Package keys (for linking/type equality) separated from package IDs.
This patch set makes us no longer assume that a package key is a human readable string, leaving Cabal free to "do whatever it wants" to allocate keys; we'll look up the PackageId in the database to display to the user. This also means we have a new level of qualifier decisions to make at the package level, and rewriting some Safe Haskell error reporting code to DTRT. Additionally, we adjust the build system to use a new ghc-cabal output Make variable PACKAGE_KEY to determine library names and other things, rather than concatenating PACKAGE/VERSION as before. Adds a new `-this-package-key` flag to subsume the old, erroneously named `-package-name` flag, and `-package-key` to select packages by package key. RFC: The md5 hashes are pretty tough on the eye, as far as the file system is concerned :( ToDo: safePkg01 test had its output updated, but the fix is not really right: the rest of the dependencies are truncated due to the fact the we're only grepping a single line, but ghc-pkg is wrapping its output. ToDo: In a later commit, update all submodules to stop using -package-name and use -this-package-key. For now, we don't do it to avoid submodule explosion. 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/D80