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# Testing a new stack resolver

When there’s been a new GHC release, it can take a little while for there to be a stack resolver for it. The following procedure can be used for some local testing if you want to get ahead of the game1.

## Where stack looks for resolvers

If you execute the command,

    \$stack setup --resolver ghc-x.y.z

you’ll see something like

    No setup information found for ghc-x.y.z on your platform.

if there isn’t yet a resolver for ghc-x.y.z.

The default set of resolvers stack “knows about” are those enumerated in the file stack-setup-2.yaml in the commericalhaskell/stackage-content repository.

## Create a local stack setup file

• size (in bytes):
       stat -f%z ghc-x.y.z-x86_64-apple-darwin.tar.xz
• SHA1 hash:
       shasum -a 1 ghc-x.y.z-x86_64-apple-darwin.tar.xz
• SHA256 hash:
       shasum -a 256 ghc-x.y.z-x86_64-apple-darwin.tar.xz
• Now, create stack-setup-2-ghc-x.y.z.yaml with contents along the lines of
        ghc:
macosx:
x.y.z:
content-length: 177152992
sha1: 2dbd726860ed2c0ea04c7aca29c22df20b952ee1
sha256: f2e8366fd3754dd9388510792aba2d2abecb1c2f7f1e5555f6065c3c5e2ffec4

Update: Here’s an even easier way.

    ghc:
macosx:
x.y.z:
url: /path/to/ghc-x.y.z-x86_64-apple-darwin.tar.xz

## Install GHC version x.y.z via the setup file

The following stack setup command will use the setup file created above to download and install ghc-x.y.z:

  stack --setup-info-yaml stack-setup-2-ghc-x.y.z.yaml --resolver ghc-x.y.z setup

Once stack has got GHC installed, there’s no further any need to pass a setup-info-yaml argument to subsequent stack commands, it’s ready to go!

1. Kindly explained to me by Mike Pilgrem in this ticket. This note is biased towards my needs on macOS. See the linked issue for further details especially for Windows installations.↩︎