Non-standard project initialization¶
The purpose of this page is to collect information about issues that arise when users either have an existing cabal project or another nonstandard setup such as a private hackage database.
Using a Cabal File¶
New users may be confused by the fact that you must add dependencies to the package’s cabal file, even in the case when you have already listed the package in the
stack.yaml. In most cases, dependencies for your package that are in the Stackage snapshot need only be added to the cabal file. stack makes heavy use of Cabal the library under the hood. In general, your stack packages should also end up being valid cabal-install packages.
Passing Flags to Cabal¶
Any build command,
test, etc. takes a
--flag option which passes flags to cabal. Another way to do this is using the flags field in a
stack.yaml, with the option to specify flags on a per package basis.
As an example, in a
stack.yaml for multi-package project with packages
flags: foo: release: true bar: default: true baz: manual: true
It is also possible to pass the same flag to multiple packages, i.e.
stack build --flag *:necessary
Currently one needs to list all of your modules that interpret flags in the
other-modules section of a cabal file.
cabal-install has a different behavior currently and doesn’t require that the modules be listed. This may change in a future release.
Selecting a Resolver¶
stack init or
stack new will try to default to the current Haskell LTS present on
https://www.stackage.org/snapshots if no snapshot has been previously used locally, and to the latest LTS snapshot locally used for a build otherwise. Using an incorrect resolver can cause a build to fail if the version of GHC it requires is not present.
In order to override the resolver entry at project initialization one can pass
--prefer-nightly. These options will choose the latest LTS or nightly versions locally used.
--resolver option can be used with the name of any snapshots on Stackage, or with
nightly to select the latest versions, disregarding previously used ones. This is not the default so as to avoid unnecessary recompilation time.
Using git Repositories¶
stack has support for packages that reside in remote git locations.
packages: - '.' - location: git: https://github.com/kolmodin/binary commit: 8debedd3fcb6525ac0d7de2dd49217dce2abc0d9
Working with a private Hackage is currently supported in certain situations.
There exist special entries in
stack.yaml that may help you. In a
stack.yaml file, it is possible
to add lines for packages in your database referencing the sdist locations via an
http entry, or to use a
The recommended stack workflow is to use git submodules instead of a private Hackage. Either by using git submodules and listing the directories in the packages section of
stack.yaml, or by adding the private dependencies as git URIs with a commit SHA to the
stack.yaml. This has the large benefit of eliminating the need to manage a Hackage database and pointless version bumps.
For further information see YAML configuration
stack supports intra-package targets, similar to
cabal build COMPONENTS for situations when you don’t want to build every target inside your package.
stack build stack:lib:stack stack test stack:test:stack-integration-test
Note: this does require prefixing the component name with the package name.