The name and version of a package.

Type alias so we can use the shorter name PackageId.

An InstalledPackageId uniquely identifies an instance of an installed package. There can be at most one package with a given InstalledPackageId in a package database, or overlay of databases.

A PackageKey is the notion of "package ID" which is visible to the compiler. Why is this not a PackageId? The PackageId is a user-visible concept written explicity in Cabal files; on the other hand, a PackageKey may contain, for example, information about the transitive dependency tree of a package. Why is this not an InstalledPackageId? A PackageKey affects the ABI because it is used for linker symbols; however, an InstalledPackageId can be used to distinguish two ABI-compatible versions of a library.

The key is defined to be a 128-bit MD5 hash, separated into two 64-bit components (the most significant component coming first) which are individually base-62 encoded (A-Z, a-z, 0-9).

     key         ::= hash64 hash64
     hash64      ::= [A-Za-z0-9]{11}

The string that is hashed is specified as raw_key:

     raw_key     ::= package_id "n"
                     holes_nl
                     depends_nl
     package_id  ::= package_name "-" package_version
     holes_nl    ::= ""
                   | hole_inst "n" holes_nl
     hole_inst   ::= modulename " " key ":" modulename
     depends_nl  ::= ""
                   | depend "n" depends_nl
     depend      ::= key

The holes list MUST be sorted by the first modulename; the depends list MUST be sorted by the key. holes describes the backing implementations of all holes in the package; depends describes all of the build-depends of a package. A package key MAY be used in holes even if it is not mentioned in depends: depends contains STRICTLY packages which are textually mentioned in the package description.

The trailing newline is MANDATORY.

There is also a variant of package key which is prefixed by a informational string. This key MUST NOT be used in the computation of the hash proper, but it is useful for human-readable consumption.

     infokey     ::= infostring "_" key
     infostring  ::= [A-Za-z0-9-]+

For example, Cabal provides a key with the first five characters of the package name for linker symbols.

Generates a PackageKey from a PackageId, sorted package keys of the immediate dependencies.

Describes a dependency on a source package (API)

Simplify the VersionRange expression in a Dependency. See simplifyVersionRange.

Class of things that have a PackageIdentifier

Types in this class are all notions of a package. This allows us to have different types for the different phases that packages go though, from simple name/id, package description, configured or installed packages.

Not all kinds of packages can be uniquely identified by a PackageIdentifier. In particular, installed packages cannot, there may be many installed instances of the same source package.

Subclass of packages that have specific versioned dependencies.

So for example a not-yet-configured package has dependencies on version ranges, not specific versions. A configured or an already installed package depends on exact versions. Some operations or data structures (like dependency graphs) only make sense on this subclass of package types.

Class of installed packages.

The primary data type which is an instance of this package is InstalledPackageInfo, but when we are doing install plans in Cabal install we may have other, installed package-like things which contain more metadata. Installed packages have exact dependencies installedDepends.