Refactoring unit management code

Over the years the unit management code has been modified a lot to keep
up with changes in Cabal (e.g. support for several library components in
the same package), to integrate BackPack, etc. I found it very hard to
understand as the terminology wasn't consistent, was referring to past
concepts, etc.

The terminology is now explained as clearly as I could in the Note
"About Units" and the code is refactored to reflect it.

-------------------

Many names were misleading: UnitId is not an Id but could be a virtual
unit (an indefinite one instantiated on the fly), IndefUnitId
constructor may contain a definite instantiated unit, etc.

   * Rename IndefUnitId into InstantiatedUnit
   * Rename IndefModule into InstantiatedModule
   * Rename UnitId type into Unit
   * Rename IndefiniteUnitId constructor into VirtUnit
   * Rename DefiniteUnitId constructor into RealUnit
   * Rename packageConfigId into mkUnit
   * Rename getPackageDetails into unsafeGetUnitInfo
   * Rename InstalledUnitId into UnitId

Remove references to misleading ComponentId: a ComponentId is just an
indefinite unit-id to be instantiated.

   * Rename ComponentId into IndefUnitId
   * Rename ComponentDetails into UnitPprInfo
   * Fix display of UnitPprInfo with empty version: this is now used for
     units dynamically generated by BackPack

Generalize several types (Module, Unit, etc.) so that they can be used
with different unit identifier types: UnitKey, UnitId, Unit, etc.

   * GenModule: Module, InstantiatedModule and InstalledModule are now
     instances of this type
   * Generalize DefUnitId, IndefUnitId, Unit, InstantiatedUnit,
     PackageDatabase

Replace BackPack fake "hole" UnitId by a proper HoleUnit constructor.

Add basic support for UnitKey. They should be used more in the future to
avoid mixing them up with UnitId as we do now.

Add many comments.

Update Haddock submodule

1 files changed, 7 insertions, 7 deletions

diff --git a/compiler/GHC/Iface/Recomp.hs b/compiler/GHC/Iface/Recomp.hs
index 430f7b4207..bec782ff48 100644
--- a/compiler/GHC/Iface/Recomp.hs
+++ b/compiler/GHC/Iface/Recomp.hs
@@ -209,10 +209,10 @@ checkVersions hsc_env mod_summary iface
   = do { traceHiDiffs (text "Considering whether compilation is required for" <+>
                         ppr (mi_module iface) <> colon)
 
-       -- readIface will have verified that the InstalledUnitId matches,
+       -- readIface will have verified that the UnitId matches,
        -- but we ALSO must make sure the instantiation matches up.  See
        -- test case bkpcabal04!
-       ; if moduleUnitId (mi_module iface) /= thisPackage (hsc_dflags hsc_env)
+       ; if moduleUnit (mi_module iface) /= thisPackage (hsc_dflags hsc_env)
             then return (RecompBecause "-this-unit-id changed", Nothing) else do {
        ; recomp <- checkFlagHash hsc_env iface
        ; if recompileRequired recomp then return (recomp, Nothing) else do {
@@ -332,7 +332,7 @@ checkHsig mod_summary iface = do
     dflags <- getDynFlags
     let outer_mod = ms_mod mod_summary
         inner_mod = canonicalizeHomeModule dflags (moduleName outer_mod)
-    MASSERT( moduleUnitId outer_mod == thisPackage dflags )
+    MASSERT( moduleUnit outer_mod == thisPackage dflags )
     case inner_mod == mi_semantic_module iface of
         True -> up_to_date (text "implementing module unchanged")
         False -> return (RecompBecause "implementing module changed")
@@ -405,7 +405,7 @@ checkMergedSignatures mod_summary iface = do
         new_merged = case Map.lookup (ms_mod_name mod_summary)
                                      (requirementContext (pkgState dflags)) of
                         Nothing -> []
-                        Just r -> sort $ map (indefModuleToModule dflags) r
+                        Just r -> sort $ map (instModuleToModule (pkgState dflags)) r
     if old_merged == new_merged
         then up_to_date (text "signatures to merge in unchanged" $$ ppr new_merged)
         else return (RecompBecause "signatures to merge in changed")
@@ -463,7 +463,7 @@ checkDependencies hsc_env summary iface
                  else
                          return UpToDate
           | otherwise
-           -> if toInstalledUnitId pkg `notElem` (map fst prev_dep_pkgs)
+           -> if toUnitId pkg `notElem` (map fst prev_dep_pkgs)
                  then do traceHiDiffs $
                            text "imported module " <> quotes (ppr mod) <>
                            text " is from package " <> quotes (ppr pkg) <>
@@ -471,7 +471,7 @@ checkDependencies hsc_env summary iface
                          return (RecompBecause reason)
                  else
                          return UpToDate
-           where pkg = moduleUnitId mod
+           where pkg = moduleUnit mod
         _otherwise  -> return (RecompBecause reason)
 
    old_deps = Set.fromList $ map fst $ filter (not . snd) prev_dep_mods
@@ -561,7 +561,7 @@ getFromModIface doc_msg mod getter
 -- | Given the usage information extracted from the old
 -- M.hi file for the module being compiled, figure out
 -- whether M needs to be recompiled.
-checkModUsage :: UnitId -> Usage -> IfG RecompileRequired
+checkModUsage :: Unit -> Usage -> IfG RecompileRequired
 checkModUsage _this_pkg UsagePackageModule{
                                 usg_mod = mod,
                                 usg_mod_hash = old_mod_hash }