Generalise Package Support

This patch pushes through one fundamental change: a module is now
identified by the pair of its package and module name, whereas
previously it was identified by its module name alone.  This means
that now a program can contain multiple modules with the same name, as
long as they belong to different packages.

This is a language change - the Haskell report says nothing about
packages, but it is now necessary to understand packages in order to
understand GHC's module system.  For example, a type T from module M
in package P is different from a type T from module M in package Q.
Previously this wasn't an issue because there could only be a single
module M in the program.

The "module restriction" on combining packages has therefore been
lifted, and a program can contain multiple versions of the same
package.

Note that none of the proposed syntax changes have yet been
implemented, but the architecture is geared towards supporting import
declarations qualified by package name, and that is probably the next
step.

It is now necessary to specify the package name when compiling a
package, using the -package-name flag (which has been un-deprecated).
Fortunately Cabal still uses -package-name.

Certain packages are "wired in".  Currently the wired-in packages are:
base, haskell98, template-haskell and rts, and are always referred to
by these versionless names.  Other packages are referred to with full
package IDs (eg. "network-1.0").  This is because the compiler needs
to refer to entities in the wired-in packages, and we didn't want to
bake the version of these packages into the comiler.  It's conceivable
that someone might want to upgrade the base package independently of
GHC.

Internal changes:

  - There are two module-related types:

        ModuleName      just a FastString, the name of a module
        Module          a pair of a PackageId and ModuleName

    A mapping from ModuleName can be a UniqFM, but a mapping from Module
    must be a FiniteMap (we provide it as ModuleEnv).

  - The "HomeModules" type that was passed around the compiler is now
    gone, replaced in most cases by the current package name which is
    contained in DynFlags.  We can tell whether a Module comes from the
    current package by comparing its package name against the current
    package.

  - While I was here, I changed PrintUnqual to be a little more useful:
    it now returns the ModuleName that the identifier should be qualified
    with according to the current scope, rather than its original
    module.  Also, PrintUnqual tells whether to qualify module names with
    package names (currently unused).

Docs to follow.

1 files changed, 23 insertions, 22 deletions

diff --git a/compiler/rename/RnEnv.lhs b/compiler/rename/RnEnv.lhs
index 2be3bfd5c0..1c5a559ee8 100644
--- a/compiler/rename/RnEnv.lhs
+++ b/compiler/rename/RnEnv.lhs
@@ -30,13 +30,14 @@ module RnEnv (
 
 #include "HsVersions.h"
 
-import LoadIface	( loadHomeInterface, loadSrcInterface )
+import LoadIface	( loadInterfaceForName, loadSrcInterface )
 import IfaceEnv		( lookupOrig, newGlobalBinder, newIPName )
 import HsSyn		( FixitySig(..), HsExpr(..), SyntaxExpr, SyntaxTable,
 			  LHsTyVarBndr, LHsType, 
 			  Fixity, hsLTyVarLocNames, replaceTyVarName )
 import RdrHsSyn		( extractHsTyRdrTyVars )
-import RdrName		( RdrName, rdrNameModule, isQual, isUnqual, isOrig,
+import RdrName		( RdrName, isQual, isUnqual, isOrig_maybe,
+			  isQual_maybe,
 			  mkRdrUnqual, setRdrNameSpace, rdrNameOcc,
 			  pprGlobalRdrEnv, lookupGRE_RdrName, 
 			  isExact_maybe, isSrcRdrName,
@@ -52,7 +53,7 @@ import Name		( Name, nameIsLocalOrFrom, mkInternalName, isWiredInName,
 import NameSet
 import OccName		( tcName, isDataOcc, pprNonVarNameSpace, occNameSpace,
 			  reportIfUnused )
-import Module		( Module )
+import Module		( Module, ModuleName )
 import PrelNames	( mkUnboundName, rOOT_MAIN, iNTERACTIVE, consDataConKey, hasKey )
 import UniqSupply
 import BasicTypes	( IPName, mapIPName )
@@ -91,7 +92,7 @@ newTopSrcBinder this_mod mb_parent (L loc rdr_name)
 	returnM name
 
 
-  | isOrig rdr_name
+  | Just (rdr_mod, rdr_occ) <- isOrig_maybe rdr_name
   = do	checkErr (rdr_mod == this_mod || rdr_mod == rOOT_MAIN)
 	         (badOrigBinding rdr_name)
 	-- When reading External Core we get Orig names as binders, 
@@ -111,13 +112,11 @@ newTopSrcBinder this_mod mb_parent (L loc rdr_name)
 	-- the RdrName, not from the environment.  In principle, it'd be fine to 
 	-- have an arbitrary mixture of external core definitions in a single module,
 	-- (apart from module-initialisation issues, perhaps).
-	newGlobalBinder rdr_mod (rdrNameOcc rdr_name) mb_parent 
+	newGlobalBinder rdr_mod rdr_occ mb_parent 
 	    	        (srcSpanStart loc) --TODO, should pass the whole span
 
   | otherwise
   = newGlobalBinder this_mod (rdrNameOcc rdr_name) mb_parent (srcSpanStart loc)
-  where
-    rdr_mod  = rdrNameModule rdr_name
 \end{code}
 
 %*********************************************************
@@ -164,13 +163,12 @@ lookupTopBndrRn rdr_name
   | Just name <- isExact_maybe rdr_name
   = returnM name
 
-  | isOrig rdr_name	
+  | Just (rdr_mod, rdr_occ) <- isOrig_maybe rdr_name	
 	-- This deals with the case of derived bindings, where
 	-- we don't bother to call newTopSrcBinder first
 	-- We assume there is no "parent" name
   = do	{ loc <- getSrcSpanM
-	; newGlobalBinder (rdrNameModule rdr_name)
-		          (rdrNameOcc rdr_name) Nothing (srcSpanStart loc) }
+	; newGlobalBinder rdr_mod rdr_occ Nothing (srcSpanStart loc) }
 
   | otherwise
   = do	{ mb_gre <- lookupGreLocalRn rdr_name
@@ -278,9 +276,12 @@ lookupImportedName rdr_name
 	-- This happens in derived code
   = returnM n
 
-  | otherwise	-- Always Orig, even when reading a .hi-boot file
-  = ASSERT( not (isUnqual rdr_name) )
-    lookupOrig (rdrNameModule rdr_name) (rdrNameOcc rdr_name)
+	-- Always Orig, even when reading a .hi-boot file
+  | Just (rdr_mod, rdr_occ) <- isOrig_maybe rdr_name
+  = lookupOrig rdr_mod rdr_occ
+
+  | otherwise
+  = pprPanic "RnEnv.lookupImportedName" (ppr rdr_name)
 
 unboundName :: RdrName -> RnM Name
 unboundName rdr_name 
@@ -337,13 +338,10 @@ lookupGreRn_help rdr_name lookup
 -- try to load the interface if we don't already have it.
 lookupQualifiedName :: RdrName -> RnM Name
 lookupQualifiedName rdr_name
- = let 
-       mod = rdrNameModule rdr_name
-       occ = rdrNameOcc rdr_name
-   in
+  | Just (mod,occ) <- isQual_maybe rdr_name
    -- Note: we want to behave as we would for a source file import here,
    -- and respect hiddenness of modules/packages, hence loadSrcInterface.
-   loadSrcInterface doc mod False	`thenM` \ iface ->
+   = loadSrcInterface doc mod False	`thenM` \ iface ->
 
    case  [ (mod,occ) | 
 	   (mod,avails) <- mi_exports iface,
@@ -353,6 +351,9 @@ lookupQualifiedName rdr_name
       ((mod,occ):ns) -> ASSERT (null ns) 
 			lookupOrig mod occ
       _ -> unboundName rdr_name
+
+  | otherwise
+  = pprPanic "RnEnv.lookupQualifiedName" (ppr rdr_name)
   where
     doc = ptext SLIT("Need to find") <+> ppr rdr_name
 \end{code}
@@ -421,7 +422,7 @@ lookupFixityRn name
 
     else	-- It's imported
       -- For imported names, we have to get their fixities by doing a
-      -- loadHomeInterface, and consulting the Ifaces that comes back
+      -- loadInterfaceForName, and consulting the Ifaces that comes back
       -- from that, because the interface file for the Name might not
       -- have been loaded yet.  Why not?  Suppose you import module A,
       -- which exports a function 'f', thus;
@@ -434,9 +435,9 @@ lookupFixityRn name
       -- 'f', we need to know its fixity, and it's then, and only
       -- then, that we load B.hi.  That is what's happening here.
       --
-      -- loadHomeInterface will find B.hi even if B is a hidden module,
+      -- loadInterfaceForName will find B.hi even if B is a hidden module,
       -- and that's what we want.
-        loadHomeInterface doc name	`thenM` \ iface ->
+        loadInterfaceForName doc name	`thenM` \ iface ->
 	returnM (mi_fix_fn iface (nameOccName name))
   where
     doc = ptext SLIT("Checking fixity for") <+> ppr name
@@ -705,7 +706,7 @@ mapFvRn f xs = mappM f xs	`thenM` \ stuff ->
 %************************************************************************
 
 \begin{code}
-warnUnusedModules :: [(Module,SrcSpan)] -> RnM ()
+warnUnusedModules :: [(ModuleName,SrcSpan)] -> RnM ()
 warnUnusedModules mods
   = ifOptM Opt_WarnUnusedImports (mappM_ bleat mods)
   where