RnIfaces.lhs 44.6 KB
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%
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% (c) The GRASP/AQUA Project, Glasgow University, 1992-1998
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%
\section[RnIfaces]{Cacheing and Renaming of Interfaces}

\begin{code}
module RnIfaces (
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	findAndReadIface, 

	getInterfaceExports, getDeferredDecls,
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	getImportedInstDecls, getImportedRules,
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	lookupFixityRn, loadHomeInterface,
	importDecl, ImportDeclResult(..), recordLocalSlurps, loadBuiltinRules,
	mkImportExportInfo, getSlurped, 
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	checkModUsage, outOfDate, upToDate,
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	getDeclBinders, getDeclSysBinders,
	removeContext	 	-- removeContext probably belongs somewhere else
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    ) where

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#include "HsVersions.h"
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import CmdLineOpts	( opt_NoPruneDecls, opt_NoPruneTyDecls, opt_IgnoreIfacePragmas )
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import HsSyn		( HsDecl(..), TyClDecl(..), InstDecl(..), IfaceSig(..), 
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			  HsType(..), ConDecl(..), IE(..), ConDetails(..), Sig(..),
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			  ForeignDecl(..), ForKind(..), isDynamicExtName,
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			  FixitySig(..), RuleDecl(..),
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			  isClassOpSig, DeprecDecl(..)
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			)
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import HsImpExp		( ieNames )
import CoreSyn		( CoreRule )
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import BasicTypes	( Version, NewOrData(..) )
import RdrHsSyn		( RdrNameHsDecl, RdrNameInstDecl, RdrNameRuleDecl,
			  RdrNameDeprecation, RdrNameIE,
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			  extractHsTyRdrNames 
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			)
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import RnEnv
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import RnMonad
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import ParseIface	( parseIface, IfaceStuff(..) )
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import Name		( Name {-instance NamedThing-}, nameOccName,
			  nameModule, isLocallyDefined, 
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			  isWiredInName, NamedThing(..),
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			  elemNameEnv, extendNameEnv
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			 )
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import Module		( Module, mkVanillaModule, pprModuleName,
			  moduleName, isLocalModule,
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			  ModuleName, WhereFrom(..),
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			)
import RdrName		( RdrName, rdrNameOcc )
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import NameSet
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import SrcLoc		( mkSrcLoc, SrcLoc )
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import PrelInfo		( cCallishTyKeys )
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import Maybes		( maybeToBool )
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import Unique		( Uniquable(..) )
import StringBuffer     ( hGetStringBuffer )
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import FastString	( mkFastString )
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import ErrUtils         ( Message )
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import Util		( sortLt )
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import Lex
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import FiniteMap
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import Outputable
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import Bag
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import List	( nub )
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\end{code}

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%*********************************************************
%*							*
\subsection{Loading a new interface file}
%*							*
%*********************************************************
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\begin{code}
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loadHomeInterface :: SDoc -> Name -> RnM d Ifaces
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loadHomeInterface doc_str name
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  = loadInterface doc_str (moduleName (nameModule name)) ImportBySystem
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loadOrphanModules :: [ModuleName] -> RnM d ()
loadOrphanModules mods
  | null mods = returnRn ()
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  | otherwise = traceRn (text "Loading orphan modules:" <+> 
			 fsep (map pprModuleName mods))		`thenRn_` 
		mapRn_ load mods				`thenRn_`
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		returnRn ()
  where
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    load mod   = loadInterface (mk_doc mod) mod ImportBySystem
    mk_doc mod = pprModuleName mod <+> ptext SLIT("is a orphan-instance module")
	   
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loadInterface :: SDoc -> ModuleName -> WhereFrom -> RnM d Ifaces
loadInterface doc mod from 
  = tryLoadInterface doc mod from	`thenRn` \ (ifaces, maybe_err) ->
    case maybe_err of
	Nothing  -> returnRn ifaces
	Just err -> failWithRn ifaces err

tryLoadInterface :: SDoc -> ModuleName -> WhereFrom -> RnM d (Ifaces, Maybe Message)
	-- Returns (Just err) if an error happened
	-- Guarantees to return with iImpModInfo m --> (... Just cts)
	-- (If the load fails, we plug in a vanilla placeholder
tryLoadInterface doc_str mod_name from
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 = getIfacesRn 			`thenRn` \ ifaces ->
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   let
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	mod_map  = iImpModInfo ifaces
	mod_info = lookupFM mod_map mod_name

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	hi_boot_file 
	  = case (from, mod_info) of
		(ImportByUser,       _)    	       -> False 	-- Not hi-boot
		(ImportByUserSource, _)		       -> True 		-- hi-boot
		(ImportBySystem, Just (_, is_boot, _)) -> is_boot 	-- 
		(ImportBySystem, Nothing)	       -> False
			-- We're importing a module we know absolutely
			-- nothing about, so we assume it's from
			-- another package, where we aren't doing 
			-- dependency tracking. So it won't be a hi-boot file.

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	redundant_source_import 
	  = case (from, mod_info) of 
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		(ImportByUserSource, Just (_,False,_)) -> True
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		other				       -> False
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   in
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	-- CHECK WHETHER WE HAVE IT ALREADY
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   case mod_info of {
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	Just (_, _, True)
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		-> 	-- We're read it already so don't re-read it
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		    returnRn (ifaces, Nothing) ;
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	_ ->

	-- Issue a warning for a redundant {- SOURCE -} import
	-- NB that we arrange to read all the ordinary imports before 
	-- any of the {- SOURCE -} imports
   warnCheckRn	(not redundant_source_import)
		(warnRedundantSourceImport mod_name)	`thenRn_`
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	-- READ THE MODULE IN
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   findAndReadIface doc_str mod_name hi_boot_file   `thenRn` \ read_resultb ->
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   case read_result of {
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	Left err -> 	-- Not found, so add an empty export env to the Ifaces map
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			-- so that we don't look again
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	   let
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		new_mod_map = addToFM mod_map mod_name (False, False, True)
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		new_ifaces  = ifaces { iImpModInfo = new_mod_map }
	   in
	   setIfacesRn new_ifaces		`thenRn_`
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	   returnRn (new_ifaces, Just err) ;
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	-- Found and parsed!
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	Right (mod, iface) ->
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	-- LOAD IT INTO Ifaces
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	-- NB: *first* we do loadDecl, so that the provenance of all the locally-defined
	---    names is done correctly (notably, whether this is an .hi file or .hi-boot file).
	--     If we do loadExport first the wrong info gets into the cache (unless we
	-- 	explicitly tag each export which seems a bit of a bore)
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	-- Sanity check.  If we're system-importing a module we know nothing at all
	-- about, it should be from a different package to this one
    WARN( not (maybeToBool mod_info) && 
	  case from of { ImportBySystem -> True; other -> False } &&
	  isLocalModule mod,
	  ppr mod )
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    loadDecls mod		(iDecls ifaces)	  (pi_decls iface)	`thenRn` \ (decls_vers, new_decls) ->
    loadRules mod		(iRules ifaces)   (pi_rules iface)	`thenRn` \ (rule_vers, new_rules) ->
    loadFixDecls mod_name	 		  (pi_fixity iface)	`thenRn` \ (fix_vers, fix_env) ->
    foldlRn (loadDeprec mod)	emptyDeprecEnv	  (pi_deprecs iface)	`thenRn` \ deprec_env ->
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    foldlRn (loadInstDecl mod)	(iInsts ifaces)   (pi_insts iface)	`thenRn` \ new_insts ->
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    loadExports 			 	  (pi_exports iface)	`thenRn` \ avails ->
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    let
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	version	= VersionInfo { modVers  = pi_vers iface, 
				fixVers  = fix_vers,
				ruleVers = rule_vers,
				declVers = decl_vers }

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	-- For an explicit user import, add to mod_map info about
	-- the things the imported module depends on, extracted
	-- from its usage info.
	mod_map1 = case from of
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			ImportByUser -> addModDeps mod (pi_usages iface) mod_map
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			other        -> mod_map
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	mod_map2 = addToFM mod_map1 mod_name (pi_orphan iface, hi_boot_file, True)
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	-- Now add info about this module to the PST
	new_pst     = extendModuleEnv pst mod mod_detils
 	mod_details = ModDetails { mdModule = mod, mvVersion = version,
				   mdExports = avails,
				   mdFixEnv = fix_env, mdDeprecEnv = deprec_env }
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	new_ifaces = ifaces { iPST	  = new_pst,
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			      iDecls      = new_decls,
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			      iInsts      = new_insts,
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			      iRules	  = new_rules,
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			      iImpModInfo = mod_map2  }
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    in
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    setIfacesRn new_ifaces		`thenRn_`
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    returnRn (new_ifaces, Nothing)
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    }}

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-----------------------------------------------------
--	Adding module dependencies from the 
--	import decls in the interface file
-----------------------------------------------------

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addModDeps :: Module -> PackageSymbolTable -> [ImportVersion a] 
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	   -> ImportedModuleInfo -> ImportedModuleInfo
-- (addModDeps M ivs deps)
-- We are importing module M, and M.hi contains 'import' decls given by ivs
addModDeps mod new_deps mod_deps
  = foldr add mod_deps filtered_new_deps
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  where
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	-- Don't record dependencies when importing a module from another package
	-- Except for its descendents which contain orphans,
	-- and in that case, forget about the boot indicator
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    filtered_new_deps :: (ModuleName, (WhetherHasOrphans, IsBootInterface))
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    filtered_new_deps
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	| isLocalModule mod = [ (imp_mod, (has_orphans, is_boot, False))
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			      | (imp_mod, has_orphans, is_boot, _) <- new_deps 
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			      ]			      
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	| otherwise	    = [ (imp_mod, (True, False, False))
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			      | (imp_mod, has_orphans, _, _) <- new_deps, 
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				has_orphans
			      ]
    add (imp_mod, dep) deps = addToFM_C combine deps imp_mod dep
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    combine old@(_, old_is_boot, old_is_loaded) new
	| old_is_loaded || not old_is_boot = old	-- Keep the old info if it's already loaded
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							-- or if it's a non-boot pending load
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	| otherwise			    = new	-- Otherwise pick new info
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-----------------------------------------------------
--	Loading the export list
-----------------------------------------------------

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loadExports :: [ExportItem] -> RnM d Avails
loadExports items
  = getModuleRn 				`thenRn` \ this_mod ->
    mapRn (loadExport this_mod) items		`thenRn` \ avails_s ->
    returnRn (concat avails_s)


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loadExport :: Module -> ExportItem -> RnM d [AvailInfo]
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loadExport this_mod (mod, entities)
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  | mod == moduleName this_mod = returnRn []
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	-- If the module exports anything defined in this module, just ignore it.
	-- Reason: otherwise it looks as if there are two local definition sites
	-- for the thing, and an error gets reported.  Easiest thing is just to
	-- filter them out up front. This situation only arises if a module
	-- imports itself, or another module that imported it.  (Necessarily,
	-- this invoves a loop.)  Consequence: if you say
	--	module A where
	--	   import B( AType )
	--	   type AType = ...
	--
	--	module B( AType ) where
	--	   import {-# SOURCE #-} A( AType )
	--
	-- then you'll get a 'B does not export AType' message.  A bit bogus
	-- but it's a bogus thing to do!

  | otherwise
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  = mapRn (load_entity mod) entities
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  where
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    new_name mod occ = newGlobalName mod occ
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    load_entity mod (Avail occ)
      =	new_name mod occ	`thenRn` \ name ->
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	returnRn (Avail name)
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    load_entity mod (AvailTC occ occs)
      =	new_name mod occ	      `thenRn` \ name ->
        mapRn (new_name mod) occs     `thenRn` \ names ->
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        returnRn (AvailTC name names)
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-----------------------------------------------------
--	Loading type/class/value decls
-----------------------------------------------------
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loadDecls :: Module 
	  -> DeclsMap
	  -> [(Version, RdrNameHsDecl)]
	  -> RnM d (NameEnv Version, DeclsMap)
loadDecls mod decls_map decls
  = foldlRn (loadDecl mod) (emptyNameEnv, decls_map) decls

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loadDecl :: Module 
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	 -> (NameEnv Version, DeclsMap)
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	 -> (Version, RdrNameHsDecl)
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	 -> RnM d (NameEnv Version, DeclsMap)
loadDecl mod (version_map, decls_map) (version, decl)
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  = getDeclBinders new_name decl	`thenRn` \ maybe_avail ->
    case maybe_avail of {
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	Nothing    -> returnRn (version_map, decls_map);	-- No bindings
	Just avail -> 
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    getDeclSysBinders new_name decl	`thenRn` \ sys_bndrs ->
    let
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	full_avail    = addSysAvails avail sys_bndrs
		-- Add the sys-binders to avail.  When we import the decl,
		-- it's full_avail that will get added to the 'already-slurped' set (iSlurp)
		-- If we miss out sys-binders, we'll read the decl multiple times!

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	main_name     = availName avail
	new_decls_map = foldl add_decl decls_map
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				       [ (name, (full_avail, name==main_name, (mod, decl'))) 
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				       | name <- availNames full_avail]
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	add_decl decls_map (name, stuff)
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	  = WARN( name `elemNameEnv` decls_map, ppr name )
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	    extendNameEnv decls_map name stuff
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	new_version_map = extendNameEnv version_map main_name version
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    in
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    returnRn (new_version_map, new_decls_map)
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    }
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  where
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	-- newTopBinder puts into the cache the binder with the
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	-- module information set correctly.  When the decl is later renamed,
	-- the binding site will thereby get the correct module.
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	-- There maybe occurrences that don't have the correct Module, but
	-- by the typechecker will propagate the binding definition to all 
	-- the occurrences, so that doesn't matter
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    new_name rdr_name loc = newTopBinder mod rdr_name loc
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    {-
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      If a signature decl is being loaded, and optIgnoreIfacePragmas is on,
      we toss away unfolding information.
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      Also, if the signature is loaded from a module we're importing from source,
      we do the same. This is to avoid situations when compiling a pair of mutually
      recursive modules, peering at unfolding info in the interface file of the other, 
      e.g., you compile A, it looks at B's interface file and may as a result change
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      its interface file. Hence, B is recompiled, maybe changing its interface file,
      which will the unfolding info used in A to become invalid. Simple way out is to
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      just ignore unfolding info.
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      [Jan 99: I junked the second test above.  If we're importing from an hi-boot
       file there isn't going to *be* any pragma info.  Maybe the above comment
       dates from a time where we picked up a .hi file first if it existed?]
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    -}
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    decl' = case decl of
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	       SigD (IfaceSig name tp ls loc) | opt_IgnoreIfacePragmas
			 ->  SigD (IfaceSig name tp [] loc)
	       other	 -> decl
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-----------------------------------------------------
--	Loading fixity decls
-----------------------------------------------------

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loadFixDecls mod_name (version, decls)
  | null decls = returnRn (version, emptyNameEnv)
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  | otherwise
  = mapRn (loadFixDecl mod_name) decls	`thenRn` \ to_add ->
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    returnRn (version, mkNameEnv to_add)
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loadFixDecl mod_name sig@(FixitySig rdr_name fixity loc)
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  = newGlobalName mod_name (rdrNameOcc rdr_name) 	`thenRn` \ name ->
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    returnRn (name, FixitySig name fixity loc)


-----------------------------------------------------
--	Loading instance decls
-----------------------------------------------------

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loadInstDecl :: Module
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	     -> IfaceInsts
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	     -> RdrNameInstDecl
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	     -> RnM d IfaceInsts
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loadInstDecl mod insts decl@(InstDecl inst_ty binds uprags dfun_name src_loc)
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  = 
	-- Find out what type constructors and classes are "gates" for the
	-- instance declaration.  If all these "gates" are slurped in then
	-- we should slurp the instance decl too.
	-- 
	-- We *don't* want to count names in the context part as gates, though.
	-- For example:
	--		instance Foo a => Baz (T a) where ...
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	--
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	-- Here the gates are Baz and T, but *not* Foo.
    let 
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	munged_inst_ty = removeContext inst_ty
	free_names     = extractHsTyRdrNames munged_inst_ty
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    in
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    setModuleRn mod $
    mapRn lookupOrigName free_names	`thenRn` \ gate_names ->
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    returnRn ((mkNameSet gate_names, (mod, InstD decl)) `consBag` insts)

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-- In interface files, the instance decls now look like
--	forall a. Foo a -> Baz (T a)
-- so we have to strip off function argument types as well
-- as the bit before the '=>' (which is always empty in interface files)
removeContext (HsForAllTy tvs cxt ty) = HsForAllTy tvs [] (removeFuns ty)
removeContext ty		      = removeFuns ty

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removeFuns (HsFunTy _ ty) = removeFuns ty
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removeFuns ty		    = ty


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-----------------------------------------------------
--	Loading Rules
-----------------------------------------------------

loadRules :: Module -> IfaceRules 
	  -> (Version, [RdrNameRuleDecl])
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	  -> RnM d (Version, IfaceRules)
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loadRules mod rule_bag (version, rules)
  | null rules || opt_IgnoreIfacePragmas 
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  = returnRn (version, rule_bag)
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  | otherwise
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  = setModuleRn mod		 	$
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    mapRn (loadRule mod) rules		`thenRn` \ new_rules ->
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    returnRn (version, rule_bag `unionBags` listToBag new_rules)
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loadRule :: Module -> RdrNameRuleDecl -> RnM d GatedDecl
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-- "Gate" the rule simply by whether the rule variable is
-- needed.  We can refine this later.
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loadRule mod decl@(IfaceRule _ _ var _ _ src_loc)
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  = lookupOrigName var		`thenRn` \ var_name ->
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    returnRn (unitNameSet var_name, (mod, RuleD decl))

loadBuiltinRules :: [(RdrName, CoreRule)] -> RnMG ()
loadBuiltinRules builtin_rules
  = getIfacesRn				`thenRn` \ ifaces ->
    mapRn loadBuiltinRule builtin_rules	`thenRn` \ rule_decls ->
    setIfacesRn (ifaces { iRules = iRules ifaces `unionBags` listToBag rule_decls })

loadBuiltinRule (var, rule)
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  = lookupOrigName var		`thenRn` \ var_name ->
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    returnRn (unitNameSet var_name, (nameModule var_name, RuleD (IfaceRuleOut var rule)))


-----------------------------------------------------
--	Loading Deprecations
-----------------------------------------------------
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loadDeprec :: Module -> DeprecationEnv -> RdrNameDeprecation -> RnM d DeprecationEnv
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loadDeprec mod deprec_env (Deprecation (IEModuleContents _) txt _)
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  = traceRn (text "module deprecation not yet implemented:" <+> ppr mod <> colon <+> ppr txt) `thenRn_`
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	-- SUP: TEMPORARY HACK, ignoring module deprecations for now
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    returnRn deprec_env
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loadDeprec mod deprec_env (Deprecation ie txt _)
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  = setModuleRn mod					$
    mapRn lookupOrigName (ieNames ie)		`thenRn` \ names ->
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    traceRn (text "loaded deprecation(s) for" <+> hcat (punctuate comma (map ppr names)) <> colon <+> ppr txt) `thenRn_`
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    returnRn (extendNameEnvList deprec_env (zip names (repeat txt)))
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\end{code}
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%********************************************************
%*							*
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\subsection{Checking usage information}
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%*							*
%********************************************************

\begin{code}
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upToDate  = True
outOfDate = False

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checkModUsage :: [ImportVersion OccName] -> RnMG Bool
-- Given the usage information extracted from the old
-- M.hi file for the module being compiled, figure out
-- whether M needs to be recompiled.
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checkModUsage [] = returnRn upToDate		-- Yes!  Everything is up to date!
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checkModUsage ((mod_name, _, _, NothingAtAll) : rest)
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	-- If CurrentModule.hi contains 
	--	import Foo :: ;
	-- then that simply records that Foo lies below CurrentModule in the
	-- hierarchy, but CurrentModule doesn't depend in any way on Foo.
	-- In this case we don't even want to open Foo's interface.
  = traceRn (ptext SLIT("Nothing used from:") <+> ppr mod_name)	`thenRn_`
    checkModUsage rest	-- This one's ok, so check the rest

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checkModUsage ((mod_name, _, _, whats_imported)  : rest)
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  = tryLoadInterface doc_str mod_name ImportBySystem	`thenRn` \ (ifaces, maybe_err) ->
    case maybe_err of {
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	Just err -> out_of_date (sep [ptext SLIT("Can't find version number for module"), 
				      pprModuleName mod_name]) ;
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		-- Couldn't find or parse a module mentioned in the
		-- old interface file.  Don't complain -- it might just be that
		-- the current module doesn't need that import and it's been deleted
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	Nothing -> 
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    let
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	(_, new_mod_vers, new_fix_vers, new_rule_vers, _, _) 
		= case lookupFM (iImpModInfo ifaces) mod_name of
			   Just (_, _, Just stuff) -> stuff

        old_mod_vers = case whats_imported of
			 Everything v 	     -> v
			 Specifically v _ _ _ -> v
			 -- NothingAtAll case dealt with by previous eqn for checkModUsage
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    in
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	-- If the module version hasn't changed, just move on
    if new_mod_vers == old_mod_vers then
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	traceRn (sep [ptext SLIT("Module version unchanged:"), pprModuleName mod_name])
	`thenRn_` checkModUsage rest
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    else
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    traceRn (sep [ptext SLIT("Module version has changed:"), pprModuleName mod_name])
    `thenRn_`
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	-- Module version changed, so check entities inside

	-- If the usage info wants to say "I imported everything from this module"
	--     it does so by making whats_imported equal to Everything
	-- In that case, we must recompile
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    case whats_imported of {	-- NothingAtAll dealt with earlier
	
      Everything _ 
	-> out_of_date (ptext SLIT("...and I needed the whole module")) ;
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      Specifically _ old_fix_vers old_rule_vers old_local_vers ->
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    if old_fix_vers /= new_fix_vers then
	out_of_date (ptext SLIT("Fixities changed"))
    else if old_rule_vers /= new_rule_vers then
	out_of_date (ptext SLIT("Rules changed"))
    else	
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	-- Non-empty usage list, so check item by item
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    checkEntityUsage mod_name (iDecls ifaces) old_local_vers	`thenRn` \ up_to_date ->
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    if up_to_date then
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	traceRn (ptext SLIT("...but the bits I use haven't."))	`thenRn_`
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	checkModUsage rest	-- This one's ok, so check the rest
    else
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	returnRn outOfDate	-- This one failed, so just bail out now
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    }}
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  where
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    doc_str = sep [ptext SLIT("need version info for"), pprModuleName mod_name]
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checkEntityUsage mod decls [] 
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  = returnRn upToDate	-- Yes!  All up to date!
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checkEntityUsage mod decls ((occ_name,old_vers) : rest)
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  = newGlobalName mod occ_name 	`thenRn` \ name ->
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    case lookupNameEnv decls name of
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	Nothing       -> 	-- We used it before, but it ain't there now
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			  out_of_date (sep [ptext SLIT("No longer exported:"), ppr name])
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	Just (new_vers,_,_,_) 	-- It's there, but is it up to date?
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		| new_vers == old_vers
			-- Up to date, so check the rest
		-> checkEntityUsage mod decls rest

		| otherwise
			-- Out of date, so bale out
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		-> out_of_date (sep [ptext SLIT("Out of date:"), ppr name])

out_of_date msg = traceRn msg `thenRn_` returnRn outOfDate
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\end{code}


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%*********************************************************
%*							*
\subsection{Getting in a declaration}
%*							*
%*********************************************************
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\begin{code}
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importDecl :: Name -> RnMG ImportDeclResult

data ImportDeclResult
  = AlreadySlurped
  | WiredIn	
  | Deferred
  | HereItIs (Module, RdrNameHsDecl)
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importDecl name
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  = getIfacesRn				`thenRn` \ ifaces ->
    getHomeSymbolTableRn		`thenRn` \ hst ->
    if name `elemNameSet` iSlurp ifaces
    || inTypeEnv (iPST ifaces) name
    || inTypeEnv hst	       name
    then	-- Already dealt with
	returnRn AlreadySlurped	
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    else if isLocallyDefined name then	-- Don't bring in decls from
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					-- the renamed module's own interface file
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	addWarnRn (importDeclWarn name) `thenRn_`
	returnRn AlreadySlurped
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    else if isWiredInName name then
	-- When we find a wired-in name we must load its
	-- home module so that we find any instance decls therein
	loadHomeInterface doc name	`thenRn_`
	returnRn WiredIn

    else getNonWiredInDecl name
  where
    doc = ptext SLIT("need home module for wired in thing") <+> ppr name

getNonWiredInDecl :: Name -> RnMG ImportDeclResult
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getNonWiredInDecl needed_name 
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  = traceRn doc_str				`thenRn_`
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    loadHomeInterface doc_str needed_name	`thenRn` \ ifaces ->
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    case lookupNameEnv (iDecls ifaces) needed_name of
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      Just (version, avail, is_tycon_name, decl@(_, TyClD (TyData DataType _ _ _ _ ncons _ _ _ _ _)))
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	-- This case deals with deferred import of algebraic data types

	|  not opt_NoPruneTyDecls

	&& (opt_IgnoreIfacePragmas || ncons > 1)
		-- We only defer if imported interface pragmas are ingored
		-- or if it's not a product type.
		-- Sole reason: The wrapper for a strict function may need to look
		-- inside its arg, and hence need to see its arg type's constructors.

	&& not (getUnique tycon_name `elem` cCallishTyKeys)
		-- Never defer ccall types; we have to unbox them, 
		-- and importing them does no harm

	-> 	-- OK, so we're importing a deferrable data type
	    if needed_name == tycon_name then	
		-- The needed_name is the TyCon of a data type decl
		-- Record that it's slurped, put it in the deferred set
		-- and don't return a declaration at all
		setIfacesRn (recordSlurp (ifaces {iDeferred = iDeferred ifaces 
							      `addOneToNameSet` tycon_name})
				    	 version (AvailTC needed_name [needed_name]))	`thenRn_`
		returnRn Deferred
	    else
	 	-- The needed name is a constructor of a data type decl,
		-- getting a constructor, so remove the TyCon from the deferred set
		-- (if it's there) and return the full declaration
		 setIfacesRn (recordSlurp (ifaces {iDeferred = iDeferred ifaces 
							       `delFromNameSet` tycon_name})
				    version avail)	`thenRn_`
		 returnRn (HereItIs decl)
	where
	   tycon_name = availName avail

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      Just (version,avail,_,decl)
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	-> setIfacesRn (recordSlurp ifaces version avail)	`thenRn_`
	   returnRn (HereItIs decl)
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      Nothing 
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	-> addErrRn (getDeclErr needed_name)	`thenRn_` 
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	   returnRn AlreadySlurped
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  where
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     doc_str = ptext SLIT("need decl for") <+> ppr needed_name
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getDeferredDecls :: RnMG [(Module, RdrNameHsDecl)]
getDeferredDecls 
  = getIfacesRn		`thenRn` \ ifaces ->
    let
	decls_map   	    = iDecls ifaces
	deferred_names	    = nameSetToList (iDeferred ifaces)
        get_abstract_decl n = case lookupNameEnv decls_map n of
				 Just (_, _, _, decl) -> decl
    in
    traceRn (sep [text "getDeferredDecls", nest 4 (fsep (map ppr deferred_names))])	`thenRn_`
    returnRn (map get_abstract_decl deferred_names)
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\end{code}

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@getWiredInDecl@ maps a wired-in @Name@ to what it makes available.
It behaves exactly as if the wired in decl were actually in an interface file.
Specifically,
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\begin{itemize}
\item	if the wired-in name is a data type constructor or a data constructor, 
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	it brings in the type constructor and all the data constructors; and
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	marks as ``occurrences'' any free vars of the data con.
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\item 	similarly for synonum type constructor
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\item 	if the wired-in name is another wired-in Id, it marks as ``occurrences''
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	the free vars of the Id's type.
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\item	it loads the interface file for the wired-in thing for the
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	sole purpose of making sure that its instance declarations are available
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\end{itemize}
All this is necessary so that we know all types that are ``in play'', so
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that we know just what instances to bring into scope.
	
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%*********************************************************
%*							*
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\subsection{Getting what a module exports}
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%*							*
%*********************************************************
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@getInterfaceExports@ is called only for directly-imported modules.
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\begin{code}
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getInterfaceExports :: ModuleName -> WhereFrom -> RnMG (Module, Avails)
getInterfaceExports mod_name from
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  = getHomeSymbolTableRn 		`thenRn` \ hst ->
    case lookupModuleEnvByName hst mod_name of {
	Just mds -> returnRn (mdModule mds, mdExports mds) ;

 
    loadInterface doc_str mod_name from	`thenRn` \ ifaces ->
    case lookupModuleEnv (iPST ifaces) mod_name of
	Just mds -> returnRn (mdModule mod, mdExports mds)
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	-- loadInterface always puts something in the map
	-- even if it's a fake
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  where
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    doc_str = sep [pprModuleName mod_name, ptext SLIT("is directly imported")]
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\end{code}


%*********************************************************
%*							*
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\subsection{Instance declarations are handled specially}
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%*							*
%*********************************************************

\begin{code}
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getImportedInstDecls :: NameSet -> RnMG [(Module,RdrNameHsDecl)]
getImportedInstDecls gates
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  =    	-- First, load any orphan-instance modules that aren't aready loaded
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	-- Orphan-instance modules are recorded in the module dependecnies
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    getIfacesRn 					`thenRn` \ ifaces ->
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    let
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	orphan_mods =
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	  [mod | (mod, (True, _, Nothing)) <- fmToList (iImpModInfo ifaces)]
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    in
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    loadOrphanModules orphan_mods			`thenRn_` 
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	-- Now we're ready to grab the instance declarations
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	-- Find the un-gated ones and return them, 
	-- removing them from the bag kept in Ifaces
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    getIfacesRn 					`thenRn` \ ifaces ->
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    let
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	(decls, new_insts) = selectGated gates (iInsts ifaces)
    in
    setIfacesRn (ifaces { iInsts = new_insts })		`thenRn_`
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    traceRn (sep [text "getImportedInstDecls:", 
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		  nest 4 (fsep (map ppr gate_list)),
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		  text "Slurped" <+> int (length decls) <+> text "instance declarations",
		  nest 4 (vcat (map ppr_brief_inst_decl decls))])	`thenRn_`
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    returnRn decls
  where
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    gate_list      = nameSetToList gates

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ppr_brief_inst_decl (mod, InstD (InstDecl inst_ty _ _ _ _))
  = case inst_ty of
	HsForAllTy _ _ tau -> ppr tau
	other		   -> ppr inst_ty

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getImportedRules :: RnMG [(Module,RdrNameHsDecl)]
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getImportedRules 
  | opt_IgnoreIfacePragmas = returnRn []
  | otherwise
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  = getIfacesRn 	`thenRn` \ ifaces ->
    let
	gates		   = iSlurp ifaces	-- Anything at all that's been slurped
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	rules		   = iRules ifaces
	(decls, new_rules) = selectGated gates rules
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    in
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    if null decls then
	returnRn []
    else
    setIfacesRn (ifaces { iRules = new_rules })		     `thenRn_`
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    traceRn (sep [text "getImportedRules:", 
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		  text "Slurped" <+> int (length decls) <+> text "rules"])   `thenRn_`
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    returnRn decls
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selectGated gates decl_bag
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	-- Select only those decls whose gates are *all* in 'gates'
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#ifdef DEBUG
  | opt_NoPruneDecls	-- Just to try the effect of not gating at all
  = (foldrBag (\ (_,d) ds -> d:ds) [] decl_bag, emptyBag)	-- Grab them all
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  | otherwise
#endif
  = foldrBag select ([], emptyBag) decl_bag
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  where
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    select (reqd, decl) (yes, no)
	| isEmptyNameSet (reqd `minusNameSet` gates) = (decl:yes, no)
	| otherwise				     = (yes,      (reqd,decl) `consBag` no)

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lookupFixityRn :: Name -> RnMS Fixity
lookupFixityRn name
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  | isLocallyDefined name
  = getFixityEnv			`thenRn` \ local_fix_env ->
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    returnRn (lookupLocalFixity local_fix_env name)
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  | otherwise	-- Imported
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      -- For imported names, we have to get their fixities by doing a loadHomeInterface,
      -- 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', which is defined in module B.  Then B isn't loaded
      -- right away (after all, it's possible that nothing from B will be used).
      -- When we come across a use of '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.
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  = getHomeSymbolTableRn 		`thenRn` \ hst ->
    case lookupFixityEnv hst name of {
	Just fixity -> returnRn fixity ;
	Nothing	    -> 

    loadHomeInterface doc name		`thenRn` \ ifaces ->
    returnRn (lookupFixityEnv (iPST ifaces) name `orElse` defaultFixity) 
    }
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  where
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    doc = ptext SLIT("Checking fixity for") <+> ppr name
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\end{code}

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%*********************************************************
%*							*
\subsection{Keeping track of what we've slurped, and version numbers}
%*							*
%*********************************************************

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getImportVersions figures out what the ``usage information'' for this
moudule is; that is, what it must record in its interface file as the
things it uses.  It records:

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\begin{itemize}
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\item	(a) anything reachable from its body code
\item	(b) any module exported with a @module Foo@
\item   (c) anything reachable from an exported item
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\end{itemize}
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Why (b)?  Because if @Foo@ changes then this module's export list
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will change, so we must recompile this module at least as far as
making a new interface file --- but in practice that means complete
recompilation.

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Why (c)?  Consider this:
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\begin{verbatim}
	module A( f, g ) where	|	module B( f ) where
	  import B( f )		|	  f = h 3
	  g = ...		|	  h = ...
\end{verbatim}
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Here, @B.f@ isn't used in A.  Should we nevertheless record @B.f@ in
@A@'s usages?  Our idea is that we aren't going to touch A.hi if it is
*identical* to what it was before.  If anything about @B.f@ changes
than anyone who imports @A@ should be recompiled in case they use
@B.f@ (they'll get an early exit if they don't).  So, if anything
about @B.f@ changes we'd better make sure that something in A.hi
changes, and the convenient way to do that is to record the version
number @B.f@ in A.hi in the usage list.  If B.f changes that'll force a
complete recompiation of A, which is overkill but it's the only way to 
write a new, slightly different, A.hi.

But the example is tricker.  Even if @B.f@ doesn't change at all,
@B.h@ may do so, and this change may not be reflected in @f@'s version
number.  But with -O, a module that imports A must be recompiled if
@B.h@ changes!  So A must record a dependency on @B.h@.  So we treat
the occurrence of @B.f@ in the export list *just as if* it were in the
code of A, and thereby haul in all the stuff reachable from it.

[NB: If B was compiled with -O, but A isn't, we should really *still*
haul in all the unfoldings for B, in case the module that imports A *is*
compiled with -O.  I think this is the case.]

Even if B is used at all we get a usage line for B
	import B <n> :: ... ;
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in A.hi, to record the fact that A does import B.  This is used to decide
to look to look for B.hi rather than B.hi-boot when compiling a module that
imports A.  This line says that A imports B, but uses nothing in it.
So we'll get an early bale-out when compiling A if B's version changes.
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\begin{code}
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mkImportExportInfo :: ModuleName			-- Name of this module
		   -> Avails				-- Info about exports 
		   -> Maybe [RdrNameIE]			-- The export header
		   -> RnMG ([ExportItem], 		-- Export info for iface file; sorted
			    [ImportVersion OccName])	-- Import info for iface file; sorted
			-- Both results are sorted into canonical order to
			-- reduce needless wobbling of interface files

mkImportExportInfo this_mod export_avails exports
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  = getIfacesRn					`thenRn` \ ifaces ->
    let
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	export_all_mods = case exports of
				Nothing -> []
				Just es -> [mod | IEModuleContents mod <- es, 
						  mod /= this_mod]

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	mod_map   = iImpModInfo ifaces
	imp_names = iVSlurp     ifaces
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	-- mv_map groups together all the things imported from a particular module.
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	mv_map :: FiniteMap ModuleName [(OccName,Version)]
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	mv_map = foldr add_mv emptyFM imp_names
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        add_mv (name, version) mv_map = addItem mv_map (moduleName (nameModule name)) 
						       (nameOccName name, version)

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	-- Build the result list by adding info for each module.
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	-- For (a) a library module, we don't record it at all unless it contains orphans
	-- 	   (We must never lose track of orphans.)
	-- 
	--     (b) a source-imported module, don't record the dependency at all
	--	
	-- (b) may seem a bit strange.  The idea is that the usages in a .hi file records
	-- *all* the module's dependencies other than the loop-breakers.  We use
	-- this info in findAndReadInterface to decide whether to look for a .hi file or
	-- a .hi-boot file.  
	--
	-- This means we won't track version changes, or orphans, from .hi-boot files.
	-- The former is potentially rather bad news.  It could be fixed by recording
	-- whether something is a boot file along with the usage info for it, but 
	-- I can't be bothered just now.

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	mk_imp_info mod_name (has_orphans, is_boot, contents) so_far
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	   | mod_name == this_mod	-- Check if M appears in the set of modules 'below' M
					-- This seems like a convenient place to check
	   = WARN( not is_boot, ptext SLIT("Wierd:") <+> ppr this_mod <+> 
			        ptext SLIT("imports itself (perhaps indirectly)") )
	     so_far
 
	   | otherwise
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	   = let
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                                    : so_far
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	     in 
	     case contents of
		Nothing -> 	-- We didn't even open the interface
			-- This happens when a module, Foo, that we explicitly imported has 
			-- 'import Baz' in its interface file, recording that Baz is below
			-- Foo in the module dependency hierarchy.  We want to propagate this
			-- information.  The Nothing says that we didn't even open the interface
			-- file but we must still propagate the dependeny info.
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			-- The module in question must be a local module (in the same package)
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		   go_for_it NothingAtAll
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		Just (mod, mod_vers, fix_vers, rule_vers, how_imported, _)
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		   |  is_sys_import && is_lib_module && not has_orphans
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		   -> so_far		
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		   |  is_lib_module 			-- Record the module but not detailed
		   || mod_name `elem` export_all_mods	-- version information for the imports
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		   -> go_for_it (Everything mod_vers)
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		   |  otherwise
		   -> case lookupFM mv_map mod_name of
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			Just whats_imported -> go_for_it (Specifically mod_vers fix_vers rule_vers 
								       (sortImport whats_imported))
			Nothing		    -> go_for_it NothingAtAll
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						-- This happens if you have
						--	import Foo
						-- but don't actually *use* anything from Foo
					 	-- In which case record an empty dependency list
		   where
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		     is_lib_module = not (isLocalModule mod)
		     is_sys_import = case how_imported of
					ImportBySystem -> True
					other	       -> False
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	import_info = foldFM mk_imp_info [] mod_map

	-- Sort exports into groups by module
	export_fm :: FiniteMap ModuleName [RdrAvailInfo]
	export_fm = foldr insert emptyFM export_avails

        insert avail efm = addItem efm (moduleName (nameModule (availName avail)))
				       (rdrAvailInfo avail)

	export_info = [(m, sortExport as) | (m,as) <- fmToList export_fm]
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    in
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    traceRn (text "Modules in Ifaces: " <+> fsep (map ppr (keysFM mod_map)))	`thenRn_`
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    returnRn (export_info, import_info)
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addItem :: FiniteMap ModuleName [a] -> ModuleName -> a -> FiniteMap ModuleName [a]
addItem fm mod x = addToFM_C add_item fm mod [x]
		 where
		   add_item xs _ = x:xs

sortImport :: [(OccName,Version)] -> [(OccName,Version)]
	-- Make the usage lists appear in canonical order
sortImport vs = sortLt lt vs
	      where
		lt (n1,v1) (n2,v2) = n1 < n2

sortExport :: [RdrAvailInfo] -> [RdrAvailInfo]
sortExport as = sortLt lt as
	      where
		lt a1 a2 = availName a1 < availName a2
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\end{code}
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\begin{code}
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getSlurped
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  = getIfacesRn 	`thenRn` \ ifaces ->
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    returnRn (iSlurp ifaces)
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recordSlurp ifaces@(Ifaces { iSlurp = slurped_names, iVSlurp = imp_names })
	    version avail
  = let
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	new_slurped_names = addAvailToNameSet slurped_names avail
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	new_imp_names = (availName avail, version) : imp_names
    in
    ifaces { iSlurp  = new_slurped_names, iVSlurp = new_imp_names }
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recordLocalSlurps local_avails
  = getIfacesRn 	`thenRn` \ ifaces ->
    let
	new_slurped_names = foldl addAvailToNameSet (iSlurp ifaces) local_avails
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    in
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    setIfacesRn (ifaces { iSlurp  = new_slurped_names })
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\end{code}


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%*********************************************************
%*							*
\subsection{Getting binders out of a declaration}
%*							*
%*********************************************************

@getDeclBinders@ returns the names for a @RdrNameHsDecl@.
It's used for both source code (from @availsFromDecl@) and interface files
(from @loadDecl@).

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It doesn't deal with source-code specific things: @ValD@, @DefD@.  They
are handled by the sourc-code specific stuff in @RnNames@.
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\begin{code}
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getDeclBinders :: (RdrName -> SrcLoc -> RnM d Name)	-- New-name function
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		-> RdrNameHsDecl
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		-> RnM d (Maybe AvailInfo)
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getDeclBinders new_name (TyClD (TyData _ _ tycon _ condecls _ _ _ src_loc _ _))
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  = new_name tycon src_loc			`thenRn` \ tycon_name ->
    getConFieldNames new_name condecls		`thenRn` \ sub_names ->
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    returnRn (Just (AvailTC tycon_name (tycon_name : nub sub_names)))
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	-- The "nub" is because getConFieldNames can legitimately return duplicates,
	-- when a record declaration has the same field in multiple constructors
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getDeclBinders new_name (TyClD (TySynonym tycon _ _ src_loc))
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  = new_name tycon src_loc		`thenRn` \ tycon_name ->
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    returnRn (Just (AvailTC tycon_name [tycon_name]))
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getDeclBinders new_name (TyClD (ClassDecl _ cname _ _ sigs _ _ _ src_loc))
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  = new_name cname src_loc			`thenRn` \ class_name ->
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	-- Record the names for the class ops
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    let
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	-- just want class-op sigs
	op_sigs = filter isClassOpSig sigs
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    in
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    mapRn (getClassOpNames new_name) op_sigs	`thenRn` \ sub_names ->
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    returnRn (Just (AvailTC class_name (class_name : sub_names)))
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getDeclBinders new_name (SigD (IfaceSig var ty prags src_loc))
  = new_name var src_loc			`thenRn` \ var_name ->
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    returnRn (Just (Avail var_name))
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getDeclBinders new_name (FixD _)    = returnRn Nothing
getDeclBinders new_name (DeprecD _) = returnRn Nothing
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    -- foreign declarations
getDeclBinders new_name (ForD (ForeignDecl nm kind _ dyn _ loc))
  | binds_haskell_name kind dyn
  = new_name nm loc		    `thenRn` \ name ->
    returnRn (Just (Avail name))

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  | otherwise 		-- a foreign export
  = lookupOrigName nm `thenRn_` 
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    returnRn Nothing

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getDeclBinders new_name (DefD _)  = returnRn Nothing
getDeclBinders new_name (InstD _) = returnRn Nothing
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getDeclBinders new_name (RuleD _) = returnRn Nothing
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binds_haskell_name (FoImport _) _   = True
binds_haskell_name FoLabel      _   = True
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binds_haskell_name FoExport  ext_nm = isDynamicExtName ext_nm
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----------------
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getConFieldNames new_name (ConDecl con _ _ _ (RecCon fielddecls) src_loc : rest)
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  = mapRn (\n -> new_name n src_loc) (con:fields)	`thenRn` \ cfs ->
    getConFieldNames new_name rest			`thenRn` \ ns  -> 
    returnRn (cfs ++ ns)
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  where
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    fields = concat (map fst fielddecls)

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getConFieldNames new_name (ConDecl con _ _ _ condecl src_loc : rest)
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  = new_name con src_loc		`thenRn` \ n ->
    getConFieldNames new_name rest	`thenRn` \ ns -> 
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