tweag / stackage-curator

Tools for curating Stackage package sets and building reusable package databases

stackage-curator

This repository contains the code for curating Stackage package sets and building reusable package databases. It was originally simply called the stackage package and was part of the stackage repository, but since this is a tool very few people need to use, we split it into its own package with a name to indicate it's limited usage (curators only).

More information on Stackage:

• Stackage Homepage
• Main stackage repo

Code explanation

We start off with constraints. Constraints state things like "package X has a given version range," who the maintainer is for a package, the description of the system/compiler being used, etc. BuildConstraints describes the build as a whole, whereas PackageConstraints describes the constraints on an individual package.

There are two primary ways of getting a BuildConstraints. defaultBuildConstraints inspects the first GHC in the PATH environment variable to determine GHC version, core packages, core tools, etc. It then uses the Stackage.Config module to extract information on additional packages to be installed. The secondary approach is in Stackage2.UpdateBuildPlan, which will be discussed later.

BuildConstraints does not specify a build completely. That is given by a BuildPlan, which is similarly broken down into BuildPlan and PackagePlan. In order to get a BuildPlan, we need two pieces of information: the BuildConstraints, and a package index. The package index (usually downloaded from Hackage) is a collection of all of the cabal files available.

By applying a BuildConstraints to a package index (via newBuildPlan), we get a proposed BuildPlan. There is no guarantee that this BuildPlan is valid. To validate it, we use checkBuildPlan. A BuildPlan is an instance of both ToJSON and FromJSON, and therefore can be serialized to a file for later use.

When dealing with LTS Haskell, we want to be able to take a BuildPlan, and update to a newer BuildPlan that keeps all packages at the same major version. updateBuildConstraints turns a BuildPlan into a new BuildConstraints with that restriction, and updateBuildPlan applies newBuildPlan to that result. As mentioned previously: this is not a validated result, and therefore checkBuildPlan must be used.

A BuildPlan can be acted on. This is done to check that all packages compile together, run relevant test suites, test Haddock documentation is correct, and produce as artifacts both a self-contained GHC binary package database and a set of Haddock documentation. (Not yet implemented.)

A BuildPlan may be converted into a bundle to be uploaded to Stackage Server. (Not yet implemented.)