Stanza reference — dune documentation

# Stanza reference

## dune-project

These files are used to mark the root of projects as well as define project-wide parameters. These files are required to have a `lang` which controls the names and contents of all configuration files read by Dune. The `lang` stanza looks like:

    (lang dune 2.5)

Additionally, they can contains the following stanzas.

### name

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

    (name <name>)

### version

Sets the version of the project:

    (version <version>)

### implicit_transitive_deps

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.

### wrapped_executables

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)`

### explicit_js_mode

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:

    (explicit_js_mode)

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.

### dialect

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.

    (dialect
     (name <name>)
     (implementation
      (extension <string>)
      <optional fields>)
     (interface
      (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.

### formatting

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.

### generate_opam_files

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

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.

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+

## dune

`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:

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

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

The following sections describe the available stanzas and their meaning.

### jbuild_version

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

### library

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

    (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.

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
- `(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 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
- `(no_keep_locs)` does nothing. It used to be a necessary hack when we were waiting for proper support for virtual libraries. Do not use in new code, it will be deleted in dune 2.0
- `(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`

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 ...))`.

### foreign_library

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.

#### js_of_ocaml

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.

### deprecated_library_name

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

    (deprecated_library_name
     (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.

### executable

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

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

`<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:

  >     (install
  >      (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
- `(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:

    (executables
      (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 implicitely 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)`.

### executables

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

### rule

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:

    (rule
     (target[s] <filenames>)
     (action  <action>)
     <optional-fields>)

`<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.

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.

#### modes

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 will `(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:

    (rule
     (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

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

    (rule
     (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:

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

### ocamlyacc

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

    (rule
     (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:

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

### menhir

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:

    (menhir
     (modules <parser1> <parser2> ...)
     <optional-fields>)

`<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.

### cinaps

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

### documentation

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.

### 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 follows:

    (alias
     (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 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:

    (rule
     (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.

### install

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 the 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:

    (install
     (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.

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:

    (install
     (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.

### copy_files

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:

    (copy_files <glob>)

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

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.

### include

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:

    (include dune.inc)

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

    (rule
     (alias  runtest)
     (action (diff dune.inc dune.inc.gen)))

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

    $ dune build @runtest --auto-promote

### tests

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

    (tests
     (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:

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

### test

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

    (test
     (name foo)
     <optional fields>)

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

### env

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

    (env
     (<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.

### 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.

Examples:

    (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.

Example:

    ;; 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.

Example:

    (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.

Example:

    (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.

### include_subdirs

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)`

### toplevel

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:

    (toplevel
     (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.

### subdir

The `subdir` stanza can be used to evaluate stanzas in sub directories. This is useful for generated files or to override stanzas in vendored direcotries 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))))

### external_variant

The `external_variant` allow to declare a tagged implementation that does not live inside the virtual library project.

    (external_variant
     (variant foo)
     (implementation lib-foo)
     (virtual_library vlib))

This will add lib-foo to the list of known implementations of vlib. For more details see Variants

### coq.theory

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`, and `0.2` which adds support for the `theories` field. We don’t provide any guarantees with respect to stability yet, however, as implementation of features progresses, we hope 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:

    (coq.theory
     (name <module_prefix>)
     (package <package>)
     (synopsis <text>)
     (modules <ordered_set_lang>)
     (libraries <ocaml_libraries>)
     (flags <coq_flags>)
     (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,
- 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`.

#### 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`.

#### Limitations

- `.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 <https://github.com/ejgallego/coq-plugin-template>

### coq.pp

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:

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

### coq.extraction

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

    (coq.extraction
     (prelude <name>)
     (extracted_modules <names>)
     <optional-fields>)

- `(prelude <name>)` refers to the Coq source that contains the extraction commands.
- `(extraced_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.

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.

## dune-workspace

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 `dune-workspace.dev` 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 dune-workspace.dev @all @runtest

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

    (lang dune 2.5)
    (context (opam (switch 4.02.3)))
    (context (opam (switch 4.03.0)))
    (context (opam (switch 4.04.0)))

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 2.5)
    (context default)

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

### profile

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.

### env

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.

### context

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>))

`<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.