Computes the package name for a library. If this is the public library, it will just be the original package name; otherwise, it will be a munged package name recording the original package name as well as the name of the internal library.

A lot of tooling in the Haskell ecosystem assumes that if something is installed to the package database with the package name foo, then it actually is an entry for the (only public) library in package foo. With internal packages, this is not necessarily true: a public library as well as arbitrarily many internal libraries may come from the same package. To prevent tools from getting confused in this case, the package name of these internal libraries is munged so that they do not conflict the public library proper. A particular case where this matters is ghc-pkg: if we don't munge the package name, the inplace registration will OVERRIDE a different internal library.

We munge into a reserved namespace, "z-", and encode both the component name and the package name of an internal library using the following format:

compat-pkg-name ::= "z-" package-name "-z-" library-name

where package-name and library-name have "-" ( "z" + ) "-" segments encoded by adding an extra "z".

When we have the public library, the compat-pkg-name is just the package-name, no surprises there!

>>> prettyShow $ MungedPackageName "servant" LMainLibName
"servant"

>>> prettyShow $ MungedPackageName "servant" (LSubLibName "lackey")
"z-servant-z-lackey"

The textual format for UnitId coincides with the format GHC accepts for -package-id.

>>> prettyShow $ MungedPackageId (MungedPackageName "servant" LMainLibName) (mkVersion [1,2,3])
"servant-1.2.3"

>>> prettyShow $ MungedPackageId (MungedPackageName "servant" (LSubLibName "lackey")) (mkVersion [0,1,2])
"z-servant-z-lackey-0.1.2"