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, 10 insertions, 12 deletions

diff --git a/compiler/codeGen/CgMonad.lhs b/compiler/codeGen/CgMonad.lhs
index 22462e79e5..1866df4cef 100644
--- a/compiler/codeGen/CgMonad.lhs
+++ b/compiler/codeGen/CgMonad.lhs
@@ -47,7 +47,7 @@ module CgMonad (
 	Sequel(..), -- ToDo: unabstract?
 
 	-- ideally we wouldn't export these, but some other modules access internal state
-	getState, setState, getInfoDown, getDynFlags, getHomeModules,
+	getState, setState, getInfoDown, getDynFlags, getThisPackage,
 
 	-- more localised access to monad state	
 	getStkUsage, setStkUsage,
@@ -61,8 +61,8 @@ module CgMonad (
 
 import {-# SOURCE #-} CgBindery ( CgBindings, nukeVolatileBinds )
 
-import DynFlags		( DynFlags )
-import Packages		( HomeModules )
+import DynFlags		( DynFlags(..) )
+import PackageConfig	( PackageId )
 import Cmm
 import CmmUtils		( CmmStmts, isNopStmt )
 import CLabel
@@ -97,7 +97,6 @@ along.
 data CgInfoDownwards	-- information only passed *downwards* by the monad
   = MkCgInfoDown {
 	cgd_dflags  :: DynFlags,
-	cgd_hmods   :: HomeModules,	-- Packages we depend on
 	cgd_mod     :: Module,		-- Module being compiled
 	cgd_statics :: CgBindings,	-- [Id -> info] : static environment
 	cgd_srt     :: CLabel,		-- label of the current SRT
@@ -105,10 +104,9 @@ data CgInfoDownwards	-- information only passed *downwards* by the monad
 	cgd_eob     :: EndOfBlockInfo	-- Info for stuff to do at end of basic block:
   }
 
-initCgInfoDown :: DynFlags -> HomeModules -> Module -> CgInfoDownwards
-initCgInfoDown dflags hmods mod
+initCgInfoDown :: DynFlags -> Module -> CgInfoDownwards
+initCgInfoDown dflags mod
   = MkCgInfoDown {	cgd_dflags  = dflags,
-			cgd_hmods   = hmods,
 			cgd_mod     = mod,
 			cgd_statics = emptyVarEnv,
 			cgd_srt     = error "initC: srt",
@@ -378,11 +376,11 @@ instance Monad FCode where
 The Abstract~C is not in the environment so as to improve strictness.
 
 \begin{code}
-initC :: DynFlags -> HomeModules -> Module -> FCode a -> IO a
+initC :: DynFlags -> Module -> FCode a -> IO a
 
-initC dflags hmods mod (FCode code)
+initC dflags mod (FCode code)
   = do	{ uniqs <- mkSplitUniqSupply 'c'
-	; case code (initCgInfoDown dflags hmods mod) (initCgState uniqs) of
+	; case code (initCgInfoDown dflags mod) (initCgState uniqs) of
 	      (res, _) -> return res
 	}
 
@@ -510,8 +508,8 @@ getInfoDown = FCode $ \info_down state -> (info_down,state)
 getDynFlags :: FCode DynFlags
 getDynFlags = liftM cgd_dflags getInfoDown
 
-getHomeModules :: FCode HomeModules
-getHomeModules = liftM cgd_hmods getInfoDown
+getThisPackage :: FCode PackageId
+getThisPackage = liftM thisPackage getDynFlags
 
 withInfoDown :: FCode a -> CgInfoDownwards -> FCode a
 withInfoDown (FCode fcode) info_down = FCode $ \_ state -> fcode info_down state