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Snapshot and package location


This document describes:

  • the specification of a snapshot location (in the resolver key)
  • the specification of a package location (in the extra-deps key and in a snapshot)


Stack uses the Pantry to specify the location of snapshots and packages. Pantry is geared towards reproducible build plans with cryptographically secure specification of snapshots and packages.

Snapshot location

There are essentially four different ways of specifying a snapshot location:

  1. Via a compiler version, which is a "compiler only" snapshot. This could be, for example:

    resolver: ghc-8.6.5`
  2. Via a URL pointing to a snapshot configuration file, for example:

  3. Via a local file path pointing to a snapshot configuration file, for example:

    resolver: my-local-snapshot.yaml
  4. Via a convenience synonym, which provides a short form for some common URLs. These are:

    • GitHub: github:user/repo:path is treated as:
    • LTS Haskell: lts-X.Y is treated (by default) as:

    • Stackage Nightly: nightly-YYYY-MM-DD is treated (by default) as:



By default, LTS Haskell and Stackage Nightly snapshot configurations are retrieved from the stackage-snapshots GitHub repository of user commercialhaskell. The snapshot-location-base option allows a custom location to be set.

For safer, more reproducible builds, you can optionally specify a URL together with a cryptographic hash of its content. For example:

  size: 499143
  sha256: 781ea577595dff08b9c8794761ba1321020e3e1ec3297fb833fe951cce1bee11

size is the number of bytes in the file and sha256 is the file's SHA256 hash. If not provided, the information will automatically be generated and stored in a lock file.

Package location

There are three types of package locations:

  1. Hackage packages
  2. Git and Mecurial repositories
  3. Local or remote archives

All three types support optional tree metadata to be added, which can be used for reproducibility and faster downloads. This information can automatically be generated in a lock file.

Hackage packages

Packages can be stated by a name-version combination. The basic syntax for this is:

- acme-missiles-0.3

Using this syntax, the most recent Cabal file revision available will be used.

You can specify a specific revision number, with 0 being the original file, like this:

- acme-missiles-0.3@rev:0

For safer, more reproducible builds, you can optionally specify the SHA256 hash of the Cabal file's contents, like this:

- acme-missiles-0.3@sha256:2ba66a092a32593880a87fb00f3213762d7bca65a687d45965778deb8694c5d1

You can optionally also specify the size of the Cabal file in bytes, like this:

- acme-missiles-0.3@sha256:2ba66a092a32593880a87fb00f3213762d7bca65a687d45965778deb8694c5d1,631


Specifying package using SHA256 is slightly more resilient in that it does not rely on correct ordering in the package index, while revision number is likely simpler to use. In practice, both should guarantee equally reproducible build plans.

You can also include the Pantry tree information. The following would be generated and stored in the lock file:

- hackage: acme-missiles-0.3@sha256:2ba66a092a32593880a87fb00f3213762d7bca65a687d45965778deb8694c5d1,613
    size: 226
    sha256: 614bc0cca76937507ea0a5ccc17a504c997ce458d7f2f9e43b15a10c8eaeb033

Git and Mercurial repositories

You can give a Git or Mercurial repository at a specific commit, and Stack will clone that repository. For example:

- git:
  commit: 6a86ee32e5b869a877151f74064572225e1a0398
- git:
  commit: "a5f4f3"
- hg:
  commit: da39a3ee5e6b4b0d3255bfef95601890afd80709


It is highly recommended that you only use SHA1 values for a Git or Mercurial commit. Other values may work, but they are not officially supported, and may result in unexpected behavior (namely, Stack will not automatically pull to update to new versions). Another problem with this is that your build will not be deterministic, because when someone else tries to build the project they can get a different checkout of the package.

A common practice in the Haskell world is to use "megarepos", or repositories with multiple packages in various subdirectories. Some common examples include wai and digestive-functors. To support this, you may also specify subdirs for repositories. For example:

- git:
  commit: 2f8a8e1b771829f4a8a77c0111352ce45a14c30f
  - auto-update
  - wai

If unspecified, subdirs defaults to ['.'] meaning looking for a package in the root of the repository. If you specify a value of subdirs, then '.' is not included by default and needs to be explicitly specified if a required package is found in the top-level directory of the repository.



You can specify packages from GitHub repository name using github. For example:

- github: snoyberg/http-client
  commit: a5f4f30f01366738f913968163d856366d7e0342


git-annex is not supported. This is because git archive does not handle symbolic links outside the work tree. It is still possible to use repositories which use git-annex but do not require the annex files for the package to be built.

To do so, ensure that any files or directories stored by git-annex are marked export-ignore in the .gitattributes file in the repository. For further information, see issue #4579.

For example, if the directory fonts/ is controlled by git-annex, use the following line:

fonts export-ignore

Local or remote archives

You can use filepaths referring to local archive files or HTTP or HTTPS URLs referring to remote archive files, either tarballs or ZIP files.


Stack assumes that these archive files never change after downloading to avoid needing to make an HTTP request on each build.

For safer, more reproducible builds, you can optionally specify a cryptographic hash of the archive file.

For example:

- archive:
  - wai
  - warp
- archive: ../acme-missiles-0.3.tar.gz
  sha256: e563d8b524017a06b32768c4db8eff1f822f3fb22a90320b7e414402647b735b