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, 10 insertions, 10 deletions

diff --git a/compiler/GHC.hs b/compiler/GHC.hs
index a46218665a..d6878ad63d 100644
--- a/compiler/GHC.hs
+++ b/compiler/GHC.hs
@@ -159,11 +159,11 @@ module GHC (
 
         -- * Abstract syntax elements
 
-        -- ** Packages
-        UnitId,
+        -- ** Units
+        Unit,
 
         -- ** Modules
-        Module, mkModule, pprModule, moduleName, moduleUnitId,
+        Module, mkModule, pprModule, moduleName, moduleUnit,
         ModuleName, mkModuleName, moduleNameString,
 
         -- ** Names
@@ -594,7 +594,7 @@ checkBrokenTablesNextToCode' dflags
 -- flags.  If you are not doing linking or doing static linking, you
 -- can ignore the list of packages returned.
 --
-setSessionDynFlags :: GhcMonad m => DynFlags -> m [InstalledUnitId]
+setSessionDynFlags :: GhcMonad m => DynFlags -> m [UnitId]
 setSessionDynFlags dflags = do
   dflags' <- checkNewDynFlags dflags
   dflags'' <- liftIO $ interpretPackageEnv dflags'
@@ -643,7 +643,7 @@ setSessionDynFlags dflags = do
 -- | Sets the program 'DynFlags'.  Note: this invalidates the internal
 -- cached module graph, causing more work to be done the next time
 -- 'load' is called.
-setProgramDynFlags :: GhcMonad m => DynFlags -> m [InstalledUnitId]
+setProgramDynFlags :: GhcMonad m => DynFlags -> m [UnitId]
 setProgramDynFlags dflags = setProgramDynFlags_ True dflags
 
 -- | Set the action taken when the compiler produces a message.  This
@@ -655,7 +655,7 @@ setLogAction action = do
   void $ setProgramDynFlags_ False $
     dflags' { log_action = action }
 
-setProgramDynFlags_ :: GhcMonad m => Bool -> DynFlags -> m [InstalledUnitId]
+setProgramDynFlags_ :: GhcMonad m => Bool -> DynFlags -> m [UnitId]
 setProgramDynFlags_ invalidate_needed dflags = do
   dflags' <- checkNewDynFlags dflags
   dflags_prev <- getProgramDynFlags
@@ -1357,7 +1357,7 @@ packageDbModules only_exposed = do
      [ mkModule pid modname
      | p <- pkgs
      , not only_exposed || exposed p
-     , let pid = packageConfigId p
+     , let pid = mkUnit p
      , modname <- exposedModules p
                ++ map exportName (reexportedModules p) ]
                -}
@@ -1489,7 +1489,7 @@ findModule mod_name maybe_pkg = withSession $ \hsc_env -> do
     this_pkg = thisPackage dflags
   --
   case maybe_pkg of
-    Just pkg | fsToUnitId pkg /= this_pkg && pkg /= fsLit "this" -> liftIO $ do
+    Just pkg | fsToUnit pkg /= this_pkg && pkg /= fsLit "this" -> liftIO $ do
       res <- findImportedModule hsc_env mod_name maybe_pkg
       case res of
         Found _ m -> return m
@@ -1501,7 +1501,7 @@ findModule mod_name maybe_pkg = withSession $ \hsc_env -> do
         Nothing -> liftIO $ do
            res <- findImportedModule hsc_env mod_name maybe_pkg
            case res of
-             Found loc m | moduleUnitId m /= this_pkg -> return m
+             Found loc m | moduleUnit m /= this_pkg -> return m
                          | otherwise -> modNotLoadedError dflags m loc
              err -> throwOneError $ noModError dflags noSrcSpan mod_name err
 
@@ -1545,7 +1545,7 @@ isModuleTrusted m = withSession $ \hsc_env ->
     liftIO $ hscCheckSafe hsc_env m noSrcSpan
 
 -- | Return if a module is trusted and the pkgs it depends on to be trusted.
-moduleTrustReqs :: GhcMonad m => Module -> m (Bool, Set InstalledUnitId)
+moduleTrustReqs :: GhcMonad m => Module -> m (Bool, Set UnitId)
 moduleTrustReqs m = withSession $ \hsc_env ->
     liftIO $ hscGetSafe hsc_env m noSrcSpan