Library names, with Cabal submodule update

A library name is a package name, package version, and hash of the
version names of all textual dependencies (i.e. packages which were included.) A library
name is a coarse approximation of installed package IDs, which are suitable for
inclusion in package keys (you don't want to put an IPID in a package key, since
it means the key will change any time the source changes.)

    - We define ShPackageKey, which is the semantic object which
      is hashed into a PackageKey.  You can use 'newPackageKey'
      to hash a ShPackageKey to a PackageKey

    - Given a PackageKey, we can lookup its ShPackageKey with
      'lookupPackageKey'.  The way we can do this is by consulting
      the 'pkgKeyCache', which records a reverse mapping from
      every hash to the ShPackageKey.  This means that if you
      load in PackageKeys from external sources (e.g. interface
      files), you also need to load in a mapping of PackageKeys
      to their ShPackageKeys so we can populate the cache.

    - We define a 'LibraryName' which encapsulates the full
      depenency resolution that Cabal may have selected; this
      is opaque to GHC but can be used to distinguish different
      versions of a package.

    - Definite packages don't have an interesting PackageKey,
      so we rely on Cabal to pass them to us.

    - We can pretty-print package keys while displaying the
      instantiation, but it's not wired up to anything (e.g.
      the Outputable instance of PackageKey).

Signed-off-by: Edward Z. Yang <ezyang@cs.stanford.edu>

Test Plan: validate

Reviewers: austin, bgamari

Subscribers: thomie

Differential Revision: https://phabricator.haskell.org/D1056

GHC Trac Issues: #10566

1 files changed, 5 insertions, 3 deletions

diff --git a/compiler/main/Packages.hs b/compiler/main/Packages.hs
index 16ee352243..20822476cd 100644
--- a/compiler/main/Packages.hs
+++ b/compiler/main/Packages.hs
@@ -363,7 +363,7 @@ initPackages dflags = do
                 Nothing -> readPackageConfigs dflags
                 Just db -> return $ setBatchPackageFlags dflags db
   (pkg_state, preload, this_pkg)
-        <- mkPackageState dflags pkg_db [] (thisPackage dflags)
+        <- mkPackageState dflags pkg_db []
   return (dflags{ pkgDatabase = Just pkg_db,
                   pkgState = pkg_state,
                   thisPackage = this_pkg },
@@ -885,15 +885,17 @@ mkPackageState
     :: DynFlags
     -> [PackageConfig]          -- initial database
     -> [PackageKey]              -- preloaded packages
-    -> PackageKey                -- this package
     -> IO (PackageState,
            [PackageKey],         -- new packages to preload
            PackageKey) -- this package, might be modified if the current
                       -- package is a wired-in package.
 
-mkPackageState dflags0 pkgs0 preload0 this_package = do
+mkPackageState dflags0 pkgs0 preload0 = do
   dflags <- interpretPackageEnv dflags0
 
+  -- Compute the package key
+  let this_package = thisPackage dflags
+
 {-
    Plan.