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Configuration
=============

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.. highlight:: cabal

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Overview
--------

The global configuration file for ``cabal-install`` is
``~/.cabal/config``. If you do not have this file, ``cabal`` will create
it for you on the first call to ``cabal update``. Alternatively, you can
explicitly ask ``cabal`` to create it for you using

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.. code-block:: console

    $ cabal user-config update
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Most of the options in this configuration file are also available as
command line arguments, and the corresponding documentation can be used
to lookup their meaning. The created configuration file only specifies
values for a handful of options. Most options are left at their default
value, which it documents; for instance,

::

    -- executable-stripping: True

means that the configuration file currently does not specify a value for
the ``executable-stripping`` option (the line is commented out), and
that the default is ``True``; if you wanted to disable stripping of
executables by default, you would change this line to

::

    executable-stripping: False

You can also use ``cabal user-config update`` to migrate configuration
files created by older versions of ``cabal``.

Repository specification
------------------------

An important part of the configuration if the specification of the
repository. When ``cabal`` creates a default config file, it configures
the repository to be the central Hackage server:

::

    repository hackage.haskell.org
      url: http://hackage.haskell.org/

The name of the repository is given on the first line, and can be
anything; packages downloaded from this repository will be cached under
``~/.cabal/packages/hackage.haskell.org`` (or whatever name you specify;
you can change the prefix by changing the value of
``remote-repo-cache``). If you want, you can configure multiple
repositories, and ``cabal`` will combine them and be able to download
packages from any of them.

Using secure repositories
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^^^^^^^^^^^^^^^^^^^^^^^^^
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For repositories that support the TUF security infrastructure (this
includes Hackage), you can enable secure access to the repository by
specifying:

::

    repository hackage.haskell.org
      url: http://hackage.haskell.org/
      secure: True
      root-keys: <root-key-IDs>
      key-threshold: <key-threshold>

The ``<root-key-IDs>`` and ``<key-threshold>`` values are used for
bootstrapping. As part of the TUF infrastructure the repository will
contain a file ``root.json`` (for instance,
http://hackage.haskell.org/root.json) which the client needs to do
verification. However, how can ``cabal`` verify the ``root.json`` file
*itself*? This is known as bootstrapping: if you specify a list of root
key IDs and a corresponding threshold, ``cabal`` will verify that the
downloaded ``root.json`` file has been signed with at least
``<key-threshold>`` keys from your set of ``<root-key-IDs>``.

You can, but are not recommended to, omit these two fields. In that case
``cabal`` will download the ``root.json`` field and use it without
verification. Although this bootstrapping step is then unsafe, all
subsequent access is secure (provided that the downloaded ``root.json``
was not tempered with). Of course, adding ``root-keys`` and
``key-threshold`` to your repository specification only shifts the
problem, because now you somehow need to make sure that the key IDs you
received were the right ones. How that is done is however outside the
scope of ``cabal`` proper.

More information about the security infrastructure can be found at
https://github.com/well-typed/hackage-security.

Legacy repositories
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^^^^^^^^^^^^^^^^^^^
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Currently ``cabal`` supports two kinds of legacy repositories. The
first is specified using

::

    remote-repo: hackage.haskell.org:http://hackage.haskell.org/packages/archive

This is just syntactic sugar for

::

    repository hackage.haskell.org
      url: hackage.haskell.org:http://hackage.haskell.org/packages/archive

although, in (and only in) the specific case of Hackage, the URL
``http://hackage.haskell.org/packages/archive`` will be silently
translated to ``http://hackage.haskell.org/``.

The second kind of legacy repositories are so-called local
repositories:

::

    local-repo: my-local-repo:/path/to/local/repo

This can be used to access repositories on the local file system.
However, the layout of these local repositories is different from the
layout of remote repositories, and usage of these local repositories is
deprecated.

Secure local repositories
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^^^^^^^^^^^^^^^^^^^^^^^^^
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If you want to use repositories on your local file system, it is
recommended instead to use a *secure* local repository:

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::
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    repository my-local-repo
      url: file:/path/to/local/repo
      secure: True
      root-keys: <root-key-IDs>
      key-threshold: <key-threshold>

The layout of these secure local repos matches the layout of remote
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repositories exactly; the :hackage-pkg:`hackage-repo-tool`
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can be used to create and manage such repositories.

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.. _installing-packages:

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Building and installing packages
================================

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.. highlight:: console

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After you've unpacked a Cabal package, you can build it by moving into
the root directory of the package and running the ``cabal`` tool there:

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::

    $ cabal [command] [option...]
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The *command* argument selects a particular step in the build/install
process.

You can also get a summary of the command syntax with

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::

    $ cabal help
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Alternatively, you can also use the ``Setup.hs`` or ``Setup.lhs``
script:

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::

    $ runhaskell Setup.hs [command] [option...]
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For the summary of the command syntax, run:

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::

    $ cabal help
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or

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::

    $ runhaskell Setup.hs --help
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Building and installing a system package
----------------------------------------

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::
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    $ runhaskell Setup.hs configure --ghc
    $ runhaskell Setup.hs build
    $ runhaskell Setup.hs install
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The first line readies the system to build the tool using GHC; for
example, it checks that GHC exists on the system. The second line
performs the actual building, while the last both copies the build
results to some permanent place and registers the package with GHC.

Building and installing a user package
--------------------------------------

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::
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    $ runhaskell Setup.hs configure --user
    $ runhaskell Setup.hs build
    $ runhaskell Setup.hs install
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The package is installed under the user's home directory and is
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registered in the user's package database (:option:`setup configure --user`).
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Installing packages from Hackage
--------------------------------

The ``cabal`` tool also can download, configure, build and install a
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Hackage_ package and all of its
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dependencies in a single step. To do this, run:

::

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   $ cabal install [PACKAGE...]
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To browse the list of available packages, visit the
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Hackage_ web site.
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Developing with sandboxes
-------------------------

By default, any dependencies of the package are installed into the
global or user package databases (e.g. using
``cabal install --only-dependencies``). If you're building several
different packages that have incompatible dependencies, this can cause
the build to fail. One way to avoid this problem is to build each
package in an isolated environment ("sandbox"), with a sandbox-local
package database. Because sandboxes are per-project, inconsistent
dependencies can be simply disallowed.

For more on sandboxes, see also `this
article <http://coldwa.st/e/blog/2013-08-20-Cabal-sandbox.html>`__.

Sandboxes: basic usage
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^^^^^^^^^^^^^^^^^^^^^^
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To initialise a fresh sandbox in the current directory, run
``cabal sandbox init``. All subsequent commands (such as ``build`` and
``install``) from this point will use the sandbox.

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::
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    $ cd /path/to/my/haskell/library
    $ cabal sandbox init                   # Initialise the sandbox
    $ cabal install --only-dependencies    # Install dependencies into the sandbox
    $ cabal build                          # Build your package inside the sandbox

It can be useful to make a source package available for installation in
the sandbox - for example, if your package depends on a patched or an
unreleased version of a library. This can be done with the
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``cabal sandbox add-source`` command - think of it as "local Hackage_".
If an add-source dependency is later modified, it is reinstalled automatically.
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::
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    $ cabal sandbox add-source /my/patched/library # Add a new add-source dependency
    $ cabal install --dependencies-only            # Install it into the sandbox
    $ cabal build                                  # Build the local package
    $ $EDITOR /my/patched/library/Source.hs        # Modify the add-source dependency
    $ cabal build                                  # Modified dependency is automatically reinstalled

Normally, the sandbox settings (such as optimisation level) are
inherited from the main Cabal config file (``$HOME/cabal/config``).
Sometimes, though, you need to change some settings specifically for a
single sandbox. You can do this by creating a ``cabal.config`` file in
the same directory with your ``cabal.sandbox.config`` (which was created
by ``sandbox init``). This file has the same syntax as the main Cabal
config file.

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::
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    $ cat cabal.config
    documentation: True
    constraints: foo == 1.0, bar >= 2.0, baz
    $ cabal build                                  # Uses settings from the cabal.config file

When you have decided that you no longer want to build your package
inside a sandbox, just delete it:

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::
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    $ cabal sandbox delete                       # Built-in command
    $ rm -rf .cabal-sandbox cabal.sandbox.config # Alternative manual method

Sandboxes: advanced usage
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^^^^^^^^^^^^^^^^^^^^^^^^^
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The default behaviour of the ``add-source`` command is to track
modifications done to the added dependency and reinstall the sandbox
copy of the package when needed. Sometimes this is not desirable: in
these cases you can use ``add-source --snapshot``, which disables the
change tracking. In addition to ``add-source``, there are also
``list-sources`` and ``delete-source`` commands.

Sometimes one wants to share a single sandbox between multiple packages.
This can be easily done with the ``--sandbox`` option:

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::
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    $ mkdir -p /path/to/shared-sandbox
    $ cd /path/to/shared-sandbox
    $ cabal sandbox init --sandbox .
    $ cd /path/to/package-a
    $ cabal sandbox init --sandbox /path/to/shared-sandbox
    $ cd /path/to/package-b
    $ cabal sandbox init --sandbox /path/to/shared-sandbox

Note that ``cabal sandbox init --sandbox .`` puts all sandbox files into
the current directory. By default, ``cabal sandbox init`` initialises a
new sandbox in a newly-created subdirectory of the current working
directory (``./.cabal-sandbox``).

Using multiple different compiler versions simultaneously is also
supported, via the ``-w`` option:

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::
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    $ cabal sandbox init
    $ cabal install --only-dependencies -w /path/to/ghc-1 # Install dependencies for both compilers
    $ cabal install --only-dependencies -w /path/to/ghc-2
    $ cabal configure -w /path/to/ghc-1                   # Build with the first compiler
    $ cabal build
    $ cabal configure -w /path/to/ghc-2                   # Build with the second compiler
    $ cabal build

It can be occasionally useful to run the compiler-specific package
manager tool (e.g. ``ghc-pkg``) tool on the sandbox package DB directly
(for example, you may need to unregister some packages). The
``cabal sandbox hc-pkg`` command is a convenient wrapper that runs the
compiler-specific package manager tool with the arguments:

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::
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    $ cabal -v sandbox hc-pkg list
    Using a sandbox located at /path/to/.cabal-sandbox
    'ghc-pkg' '--global' '--no-user-package-conf'
        '--package-conf=/path/to/.cabal-sandbox/i386-linux-ghc-7.4.2-packages.conf.d'
        'list'
    [...]

The ``--require-sandbox`` option makes all sandbox-aware commands
(``install``/``build``/etc.) exit with error if there is no sandbox
present. This makes it harder to accidentally modify the user package
database. The option can be also turned on via the per-user
configuration file (``~/.cabal/config``) or the per-project one
(``$PROJECT_DIR/cabal.config``). The error can be squelched with
``--no-require-sandbox``.

The option ``--sandbox-config-file`` allows to specify the location of
the ``cabal.sandbox.config`` file (by default, ``cabal`` searches for it
in the current directory). This provides the same functionality as
shared sandboxes, but sometimes can be more convenient. Example:

::

    $ mkdir my/sandbox
    $ cd my/sandbox
    $ cabal sandbox init
    $ cd /path/to/my/project
    $ cabal --sandbox-config-file=/path/to/my/sandbox/cabal.sandbox.config install
    # Uses the sandbox located at /path/to/my/sandbox/.cabal-sandbox
    $ cd ~
    $ cabal --sandbox-config-file=/path/to/my/sandbox/cabal.sandbox.config install
    # Still uses the same sandbox

The sandbox config file can be also specified via the
``CABAL_SANDBOX_CONFIG`` environment variable.

Finally, the flag ``--ignore-sandbox`` lets you temporarily ignore an
existing sandbox:

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::
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    $ mkdir my/sandbox
    $ cd my/sandbox
    $ cabal sandbox init
    $ cabal --ignore-sandbox install text
    # Installs 'text' in the user package database ('~/.cabal').

Creating a binary package
-------------------------

When creating binary packages (e.g. for Red Hat or Debian) one needs to
create a tarball that can be sent to another system for unpacking in the
root directory:

::

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    $ runhaskell Setup.hs configure --prefix=/usr
    $ runhaskell Setup.hs build
    $ runhaskell Setup.hs copy --destdir=/tmp/mypkg
    $ tar -czf mypkg.tar.gz /tmp/mypkg/
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If the package contains a library, you need two additional steps:

::

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    $ runhaskell Setup.hs register --gen-script
    $ runhaskell Setup.hs unregister --gen-script
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This creates shell scripts ``register.sh`` and ``unregister.sh``, which
must also be sent to the target system. After unpacking there, the
package must be registered by running the ``register.sh`` script. The
``unregister.sh`` script would be used in the uninstall procedure of the
package. Similar steps may be used for creating binary packages for
Windows.

The following options are understood by all commands:

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.. program:: setup

.. option:: --help, -h or -?

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    List the available options for the command.
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.. option:: --verbose=n or -v n

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    Set the verbosity level (0-3). The normal level is 1; a missing *n*
    defaults to 2.

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    There is also an extended version of this command which can be
    used to fine-tune the verbosity of output.  It takes the
    form ``[silent|normal|verbose|debug]``\ *flags*, where *flags*
    is a list of ``+`` flags which toggle various aspects of
    output.  At the moment, only ``+callsite`` and ``+callstack``
    are supported, which respectively toggle call site and call
    stack printing (these are only supported if Cabal
    is built with a sufficiently recent GHC.)

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The various commands and the additional options they support are
described below. In the simple build infrastructure, any other options
will be reported as errors.

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.. _setup-configure:

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setup configure
---------------

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.. program:: setup configure

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Prepare to build the package. Typically, this step checks that the
target platform is capable of building the package, and discovers
platform-specific features that are needed during the build.

The user may also adjust the behaviour of later stages using the options
listed in the following subsections. In the simple build infrastructure,
the values supplied via these options are recorded in a private file
read by later stages.

If a user-supplied ``configure`` script is run (see the section on
`system-dependent
parameters <developing-packages.html#system-dependent-parameters>`__ or
on `complex
packages <developing-packages.html#more-complex-packages>`__), it is
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passed the :option:`--with-hc-pkg`, :option:`--prefix`, :option:`--bindir`,
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:option:`--libdir`, :option:`--dynlibdir`, :option:`--datadir`, :option:`--libexecdir` and
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:option:`--sysconfdir` options. In addition the value of the
:option:`--with-compiler` option is passed in a :option:`--with-hc-pkg` option
and all options specified with :option:`--configure-option` are passed on.
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In Cabal 2.0, support for a single positional argument was added to
``setup configure`` This makes Cabal configure a the specific component
to be configured. Specified names can be qualified with ``lib:`` or
``exe:`` in case just a name is ambiguous (as would be the case for a
package named ``p`` which has a library and an executable named ``p``.)
This has the following effects:

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-  Subsequent invocations of ``cabal build``, ``register``, etc. operate only
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   on the configured component.

-  Cabal requires all "internal" dependencies (e.g., an executable
   depending on a library defined in the same package) must be found in
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   the set of databases via :option:`--package-db` (and related flags): these
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   dependencies are assumed to be up-to-date. A dependency can be
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   explicitly specified using :option:`--dependency` simply by giving the name
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   of the internal library; e.g., the dependency for an internal library
   named ``foo`` is given as
   ``--dependency=pkg-internal=pkg-1.0-internal-abcd``.

-  Only the dependencies needed for the requested component are
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   required. Similarly, when :option:`--exact-configuration` is specified,
   it's only necessary to specify :option:`--dependency` for the component.
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   (As mentioned previously, you *must* specify internal dependencies as
   well.)

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-  Internal ``build-tool-depends`` and ``build-tools`` dependencies are expected
   to be in the ``PATH`` upon subsequent invocations of ``setup``.
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Full details can be found in the `Componentized Cabal
proposal <https://github.com/ezyang/ghc-proposals/blob/master/proposals/0000-componentized-cabal.rst>`__.

Programs used for building
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^^^^^^^^^^^^^^^^^^^^^^^^^^
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The following options govern the programs used to process the source
files of a package:

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.. option:: --ghc or -g, --jhc, --lhc, --uhc

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    Specify which Haskell implementation to use to build the package. At
    most one of these flags may be given. If none is given, the
    implementation under which the setup script was compiled or
    interpreted is used.
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.. option:: --with-compiler=path or -w *path*

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    Specify the path to a particular compiler. If given, this must match
    the implementation selected above. The default is to search for the
    usual name of the selected implementation.

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    This flag also sets the default value of the :option:`--with-hc-pkg`
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    option to the package tool for this compiler. Check the output of
    ``setup configure -v`` to ensure that it finds the right package
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    tool (or use :option:`--with-hc-pkg` explicitly).

.. option:: --with-hc-pkg=path
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    Specify the path to the package tool, e.g. ``ghc-pkg``. The package
    tool must be compatible with the compiler specified by
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    :option:`--with-compiler`. If this option is omitted, the default value is
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    determined from the compiler selected.
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.. option:: --with-prog=path

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    Specify the path to the program *prog*. Any program known to Cabal
    can be used in place of *prog*. It can either be a fully path or the
    name of a program that can be found on the program search path. For
    example: ``--with-ghc=ghc-6.6.1`` or
    ``--with-cpphs=/usr/local/bin/cpphs``. The full list of accepted
    programs is not enumerated in this user guide. Rather, run
    ``cabal install --help`` to view the list.
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.. option:: --prog-options=options

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    Specify additional options to the program *prog*. Any program known
    to Cabal can be used in place of *prog*. For example:
    ``--alex-options="--template=mytemplatedir/"``. The *options* is
    split into program options based on spaces. Any options containing
    embedded spaced need to be quoted, for example
    ``--foo-options='--bar="C:\Program File\Bar"'``. As an alternative
    that takes only one option at a time but avoids the need to quote,
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    use :option:`--prog-option` instead.

.. option:: --prog-option=option

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    Specify a single additional option to the program *prog*. For
    passing an option that contain embedded spaces, such as a file name
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    with embedded spaces, using this rather than :option:`--prog-options`
    means you do not need an additional level of quoting. Of course if you
    are using a command shell you may still need to quote, for example
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    ``--foo-options="--bar=C:\Program File\Bar"``.

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All of the options passed with either :option:`--prog-options`
or :option:`--prog-option` are passed in the order they were
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specified on the configure command line.

Installation paths
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^^^^^^^^^^^^^^^^^^
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The following options govern the location of installed files from a
package:

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.. option:: --prefix=dir

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    The root of the installation. For example for a global install you
    might use ``/usr/local`` on a Unix system, or ``C:\Program Files``
    on a Windows system. The other installation paths are usually
    subdirectories of *prefix*, but they don't have to be.

    In the simple build system, *dir* may contain the following path
    variables: ``$pkgid``, ``$pkg``, ``$version``, ``$compiler``,
    ``$os``, ``$arch``, ``$abi``, ``$abitag``

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.. option:: --bindir=dir

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    Executables that the user might invoke are installed here.

    In the simple build system, *dir* may contain the following path
    variables: ``$prefix``, ``$pkgid``, ``$pkg``, ``$version``,
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    ``$compiler``, ``$os``, ``$arch``, ``$abi``, ``$abitag``
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.. option:: --libdir=dir

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    Object-code libraries are installed here.

    In the simple build system, *dir* may contain the following path
    variables: ``$prefix``, ``$bindir``, ``$pkgid``, ``$pkg``,
    ``$version``, ``$compiler``, ``$os``, ``$arch``, ``$abi``,
    ``$abitag``

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.. option:: --dynlibdir=dir

    Dynamic libraries are installed here.

    By default, this is set to `$libdir/$abi`, which is usually not equal to
    `$libdir/$libsubdir`.

    In the simple build system, *dir* may contain the following path
    variables: ``$prefix``, ``$bindir``, ``$libdir``, ``$pkgid``, ``$pkg``,
    ``$version``, ``$compiler``, ``$os``, ``$arch``, ``$abi``,
    ``$abitag``

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.. option:: --libexecdir=dir

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    Executables that are not expected to be invoked directly by the user
    are installed here.

    In the simple build system, *dir* may contain the following path
    variables: ``$prefix``, ``$bindir``, ``$libdir``, ``$libsubdir``,
    ``$pkgid``, ``$pkg``, ``$version``, ``$compiler``, ``$os``,
    ``$arch``, ``$abi``, ``$abitag``

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.. option:: --datadir=dir

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    Architecture-independent data files are installed here.

    In the simple build system, *dir* may contain the following path
    variables: ``$prefix``, ``$bindir``, ``$libdir``, ``$libsubdir``,
    ``$pkgid``, ``$pkg``, ``$version``, ``$compiler``, ``$os``,
    ``$arch``, ``$abi``, ``$abitag``

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.. option:: --sysconfdir=dir

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    Installation directory for the configuration files.

    In the simple build system, *dir* may contain the following path
    variables: ``$prefix``, ``$bindir``, ``$libdir``, ``$libsubdir``,
    ``$pkgid``, ``$pkg``, ``$version``, ``$compiler``, ``$os``,
    ``$arch``, ``$abi``, ``$abitag``

In addition the simple build system supports the following installation
path options:

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.. option:: --libsubdir=dir

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    A subdirectory of *libdir* in which libraries are actually installed. For
    example, in the simple build system on Unix, the default *libdir* is
    ``/usr/local/lib``, and *libsubdir* contains the compiler ABI and package
    identifier,
    e.g. ``x86_64-linux-ghc-8.0.2/mypkg-0.1.0-IxQNmCA7qrSEQNkoHSF7A``, so
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    libraries would be installed in
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    ``/usr/local/lib/x86_64-linux-ghc-8.0.2/mypkg-0.1.0-IxQNmCA7qrSEQNkoHSF7A/``.
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    *dir* may contain the following path variables: ``$pkgid``,
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    ``$pkg``, ``$version``, ``$compiler``, ``$os``, ``$arch``, ``$abi``,
    ``$abitag``

.. option:: --libexecsubdir=dir

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    A subdirectory of *libexecdir* in which private executables are
    installed. For example, in the simple build system on Unix, the default
    *libexecdir* is ``/usr/local/libexec``, and *libsubdir* is
    ``x86_64-linux-ghc-8.0.2/mypkg-0.1.0``, so private executables would be
    installed in ``/usr/local/libexec/x86_64-linux-ghc-8.0.2/mypkg-0.1.0/``
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    *dir* may contain the following path variables: ``$pkgid``,
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    ``$pkg``, ``$version``, ``$compiler``, ``$os``, ``$arch``, ``$abi``,
    ``$abitag``

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.. option:: --datasubdir=dir

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    A subdirectory of *datadir* in which data files are actually
    installed.

    *dir* may contain the following path variables: ``$pkgid``,
    ``$pkg``, ``$version``, ``$compiler``, ``$os``, ``$arch``, ``$abi``,
    ``$abitag``

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.. option:: --docdir=dir

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    Documentation files are installed relative to this directory.

    *dir* may contain the following path variables: ``$prefix``,
    ``$bindir``, ``$libdir``, ``$libsubdir``, ``$datadir``,
    ``$datasubdir``, ``$pkgid``, ``$pkg``, ``$version``, ``$compiler``,
    ``$os``, ``$arch``, ``$abi``, ``$abitag``

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.. option:: --htmldir=dir

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    HTML documentation files are installed relative to this directory.

    *dir* may contain the following path variables: ``$prefix``,
    ``$bindir``, ``$libdir``, ``$libsubdir``, ``$datadir``,
    ``$datasubdir``, ``$docdir``, ``$pkgid``, ``$pkg``, ``$version``,
    ``$compiler``, ``$os``, ``$arch``, ``$abi``, ``$abitag``

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.. option:: --program-prefix=prefix

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    Prepend *prefix* to installed program names.

    *prefix* may contain the following path variables: ``$pkgid``,
    ``$pkg``, ``$version``, ``$compiler``, ``$os``, ``$arch``, ``$abi``,
    ``$abitag``

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.. option:: --program-suffix=suffix

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    Append *suffix* to installed program names. The most obvious use for
    this is to append the program's version number to make it possible
    to install several versions of a program at once:
    ``--program-suffix='$version'``.

    *suffix* may contain the following path variables: ``$pkgid``,
    ``$pkg``, ``$version``, ``$compiler``, ``$os``, ``$arch``, ``$abi``,
    ``$abitag``

Path variables in the simple build system
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"""""""""""""""""""""""""""""""""""""""""
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For the simple build system, there are a number of variables that can be
used when specifying installation paths. The defaults are also specified
in terms of these variables. A number of the variables are actually for
other paths, like ``$prefix``. This allows paths to be specified
relative to each other rather than as absolute paths, which is important
for building relocatable packages (see `prefix
independence <#prefix-independence>`__).

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$prefix
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    The path variable that stands for the root of the installation. For
    an installation to be relocatable, all other installation paths must
    be relative to the ``$prefix`` variable.
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$bindir
    The path variable that expands to the path given by the :option:`--bindir`
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    configure option (or the default).
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$libdir
    As above but for :option:`--libdir`
$libsubdir
    As above but for :option:`--libsubdir`
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$dynlibdir
    As above but for :option:`--dynlibdir`
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$datadir
    As above but for :option:`--datadir`
$datasubdir
    As above but for :option:`--datasubdir`
$docdir
    As above but for :option:`--docdir`
$pkgid
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    The name and version of the package, e.g. ``mypkg-0.2``
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$pkg
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    The name of the package, e.g. ``mypkg``
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$version
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    The version of the package, e.g. ``0.2``
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$compiler
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    The compiler being used to build the package, e.g. ``ghc-6.6.1``
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$os
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    The operating system of the computer being used to build the
    package, e.g. ``linux``, ``windows``, ``osx``, ``freebsd`` or
    ``solaris``
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$arch
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    The architecture of the computer being used to build the package,
    e.g. ``i386``, ``x86_64``, ``ppc`` or ``sparc``
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$abitag
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    An optional tag that a compiler can use for telling incompatible
    ABI's on the same architecture apart. GHCJS encodes the underlying
    GHC version in the ABI tag.
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$abi
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    A shortcut for getting a path that completely identifies the
    platform in terms of binary compatibility. Expands to the same value
    as ``$arch-$os-compiler-$abitag`` if the compiler uses an abi tag,
    ``$arch-$os-$compiler`` if it doesn't.

Paths in the simple build system
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""""""""""""""""""""""""""""""""
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For the simple build system, the following defaults apply:

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.. list-table:: Default installation paths

    * - Option
      - Unix Default
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      - Windows Default
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    * - :option:`--prefix` (global)
      - ``/usr/local``
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      - ``%PROGRAMFILES%\Haskell``
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    * - :option:`--prefix` (per-user)
      - ``$HOME/.cabal``
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      - ``%APPDATA%\cabal``
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    * - :option:`--bindir`
      - ``$prefix/bin``
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      - ``$prefix\bin``
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    * - :option:`--libdir`
      - ``$prefix/lib``
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      - ``$prefix``
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    * - :option:`--libsubdir` (others)
      - ``$pkgid/$compiler``
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      - ``$pkgid\$compiler``
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    * - :option:`--dynlibdir`
      - ``$libdir/$abi``
      - ``$libdir\$abi``
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    * - :option:`--libexecdir`
      - ``$prefix/libexec``
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      - ``$prefix\$pkgid``
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    * - :option:`--datadir` (executable)
      - ``$prefix/share``
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      - ``$prefix``
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    * - :option:`--datadir` (library)
      - ``$prefix/share``
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      - ``%PROGRAMFILES%\Haskell``
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    * - :option:`--datasubdir`
      - ``$pkgid``
      - ``$pkgid``
    * - :option:`--docdir`
      - ``$datadir/doc/$pkgid``
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      - ``$prefix\doc\$pkgid``
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    * - :option:`--sysconfdir`
      - ``$prefix/etc``
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      - ``$prefix\etc``
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    * - :option:`--htmldir`
      - ``$docdir/html``
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      - ``$docdir\html``
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    * - :option:`--program-prefix`
      - (empty)
      - (empty)
    * - :option:`--program-suffix`
      - (empty)
      - (empty)
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Prefix-independence
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"""""""""""""""""""
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On Windows it is possible to obtain the pathname of the running program.
This means that we can construct an installable executable package that
is independent of its absolute install location. The executable can find
its auxiliary files by finding its own path and knowing the location of
the other files relative to ``$bindir``. Prefix-independence is
particularly useful: it means the user can choose the install location
(i.e. the value of ``$prefix``) at install-time, rather than having to
bake the path into the binary when it is built.

In order to achieve this, we require that for an executable on Windows,
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all of ``$bindir``, ``$libdir``, ``$dynlibdir``, ``$datadir`` and ``$libexecdir`` begin
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with ``$prefix``. If this is not the case then the compiled executable
will have baked-in all absolute paths.

The application need do nothing special to achieve prefix-independence.
If it finds any files using ``getDataFileName`` and the `other functions
provided for the
purpose <developing-packages.html#accessing-data-files-from-package-code>`__,
the files will be accessed relative to the location of the current
executable.

A library cannot (currently) be prefix-independent, because it will be
linked into an executable whose file system location bears no relation
to the library package.

Controlling Flag Assignments
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^^^^^^^^^^^^^^^^^^^^^^^^^^^^
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Flag assignments (see the `resolution of conditions and
flags <developing-packages.html#resolution-of-conditions-and-flags>`__)
can be controlled with the following command line options.

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.. option:: -f flagname or -f -flagname

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    Force the specified flag to ``true`` or ``false`` (if preceded with
    a ``-``). Later specifications for the same flags will override
    earlier, i.e., specifying ``-fdebug -f-debug`` is equivalent to
    ``-f-debug``
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.. option:: --flags=flagspecs

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    Same as ``-f``, but allows specifying multiple flag assignments at
    once. The parameter is a space-separated list of flag names (to
    force a flag to ``true``), optionally preceded by a ``-`` (to force
    a flag to ``false``). For example,
    ``--flags="debug -feature1 feature2"`` is equivalent to
    ``-fdebug -f-feature1 -ffeature2``.

Building Test Suites
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^^^^^^^^^^^^^^^^^^^^
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.. option:: --enable-tests

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    Build the test suites defined in the package description file during
    the ``build`` stage. Check for dependencies required by the test
    suites. If the package is configured with this option, it will be
    possible to run the test suites with the ``test`` command after the
    package is built.
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.. option:: --disable-tests

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    (default) Do not build any test suites during the ``build`` stage.
    Do not check for dependencies required only by the test suites. It
    will not be possible to invoke the ``test`` command without
    reconfiguring the package.
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.. option:: --enable-coverage

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    Build libraries and executables (including test suites) with Haskell
    Program Coverage enabled. Running the test suites will automatically
    generate coverage reports with HPC.
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.. option:: --disable-coverage

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    (default) Do not enable Haskell Program Coverage.

Miscellaneous options
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^^^^^^^^^^^^^^^^^^^^^
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.. option:: --user

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    Does a per-user installation. This changes the `default installation
    prefix <#paths-in-the-simple-build-system>`__. It also allow
    dependencies to be satisfied by the user's package database, in
    addition to the global database. This also implies a default of
    ``--user`` for any subsequent ``install`` command, as packages
    registered in the global database should not depend on packages
    registered in a user's database.
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.. option:: --global

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    (default) Does a global installation. In this case package
    dependencies must be satisfied by the global package database. All
    packages in the user's package database will be ignored. Typically
    the final installation step will require administrative privileges.
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.. option:: --package-db=db

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    Allows package dependencies to be satisfied from this additional
    package database *db* in addition to the global package database.
    All packages in the user's package database will be ignored. The
    interpretation of *db* is implementation-specific. Typically it will
    be a file or directory. Not all implementations support arbitrary
    package databases.

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    This pushes an extra db onto the db stack. The :option:`--global` and
    :option:`--user` mode switches add the respective [Global] and [Global,
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    User] dbs to the initial stack. There is a compiler-implementation
    constraint that the global db must appear first in the stack, and if
    the user one appears at all, it must appear immediately after the
    global db.

    To reset the stack, use ``--package-db=clear``.

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.. option:: --ipid=ipid

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    Specifies the *installed package identifier* of the package to be
    built; this identifier is passed on to GHC and serves as the basis
    for linker symbols and the ``id`` field in a ``ghc-pkg``
    registration. When a package has multiple components, the actual
    component identifiers are derived off of this identifier (e.g., an
    internal library ``foo`` from package ``p-0.1-abcd`` will get the
    identifier ``p-0.1-abcd-foo``.
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.. option:: --cid=cid

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    Specifies the *component identifier* of the component being built;
    this is only valid if you are configuring a single component.
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.. option:: --default-user-config=file

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    Allows a "default" ``cabal.config`` freeze file to be passed in
    manually. This file will only be used if one does not exist in the
    project directory already. Typically, this can be set from the
    global cabal ``config`` file so as to provide a default set of
    partial constraints to be used by projects, providing a way for
    users to peg themselves to stable package collections.
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.. option:: --enable-optimization[=n] or -O [n]

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    (default) Build with optimization flags (if available). This is
    appropriate for production use, taking more time to build faster
    libraries and programs.

    The optional *n* value is the optimisation level. Some compilers
    support multiple optimisation levels. The range is 0 to 2. Level 0
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    is equivalent to :option:`--disable-optimization`, level 1 is the
    default if no *n* parameter is given. Level 2 is higher optimisation
    if the compiler supports it. Level 2 is likely to lead to longer
    compile times and bigger generated code.

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    When optimizations are enabled, Cabal passes ``-O2`` to the C compiler.

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.. option:: --disable-optimization
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    Build without optimization. This is suited for development: building
    will be quicker, but the resulting library or programs will be
    slower.
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.. option:: --enable-profiling

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    Build libraries and executables with profiling enabled (for
    compilers that support profiling as a separate mode). For this to
    work, all libraries used by this package must also have been built
    with profiling support. For libraries this involves building an
    additional instance of the library in addition to the normal
    non-profiling instance. For executables it changes the single
    executable to be built in profiling mode.

    This flag covers both libraries and executables, but can be
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    overridden by the :option:`--enable-library-profiling` flag.

    See also the :option:`--profiling-detail` flag below.
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.. option:: --disable-profiling
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    (default) Do not enable profiling in generated libraries and
    executables.
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.. option:: --enable-library-profiling or -p

    As with :option:`--enable-profiling` above, but it applies only for
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    libraries. So this generates an additional profiling instance of the
    library in addition to the normal non-profiling instance.

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    The :option:`--enable-profiling` flag controls the profiling mode for both
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    libraries and executables, but if different modes are desired for
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    libraries versus executables then use :option:`--enable-library-profiling`
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    as well.

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.. option:: --disable-library-profiling

    (default) Do not generate an additional profiling version of the library.

.. option:: --profiling-detail[=level]

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    Some compilers that support profiling, notably GHC, can allocate
    costs to different parts of the program and there are different
    levels of granularity or detail with which this can be done. In
    particular for GHC this concept is called "cost centers", and GHC
    can automatically add cost centers, and can do so in different ways.

    This flag covers both libraries and executables, but can be
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    overridden by the :option:`--library-profiling-detail` flag.
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    Currently this setting is ignored for compilers other than GHC. The
    levels that cabal currently supports are:

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    default
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        For GHC this uses ``exported-functions`` for libraries and
        ``toplevel-functions`` for executables.
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    none
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        No costs will be assigned to any code within this component.
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    exported-functions
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        Costs will be assigned at the granularity of all top level
        functions exported from each module. In GHC specifically, this
        is for non-inline functions.
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    toplevel-functions
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        Costs will be assigned at the granularity of all top level
        functions in each module, whether they are exported from the
        module or not. In GHC specifically, this is for non-inline
        functions.
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    all-functions
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        Costs will be assigned at the granularity of all functions in
        each module, whether top level or local. In GHC specifically,
        this is for non-inline toplevel or where-bound functions or
        values.

    This flag is new in Cabal-1.24. Prior versions used the equivalent
    of ``none`` above.

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.. option:: --library-profiling-detail[=level]

    As with :option:`--profiling-detail` above, but it applies only for
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    libraries.

    The level for both libraries and executables is set by the
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    :option:`--profiling-detail` flag, but if different levels are desired
    for libraries versus executables then use
    :option:`--library-profiling-detail` as well.

.. option:: --enable-library-vanilla
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    (default) Build ordinary libraries (as opposed to profiling
    libraries). This is independent of the
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    :option:`--enable-library-profiling` option. If you enable both, you get
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    both.
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.. option:: --disable-library-vanilla

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    Do not build ordinary libraries. This is useful in conjunction with
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    :option:`--enable-library-profiling` to build only profiling libraries,
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    rather than profiling and ordinary libraries.
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.. option:: --enable-library-for-ghci

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    (default) Build libraries suitable for use with GHCi.
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.. option:: --disable-library-for-ghci

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    Not all platforms support GHCi and indeed on some platforms, trying
    to build GHCi libs fails. In such cases this flag can be used as a
    workaround.
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.. option:: --enable-split-objs

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    Use the GHC ``-split-objs`` feature when building the library. This
    reduces the final size of the executables that use the library by
    allowing them to link with only the bits that they use rather than
    the entire library. The downside is that building the library takes
    longer and uses considerably more memory.
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.. option:: --disable-split-objs

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    (default) Do not use the GHC ``-split-objs`` feature. This makes
    building the library quicker but the final executables that use the
    library will be larger.
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.. option:: --enable-executable-stripping

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    (default) When installing binary executable programs, run the
    ``strip`` program on the binary. This can considerably reduce the
    size of the executable binary file. It does this by removing
    debugging information and symbols. While such extra information is
    useful for debugging C programs with traditional debuggers it is
    rarely helpful for debugging binaries produced by Haskell compilers.

    Not all Haskell implementations generate native binaries. For such
    implementations this option has no effect.

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.. option:: --disable-executable-stripping

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    Do not strip binary executables during installation. You might want
    to use this option if you need to debug a program using gdb, for
    example if you want to debug the C parts of a program containing
    both Haskell and C code. Another reason is if your are building a
    package for a system which has a policy of managing the stripping
    itself (such as some Linux distributions).
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.. option:: --enable-shared

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    Build shared library. This implies a separate compiler run to
    generate position independent code as required on most platforms.
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.. option:: --disable-shared

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    (default) Do not build shared library.
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.. option:: --enable-static

   Build a static library. This passes ``-staticlib`` to GHC (avaiable
   for iOS, and with 8.4 more platforms).  The result is an archive ``.a``
   containing all dependent haskell libararies combined.

.. option:: --disable-static

    (default) Do not build a static library.

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.. option:: --enable-executable-dynamic

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    Link executables dynamically. The executable's library dependencies
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    should be built as shared objects. This implies :option:`--enable-shared`
    unless :option:`--disable-shared` is explicitly specified.

.. option:: --disable-executable-dynamic

   (default) Link executables statically.

.. option:: --configure-option=str

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    An extra option to an external ``configure`` script, if one is used
    (see the section on `system-dependent
    parameters <developing-packages.html#system-dependent-parameters>`__).
    There can be several of these options.
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.. option:: --extra-include-dirs[=dir]

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    An extra directory to search for C header files. You can use this
    flag multiple times to get a list of directories.

    You might need to use this flag if you have standard system header
    files in a non-standard location that is not mentioned in the
    package's ``.cabal`` file. Using this option has the same affect as
    appending the directory *dir* to the ``include-dirs`` field in each
    library and executable in the package's ``.cabal`` file. The
    advantage of course is that you do not have to modify the package at
    all. These extra directories will be used while building the package
    and for libraries it is also saved in the package registration
    information and used when compiling modules that use the library.

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.. option:: --extra-lib-dirs[=dir]

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    An extra directory to search for system libraries files. You can use
    this flag multiple times to get a list of directories.
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.. option:: --extra-framework-dirs[=dir]