Any directory containing at least one <package>.opam
file defines a scope. This scope is the subtree starting from this directory, excluding any other scopes rooted in subdirectories.
Typically, any given project will define a single scope. Libraries and executables that aren't meant to be installed will be visible inside this scope only.
Because scopes are exclusive, if you wish to include your current project's dependencies in your workspace, you can copy them in a vendor
directory, or any name of your choice. Dune will look for them there rather than in the installed world
, and there will be no overlap between the various scopes.
A few fields take an ordered set as argument and can be specified using a small DSL.
This DSL is interpreted by Dune into an ordered set of strings using the following rules:
:standard
denotes the standard value of the field when it's absent- an atom not starting with a
:
is a singleton containing only this atom - a list of sets is the concatenation of its inner sets
(<sets1> \ <sets2>)
is the set composed of elements of<sets1>
that do not appear in<sets2>
In addition, some fields support the inclusion of an external file using the syntax (:include <filename>)
. For instance, this is useful when you need to run a script to figure out some compilation flags. <filename>
is expected to contain a single S-expression and cannot contain (:include ...)
forms.
Note that inside an ordered set, the first element of a list cannot be an atom except if it starts with -
or :
. The reason for this is that we're planning to add simple programmatic features in the future so that one may write:
(flags (if (>= %{ocaml_version} 4.06) ...))
This restriction will allow you to add this feature without introducing breaking changes. If you want to write a list where the first element doesn't start with -
, you can simply quote it: ("x" y z)
.
Most fields using the ordered set language also support variables
. Variables are expanded after the set language is interpreted.
The Boolean language allows the user to define simple Boolean expressions that Dune can evaluate. Here's a semi-formal specification of the language:
blang op : '=' | '<' | '>' | '<>' | '>=' | '<=' expr : (and <expr>+) : (or <expr>+) : (<op> <template> <template>) : (not <expr>) : <template>
After an expression is evaluated, it must be exactly the string true
or false
to be considered as a Boolean. Any other value will be treated as an error.
Below is a simple example of a condition expressing that the build has a Flambda compiler, with the help of variable expansion, and is targeting OSX:
(and %{ocaml-config:flambda} (= %{ocaml-config:system} macosx))
The predicate language allows the user to define simple predicates (Boolean-valued functions) that Dune can evaluate. Here is a semi-formal specification of the predicate language:
pred : (and pred pred) : (or pred pred) : (not pred) : :standard : element
The exact meaning of :standard
and the nature of element
depends on the context. For example, in the case of the dune-subdirs
, an element
corresponds to file glob patterns. Another example is the user action (with-accepted-exit-codes ...) <user-actions>
, where an element
corresponds to a literal integer.
Some fields can contains variables that are expanded by Dune. The syntax of variables is as follows:
%{var}
or, for more complex forms that take an argument:
%{fun:arg}
In order to write a plain %{
, you need to write \%{
in a string.
Dune supports the following variables:
project_root
is the root of the current project. It is typically the root of your project, and as long as you have adune-project
file there,project_root
is independent of the workspace configuration.workspace_root
is the root of the current workspace. Note that the value ofworkspace_root
isn't constant and depends on whether your project is vendored or not.CC
is the C compiler command line (list made of the compiler name followed by its flags) that will be used to compile foreign code. For more details about its content, please seethis section <flags-flow>
.CXX
is the C++ compiler command line being used in the current build context.ocaml_bin
is the path whereocamlc
lives.ocaml
is theocaml
binary.ocamlc
is theocamlc
binary.ocamlopt
is theocamlopt
binary.ocaml_version
is the version of the compiler used in the current build context.ocaml_where
is the output ofocamlc -where
.arch_sixtyfour
istrue
if using a compiler that targets a 64-bit architecture andfalse
otherwise.null
is/dev/null
on Unix ornul
on Windows.ext_obj
,ext_asm
,ext_lib
,ext_dll
, andext_exe
are the file extensions used for various artifacts.ext_plugin
is.cmxs
ifnatdynlink
is supported and.cma
otherwise.ocaml-config:v
is for every variablev
in the output ofocamlc -config
. Note that Dune processes the output ofocamlc -config
in order to make it a bit more stable across versions, so the exact set of variables accessible this way might not be exactly the same as what you can see in the output ofocamlc -config
. In particular, variables added in new OCaml versions need to be registered in Dune before they can be used.profile
is the profile selected via--profile
.context_name
is the name of the context (default
, or defined in the workspace file)os_type
is the type of the OS the build is targeting. This is the same asocaml-config:os_type
.architecture
is the type of the architecture the build is targeting. This is the same asocaml-config:architecture
.model
is the type of the CPU the build is targeting. This is the same asocaml-config:model
.system
is the name of the OS the build is targeting. This is the same asocaml-config:system
.ignoring_promoted_rule
istrue
if--ignore-promoted-rules
was passed on the command line andfalse
otherwise.<ext>:<path>
where<ext>
is one ofcmo
,cmi
,cma
,cmx
, orcmxa
. Seevariables-for-artifacts
.env:<var>=<default
expands to the value of the environment variable<var>
, or<default>
if it does not exist. For example,%{env:BIN=/usr/bin}
. Available since Dune 1.4.0.- There are some Coq-specific variables detailed in
coq-variables
.
In addition, (action ...)
fields support the following special variables:
target
expands to the one target.targets
expands to the list of target.deps
expands to the list of dependencies.^
expands to the list of dependencies, separated by spaces.dep:<path>
expands to<path>
(and adds<path>
as a dependency of the action).exe:<path>
is the same as<path>
, except when cross-compiling, in which case it will expand to<path>
from the host build context.bin:<program>
expands<path>
toprogram
. Ifprogram
is installed by a workspace package (seeinstall
stanzas), the locally built binary will be used, otherwise it will be searched in the<path>
of the current build context. Note that(run %{bin:program} ...)
and(run program ...)
behave in the same way.%{bin:...}
is only necessary when you are using(bash ...)
or(system ...)
.bin-available:<program>
expands totrue
orfalse
, depending on whether<program>
is available or not.lib:<public-library-name>:<file>
expands to the file's installation path<file>
in the library<public-library-name>
. If<public-library-name>
is available in the current workspace, the local file will be used, otherwise the one from theinstalled world
will be used.lib-private:<library-name>:<file>
expands to the file's build path<file>
in the library<library-name>
. Both public and private library names are allowed as long as they refer to libraries within the same project.libexec:<public-library-name>:<file>
is the same aslib:...
, except when cross-compiling, in which case it will expand to the file from the host build context.libexec-private:<library-name>:<file>
is the same aslib-private:...
except when cross-compiling, in which case it will expand to the file from the host build context.lib-available:<library-name>
expands totrue
orfalse
depending on whether the library is available or not. A library is available if at least one of the following conditions holds:- It's part the
installed world
. - It's available locally and is not optional.
- It's available locally, and all its library dependencies are available.
- It's part the
version:<package>
expands to the version of the given package. Packages defined in the current scope have priority over the public packages. Public packages that don't install any libraries will not be detected. How Dune determines the version of a package is describedhere <package-version>
.read:<path>
expands to the contents of the given file.read-lines:<path>
expands to the list of lines in the given file.read-strings:<path>
expands to the list of lines in the given file, unescaped using OCaml lexical convention.
The %{<kind>:...}
forms are what allows you to write custom rules that work transparently, whether things are installed or not.
Note that aliases are ignored by %{deps}
The intent of this last form is to reliably read a list of strings generated by an OCaml program via:
List.iter (fun s -> print_string (String.escaped s)) l
- Dealing with circular dependencies introduced by variables
If you ever see Dune reporting a dependency cycle that involves a variable such as %{read:<path>}, try to move <path> to a different directory.
The reason you might see such dependency cycle is because Dune is trying to evaluate the %{read:<path>} too early. For instance, let's consider the following example:
(rule
(targets x)
(enabled_if %{read:y})
(action ...)
(rule
(with-stdout-to y (...)))
When Dune loads and interprets this file, it decides whether the first rule is enabled by evaluating %{read:y}
. To evaluate %{read:y}
, it must build y
. To build y
, it must figure out the build rule that produces y
, and in order to do that, it must first load and evaluate the above dune
file. You can see how this creates a cycle.
Some cycles might be more complex. In any case, when you see such an error, the easiest thing to do is move the file that's being read to a different directory, preferably a standalone one. You can use the subdir
stanza to keep the logic self-contained in the same dune
file:
(rule
(targets x)
(enabled_if %{read:dir-for-y/y})
(action ...)
(subdir
dir-for-y
(rule
(with-stdout-to y (...))))
Forms that expand to a list of items, such as %{cc}
, %{deps}
, %{targets}
, or %{read-lines:...}
, are suitable to be used in (run <prog> <arguments>)
. For instance in:
(run foo %{deps})
If there are two dependencies, a
and b
, the produced command will be equivalent to the shell command:
$ foo "a" "b"
If you want both dependencies to be passed as a single argument, you must quote the variable:
(run foo "%{deps}")
which is equivalent to the following shell command:
$ foo "a b"
(The items of the list are concatenated with space.) Please note: since %{deps}
is a list of items, the first one may be used as a program name. For instance:
(rule
(targets result.txt)
(deps foo.exe (glob_files *.txt))
(action (run %{deps})))
Here is another example:
(rule
(target foo.exe)
(deps foo.c)
(action (run %{cc} -o %{target} %{deps} -lfoolib)))
Library dependencies are specified using (libraries ...)
fields in library
and executables
stanzas.
For libraries defined in the current scope, you can either use the real name or the public name. For libraries that are part of the installed world
, or for libraries that are part of the current workspace but in another scope, you need to use the public name. For instance: (libraries base re)
.
When resolving libraries, ones that are part of the workspace are always preferred to ones that are part of the installed world
.
Sometimes, one doesn't want to depend on a specific library but rather on whatever is already installed, e.g., to use a different backend, depending on the target.
Dune allows this by using a (select ... from ...)
form inside the list of library dependencies.
Select forms are specified as follows:
(select <target-filename> from
(<literals> -> <filename>)
(<literals> -> <filename>)
...)
<literals>
are lists of literals, where each literal is one of:
<library-name>
, which will evaluate to true if<library-name>
is available, either in the workspace or in theinstalled world
!<library-name>
, which will evaluate to true if<library-name>
is not available in the workspace or in theinstalled world
When evaluating a select form, Dune will create <target-filename>
by copying the file given by the first (<literals> -> <filename>)
case where all the literals evaluate to true. It is an error if none of the clauses are selectable. You can add a fallback by adding a clause of the form (-> <file>)
at the end of the list.
A dependency foo
may be marked as always re-exported using the following syntax:
(re_export foo)
For instance:
(library
(name bar)
(libraries (re_export foo)))
This states that this library explicitly re-exports the interface of foo
. Concretely, when something depends on bar
, it will also be able to see foo
independently of whether implicit
transitive dependencies<implicit_transitive_deps>
are allowed or not. When they are allowed, which is the default, all transitive dependencies are visible, whether they are marked as re-exported or not.
Dune accepts three kinds of preprocessing:
no_preprocessing
means that files are given as-is to the compiler, which is the default.(action <action>)
is used to preprocess files using the given action.(pps <ppx-rewriters-and-flags>)
used to preprocess files using the given list of PPX rewriters.(staged_pps <ppx-rewriters-and-flags>)
is similar to(pps ...)
but behave slightly differently. It's needed for certain PPX rewriters (see below for details).future_syntax
is a special value that brings some of the newer OCaml syntaxes to older compilers. SeeFuture syntax <future-syntax>
for more details.
Dune normally assumes that the compilation pipeline is sequenced as follows:
- code generation (including preprocessing)
- dependency analysis
- compilation
Dune uses this fact to optimize the pipeline and, in particular, share the result of code generation and preprocessing between the dependency analysis and compilation phases. However, some specific code generators or preprocessors require feedback from the compilation phase. As a result, they must be applied in stages as follows:
- first stage of code generation
- dependency analysis
- second step of code generation in parallel with compilation
This is the case for PPX rewriters using the OCaml typer, for instance. When using such PPX rewriters, you must use staged_pps
instead of pps
in order to force Dune to use the second pipeline, which is slower but necessary in this case.
<action>
uses the same DSL as described in the User actions section, and for the same reason given in that section, it will be executed from the root of the current build context. It's expected to be an action that reads the file given as a dependency named input-file
and outputs the preprocessed file on its standard output.
More precisely, (preprocess (action <action>))
acts as if you had set up a rule for every file of the form:
(rule (target file.pp.ml) (deps file.ml) (action (with-stdout-to %{target} (chdir %{workspace_root} <action>))))
The equivalent of a -pp <command>
option passed to the OCaml compiler is (system "<command> %{input-file}")
.
<ppx-rewriters-and-flags>
is expected to be a sequence where each element is either a command line flag if starting with a -
or the name of a library. If you want to pass command line flags that don't start with a -
, you can separate library names from flags using --
. So for instance from the following preprocess
field:
(preprocess (pps ppx1 -foo ppx2 -- -bar 42))
The list of libraries will be ppx1
and ppx2
, and the command line arguments will be: -foo -bar 42
.
Libraries listed here should be ones implementing an OCaml AST rewriter and registering themselves using the ocaml-migrate-parsetree.driver API.
Dune will build a single executable by linking all these libraries and their dependencies together. Note that it is important that all these libraries are linked with -linkall
. Dune automatically uses -linkall
when the (kind ...)
field is set to ppx_rewriter
or ppx_deriver
.
By default, a preprocessing specification applies to all modules in the library/set of executables. It's possible to select the preprocessing on a module-by-module basis by using the following syntax:
(preprocess (per_module (<spec1> <module-list1>) (<spec2> <module-list2>) ...))
Where <spec1>
, <spec2>
, etc. are preprocessing specifications and <module-list1>
, <module-list2>
, etc., are list of module names.
For instance:
(preprocess (per_module (((action (run ./pp.sh X=1 %{input-file})) foo bar)) (((action (run ./pp.sh X=2 %{input-file})) baz))))
The future_syntax
preprocessing specification is equivalent to no_preprocessing
when using one of the most recent versions of the compiler. When using an older one, it is a shim preprocessor that backports some of the newer syntax elements. This allows you to use some of the new OCaml features while keeping compatibility with older compilers.
One example of supported syntax is the custom let-syntax
that was introduced in 4.08, allowing the user to define custom let
operators.
Note that this feature is implemented by the third-party ocaml-syntax-shims project, so if you use this feature, you must also declare a dependency on this package.
If your preprocessor needs extra dependencies you should use the preprocessor_deps
field available in the library
, executable
, and executables
stanzas.
Dependencies in dune
files can be specified using one of the following:
(:name <dependencies>)
will bind the list of dependencies to thename
variable. This variable will be available as%{name}
in actions.(file <filename>)
, or simply<filename>
, depend on this file.(alias <alias-name>)
depends on the construction of this alias. For instance:(alias src/runtest)
.(alias_rec <alias-name>)
depends on the construction of this alias recursively in all children directories wherever it is defined. For instance:(alias_rec src/runtest)
might depend on(alias src/runtest)
,(alias src/foo/bar/runtest)
, etc.(glob_files <glob>)
depends on all files matched by<glob>
. See theglob <glob>
for details.(glob_files_rec <glob>)
is the recursive version of(glob_files <glob>)
. See theglob <glob>
for details.(source_tree <dir>)
depends on all source files in the subtree with root<dir>
.(universe)
depends on everything in the universe. This is for cases where dependencies are too hard to specify. Note that Dune will not be able to cache the result of actions that depend on the universe. In any case, this is only for dependencies in theinstalled world
. You must still specify all dependencies that come from the workspace.(package <pkg>)
depends on all files installed by<package>
, as well as on the transitive package dependencies of<package>
. This can be used to test a command against the files that will be installed.(env_var <var>)
depends on the value of the environment variable<var>
. If this variable becomes set, becomes unset, or changes value, the target will be rebuilt.(sandbox <config>)
requires a particular sandboxing configuration.<config>
can be one (or many) of:always
: the action requires a clean environmentnone
: the action must run in the build directorypreserve_file_kind
: the action needs the files it reads to look like normal files (so Dune won't use symlinks for sandboxing)
(include <file>)
read the s-expression in<file>
and interpret it as additional dependencies. The s-expression is expected to be a list of the same constructs enumerated here.
In all these cases, the argument supports variables
.
Dune allows a user to organize dependency lists by naming them. The user is allowed to assign a group of dependencies a name that can later be referred to in actions (like the %{deps}
, %{target}
, and %{targets}
built in variables).
One instance where this is useful is for naming globs. Here's an example of an imaginary bundle command:
(rule
(target archive.tar)
(deps
index.html
(:css (glob_files *.css))
(:js foo.js bar.js)
(:img (glob_files *.png) (glob_files *.jpg)))
(action
(run %{bin:bundle} index.html -css %{css} -js %{js} -img %{img} -o %{target})))
Note that a named dependency list can also include unnamed dependencies (like index.html
in the example above). Also, such user defined names will shadow build in variables, so (:workspace_root x)
will shadow the built-in %{workspace_root}
variable.
You can use globs to declare dependencies on a set of files. Note that globs will match files that exist in the source tree as well as buildable targets, so for instance you can depend on *.cmi
.
Dune supports globbing files in a single directory via (glob_files ...)
and, starting with Dune 3.0, in all sub-directories recursively via (glob_files_rec ...)
. The glob is interpreted as follows:
- anything before the last
/
is taken as a literal path - anything after the last
/
, or everything if the glob contains no/
, is interpreted using the glob syntax
Absolute paths are permitted in the (glob_files ...)
term only. It's an error to pass an absolute path (i.e., a path beginning with a /
) to (glob_files_rec ...)
`.
The glob syntax is interpreted as follows:
\<char>
matches exactly<char>
, even if it's a special character (*
,?
, ...).*
matches any sequence of characters, except if it comes first, in which case it matches any character that is not.
followed by anything.**
matches any character that is not.
followed by anything, except if it comes first, in which case it matches anything.?
matches any single character.[<set>]
matches any character that is part of<set>
.[!<set>]
matches any character that is not part of<set>
.{<glob1>,<glob2>,...,<globn>}
matches any string that is matched by one of<glob1>
,<glob2>
, etc.
Syntax | Files matched | Files not matched |
---|---|---|
x |
x |
y |
\* |
* |
x |
file*.txt |
file1.txt , file2.txt |
f.txt |
*.txt |
f.txt |
.hidden.txt |
a** |
aml |
a.ml |
** |
a/b , a.b |
(none) |
a?.txt |
a1.txt , a2.txt |
b1.txt , a10.txt |
f[xyz].txt |
fx.txt , fy.txt , fz.txt |
f2.txt , f.txt |
f[!xyz].txt |
f2.txt , fa.txt |
fx.txt , f.txt |
a.{ml,mli} |
a.ml , a.mli |
a.txt , b.ml |
../a.{ml,mli} |
../a.ml , ../a.mli |
a.ml |
In library
, executable
, executables
, and env
stanzas, you can specify OCaml compilation flags using the following fields:
(flags <flags>)
to specify flags passed to bothocamlc
andocamlopt
(ocamlc_flags <flags>)
to specify flags passed toocamlc
only(ocamlopt_flags <flags>)
to specify flags passed toocamlopt
only
For all these fields, <flags>
is specified in the Ordered set language. These fields all support (:include ...)
forms.
The default value for (flags ...)
is taken from the environment, as a result it's recommended to write (flags ...)
fields as follows:
(flags (:standard <my options>))
(action ...)
fields describe user actions.
User actions are always run from the same subdirectory of the current build context as the dune
file they are defined in, so for instance, an action defined in src/foo/dune
will be run from $build/<context>/src/foo
.
The argument of (action ...)
fields is a small DSL that's interpreted by Dune directly and doesn't require an external shell. All atoms in the DSL support variables
. Moreover, you don't need to specify dependencies explicitly for the special %{<kind>:...}
forms; these are recognized and automatically handled by Dune.
The DSL is currently quite limited, so if you want to do something complicated it's recommended to write a small OCaml program and use the DSL to invoke it. You can use shexp to write portable scripts or configurator
for configuration related tasks. You can also use dune-action-plugin
to express program dependencies directly in the source code.
The following constructions are available:
(run <prog> <args>)
to execute a program.<prog>
is resolved locally if it is available in the current workspace, otherwise it is resolved using thePATH
(dynamic-run <prog> <args>)
to execute a program that was linked againstdune-action-plugin
library.<prog>
is resolved in the same way as inrun
(chdir <dir> <DSL>)
to change the current directory(setenv <var> <value> <DSL>)
to set an environment variable(with-<outputs>-to <file> <DSL>)
to redirect the output to a file, where<outputs>
is one of:stdout
,stderr
oroutputs
(for bothstdout
andstderr
)(ignore-<outputs> <DSL>)
to ignore the output, where<outputs>
is one of:stdout
,stderr
oroutputs
(with-stdin-from <file> <DSL>)
to redirect the input from a file(with-accepted-exit-codes <pred> <DSL>)
specifies the list of expected exit codes for the programs executed in<DSL>
.<pred>
is a predicate on integer values, and is specified using thepredicate-lang
.<DSL>
can only contain nested occurrences ofrun
,bash
,system
,chdir
,setenv
,ignore-<outputs>
,with-stdin-from
andwith-<outputs>-to
. This action is available since Dune 2.0.(progn <DSL>...)
to execute several commands in sequence(echo <string>)
to output a string on stdout(write-file <file> <string>)
writes<string>
to<file>
(cat <file> ...)
to sequentially print the contents of files to stdout(copy <src> <dst>)
to copy a file. If these files are OCaml sources you should follow themodule_name.xxx.ml
naming convention <merlin-filenames>
to preserve Merlin's functionality.(copy# <src> <dst>)
to copy a file and add a line directive at the beginning(system <cmd>)
to execute a command using the system shell:sh
on Unix andcmd
on Windows(bash <cmd>)
to execute a command using/bin/bash
. This is obviously not very portable.(diff <file1> <file2>)
is similar to(run diff <file1> <file2>)
but is better and allows promotion. See Diffing and promotion for more details.(diff? <file1> <file2>)
is similar to(diff <file1> <file2>)
except that<file2>
should be produced by a part of the same action rather than be a dependency, is optional and will be consumed bydiff?
.(cmp <file1> <file2>)
is similar to(run cmp <file1> <file2>)
but allows promotion. See Diffing and promotion for more details.(no-infer <DSL>)
to perform an action without inference of dependencies and targets. This is useful if you are generating dependencies in a way that Dune doesn't know about, for instance by calling an external build system.(pipe-<outputs> <DSL> <DSL> <DSL>...)
to execute several actions (at least two) in sequence, filtering the<outputs>
of the first command through the other command, piping the standard output of each one into the input of the next. This action is available since Dune 2.7.
As mentioned, copy#
inserts a line directive at the beginning of the destination file. More precisely, it inserts the following line:
# 1 "<source file name>"
Most languages recognize such lines and update their current location to report errors in the original file rather than the copy. This is important because the copy exists only under the _build
directory, and in order for editors to jump to errors when parsing the output of the build system, errors must point to files that exist in the source tree. In the beta versions of Dune, copy#
was called copy-and-add-line-directive
. However, most of time, one wants this behavior rather than a bare copy, so it was renamed to something shorter.
Note: expansion of the special %{<kind>:...}
is done relative to the current working directory of the DSL being executed. So for instance, if you have this action in a src/foo/dune
:
(action (chdir ../../.. (echo %{dep:dune})))
Then %{dep:dune}
will expand to src/foo/dune
. When you run various tools, they often use the filename given on the command line in error messages. As a result, if you execute the command from the original directory, it will only see the basename.
To understand why this is important, let's consider this Dune file living in src/foo
:
(rule
(target blah.ml)
(deps blah.mll)
(action (run ocamllex -o %{target} %{deps})))
Here the command that will be executed is:
ocamllex -o blah.ml blah.mll
And it will be executed in _build/<context>/src/foo
. As a result, if there is an error in the generated blah.ml
file it will be reported as:
File "blah.ml", line 42, characters 5-10:
Error: ...
Which can be a problem, as you editor might think that blah.ml
is at the root of your project. Instead, this is a better way to write it:
(rule
(target blah.ml)
(deps blah.mll)
(action (chdir %{workspace_root} (run ocamllex -o %{target} %{deps}))))
The user actions that run external commands (run
, bash
, system
) are opaque to Dune, so Dune has to rely on manual specification of dependencies and targets. One problem with manual specification is that it's error-prone. It's often hard to know in advance what files the command will read, and knowing a correct set of dependencies is very important for build reproducibility and incremental build correctness.
To help with this problem Dune supports sandboxing. An idealized view of sandboxing is that it runs the action in an environment where it can't access anything except for its declared dependencies.
In practice, we have to make compromises and have some trade-offs between simplicity, information leakage, performance, and portability.
The way sandboxing is currently implemented is that for each sandboxed action we build a separate directory tree (sandbox directory) that mirrors the build directory, filtering it to only contain the files that were declared as dependencies. We run the action in that directory, and then we copy the targets back to the build directory.
You can configure Dune to use sandboxing modes symlink
, hardlink
or copy
, which determines how the individual files are populated (they will be symlinked, hardlinked, or copied into the sandbox directory).
This approach is very simple and portable, but that comes with certain limitations:
- The actions in the sandbox can use absolute paths to refer to anywhere outside the sandbox. This means that only dependencies on relative paths in the build tree can be enforced/detected by sandboxing.
- The sandboxed actions still run with full permissions of Dune itself so sandboxing is not a security feature. It won't prevent network access either.
- We don't erase the environment variables of the sandboxed commands. This is something we want to change.
- Performance impact is usually small, but it can get noticeable for fast actions with very large sets of dependencies.
Some actions may rely on sandboxing to work correctly. For example, an action may need the input directory to contain nothing except the input files, or the action might create temporary files that break other build actions.
Some other actions may refuse to work with Sandboxing. Cor example, if they rely on absolute path to the build directory staying fixed, or if they deliberately use some files without declaring dependencies (this is usually a very bad idea, by the way).
Generally it's better to improve the action so it works with or without sandboxing (especially with), but sometimes you just can't do that.
Things like this can be described using the "sandbox" field in the dependency specification language (see deps-field
).
Dune always respects per-action sandboxing specification. You can configure it globally to prefer a certain sandboxing mode if the action allows it.
This is controlled by:
dune --sandbox <...>
cli flag (seeman dune-build
)DUNE_SANDBOX
environment (seeman dune-build
)(sandboxing_preference ..)
field in the dune config (seeman dune-config
)
Given two rules that are independent, Dune will assume that their associated actions can be run concurrently. Two rules are considered independent if neither of them depend on the other, either directly or through a chain of dependencies. This basic assumption allows Dune to parallelize the build.
However, it is sometimes the case that two independent rules cannot be executed concurrently. For instance this can happen for more complicated tests. In order to prevent Dune from running the actions at the same time, you can specify that both actions take the same lock:
(rule
(alias runtest)
(deps foo)
(locks m)
(action (run test.exe %{deps})))
(alias
(rule runtest)
(deps bar)
(locks m)
(action (run test.exe %{deps})))
Dune will make sure that the executions of test.exe foo
and test.exe bar
are serialized.
Although they don't live in the filesystem, lock names are interpreted as file names. So for instance (with-lock m ...)
in src/dune
and (with-lock ../src/m)
in test/dune
refer to the same lock.
Note also that locks are per build context. So if your workspace has two build contexts setup, the same rule might still be executed concurrently between the two build contexts. If you want a lock that is global to all build contexts, simply use an absolute filename:
(rule
(alias runtest)
(deps foo)
(locks /tcp-port/1042)
(action (run test.exe %{deps})))
(diff <file1> <file2>)
is very similar to (run diff <file1> <file2>)
. In particular it behaves in the same way:
- When
<file1>
and<file2>
are equal, it does nothing. - When they are not, the differences are shown and the action fails.
However, it is different for the following reason:
- The exact command used for diff files can be configured via the
--diff-command
command line argument. Note that it's only called when the files are not byte equals By default, it will use
patdiff
if it is installed.patdiff
is a better diffing program. You can install it via opam with:$ opam install patdiff
- On Windows, both
(diff a b)
and(diff? a b)
normalize end-of-line characters before comparing the files. - Since
(diff a b)
is a built-in action, Dune knows thata
andb
are needed, so you don't need to specify them explicitly as dependencies. - You can use
(diff? a b)
after a command that might or might not produceb
, for cases where commands optionally produce a corrected file - If
<file1>
doesn't exist, it will compare with the empty file. - It allows promotion. See below.
Note that (cmp a b)
does no end-of-line normalization and doesn't print a diff when the files differ. cmp
is meant to be used with binary files.
Whenever an action (diff <file1> <file2>)
or (diff? <file1> <file2>)
fails because the two files are different, Dune allows you to promote <file2>
as <file1>
if <file1>
is a source file and <file2>
is a generated file.
More precisely, let's consider the following Dune file:
(rule
(with-stdout-to data.out (run ./test.exe)))
(rule
(alias runtest)
(action (diff data.expected data.out)))
Where data.expected
is a file committed in the source repository. You can use the following workflow to update your test:
- Update the code of your test.
- Run
dune runtest
. The diff action will fail and a diff will be printed. - Check the diff to make sure it's what you expect. This diff can be displayed again by running
dune promotion diff
. - Run
dune promote
. This will copy the generateddata.out
file todata.expected
directly in the source tree.
You can also use dune runtest --auto-promote
, which will automatically do the promotion.
Installation is the process of copying freshly built libraries, binaries, and other files from the build directory to the system. Dune offers two ways of doing this: via opam or directly via the install
command. In particular, the installation model implemented by Dune was copied from opam. Opam is the standard OCaml package manager.
In both cases, Dune only know how to install whole packages. A package being a collection of executables, libraries, and other files. In this section, we'll describe how to define a package, how to "attach" various elements to it, and how to proceed with installing it on the system.
To declare a package, simply add a package
stanza to your dune-project
file:
(package
(name mypackage)
(synopsis "My first Dune package!")
(description "\| This is my first attempt at creating
"\| a project with Dune.
))
Once you have done this, Dune will know about the package named mypackage
and you will be able to attach various elements to it. The package
stanza accepts more fields, such as dependencies.
Note that package names are in a global namespace, so the name you choose must be universally unique. In particular, package managers never allow to release two packages with the same name.
In older projects using Dune, packages were defined by manually writing a file called <package-name>.opam
at the root of the project. However, it's not recommended to use this method in new projects, as we expect to deprecate it in the future. The right way to define a package is with a package
stanza in the dune-project
file.
See opam-generation
for instructions on configuring Dune to automatically generate .opam
files based on the package
stanzas.
Attaching an element to a package means declaring to Dune that this element is part of the said package. The method to attach an element to a package depends on the kind of the element. In this sub-section, we will go through the various kinds of elements and describe how to attach each of them to a package.
In the rest of this section, <prefix>
refers to the directory in which the user chooses to install packages. When installing via opam, it's opam that sets this directory. When calling dune install
, the installation directory is either guessed or can be manually specified by the user. Defaults directories which replace guessing can be set during the compilation of dune.
When packages need additional resources outside their binary, their location could be hard to find. Moreover some packages could add resources to another package, for example in the case of plugins. These location are called sites in Dune. One package can define them. During execution, one site corresponds to a list of directories. They are like layers, and the first directories have a higher priority. Examples and precisions are available at sites
.
In order to attach a library to a package, merely add a public_name
field to your library. This is the name that external users of your libraries must use in order to refer to it. Dune requires that the public name of a library is either the name of the package it is part of or start with the package name followed by a dot character.
For instance:
(library
(name mylib)
(public_name mypackage.mylib))
After you have added a public name to a library, Dune will know to install it as part of the package it is attached to. Dune installs the library files in a directory <prefix>/lib/<package-name>
.
If the library name contains dots, the full directory in which the library files are installed is lib/<comp1>/<comp2/.../<compn>
, where <comp1>
, <comp2>
, ... <compn>
are the dot separated component of the public library name. By definition, <comp1>
is always the package name.
Similarly to libraries, to attach an executable to a package simply add a public_name
field to your executable
stanza or a public_names
field for executables
stanzas. Designate this name to match the available executables through the installed PATH
(i.e., the name users must type in their shell to execute the program), because Dune cannot guess an executable's relevant package from its public name. It's also necessary to add a package
field unless the project contains a single package, in which case the executable will be attached to this package.
For instance:
(executable
(name main)
(public_name myprog)
(package mypackage))
Once mypackage
is installed on the system, the user will be able to type the following in their shell:
$ myprog
to execute the program.
For all other kinds of elements, you must attach them manually via an install
stanza.
Dune provides basic support for including foreign source files as well as archives of foreign object files into OCaml projects via the foreign_stubs
and foreign_archives
fields. Individual object files can also be included via the extra_objects
field.
You can specify foreign sources using the foreign_stubs
field of the library
and executable
stanzas. For example:
(library
(name lib)
(foreign_stubs (language c) (names src1 src2))
(foreign_stubs (language cxx) (names src3) (flags -O2)))
Here we declare an OCaml library lib
, which contains two C sources src1
and src2
, and one C++ source, src3
, which need to be compiled with -O2
. These source files will be compiled and packaged with the library, along with the link-time flags to be used when linking the final executables. When matching names
to source files, Dune treats *.c
files as C sources, and *.cpp
, *.cc
, and *.cxx
files as C++ sources.
Here is a complete list of supported subfields:
language
specifies the source language, wherec
means C andcxx
means C++. In future, more languages may be supported.names
specifies the names of source files. When specifying a source file, omit the extension and any relative parts of the path; Dune will scan all library directories to find all matching files and raise an error if multiple source files map to the same object name. If you need to have multiple object files with the same name, you can package them into differentforeign-archives
via theforeign_archives
field. This field uses theordered-set-language
where the:standard
value corresponds to the set of names of all source files whose extensions match the specifiedlanguage
.flags
are passed when compiling source files. This field is specified using theordered-set-language
, where the:standard
value comes from the environment settingsc_flags
andcxx_flags
, respectively. Note that, for C stubs, Dune unconditionally adds the flags present in the OCaml config fieldsocamlc_cflags
andocamlc_cppflags
to the compiler command line. This behavior can be disabled since Dune 2.8 via thedune-project
optionalways-add-cflags
.include_dirs
are tracked as dependencies and passed to the compiler via the-I
flag. You can usevariables
in this field and refer to a library source directory using the(lib library-name)
syntax. Additionally, the syntax(include filename)
can be used to specify a file containing additional arguments to(include_dirs ...)
. The named file can either contain a single path to be added to this list of include directories, or an S-expression listing additional(include_dirs ...)
arguments (the(lib ...)
and(include ...)
syntax is also supported in files included in this way). For example,(include_dirs dir1 (lib lib1) (lib lib2) (include inc1) dir2)
specifies the directorydir1
, the source directories oflib1
andlib2
, the list of directories contained in the fileinc1
, and the directorydir2
, in this order. Some examples of possible contents of the fileinc1
are:dir3
which would adddir3
to the list of include directories((lib lib3) dir4 (include inc2))
which would add the source directory of the librarylib3
, the directorydir4
, and the result of recursively including the contents of the fileinc2
. The contents of included directories are tracked recursively, e.g., if you use(include_dir dir)
and have headersdir/base.h
anddir/lib/lib.h
, they both will be tracked as dependencies.extra_deps
specifies any other dependencies that should be tracked. This is useful when dealing with#include
statements that escape into a parent directory like#include "../a.h"
.
Since Dune 3.5, it is possible to use different foreign stubs when building in native or byte mode. This feature needs to be activated by adding (using mode_specific_stubs 0.1)
in the dune-project
file.
Then it is allowed to use the mode
field when describing foreign_stubs
. If the same stub is defined twice, Dune will automatically chose the correct one. This allows the use of different sets of flags or even different source files from which the stubs are built.
(executable
(name main)
(modes native byte_complete)
(foreign_stubs
(language c)
(mode byte)
(names c_stubs))
(foreign_stubs
(language c)
(mode native)
(flags :standard -DNATIVE_CODE) ; A flag specific to native builds
(names c_stubs))) ; This could be the name of an implementation
; specific to native builds
Note that, as of version 0.1
of this extension, this mechanism does not work for foreign_archives
.
You can also specify archives of separately compiled foreign object files that need to be packaged with an OCaml library or linked into an OCaml executable. To do that, use the foreign_archives
field of the corresponding library
or executable
stanza. For example:
(library
(name lib)
(foreign_stubs (language c) (names src1 src2))
(foreign_stubs (language cxx) (names src3) (flags -O2))
(foreign_archives arch1 some/dir/arch2))
Here, in addition to foreign-stubs
, we also specify foreign archives arch1
and arch2
, where the latter is stored in a subdirectory some/dir
.
You can build a foreign archive manually, e.g., using a custom rule
as described in foreign-sandboxing
, or ask Dune to build it via the foreign_library
stanza:
(foreign_library
(archive_name arch1)
(language c)
(names src4 src5)
(include_dir headers))
This asks Dune to compile C source files src4
and src5
with headers tracked in the headers
directory and put the resulting object files into an archive arch1
, whose full name is typically libarch1.a
for static linking and dllarch1.so
for dynamic linking.
The foreign_library
stanza supports all foreign-stubs
fields plus the archive_name
field, which specifies the archive's name. You can refer to the same archive name from multiple OCaml libraries and executables, so a foreign archive is a bit like a foreign library, hence the name of the stanza.
Foreign archives are particularly useful when embedding a library written in a foreign language and/or built with another build system. See foreign-sandboxing
for more details.
It's possible to specify native object files to be packaged with OCaml libraries or linked into OCaml executables. Do this by using the extra_objects
field of the library
or executable
stanzas. For example:
(executable
(public_name main)
(extra_objects foo bar))
(rule
(targets foo.o bar.o)
(deps foo.c bar.c)
(action (run ocamlopt %{deps})))
This example builds an executable which is linked against a pair of native object files, foo.o
and bar.o
. The extra_objects
field takes a list of object names, which correspond to the object file names with their path and extension omitted.
In this example, the sources corresponding to the objects (foo.c
and bar.c
) are assumed to be present in the same directory as the OCaml source code, and a custom rule
is used to compile the C source code into object files using ocamlopt
. This is not necessary; one can instead compile foreign object files manually and place them next to the OCaml source code.
Depending on the always-add-cflags
option, the base :standard set of flags for C will contain only ocamlc_cflags
or both ocamlc_cflags
and ocamlc_cppflags
.
There are multiple levels where one can declare custom flags (using the ordered-set-language
), and each level inherits the flags of the previous one in its :standard set:
- In the global env definition of a dune-workspace file
- In the per-context env definitions in a dune-workspace file
- In the env definition of a dune file
- In a foreign_ field of an executable or a library
The %{cc}
variable <variables>
will contain the flags from the first three levels only.