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Configuration and customisation

Stack is configured by the content of YAML files. Some Stack operations can also be customised by the use of scripts.

Info

A Haskell package is an organised collection of Haskell code and related files. It is described by a Cabal file or a package.yaml file (which can be used to generate a Cabal file). The package description is itself part of the package. Its file is located in the root directory of a project package or dependency located locally.

A Stack project is a local directory that contains a Stack project-level configuration file (stack.yaml, by default). A project may relate to more than one project package. A single-package project's directory will usually also be the project package's root directory.

YAML configuration

Stack's YAML configuration options break down into project-specific options and non-project-specific options. The former are configured at the project level. The latter are configured at the project level or globally.

The project-level configuration file (stack.yaml, by default) contains project-specific options and may contain non-project-specific options. However, non-project-specific options in the project-level configuration file in the global-project directory (see below) are ignored by Stack.

Stack obtains project-level configuration from one of the following (in order of preference):

  1. A file specified by the --stack-yaml command line option.
  2. A file specified by the STACK_YAML environment variable.
  3. A file named stack.yaml in the current directory or an ancestor directory.
  4. A file name stack.yaml in the global-project directory in the Stack root.

The global configuration files (config.yaml) contain only non-project-specific options. There is a user-specific global confguration file and there may be an optional system-wide global configuration file. If a user-specific global configuration file does not exist, then Stack will create one. An option set in the user-specific file will override a corresponding option set in the system-wide file (if it exists).

The default location of these files depends on the operating system and, in the case of the user-specific file, whether Stack is configured to use the XDG Base Directory Specification. An absolute path to these files can be specified by the STACK_CONFIG and STACK_GLOBAL_CONFIG environment variables, respectively.

The default locations are:

  • system-wide: /etc/stack/config.yaml; and
  • user-specific: config.yaml in the Stack root.

Note

For compatibility with Stack 0.1.5.0 and earlier, if deprecated file /etc/stack/config exists, then Stack will use it instead of /etc/stack/config.yaml.

The default locations are:

  • system-wide: none; and
  • user-specific: config.yaml in the Stack root.

On Unix-like operating systems and Windows, Stack can be configured to follow the XDG Base Directory Specification if the environment variable STACK_XDG is set to any non-empty value. However, Stack will ignore that configuration if the Stack root location has been set on the command line or the STACK_ROOT environment variable exists.

If Stack is following the XDG Base Directory Specification, the location of config.yaml (for user-specific options) is <XDG_CONFIG_HOME>/stack. If the XDG_CONFIG_HOME environment variable does not exist, the default is ~/.config/stack on Unix-like operating systems and %APPDIR%\stack on Windows.

This page is intended to document fully all YAML configuration options. If you identify any inaccuracies or incompleteness, please update the page, and if you're not sure how, open an issue labeled "question".

If you wish to understand the difference between a stack.yaml files and a Cabal file (named <package_name>.cabal), see the stack.yaml vs a Cabal file documentation.

Project-specific configuration

Project-specific configuration options are valid only in a project-level configuration file (stack.yaml, by default).

Each of the Haskell packages to which a Stack project relates is either a project package that is part of the project and located locally or a package on which one or more of the project packages depends (directly or indirectly). The latter is referred to as a dependency and it may be located locally or elsewhere.

Info

Project packages are built by default. Dependencies are only built when needed. Building can target individual components of a project package. The individual components of dependencies cannot be targeted. Test suite and benchmark components of a project package can be built and run. The library and executable components of a dependency, and only those components, are built when the dependency is needed.

In your project-specific options, you specify both which project packages to build and which dependencies to use when building these packages.

A dependency specified as an extra-dep will shadow a package of the same name specified in a snapshot. A project package will shadow a dependency of the same name.

snapshot

Command line equivalent (takes precedence): --snapshot or --resolver option

The snapshot key specifies which snapshot is to be used for this project. A snapshot defines a GHC version, the package version of packages available for installation, and various settings like build flags. It is also called a resolver since a snapshot states how dependencies are resolved. There are currently four snapshot types:

  • LTS Haskell snapshots, e.g. snapshot: lts-22.21
  • Stackage Nightly snapshots, e.g. snapshot: nightly-2024-05-06
  • No snapshot, just use packages shipped with the compiler. For GHC this looks like snapshot: ghc-9.6.5
  • Custom snapshot, via a URL or relative file path. For further information, see the snapshot and package location documentation.

Each of these snapshots will also determine what constraints are placed on the compiler version. See the compiler-check option for some additional control over compiler version.

A package version specified in a snapshot can be shadowed by an extra-dep of the same name or a project package of the same name.

resolver

resolver and snapshot are synonyms. Only one of these keys is permitted, not both.

packages

Default:

packages:
- .

The packages key specifies a list of the project packages that are part of your project. These are specified via paths to local directories. A path is considered relative to the directory containing the project-level configuration file (stack.yaml, by default). For example, if the stack.yaml file is located at /dir1/dir2/stack.yaml, and has:

packages:
- my-package
- dir3/my-other-package

the configuration means "project packages in directories /dir1/dir2/my-package and /dir1/dir2/dir3/my-other-package".

The packages key is optional. The default value, '.', means that the project has a single project package located in the current directory.

A project package will shaddow a dependency of the same name.

A package version specified in a snapshot can be shadowed by an extra-dep of the same name or a project package of the same name.

Each specified project package directory must have a valid Cabal file or Hpack package.yaml file present. Any subdirectories of the directory are not searched for Cabal files. A subdirectory has to be specified as an independent item in the list of project packages.

A project package is different from a dependency (located locally or elsewhere) specified as an extra-dep or via a snapshot. For example:

  • a project package will be built by default by commanding stack build without specific targets. A dependency will only be built if it is needed; and
  • test suites and benchmarks may be built and run for a project package. They are never run for a dependency.

extra-deps

Default: []

The extra-deps key specifies a list of extra dependencies on top of what is defined in the snapshot. A dependency may come from either a Pantry package location or a local file path.

A Pantry package location is one or three different kinds of sources:

  • the package index (Hackage);
  • an archive (a tarball or zip file, either local or over HTTP or HTTPS); or
  • a Git or Mercurial repository.

For further information on the format for specifying a Pantry package location, see the Pantry documentation. For example:

extra-deps:
# The latest revision of a package in the package index (Hackage):
- acme-missiles-0.3
# A specific revision of a package in the package index (Hackage):
- acme-missiles-0.3@rev:0
# An *.tar.gz archive file over HTTPS:
- url: https://github.com/example-user/my-repo/archive/08c9b4cdf977d5bcd1baba046a007940c1940758.tar.gz
  subdirs:
  - my-package
# A Git repository at a specific commit:
- git: https://github.com/example-user/my-repo.git
  commit: '08c9b4cdf977d5bcd1baba046a007940c1940758'
# An archive of files at a point in the history of a GitHub repository
# (identified by a specific commit):
- github: example-user/my-repo
  commit: '08c9b4cdf977d5bcd1baba046a007940c1940758'
  subdirs:
  - my-package

Note

GHC boot packages are special. An extra-dep with the same package name and version as a GHC boot package will be ignored.

Note

The commit: key expects a YAML string. A commit hash, or partial hash, comprised only of digits represents a YAML number, unless it is enclosed in quotation marks.

For a local file path source, the path is considered relative to the directory containing the stack.yaml file. For example, if the stack.yaml is located at /dir1/dir2/stack.yaml, and has:

extra-deps:
- my-package
- dir3/my-other-package

the configuration means "extra-deps packages in directories /dir1/dir2/my-package and /dir1/dir2/dir3/my-other-package".

Note

A local file path that has the format of a package identifier will be interpreted as a reference to a package on Hackage. Prefix it with ./ to avoid that confusion.

Note

A specified extra-dep that does not have the format of a valid Pantry package location (for example, a reference to a package on Hackage that omits the package's version) will be interpreted as a local file path.

An extra-dep will shadow a dependency specified in a snapshot of the same name. An extra-dep can be shadowed by a project package of the same name.

Info

Some Haskell packages published on Hackage, for example base and ghc, are referred to as 'wired-in' to one or more versions of GHC or as 'magic'. They can be distinguished from normal packages by the contents of their Cabal files: GHC's -this-unit-id option is set as the name of the package without a version. For example, the base.cabal for base-4.19.1.0 includes:

-- We need to set the unit id to base (without a version number)
-- as it's magic.
ghc-options: -this-unit-id base

The GHC boot packages that are 'wired-in' cannot be shaddowed with different versions of the same package. Given their dependencies, the use of these boot packages in a build plan may limit what can be specified as an extra-dep.

For example, GHC boot package ghc-9.8.2 has a dependency on process. Its *.conf file identifies the dependency as process-1.6.18.0-4fb7. If package ghc-9.8.2 is part of a build plan and a different version of process is specified as an extra-dep, during a build, Stack will identify that the build plan refers to two versions of process and warn that the build is likely to fail.

Stack treats the following as the names of 'wired-in' packages: base, dph-par, dph-seq, ghc-bignum, ghc-prim, ghc, integer-gmp, integer-simple, interactive, rts and template-haskell.

flags

Default: {}

Command line equivalent (takes precedence): stack build --flag option

Cabal flags can be set for each package separately. For example:

flags:
  package-name:
    flag-name: true

This overrides all Cabal flag specifications (if any) for the specified packages in the snapshot.

Note

For a package included directly in the snapshot, if the Cabal flag specifications differ from the Cabal flag specifications (if any) in the snapshot, then the package will automatically be promoted to be an extra-dep.

Note

In order to set a Cabal flag for a GHC boot package, the package must be specified as an extra-dep.

drop-packages

2.1.1

Default: []

Packages which, when present in the snapshot specified in the snapshot or resolver key, should not be included in our project. This can be used for a few different purposes, e.g.:

  • Ensure that packages you don't want used in your project cannot be used in a package.yaml file (e.g., for license reasons)
  • When using a custom GHC build, avoid incompatible packages (see this comment).
drop-packages:
- buggy-package
- package-with-unacceptable-license

Info

Stackage snapshots LTS Haskell 14.27 (GHC 8.6.5) and earlier, and Nightly 2022-02-08 (GHC 8.8.2) and earlier, included directly the Cabal package. Later snapshots do not include directly that package (which is a GHC boot package).

For the older Stackage snapshots, it could be handy to drop the snapshot-specified Cabal package, to avoid building that version of the package. For the later snapshots, there is no package version to drop.

user-message

If present, specifies a message to be displayed every time the configuration is loaded by Stack. It can serve as a reminder for the user to review the configuration and make any changes if needed. The user can delete this message if the generated configuration is acceptable.

For example, a user-message is inserted by stack init when it omits packages or adds external dependencies, namely:

user-message: ! 'Warning: Some packages were found to be incompatible with the resolver
  and have been left commented out in the packages section.

  Warning: Specified resolver could not satisfy all dependencies. Some external packages
  have been added as dependencies.

  You can omit this message by removing it from stack.yaml

'

custom-preprocessor-extensions

Default: []

Command line equivalent: --customer-preprocessor-extensions option

In order for Stack to be aware of any custom preprocessors you are using, add their extensions here

custom-preprocessor-extensions:
- erb

TODO: Add a simple example of how to use custom preprocessors.

extra-package-dbs

0.1.6.0

Default: []

A list of relative or absolute paths to package databases. These databases will be added on top of GHC's global package database before the addition of other package databases.

Warning

Use of this feature may result in builds that are not reproducible, as Stack has no control over the contents of the extra package databases.

curator

Experimental

2.1.0.1

Default: {}

Configuration intended for use only by the curator tool, which uses Stack to build packages. For given package names (which need not exist in the project), Stack can be configured to ignore (skip) silently building test suites, building benchmarks and/or creating Haddock documentation or to expect that building test suites, building benchmarks and/or creating Haddock documentation will fail.

For example:

curator:
  skip-test:
  - my-package1
  expect-test-failure:
  - my-package2
  skip-bench:
  - my-package3
  expect-benchmark-failure:
  - my-package4
  skip-haddock:
  - my-package5
  expect-haddock-failure:
  - my-package6

Non-project-specific configuration

Non-project configuration options can be included in a project-level configuration file (stack.yaml, by default) or in global configuration files (config.yaml). However, non-project-specific options in the project-level configuration file in the global-project directory are ignored by Stack. The options below are listed in alphabetic order.

allow-different-user

1.0.1.0

Restrictions: POSIX systems only.

Default: false

Command line equivalent (takes precedence): --[no-]allow-different-user flag

Allow users other than the owner of the Stack root to use the Stack installation.

allow-different-user: true

The intention of this option is to prevent file permission problems, for example as the result of a Stack command executed under sudo.

The option is automatically enabled when Stack is re-spawned in a Docker process.

allow-newer

0.1.8.0

Default: false

Whether to ignore version bounds in Cabal files. This also ignores lower bounds. The name allow-newer is chosen to match the commonly-used Cabal option.

allow-newer: true

allow-newer-deps

Experimental

2.9.3

Default: none

Determines a subset of packages to which allow-newer should apply. This option has no effect (but warns) if allow-newer is false.

allow-newer-deps:
  - foo
  - bar

apply-ghc-options

0.1.6.0

Default: locals

Related command line: stack build --ghc-options option

Determines to which packages any GHC command line options specified on the command line are applied. Possible values are: everything (all packages, project packages or otherwise), locals (all project packages, targets or otherwise), and targets (all project packages that are targets).

Note

The use of everything can break invariants about your snapshot database.

Info

Before Stack 0.1.6.0, the default value was targets.

apply-prog-options

2.11.1

Default: locals

Related command line: stack build --PROG-option options

Determines to which packages all and any --PROG-option command line options specified on the command line are applied. Possible values are: everything (all packages, project packages or otherwise), locals (all project packages, targets or otherwise), and targets (all project packages that are targets).

Note

The use of everything can break invariants about your snapshot database.

arch

Default: The machine architecture on which Stack is running.

Command line equivalent (takes precedence): --arch option

Stack identifies different GHC executables by platform (operating system and machine architecture), (optional) GHC variant and (optional) GHC build. See setup-info.

arch sets the machine architecture. Values can be those recognized by Cabal (the library) (which are case-insensitive and include i386, x86_64, and aarch64 / arm64), or other values (which are case-sensitive and treated as an unknown 'other' architecture of the specified name).

By default, Stack will warn the user if the specified machine architecture is an unknown 'other' architecture. The warning can be muted; see notify-if-arch-unknown

Note

The machine architecture on which Stack is running is as classified by Cabal (the library). Cabal does not distinguish between certain architectures. Examples are ppc64/powerpc64/powerpc64le (classified as ppc64) and arm/armel/armeb (classified as arm).

Note

As Cabal (the library) does not distinguish between machine architectures powerpc64 and powerpc64le, the latter can be specified in Stack's configuration as an 'other' architecture, such as arch: ppc64le.

build

1.1.0

Default:

build:
  library-profiling: false
  executable-profiling: false
  library-stripping: true
  executable-stripping: true

  # NOTE: global usage of haddock can cause build failures when documentation is
  # incorrectly formatted.  This could also affect scripts which use Stack.
  haddock: false
  haddock-arguments:

    # Additional arguments passed to haddock. The corresponding command line
    # option is --haddock-arguments. Example of use:
    #
    # haddock-args:
    # - "--css=/home/user/my-css"
    haddock-args: []

  # The corresponding command line flag is --[no-]open.
  open-haddocks: false

  # If Stack is configured to build Haddock documentation, defaults to true.
  haddock-deps: false

  # The configuration is ignored, if haddock-for-hackage: true.
  haddock-internal: false

  # The configuration is ignored, if haddock-for-hackage: true.
  haddock-hyperlink-source: true

  # If specified, implies haddock-internal: false and
  # haddock-hyperlink-source: true. Since Stack 2.15.1.
  haddock-for-hackage: false
  copy-bins: false
  copy-compiler-tool: false
  prefetch: false
  keep-going: false
  keep-tmp-files: false

  # These are inadvisable to use in your global configuration, as they make the
  # Stack build command line behave quite differently.
  force-dirty: false
  test: false
  test-arguments:
    rerun-tests: true   # Rerun successful tests

    # The corresponding command line option is --test-arguments. Example of use:
    #
    # additional-args:
    # - "--fail-fast"
    additional-args: []
    coverage: false
    no-run-tests: false
  bench: false
  benchmark-opts:

    # Example of use:
    #
    # benchmark-arguments: "--csv bench.csv"
    benchmark-arguments: ""
    no-run-benchmarks: false
  reconfigure: false
  cabal-verbosity: normal
  cabal-verbose: false
  split-objs: false
  skip-components: [] # --skip

  # Since Stack 1.8. Starting with Stack 2.0, the default is true
  interleaved-output: true

  # Since Stack 2.13.1. Available options are none, count-only, capped and full.
  progress-bar: capped

  # Since Stack 1.10.
  ddump-dir: ""

Command line equivalents (take precedence): Yes, see below.

Allows setting build options which are usually specified on the command line.

The meanings of these settings correspond directly with the command line flags of the same name. For further information, see the stack build command documentation and the users guide.

casa

2.13.1

Default:

casa:
  enable: true # Use a Casa server?
  repo-prefix: https://casa.stackage.org # Unless casa-repo-prefix is set.
  max-keys-per-request: 1280 # Maximum number of keys per request.

This option specifies whether or not Stack should use a Casa (content-addressable storage archive) server to cache Cabal files and all other files in packages; and, if so, the prefix for the URL used to pull information from the server and the maximum number of keys per request. For further information, see this blog post about Casa and Stack.

repo-prefix replaces casa-repo-prefix (which is deprecated) and has precedence if both keys are set.

casa-repo-prefix

2.3.1

Deprecated in favour of casa, which takes precedence if present.

Default: https://casa.stackage.org

This option specifies the prefix for the URL used to pull information from the Casa server.

color

Command line equivalent (takes precedence): --color option

This option specifies when to use color in output. The option is used as color: <WHEN>, where <WHEN> is 'always', 'never', or 'auto'. On Windows versions before Windows 10, for terminals that do not support color codes, the default is 'never'; color may work on terminals that support color codes.

(The British English spelling (colour) is also accepted. In yaml configuration files, the American spelling is the alternative that has priority.)

compiler

0.1.8.0

Command line equivalent (takes precedence): --compiler option

Overrides the compiler version in the snapshot. Note that the compiler-check flag also applies to the version numbers. This uses the same syntax as compiler snapshots like ghc-9.6.5. This can be used to override the compiler for a Stackage snapshot, like this:

snapshot: lts-22.21
compiler: ghc-9.6.4
compiler-check: match-exact

Building GHC from source

Experimental

2.1.1

Stack supports building the GHC compiler from source, using Hadrian (the build system for GHC). The GHC version to build and to use is defined by a a Git commit ID and a Hadrian "flavour", with the following syntax:

compiler: ghc-git-<commit_id>-<Hadrian_flavour>

In the following example the commit ID is "5be7ad..." and the flavour is "quick":

compiler: ghc-git-5be7ad7861c8d39f60b7101fd8d8e816ff50353a-quick

By default, the code is retrieved from the main GHC repository. If you want to select another repository, use the compiler-repository option:

compiler-repository: git://my/ghc/repository
# default
# compiler-repository: https://gitlab.haskell.org/ghc/ghc.git

Stack does not check the compiler version when it uses a compiler built from source. It is assumed that the built compiler is recent enough as Stack doesn't enable any known workaround to make older compilers work.

Building the compiler can take a very long time (more than one hour). For faster build times, use Hadrian flavours that disable documentation generation.

Bootstrap compiler

Building GHC from source requires a working GHC (known as the bootstrap compiler). As we use a Stack based version of Hadrian (hadrian/build-stack in GHC sources), the bootstrap compiler is configured into hadrian/stack.yaml and fully managed by Stack.

Note

For some commit IDs, the snapshot specified in hadrian/stack.yaml specifies a version of GHC that cannot be used to build GHC. This results in GHC's configure script reporting messages similar to the following before aborting:

checking version of ghc... 9.0.2
configure: error: GHC version 9.2 or later is required to compile GHC.

The resolution is: (1) to specify an alternative snapshot (one that specifies a sufficiently recent version of GHC) on the command line, using Stack's option --snapshot <snapshot>. Stack will use that snapshot when running GHC's configure script; and (2) to set the contents of the STACK environment variable to be stack --snapshot <snapshot>. Hadrian's build-stack script wil refer to that environment variable for the Stack command it uses.

Hadrian prerequisites

The Hadrian build system has certain prerequisites. It requires certain versions of the happy and alex executables on the PATH. Stack will build and install happy and alex, if not already on the PATH.

Hadrian requires, or case use, certain tools or Python packages that do not come with macOS by default and that need to be installed using brew or pip3 (Python). Hadrian's LaTeX documentation also requires the DejaVu fonts to be installed.

brew install python@3.11
# GHC uses a Python script named `boot`.
brew install automake
# Tool for generating GNU Standards-compliant Makefiles.
brew install texinfo
# Official documentation format of the GNU project.
pip3 install -U sphinx
# Sphinx is the Python documentation generator.
brew install --cask mactex
# MacTeX: Full TeX Live distribution with GUI applications

Hadrian requires, or can use, certain MSYS2 or Python packages that do not come with the Stack-supplied MSYS2 by default and need to be installed using pacman (MSYS2) or pip (Python). Hadrian's LaTeX documentation also requires the DejaVu fonts to be installed.

stack exec -- pacman --sync --refresh
# Synchronize MSYS2 package databases
stack exec -- pacman --sync mingw-w64-x86_64-python-pip
# The PyPA recommended tool (pip) for installing Python packages. Also
# installs Python as a dependency. GHC uses a Python script named `boot`.
# The package must be the one from the `mingw64` MSYS2 repository, as Python
# from the `msys` repository cannot interpret Windows file paths correctly.
stack exec -- pacman --sync mingw-w64-x86_64-autotools
# The GNU autotools build system, including `autoreconf`, `aclocal`
# and `make`. GHC uses a sh script named `configure` which is itself created
# from a file named `configure.ac`.
stack exec -- pacman --sync patch
# A utility to apply patch files to original sources.
stack exec -- pacman --sync texinfo
# Utilities to work with and produce manuals, ASCII text, and on-line
# documentation from a single source file, including `makeinfo`.
stack exec -- pacman --sync mingw-w64-x86_64-ca-certificates
# Common CA (certificate authority) certificates.
stack exec -- pip install -U sphinx
# Sphinx is the Python documentation generator.

Hadrian may require certain LaTeX packages and may prompt for these to be installed duing the build process.

Global packages

The GHC compiler you build from sources may depend on unreleased versions of some global packages (e.g. Cabal). It may be an issue if a package you try to build with this compiler depends on such global packages because Stack may not be able to find versions of those packages (on Hackage, etc.) that are compatible with the compiler.

The easiest way to deal with this issue is to drop the offending packages as follows. Instead of using the packages specified in the snapshot, the global packages bundled with GHC will be used.

drop-packages:
- Cabal
- ...

Another way to deal with this issue is to add the relevant packages as extra-deps built from source. To avoid mismatching versions, you can use exactly the same commit id you used to build GHC as follows:

extra-deps:
- git: https://gitlab.haskell.org/ghc/ghc.git
  commit: '5be7ad7861c8d39f60b7101fd8d8e816ff50353a'
  subdirs:
    - libraries/Cabal/Cabal
    - libraries/...

compiler-check

0.1.4.0

Default: match-minor

Specifies how the compiler version in the snapshot is matched against concrete versions. Valid values:

  • match-minor: make sure that the first three components match, but allow patch-level differences. For example< 7.8.4.1 and 7.8.4.2 would both match 7.8.4. This is useful to allow for custom patch levels of a compiler.
  • match-exact: the entire version number must match precisely
  • newer-minor: the third component can be increased, e.g. if your snapshot is ghc-7.10.1, then 7.10.2 will also be allowed. This was the default up through Stack 0.1.3

concurrent-tests

0.1.2.0

Default: true

This option specifies whether test suites should be executed concurrently with each other. The default is true since this is usually fine and it often means that tests can complete earlier. However, if some test suites require exclusive access to some resource, or require a great deal of CPU or memory resources, then it makes sense to set this to false.

concurrent-tests: false

configure-options

2.1.1

Related command line (takes precedence): stack build --PROG-option options

configure-options can specify Cabal (the library) options (including --PROG-option or --PROG-options options) for the configure step of the Cabal build process for a named package, all project packages that are targets (using the $targets key), all project packages (targets or otherwise) (using the $locals key), or all packages (project packages or otherwise) (using the $everything key).

configure-options:
  $everything:
  - --with-gcc
  - /some/path
  $locals:
  - --happy-option=--ghc
  $targets:
  # Only works on platforms where GHC supports linking against shared Haskell
  # libraries:
  - --enable-executable-dynamic
  my-package:
  - --another-flag

On platforms where GHC supports linking against shared Haskell libraries (that currently excludes Windows), Cabal's --enable-executable-dynamic flag (which implies --enable-shared, unless --disable-shared is specified) links dependent Haskell libraries into executables dynamically.

connection-count

Default: 8

Integer indicating how many simultaneous downloads are allowed to happen.

default-template

Default: new-template in the stack-templates repository.

This option specifies which template to use with stack new, when none is specified. Other templates are listed in the stack-templates repository. See the output of stack templates.

docker

Command line equivalents: --docker-* flags and options (see stack --docker-help for details).

For further information, see the Docker integration documentation.

dump-logs

1.3.0

Default: warning

Command line equivalent (takes precedence): --[no-]dump-logs flag

In the case of non-interleaved output and more than one target package, Stack sends the build output from GHC for each target package to a log file, unless an error occurs that prevents that. For further information, see the stack build --[no-]interleaved-output flag documentation.

The value of the dump-logs key controls what, if any, log file content is sent ('dumped') to the standard error stream of the console at the end of the build. Possible values are:

dump-logs: none    # don't dump the content of any log files
dump-logs: warning # dump the content of any log files that include GHC warnings
dump-logs: all     # dump the content of all log files

At the command line, --no-dump-logs is equivalent to dump-logs: none and --dump-logs is equivalent to dump-logs: all.

If GHC reports an error during the build and a log file is created, that build output will be included in the log file. Stack will also report errors during building to the standard error stream. That stream can be piped to a file. For example, for a file named stderr.log:

stack --no-dump-logs --color always build --no-interleaved-output 2> stderr.log

extra-include-dirs

Default: []

Command line equivalent: --extra-include-dirs option (repeat for each directory)

A list of extra paths to be searched for header files. Paths should be absolute

extra-include-dirs:
- /opt/foo/include

Since these are system-dependent absolute paths, it is recommended that you specify these in your config.yaml file. If you control the build environment in your project's stack.yaml, perhaps through docker or other means, then it may well make sense to include these there as well.

extra-lib-dirs

Default: []

Command line equivalent: --extra-lib-dirs option (repeat for each directory)

A list of extra paths to be searched for libraries. Paths should be absolute

extra-lib-dirs:
- /opt/foo/lib

Since these are system-dependent absolute paths, it is recommended that you specify these in your config.yaml file. If you control the build environment in your project's stack.yaml, perhaps through Docker or other means, then it may well make sense to include these there as well.

extra-path

0.1.4.0

This option specifies additional directories to prepend to the PATH. These will be used when resolving the location of executables, and will also be visible in the PATH of processes run by Stack.

For example, to prepend /path-to-some-dep/bin to your PATH:

extra-path:
- /path-to-some-dep/bin

Other paths added by Stack - things like the project's binary directory and the compiler's binary directory - will take precedence over those specified here (the automatic paths get prepended).

ghc-build

1.3.0

Default: standard

Command line equivalent (takes precedence): --ghc-build option

Stack identifies different GHC executables by platform (operating system and machine architecture), (optional) GHC variant and (optional) GHC build. See setup-info.

ghc-build specifies a specialized architecture for the GHC executable. Normally this is determined automatically, but it can be overridden. Possible arguments include standard, gmp4, nopie, tinfo6, tinfo6-libc6-pre232, tinfo6-nopie, ncurses6, int-native and integersimple.

ghc-options

0.1.4.0

Default: {}

Related command line (takes precedence): stack build --ghc-options option

GHC command line options can be specified for a package in its Cabal file (including one created from a package.yaml file). This option augments and, if applicable (see below), overrides any such GHC command line options.

ghc-options can specify GHC command line options for a named package, all project packages that are targets (using the $targets key), all project packages (targets or otherwise) (using the $locals key), or all packages (project packages or otherwise) (using the $everything key).

ghc-options:
  "$everything": -O2
  "$locals": -Wall
  "$targets": -Werror
  some-package: -DSOME_CPP_FLAG

GHC's command line options are order-dependent and evaluated from left to right. Later options can override the effect of earlier ones. Stack applies options (as applicable) in the order of $everything, $locals, $targets, and then those for the named package. Any GHC command line options for a package specified at Stack's command line are applied after those specified in Stack's YAML configuration files.

Since Stack 1.6.1, setting a GHC options for a specific package will automatically promote it to a project package (much like setting a custom package flag). However, setting options via $everything on all flags will not do so (see GitHub discussion for reasoning). This can lead to unpredictable behavior by affecting your snapshot packages.

Info

Before Stack 1.6.1, the key * (then deprecated) had the same function as the key $everything.

ghc-variant

0.1.5.0

Default: standard

Command line equivalent (takes precedence): --ghc-variant option

Stack identifies different GHC executables by platform (operating system and machine architecture), (optional) GHC variant and (optional) GHC build. See setup-info.

ghc-variant specifies a variant of the GHC executable. Known values are:

  • standard: Use the standard GHC binary distribution
  • int-native: From GHC 9.4.1, use a GHC bindist that uses the Haskell-native big-integer backend. For further information, see this article.
  • integersimple: Use a GHC bindist that uses integer-simple instead of GMP
  • any other value: Use a custom GHC bindist. You should specify setup-info or setup-info-locations so stack setup knows where to download it, or pass the stack setup --ghc-bindist argument on the command-line

This option is incompatible with system-ghc: true.

hackage-base-url

1.9.1

Default: https://hackage.haskell.org/

Sets the address of the Hackage server to upload the package to.

hackage-base-url: https://hackage.example.com/

hide-source-paths

Default: true ( 2.1.1)

Whether to use the -fhide-source-paths option by default for GHC >= 8.2:

hide-source-paths: false

Build output when enabled:

...
[1 of 2] Compiling Lib
[2 of 2] Compiling Paths_test_pr
...

Build output when disabled:

...
[1 of 2] Compiling Lib              ( src/Lib.hs, .stack-work/dist/x86_64-linux-tinfo6/Cabal-2.4.0.1/build/Lib.o )
...

hide-th-loading

Default: true

Strip out the "Loading ..." lines from GHC build output, produced when using Template Haskell.

ignore-revision-mismatch

(Removed 1.11)

This flag was introduced in Stack 1.6, and removed on the move to Pantry. You will receive a warning if this configuration value is set.

install-ghc

Default: true ( 1.5.0)

Command line equivalent (takes precedence): --[no-]install-ghc flag

Whether or not to automatically install GHC when necessary.

jobs

Default: the number of CPUs (cores) that the machine has.

Command line equivalent (takes precedence): -j, --jobs option

Specifies the number of concurrent jobs (principally, Stack actions during building - see further below) to run.

When building GHC from source, specifies the -j[<n>] flag of GHC's Hadrian build system.

In some circumstances, the default can cause some machines to run out of memory during building. If those circumstances arise, specify jobs: 1.

This configuration option is distinct from GHC's own -j[<n>] flag, which relates to parallel compilation of modules within a package.

local-bin-path

Default (on Unix-like operating systems): ~/.local/bin

Default (on Windows): %APPDATA%\local\bin

Command line equivalent (takes precedence): --local-bin-path option

Specifies the target directory for stack build --copy-bins and stack install. An absolute or relative path can be specified.

If the project-level configuration is provided in the global-project directory in the Stack root, a relative path is assumed to be relative to the current directory. Otherwise, it is assumed to be relative to the directory of the project-level configuration file.

local-programs-path

1.3.0

This overrides the location of the Stack 'programs' directory, where tools like GHC get installed. The path must be an absolute one.

Stack's defaults differ between Unix-like operating systems and Windows.

Default: programs directory in the Stack root.

Default: %LOCALAPPDATA%\Programs\stack, if the %LOCALAPPDATA% environment variable exists. Otherwise, the programs directory in the Stack root.

The MSYS2 tool is also installed in the Stack 'programs' directory.

Warning

If there is a space character in the path to Stack's 'programs' directory this may cause problems with building packages that make use of the GNU project's autoconf package and configure shell script files. That may be the case particularly if there is no corresponding short name ('8 dot 3' name) for the directory in the path with the space (which may be the case if '8 dot 3' names have been stripped or their creation not enabled by default). If there are problems building, it will be necessary to specify an alternative path that does not contain space characters. Examples of packages on Hackage that make use of configure are network and process.

modify-code-page

0.1.6.0

Restrictions: Windows systems only.

Default: true

Command line equivalent (takes precedence): --[no-]modify-code-page flag

Whether to modify the code page for UTF-8 output.

modify-code-page: false

nix

0.1.10.0

Default:

nix:
  enable: false # Except on NixOS, where `enable: true`
  pure: true
  packages: []
  shell-file:
  nix-shell-options: []
  path: []
  add-gc-roots: false

Command line equivalents: --nix-* flags and options (see stack --nix-help for details).

For further information, see the Nix integration documentation.

notify-if-arch-unknown

2.15.1

Default: true

If the specified machine architecture value is unknown to Cabal (the library), should Stack notify the user of that?

notify-if-cabal-untested

2.15.1

Default: true

If Stack has not been tested with the version of Cabal (the library) that has been found, should Stack notify the user of that?

notify-if-ghc-untested

2.15.1

Default: true

If Stack has not been tested with the version of GHC that is being used, should Stack notify the user of that?

notify-if-nix-on-path

2.15.1

Default: true

If Stack's integration with the Nix package manager is not enabled, should Stack notify the user if a nix executable is on the PATH?

package-index

2.9.3

Default:

package-index:
  download-prefix: https://hackage.haskell.org/
  hackage-security:
    keyids:
    - 0a5c7ea47cd1b15f01f5f51a33adda7e655bc0f0b0615baa8e271f4c3351e21d
    - 1ea9ba32c526d1cc91ab5e5bd364ec5e9e8cb67179a471872f6e26f0ae773d42
    - 2c6c3627bd6c982990239487f1abd02e08a02e6cf16edb105a8012d444d870c3
    - 51f0161b906011b52c6613376b1ae937670da69322113a246a09f807c62f6921
    - fe331502606802feac15e514d9b9ea83fee8b6ffef71335479a2e68d84adc6b0
    key-threshold: 3
    ignore-expiry: true

Takes precedence over the package-indices key, which is deprecated.

Specify the package index. The index must use the Hackage Security format. This setting is most useful for providing a mirror of the official Hackage server for

  • bypassing a firewall; or
  • faster downloads.

If the setting specifies an index that does not mirror Hackage, it is likely that will result in significant breakage, including most snapshots failing to work.

In the case of Hackage, the keys of its root key holders are contained in the haskell-infra/hackage-root-keys repository. The Hackage package index is signed. A signature is valid when three key holders have signed. The Hackage timestamp is also signed. A signature is valid when one key holder has signed.

If the hackage-security key is absent, the Hackage Security configuration will default to that for the official Hackage server.

key-threshold specifies the minimum number of keyholders that must have signed the package index for it to be considered valid.

ignore-expiry specifies whether or not the expiration of timestamps should be ignored.

package-indices

2.1.1

Deprecated in favour of package-index, which takes precedence if present.

Default:

package-indices:
- download-prefix: https://hackage.haskell.org/
  hackage-security:
    keyids:
    - 0a5c7ea47cd1b15f01f5f51a33adda7e655bc0f0b0615baa8e271f4c3351e21d
    - 1ea9ba32c526d1cc91ab5e5bd364ec5e9e8cb67179a471872f6e26f0ae773d42
    - 2c6c3627bd6c982990239487f1abd02e08a02e6cf16edb105a8012d444d870c3
    - 51f0161b906011b52c6613376b1ae937670da69322113a246a09f807c62f6921
    - fe331502606802feac15e514d9b9ea83fee8b6ffef71335479a2e68d84adc6b0
    key-threshold: 3
    ignore-expiry: true

Info

Before Stack 2.1.3, the default for ignore-expiry was false. For more information, see issue #4928.

Info

Before Stack 2.1.1, Stack had a different approach to package-indices. For more information, see issue #4137.

Specify the package index. For further information, see the package-index documentation.

pvp-bounds

0.1.5.0

Default: none

Command line equivalent (takes precedence): stack sdist --pvp-bounds option or stack upload --pvp-bounds option

Warning

As of Stack 1.6.0, this feature does not reliably work, due to issues with the Cabal library's printer. Stack will generate a warning when a lossy conversion occurs, in which case you may need to disable this setting. For further information, see issue #3550.

When using the sdist and upload commands, this setting determines whether the Cabal file's dependencies should be modified to reflect PVP lower and upper bounds.

Basic use

Values are none (unchanged), upper (add upper bounds), lower (add lower bounds), and both (and upper and lower bounds). The algorithm Stack follows is:

  • If an upper or lower bound (other than >= 0 - 'any version') already exists on a dependency, it is left alone
  • When adding a lower bound, Stack looks at the current version specified by stack.yaml, and sets it as the lower bound (e.g., foo >= 1.2.3)
  • When adding an upper bound, Stack sets it as less than the next major version (e.g., foo < 1.3)
pvp-bounds: none

For further information, see the announcement blog post.

Use with Cabal file revisions

1.5.0

Each of the values listed above supports adding -revision to the end of the value, e.g. pvp-bounds: both-revision. This means that, when uploading to Hackage, Stack will first upload your tarball with an unmodified Cabal file, and then upload a Cabal file revision with the PVP bounds added.

This can be useful - especially combined with the Stackage no-revisions feature - as a method to ensure PVP compliance without having to proactively fix bounds issues for Stackage maintenance.

recommend-stack-upgrade

2.1.1

Default: true

When Stack notices that a new version of Stack is available, should it notify the user?

rebuild-ghc-options

0.1.6.0

Default: false

Should Stack rebuild a package when its GHC options change?

The default value reflects that, in most cases, GHC options are used to affect optimization levels and warning behavior, for which GHC does not recompile the modules.

Info

Before Stack 0.1.6.0, Stack rebuilt a package when its GHC options changed.

require-stack-version

Default: "-any"

Require a version of Stack within the specified range (cabal-style) to be used for this project. Example: require-stack-version: "== 0.1.*"

save-hackage-creds

1.5.0

Default: true

Controls whether, when using stack upload, the user's Hackage username and password are stored in a local file.

save-hackage-creds: true

setup-info

0.1.5.0

The setup-info dictionary specifies download locations for tools to be installed during set-up, such as GHC or, on Windows, 7z and MSYS2. The dictionary maps ('Tool', 'Platform', 'Version') to the location where it can be obtained. For example, mapping (GHC, 64-bit Windows, 9.2.3) to the URL hosting the archive file for GHC's installation.

Possible usages of this configuration option are:

  1. Using Stack offline or behind a firewall.
  2. Extending the tools known to Stack, such as cutting-edge versions of GHC or builds for custom Linux distributions (for use with the ghc-variant option).

By default, Stack obtains the dictionary from stack-setup-2.yaml.

The setup-info dictionary is constructed in the following order:

  1. setup-info in the YAML configuration - inline configuration
  2. --setup-info-yaml command line arguments - URLs or paths. Multiple locations may be specified.
  3. setup-info-locations in the YAML configuration - URLs or paths. See further below.

The format of this key is the same as in the default stack-setup-2.yaml. For example, GHC 9.2.3 of custom variant myvariant (see further below) on 64-bit Windows:

setup-info:
  ghc:
    windows64-custom-myvariant:
      9.2.3:
        url: "https://example.com/ghc-9.2.3-x86_64-unknown-mingw32-myvariant.tar.xz"

'Platforms' are pairs of an operating system and a machine architecture (for example, 32-bit i386 or 64-bit x86-64) (represented by the Cabal.Distribution.Systems.Platform type). Stack currently (version 2.15.1) supports the following pairs in the format of the setup-info key:

Operating system I386 arch X86_64 arch Other machine architectures
Linux linux32 linux64 AArch64: linux-aarch64, Arm: linux-armv7, Sparc: linux-sparc
OSX macosx macosx
Windows windows32 windows64
FreeBSD freebsd32 freebsd64 AArch64: freebsd-aarch64
OpenBSD openbsd32 openbsd64

For GHC, the distinguishing 'Version' in the key format includes a 'tag' for any (optional) GHC variant (see ghc-variant) and a further 'tag' for any (optional) specialised GHC build (see ghc-build).

The optional variant 'tag' is either -integersimple or -custom-<custom_variant_name>.

For example, for GHC 9.0.2 of specialised GHC build tinfo6 on x86_64 Linux:

setup-info:
  ghc:
    linux64-tinfo6:
      9.0.2:
        url: "http://downloads.haskell.org/~ghc/9.0.2/ghc-9.0.2a-x86_64-fedora27-linux.tar.xz"
        content-length: 237286244
        sha1: affc2aaa3e6a1c446698a884f56a0a13e57f00b4
        sha256: b2670e9f278e10355b0475c2cc3b8842490f1bca3c70c306f104aa60caff37b0

On Windows, the required 7z executable and DLL tools are represented in the format of the setup-info key simply by sevenzexe-info and sevenzdll-info.

This configuration adds the specified setup information metadata to the default. Specifying this configuration does not prevent the default stack-setup-2.yaml from being consulted as a fallback. If, however, you need to replace the default setup-info dictionary, use the following:

setup-info-locations: []

setup-info-locations

2.3.1

Command line equivalent (takes precedence): --setup-info-yaml option

By way of introduction, see the setup-info option. This option specifies the location(s) of setup-info dictionaries.

The first location which provides a dictionary that specifies the location of a tool - ('Tool', 'Platform', 'Version') - takes precedence. For example, you can extend the default tools, with a fallback to the default setup-info location, as follows:

setup-info-locations:
- C:/stack-offline/my-stack-setup.yaml
- relative/inside/my/project/setup-info.yaml
- \\smbShare\stack\my-stack-setup.yaml
- http://stack-mirror.com/stack-setup.yaml
# Fallback to the default location
- https://github.com/commercialhaskell/stackage-content/raw/master/stack/stack-setup-2.yaml

Stack only refers to the default setup-info location if no locations are specified in the setup-info-locations configuration or on the command line using the --setup-info-yaml option.

For example, both of the following will cause stack setup not to consult the default setup-info location:

setup-info-locations:
- C:/stack-offline/my-stack-setup.yaml

and

setup-info-locations: []

Relative paths are resolved relative to the stack.yaml file (either the one in the local project or the global stack.yaml).

Relative paths may also be used for the installation paths to tools (such as GHC or 7z). This allows vendoring the tools inside a monorepo (a single repository storing many projects). For example:

Directory structure:

- src/
- installs/
  - my-stack-setup.yaml
  - 7z.exe
  - 7z.dll
  - ghc-9.2.3.tar.xz
- stack.yaml

In the project's stack.yaml:

setup-info-locations:
- installs/my-stack-setup.yaml

In installs/my-stack-setup.yaml:

sevenzexe-info:
  url: "installs/7z.exe"

sevenzdll-info:
  url: "installs/7z.dll"

ghc:
  windows64:
    9.2.3:
      url: "installs/ghc-9.2.3.tar.xz"

skip-ghc-check

Default: false

Command line equivalent (takes precedence): --[no-]skip-ghc-check flag

Should we skip the check to confirm that your system GHC version (on the PATH) matches what your project expects?

skip-msys

0.1.2.0

Restrictions: Windows systems only

Default: false

Command line equivalent (takes precedence): --[no-]skip-msys flag

Skips checking for the Stack-supplied MSYS2 (and installing that MSYS2, if it is not installed) when Stack is setting up the environment.

skip-msys: true

Note

Usually, the use of this option does not make sense in project-level configuration and it is used only in global configuration.

snapshot-location-base

2.5.1

Default: https://raw.githubusercontent.com/commercialhaskell/stackage-snapshots/master/ (as set in the pantry library)

Command line equivalent (takes precedence): --snapshot-location-base option

Sets the base location of the LTS Haskell or Stackage Nightly snapshots.

For example:

snapshot-location-base: https://example.com/snapshots/location/

has the following effect:

  • lts-X.Y expands to https://example.com/snapshots/location/lts/X/Y.yaml
  • nightly-YYYY-MM-DD expands to https://example.com/snapshots/location/nightly/YYYY/M/D.yaml

This key is convenient in setups that restrict access to GitHub, for instance closed corporate setups. In this setting, it is common for the development environment to have general access to the internet, but not for testing/building environments. To avoid the firewall, one can run a local snapshots mirror and then use a custom snapshot-location-base in the closed environments only.

stack-colors

Command line equivalent (takes precedence): --stack-colors option

Stack uses styles to format some of its output. The default styles do not work well with every terminal theme. This option specifies Stack's output styles, allowing new styles to replace the defaults. The option is used as stack-colors: <STYLES>, where <STYLES> is a colon-delimited sequence of key=value, 'key' is a style name and 'value' is a semicolon-delimited list of 'ANSI' SGR (Select Graphic Rendition) control codes (in decimal). Use the command stack ls stack-colors --basic to see the current sequence.

The 'ANSI' standards refer to (1) standard ECMA-48 'Control Functions for Coded Character Sets' (5th edition, 1991); (2) extensions in ITU-T Recommendation (previously CCITT Recommendation) T.416 (03/93) 'Information Technology – Open Document Architecture (ODA) and Interchange Format: Character Content Architectures' (also published as ISO/IEC International Standard 8613-6); and (3) further extensions used by 'XTerm', a terminal emulator for the X Window System. The 'ANSI' SGR codes are described in a Wikipedia article and those codes supported on current versions of Windows in Microsoft's documentation.

For example, users of the popular Solarized Dark terminal theme might wish to set the styles as follows:

stack-colors: error=31:good=32:shell=35:dir=34:recommendation=32:target=95:module=35:package-component=95:secondary=92:highlight=32
In respect of styles used in verbose output, some of that output occurs before the configuration file is processed.

(The British English spelling (colour) is also accepted. In YAML configuration files, the American spelling is the alternative that has priority.)

stack-developer-mode

2.3.3

Default (official distributed binaries): false

Default (built from source): true

Turns on a mode where some messages are printed at WARN level instead of DEBUG level, especially useful for developers of Stack itself.

stack-developer-mode: false

system-ghc

Default: false, unless the Docker or Nix integration is enabled.

Command line equivalent (takes precedence): --[no-]system-ghc flag

Enables or disables using the GHC available on the PATH. (Make sure PATH is explicit, i.e., don't use ~.) Useful to enable if you want to save the time, bandwidth or storage space needed to setup an isolated GHC.

In a Nix-enabled configuration, Stack is incompatible with system-ghc: false.

# Turn on system GHC
system-ghc: true

templates

Command line equivalent (takes precedence): stack new --param <key>:<value> (or -p) option

Templates used with stack new have a number of parameters that affect the generated code. These can be set for all new projects you create. The result of them can be observed in the generated LICENSE and Cabal files. The value for all of these parameters must be strings.

The parameters are: author-email, author-name, category, copyright, year and github-username.

  • author-email - sets the maintainer property in Cabal
  • author-name - sets the author property in Cabal and the name used in LICENSE
  • category - sets the category property in Cabal. This is used in Hackage. For examples of categories see Packages by category. It makes sense for category to be set on a per project basis because it is uncommon for all projects a user creates to belong to the same category. The category can be set per project by passing -p "category:value" to the stack new command.
  • copyright - sets the copyright property in Cabal. It is typically the name of the holder of the copyright on the package and the year(s) from which copyright is claimed. For example: Copyright (c) 2023-2024 Joe Bloggs
  • year - if copyright is not specified, year and author-name are used to generate the copyright property in Cabal. If year is not specified, it defaults to the current year.
  • github-username - used to generate homepage and source-repository in Cabal. For instance github-username: myusername and stack new my-project new-template would result:
homepage: http://github.com/myusername/my-project#readme

source-repository head
  type: git
  location: https://github.com/myusername/my-project

These properties can be set in config.yaml as follows:

templates:
  params:
    author-name: Your Name
    author-email: youremail@example.com
    category: Your Projects Category
    copyright: 'Copyright (c) 2024 Your Name'
    github-username: yourusername

Additionally, stack new can automatically initialize source control repositories in the directories it creates. Source control tools can be specified with the scm-init option. At the moment, only git is supported.

templates:
  scm-init: git

urls

Default:

urls:
  latest-snapshot: https://stackage-haddock.haskell.org/snapshots.json

Customize the URLs where Stack looks for snapshot build plans.

Note

The default for Stack 1.3.0 to 2.15.3 was https://s3.amazonaws.com/haddock.stackage.org/snapshots.json. Following the handover of the Stackage project to the Haskell Foundation in early 2024, the file at that URL may not be up to date. Users of those versions of Stack should configure the URL to be the default above.

with-gcc

Command line equivalent (takes precedence): --with-gcc option

Specify a path to GCC explicitly, rather than relying on the normal path resolution.

with-gcc: /usr/local/bin/gcc-5

with-hpack

Command line equivalent (takes precedence): --with-hpack option

Use an Hpack executable, rather than Stack's in-built version of the Hpack functionality.

with-hpack: /usr/local/bin/hpack

work-dir

0.1.10.0

Default: .stack-work

Command line equivalent (takes precedence): --work-dir option

Environment variable alternative (lowest precedence): STACK_WORK

work-dir specifies the path of Stack's work directory, within a local project or package directory. The path must be a relative one, relative to the root directory of the project or package. The relative path cannot include a .. (parent directory) component.

Customisation scripts

GHC installation customisation

2.9.1

On Unix-like operating systems and Windows, Stack's installation procedure can be fully customised by placing a sh shell script (a 'hook') in the Stack root directory at hooks/ghc-install.sh. On Unix-like operating systems, the script file must be made executable. The script is run by the sh application (which is provided by MSYS2 on Windows).

The script must return an exit code of 0 and the standard output must be the absolute path to the GHC binary that was installed. Otherwise Stack will ignore the script and possibly fall back to its own installation procedure.

When system-ghc: true, the script is not run. That is because the two mechanisms reflect distinct concepts, namely:

  • system-ghc: true causes Stack to search the PATH for a version of GHC; and

  • hooks/ghc-install.sh causes Stack to execute a script that is intended to send to standard output a path to a version of GHC. The path in question may or may not be in the PATH. The script may also do other things, including installation.

When install-ghc: false, the script is still run. That allows you to ensure that only your script will install GHC and Stack won't default to its own installation logic, even when the script fails.

The following environment variables are always available to the script:

  • HOOK_GHC_TYPE = "bindist" | "git" | "ghcjs"

For "bindist", additional variables are:

  • HOOK_GHC_VERSION = <ver>

For "git", additional variables are:

  • HOOK_GHC_COMMIT = <commit>
  • HOOK_GHC_FLAVOR = <flavor>

For "ghcjs", additional variables are:

  • HOOK_GHC_VERSION = <ver>
  • HOOK_GHCJS_VERSION = <ver>

An example script is:

#!/bin/sh

set -eu

case $HOOK_GHC_TYPE in
    bindist)
        # install GHC here, not printing to stdout, e.g.:
        #   command install $HOOK_GHC_VERSION >/dev/null
        ;;
    git)
        >&2 echo "Hook doesn't support installing from source"
        exit 1
        ;;
    *)
        >&2 echo "Unsupported GHC installation type: $HOOK_GHC_TYPE"
        exit 2
        ;;
esac

echo "location/to/ghc/executable"

If the following script is installed by GHCup, GHCup makes use of it, so that if Stack needs a version of GHC, GHCup takes over obtaining and installing that version:

#!/bin/sh

set -eu

case $HOOK_GHC_TYPE in
    bindist)
        ghcdir=$(ghcup whereis --directory ghc "$HOOK_GHC_VERSION" || ghcup run --ghc "$HOOK_GHC_VERSION" --install) || exit 3
        printf "%s/ghc" "${ghcdir}"
        ;;
    git)
        # TODO: should be somewhat possible
        >&2 echo "Hook doesn't support installing from source"
        exit 1
        ;;
    *)
        >&2 echo "Unsupported GHC installation type: $HOOK_GHC_TYPE"
        exit 2
        ;;
esac