Rename PackageId to PackageKey, distinguishing it from Cabal's PackageId.
Summary: Previously, both Cabal and GHC defined the type PackageId, and we expected them to be roughly equivalent (but represented differently). This refactoring separates these two notions. A package ID is a user-visible identifier; it's the thing you write in a Cabal file, e.g. containers-0.9. The components of this ID are semantically meaningful, and decompose into a package name and a package vrsion. A package key is an opaque identifier used by GHC to generate linking symbols. Presently, it just consists of a package name and a package version, but pursuant to #9265 we are planning to extend it to record other information. Within a single executable, it uniquely identifies a package. It is *not* an InstalledPackageId, as the choice of a package key affects the ABI of a package (whereas an InstalledPackageId is computed after compilation.) Cabal computes a package key for the package and passes it to GHC using -package-name (now *extremely* misnamed). As an added bonus, we don't have to worry about shadowing anymore. As a follow on, we should introduce -current-package-key having the same role as -package-name, and deprecate the old flag. This commit is just renaming. The haddock submodule needed to be updated. Signed-off-by: Edward Z. Yang <email@example.com> Test Plan: validate Reviewers: simonpj, simonmar, hvr, austin Subscribers: simonmar, relrod, carter Differential Revision: https://phabricator.haskell.org/D79 Conflicts: compiler/main/HscTypes.lhs compiler/main/Packages.lhs utils/haddock