Cabal- A framework for packaging Haskell software

CopyrightThomas Schilling, 2007
Safe HaskellNone



This is about the cabal configurations feature. It exports finalizePackageDescription and flattenPackageDescription which are functions for converting GenericPackageDescriptions down to PackageDescriptions. It has code for working with the tree of conditions and resolving or flattening conditions.



finalizePackageDescription Source


:: FlagAssignment

Explicitly specified flag assignments

-> (Dependency -> Bool)

Is a given dependency satisfiable from the set of available packages? If this is unknown then use True.

-> Platform

The Arch and OS

-> CompilerInfo

Compiler information

-> [Dependency]

Additional constraints

-> GenericPackageDescription 
-> Either [Dependency] (PackageDescription, FlagAssignment)

Either missing dependencies or the resolved package description along with the flag assignments chosen.

Create a package description with all configurations resolved.

This function takes a GenericPackageDescription and several environment parameters and tries to generate PackageDescription by finding a flag assignment that result in satisfiable dependencies.

It takes as inputs a not necessarily complete specifications of flags assignments, an optional package index as well as platform parameters. If some flags are not assigned explicitly, this function will try to pick an assignment that causes this function to succeed. The package index is optional since on some platforms we cannot determine which packages have been installed before. When no package index is supplied, every dependency is assumed to be satisfiable, therefore all not explicitly assigned flags will get their default values.

This function will fail if it cannot find a flag assignment that leads to satisfiable dependencies. (It will not try alternative assignments for explicitly specified flags.) In case of failure it will return the missing dependencies that it encountered when trying different flag assignments. On success, it will return the package description and the full flag assignment chosen.

flattenPackageDescription :: GenericPackageDescription -> PackageDescription Source

Flatten a generic package description by ignoring all conditions and just join the field descriptors into on package description. Note, however, that this may lead to inconsistent field values, since all values are joined into one field, which may not be possible in the original package description, due to the use of exclusive choices (if ... else ...).

TODO: One particularly tricky case is defaulting. In the original package description, e.g., the source directory might either be the default or a certain, explicitly set path. Since defaults are filled in only after the package has been resolved and when no explicit value has been set, the default path will be missing from the package description returned by this function.

parseCondition :: ReadP r (Condition ConfVar) Source

Parse a configuration condition from a string.

extractCondition :: Eq v => (a -> Bool) -> CondTree v c a -> Condition v Source

Extract buildable condition from a cond tree.

Background: If the conditions in a cond tree lead to Buildable being set to False, then none of the dependencies for this cond tree should actually be taken into account. On the other hand, some of the flags may only be decided in the solver, so we cannot necessarily make the decision whether a component is Buildable or not prior to solving.

What we are doing here is to partially evaluate a condition tree in order to extract the condition under which Buildable is True. The predicate determines whether data under a CondTree is buildable.

addBuildableCondition :: (Eq v, Monoid a, Monoid c) => (a -> BuildInfo) -> CondTree v c a -> CondTree v c a Source

Transforms a CondTree by putting the input under the "then" branch of a conditional that is True when Buildable is True. If addBuildableCondition can determine that Buildable is always True, it returns the input unchanged. If Buildable is always False, it returns the empty CondTree.

mapCondTree :: (a -> b) -> (c -> d) -> (Condition v -> Condition w) -> CondTree v c a -> CondTree w d b Source

mapTreeData :: (a -> b) -> CondTree v c a -> CondTree v c b Source

mapTreeConds :: (Condition v -> Condition w) -> CondTree v c a -> CondTree w c a Source

mapTreeConstrs :: (c -> d) -> CondTree v c a -> CondTree v d a Source