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.

3 files changed, 14 insertions, 10 deletions

diff --git a/compiler/hsSyn/Convert.lhs b/compiler/hsSyn/Convert.lhs
index 77e9e08224..88d8954bf1 100644
--- a/compiler/hsSyn/Convert.lhs
+++ b/compiler/hsSyn/Convert.lhs
@@ -17,9 +17,10 @@ import HsSyn as Hs
 import qualified Class (FunDep)
 import RdrName	( RdrName, mkRdrUnqual, mkRdrQual, mkOrig, getRdrName, nameRdrName )
 import qualified Name	( Name, mkInternalName, getName )
-import Module   ( Module, mkModule )
+import Module   ( ModuleName, mkModuleName, mkModule )
 import RdrHsSyn	( mkClassDecl, mkTyData )
 import qualified OccName
+import PackageConfig    ( PackageId, stringToPackageId )
 import OccName	( startsVarId, startsVarSym, startsConId, startsConSym,
 		  pprNameSpace )
 import SrcLoc	( Located(..), SrcSpan )
@@ -569,7 +570,7 @@ thRdrName :: OccName.NameSpace -> String -> TH.NameFlavour -> RdrName
 -- 	 which will give confusing error messages later
 -- 
 -- The strict applications ensure that any buried exceptions get forced
-thRdrName ctxt_ns occ (TH.NameG th_ns mod) = (mkOrig     $! (mk_mod mod)) $! (mk_occ (mk_ghc_ns th_ns) occ)
+thRdrName ctxt_ns occ (TH.NameG th_ns pkg mod) = (mkOrig $! (mkModule (mk_pkg pkg) (mk_mod mod))) $! (mk_occ (mk_ghc_ns th_ns) occ)
 thRdrName ctxt_ns occ (TH.NameL uniq)      = nameRdrName $! (((Name.mkInternalName $! (mk_uniq uniq)) $! (mk_occ ctxt_ns occ)) noSrcLoc)
 thRdrName ctxt_ns occ (TH.NameQ mod)       = (mkRdrQual  $! (mk_mod mod)) $! (mk_occ ctxt_ns occ)
 thRdrName ctxt_ns occ (TH.NameU uniq)      = mkRdrUnqual $! (mk_uniq_occ ctxt_ns occ uniq)
@@ -617,8 +618,11 @@ mk_ghc_ns TH.DataName  = OccName.dataName
 mk_ghc_ns TH.TcClsName = OccName.tcClsName
 mk_ghc_ns TH.VarName   = OccName.varName
 
-mk_mod :: TH.ModName -> Module
-mk_mod mod = mkModule (TH.modString mod)
+mk_mod :: TH.ModName -> ModuleName
+mk_mod mod = mkModuleName (TH.modString mod)
+
+mk_pkg :: TH.ModName -> PackageId
+mk_pkg pkg = stringToPackageId (TH.pkgString pkg)
 
 mk_uniq :: Int# -> Unique
 mk_uniq u = mkUniqueGrimily (I# u)
diff --git a/compiler/hsSyn/HsImpExp.lhs b/compiler/hsSyn/HsImpExp.lhs
index 220afb7499..f63d86aec2 100644
--- a/compiler/hsSyn/HsImpExp.lhs
+++ b/compiler/hsSyn/HsImpExp.lhs
@@ -8,7 +8,7 @@ module HsImpExp where
 
 #include "HsVersions.h"
 
-import Module		( Module )
+import Module		( ModuleName )
 import Outputable
 import FastString
 import SrcLoc		( Located(..) )
@@ -26,10 +26,10 @@ One per \tr{import} declaration in a module.
 type LImportDecl name = Located (ImportDecl name)
 
 data ImportDecl name
-  = ImportDecl	  (Located Module)		-- module name
+  = ImportDecl	  (Located ModuleName)		-- module name
 		  Bool				-- True <=> {-# SOURCE #-} import
 		  Bool				-- True => qualified
-		  (Maybe Module)		-- as Module
+		  (Maybe ModuleName)		-- as Module
 		  (Maybe (Bool, [LIE name]))	-- (True => hiding, names)
 \end{code}
 
@@ -72,7 +72,7 @@ data IE name
   | IEThingAbs          name		-- Class/Type (can't tell)
   | IEThingAll          name		-- Class/Type plus all methods/constructors
   | IEThingWith		name [name]	-- Class/Type plus some methods/constructors
-  | IEModuleContents    Module		-- (Export Only)
+  | IEModuleContents    ModuleName	-- (Export Only)
 \end{code}
 
 \begin{code}
diff --git a/compiler/hsSyn/HsSyn.lhs b/compiler/hsSyn/HsSyn.lhs
index a9982a630a..0efa1e32c8 100644
--- a/compiler/hsSyn/HsSyn.lhs
+++ b/compiler/hsSyn/HsSyn.lhs
@@ -40,14 +40,14 @@ import HsUtils
 import IfaceSyn		( IfaceBinding )
 import Outputable
 import SrcLoc		( Located(..) )
-import Module		( Module )
+import Module		( Module, ModuleName )
 \end{code}
 
 All we actually declare here is the top-level structure for a module.
 \begin{code}
 data HsModule name
   = HsModule
-	(Maybe (Located Module))-- Nothing => "module X where" is omitted
+	(Maybe (Located ModuleName))-- Nothing => "module X where" is omitted
 				--	(in which case the next field is Nothing too)
 	(Maybe [LIE name])	-- Export list; Nothing => export list omitted, so export everything
 				-- Just [] => export *nothing*