Snapshot location¶

2.1.1

This document describes the specification of a snapshot location (in the snapshot or resolver key).

Info

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

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

Via a compiler version, which is a "compiler only" snapshot. This could be, for example:
```
snapshot: ghc-8.6.5
```

Via a URL pointing to a snapshot configuration file, for example:

snapshot: https://raw.githubusercontent.com/commercialhaskell/stackage-snapshots/master/nightly/2018/8/21.yaml`

Via a local file path pointing to a snapshot configuration file, for example:
```
snapshot: my-local-snapshot.yaml
```

Via a convenience synonym, which provides a short form for some common URLs. These are:

GitHub: github:user/repo:path is treated as:

https://raw.githubusercontent.com/user/repo/master/path

LTS Haskell: lts-X.Y is treated (by default) as:

github:commercialhaskell/stackage-snapshots:lts/X/Y.yaml

and, consequently, expands to:

https://raw.githubusercontent.com/commercialhaskell/stackage-snapshots/master/lts/X/Y.yaml

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

github:commercialhaskell/stackage-snapshots:nightly/YYYY/M/D.yaml

and, consequently, expands to:

https://raw.githubusercontent.com/commercialhaskell/stackage-snapshots/master/nightly/YYYY/M/D.yaml

Overriding the default snapshot location base

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:

snapshot:
  url: https://raw.githubusercontent.com/commercialhaskell/stackage-snapshots/master/lts/12/0.yaml
  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.