stackage/ROADMAP.md

Processing

High level series of steps for processing

Nightlies

1. Get list of core packages
2. Get build constraints from list of maintained packages
3. Load up package index
4. Calculate build plan using newest versions of packages
5. Write out a YAML file with complete build plan
6. Verify that the build plan can be compiled
7. Perform the build

LTS

1. Load up most recent build plan
2. Convert build plan into constraints for next build
3. Continue from step (3) above

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 discuss the build as a whole, whereas PackageConstraints discuss the constraints on an individual package.

There are two primary ways of getting a BuildConstraints. defaultBuildConstraints inspects the 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 UpdateBuildPlan, which will be discussed later.

BuildConstraints do 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 in 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 actually 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.)