nix-local-build.rst 52.2 KB
Newer Older
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92

Quickstart
==========

Suppose that you are in a directory containing a single Cabal package
which you wish to build. You can configure and build it using Nix-style
local builds with this command (configuring is not necessary):

::

    cabal new-build

To open a GHCi shell with this package, use this command:

::

    cabal new-repl

Developing multiple packages
----------------------------

Many Cabal projects involve multiple packages which need to be built
together. To build multiple Cabal packages, you need to first create a
``cabal.project`` file which declares where all the local package
directories live. For example, in the Cabal repository, there is a root
directory with a folder per package, e.g., the folders ``Cabal`` and
``cabal-install``. The ``cabal.project`` file specifies each folder as
part of the project:

::

    packages: Cabal/
              cabal-install/

The expectation is that a ``cabal.project`` is checked into your source
control, to be used by all developers of a project. If you need to make
local changes, they can be placed in ``cabal.project.local`` (which
should not be checked in.)

Then, to build every component of every package, from the top-level
directory, run the command: (Warning: cabal-install-1.24 does NOT have
this behavior; you will need to upgrade to HEAD.)

::

    cabal new-build

To build a specific package, you can either run ``new-build`` from the
directory of the package in question:

::

    cd cabal-install
    cabal new-build

or you can pass the name of the package as an argument to
``cabal new-build`` (this works in any subdirectory of the project):

::

    cabal new-build cabal-install

You can also specify a specific component of the package to build. For
example, to build a test suite named ``package-tests``, use the command:

::

    cabal new-build package-tests

Targets can be qualified with package names. So to request
``package-tests`` *from* the ``Cabal`` package, use
``Cabal:package-tests``.

Unlike sandboxes, there is no need to setup a sandbox or ``add-source``
projects; just check in ``cabal.project`` to your repository and
``new-build`` will just work.

How it works
============

Local versus external packages
------------------------------

One of the primary innovations of Nix-style local builds is the
distinction between local packages, which users edit and recompile and
must be built per-project, versus external packages, which can be cached
across packages. To be more precise:

1. A **local package** is one that is listed explicitly in the
   ``packages``, ``optional-packages`` or ``extra-packages`` field of a
   project. Usually, these refer to packages whose source code lives
   directly in a folder in your project (although, you can list an
93
   arbitrary Hackage package in ``extra-packages`` to force it to be
94 95 96 97 98 99 100 101
   treated as local).

Local packages, as well as the external packages (below) which depend on
them, are built **inplace**, meaning that they are always built
specifically for the project and are not installed globally. Inplace
packages are not cached and not given unique hashes, which makes them
suitable for packages which you want to edit and recompile.

102
2. An **external package** is any package which is not listed in the
103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149 150 151 152 153 154 155 156 157 158 159 160 161 162 163 164 165 166 167 168 169 170 171 172 173 174 175 176 177 178 179 180 181 182 183 184 185 186 187 188 189 190 191 192 193 194 195 196 197 198 199 200 201 202 203 204 205 206 207 208 209 210 211 212 213 214 215 216 217 218 219 220 221 222 223 224 225 226 227 228 229 230 231 232 233 234 235 236 237 238 239 240 241 242 243 244 245 246 247 248 249 250 251 252 253 254 255 256 257 258 259 260 261 262 263 264 265 266 267 268 269 270 271 272 273 274 275 276 277 278 279 280 281 282 283 284 285 286 287 288 289 290 291 292 293 294 295 296 297 298 299 300 301 302 303 304 305 306 307 308 309 310 311 312 313 314 315 316 317 318 319 320
   ``packages`` field. The source code for external packages is usually
   retrieved from Hackage.

When an external package does not depend on an inplace package, it can
be built and installed to a **global** store, which can be shared across
projects. These build products are identified by a hash that over all of
the inputs which would influence the compilation of a package (flags,
dependency selection, etc.). Just as in Nix, these hashes uniquely
identify the result of a build; if we compute this identifier and we
find that we already have this ID built, we can just use the already
built version.

The global package store is ``~/.cabal/store``; if you need to clear
your store for whatever reason (e.g., to reclaim disk space or because
the global store is corrupted), deleting this directory is safe
(``new-build`` will just rebuild everything it needs on its next
invocation).

This split motivates some of the UI choices for Nix-style local build
commands. For example, flags passed to ``cabal new-build`` are only
applied to *local* packages, so that adding a flag to
``cabal new-build`` doesn't necessitate a rebuild of *every* transitive
dependency in the global package store.

In cabal-install HEAD, Nix-style local builds also take advantage of a
new Cabal library feature, `per-component
builds <https://github.com/ezyang/ghc-proposals/blob/master/proposals/0000-componentized-cabal.rst>`__,
where each component of a package is configured and built separately.
This can massively speed up rebuilds of packages with lots of components
(e.g., a package that defines multiple executables), as only one
executable needs to be rebuilt. Packages that use Custom setup scripts
are not currently built on a per-component basis.

Where are my build products?
----------------------------

A major deficiency in the current implementation of new-build is that
there is no programmatic way to access the location of build products.
The location of the build products is intended to be an internal
implementation detail of new-build, but we also understand that many
unimplemented features (e.g., ``new-test``) can only be reasonably
worked around by accessing build products directly.

The location where build products can be found varies depending on the
version of cabal-install:

-  In cabal-install-1.24, the dist directory for a package ``p-0.1`` is
   stored in ``dist-newstyle/build/p-0.1``. For example, if you built an
   executable or test suite named ``pexe``, it would be located at
   ``dist-newstyle/build/p-0.1/build/pexe/pexe``.

-  In cabal-install HEAD, the dist directory for a package ``p-0.1``
   defining a library built with GHC 8.0.1 on 64-bit Linux is
   ``dist-newstyle/build/x86_64-linux/ghc-8.0.1/p-0.1``. When
   per-component builds are enabled (any non-Custom package), a
   subcomponent like an executable or test suite named ``pexe`` will be
   stored at
   ``dist-newstyle/build/x86_64-linux/ghc-8.0.1/p-0.1/c/pexe``; thus,
   the full path of the executable is
   ``dist-newstyle/build/x86_64-linux/ghc-8.0.1/p-0.1/c/pexe/build/pexe/pexe``
   (you can see why we want this to be an implementation detail!)

The paths are a bit longer in HEAD but the benefit is that you can
transparently have multiple builds with different versions of GHC. We
plan to add the ability to create aliases for certain build
configurations, and more convenient paths to access particularly useful
build products like executables.

Caching
-------

Nix-style local builds sport a robust caching system which help reduce
the time it takes to execute a rebuild cycle. While the details of how
``cabal-install`` does caching are an implementation detail and may
change in the future, knowing what gets cached is helpful for
understanding the performance characteristics of invocations to
``new-build``. The cached intermediate results are stored in
``dist-newstyle/cache``; this folder can be safely deleted to clear the
cache.

The following intermediate results are cached in the following files in
this folder (the most important two are first):

``solver-plan`` (binary)
    The result of calling the dependency solver, assuming that the
    Hackage index, local ``cabal.project`` file, and local ``cabal``
    files are unmodified. (Notably, we do NOT have to dependency solve
    again if new build products are stored in the global store; the
    invocation of the dependency solver is independent of what is
    already available in the store.)
``source-hashes`` (binary)
    The hashes of all local source files. When all local source files of
    a local package are unchanged, ``cabal new-build`` will skip
    invoking ``setup build`` entirely (saving us from a possibly
    expensive call to ``ghc --make``). The full list of source files
    participating in compilation are determined using
    ``setup sdist --list-sources`` (thus, if you do not list all your
    source files in a Cabal file, you may fail to recompile when you
    edit them.)
``config`` (same format as ``cabal.project``)
    The full project configuration, merged from ``cabal.project`` (and
    friends) as well as the command line arguments.
``compiler`` (binary)
    The configuration of the compiler being used to build the project.
``improved-plan`` (binary)
    Like ``solver-plan``, but with all non-inplace packages improved
    into pre-existing copies from the store.

Note that every package also has a local cache managed by the Cabal
build system, e.g., in ``$distdir/cache``.

There is another useful file in ``dist-newstyle/cache``, ``plan.json``,
which is a JSON serialization of the computed install plan. (TODO: docs)

Commands
========

We now give an in-depth description of all the commands, describing the
arguments and flags they accept.

cabal new-configure
-------------------

``cabal new-configure`` takes a set of arguments and writes a
``cabal.project.local`` file based on the flags passed to this command.
``cabal new-configure FLAGS; cabal new-build`` is roughly equivalent to
``cabal new-build FLAGS``, except that with ``new-configure`` the flags
are persisted to all subsequent calls to ``new-build``.

``cabal new-configure`` is intended to be a convenient way to write out
a ``cabal.project.local`` for simple configurations; e.g.,
``cabal new-configure -w ghc-7.8`` would ensure that all subsequent
builds with ``cabal new-build`` are performed with the compiler
``ghc-7.8``. For more complex configuration, we recommend writing the
``cabal.project.local`` file directly (or placing it in
``cabal.project``!)

``cabal new-configure`` inherits options from ``Cabal``. semantics:

-  Any flag accepted by ``./Setup configure``.

-  Any flag accepted by ``cabal configure`` beyond
   ``./Setup configure``, namely ``--cabal-lib-version``,
   ``--constraint``, ``--preference`` and ``--solver.``

-  Any flag accepted by ``cabal install`` beyond ``./Setup configure``.

-  Any flag accepted by ``./Setup haddock``.

The options of all of these flags apply only to *local* packages in a
project; this behavior is different than that of ``cabal install``,
which applies flags to every package that would be built. The motivation
for this is to avoid an innocuous addition to the flags of a package
resulting in a rebuild of every package in the store (which might need
to happen if a flag actually applied to every transitive dependency). To
apply options to an external package, use a ``package`` stanza in a
``cabal.project`` file.

cabal new-build
---------------

``cabal new-build`` takes a set of targets and builds them. It
automatically handles building and installing any dependencies of these
targets.

A target can take any of the following forms:

-  A package target: ``package``, which specifies that all enabled
   components of a package to be built. By default, test suites and
   benchmarks are *not* enabled, unless they are explicitly requested
   (e.g., via ``--enable-tests``.)

-  A component target: ``[package:][ctype:]component``, which specifies
   a specific component (e.g., a library, executable, test suite or
   benchmark) to be built.

In component targets, ``package:`` and ``ctype:`` (valid component types
are ``lib``, ``exe``, ``test`` and ``bench``) can be used to
disambiguate when multiple packages define the same component, or the
same component name is used in a package (e.g., a package ``foo``
defines both an executable and library named ``foo``). We always prefer
interpreting a target as a package name rather than as a component name.

Some example targets:

::

    cabal new-build lib:foo-pkg       # build the library named foo-pkg
    cabal new-build foo-pkg:foo-tests # build foo-tests in foo-pkg

(There is also syntax for specifying module and file targets, but it
doesn't currently do anything.)

Beyond a list of targets, ``cabal new-build`` accepts all the flags that
``cabal new-configure`` takes. Most of these flags are only taken into
consideration when building local packages; however, some flags may
cause extra store packages to be built (for example,
``--enable-profiling`` will automatically make sure profiling libraries
for all transitive dependencies are built and installed.)

cabal new-repl
--------------

``cabal new-repl TARGET`` loads all of the modules of the target into
GHCi as interpreted bytecode. It takes the same flags as
``cabal new-build``.

Currently, it is not supported to pass multiple targets to ``new-repl``
(``new-repl`` will just successively open a separate GHCi session for
each target.)

cabal new-freeze
----------------

``cabal new-freeze`` writes out a ``cabal.project.freeze`` file which
records all of the versions and flags which that are picked by the
solver under the current index and flags. A ``cabal.project.freeze``
file has the same syntax as ``cabal.project`` and looks something like
321
this:
322 323 324 325 326 327 328

::

    constraints: HTTP ==4000.3.3,
                 HTTP +warp-tests -warn-as-error -network23 +network-uri -mtl1 -conduit10,
                 QuickCheck ==2.9.1,
                 QuickCheck +templatehaskell,
329 330
                 -- etc...

331 332 333 334 335 336 337 338 339 340 341 342

For end-user executables, it is recommended that you distribute the
``cabal.project.freeze`` file in your source repository so that all
users see a consistent set of dependencies. For libraries, this is not
recommended: users often need to build against different versions of
libraries than what you developed against.

Unsupported commands
--------------------

The following commands are not currently supported:

343
``cabal new-test`` (:issue:`3638`)
344 345
    Workaround: run the test executable directly (see `Where are my
    build products <#where-are-my-build-products>`__?)
346

347
``cabal new-bench`` (:issue:`3638`)
348 349
    Workaround: run the benchmark executable directly (see `Where are my
    build products <#where-are-my-build-products>`__?)
350

351
``cabal new-run`` (:issue:`3638`)
352 353
    Workaround: run the executable directly (see `Where are my build
    products <#where-are-my-build-products>`__?)
354

355 356 357 358
``cabal new-exec``
    Workaround: if you wanted to execute GHCi, consider using
    ``cabal new-repl`` instead. Otherwise, use ``-v`` to find the list
    of flags GHC is being invoked with and pass it manually.
359

360
``cabal new-haddock`` (:issue:`3535`)
361 362 363
    Workaround: run
    ``cabal act-as-setup -- haddock --builddir=dist-newstyle/build/pkg-0.1``
    (or execute the Custom setup script directly).
364

365
``cabal new-install`` (:issue:`3737`)
366 367 368 369 370 371 372 373 374 375 376 377 378 379 380 381 382 383 384 385 386 387 388 389 390 391 392 393 394 395 396 397 398 399 400
    Workaround: no good workaround at the moment. (But note that you no
    longer need to install libraries before building!)

Configuring builds with cabal.project
=====================================

``cabal.project`` files support a variety of options which configure the
details of your build. The general syntax of a ``cabal.project`` file is
similar to that of a Cabal file: there are a number of fields, some of
which live inside stanzas:

::

    packages: */*.cabal
    with-compiler: /opt/ghc/8.0.1/bin/ghc

    package cryptohash
      optimization: False

In general, the accepted field names coincide with the accepted command
line flags that ``cabal install`` and other commands take. For example,
``cabal new-configure --library-profiling`` will write out a project
file with ``library-profiling: True``.

The full configuration of a project is determined by combining the
following sources (later entries override earlier ones):

1. ``~/.cabal/config`` (the user-wide global configuration)

2. ``cabal.project`` (the project configuratoin)

3. ``cabal.project.freeze`` (the output of ``cabal new-freeze``)

4. ``cabal.project.local`` (the output of ``cabal new-configure``)

401

402 403 404 405 406 407 408 409
Specifying the local packages
-----------------------------

The following top-level options specify what the local packages of a
project are:

``packages:`` *package location list* (space or comma separated,
default: ``./*.cabal``)
410

411 412 413 414 415 416 417 418 419 420 421 422 423 424 425 426 427 428 429 430
    Specifies the list of package locations which contain the local
    packages to be built by this project. Package locations can take the
    following forms:

    1. They can specify a Cabal file, or a directory containing a Cabal
       file, e.g., ``packages: Cabal cabal-install/cabal-install.cabal``

    2. They can specify a glob-style wildcards, which must match one or
       more (a) directories containing a (single) Cabal file, (b) Cabal
       files (extension ``.cabal``), or (c) [STRIKEOUT:tarballs which
       contain Cabal packages (extension ``.tar.gz``)] (not implemented
       yet). For example, to match all Cabal files in all
       subdirectories, as well as the Cabal projects in the parent
       directories ``foo`` and ``bar``, use
       ``packages: */*.cabal ../{foo,bar}/``

    3. [STRIKEOUT:They can specify an ``http``, ``https`` or ``file``
       URL, representing the path to a remote tarball to be downloaded
       and built.] (not implemented yet)

431
    There is no command line variant of this field; see :issue:`3585`.
432

433
``optional-packages:`` *package location list* (space or comma-separated, default: ``./*/*.cabal``)
434 435 436 437 438 439 440 441 442 443 444 445 446 447 448 449 450 451 452 453 454 455 456 457 458 459 460 461 462 463 464 465 466 467 468
    Like ``packages:``, specifies a list of package locations containing
    local packages to be built. Unlike ``packages:``, if we glob for a
    package, it is permissible for the glob to match against zero
    packages. The intended use-case for ``optional-packages`` is to make
    it so that vendored packages can be automatically picked up if they
    are placed in a subdirectory, but not error if there aren't any.

    There is no command line variant of this field.

``extra-packages:`` *package list with version bounds* (comma separated)
    [STRIKEOUT:Specifies a list of external packages from Hackage which
    should be considered local packages.] (Not implemented)

    There is no command line variant of this field.

[STRIKEOUT:There is also a stanza ``source-repository-package`` for
specifying packages from an external version control.] (Not
implemented.)

All of these options support globs. ``cabal new-build`` has its own glob
format:

-  Anywhere in a path, as many times as you like, you can specify an
   asterisk ``*`` wildcard. E.g., ``*/*.cabal`` matches all ``.cabal``
   files in all immediate subdirectories. Like in glob(7), asterisks do
   not match hidden files unless there is an explicit period, e.g.,
   ``.*/foo.cabal`` will match ``.private/foo.cabal`` (but
   ``*/foo.cabal`` will not).

-  You can use braces to specify specific directories; e.g.,
   ``{vendor,pkgs}/*.cabal`` matches all Cabal files in the ``vendor``
   and ``pkgs`` subdirectories.

Formally, the format described by the following BNF:

469
.. code-block:: abnf
470 471 472 473 474 475 476 477 478 479 480 481 482 483 484 485 486 487 488 489 490 491 492 493 494 495 496 497 498 499 500 501 502 503 504 505 506 507 508 509 510 511 512 513 514

    FilePathGlob    ::= FilePathRoot FilePathGlobRel
    FilePathRoot    ::= {- empty -}        # relative to cabal.project
                      | "/"                # Unix root
                      | [a-zA-Z] ":" [/\\] # Windows root
                      | "~"                # home directory
    FilePathGlobRel ::= Glob "/"  FilePathGlobRel # Unix directory
                      | Glob "\\" FilePathGlobRel # Windows directory
                      | Glob         # file
                      | {- empty -}  # trailing slash
    Glob      ::= GlobPiece *
    GlobPiece ::= "*"            # wildcard
                | [^*{},/\\] *   # literal string
                | "\\" [*{},]    # escaped reserved character
                | "{" Glob "," ... "," Glob "}" # union (match any of these)

Global configuration options
----------------------------

The following top-level configuration options are not specific to any
package, and thus apply globally:

``verbose:`` *nat* (default: 1)
    Control the verbosity of ``cabal`` commands, valid values are from 0
    to 3.

    The command line variant of this field is ``--verbose=2``; a short
    form ``-v2`` is also supported.

``jobs:`` *nat* or ``$ncpus`` (default: 1)
    Run *nat* jobs simultaneously when building. If ``$ncpus`` is
    specified, run the number of jobs equal to the number of CPUs.
    Package building is often quite parallel, so turning on parallelism
    can speed up build times quite a bit!

    The command line variant of this field is ``--jobs=2``; a short form
    ``-j2`` is also supported; a bare ``--jobs`` or ``-j`` is equivalent
    to ``--jobs=$ncpus``.

``keep-going:`` *boolean* (default: False)
    If true, after a build failure, continue to build other unaffected
    packages.

    The command line variant of this field is ``--keep-going``.

515

516 517 518 519 520 521 522 523 524 525 526 527 528 529 530 531 532 533
Solver configuration options
----------------------------

The following settings control the behavior of the dependency solver:

``constraints:`` *constraints* (comma separated)
    Add extra constraints to the version bounds, flag settings, and
    other properties a solver can pick for a package. For example, to
    only consider install plans that do not use ``bar`` at all, or use
    ``bar-2.1``, write:

    ::

        constraints: bar == 2.1

    Version bounds have the same syntax as ``build-depends``. You can
    also specify flag assignments:

534
     .. code-block:: yaml
535 536 537 538 539 540 541 542 543 544 545 546 547 548 549 550 551 552 553 554 555 556 557 558 559 560 561 562 563 564 565 566 567 568 569 570 571 572 573 574 575 576 577 578 579 580 581 582 583 584 585 586 587 588 589 590 591 592 593 594 595 596 597 598 599 600 601 602 603

        # Require bar to be installed with the foo flag turned on and
        # the baz flag turned off
        constraints: bar +foo -baz

        # Require that bar NOT be present in the install plan. Note:
        # this is just syntax sugar for '> 1 && < 1', and is supported
        # by build-depends.
        constraints: bar -none

    A package can be specified multiple times in ``constraints``, in
    which case the specified constraints are intersected. This is
    useful, since the syntax does not allow you to specify multiple
    constraints at once. For example, to specify both version bounds and
    flag assignments, you would write:

    ::

        constraints: bar == 2.1,
                     bar +foo -baz,

    There are also some more specialized constraints, which most people
    don't generally need:

    ::

        # Require bar to be preinstalled in the global package database
        # (this does NOT include the Nix-local build global store.)
        constraints: bar installed

        # Require the local source copy of bar to be used
        # (Note: By default, if we have a local package we will
        # automatically use it, so it generally not be necessary to
        # specify this)
        constraints: bar source

        # Require that bar be solved with test suites and benchmarks enabled
        # (Note: By default, new-build configures the solver to make
        # a best-effort attempt to enable these stanzas, so this generally
        # should not be necessary.)
        constraints: bar test,
                     bar bench

    The command line variant of this field is
    ``--constraint="pkg >= 2.0"``; to specify multiple constraints, pass
    the flag multiple times.

``preferences:`` *preference* (comma separated)
    Like ``constraints``, but the solver will attempt to satisfy these
    preferences on a best-effort basis. The resulting install is locally
    optimal with respect to preferences; specifically, no single package
    could be replaced with a more preferred version that still satisfies
    the hard constraints.

    Operationally, preferences can cause the solver to attempt certain
    version choices of a package before others, which can improve
    dependency solver runtime.

    One way to use ``preferences`` is to take a known working set of
    constraints (e.g., via ``cabal new-freeze``) and record them as
    preferences. In this case, the solver will first attempt to use this
    configuration, and if this violates hard constraints, it will try to
    find the minimal number of upgrades to satisfy the hard constraints
    again.

    The command line variant of this field is
    ``--preference="pkg >= 2.0"``; to specify multiple preferences, pass
    the flag multiple times.

604
``allow-newer:`` ``none`` *or* ``all`` *or* *list of scoped package names* (space or comma separated, default: ``none``)
605 606 607 608 609 610 611 612 613 614 615 616 617 618 619 620 621 622 623 624 625 626 627 628 629 630 631 632 633 634 635 636 637 638 639 640 641 642 643
    Allow the solver to pick an newer version of some packages than
    would normally be permitted by than the ``build-depends`` bounds of
    packages in the install plan. This option may be useful if the
    dependency solver cannot otherwise find a valid install plan.

    For example, to relax ``pkg``\ s ``build-depends`` upper bound on
    ``dep-pkg``, write a scoped package name of the form:

    ::

        allow-newer: pkg:dep-pkg

    This syntax is recommended, as it is often only a single package
    whose upper bound is misbehaving. In this case, the upper bounds of
    other packages should still be respected; indeed, relaxing the bound
    can break some packages which test the selected version of packages.

    However, in some situations (e.g., when attempting to build packages
    on a new version of GHC), it is useful to disregard *all*
    upper-bounds, with respect to a package or all packages. This can be
    done by specifying just a package name, or using the keyword ``all``
    to specify all packages:

    ::

        # Disregard upper bounds involving the dependencies on
        # packages bar, baz and quux
        allow-newer: bar, baz, quux

        # Disregard all upper bounds when dependency solving
        allow-newer: all

    ``allow-newer`` is often used in conjunction with a constraint (in
    the ``constraints`` field) forcing the usage of a specific, newer
    version of a package.

    The command line variant of this field is ``--allow-newer=bar``. A
    bare ``--allow-newer`` is equivalent to ``--allow-newer=all``.

644
``allow-older:`` ``none`` *or* ``all`` *or* *list of scoped package names* (space or comma separated, default: ``none``)
645 646 647 648 649 650 651 652 653 654 655 656 657 658 659 660 661 662 663 664 665 666 667 668 669 670 671 672 673 674
    Like ``allow-newer``, but applied to lower bounds rather than upper
    bounds.

    The command line variant of this field is ``--allow-older=all``. A
    bare ``--allow-older`` is equivalent to ``--allow-older=all``.

Package configuration options
-----------------------------

Package options affect the building of specific packages. There are two
ways a package option can be specified:

-  They can be specified at the top-level, in which case they apply only
   to **local package**, or

-  They can be specified inside a ``package`` stanza, in which case they
   apply to the build of the package, whether or not it is local or
   external.

For example, the following options specify that ``optimization`` should
be turned off for all local packages, and that ``bytestring`` (possibly
an external dependency) should be built with ``-fno-state-hack``:

::

    optimization: False

    package bytestring
        ghc-options: -fno-state-hack

675 676 677 678
``ghc-options`` is not specifically described in this documentation,
but is one of many fields for configuring programs.  They take the form
``progname-options`` and ``progname-location``, and
can only be set inside package stanzas.  (TODO: They are not supported
679
at top-level, see :issue:`3579`.
680

681 682 683 684 685 686 687 688 689 690 691 692 693 694 695 696 697 698 699 700 701 702 703 704 705 706 707 708 709 710 711 712 713 714 715 716 717 718 719 720 721 722 723 724 725 726 727 728 729 730 731 732 733 734 735 736 737 738 739 740 741 742 743 744 745 746 747 748 749 750 751 752 753 754 755 756 757 758 759 760 761 762 763 764 765 766 767 768 769 770 771 772 773 774 775 776 777
At the moment, there is no way to specify an option to apply to all
external packages or all inplace packages. Additionally, it is only
possible to specify these options on the command line for all local
packages (there is no per-package command line interface.)

Some flags were added by more recent versions of the Cabal library. This
means that they are NOT supported by packages which use Custom setup
scripts that require a version of the Cabal library older than when the
feature was added.

``flags:`` *list of +flagname or -flagname* (space separated)
    Force all flags specified as ``+flagname`` to be true, and all flags
    specified as ``-flagname`` to be false. For example, to enable the
    flag ``foo`` and disable ``bar``, set:

    ::

        flags: +foo -bar

    If there is no leading punctuation, it is assumed that the flag
    should be enabled; e.g., this is equivalent:

    ::

        flags: foo -bar

    Flags are *per-package*, so it doesn't make much sense to specify
    flags at the top-level, unless you happen to know that *all* of your
    local packages support the same named flags. If a flag is not
    supported by a package, it is ignored.

    See also the solver configuration field ``constraints``.

    The command line variant of this flag is ``--flags``. There is also
    a shortened form ``-ffoo -f-bar``.

    A common mistake is to say ``cabal new-build -fhans``, where
    ``hans`` is a flag for a transitive dependency that is not in the
    local package; in this case, the flag will be silently ignored. If
    ``haskell-tor`` is the package you want this flag to apply to, try
    ``--constraint="haskell-tor +hans"`` instead.

``with-compiler:`` *executable*
    Specify the path to a particular compiler to be used. If not an
    absolute path, it will be resolved according to the ``PATH``
    environment. The type of the compiler (GHC, GHCJS, etc) must be
    consistent with the setting of the ``compiler`` field.

    The most common use of this option is to specify a different version
    of your compiler to be used; e.g., if you have ``ghc-7.8`` in your
    path, you can specify ``with-compiler: ghc-7.8`` to use it.

    This flag also sets the default value of ``with-hc-pkg``, using the
    heuristic that it is named ``ghc-pkg-7.8`` (if your executable name
    is suffixed with a version number), or is the executable named
    ``ghc-pkg`` in the same directory as the ``ghc`` directory. If this
    heuristic does not work, set ``with-hc-pkg`` explicitly.

    For inplace packages, ``cabal new-build`` maintains a separate build
    directory for each version of GHC, so you can maintain multiple
    build trees for different versions of GHC without clobbering each
    other.

    At the moment, it's not possible to set ``with-compiler`` on a
    per-package basis, but eventually we plan on relaxing this
    restriction. If this is something you need, give us a shout.

    The command line variant of this flag is
    ``--with-compiler=ghc-7.8``; there is also a short version
    ``-w ghc-7.8``.

``with-hc-pkg:`` *executable*
    Specify the path to the package tool, e.g., ``ghc-pkg``. This
    package tool must be compatible with the compiler specified by
    ``with-compiler`` (generally speaking, it should be precisely the
    tool that was distributed with the compiler). If this option is
    omitted, the default value is determined from ``with-compiler``.

    The command line variant of this flag is
    ``--with-hc-pkg=ghc-pkg-7.8``.

``optimization:`` *nat* (default: ``1``)
    Build with optimization. This is appropriate for production use,
    taking more time to build faster libraries and programs.

    The optional *nat* value is the optimisation level. Some compilers
    support multiple optimisation levels. The range is 0 to 2. Level 0
    disables optimization, level 1 is the default. Level 2 is higher
    optimisation if the compiler supports it. Level 2 is likely to lead
    to longer compile times and bigger generated code. If you are not
    planning to run code, turning off optimization will lead to better
    build times and less code to be rebuilt when a module changes.

    We also accept ``True`` (equivalent to 1) and ``False`` (equivalent
    to 0).

    Note that as of GHC 8.0, GHC does not recompile when optimization
778
    levels change (see :ghc-ticket:`10923`), so if
779 780 781 782 783 784 785 786 787 788 789 790 791 792 793 794 795 796
    you change the optimization level for a local package you may need
    to blow away your old build products in order to rebuild with the
    new optimization level.

    The command line variant of this flag is ``-O2`` (with ``-O1``
    equivalent to ``-O``). There are also long-form variants
    ``--enable-optimization`` and ``--disable-optimization``.

``configure-options:`` *args* (space separated)
    A list of extra arguments to pass to the external ``./configure``
    script, if one is used. This is only useful for packages which have
    the ``Configure`` build type. See also the section on
    `system-dependent
    parameters <developing-packages.html#system-dependent-parameters>`__.

    The command line variant of this flag is ``--configure-option=arg``,
    which can be specified multiple times to pass multiple options.

797
``compiler:`` ``ghc`` *or* ``ghcjs`` *or* ``jhc`` *or* ``lhc`` *or* ``uhc`` *or* ``haskell-suite`` (default: ``ghc``)
798 799 800 801 802 803 804 805 806 807 808 809 810 811 812 813 814 815 816 817 818 819 820 821
    Specify which compiler toolchain to be used. This is independent of
    ``with-compiler``, because the choice of toolchain affects Cabal's
    build logic.

    The command line variant of this flag is ``--compiler=ghc``.

``tests:`` *boolean* (default: ``False``)
    Force test suites to be enabled. For most users this should not be
    needed, as we always attempt to solve for test suite dependencies,
    even when this value is ``False``; furthermore, test suites are
    automatically enabled if they are requested as a built target.

    The command line variant of this flag is ``--enable-tests`` and
    ``--disable-tests``.

``benchmarks:`` *boolean* (default: ``False``)
    Force benchmarks to be enabled. For most users this should not be
    needed, as we always attempt to solve for benchmark dependencies,
    even when this value is ``False``; furthermore, benchmarks are
    automatically enabled if they are requested as a built target.

    The command line variant of this flag is ``--enable-benchmarks`` and
    ``--disable-benchmarks``.

822
``extra-prog-path:`` *paths* (newline or comma separated, added in Cabal 1.18)
823 824 825 826 827 828 829 830 831 832 833 834 835 836 837 838 839 840 841 842 843 844
    A list of directories to search for extra required programs. Most
    users should not need this, as programs like ``happy`` and ``alex``
    will automatically be installed and added to the path. This can be
    useful if a ``Custom`` setup script relies on an exotic extra
    program.

    The command line variant of this flag is ``--extra-prog-path=PATH``,
    which can be specified multiple times.

``run-tests:`` *boolean* (default: ``False``)
    Run the package test suite upon installation. This is useful for
    saying "When this package is installed, check that the test suite
    passes, terminating the rest of the build if it is broken."

    One deficiency: the ``run-test`` setting of a package is NOT
    recorded as part of the hash, so if you install something without
    ``run-tests`` and then turn on ``run-tests``, we won't subsequently
    test the package. If this is causing you problems, give us a shout.

    The command line variant of this flag is ``--run-tests``.

Object code options
845
^^^^^^^^^^^^^^^^^^^
846 847 848 849

``debug-info:`` *boolean* (default: False, added in Cabal 1.22)
    If the compiler (e.g., GHC 7.10 and later) supports outputing OS
    native debug info (e.g., DWARF), setting ``debug-info: True`` will
850 851
    instruct it to do so. See the GHC wiki page on :ghc-wiki:`DWARF`
    for more information about this feature.
852 853 854 855 856 857 858 859 860 861 862 863 864 865 866 867 868 869 870 871 872 873 874 875 876 877 878 879 880 881 882 883 884 885 886 887 888 889 890 891 892

    (This field also accepts numeric syntax, but as of GHC 8.0 this
    doesn't do anything.)

    The command line variant of this flag is ``--enable-debug-info`` and
    ``--disable-debug-info``.

``split-objs:`` *boolean* (default: False)
    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.

    The command line variant of this flag is ``--enable-split-objs`` and
    ``--disable-split-objs``.

``executable-stripping:`` *boolean* (default: True)
    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.

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

    (TODO: Check what happens if you combine this with ``debug-info``.)

    The command line variant of this flag is
    ``--enable-executable-stripping`` and
    ``--disable-executable-stripping``.

``library-stripping:`` *boolean* (added in Cabal 1.19)
    When installing binary libraries, run the ``strip`` program on the
    binary, saving space on the file system. See also
    ``executable-stripping``.

    The command line variant of this flag is
    ``--enable-library-stripping`` and ``--disable-library-stripping``.

Executable options
893
^^^^^^^^^^^^^^^^^^
894 895 896 897 898 899 900 901 902 903 904 905 906 907 908 909 910 911 912 913 914 915 916 917 918 919 920 921 922

``program-prefix:`` *prefix*
    [STRIKEOUT:Prepend *prefix* to installed program names.] (Currently
    implemented in a silly and not useful way. If you need this to work
    give us a shout.)

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

    The command line variant of this flag is ``--program-prefix=foo-``.

``program-suffix:`` *suffix*
    [STRIKEOUT:Append *suffix* to installed program names.] (Currently
    implemented in a silly and not useful way. If you need this to work
    give us a shout.)

    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``

    The command line variant of this flag is
    ``--program-suffix='$version'``.

Dynamic linking options
923
^^^^^^^^^^^^^^^^^^^^^^^
924 925 926 927 928 929 930 931 932 933 934 935 936 937 938 939 940 941 942 943 944 945 946 947 948 949 950 951 952 953 954 955 956 957 958

``shared:`` *boolean* (default: False)
    Build shared library. This implies a separate compiler run to
    generate position independent code as required on most platforms.

    The command line variant of this flag is ``--enable-shared`` and
    ``--disable-shared``.

``executable-dynamic:`` *boolean* (default: False)
    Link executables dynamically. The executable's library dependencies
    should be built as shared objects. This implies ``shared: True``
    unless ``shared: False`` is explicitly specified.

    The command line variant of this flag is
    ``--enable-executable-dynamic`` and
    ``--disable-executable-dynamic``.

``library-for-ghci:`` *boolean* (default: True)
    Build libraries suitable for use with GHCi. This involves an extra
    linking step after the build.

    Not all platforms support GHCi and indeed on some platforms, trying
    to build GHCi libs fails. In such cases, consider setting
    ``library-for-ghci: False``.

    The command line variant of this flag is
    ``--enable-library-for-ghci`` and ``--disable-library-for-ghci``.

``relocatable:`` (default: False, added in Cabal 1.21)
    [STRIKEOUT:Build a package which is relocatable.] (TODO: It is not
    clear what this actually does, or if it works at all.)

    The command line variant of this flag is ``--relocatable``.

Foreign function interface options
959
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
960 961 962 963 964 965 966 967 968 969 970 971 972 973 974 975 976 977 978 979 980 981 982 983

``extra-include-dirs:`` *directories* (comma or newline separated list)
    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.

    The command line variant of this flag is
    ``--extra-include-dirs=DIR``, which can be specified multiple times.

``extra-lib-dirs:`` *directories* (comma or newline separated list)
    An extra directory to search for system libraries files.

    The command line variant of this flag is ``--extra-lib-dirs=DIR``,
    which can be specified multiple times.

984
``extra-framework-dirs:`` *directories* (comma or newline separated list)
985 986 987 988 989 990 991 992 993 994 995 996 997 998 999 1000 1001
    An extra directory to search for frameworks (OS X only).

    You might need to use this flag if you have standard system
    libraries 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 ``extra-lib-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.

    The command line variant of this flag is
    ``--extra-framework-dirs=DIR``, which can be specified multiple
    times.

Profiling options
1002
^^^^^^^^^^^^^^^^^
1003 1004 1005 1006 1007 1008 1009 1010 1011 1012 1013 1014 1015 1016 1017 1018 1019 1020 1021 1022 1023 1024 1025 1026 1027 1028 1029 1030 1031 1032 1033

``profiling:`` *boolean* (default: False, added in Cabal 1.21)
    Build libraries and executables with profiling enabled (for
    compilers that support profiling as a separate mode). It is only
    necessary to specify ``profiling`` for the specific package you want
    to profile; ``cabal new-build`` will ensure that all of its
    transitive dependencies are built with profiling enabled.

    To enable profiling for only libraries or executables, see
    ``library-profiling`` and ``executable-profiling``.

    For useful profiling, it can be important to control precisely what
    cost centers are allocated; see ``profiling-detail``.

    The command line variant of this flag is ``--enable-profiling`` and
    ``--disable-profiling``.

``library-vanilla:`` *boolean* (default: True)
    Build ordinary libraries (as opposed to profiling libraries).
    Mostly, you can set this to False to avoid building ordinary
    libraries when you are profiling.

    The command line variant of this flag is
    ``--enable-library-vanilla`` and ``--disable-library-vanilla``.

``library-profiling:`` *boolean* (default: False, added in Cabal 1.21)
    Build libraries with profiling enabled.

    The command line variant of this flag is
    ``--enable-library-profiling`` and ``--disable-library-profiling``.

1034
``executable-profiling:`` *boolean* (default: False, added in Cabal 1.21)
1035 1036 1037 1038 1039 1040 1041 1042 1043 1044 1045 1046 1047 1048 1049 1050 1051 1052 1053 1054 1055 1056 1057 1058 1059 1060 1061 1062 1063 1064 1065 1066 1067 1068 1069 1070 1071 1072 1073 1074 1075 1076 1077 1078 1079 1080 1081 1082 1083
    Build executables with profiling enabled.

    The command line variant of this flag is
    ``--enable-executable-profiling`` and
    ``--disable-executable-profiling``.

``profiling-detail:`` *level* (added in Cabal 1.23)
    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
    overridden by the ``library-profiling-detail`` field.

    Currently this setting is ignored for compilers other than GHC. The
    levels that cabal currently supports are:

    ``default``
        For GHC this uses ``exported-functions`` for libraries and
        ``toplevel-functions`` for executables.
    ``none``
        No costs will be assigned to any code within this component.
    ``exported-functions``
        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.
    ``toplevel-functions``
        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.
    ``all-functions``
        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.

    The command line variant of this flag is
    ``--profiling-detail=none``.

``library-profiling-detail:`` *level* (added in Cabal 1.23)
    Like ``profiling-detail``, but applied only to libraries

    The command line variant of this flag is
    ``--library-profiling-detail=none``.

Coverage options
1084
^^^^^^^^^^^^^^^^
1085 1086 1087 1088 1089 1090 1091 1092 1093 1094 1095 1096 1097 1098 1099 1100

``coverage:`` *boolean* (default: False, added in Cabal 1.21)
    Build libraries and executables (including test suites) with Haskell
    Program Coverage enabled. Running the test suites will automatically
    generate coverage reports with HPC.

    The command line variant of this flag is ``--enable-coverage`` and
    ``--disable-coverage``.

``library-coverage:`` *boolean* (default: False, added in Cabal 1.21)
    Deprecated, use ``coverage``.

    The command line variant of this flag is
    ``--enable-library-coverage`` and ``--disable-library-coverage``.

Haddock options
1101
^^^^^^^^^^^^^^^
1102 1103 1104 1105 1106 1107 1108 1109 1110 1111 1112 1113 1114 1115 1116 1117 1118 1119 1120 1121 1122 1123 1124 1125 1126 1127 1128 1129 1130 1131 1132 1133 1134 1135 1136 1137 1138 1139 1140 1141 1142 1143 1144 1145 1146 1147 1148 1149 1150 1151 1152 1153 1154 1155 1156 1157 1158 1159 1160 1161 1162 1163 1164 1165 1166 1167 1168 1169 1170 1171 1172 1173 1174 1175 1176 1177 1178 1179 1180 1181 1182 1183 1184 1185 1186 1187 1188 1189 1190 1191 1192 1193 1194 1195 1196 1197 1198 1199 1200 1201 1202 1203 1204 1205 1206 1207 1208 1209 1210 1211 1212 1213 1214 1215 1216 1217 1218 1219 1220 1221

Documentation building support is fairly sparse at the moment. Let us
know if it's a priority for you!

``documentation:`` *boolean* (default: False)
    Enables building of Haddock documentation

    The command line variant of this flag is ``--enable-documentation``
    and ``--disable-documentation``.

``doc-index-file``: *templated path*
    A central index of Haddock API documentation (template cannot use
    ``$pkgid``), which should be updated as documentation is built.

    The command line variant of this flag is
    ``--doc-index-file=TEMPLATE``

The following commands are equivalent to ones that would be passed when
running ``setup haddock``. (TODO: Where does the documentation get put.)

``haddock-hoogle:`` *boolean* (default: False)
    Generate a text file which can be converted by
    `Hoogle <http://www.haskell.org/hoogle/>`__ into a database for
    searching. This is equivalent to running ``haddock`` with the
    ``--hoogle`` flag.

    The command line variant of this flag is ``--hoogle`` (for the
    ``haddock`` command).

``haddock-html:`` *boolean* (default: True)
    Build HTML documentation.

    The command line variant of this flag is ``--html`` (for the
    ``haddock`` command).

``haddock-html-location:`` *templated path*
    Specify a template for the location of HTML documentation for
    prerequisite packages. The substitutions are applied to the template
    to obtain a location for each package, which will be used by
    hyperlinks in the generated documentation. For example, the
    following command generates links pointing at [Hackage] pages:

    ::

        html-location: 'http://hackage.haskell.org/packages/archive/$pkg/latest/doc/html'

    Here the argument is quoted to prevent substitution by the shell. If
    this option is omitted, the location for each package is obtained
    using the package tool (e.g. ``ghc-pkg``).

    The command line variant of this flag is ``--html-location`` (for
    the ``haddock`` subcommand).

``haddock-executables:`` *boolean* (default: False)
    Run haddock on all executable programs.

    The command line variant of this flag is ``--executables`` (for the
    ``haddock`` subcommand).

``haddock-tests:`` *boolean* (default: False)
    Run haddock on all test suites.

    The command line variant of this flag is ``--tests`` (for the
    ``haddock`` subcommand).

``haddock-benchmarks:`` *boolean* (default: False)
    Run haddock on all benchmarks.

    The command line variant of this flag is ``--benchmarks`` (for the
    ``haddock`` subcommand).

``haddock-all:`` *boolean* (default: False)
    Run haddock on all components.

    The command line variant of this flag is ``--all`` (for the
    ``haddock`` subcommand).

``haddock-internal:`` *boolean* (default: False)
    Build haddock documentation which includes unexposed modules and
    symbols.

    The command line variant of this flag is ``--internal`` (for the
    ``haddock`` subcommand).

``haddock-css:`` *path*
    The CSS file that should be used to style the generated
    documentation (overriding haddock's default.)

    The command line variant of this flag is ``--css`` (for the
    ``haddock`` subcommand).

``haddock-hyperlink-source:`` *boolean* (default: False)
    Generated hyperlinked source code using ``HsColour``, and have
    Haddock documentation link to it.

    The command line variant of this flag is ``--hyperlink-source`` (for
    the ``haddock`` subcommand).

``haddock-hscolour-css:`` *path*
    The CSS file that should be used to style the generated hyperlinked
    source code (from ``HsColour``).

    The command line variant of this flag is ``--hscolour-css`` (for the
    ``haddock`` subcommand).

``haddock-contents-location:`` *url*
    A baked-in URL to be used as the location for the contents page.

    The command line variant of this flag is ``--contents-location``
    (for the ``haddock`` subcommand).

``haddock-keep-temp-files:``
    Keep temporary files.

    The command line variant of this flag is ``--keep-temp-files`` (for
    the ``haddock`` subcommand).

Advanced global configuration options
-------------------------------------

1222
``http-transport:`` ``curl`` or ``wget`` or ``powershell`` or ``plain-http`` (default: ``curl``)
1223 1224 1225 1226 1227 1228 1229 1230 1231 1232 1233 1234 1235 1236 1237 1238 1239 1240 1241 1242 1243 1244 1245 1246 1247 1248 1249 1250
    Set a transport to be used when making http(s) requests.

    The command line variant of this field is ``--http-transport=curl``.

``ignore-expiry:`` *boolean* (default: False)
    If ``True``, we will ignore expiry dates on metadata from Hackage.

    In general, you should not set this to ``True`` as it will leave you
    vulnerable to stale cache attacks. However, it may be temporarily
    useful if the main Hackage server is down, and we need to rely on
    mirrors which have not been updated for longer than the expiry
    period on the timestamp.

    The command line variant of this field is ``--ignore-expiry``.

``remote-repo-cache:`` *directory* (default: ``~/.cabal/packages``)
    [STRIKEOUT:The location where packages downloaded from remote
    repositories will be cached.] Not implemented yet.

    The command line variant of this flag is
    ``--remote-repo-cache=DIR``.

``logs-dir:`` *directory* (default: ``~/.cabal/logs``)
    [STRIKEOUT:The location where build logs for packages are stored.]
    Not implemented yet.

    The command line variant of this flag is ``--logs-dir=DIR``.

1251
``build-summary:`` *template filepath* (default: ``~/.cabal/logs/build.log``)
1252 1253 1254 1255 1256 1257 1258 1259 1260 1261 1262 1263 1264 1265 1266 1267 1268 1269 1270 1271 1272 1273 1274
    [STRIKEOUT:The file to save build summaries. Valid variables which
    can be used in the path are ``$pkgid``, ``$compiler``, ``$os`` and
    ``$arch``.] Not implemented yet.

    The command line variant of this flag is
    ``--build-summary=TEMPLATE``.

``local-repo:`` *directory*
    [STRIKEOUT:The location of a local repository.] Deprecated. See
    "Legacy repositories."

    The command line variant of this flag is ``--local-repo=DIR``.

``world-file:`` *path*
    [STRIKEOUT:The location of the world file.] Deprecated.

    The command line variant of this flag is ``--world-file=FILE``.

Undocumented fields: ``root-cmd``, ``symlink-bindir``, ``build-log``,
``remote-build-reporting``, ``report-planned-failure``, ``one-shot``,
``offline``.

Advanced solver options
1275
^^^^^^^^^^^^^^^^^^^^^^^
1276 1277 1278 1279 1280 1281 1282 1283 1284 1285 1286 1287 1288 1289 1290 1291 1292 1293 1294 1295 1296 1297

Most users generally won't need these.

``solver:`` ``modular``
    This field is reserved to allow the specification of alternative
    dependency solvers. At the moment, the only accepted option is
    ``modular``.

    The command line variant of this field is ``--solver=modular``.

``max-backjumps:`` *nat* (default: 2000)
    Maximum number of backjumps (backtracking multiple steps) allowed
    while solving. Set -1 to allow unlimited backtracking, and 0 to
    disable backtracking completely.

    The command line variant of this field is ``--max-backjumps=2000``.

``reorder-goals:`` *boolean* (default: False)
    When enabled, the solver will reorder goals according to certain
    heuristics. Slows things down on average, but may make backtracking
    faster for some packages. It's unlikely to help for small projects,
    but for big install plans it may help you find a plan when otherwise
1298
    this is not possible. See :issue:`1780` for more commentary.
1299 1300 1301 1302 1303 1304 1305 1306 1307 1308 1309 1310 1311 1312 1313 1314 1315 1316 1317 1318 1319 1320 1321 1322

    The command line variant of this field is ``--(no-)reorder-goals``.

``count-conflicts:`` *boolean* (default: True)
    Try to speed up solving by preferring goals that are involved in a
    lot of conflicts.

    The command line variant of this field is
    ``--(no-)count-conflicts``.

``strong-flags:`` *boolean* (default: False)
    Do not defer flag choices. (TODO: Better documentation.)

    The command line variant of this field is ``--(no-)strong-flags``.

``cabal-lib-version:`` *version*
    This field selects the version of the Cabal library which should be
    used to build packages. This option is intended primarily for
    internal development use (e.g., forcing a package to build with a
    newer version of Cabal, to test a new version of Cabal.) (TODO:
    Specify its semantics more clearly.)

    The command line variant of this field is
    ``--cabal-lib-version=1.24.0.1``.