61 lines
2.3 KiB
ReStructuredText
61 lines
2.3 KiB
ReStructuredText
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Findlib Integration
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===================
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Dune integrates with `findlib`_ so that it is possible to use a dependency
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built with Dune in a project that does not use Dune, or vice versa.
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.. _findlib: https://github.com/ocaml/ocamlfind
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.. seealso:: :doc:`../explanation/ocaml-ecosystem` explains the role of
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findlib and its relation with Dune.
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To do so, Dune both interprets and generates ``META`` files.
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How Dune Interprets ``META`` files
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----------------------------------
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``META`` files use the concept of *predicates*, which can be used to change the
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interpretation of the directives the files contain. However, Dune does not
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expose this to the user.
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Instead, Dune interprets ``META`` files assuming the following set of
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predicates:
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- ``mt``: refers to a library that can be used with or without threads. Dune
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will force the threaded version.
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- ``mt_posix``: forces the use of POSIX threads rather than VM threads. VM
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threads are deprecated and will soon be obsolete.
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- ``ppx_driver``: when a library acts differently depending on whether
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it's linked as part of a driver or meant to add a ``-ppx`` argument
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to the compiler, choose the former behavior.
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The Special Case of the OCaml Compiler
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--------------------------------------
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Libraries installed by the compiler are a special case: when the OCaml compiler
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is older than version 5.0, it does not include ``META`` files. In that
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situation, Dune uses its own internal database.
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How Dune Generates ``META`` Files
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---------------------------------
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When Dune builds a library, it generates a corresponding ``META`` file
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automatically. Usually, there is nothing to do. However, for the rare cases
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where a specific ``META`` file is needed, or to ease the transition of a
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project to Dune, it is possible to write/generate a specific one.
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If a ``META.<package>.template`` is found in the same directory as
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``<package>.OPAM``, the generated ``META.<package>`` file will be produced by
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starting from the contents of ``META.<package>.template`` and replacing lines
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of the form ``# DUNE_GEN`` with the contents of the ``META`` it would normally
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generate.
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For instance, to add ``field = "..."`` to the generated ``META`` file of
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package ``pkg``, you can create a file named ``META.pkg.template`` with the
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following contents::
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# DUNE_GEN
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blah = "..."
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