5.1. 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

To run an executable defined in this package, use this command:

$ cabal new-run <executable name> [executable args]

5.1.1. 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.

5.2. Cookbook

5.2.1. How can I profile my library/application?

First, make sure you have HEAD; 1.24 is affected by #3790, which means that if any project which transitively depends on a package which has a Custom setup built against Cabal 1.22 or earlier will silently not work.

Create or edit your cabal.project.local, adding the following line:

profiling: True

Now, cabal new-build will automatically build all libraries and executables with profiling. You can fine-tune the profiling settings for each package using profiling-detail:

package p
    profiling-detail: toplevel-functions

Alternately, you can call cabal new-build --enable-profiling to temporarily build with profiling.

5.3. How it works

5.3.1. 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 projects. 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 arbitrary Hackage package in extra-packages to force it to be 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.

  1. An external package is any package which is not listed in the 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 (configurable via global store-dir option); 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, 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.

5.3.2. 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-install) 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.

5.3.3. 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)

5.4. Commands

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

5.4.1. 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.

5.4.2. 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.
  • All packages: all, which specifies all packages within the project.
  • Components of a particular type: ctype, package:ctype, all:ctype: which specifies all components of the given type.

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.)

5.4.3. 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.)

5.4.4. cabal new-run

cabal new-run [TARGET [ARGS]] runs the executable specified by the target, which can be a component, a package or can be left blank, as long as it can uniquely identify an executable within the project.

See the new-build section for the target syntax.

Except in the case of the empty target, the strings after it will be passed to the executable as arguments.

If one of the arguments starts with - it will be interpreted as a cabal flag, so if you need to pass flags to the executable you have to separate them with --.

$ cabal new-run target -- -a -bcd --argument

5.4.5. 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 this:

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

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.

5.4.6. cabal new-bench

cabal new-bench [TARGETS] [OPTIONS] runs the specified benchmarks (all the benchmarks in the current package by default), first ensuring they are up to date.

5.4.7. Unsupported commands

The following commands are not currently supported:

cabal new-test (#3638)
Workaround: run the test executable directly (see Where are my build products?)
cabal new-bench (#3638)
Workaround: run the benchmark executable directly (see Where are my build products?)
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.
cabal new-haddock (#3535)
Workaround: run cabal act-as-setup -- haddock --builddir=dist-newstyle/build/pkg-0.1 (or execute the Custom setup script directly).
cabal new-install (#3737)
Workaround: no good workaround at the moment. (But note that you no longer need to install libraries before building!)

5.5. 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 --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):

  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)

5.5.1. 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 value:./*.cabal

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)

There is no command line variant of this field; see #3585.

optional-packages: package location list (space or comma-separated)
Default value:./*/*.cabal

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 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. This motivates the default settings:

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

...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 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:

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)

5.5.2. Global configuration options

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

verbose: nat
--verbose=n, -vn
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 $ncpus
--jobs=n, -jn , --jobs=$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.

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 cannot be specified via a cabal.project file.

--project-file=FILE

Specifies the 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 the specified project file is a relative path, 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 cannot be specified via a cabal.project file.

--store-dir=DIR

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

5.5.3. Solver configuration options

The following settings control the behavior of the dependency solver:

constraints: constraints list (comma separated)
--constraint="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

Valid constraints take the same form as for the constraint command line option.

preferences: preference (comma separated)
--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 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.

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 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 pkgs 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 cfg-field: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 new-configure'
-- for storing `--index-state` values.
index-state: 2016-09-24T17:47:48Z

5.5.4. 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

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 at top-level, see #3579.)

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)
--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

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
--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
--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
--enable-optimization
--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 #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: args (space separated)
--configure-option=arg

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, uhc or haskell-suite
--compiler=compiler
Default value:ghc

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
--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: paths (newline or comma separated)
--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.

run-tests: boolean
--run-tests
Default value: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.”

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.

5.5.4.1. Object code options

debug-info: boolean
--enable-debug-info
--disable-debug-info
Since:Cabal 1.22
Default value:False

If the compiler (e.g., GHC 7.10 and later) supports outputing 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 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
--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.

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.

(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
--enable-library-stripping
--disable-library-stripping
Since: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.

5.5.4.2. Executable options

program-prefix: prefix
--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
--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'.

5.5.4.3. 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 1.21
Default value:False

[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.

5.5.4.4. 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 avaiable for iOS and with GHC 8.4 and later for other platforms as well.

5.5.4.5. 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.

5.5.4.6. Profiling options

profiling: boolean
--enable-profiling
--disable-profiling
Since:Cabal 1.21
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 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.

profiling-detail: level
--profiling-detail=level
Since: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, 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.

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

library-profiling-detail: level
--library-profiling-detail=level
Since:Cabal 1.23

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 1.21
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 1.21
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.

5.5.4.7. Coverage options

coverage: boolean
--enable-coverage
--disable-coverage
Since:Cabal 1.21
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 1.21
Default value:False

Deprecated, use coverage.

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

5.5.4.8. Haddock options

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

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

Enables building of Haddock documentation

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

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 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 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.

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

haddock-html: boolean
Default value: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 value:False

Run haddock on all executable programs.

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

haddock-tests: boolean
Default value:False

Run haddock on all test suites.

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

haddock-benchmarks: boolean
Default value:False

Run haddock on all benchmarks.

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

haddock-all: boolean
Default value:False

Run haddock on all components.

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

haddock-internal: boolean
Default value: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).

Default value: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: boolean

Keep temporary files.

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

5.5.5. Advanced global configuration options

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.

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

[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
--logs-dir=DIR
Default value:~/.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.

build-summary: template filepath
--build-summary=TEMPLATE
Default value:~/.cabal/logs/build.log

[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
--local-repo=DIR
Deprecated:

[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
--world-file=FILE
Deprecated:

[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.

5.5.5.1. Advanced solver options

Most users generally won’t need these.

solver: modular
--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
--max-backjumps=N
Default value: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
--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 #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.

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.