controls the names and contents of all configuration files read by Dune and looks like:

(lang dune 2.8)

Additionally, they can contains the following stanzas.


Sets the name of the project. This is used by dune subst and error messages.

(name <name>)


Sets the version of the project:

(version <version>)


By default, dune allows transitive dependencies of dependencies to be used directly when compiling OCaml. However, this setting can be controlled per project:

(implicit_transitive_deps <bool>)

When set to false, all dependencies that are directly used by a library or an executable must be directly added in the libraries field. We recommend users to experiment with this mode and report any problems.

Note that you must use threads.posix instead of threads when using this mode. This is not an important limitation as threads.vm are deprecated anyways.

In some situations, it’s desirable to selectively preserve the behavior of transitive dependencies being available to users of a library. For example, if we define a library foo_more, that extends foo, we might want users of foo_more to immediately have foo available as well. To do this, we must define the dependency on foo as re-exported:

 (name foo_more)
 (libraries (re_export foo)))


Executables are made of compilation units whose names may collide with the compilation units of libraries. To avoid this possibility, dune prefixes these compilation unit names with Dune__exe__. This is entirely transparent to users except for when such executables are debugged. In which case the mangled names will be visible in the debugger.

Starting from dune 1.11, an option is available to turn on/off name mangling for executables on a per project basis:

(wrapped_executables <bool>)

Starting from dune 2.0, dune mangles compilation units of executables by default. However, this can still be turned off using (wrapped_executables false)


Traditionally, JavaScript targets were defined for every bytecode executable. This was not very precise and did not interact well with the @all alias.

You can opt out of this behaviour by using:


When this mode is enabled, an explicit js mode needs to be added to the (modes ...) field of executables in order to trigger JavaScript compilation. Explicit JS targets declared like this will be attached to the @all alias.

Starting from dune 2.0 this behaviour is the default, and there is no way to disable it.


A dialect is an alternative frontend to OCaml (such as ReasonML). It is described by a pair of file extensions, one corresponding to interfaces and one to implementations.

A dialect can use the standard OCaml syntax or it can specify an action to convert from a custom syntax to a binary OCaml abstract syntax tree.

Similarly, a dialect can specify a custom formatter to implement the @fmt alias, see Automatic formatting.

When not using a custom syntax or formatting action, a dialect is nothing but a way to specify custom file extensions for OCaml code.

 (name <name>)
  (extension <string>)
  <optional fields>)
  (extension <string>)
  <optional fields>))

<name> is the name of the dialect being defined. It must be unique in a given project.

(extension <string>) specifies the file extension used for this dialect, for interfaces and implementations. The extension string must not contain any dots, and be unique in a given project (so that a given extension can be mapped back to a corresponding dialect).

<optional fields> are:

  • (preprocess <action>) is the action to run to produce a valid OCaml abstract syntax tree. It is expected to read the file given in the variable named input-file and output a binary abstract syntax tree on its standard output. See Preprocessing with actions for more information.

    If the field is not present, it is assumed that the corresponding source code is already valid OCaml code and can be passed to the OCaml compiler as-is.

  • (format <action>) is the action to run to format source code for this dialect. The action is expected to read the file given in the variable named input-file and output the formatted source code on its standard output. For more information. See Automatic formatting for more information.

    If the field is not present, then if (preprocess <action>) is not present (so that the dialect consists of valid OCaml code), then by default the dialect will be formatted as any other OCaml code. Otherwise no special formatting will be done.


Starting in dune 2.0, Automatic formatting is automatically enabled. This can be controlled by using

(formatting <setting>)

where <setting> is one of:

  • disabled, meaning that automatic formatting is disabled
  • (enabled_for <languages>) can be used to restrict the languages that are considered for formatting.


Dune is able to use metadata specified in the dune-project file to generate .opam files, see Generating opam files. To enable this integration, add the following field to the dune-project file:

(generate_opam_files true)

Dune uses the following global fields to set the metadata for all packages defined in the project:

  • (license <name>) - Specifies the license of the project, ideally as an identifier from the SPDX License List
  • (authors <authors>) - A list of authors
  • (maintainers <maintainers>) - A list of maintainers
  • (source <source>) - where the source is specified two ways: (github <user/repo>) or (uri <uri>)
  • (bug_reports <url>) - Where to report bugs. This defaults to the GitHub issue tracker if the source is specified as a GitHub repository
  • (homepage <url>) - The homepage of the project
  • (documentation <url>) - Where the documentation is hosted

With this fields in, every time dune is called to execute some rules (either via dune build, dune runtest or something else), the opam files get generated.

Some or all of these fields may be overridden for each package of the project, see package.


Package specific information is specified in the (package <package>) stanza. It contains the following fields:

  • (name <string>) is the name of the package. This must be specified.
  • (synopsis <string>) is a short package description
  • (description <string>) is a longer package description
  • (depends <dep-specification>) are package dependencies
  • (conflicts <dep-specification) are package conflicts
  • (depopts <dep-specification) are optional package dependencies
  • (tags <tags>) are the list of tags for the package
  • (deprecated_package_names <name list>) is a list of names that can be used with the deprecated_library_name stanza to migrate legacy libraries from other build systems which do not follow Dune’s convention of prefixing the public name of the library with the package name.
  • (license <name>), (authors <authors>), (maintainers <maintainers>), (source <source>), (bug_reports <url>), (homepage <url>), (documentation <url>) are the same (and take precedence over) the corresponding global fields. These fields are available since Dune 2.0.
  • (sites (<section> <name>) ...) define a site named <name> in the section <section>.

Adding libraries to different packages is done via public_name field. See library section for details.

The list of dependencies <dep-specification> is modeled after opam’s own language: The syntax is as a list of the following elements:

op := '=' | '<' | '>' | '<>' | '>=' | '<='

stage := :with-test | :build | :dev

constr := (<op> <version>)

logop := or | and

dep := (name <stage>)
     | (name <constr>)
     | (name (<logop> (<stage> | <constr>)*))

dep-specification = dep+


Since Dune 2.8, it is possible to deactivate the systematic prepending of flags coming from ocamlc -config to the C compiler command line. This is done adding the following field to the dune-project file:

(use_standard_c_and_cxx_flags true)

In this mode, dune will populate the :standard set of C flags with the content of ocamlc_cflags and ocamlc_cppflags. These flags can be completed or overridden using the Ordered set language.


dune files are the main part of dune. They are used to describe libraries, executables, tests, and everything dune needs to know about.

The syntax of dune files is described in Lexical conventions section.

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

 (name mylib)
 (libraries base lwt))

 (deps   generator/gen.exe)
 (action (run %{deps} -o %{target})))

The following sections describe the available stanzas and their meaning.


Deprecated. This stanza is no longer used and will be removed in the future.


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

 (name <library-name>)

<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.

Note that by default libraries and other things that consume OCaml/Reason modules only consume modules from the directory where the stanza appear. In order to declare a multi-directory library, you need to use the include_subdirs stanza.

<optional-fields> are:

  • (public_name <name>) this is the name under which the library can be referred to 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 dune. 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 packages that dune knows about, as determined by the <package>.opam files
  • (package <package>) Install private library under the specified package. Such a library is now usable by public libraries defined in the same project. The findlib name for this library will be <package>.__private__.<name>, however the library’s interface will be hidden from consumers outside the project.
  • (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 dune will use all the .ml/.re files in the same directory as the dune 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 specify the dependencies of the library. See the section about Library dependencies for more details
  • (wrapped <boolean>) specifies whether the modules of the library should be available only through the top-level library module, or should all be exposed at the top level. The default is true and it is highly recommended to keep it this way. Because OCaml top-level modules must all be unique when linking an executables, polluting the top-level 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 and to ease porting of existing projects to dune
  • (wrapped (transition <message>)) Is the same as (wrapped true) except that it will also generate unwrapped (not prefixed by the library name) modules to preserve compatibility. This is useful for libraries that would like to transition from (wrapped false) to (wrapped true) without breaking compatibility for users. The <message> will be included in the deprecation notice for the unwrapped modules.
  • (preprocess <preprocess-spec>) specifies how to preprocess files if needed. The default is no_preprocessing. 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
  • (foreign_stubs <foreign-stubs-spec>) specifies foreign source files, e.g. C or C++ stubs, to be compiled and packaged together with the library. See the section Foreign sources and archives for more details. This field replaces the now deleted fields c_names, c_flags, cxx_names and cxx_flags.
  • (foreign_archives <foreign-archives-list>) specifies archives of foreign object files to be packaged with the library. See the section Foreign archives for more details. This field replaces the now deleted field self_build_stubs_archive.
  • (install_c_headers (<names>)), if your library has public C header files that must be installed, you must list them in this field, without the .h extension
  • (modes <modes>) modes which should be built by default. The most common use for this feature is to disable native compilation when writing libraries for the OCaml toplevel. The following modes are available: byte, native and best. best is native or byte when native compilation is not available
  • (no_dynlink) is to disable dynamic linking of the library. This is for advanced use only, by default you shouldn’t set this option
  • (kind <kind>) is the kind of the library. The default is normal, other available choices are ppx_rewriter and ppx_deriver and must be set when the library is intended to be used as a ppx rewriter or a [@@deriving ...] plugin. The reason why ppx_rewriter and ppx_deriver are split is historical and hopefully we won’t need two options soon. Both ppx kinds support an optional field (cookies <cookies>) where <cookies> is a list of pairs (<name> <value>) with <name> being the cookie name and <value> is a string that supports Variables evaluated by each invocation of the preprocessor (note: libraries that share cookies with the same name should agree on their expanded value)
  • (ppx_runtime_libraries (<library-names>)) is for when the library is a ppx rewriter or a [@@deriving ...] plugin and has runtime dependencies. You need to specify these runtime dependencies 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-foreign package is installed. You can specify such virtual dependencies here. You don’t need to do so unless you use dune to synthesize the depends and depopts sections of your opam file
  • js_of_ocaml sets options for JavaScript compilation, see js_of_ocaml
  • flags, ocamlc_flags and ocamlopt_flags. See the section about 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
  • (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 link against this library
  • (modules_without_implementation <modules>) specifies a list of modules that have only a .mli or .rei but no .ml or .re file. Such modules are usually referred as mli only modules. They are not officially supported by the OCaml compiler, however they are commonly used. Such modules must only define types. Since it is not reasonably possible for dune to check that this is the case, dune requires the user to explicitly list such modules to avoid surprises. Note that the modules_without_implementation field is not merged in modules, which represents the total set of modules in a library. If a directory has more than one stanza and thus a modules field must be specified, <modules> still need to be added in modules.
  • (private_modules <modules>) specifies a list of modules that will be marked as private. Private modules are inaccessible from outside the libraries they are defined in. Note that the private_modules field is not merged in modules, which represents the total set of modules in a library. If a directory has more than one stanza and thus a modules field must be specified, <modules> still need to be added in modules.
  • (allow_overlapping_dependencies) allows external dependencies to overlap with libraries that are present in the workspace
  • (enabled_if <blang expression>) conditionally disables a library. A disabled library cannot be built and will not be installed. The condition is specified using the Boolean language, and the field allows for the %{os_type} variable, which is expanded to the type of OS being targeted by the current build. Its value is the same as the value of the os_type parameter in the output of ocamlc -config
  • (inline_tests) enables inline tests for this library. They can be configured through options using (inline_tests <options>). See Inline tests for a reference of corresponding options.
  • (root_module <module>) this field instructs dune to generate a module that will contain module aliases for every library specified in dependencies. This is useful whenever a library is shadowed by a local module. The library may then still be accessible via this root module

Note that when binding C libraries, dune 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 ...)).


The foreign_library stanza describes archives of separately compiled foreign object files that can be packaged with an OCaml library or linked into an OCaml executable. See Foreign sources and archives for further details and examples.


In library and executables stanzas, you can specify js_of_ocaml options using (js_of_ocaml (<js_of_ocaml-options>)).

<js_of_ocaml-options> are all optional:

  • (flags <flags>) to specify flags passed to js_of_ocaml. This field supports (:include ...) forms
  • (javascript_files (<files-list>)) to specify js_of_ocaml JavaScript runtime files.

<flags> is specified in the Ordered set language.

The default value for (flags ...) depends on the selected build profile. The build profile dev (the default) will enable sourcemap and the pretty JavaScript output.

See JavaScript compilation for more information.


The deprecated_library_name stanza enables redirecting an old deprecated name after a library has been renamed. It’s syntax is as follows:

 (old_public_name <name>)
 (new_public_name <name>))

When a developer uses the old public name in a list of library dependencies, it will be transparently replaced by the new name. Note that it is not necessary for the new name to exist at definition time as it is only resolved at the point where the old name is used.

The old_public_name can also be one of the names declared in the deprecated_package_names field of the package declaration in dune-project file. In this case, the “old” library is understood to be a library whose name is not prefixed by the package name. Such a library cannot be defined in Dune, but other build systems allow it and this feature is meant to help migration from those systems.


The executable stanza must be used to describe an executable. The format of executable stanzas is as follows:

 (name <name>)

<name> is a module name that contains the main entry point of the executable. There can be additional modules in the current directory, you only need to specify the entry point. Given an executable stanza with (name <name>), dune will know how to build <name>.exe. If requested, it will also know how to build <name>.bc and <name>.bc.js (dune 2.0 and up also need specific configuration, see the modes optional field below). <name>.exe is a native code executable, <name>.bc is a bytecode executable which requires ocamlrun to run and <name>.bc.js is a JavaScript generated using js_of_ocaml.

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 being available. Moreover, it is usually preferable to use <name>.exe in custom rules or when calling the executable by hand. This is because running a byte-code executable often requires loading shared libraries that are locally built, and so requires additional setup such as setting specific environment variables and dune doesn’t do at the moment.

Native compilation is considered not available when there is no ocamlopt binary at the same place as where ocamlc was found.

Executables can also be linked as object or shared object files. See linking modes for more information.

<optional-fields> are:

  • (public_name <public-name>) specifies that the executable should be installed under that name. It is the same as adding the following stanza to your dune file:

     (section bin)
     (files (<name>.exe as <public-name>)))
  • (package <package>) if there is a (public_name ...) field, this specifies the package the executables are part of
  • (libraries <library-dependencies>) specifies the library dependencies. See the section about Library dependencies for more details
  • (link_flags <flags>) specifies additional flags to pass to the linker. This field supports (:include ...) forms
  • (link_deps (<deps-conf list>)) specifies the dependencies used only by the linker, for example when using a version script. See the Dependency specification section for more details.
  • (modules <modules>) specifies which modules in the current directory dune should consider when building this executable. Modules not listed here will be ignored and cannot be used inside the executable described by the current stanza. It is interpreted in the same way as the (modules ...) field of library
  • (root_module <module>) specifies a root_module that collects all dependencies specified in libraries. See the documentation for root_module in the library stanza.
  • (modes (<modes>)) sets the linking modes. The default is (exe). Before 2.0, it used to be (byte exe).
  • (preprocess <preprocess-spec>) is the same as the (preprocess ...) field of library
  • (preprocessor_deps (<deps-conf list>)) is the same as the (preprocessor_deps ...) field of library
  • js_of_ocaml. See the section about js_of_ocaml
  • flags, ocamlc_flags and ocamlopt_flags. See the section about specifying OCaml flags
  • (modules_without_implementation <modules>) is the same as the corresponding field of library
  • (allow_overlapping_dependencies) is the same as the corresponding field of library
  • (optional) is the same as the corresponding field of library
  • (enabled_if <blang expression>) is the same as the corresponding field of library
  • (promote <options>) allows promoting the linked executables to the source tree. The options are the same as for the rule promote mode. Adding (promote (until-clean)) to an executable stanza will cause Dune to copy the .exe files to the source tree and dune clean to delete them
  • (foreign_stubs <foreign-stubs-spec>) specifies foreign source files, e.g. C or C++ stubs, to be linked into the executable. See the section Foreign sources and archives for more details.
  • (foreign_archives <foreign-archives-list>) specifies archives of foreign object files to be linked into the executable. See the section Foreign archives for more details.
  • (forbidden_libraries <libraries>) ensures that the given libraries are not linked in the resulting executable. If they end up being pulled in, either through a direct or transitive dependency, Dune fails with an error message explaining how the library was pulled in. This field is available since the 2.0 version of the dune language.
  • (embed_in_plugin_libraries <library-list>) specifies a list of libraries to link statically when using plugin linking mode. By default, no libraries are linked in. Note that you may need to also use the -linkall flag if some of the libraries listed here are not referenced from any of the plugin modules.

Linking modes

The modes field allows selecting what linking modes should be used to link executables. Each mode is a pair (<compilation-mode> <binary-kind>) where <compilation-mode> describes whether the byte code or native code backend of the OCaml compiler should be used and <binary-kind> describes what kind of file should be produced.

<compilation-mode> must be byte, native or best, where best is native with a fallback to byte-code when native compilation is not available.

<binary-kind> is one of:

  • c for producing OCaml bytecode embedded in a C file
  • exe for normal executables
  • object for producing static object files that can be manually linked into C applications
  • shared_object for producing object files that can be dynamically loaded into an application. This mode can be used to write a plugin in OCaml for a non-OCaml application.
  • js for producing JavaScript from bytecode executables, see explicit_js_mode.
  • plugin for producing a plugin (.cmxs if native or .cma if bytecode).

For instance the following executables stanza will produce byte code executables and native shared objects:

  (names a b c)
  (modes (byte exe) (native shared_object)))

Additionally, you can use the following short-hands:

  • c for (byte c)
  • exe for (best exe)
  • object for (best object)
  • shared_object for (best shared_object)
  • byte for (byte exe)
  • native for (native exe)
  • js for (byte js)
  • plugin for (best plugin)

For instance the following modes fields are all equivalent:

(modes (exe object shared_object))
(modes ((best exe)
        (best object)
        (best shared_object)))

And finally, you can use the special mode byte_complete for building a bytecode executable as a native self-contained executable. I.e. an executable that does not require the ocamlrun program to run and does not requires the C stubs to be installed as shared object files.

The extensions for the various linking modes are chosen as follows:

linking mode extensions
byte .bc
native/best .exe
byte_complete .bc.exe
(byte object) .bc%{ext_obj}
(native/best object) .exe%{ext_obj}
(byte shared_object) .bc%{ext_dll}
(native/best shared_object) %{ext_dll}
c .bc.c
js .bc.js
(best plugin) %{ext_plugin}
(byte plugin) .cma
(native plugin) .cmxs

Where %{ext_obj} and %{ext_dll} are the extensions for object and shared object files. Their value depends on the OS, for instance on Unix %{ext_obj} is usually .o and %{ext_dll} is usually .so while on Windows %{ext_obj} is .obj and %{ext_dll} is .dll.

Up to version 3.0 of the dune language, when byte is specified but none of native, exe or byte_complete are specified Dune implicitly adds a linking mode that is the same as byte_complete but using the extension .exe. .bc files require additional files at runtime that are not currently tracked by Dune, so you should not run .bc files during the build. Run the .bc.exe or .exe ones instead as these are self-contained.

Lastly, note that .bc executables cannot contain C stubs. If your executable contains C stubs you may want to use (modes exe).


The executables stanza is the same as the executable stanza, except that it is used to describe several executables sharing the same configuration.

It shares the same fields as the executable stanza, except that instead of (name ...) and (public_name ...) you must use:

  • (names <names>) where <names> is a list of entry point names. As for executable you only need to specify the modules containing the entry point of each executable
  • (public_names <names>) describes under what name each executable should be installed. The list of names must be of the same length as the list in the (names ...) field. Moreover you can use - for executables that shouldn’t be installed


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

The syntax is as follows:

 (target[s] <filenames>)
 (action  <action>)

<filenames> is a list of file names (if defined with targets) or exactly one file name (if defined with target). Note that currently dune only supports user rules with targets in the current directory.

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

<optional-fields> are:

  • (deps <deps-conf list>) to specify the dependencies of the rule. See the Dependency specification section for more details.
  • (mode <mode>) to specify how to handle the targets, see modes for details
  • (fallback) is deprecated and is the same as (mode fallback)
  • (locks (<lock-names>)) specify that the action must be run while holding the following locks. See the Locks section for more details.
  • (alias <alias-name>) specify the alias this rule belongs to. Building this alias means building the targets of this rule.
  • (package <package>) specify the package this rule belongs to. This rule will be unavailable when installing other packages in release mode.
  • (enabled_if <blang expression>) specifies the boolean condition that must be true for the rule to be considered. The condition is specified using the Boolean language, and the field allows for Variables to appear in the expressions.

Note that contrary to makefiles or other build systems, user rules currently don’t support patterns, such as a rule to produce %.y from %.x for any given %. This might be supported in the future.


By default, the target of a rule must not exist in the source tree and dune will error out when this is the case.

However, it is possible to change this behavior using the mode field. The following modes are available:

  • standard, this is the standard mode
  • fallback, in this mode, when the targets are already present in the source tree, dune will ignore the rule. It is an error if only a subset of the targets are present in the tree. The common use of fallback rules is to generate default configuration files that may be generated by a configure script.
  • promote or (promote <options>), in this mode, the files in the source tree will be ignored. Once the rule has been executed, the targets will be copied back to the source tree The following options are available:
    • (until-clean) means that dune clean will remove the promoted files from the source tree.
    • (into <dir>) means that the files are promoted in <dir> instead of the current directory. This feature is available since Dune 1.8.
    • (only <predicate>) means that only a subset of the targets should be promoted. The argument is similar to the argument of (dirs …), specified using the Predicate language. This feature is available since dune 1.10.
  • promote-until-clean is the same as (promote (until-clean))
  • (promote-into <dir>) is the same as (promote (into <dir>))
  • (promote-until-clean-into <dir>) is the same as (promote (until-clean) (into <dir>))

The (promote <options>) form is only available since Dune 1.10. Before Dune 1.10, you need to use one of the promote-... forms. The promote-... forms should disappear in Dune 2.0, so using the more generic (promote <options>) form should be preferred in new projects.

There are two use cases for promote rules. The first one is when the generated code is easier to review than the generator, so it’s easier to commit the generated code and review it. The second is to cut down dependencies during releases: by passing --ignore-promoted-rules to dune, rules with (mode promote) will be ignored and the source files will be used instead. The -p/--for-release-of-packages flag implies --ignore-promote-rules. However, rules that promotes only a subset of their targets via (only ...) are never ignored.

inferred rules

When using the action DSL (see User actions), it is most of the time obvious what are the dependencies and targets.

For instance:

 (target b)
 (deps   a)
 (action (copy %{deps} %{target})))

In this example it is obvious by inspecting the action what the dependencies and targets are. When this is the case you can use the following shorter syntax, where dune infers dependencies and targets for you:

(rule <action>)

For instance:

(rule (copy a b))

Note that in dune, targets must always be known statically. For instance, this (rule ...) stanza is rejected by dune:

(rule (copy a b.%{read:file}))


(ocamllex <names>) is essentially a shorthand for:

 (target <name>.ml)
 (deps   <name>.mll)
 (action (chdir %{workspace_root}
          (run %{bin:ocamllex} -q -o %{target} %{deps}))))

To use a different rule mode, use the long form:

 (modules <names>)
 (mode    <mode>))


(ocamlyacc <names>) is essentially a shorthand for:

 (targets <name>.ml <name>.mli)
 (deps    <name>.mly)
 (action  (chdir %{workspace_root}
           (run %{bin:ocamlyacc} %{deps}))))

To use a different rule mode, use the long form:

 (modules <names>)
 (mode    <mode>))


A menhir stanza is available to support the menhir parser generator.

To use menhir in a dune project, the language version should be selected in the dune-project file. For example:

(using menhir 2.0)

This will enable support for menhir stanzas in the current project. If the language version is absent, dune will automatically add this line with the latest menhir version to the project file once a menhir stanza is used anywhere.

The basic form for defining menhir-git parsers (analogous to ocamlyacc) is:

 (modules <parser1> <parser2> ...)

<optional-fields> are:

  • (merge_into <base_name>) is used to define modular parsers. This correspond to the --base command line option of menhir. With this option, a single parser named base_name is generated.
  • (flags <option1> <option2> ...) can be used to pass extra flags can be passed to menhir.
  • (infer <bool>) can be used to enable using menhir with type inference. This option is enabled by default with Menhir language 2.0.

Menhir supports writing the grammar and automaton to .cmly file. Therefore, if this is flag is passed to menhir, dune will know to introduce a .cmly target for the module.


A cinaps stanza is available to support the cinaps tool. See the cinaps website for more details.


Additional manual pages may be attached to packages using the documentation stanza. These .mld files must contain text in the same syntax as ocamldoc comments.

(documentation (<optional-fields>))

Where <optional-fields> are:

  • (package <name>) the package this documentation should be attached to. If this absent, dune will try to infer it based on the location of the stanza.
  • (mld_files <arg>) where <arg> field follows the Ordered set language. This is a set of extension-less, mld file base names that are attached to the package. Where :standard refers to all the .mld files in the stanza’s directory.

The index.mld file (specified as index in mld_files) is treated specially by dune. This will be the file used to generate the entry page for the package. This is the page that will be linked from the main package listing. If you omit writing an index.mld, dune will generate one with the entry modules for your package. But this generated will not be installed.

All mld files attached to a package will be included in the generated .install file for that package, and hence will be installed by opam.


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

The syntax is as follows:

 (name    <alias-name>)
 (deps    <deps-conf list>)

<name> is an alias name such as runtest.

<deps-conf list> specifies the dependencies of the alias. See the Dependency specification section for more details.

<optional-fields> are:

  • <action>, an action to run when constructing the alias. See the User actions section for more details. Note that this is removed in the 2.0 version of the dune language. Users should port their code to use the rule stanza with the alias field instead.
  • (package <name>) indicates that this alias stanza is part of package <name> and should be filtered out if <name> is filtered out from the command line, either with --only-packages <pkgs> or -p <pkgs>
  • (locks (<lock-names>)) specify that the action must be run while holding the following locks. See the Locks section for more details.
  • (enabled_if <blang expression>) specifies the boolean condition that must be true for the tests to run. The condition is specified using the Boolean language, and the field allows for Variables to appear in the expressions.

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

 (alias   runtest)
 (action (run %{exe:my-test-program.exe} blah)))

See the section about Running tests for details.

Note that if your project contains several packages and you run the tests from the opam file using a build-test field, then all your runtest alias stanzas should have a (package ...) field in order to partition the set of tests.


Dune supports installing packages on the system, i.e. copying freshly built artifacts from the workspace to the system. The install stanza takes three pieces of information:

  • the list of files to install
  • the package to attach these files to. This field is optional if your project contains a single package
  • the section in which the files will be installed

For instance:

 (files hello.txt)
 (section share)
 (package mypackage))

Indicate that the file hello.txt in the current directory is to be installed in <prefix>/share/mypackage.

The following sections are available:

  • lib installs to <prefix>/lib/<pkgname>/
  • lib_root installs to <prefix>/lib/
  • libexec installs to <prefix>/lib/<pkgname>/ with the executable bit set
  • libexec_root installs to <prefix>/lib/ with the executable bit set
  • bin installs to <prefix>/bin/ with the executable bit set
  • sbin installs to <prefix>/sbin/ with the executable bit set
  • toplevel installs to <prefix>/lib/toplevel/
  • share installs to <prefix>/share/<pkgname>/
  • share_root installs to <prefix>/share/
  • etc installs to <prefix>/etc/<pkgname>/
  • doc installs to <prefix>/doc/<pkgname>/
  • stublibs installs to <prefix>/lib/stublibs/ with the executable bit set
  • man installs relative to <prefix>/man with the destination directory extracted from the extension of the source file (so that installing foo.1 is equivalent to a destination of man1/foo.1)
  • misc requires files to specify an absolute destination, and the user will be prompted before the installation when it is done via opam. Only use this for advanced cases.
  • (site (<package> <site>)) install in the <site> directory of <package>. If the prefix is not the same than the one used when installing <package>, <package> will not find the files.

Normally, Dune uses the basename of the file to install to determine the name of the file once installed. However, you can change that fact by using the form (<filename> as <destination>) in the files field. For instance, to install a file mylib.el as <prefix>/emacs/site-lisp/mylib.el you must write the following:

 (section share_root)
 (files   (mylib.el as emacs/site-lisp/mylib.el)))

Handling of the .exe extension on Windows

Under Microsoft Windows, executables must be suffixed with .exe. Dune tries to make sure that executables are always installed with this extension on Windows.

More precisely, when installing a file via an (install ...) stanza, if the source file has extension .exe or .bc, then dune implicitly adds the .exe extension to the destination, if not already present.


The copy_files and copy_files# stanzas allow to specify that files from another directory could be copied if needed to the current directory.

The syntax is as follows:

 (files <glob>))

<glob> represents the set of files to copy, see the glob for details.

<optional-fields> are:

  • (alias <alias-name>) to specify an alias to which to attach the targets.
  • (mode <mode>) to specify how to handle the targets, see modes for details.
  • (enabled_if <blang expression>) conditionally disables this stanza. The condition is specified using the Boolean language.

The short form

(copy_files <glob>)

is equivalent to

(copy_files (files <glob>))

The difference between copy_files and copy_files# is the same as the difference between the copy and copy# action. See the User actions section for more details.


The include stanza allows including the contents of another file in the current dune file. Currently, the included file cannot be generated and must be present in the source tree. This feature is intended to be used in conjunction with promotion, when parts of a dune file are to be generated.

For instance:


(rule (with-stdout-to (run ./gen-dune.exe)))

 (alias  runtest)
 (action (diff

With this dune file, running dune as follows will replace the file in the source tree by the generated one:

$ dune build @runtest --auto-promote


The tests stanza allows one to easily define multiple tests. For example we can define two tests at once with:

 (names mytest expect_test)
 <optional fields>)

This will define an executable named mytest.exe that will be executed as part of the runtest alias. If the directory also contains an expect_test.expected file, then expect_test will be used to define an expect test. That is, the test will be executed and its output will be compared to expect_test.expected.

The optional fields that are supported are a subset of the alias and executables fields. In particular, all fields except for public_names are supported from the executables stanza. Alias fields apart from name are allowed.

By default the test binaries are run without options. The action field can be used to override the test binary invocation, for example if you’re using alcotest and wish to see all the test failures on the standard output when running dune runtest you can use the following stanza:

 (names mytest)
 (libraries alcotest mylib)
 (action (run %{test} -e)))


The test stanza is the singular form of tests. The only difference is that it’s of the form:

 (name foo)
 <optional fields>)

where the name field is singular. The same optional fields are supported.


The env stanza allows one to modify the environment. The syntax is as follow:

 (<profile1> <settings1>)
 (<profile2> <settings2>)
 (<profilen> <settingsn>))

The first form (<profile> <settings>) that correspond to the selected build profile will be used to modify the environment in this directory. You can use _ to match any build profile.

Fields supported in <settings> are:

  • any OCaml flags field, see OCaml flags for more details.
  • (c_flags <flags>) and (cxx_flags <flags>) to specify compilation flags for C and C++ stubs, respectively. See library for more details.
  • (env-vars (<var1> <val1>) .. (<varN> <valN>)). This will add the corresponding variables to the environment in which the build commands are executed, and under which dune exec runs.
  • (menhir_flags <flags>)) to specify flags for menhir stanzas.
  • (binaries <binaries>) where <binaries> is a list of entries of the form (<filepath> as <name>). (<filepath> as <name>) makes the binary <filepath> available in the command search as just <name>. For instance in a (run <name> ...) action <name> will resolve to this file path. You can also write just the file path, in which case the name will be inferred from the basename of <filepath> by dropping the .exe suffix if it exists. For instance (binaries bin/foo.exe (bin/main.exe as bar)) would add the commands foo and bar to the search path.
  • (inline_tests <state>) where state is either enabled, disabled or ignored. This field is available since Dune 1.11. It controls the value of the variable %{inline_tests} that is read by the inline test framework. The default value is disabled for the release profile and enabled otherwise.
  • (odoc <fields>). This allows to pass options to Odoc, see Passing options to Odoc for more details.
  • (coq (flags <flags>)). This allows to pass options to Coq, see coq.theory for more details.
  • (formatting <settings>). This allows to set auto-formatting in the current directory subtree, see formatting.

dirs (since 1.6)

The dirs stanza allows specifying the sub-directories dune will include in a build. The syntax is based on dune’s Predicate language and allows the user the following operations:

  • The special value :standard which refers to the default set of used directories. These are the directories that don’t start with . or _.
  • Set operations. Differences are expressed with backslash: * \ bar, unions are done by listing multiple items.
  • Sets can be defined using globs.


(dirs *) ;; include all directories
(dirs :standard \ ocaml) ;; include all directories except ocaml
(dirs :standard \ test* foo*) ;; exclude all directories that start with test or foo

A directory that is not included by this stanza will not be eagerly scanned by Dune. Any dune or other special files in it won’t be interpreted either and will be treated as raw data. It is however possible to depend on files inside ignored sub-directories.

data_only_dirs (since 1.6)

Dune allows the user to treat directories as data only. Dune files in these directories will not be evaluated for their rules, but the contents of these directories will still be usable as dependencies for other rules.

The syntax is the same as for the dirs stanza except that :standard is by default empty.


;; dune files in fixtures_* dirs are ignored
(data_only_dirs fixtures_*)

ignored_subdirs (deprecated in 1.6)

One may also specify data only directories using the ignored_subdirs stanza. The meaning is the same as data_only_dirs but the syntax isn’t as flexible and only accepts a list of directory names. It is advised to switch to the new data_only_dirs stanza.


(ignored_subdirs (<sub-dir1> <sub-dir2> ...))

All of the specified <sub-dirn> will be ignored by dune. Note that users should rely on the dirs stanza along with the appropriate set operations instead of this stanza. For example:

(dirs :standard \ <sub-dir1> <sub-dir2> ...)

vendored_dirs (since 1.11)

Dune supports vendoring of other dune-based projects natively since simply copying a project into a subdirectory of your own project will work. Simply doing that has a few limitations though. You can workaround those by explicitly marking such directories as containing vendored code.


(vendored_dirs vendor)

Dune will not resolve aliases in vendored directories meaning by default it will not build all installable targets, run the test, format or lint the code located in such a directory while still building the parts your project depend upon. Libraries and executable in vendored directories will also be built with a -w -a flag to suppress all warnings and prevent pollution of your build output.


The include_subdirs stanza is used to control how dune considers sub-directories of the current directory. The syntax is as follows:

(include_subdirs <mode>)

Where <mode> maybe be one of:

  • no, the default
  • unqualified

When the include_subdirs stanza is not present or <mode> is no, dune considers sub-directories as independent. When <mode> is unqualified, dune will assume that the sub-directories of the current directory are part of the same group of directories. In particular, dune will scan all these directories at once when looking for OCaml/Reason files. This allows you to split a library between several directories. unqualified means that modules in sub-directories are seen as if they were all in the same directory. In particular, you cannot have two modules with the same name in two different directories. It is planned to add a qualified mode in the future.

Note that sub-directories are included recursively, however the recursion will stop when encountering a sub-directory that contains another include_subdirs stanza. Additionally, it is not allowed for a sub-directory of a directory with (include_subdirs <x>) where <x> is not no to contain one of the following stanzas:

  • library
  • executable(s)
  • test(s)


The toplevel stanza allows one to define custom toplevels. Custom toplevels automatically load a set of specified libraries and are runnable like normal executables. Example:

 (name tt)
 (libraries str))

This will create a toplevel with the str library loaded. We may build and run this toplevel with:

$ dune exec ./tt.exe

(preprocess (pps ...)) is the same as the (preprocess (pps ...)) field of library. Currently, action and future_syntax are not supported in the toplevel.


The subdir stanza can be used to evaluate stanzas in sub directories. This is useful for generated files or to override stanzas in vendored directories without editing vendored dune files.

In this example, a bar target is created in the foo directory, and a bar target will be created in a/b/bar:

(subdir foo (rule (with-stdout-to bar (echo baz))))
(subdir a/b (rule (with-stdout-to bar (echo baz))))


This stanza was experimental and removed in dune 2.6. see Variants


Dune is also able to build Coq developments. A Coq project is a mix of Coq .v files and (optionally) OCaml libraries linking to the Coq API (in which case we say the project is a Coq plugin). To enable Coq support in a dune project, the language version should be selected in the dune-project file. For example:

(using coq 0.2)

This will enable support for the coq.theory stanza in the current project. If the language version is absent, dune will automatically add this line with the latest Coq version to the project file once a (coq.theory ...) stanza is used anywhere.

The supported Coq language versions are: - 0.1: basic Coq theory support, - 0.2: support for the theories field, and composition of theories in the same scope, - 0.3: support for (mode native).

Guarantees with respect to stability are not provided yet, however, as implementation of features progresses, we hope to reach 1.0 soon. The 1.0 version will commit to a stable set of functionality; all the features below are expected to reach 1.0 unchanged or minimally modified.

The basic form for defining Coq libraries is very similar to the OCaml form:

 (name <module_prefix>)
 (package <package>)
 (synopsis <text>)
 (modules <ordered_set_lang>)
 (libraries <ocaml_libraries>)
 (flags <coq_flags>)
 (mode <coq_native_mode>)
 (theories <coq_theories>))

The stanza will build all .v files on the given directory. The semantics of fields is:

  • <module_prefix> is a dot-separated list of valid Coq module names and determines the module scope under which the theory is compiled [-R option]. For example, if <module_prefix> is foo.Bar, the theory modules will be named as foo.Bar.module1, foo.Bar.module2, etc… Note that modules in the same theory don’t see the foo.Bar prefix, in the same way that OCaml wrapped libraries do. For compatibility reasons, the 1.0 version of the Coq language installs a theory named foo.Bar under foo/Bar. Also note that Coq supports composing a module path from different theories, thus you can name a theory foo.Bar and a second one foo.Baz and things will work properly,
  • the modules field enables constraining the set of modules included in the theory, similarly to its OCaml counterpart. Modules are specified in Coq notation, that is to say A/b.v is written A.b in this field,
  • if package is present, Dune will generate install rules for the .vo files on the theory. pkg_name must be a valid package name. Note that the 1.0 version of the language uses the Coq legacy install setup, where all packages share a common root namespace and install directory, lib/coq/user-contrib/<module_prefix>, as customary in the make-based Coq package ecosystem. For compatibility, we also install under the user-contrib prefix the .cmxs files appearing in <ocaml_libraries>,
  • <coq_flags> will be passed to coqc as command-line options. :standard is taken from the value set in the (coq (flags <flags>)) field in env profile. See env for more information.
  • the path to installed locations of <ocaml_libraries> will be passed to coqdep and coqc using Coq’s -I flag; this allows for a Coq theory to depend on a ML plugin,
  • your Coq theory can depend on other theories by specifying them in the <coq_theories> field. Dune will then pass to Coq the corresponding flags for everything to compile correctly [ -Q ]. As of today, we only support composition with libraries defined in the same scope (that is to say, under the same dune-project domain). We will lift this restriction in the future. Note that composition with the Coq’s standard library is supported, but in this case the Coq prefix will be made available in a qualified way. Since Coq’s lang version 0.2.
  • you can enable the production of Coq’s native compiler object files by setting <coq_native_mode> to native, this will pass -native-compiler on to Coq and install the corresponding object files under .coq-native when in release profile. The regular dev profile will skip native compilation to make the build faster. Since Coq’s lang version 0.3. Note that the support for native compute is experimental, and requires Coq >= 8.12.1; moreover, depending libraries must be built with (mode native) too for this to work; also Coq must be configured to support native compilation. Note that Dune will explicitly disable output of native compilation objects when (mode vo) even if the default Coq’s configure flag enabled it. This will be improved in the future.

Recursive qualification of modules

If you add:

(include_subdirs qualified)

to a dune file, Dune will consider all the modules in the directory and its sub-directories, adding a prefix to the module name in the usual Coq style for sub-directories. For example, file A/b/C.v will be module A.b.C.


  • .v files always depend on the native version of Coq / plugins,
  • a foo.mlpack file must the present in directories of locally defined plugins for things to work, this is a limitation of coqdep, see the template at <>


Coq plugin writers usually need to write .mlg files to extend Coq grammar. Such files are pre-processed with coqpp; to help plugin writers avoid boilerplate we provide a (coqpp …) stanza:

(coq.pp (modules <mlg_list>))

which for each g_mod in <mlg_list> is equivalent to:

 (deps (:mlg-file g_mod.mlg))
 (action (run coqpp %{mlg-file})))


Coq may be instructed to extract OCaml sources as part of the compilation process. This is done using the coq.extraction stanza:

 (prelude <name>)
 (extracted_modules <names>)
  • (prelude <name>) refers to the Coq source that contains the extraction commands.
  • (extracted_modules <names>) is an exhaustive list of OCaml modules extracted.
  • <optional-fields> are flags, theories, and libraries. All of these fields have the same meaning as in the coq.theory stanza.

The extracted sources can then be used in executable or library stanzas as any other sources.

Note that the sources are extracted to the directory where the prelude file is; thus the common placement for the OCaml stanzas is in the same dune file. warning using Coq’s Cd command to workaround problems with the output directory is not allowed when using extraction from Dune; moreover the Cd command will be deprecated in Coq 8.12.

mdx (since 2.4)

MDX is a tool that helps you keep your markdown documentation up to date by checking that the code examples it contains are correct. When setting an MDX stanza, the checks carried out by MDX are automatically attached to the runtest alias of the stanza’s directory.

See MDX’s repository for more details.

You can define an MDX stanza to specify which files you want checked.

Note that this feature is still experimental and needs to be enabled in your dune-project with the following using stanza:

(using mdx 0.1)

The syntax is as follows:

(mdx <optional-fields>)

Where <optional-fields> are:

  • (files <globs>) are the files that you want MDX to check, described as a list of globs (see the Glob language specification ). It defaults to *.md.
  • (packages <packages>) are the local dune packages that your documentation code blocks depend on. I.e. if your documentation examples depend on a public executable or library defined from a local package, it has to be specified in the stanza.
  • (preludes <files>) are the prelude files you want to pass to MDX. See MDX’s documentation for more details on preludes.

plugin (since 2.8)

Plugins are a way to load ocaml libraries at runtime. The plugin stanza allows to declare the name of the plugin, in which How to load additional files at runtime it should be present, and which libraries it will load.

 (name <name>)
 (libraries <libaries>)
 (site (<package> <site name>))

<optional-fields> are:

  • (package <package>) if there is more than one package defined in the current scope, this specifies during the installation of which package the plugin will be installed. A plugin can be installed by one package in the site of another package.
  • (optional) will not declare the plugin if the libraries are not available

The loading of the plugin is done using the facilities generated by generate_sites_module (since 2.8)

generate_sites_module (since 2.8)

Dune proposes some facilities for dealing with How to load additional files at runtime in a program. The generate_sites_module stanza will generate code for looking up the correct locations of the sites directories and for loading plugins. It works after installation with or without the relocation mode, inside dune rules, when using dune exec. For promotion it works only if the generated modules are only in the executable (or library statically linked) promoted; generated modules in plugins will not work.

 (module <name>)

The code of the module is generated in the directory with the given name. The code is populated according to the requested facilities.

The available <facilities> are:

  • sourceroot : adds in the generated module a value val sourceroot: string option which contains the value of %{workspace_root} if the code have been built locally. It could be used to keep configuration file of the tool locally when executed with dune exec or after promotion. The value is None once it has been installed.
  • relocatable : adds in the generated module a value val relocatable: bool which indicates if the binary has been installed in the relocatable mode
  • (sites <package>) : adds in the sub-module Sites of the generated module a value val <site>: string list for each <site> of <package>. The identifier <site> is uncapitalized.
  • (plugins (<package> <site>) ...): adds in the sub-module Plugins of the generated module a sub-module <site> with the following signature S. The identifier <site> is capitalized.
module type S = sig
  val paths: string list
  (** return the locations of the directory containing the plugins *)

  val list: unit -> string list
  (** return the list of available plugins *)

  val load_all: unit -> unit
  (** load all the plugins and their dependencies *)

  val load: string -> unit
  (** load the specified plugin and its dependencies *)

The generated module as a dependency on the library dune-site, and if the facilities (plugins ...) is used, it as a dependency on the library dune-site.plugins. Those dependencies are not automatically added to the library or executable which use the module (cf. Plugins and dynamic loading of packages).


By default, a workspace has only one build context named default which correspond to the environment in which dune is run. You can define more contexts by writing a dune-workspace file.

You can point dune to an explicit dune-workspace file with the --workspace option. For instance it is good practice to write a in your project with all the version of OCaml your projects support. This way developers can tests that the code builds with all version of OCaml by simply running:

$ dune build --workspace @all @runtest

The dune-workspace file uses the S-expression syntax. This is what a typical dune-workspace file looks like:

(lang dune 2.8)
(context (opam (switch 4.07.1)))
(context (opam (switch 4.08.1)))
(context (opam (switch 4.11.1)))

The rest of this section describe the stanzas available.

Note that an empty dune-workspace file is interpreted the same as one containing exactly:

(lang dune 2.8)
(context default)

This allows you to use an empty dune-workspace file to mark the root of your project.


The build profile can be selected in the dune-workspace file by write a (profile ...) stanza. For instance:

(profile release)

Note that the command line option --profile has precedence over this stanza.


The env stanza can be used to set the base environment for all contexts in this workspace. This environment has the lowest precedence of all other env stanzas. The syntax for this stanza is the same dune’s env stanza.


The (context ...) stanza declares a build context. The argument can be either default or (default) for the default build context or can be the description of an opam switch, as follows:

(context (opam (switch <opam-switch-name>)

<optional-fields> are:

  • (name <name>) is the name of the subdirectory of _build where the artifacts for this build context will be stored.
  • (root <opam-root>) is the opam root. By default it will take the opam root defined by the environment in which dune is run which is usually ~/.opam.
  • (merlin) instructs dune to use this build context for merlin.
  • (profile <profile>) to set a different profile for a build context. This has precedence over the command line option --profile.
  • (env <env>) to set the environment for a particular context. This is of higher precedence than the root env stanza in the workspace file. This field the same options as the env stanza.
  • (toolchain <findlib_toolchain>) set findlib toolchain for the context.
  • (host <host_context>) choose a different context to build binaries that are meant to be executed on the host machine, such as preprocessors.
  • (paths (<var1> <val1>) .. (<varN> <valN>)) allows setting the value of any PATH-like variables in this context. If PATH itself is modified in this way, its value will be used to resolve binaries in the workspace, including finding the compiler and related tools. These variables will also be passed as part of the environment to any program launched by dune. For each variable, the value is specified using the Ordered set language. Relative paths are interpreted with respect to the workspace root, see Finding the root.
  • (fdo <target_exe>) build this context with feedback-direct optimizations. Requires OCamlFDO. <target_exe> is a path interpreted relative to the workspace root, see Finding the root. <target_exe> specifies which executable to optimize. Users should define a different context for each target executable built with FDO. The name of the context is derived automatically from the default name and <target-exe>, unless explicitly specified using (name ...) field. For example, if <target_exe> is src/foo.exe in a default context, then the name of the context is default-fdo-foo and the name of the file that contains execution counters is src/fdo.exe.fdo-profile. This feature is experimental and no backwards compatibility is implied.
  • By default Dune builds and installs dynamically linked foreign archives (usually named dll*.so). It is possible to disable this by setting (disable_dynamically_linked_foreign_archives true) in the workspace file, in which case bytecode executables will be built with all foreign archives statically linked into the runtime system.

Both (default ...) and (opam ...) accept a targets field in order to setup cross compilation. See Cross compilation for more information.

Merlin reads compilation artifacts and it can only read the compilation artifacts of a single context. Usually, you should use the artifacts from the default context, and if you have the (context default) stanza in your dune-workspace file, that is the one dune will use.

For rare cases where this is not what you want, you can force dune to use a different build contexts for merlin by adding the field (merlin) to this context.