2. Project Description — cabal.project File — Cabal 3.16.1.0 User's Guide

# 2. Project Description — cabal.project File

`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 (groups of fields that apply to only part of a project or can be referenced as a unit):

    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 configure --enable-profiling` will write out a project file with `profiling: True`.

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

1. The user-wide global configuration (default: `~/.config/cabal/config`)

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

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

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

Any call to `cabal build` will consider `cabal.project*` files from parent directories when there is none in the current directory.

## 2.1. Conditionals and imports

As of `cabal-install` version 3.8, cabal supports conditional logic and imports in `cabal.project` files.

> Warning

> While conditional blocks can appear anywhere within component or common sections of a package, their placement within a project is restricted. Conditions may only be introduced at the top level of a project.

> Of the condition tests, only packages can test for flags. Projects can test for operating system, architecture, compiler and the boolean constants.

> - `os(name)`

> - `arch(name)`

> - `impl(compiler)`

> - `true`

> - `false`

Imports may specify local filepaths or remote urls, and may reference either cabal.project files or v1-style cabal.config freeze files. As a usage example:

    if(os(darwin))
      optimization: False
    elif(os(freebsd))
      packages: freebsd/*.cabal
    else
      optimization: True

    import: https://some.remote.source/subdir/cabal.config

    import: relativepath/extra-project.project

    import: /absolutepath/some-project.project

Using conditionals will force cabal to find a ghc to derive architecture and version information from, which will force some commands (update, sdist) to require ghc present where otherwise it would not be necessitated.

One use case for imports is to specify a Stackage <https://www.stackage.org/> snapshot, so that your cabal project can use the same set of packages as that snapshot. To use the `lts-21.25` resolver, you can write `import: https://www.stackage.org/lts-21.25/cabal.config` in your `cabal.project`.

There are a number of limitations that come with this approach however; please see How can I have a reproducible set of versions for my dependencies? for more information.

## 2.2. Specifying the local packages

You must provide a non-empty list of local packages in your project, filling out either a `packages` field or an `optional-packages` field or both to satisfy this requirement.

When `cabal.project` doesn’t exist, `cabal-install` fabricates an ephemeral project for its own use with this simple content, a glob that will find any (but expects to find one) package in the current directory:

    packages: ./*.cabal

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

packages: package location list (space or comma separated)
  Default value:

    empty

  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 glob-style wildcards, which must match one or more (a) directories containing a (single) Cabal file, (b) Cabal files (extension `.cabal`), or (c) tarballs which contain Cabal packages (extension `.tar.gz`). 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. They can specify an `http`, `https` or `file` URL, representing the path to a remote tarball to be downloaded and built.

  There is no command line variant of this field; see issue #3585. Note that the default value is only included if there is no `cabal.project` file. The field is appendable which means there would be no way to drop the default value if it was included.

optional-packages: package location list (space or comma-separated)
  Default value:

    empty

  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)

  Specifies a list of external packages from Hackage, which should be considered local packages. The motivation for `extra-packages` is making libraries that are not dependencies of any package in the project available for use in ghci.

  There is no command line variant of this field.

All local packages are vendored, in the sense that if other packages (including external ones from Hackage) depend on a package with the name of a local package, the local package is preferentially used. For subdirectories to be considered local packages, the following setting can be used:

    packages: ./*.cabal
    optional-packages: ./*/*.cabal

…then any package can be vendored simply by making a checkout in the top-level project directory, as might be seen in this hypothetical directory layout:

    foo.cabal
    foo-helper/     # local package
    unix/           # vendored external package

All of these options support globs. `cabal 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 is described by the following BNF:

Todo

convert globbing grammar to proper ABNF syntax

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

## 2.3. Taking a dependency from a source code repository

Since version 2.4, the `source-repository-package` stanza allows for specifying packages in a remote version control system that cabal should consider during package retrieval. This allows use of a package from a remote version control system, rather than looking for that package in Hackage.

Since version 3.4, cabal-install creates tarballs for each package coming from a `source-repository-package` stanza (effectively applying cabal sdists to such packages). It gathers the names of the packages from the appropriate `.cabal` file in the version control repository, and allows their use just like Hackage or locally defined packages.

There is no command line variant of this stanza.

    packages: .

    source-repository-package
        type: git
        location: https://github.com/hvr/HsYAML.git
        tag: e70cf0c171c9a586b62b3f75d72f1591e4e6aaa1

    source-repository-package
        type: git
        location: https://github.com/well-typed/cborg
        tag: 3d274c14ca3077c3a081ba7ad57c5182da65c8c1
        subdir: cborg

    source-repository-package
        type: git
        location: https://github.com/haskell/network.git
        tag: e76fdc753e660dfa615af6c8b6a2ad9ddf6afe70
        post-checkout-command: autoreconf -i

The VCS fields of `source-repository-package` are:

type: VCS kind

  This field is required.

  Cabal supports specifying different information for various common source control systems. This is the name of the source control system used for a repository. The currently recognised types are:

  - `darcs`

  - `git`

  - `svn`

  - `cvs`

  - `mercurial` (or alias `hg`)

  - `bazaar` (or alias `bzr`)

  - `arch`

  - `monotone`

  - `pijul`

  The VCS kind will determine what other fields are appropriate to specify for a particular version control system.

location: VCS location

  This field is required.

  The location of the repository, usually a URL but the exact form of this field depends on the repository type. For example:

  - for Darcs: `http://code.haskell.org/foo/`

  - for Git: `https://github.com/foo/bar.git`

  - for CVS: `anoncvs@cvs.foo.org:/cvs`

branch: VCS branch

  This field is optional.

  Many source control systems support the notion of a branch, as a distinct concept from having repositories in separate locations. For example CVS, SVN and git use branches while darcs uses different locations for different branches. If you need to specify a branch to identify a your repository then specify it in this field.

tag: VCS tag

  This field is optional.

  A tag identifies a particular state of a source repository. The exact form of the tag depends on the repository type.

subdir: VCS subdirectory list

  Look in one or more subdirectories of the repository for cabal files, rather than the root. This field is optional.

  A field of this type is always optional because it defaults to empty, which corresponds to the root directory of the repository and is the same as specifying `.` explicitly.

  Some projects put the sources for multiple packages inside a single VCS repository. This field lets you specify the relative path from the root of the repository to the top directory for the package, i.e. the directory containing the package’s `.cabal` file.

post-checkout-command: command

  Run command in the checked out repository, prior sdisting.

## 2.4. Global configuration options

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

verbose: nat
-v[n] , --verbose[=n]
  Default value:

    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 $ncpus
-j[NUM] , --jobs[=NUM], --jobs=$ncpus
  Default value:

    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`.

semaphore: boolean
--semaphore
--no-semaphore
  Default value:

    False

  This option instructs cabal to control parallelism by creating a new system semaphore, whose number of tokens is specified by `--jobs` (or `-j`). This semaphore is passed to GHC, which allows it to use any leftover parallelism that `cabal-install` is not using.

  Requires `ghc >= 9.8`.

  The command line variant of this field is `--semaphore`.

keep-going: boolean
--keep-going
  Default value:

    False

  If true, after a build failure, continue to build other unaffected packages.

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

--builddir=DIR

  Specifies the name of the directory where build products for build will be stored; defaults to `dist-newstyle`. If a relative name is specified, this directory is resolved relative to the root of the project (i.e., where the `cabal.project` file lives.)

  This option can only be specified from the command line.

--project-dir=DIR

  Specifies the path of the project directory. If a relative project-file path is also specified, it will be resolved relative to this directory.

  The project directory does not need to contain a `cabal.project` file.

  This option can only be specified from the command line.

--project-file=FILE

  Specifies the path and name of the project file used to specify the rest of the top-level configuration; defaults to `cabal.project`. This name not only specifies the name of the main project file, but also the auxiliary project files `cabal.project.freeze` and `cabal.project.local`; for example, if you specify `--project-file=my.project`, then the other files that will be probed are `my.project.freeze` and `my.project.local`.

  If project-dir is not specified, and the path is relative, we will look for the file relative to the current working directory, and then for the parent directory, until the project file is found or we have hit the top of the user’s home directory.

  This option can only be specified from the command line.

-z, --ignore-project

  Ignores the local `cabal.project` file and uses the default configuration with the local `foo.cabal` file. Note that this flag will be ignored if either of the `--project-dir` or `--project-file` flags are also set.

--store-dir=DIR

  Specifies the name of the directory of the global package store.

package-dbs: package DB stack (comma separated)
--package-db=[clear, global , user , PATH]
  Since:

    Cabal 3.7

  By modifying `package-dbs` you can modify the default package environment which `cabal` will see. The package databases you add using `package-dbs` will not be written into and only used as immutable package stores to initialise the environment with additional packages that `cabal` can choose to use.

  There are three package databases involved with most builds:

  global

    Compiler installation of rts, base, etc.

  store

    Nix-style local build cache

  in-place

    Project-specific build directory

  By default, the initial package stack prefix you will have with v2 commands is:

      -- prefix = [global]

  So the initial set of packages which is used by cabal is just the packages installed in the global package database which comes with `ghc`.

  When cabal builds a package it will start populating the `store` package database, whose packages will then be subsequently be available to be used in future runs.

      -- prefix ++ [store]

  When cabal builds your local projects, packages are registered into the local in-place package database.

      -- prefix ++ [store, in-place]

  This flag manipulates the default prefix: `[global]` and accepts paths, the special value `global` referring to the global package db, and `clear` which removes all prior entries. For example,

      -- prefix = [global, foo]
      package-dbs: foo

      -- prefix = [foo]
      package-dbs: clear, foo

      -- prefix = [bar, baz]
      package-dbs: clear, foo, clear, bar, baz

  The command line variant of this flag is `--package-db=DB` which can be specified multiple times.

## 2.5. Phase control

The following settings apply to commands that result in build actions (`build`, `run`, `repl`, `test`…), and control which phases of the build are executed.

--dry-run

  Do not download, build, or install anything, only print what would happen.

--only-configure

  Instead of performing a full build just run the configure step. Only accepted by the `build` command.

--only-download

  Do not build anything, only fetch the packages.

--only-dependencies

  Install only the dependencies necessary to build the given packages. Not accepted by the `repl` command.

## 2.6. Solver configuration options

The following settings control the behavior of the dependency solver:

constraints: CONSTRAINT (comma separated list)
-c CONSTRAINT or -cCONSTRAINT, --constraint=CONSTRAINT
--constraint="pkg > 2.0", -c "pkg >= 2.0"

  Add extra constraints to the version bounds, flag settings, and other properties a solver can pick for a package. For example:

      constraints: bar == 2.1

  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

  This is equivalent to writing constraints and `flags` separately:

      constraints: bar == 2.1
      package bar
        flags: +foo -baz

  Valid constraints take the same form as for the `runhaskell Setup.hs configure --constraint` command line option.

preferences: CONSTRAINT (comma separated list)
--preference=CONSTRAINT
--preference="pkg > 2.0"

  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 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.

allow-newer: none, all or list of scoped package names (space or comma separated)
--allow-newer , --allow-newer=[none, all , [scope:][^]pkg]
  Default value:

    `none`

  Allow the solver to pick more recent version of some packages than would normally be permitted by 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

  If the scope shall be limited to specific releases of `pkg`, the extended form as in

      allow-newer: pkg-1.2.3:dep-pkg, pkg-1.1.2:dep-pkg

  can be used to limit the relaxation of dependencies on `dep-pkg` by the `pkg-1.2.3` and `pkg-1.1.2` releases only.

  The scoped 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.

  The syntax also allows to prefix the dependee package with a modifier symbol to modify the scope/semantic of the relaxation transformation in a additional ways. Currently only one modifier symbol is defined, i.e. `^` (i.e. caret) which causes the relaxation to be applied only to `^>=` operators and leave all other version operators untouched.

  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. For quux only, relax
      -- 'quux ^>= ...'-style constraints only.
      allow-newer: bar, baz, ^quux

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

      -- Disregard all `^>=`-style upper bounds when dependency solving
      allow-newer: ^all

  For consistency, there is also the explicit wildcard scope syntax `*` (or its alphabetic synonym `all`). Consequently, the examples above are equivalent to the explicitly scoped variants:

      allow-newer: all:bar, *:baz, *:^quux

      allow-newer: *:*
      allow-newer: all:all

      allow-newer: *:^*
      allow-newer: all:^all

  In order to ignore all bounds specified by a package `pkg-1.2.3` you can combine scoping with a right-hand-side wildcard like so

      -- Disregard any upper bounds specified by pkg-1.2.3
      allow-newer: pkg-1.2.3:*

      -- Disregard only `^>=`-style upper bounds in pkg-1.2.3
      allow-newer: pkg-1.2.3:^*

  `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 e.g. `--allow-newer=bar`. A bare `--allow-newer` is equivalent to `--allow-newer=all`.

allow-older: none, all, list of scoped package names (space or comma separated)
--allow-older , --allow-older=[none, all , [scope:][^]pkg]
  Since:

    Cabal 2.0

  Default value:

    `none`

  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`.

index-state: HEAD, unix-timestamp, ISO8601 UTC timestamp.
  Since:

    Cabal 2.0

  Default value:

    `HEAD`

  This allows to change the source package index state the solver uses to compute install-plans. This is particularly useful in combination with freeze-files in order to also freeze the state the package index was in at the time the install-plan was frozen.

      -- UNIX timestamp format example
      index-state: @1474739268

      -- ISO8601 UTC timestamp format example
      -- This format is used by 'cabal configure'
      -- for storing `--index-state` values.
      index-state: 2016-09-24T17:47:48Z

      -- Specify different index-states per package repository
      -- Supported since 3.4
      index-state:
        , hackage.haskell.org 2020-05-06T22:33:27Z
        , head.hackage 2020-04-29T04:11:05Z

active-repositories: reponame1, reponame2
  Synopsis:

    Specify active package repositories

  Since:

    3.4

  Default value:

    `:rest`

  Specifies which of the package repositories defined in the configuration should be active. It’s also useful for specifying the order and the way active repositories are merged.

  When searching for a certain version of a certain package name, the list of active repositories is searched last-to-first.

  For example, suppose hackage.haskell.org has versions 1.0 and 2.0 of package X, and my-repository has version 2.0 of a similarly named package. Then, with the following configuration:

      -- Force my-repository to be the first repository considered
      active-repositories:
        , hackage.haskell.org
        , my-repository

  version 2.0 of X will come from my-repository, and version 1.0 will come from hackage.haskell.org.

  If we want to make a repository the sole provider of certain packages, we can put it last in the active repositories list, and add the :override modifier.

  For example, if we modify the previous example like this:

      active-repositories:
        , hackage.haskell.org
        , my-repository:override

  then version 1.0 of package X won’t be found in any case, because X is present in my-repository only in version 2.0, and the :override forbids searching for other versions of X further up the list.

  :override has no effect for package names that aren’t present in the overriding repository.

  The special repository reference :rest stands for “all the other repositories” and can be useful to avoid lengthy lists of repository names:

      -- Force my-repository to be the first repository considered
      active-repositories: :rest, my-repository

  The special repository reference :none disables all repositories, effectively putting cabal in “offline” mode:

      active-repositories: :none

reject-unconstrained-dependencies: all, none
--reject-unconstrained-dependencies=[all|none]
  Default value:

    none

  Since:

    2.6

  By default, the dependency solver can include any package that it’s aware of in a build plan. If you wish to restrict the build plan to a closed set of packages (e.g., from a freeze file), use this flag.

  When set to all, all non-local packages that aren’t goals must be explicitly constrained. When set to none, the solver will consider all packages.

## 2.7. Package configuration options

Package options affect the building of specific packages. There are three 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.

- They can be specified inside an `package *` stanza, in which case they apply to all packages, local ones from the project and also external dependencies.

For example, the following options specify that `optimization` should be turned off for all local packages, and that `awesome-package` (possibly an external dependency) should have the flag `some-flag` disabled

    optimization: False

    package awesome-package
        flags: -some-flag

Note that options at the top level take precedence over those at the `package` stanza for local packages.

On the command line, these options are applied to 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.

package name or *

  Specify package configuration options for the specific package (be it an external or local package) or for all packages (external and local).

  A `package` stanza can contain the configuration fields listed in this section and `<progname>-options`:

      package awesome-package
        flags: -some-flag
        profiling: True
        cxx-options: -Wall

  Program options are not extensively described in this documentation but a good amount of them can be found in the Build information section.

flags: list of +flagname or -flagname (space separated)
-f FLAGS or -fFLAGS, --flags=FLAGS
--flags="+foo -bar", -ffoo , -f-bar

  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

  Exactly one of + or - is required before each flag.

  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.

  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 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. Flags can be specified as package `constraints`.

with-compiler: PATH
-w PATH or -wPATH, --with-compiler=PATH

  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 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.

  It’s not possible to set `with-compiler` on a per-package basis.

  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: PATH
--with-hc-pkg=PATH

  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
-O[n] , --enable-optimization[=n]
--disable-optimization
  Default value:

    `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.

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

  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 levels change (see GHC issue #10923), so if 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: OPT (space separated list)
--configure-option=OPT

  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.

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

compiler: ghc, ghcjs, jhc, lhc, or uhc
--compiler=compiler
  Default value:

    `ghc`

  Specify the 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`.

  It’s not possible to set `compiler` on a per-package basis.

tests: boolean
--enable-tests
--disable-tests
  Default value:

    `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
--enable-benchmarks
--disable-benchmarks
  Default value:

    `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`.

extra-prog-path: PATH (newline or comma separated list)
--extra-prog-path=PATH
  Since:

    Cabal 1.18

  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.

  When specifying –http-transport from the command line, only extra-prog-path from the command line are added to the program search path.

run-tests: boolean
--run-tests
  Default value:

    `False`

  Run the package test suite during 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.”

  Warning

  One deficiency: the `run-tests` 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`.

### 2.7.1. Object code options

debug-info: integer
--enable-debug-info[=n]
--disable-debug-info
  Since:

    Cabal 1.22

  Default value:

    False

  If the compiler (e.g., GHC 7.10 and later) supports outputting OS native debug info (e.g., DWARF), setting `debug-info: True` will instruct it to do so. See the GHC wiki page on DWARF for more information about this feature.

  (This field also accepts numeric syntax, but until GHC 8.2 this didn’t do anything.)

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

split-sections: boolean
--enable-split-sections
--disable-split-sections
  Since:

    Cabal 2.2

  Default value:

    False

  Use the GHC `-split-sections` 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 a bit more memory.

  This feature is supported by GHC 8.0 and later.

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

split-objs: boolean
--enable-split-objs
--disable-split-objs
  Default value:

    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.

  It is generally recommend that you use `split-sections` instead of `split-objs` where possible.

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

executable-stripping: boolean
--enable-executable-stripping
--disable-executable-stripping
  Default value:

    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.

  If `debug-info` is set explicitly then `executable-stripping` is set to `False` as otherwise all the debug symbols will be stripped.

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

library-stripping: boolean
--enable-library-stripping
--disable-library-stripping
  Since:

    Cabal 1.20

  When installing binary libraries, run the `strip` program on the binary, saving space on the file system. See also `executable-stripping`.

  If `debug-info` is set explicitly then `library-stripping` is set to `False` as otherwise all the debug symbols will be stripped.

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

### 2.7.2. Executable options

program-prefix: PREFIX
--program-prefix=PREFIX

  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
--program-suffix=SUFFIX

  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'`.

### 2.7.3. Dynamic linking options

shared: boolean
--enable-shared
--disable-shared
  Default value:

    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
--enable-executable-dynamic
--disable-executable-dynamic
  Default value:

    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
--enable-library-for-ghci
--disable-library-for-ghci
  Default value:

    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:
--relocatable
  Since:

    Cabal 1.22

  Default value:

    False

  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`.

### 2.7.4. Static linking options

static: boolean
--enable-static
--disable-static
  Default value:

    False

  Roll this and all dependent libraries into a combined `.a` archive. This uses GHCs `-staticlib` flag, which is available for iOS and with GHC 8.4 and later for other platforms as well.

executable-static: boolean
--enable-executable-static
--disable-executable-static
  Default value:

    False

  Build fully static executables. This links all dependent libraries into executables statically, including libc. This passes `-static` and `-optl=-static` to GHC.

### 2.7.5. Foreign function interface options

extra-include-dirs: directories (comma or newline separated list)
--extra-include-dirs=DIR

  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)
--extra-lib-dirs=DIR

  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.

extra-framework-dirs: directories (comma or newline separated list)
--extra-framework-dirs=DIR

  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.

### 2.7.6. Profiling options

profiling: boolean
--enable-profiling
--disable-profiling
  Since:

    Cabal 1.22

  Default value:

    False

  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 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`.

profiling-detail: level
--profiling-detail=level
  Since:

    Cabal 1.24

  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, this is for non-inline functions. Corresponds to `-fprof-auto-exported`.

  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. Corresponds to `-fprof-auto-top`.

  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. Corresponds to `-fprof-auto`.

  late-toplevel

    Like top-level but costs will be assigned to top level definitions after optimization. This lowers profiling overhead massively while giving similar levels of detail as toplevel-functions. However it means functions introduced by GHC during optimization will show up in profiles as well. Corresponds to `-fprof-late` if supported and `-fprof-auto-top` otherwise.

  late

    Currently an alias for late-toplevel

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

library-profiling-detail: level
--library-profiling-detail=level
  Since:

    Cabal 1.24

  Like `profiling-detail`, but applied only to libraries

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

library-vanilla: boolean
--enable-library-vanilla
--disable-library-vanilla
  Default value:

    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
--enable-library-profiling
--disable-library-profiling
  Since:

    Cabal 1.22

  Default value:

    False

  Build libraries with profiling enabled. You probably want to use `profiling` instead.

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

executable-profiling: boolean
--enable-executable-profiling
--disable-executable-profiling
  Since:

    Cabal 1.22

  Default value:

    False

  Build executables with profiling enabled. You probably want to use `profiling` instead.

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

### 2.7.7. Coverage options

coverage: boolean
--enable-coverage
--disable-coverage
  Since:

    Cabal 1.22

  Default value:

    False

  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
--enable-library-coverage
--disable-library-coverage
  Deprecated:

  Since:

    Cabal 1.22

  Default value:

    False

  Deprecated, use `coverage`.

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

### 2.7.8. Haddock options

documentation: boolean
--enable-documentation
--disable-documentation
  Default value:

    False

  Enables building of Haddock documentation. Implied when calling `cabal haddock`.

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

  `documentation: true` does not imply `haddock-all`, `haddock-benchmarks`, `haddock-executables`, `haddock-internal` or `haddock-tests`. These need to be enabled separately if desired.

doc-index-file: templated path
--doc-index-file=TEMPLATE

  A central index of Haddock API documentation (template cannot use `$pkgid`), which should be updated as documentation is built.

The following commands are equivalent to ones that would be passed when running `setup haddock`.

haddock-hoogle: boolean
--haddock-hoogle
  Default value:

    False

  Generate a text file which can be converted by Hoogle into a database for searching. This is equivalent to running `haddock` with the `--hoogle` flag.

haddock-html: boolean
--haddock-html
  Default value:

    True

  Build HTML documentation.

haddock-quickjump: boolean
--haddock-quickjump
  Default value:

    False

  Generate an index for interactive documentation navigation. This is equivalent to running `haddock` with the `--quickjump` flag.

haddock-html-location: URL (templated path)
--haddock-html-location=URL

  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

  If passed on the command line, the argument may be quoted to prevent substitution by the shell.

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

  If this option is omitted, the location for each package is obtained using the package tool (e.g. `ghc-pkg`).

haddock-executables: boolean
--haddock-executables
  Default value:

    False

  Run haddock on all executable programs.

haddock-tests: boolean
--haddock-tests
  Default value:

    False

  Run haddock on all test suites.

haddock-benchmarks: boolean
--haddock-benchmarks
  Default value:

    False

  Run haddock on all benchmarks.

haddock-internal: boolean
--haddock-internal
  Default value:

    False

  Build haddock documentation which includes unexposed modules and symbols.

haddock-all: boolean
--haddock-all
  Default value:

    False

  Run haddock on all components.

haddock-css: PATH
--haddock-css=PATH

  The CSS file that should be used to style the generated documentation (overriding haddock’s default).

haddock-hyperlink-source: boolean
--haddock-hyperlink-source
  Default value:

    False

  Generated hyperlinked source code using HsColour, and have Haddock documentation link to it. This is equivalent to running `haddock` with the `--hyperlinked-source` flag.

haddock-hscolour-css: PATH
--haddock-hscolour-css=PATH

  The CSS file that should be used to style the generated hyperlinked source code (from HsColour).

haddock-contents-location: URL
--haddock-contents-location=URL

  A baked-in URL to be used as the location for the contents page.

haddock-keep-temp-files: boolean

  Keep temporary files.

  There is no command line variant of this flag.

haddock-output-dir: DIR
--haddock-output-dir=DIR

  Generate haddock documentation into this directory instead of the default location next to other build products.

  This flag is provided as a technology preview and is subject to change in the next releases.

haddock-use-unicode: boolean
--haddock-use-unicode

  Generate HTML documentation which contains unicode characters.

haddock-resources-dir: DIR
--haddock-resources-dir=DIR

  Location of Haddock’s static/auxiliary files. For Haddock distributed with GHC (or, more precisely, built within the GHC source tree), this path should be automatically inferred. For Haddock built from source, however, this path should likely be explicitly set for every Haddock invocation.

open: boolean
--open

  When generating HTML documentation, attempt to open it in a browser when complete. This will use `xdg-open` on Linux and BSD systems, `open` on macOS, and `start` on Windows.

### 2.7.9. Program options

program-options

Program options can be specified once for all local packages by means of the `program-options` stanza. For example:

    program-options
        ghc-options: -Werror

indicates that all local packages will provide `-Werror` to GHC when being built. On the other hand, the following snippet:

    package *
        ghc-options: -Werror

will apply `-Werror` to all packages, local and remote.

## 2.8. Advanced global configuration options

write-ghc-environment-files: always, never, or ghc8.4.4+
--write-ghc-environment-files=always|never|ghc8.4.4+
  Default value:

    `never`

  Whether a GHC package environment file should be created after a successful build.

  Since Cabal 3.0, defaults to `never`. Before that, defaulted to creating them only when compiling with GHC 8.4.4 and later (GHC 8.4.4 is the first version that supports the `-package-env -` option that allows ignoring the package environment files).

build-info: True, False
--enable-build-info
--disable-build-info
  Default value:

    `False`

  Enable generation of build information for Cabal components. Contains very detailed information on how to build an individual component, such as compiler version, modules of a component and how to compile the component.

  The output format is in json, and the exact location can be discovered from `plan.json`, where it is identified by `build-info` within the items in the `install-plan`. Note, that this field in `plan.json` can be `null`, if and only if `build-type: Custom` is set, and the `Cabal` version is too old (i.e. `< 3.7`). If the field is missing entirely, the component is not a local one, thus, no `build-info` exists for that particular component within the `install-plan`.

  Note

  The format and fields of the generated build information is currently experimental, in the future we might add or remove fields, depending on the needs of other tooling.

http-transport: curl, wget, powershell, or plain-http
--http-transport=transport
  Default value:

    `curl`

  Set a transport to be used when making http(s) requests.

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

  If the project configuration imports remote urls, the user can only specify the http-transport option from the command line.

  When specifying the http-transport from the command line, the program search path can only be influenced using –extra-prog-path.

ignore-expiry: boolean
--ignore-expiry
  Default value:

    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
--remote-repo-cache=DIR
  Default value:

    `~/.cabal/packages`

  The location where packages downloaded from remote repositories will be cached.

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

logs-dir: directory
--logs-dir=DIR
  Default value:

    `~/.cabal/logs`

  The location where build logs for packages are stored. Not implemented yet.

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

build-summary: template filepath
--build-summary=TEMPLATE
  Default value:

    `~/.cabal/logs/build.log`

  The file to save build summaries. Not implemented yet.

  Valid variables which can be used in the path are `$pkgid`, `$compiler`, `$os` and `$arch`.

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

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

### 2.8.1. Advanced solver options

Most users generally won’t need these.

solver: SOLVER
--solver=SOLVER

  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
--max-backjumps=N
  Default value:

    4000

  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=4000`.

reorder-goals: boolean
--reorder-goals
--no-reorder-goals
  Default value:

    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 this is not possible. See issue #1780 for more commentary.

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

count-conflicts: boolean
--count-conflicts
--no-count-conflicts
  Default value:

    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`.

fine-grained-conflicts: boolean
--fine-grained-conflicts
--no-fine-grained-conflicts
  Default value:

    True

  When enabled, the solver will skip a version of a package if it does not resolve any of the conflicts encountered in the last version of that package. For example, if `foo-1.2` depended on `bar`, and the solver couldn’t find consistent versions for `bar`’s dependencies, then the solver would skip `foo-1.1` if it also depended on `bar`.

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

minimize-conflict-set: boolean
--minimize-conflict-set
--no-minimize-conflict-set
  Default value:

    False

  When there is no solution, try to improve the solver error message by finding a minimal conflict set. This option may increase run time significantly, so it is off by default.

  The command line variant of this field is `--(no-)minimize-conflict-set`.

strong-flags: boolean
--strong-flags
--no-strong-flags
  Default value:

    False

  Do not defer flag choices. (TODO: Better documentation.)

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

allow-boot-library-installs: boolean
--allow-boot-library-installs
--no-allow-boot-library-installs
  Default value:

    False

  By default, the dependency solver doesn’t allow `base`, `ghc-prim`, `integer-simple`, `integer-gmp`, and `template-haskell` to be installed or upgraded. This flag removes the restriction.

  The command line variant of this field is `--(no-)allow-boot-library-installs`.

cabal-lib-version: VERSION
--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`.

prefer-oldest: boolean
--prefer-oldest
--no-prefer-oldest
  Since:

    Cabal 3.10

  Default value:

    False

  By default, when solver has a choice of multiple versions of the same package, it will first try to derive a build plan with the latest version. This flag switches the behaviour, making the solver to prefer the oldest packages available.

  The primary use case is to help users in establishing lower bounds of upstream dependencies.

  The command line variant of this field is `--(no-)prefer-oldest`.