/ghc-7.0.4/compiler/iface/MkIface.lhs

Large files files are truncated, but you can click here to view the full file

%
% (c) The University of Glasgow 2006-2008
% (c) The GRASP/AQUA Project, Glasgow University, 1993-1998
%

\begin{code}
module MkIface ( 
        mkUsedNames,
        mkDependencies,
	mkIface, 	-- Build a ModIface from a ModGuts, 
			-- including computing version information

        mkIfaceTc,

	writeIfaceFile,	-- Write the interface file

	checkOldIface,	-- See if recompilation is required, by
			-- comparing version information

        tyThingToIfaceDecl -- Converting things to their Iface equivalents
 ) where
\end{code}

	-----------------------------------------------
        	Recompilation checking
	-----------------------------------------------

A complete description of how recompilation checking works can be
found in the wiki commentary:

 http://hackage.haskell.org/trac/ghc/wiki/Commentary/Compiler/RecompilationAvoidance

Please read the above page for a top-down description of how this all
works.  Notes below cover specific issues related to the implementation.

Basic idea: 

  * In the mi_usages information in an interface, we record the 
    fingerprint of each free variable of the module

  * In mkIface, we compute the fingerprint of each exported thing A.f.
    For each external thing that A.f refers to, we include the fingerprint
    of the external reference when computing the fingerprint of A.f.  So
    if anything that A.f depends on changes, then A.f's fingerprint will
    change.

  * In checkOldIface we compare the mi_usages for the module with
    the actual fingerprint for all each thing recorded in mi_usages

\begin{code}
#include "HsVersions.h"

import IfaceSyn
import LoadIface
import Id
import IdInfo
import Demand
import Annotations
import CoreSyn
import CoreFVs
import Class
import TyCon
import DataCon
import Type
import Coercion
import TcType
import InstEnv
import FamInstEnv
import TcRnMonad
import HsSyn
import HscTypes
import Finder
import DynFlags
import VarEnv
import Var
import Name
import RdrName
import NameEnv
import NameSet
import Module
import BinIface
import ErrUtils
import Digraph
import SrcLoc
import Outputable
import BasicTypes       hiding ( SuccessFlag(..) )
import UniqFM
import Unique
import Util             hiding ( eqListBy )
import FastString
import Maybes
import ListSetOps
import Binary
import Fingerprint
import Bag

import Control.Monad
import Data.List
import Data.Map (Map)
import qualified Data.Map as Map
import Data.IORef
import System.FilePath
\end{code}



%************************************************************************
%*				 					*
\subsection{Completing an interface}
%*				 					*
%************************************************************************

\begin{code}
mkIface :: HscEnv
	-> Maybe Fingerprint	-- The old fingerprint, if we have it
	-> ModDetails		-- The trimmed, tidied interface
	-> ModGuts		-- Usages, deprecations, etc
	-> IO (Messages,
               Maybe (ModIface, -- The new one
	              Bool))	-- True <=> there was an old Iface, and the
                                --          new one is identical, so no need
                                --          to write it

mkIface hsc_env maybe_old_fingerprint mod_details
	 ModGuts{     mg_module    = this_mod,
		      mg_boot      = is_boot,
		      mg_used_names = used_names,
		      mg_deps      = deps,
                      mg_dir_imps  = dir_imp_mods,
		      mg_rdr_env   = rdr_env,
		      mg_fix_env   = fix_env,
		      mg_warns   = warns,
	              mg_hpc_info  = hpc_info }
        = mkIface_ hsc_env maybe_old_fingerprint
                   this_mod is_boot used_names deps rdr_env 
                   fix_env warns hpc_info dir_imp_mods mod_details

-- | make an interface from the results of typechecking only.  Useful
-- for non-optimising compilation, or where we aren't generating any
-- object code at all ('HscNothing').
mkIfaceTc :: HscEnv
          -> Maybe Fingerprint	-- The old fingerprint, if we have it
          -> ModDetails		-- gotten from mkBootModDetails, probably
          -> TcGblEnv		-- Usages, deprecations, etc
	  -> IO (Messages, Maybe (ModIface, Bool))
mkIfaceTc hsc_env maybe_old_fingerprint mod_details
  tc_result@TcGblEnv{ tcg_mod = this_mod,
                      tcg_src = hsc_src,
                      tcg_imports = imports,
                      tcg_rdr_env = rdr_env,
                      tcg_fix_env = fix_env,
                      tcg_warns = warns,
                      tcg_hpc = other_hpc_info
                    }
  = do
          let used_names = mkUsedNames tc_result
          deps <- mkDependencies tc_result
          let hpc_info = emptyHpcInfo other_hpc_info
          mkIface_ hsc_env maybe_old_fingerprint
                   this_mod (isHsBoot hsc_src) used_names deps rdr_env 
                   fix_env warns hpc_info (imp_mods imports) mod_details
        

mkUsedNames :: TcGblEnv -> NameSet
mkUsedNames TcGblEnv{ tcg_dus = dus } = allUses dus
        
mkDependencies :: TcGblEnv -> IO Dependencies
mkDependencies
          TcGblEnv{ tcg_mod = mod,
                    tcg_imports = imports,
                    tcg_th_used = th_var
                  }
 = do 
      th_used   <- readIORef th_var                     -- Whether TH is used
      let
        dep_mods = eltsUFM (delFromUFM (imp_dep_mods imports) (moduleName mod))
                -- M.hi-boot can be in the imp_dep_mods, but we must remove
                -- it before recording the modules on which this one depends!
                -- (We want to retain M.hi-boot in imp_dep_mods so that 
                --  loadHiBootInterface can see if M's direct imports depend 
                --  on M.hi-boot, and hence that we should do the hi-boot consistency 
                --  check.)

        pkgs | th_used   = insertList thPackageId (imp_dep_pkgs imports)
             | otherwise = imp_dep_pkgs imports

      return Deps { dep_mods   = sortBy (stableModuleNameCmp `on` fst) dep_mods,
                    dep_pkgs   = sortBy stablePackageIdCmp pkgs,
                    dep_orphs  = sortBy stableModuleCmp (imp_orphs  imports),
                    dep_finsts = sortBy stableModuleCmp (imp_finsts imports) }
                -- sort to get into canonical order
                -- NB. remember to use lexicographic ordering

mkIface_ :: HscEnv -> Maybe Fingerprint -> Module -> IsBootInterface
         -> NameSet -> Dependencies -> GlobalRdrEnv
         -> NameEnv FixItem -> Warnings -> HpcInfo
         -> ImportedMods
         -> ModDetails
	 -> IO (Messages, Maybe (ModIface, Bool))
mkIface_ hsc_env maybe_old_fingerprint 
         this_mod is_boot used_names deps rdr_env fix_env src_warns hpc_info
         dir_imp_mods
	 ModDetails{  md_insts 	   = insts, 
		      md_fam_insts = fam_insts,
		      md_rules 	   = rules,
		      md_anns	   = anns,
                      md_vect_info = vect_info,
		      md_types 	   = type_env,
		      md_exports   = exports }
-- NB:	notice that mkIface does not look at the bindings
--	only at the TypeEnv.  The previous Tidy phase has
--	put exactly the info into the TypeEnv that we want
--	to expose in the interface

  = do	{ usages <- mkUsageInfo hsc_env this_mod dir_imp_mods used_names

	; let	{ entities = typeEnvElts type_env ;
                  decls  = [ tyThingToIfaceDecl entity
			   | entity <- entities,
			     let name = getName entity,
                             not (isImplicitTyThing entity),
	                        -- No implicit Ids and class tycons in the interface file
			     not (isWiredInName name),
	                        -- Nor wired-in things; the compiler knows about them anyhow
			     nameIsLocalOrFrom this_mod name  ]
				-- Sigh: see Note [Root-main Id] in TcRnDriver

		; fixities    = [(occ,fix) | FixItem occ fix <- nameEnvElts fix_env]
		; warns     = src_warns
		; iface_rules = map (coreRuleToIfaceRule this_mod) rules
		; iface_insts = map instanceToIfaceInst insts
		; iface_fam_insts = map famInstToIfaceFamInst fam_insts
                ; iface_vect_info = flattenVectInfo vect_info

	        ; intermediate_iface = ModIface { 
			mi_module   = this_mod,
			mi_boot     = is_boot,
			mi_deps     = deps,
			mi_usages   = usages,
			mi_exports  = mkIfaceExports exports,
	
			-- Sort these lexicographically, so that
			-- the result is stable across compilations
			mi_insts    = sortLe le_inst iface_insts,
			mi_fam_insts= sortLe le_fam_inst iface_fam_insts,
			mi_rules    = sortLe le_rule iface_rules,

                        mi_vect_info = iface_vect_info,

			mi_fixities = fixities,
			mi_warns  = warns,
			mi_anns     = mkIfaceAnnotations anns,
			mi_globals  = Just rdr_env,

			-- Left out deliberately: filled in by addVersionInfo
			mi_iface_hash = fingerprint0,
			mi_mod_hash  = fingerprint0,
 			mi_exp_hash  = fingerprint0,
 			mi_orphan_hash = fingerprint0,
			mi_orphan    = False,	-- Always set by addVersionInfo, but
						-- it's a strict field, so we can't omit it.
                        mi_finsts    = False,   -- Ditto
			mi_decls     = deliberatelyOmitted "decls",
			mi_hash_fn   = deliberatelyOmitted "hash_fn",
			mi_hpc       = isHpcUsed hpc_info,

			-- And build the cached values
			mi_warn_fn = mkIfaceWarnCache warns,
			mi_fix_fn = mkIfaceFixCache fixities }
		}

        ; (new_iface, no_change_at_all) 
	        <- {-# SCC "versioninfo" #-}
			 addFingerprints hsc_env maybe_old_fingerprint
                                         intermediate_iface decls

		-- Warn about orphans
	; let warn_orphs      = dopt Opt_WarnOrphans dflags
              warn_auto_orphs = dopt Opt_WarnAutoOrphans dflags
              orph_warnings   --- Laziness means no work done unless -fwarn-orphans
	        | warn_orphs || warn_auto_orphs = rule_warns `unionBags` inst_warns
	        | otherwise 	       	        = emptyBag
	      errs_and_warns = (orph_warnings, emptyBag)
	      unqual = mkPrintUnqualified dflags rdr_env
	      inst_warns = listToBag [ instOrphWarn unqual d 
	      		   	     | (d,i) <- insts `zip` iface_insts
	      		   	     , isNothing (ifInstOrph i) ]
	      rule_warns = listToBag [ ruleOrphWarn unqual this_mod r 
	      		    	     | r <- iface_rules
	      		   	     , isNothing (ifRuleOrph r)
                                     , if ifRuleAuto r then warn_auto_orphs
                                                       else warn_orphs ]

	; if errorsFound dflags errs_and_warns
            then return ( errs_and_warns, Nothing )
            else do {

-- XXX	; when (dopt Opt_D_dump_hi_diffs dflags) (printDump pp_diffs)
   
	   	-- Debug printing
	; dumpIfSet_dyn dflags Opt_D_dump_hi "FINAL INTERFACE" 
			(pprModIface new_iface)

                -- bug #1617: on reload we weren't updating the PrintUnqualified
                -- correctly.  This stems from the fact that the interface had
                -- not changed, so addVersionInfo returns the old ModIface
                -- with the old GlobalRdrEnv (mi_globals).
        ; let final_iface = new_iface{ mi_globals = Just rdr_env }

	; return (errs_and_warns, Just (final_iface, no_change_at_all)) }}
  where
     r1 `le_rule`     r2 = ifRuleName      r1    <=    ifRuleName      r2
     i1 `le_inst`     i2 = ifDFun          i1 `le_occ` ifDFun          i2  
     i1 `le_fam_inst` i2 = ifFamInstTcName i1 `le_occ` ifFamInstTcName i2

     le_occ :: Name -> Name -> Bool
	-- Compare lexicographically by OccName, *not* by unique, because 
	-- the latter is not stable across compilations
     le_occ n1 n2 = nameOccName n1 <= nameOccName n2

     dflags = hsc_dflags hsc_env

     deliberatelyOmitted :: String -> a
     deliberatelyOmitted x = panic ("Deliberately omitted: " ++ x)

     ifFamInstTcName = ifaceTyConName . ifFamInstTyCon

     flattenVectInfo (VectInfo { vectInfoVar   = vVar
                               , vectInfoTyCon = vTyCon
                               }) = 
       IfaceVectInfo { 
         ifaceVectInfoVar        = [ Var.varName v 
                                   | (v, _) <- varEnvElts vVar],
         ifaceVectInfoTyCon      = [ tyConName t 
                                   | (t, t_v) <- nameEnvElts vTyCon
                                   , t /= t_v],
         ifaceVectInfoTyConReuse = [ tyConName t
                                   | (t, t_v) <- nameEnvElts vTyCon
                                   , t == t_v]
       } 

-----------------------------
writeIfaceFile :: DynFlags -> ModLocation -> ModIface -> IO ()
writeIfaceFile dflags location new_iface
    = do createDirectoryHierarchy (takeDirectory hi_file_path)
         writeBinIface dflags hi_file_path new_iface
    where hi_file_path = ml_hi_file location


-- -----------------------------------------------------------------------------
-- Look up parents and versions of Names

-- This is like a global version of the mi_hash_fn field in each ModIface.
-- Given a Name, it finds the ModIface, and then uses mi_hash_fn to get
-- the parent and version info.

mkHashFun
        :: HscEnv                       -- needed to look up versions
        -> ExternalPackageState         -- ditto
        -> (Name -> Fingerprint)
mkHashFun hsc_env eps
  = \name -> 
      let 
        mod = ASSERT2( isExternalName name, ppr name ) nameModule name
        occ = nameOccName name
        iface = lookupIfaceByModule (hsc_dflags hsc_env) hpt pit mod `orElse` 
                   pprPanic "lookupVers2" (ppr mod <+> ppr occ)
      in  
        snd (mi_hash_fn iface occ `orElse` 
                  pprPanic "lookupVers1" (ppr mod <+> ppr occ))
  where
      hpt = hsc_HPT hsc_env
      pit = eps_PIT eps

-- ---------------------------------------------------------------------------
-- Compute fingerprints for the interface

addFingerprints
        :: HscEnv
        -> Maybe Fingerprint -- the old fingerprint, if any
        -> ModIface	     -- The new interface (lacking decls)
        -> [IfaceDecl]       -- The new decls
        -> IO (ModIface,     -- Updated interface
               Bool)	     -- True <=> no changes at all; 
                             -- no need to write Iface

addFingerprints hsc_env mb_old_fingerprint iface0 new_decls
 = do
   eps <- hscEPS hsc_env
   let
        -- The ABI of a declaration represents everything that is made
        -- visible about the declaration that a client can depend on.
        -- see IfaceDeclABI below.
       declABI :: IfaceDecl -> IfaceDeclABI 
       declABI decl = (this_mod, decl, extras)
        where extras = declExtras fix_fn non_orph_rules non_orph_insts decl

       edges :: [(IfaceDeclABI, Unique, [Unique])]
       edges = [ (abi, getUnique (ifName decl), out)
	       | decl <- new_decls
               , let abi = declABI decl
	       , let out = localOccs $ freeNamesDeclABI abi
               ]

       name_module n = ASSERT2( isExternalName n, ppr n ) nameModule n
       localOccs = map (getUnique . getParent . getOccName) 
                        . filter ((== this_mod) . name_module)
                        . nameSetToList
          where getParent occ = lookupOccEnv parent_map occ `orElse` occ

        -- maps OccNames to their parents in the current module.
        -- e.g. a reference to a constructor must be turned into a reference
        -- to the TyCon for the purposes of calculating dependencies.
       parent_map :: OccEnv OccName
       parent_map = foldr extend emptyOccEnv new_decls
          where extend d env = 
                  extendOccEnvList env [ (b,n) | b <- ifaceDeclSubBndrs d ]
                  where n = ifName d

        -- strongly-connected groups of declarations, in dependency order
       groups = stronglyConnCompFromEdgedVertices edges

       global_hash_fn = mkHashFun hsc_env eps

        -- how to output Names when generating the data to fingerprint.
        -- Here we want to output the fingerprint for each top-level
        -- Name, whether it comes from the current module or another
        -- module.  In this way, the fingerprint for a declaration will
        -- change if the fingerprint for anything it refers to (transitively)
        -- changes.
       mk_put_name :: (OccEnv (OccName,Fingerprint))
                   -> BinHandle -> Name -> IO  ()
       mk_put_name local_env bh name
          | isWiredInName name  =  putNameLiterally bh name 
           -- wired-in names don't have fingerprints
          | otherwise
          = ASSERT2( isExternalName name, ppr name )
	    let hash | nameModule name /= this_mod =  global_hash_fn name
                     | otherwise = 
                        snd (lookupOccEnv local_env (getOccName name)
                           `orElse` pprPanic "urk! lookup local fingerprint" 
                                       (ppr name)) -- (undefined,fingerprint0))
                -- This panic indicates that we got the dependency
                -- analysis wrong, because we needed a fingerprint for
                -- an entity that wasn't in the environment.  To debug
                -- it, turn the panic into a trace, uncomment the
                -- pprTraces below, run the compile again, and inspect
                -- the output and the generated .hi file with
                -- --show-iface.
            in 
            put_ bh hash

        -- take a strongly-connected group of declarations and compute
        -- its fingerprint.

       fingerprint_group :: (OccEnv (OccName,Fingerprint), 
                             [(Fingerprint,IfaceDecl)])
                         -> SCC IfaceDeclABI
                         -> IO (OccEnv (OccName,Fingerprint), 
                                [(Fingerprint,IfaceDecl)])

       fingerprint_group (local_env, decls_w_hashes) (AcyclicSCC abi)
          = do let hash_fn = mk_put_name local_env
                   decl = abiDecl abi
               -- pprTrace "fingerprinting" (ppr (ifName decl) ) $ do
               hash <- computeFingerprint dflags hash_fn abi
               return (extend_hash_env (hash,decl) local_env,
                       (hash,decl) : decls_w_hashes)

       fingerprint_group (local_env, decls_w_hashes) (CyclicSCC abis)
          = do let decls = map abiDecl abis
                   local_env' = foldr extend_hash_env local_env 
                                   (zip (repeat fingerprint0) decls)
                   hash_fn = mk_put_name local_env'
               -- pprTrace "fingerprinting" (ppr (map ifName decls) ) $ do
               let stable_abis = sortBy cmp_abiNames abis
                -- put the cycle in a canonical order
               hash <- computeFingerprint dflags hash_fn stable_abis
               let pairs = zip (repeat hash) decls
               return (foldr extend_hash_env local_env pairs,
                       pairs ++ decls_w_hashes)

       extend_hash_env :: (Fingerprint,IfaceDecl)
                       -> OccEnv (OccName,Fingerprint)
                       -> OccEnv (OccName,Fingerprint)
       extend_hash_env (hash,d) env0 = foldr add_imp env1 (ifaceDeclSubBndrs d)
        where
          decl_name = ifName d
          item = (decl_name, hash)
          env1 = extendOccEnv env0 decl_name item
          add_imp bndr env = extendOccEnv env bndr item
            
   --
   (local_env, decls_w_hashes) <- 
       foldM fingerprint_group (emptyOccEnv, []) groups

   -- when calculating fingerprints, we always need to use canonical
   -- ordering for lists of things.  In particular, the mi_deps has various
   -- lists of modules and suchlike, so put these all in canonical order:
   let sorted_deps = sortDependencies (mi_deps iface0)

   -- the export hash of a module depends on the orphan hashes of the
   -- orphan modules below us in the dependency tree.  This is the way
   -- that changes in orphans get propagated all the way up the
   -- dependency tree.  We only care about orphan modules in the current
   -- package, because changes to orphans outside this package will be
   -- tracked by the usage on the ABI hash of package modules that we import.
   let orph_mods = filter ((== this_pkg) . modulePackageId)
                   $ dep_orphs sorted_deps
   dep_orphan_hashes <- getOrphanHashes hsc_env orph_mods

   orphan_hash <- computeFingerprint dflags (mk_put_name local_env)
                      (map ifDFun orph_insts, orph_rules, fam_insts)

   -- the export list hash doesn't depend on the fingerprints of
   -- the Names it mentions, only the Names themselves, hence putNameLiterally.
   export_hash <- computeFingerprint dflags putNameLiterally 
                      (mi_exports iface0,
                       orphan_hash,
                       dep_orphan_hashes,
                       dep_pkgs (mi_deps iface0))
                        -- dep_pkgs: see "Package Version Changes" on
                        -- wiki/Commentary/Compiler/RecompilationAvoidance

   -- put the declarations in a canonical order, sorted by OccName
   let sorted_decls = Map.elems $ Map.fromList $
                          [(ifName d, e) | e@(_, d) <- decls_w_hashes]

   -- the ABI hash depends on:
   --   - decls
   --   - export list
   --   - orphans
   --   - deprecations
   --   - XXX vect info?
   mod_hash <- computeFingerprint dflags putNameLiterally
                      (map fst sorted_decls,
                       export_hash,
                       orphan_hash,
                       mi_warns iface0)

   -- The interface hash depends on:
   --    - the ABI hash, plus
   --    - usages
   --    - deps
   --    - hpc
   iface_hash <- computeFingerprint dflags putNameLiterally
                      (mod_hash, 
                       mi_usages iface0,
                       sorted_deps,
                       mi_hpc iface0)

   let
    no_change_at_all = Just iface_hash == mb_old_fingerprint

    final_iface = iface0 {
                mi_mod_hash    = mod_hash,
                mi_iface_hash  = iface_hash,
                mi_exp_hash    = export_hash,
                mi_orphan_hash = orphan_hash,
                mi_orphan      = not (null orph_rules && null orph_insts),
                mi_finsts      = not . null $ mi_fam_insts iface0,
                mi_decls       = sorted_decls,
                mi_hash_fn     = lookupOccEnv local_env }
   --
   return (final_iface, no_change_at_all)

  where
    this_mod = mi_module iface0
    dflags = hsc_dflags hsc_env
    this_pkg = thisPackage dflags
    (non_orph_insts, orph_insts) = mkOrphMap ifInstOrph (mi_insts iface0)
    (non_orph_rules, orph_rules) = mkOrphMap ifRuleOrph (mi_rules iface0)
        -- ToDo: shouldn't we be splitting fam_insts into orphans and
        -- non-orphans?
    fam_insts = mi_fam_insts iface0
    fix_fn = mi_fix_fn iface0


getOrphanHashes :: HscEnv -> [Module] -> IO [Fingerprint]
getOrphanHashes hsc_env mods = do
  eps <- hscEPS hsc_env
  let 
    hpt        = hsc_HPT hsc_env
    pit        = eps_PIT eps
    dflags     = hsc_dflags hsc_env
    get_orph_hash mod = 
          case lookupIfaceByModule dflags hpt pit mod of
            Nothing    -> pprPanic "moduleOrphanHash" (ppr mod)
            Just iface -> mi_orphan_hash iface
  --
  return (map get_orph_hash mods)


sortDependencies :: Dependencies -> Dependencies
sortDependencies d
 = Deps { dep_mods   = sortBy (compare `on` (moduleNameFS.fst)) (dep_mods d),
          dep_pkgs   = sortBy (compare `on` packageIdFS)  (dep_pkgs d),
          dep_orphs  = sortBy stableModuleCmp (dep_orphs d),
          dep_finsts = sortBy stableModuleCmp (dep_finsts d) }
\end{code}


%************************************************************************
%*		                					*
          The ABI of an IfaceDecl       									
%*	       	     							*
%************************************************************************

Note [The ABI of an IfaceDecl]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
The ABI of a declaration consists of:

   (a) the full name of the identifier (inc. module and package,
       because these are used to construct the symbol name by which
       the identifier is known externally).

   (b) the declaration itself, as exposed to clients.  That is, the
       definition of an Id is included in the fingerprint only if
       it is made available as as unfolding in the interface.

   (c) the fixity of the identifier
   (d) for Ids: rules
   (e) for classes: instances, fixity & rules for methods
   (f) for datatypes: instances, fixity & rules for constrs

Items (c)-(f) are not stored in the IfaceDecl, but instead appear
elsewhere in the interface file.  But they are *fingerprinted* with
the declaration itself. This is done by grouping (c)-(f) in IfaceDeclExtras,
and fingerprinting that as part of the declaration.

\begin{code}
type IfaceDeclABI = (Module, IfaceDecl, IfaceDeclExtras)

data IfaceDeclExtras 
  = IfaceIdExtras    Fixity [IfaceRule]
  | IfaceDataExtras  Fixity [IfaceInstABI] [(Fixity,[IfaceRule])]
  | IfaceClassExtras Fixity [IfaceInstABI] [(Fixity,[IfaceRule])]
  | IfaceSynExtras   Fixity
  | IfaceOtherDeclExtras

abiDecl :: IfaceDeclABI -> IfaceDecl
abiDecl (_, decl, _) = decl

cmp_abiNames :: IfaceDeclABI -> IfaceDeclABI -> Ordering
cmp_abiNames abi1 abi2 = ifName (abiDecl abi1) `compare` 
                         ifName (abiDecl abi2)

freeNamesDeclABI :: IfaceDeclABI -> NameSet
freeNamesDeclABI (_mod, decl, extras) =
  freeNamesIfDecl decl `unionNameSets` freeNamesDeclExtras extras

freeNamesDeclExtras :: IfaceDeclExtras -> NameSet
freeNamesDeclExtras (IfaceIdExtras    _ rules)
  = unionManyNameSets (map freeNamesIfRule rules)
freeNamesDeclExtras (IfaceDataExtras  _ insts subs)
  = unionManyNameSets (mkNameSet insts : map freeNamesSub subs)
freeNamesDeclExtras (IfaceClassExtras _ insts subs)
  = unionManyNameSets (mkNameSet insts : map freeNamesSub subs)
freeNamesDeclExtras (IfaceSynExtras _)
  = emptyNameSet
freeNamesDeclExtras IfaceOtherDeclExtras
  = emptyNameSet

freeNamesSub :: (Fixity,[IfaceRule]) -> NameSet
freeNamesSub (_,rules) = unionManyNameSets (map freeNamesIfRule rules)

instance Outputable IfaceDeclExtras where
  ppr IfaceOtherDeclExtras       = empty
  ppr (IfaceIdExtras  fix rules) = ppr_id_extras fix rules
  ppr (IfaceSynExtras fix)       = ppr fix
  ppr (IfaceDataExtras fix insts stuff)  = vcat [ppr fix, ppr_insts insts,
                                                 ppr_id_extras_s stuff]
  ppr (IfaceClassExtras fix insts stuff) = vcat [ppr fix, ppr_insts insts,
                                                 ppr_id_extras_s stuff]

ppr_insts :: [IfaceInstABI] -> SDoc
ppr_insts _ = ptext (sLit "<insts>")

ppr_id_extras_s :: [(Fixity, [IfaceRule])] -> SDoc
ppr_id_extras_s stuff = vcat [ppr_id_extras f r | (f,r)<- stuff]

ppr_id_extras :: Fixity -> [IfaceRule] -> SDoc
ppr_id_extras fix rules = ppr fix $$ vcat (map ppr rules)

-- This instance is used only to compute fingerprints
instance Binary IfaceDeclExtras where
  get _bh = panic "no get for IfaceDeclExtras"
  put_ bh (IfaceIdExtras fix rules) = do
   putByte bh 1; put_ bh fix; put_ bh rules
  put_ bh (IfaceDataExtras fix insts cons) = do
   putByte bh 2; put_ bh fix; put_ bh insts; put_ bh cons
  put_ bh (IfaceClassExtras fix insts methods) = do
   putByte bh 3; put_ bh fix; put_ bh insts; put_ bh methods
  put_ bh (IfaceSynExtras fix) = do
   putByte bh 4; put_ bh fix
  put_ bh IfaceOtherDeclExtras = do
   putByte bh 5

declExtras :: (OccName -> Fixity)
           -> OccEnv [IfaceRule]
           -> OccEnv [IfaceInst]
           -> IfaceDecl
           -> IfaceDeclExtras

declExtras fix_fn rule_env inst_env decl
  = case decl of
      IfaceId{} -> IfaceIdExtras (fix_fn n) 
                        (lookupOccEnvL rule_env n)
      IfaceData{ifCons=cons} -> 
                     IfaceDataExtras (fix_fn n)
                        (map ifDFun $ lookupOccEnvL inst_env n)
                        (map (id_extras . ifConOcc) (visibleIfConDecls cons))
      IfaceClass{ifSigs=sigs} -> 
                     IfaceClassExtras (fix_fn n)
                        (map ifDFun $ lookupOccEnvL inst_env n)
                        [id_extras op | IfaceClassOp op _ _ <- sigs]
      IfaceSyn{} -> IfaceSynExtras (fix_fn n)
      _other -> IfaceOtherDeclExtras
  where
        n = ifName decl
        id_extras occ = (fix_fn occ, lookupOccEnvL rule_env occ)

--
-- When hashing an instance, we hash only the DFunId, because that
-- depends on all the information about the instance.
--
type IfaceInstABI = IfExtName

lookupOccEnvL :: OccEnv [v] -> OccName -> [v]
lookupOccEnvL env k = lookupOccEnv env k `orElse` []

-- used when we want to fingerprint a structure without depending on the
-- fingerprints of external Names that it refers to.
putNameLiterally :: BinHandle -> Name -> IO ()
putNameLiterally bh name = ASSERT( isExternalName name ) 
  do { put_ bh $! nameModule name
     ; put_ bh $! nameOccName name }

computeFingerprint :: Binary a
                   => DynFlags 
                   -> (BinHandle -> Name -> IO ())
                   -> a
                   -> IO Fingerprint

computeFingerprint _dflags put_name a = do
  bh <- openBinMem (3*1024) -- just less than a block
  ud <- newWriteState put_name putFS
  bh <- return $ setUserData bh ud
  put_ bh a
  fingerprintBinMem bh

{-
-- for testing: use the md5sum command to generate fingerprints and
-- compare the results against our built-in version.
  fp' <- oldMD5 dflags bh
  if fp /= fp' then pprPanic "computeFingerprint" (ppr fp <+> ppr fp')
               else return fp

oldMD5 dflags bh = do
  tmp <- newTempName dflags "bin"
  writeBinMem bh tmp
  tmp2 <- newTempName dflags "md5"
  let cmd = "md5sum " ++ tmp ++ " >" ++ tmp2
  r <- system cmd
  case r of
    ExitFailure _ -> ghcError (PhaseFailed cmd r)
    ExitSuccess -> do
        hash_str <- readFile tmp2
        return $! readHexFingerprint hash_str
-}

instOrphWarn :: PrintUnqualified -> Instance -> WarnMsg
instOrphWarn unqual inst
  = mkWarnMsg (getSrcSpan inst) unqual $
    hang (ptext (sLit "Warning: orphan instance:")) 2 (pprInstanceHdr inst)

ruleOrphWarn :: PrintUnqualified -> Module -> IfaceRule -> WarnMsg
ruleOrphWarn unqual mod rule
  = mkWarnMsg silly_loc unqual $
    ptext (sLit "Orphan rule:") <+> ppr rule
  where
    silly_loc = srcLocSpan (mkSrcLoc (moduleNameFS (moduleName mod)) 1 1)
    -- We don't have a decent SrcSpan for a Rule, not even the CoreRule
    -- Could readily be fixed by adding a SrcSpan to CoreRule, if we wanted to

----------------------
-- mkOrphMap partitions instance decls or rules into
-- 	(a) an OccEnv for ones that are not orphans, 
--	    mapping the local OccName to a list of its decls
--	(b) a list of orphan decls
mkOrphMap :: (decl -> Maybe OccName)	-- (Just occ) for a non-orphan decl, keyed by occ
					-- Nothing for an orphan decl
	  -> [decl] 			-- Sorted into canonical order
	  -> (OccEnv [decl],	 	-- Non-orphan decls associated with their key;
					--	each sublist in canonical order
	      [decl])			-- Orphan decls; in canonical order
mkOrphMap get_key decls
  = foldl go (emptyOccEnv, []) decls
  where
    go (non_orphs, orphs) d
	| Just occ <- get_key d
	= (extendOccEnv_Acc (:) singleton non_orphs occ d, orphs)
	| otherwise = (non_orphs, d:orphs)
\end{code}


%************************************************************************
%*		                					*
       Keeping track of what we've slurped, and fingerprints
%*	       	     							*
%************************************************************************

\begin{code}
mkUsageInfo :: HscEnv -> Module -> ImportedMods -> NameSet -> IO [Usage]
mkUsageInfo hsc_env this_mod dir_imp_mods used_names
  = do	{ eps <- hscEPS hsc_env
	; let usages = mk_usage_info (eps_PIT eps) hsc_env this_mod
				     dir_imp_mods used_names
	; usages `seqList`  return usages }
	 -- seq the list of Usages returned: occasionally these
	 -- don't get evaluated for a while and we can end up hanging on to
	 -- the entire collection of Ifaces.

mk_usage_info :: PackageIfaceTable
              -> HscEnv
              -> Module
              -> ImportedMods
              -> NameSet
              -> [Usage]
mk_usage_info pit hsc_env this_mod direct_imports used_names
  = mapCatMaybes mkUsage usage_mods
  where
    hpt = hsc_HPT hsc_env
    dflags = hsc_dflags hsc_env
    this_pkg = thisPackage dflags

    used_mods    = moduleEnvKeys ent_map
    dir_imp_mods = (moduleEnvKeys direct_imports)
    all_mods     = used_mods ++ filter (`notElem` used_mods) dir_imp_mods
    usage_mods   = sortBy stableModuleCmp all_mods
                        -- canonical order is imported, to avoid interface-file
                        -- wobblage.

    -- ent_map groups together all the things imported and used
    -- from a particular module
    ent_map :: ModuleEnv [OccName]
    ent_map  = foldNameSet add_mv emptyModuleEnv used_names
     where
      add_mv name mv_map
        | isWiredInName name = mv_map  -- ignore wired-in names
        | otherwise
        = case nameModule_maybe name of
             Nothing  -> pprPanic "mkUsageInfo: internal name?" (ppr name)
             Just mod -> -- This lambda function is really just a
                         -- specialised (++); originally came about to
                         -- avoid quadratic behaviour (trac #2680)
                         extendModuleEnvWith (\_ xs -> occ:xs) mv_map mod [occ]
    		   where occ = nameOccName name
    
    -- We want to create a Usage for a home module if 
    --	a) we used something from it; has something in used_names
    --	b) we imported it, even if we used nothing from it
    --	   (need to recompile if its export list changes: export_fprint)
    mkUsage :: Module -> Maybe Usage
    mkUsage mod
      | isNothing maybe_iface		-- We can't depend on it if we didn't
                        		-- load its interface.
      || mod == this_mod                -- We don't care about usages of
                                        -- things in *this* module
      = Nothing

      | modulePackageId mod /= this_pkg
      = Just UsagePackageModule{ usg_mod      = mod,
                                 usg_mod_hash = mod_hash }
        -- for package modules, we record the module hash only

      | (null used_occs
	  && isNothing export_hash
          && not is_direct_import
	  && not finsts_mod)
      = Nothing			-- Record no usage info
        -- for directly-imported modules, we always want to record a usage
        -- on the orphan hash.  This is what triggers a recompilation if
        -- an orphan is added or removed somewhere below us in the future.
    
      | otherwise	
      = Just UsageHomeModule { 
                      usg_mod_name = moduleName mod,
    	  	      usg_mod_hash = mod_hash,
    		      usg_exports  = export_hash,
    		      usg_entities = Map.toList ent_hashs }
      where
	maybe_iface  = lookupIfaceByModule dflags hpt pit mod
		-- In one-shot mode, the interfaces for home-package 
		-- modules accumulate in the PIT not HPT.  Sigh.

        is_direct_import = mod `elemModuleEnv` direct_imports

        Just iface   = maybe_iface
	finsts_mod   = mi_finsts    iface
        hash_env     = mi_hash_fn   iface
        mod_hash     = mi_mod_hash  iface
        export_hash | depend_on_exports mod = Just (mi_exp_hash iface)
    		    | otherwise 	    = Nothing
    
        used_occs = lookupModuleEnv ent_map mod `orElse` []

    	-- Making a Map here ensures that (a) we remove duplicates
        -- when we have usages on several subordinates of a single parent,
        -- and (b) that the usages emerge in a canonical order, which
        -- is why we use Map rather than OccEnv: Map works
        -- using Ord on the OccNames, which is a lexicographic ordering.
	ent_hashs :: Map OccName Fingerprint
        ent_hashs = Map.fromList (map lookup_occ used_occs)
        
        lookup_occ occ = 
            case hash_env occ of
                Nothing -> pprPanic "mkUsage" (ppr mod <+> ppr occ <+> ppr used_names)
                Just r  -> r

        depend_on_exports mod = 
           case lookupModuleEnv direct_imports mod of
    	        Just _ -> True
                  -- Even if we used 'import M ()', we have to register a
                  -- usage on the export list because we are sensitive to
                  -- changes in orphan instances/rules.
	    	Nothing -> False
                  -- In GHC 6.8.x the above line read "True", and in
                  -- fact it recorded a dependency on *all* the
                  -- modules underneath in the dependency tree.  This
                  -- happens to make orphans work right, but is too
                  -- expensive: it'll read too many interface files.
                  -- The 'isNothing maybe_iface' check above saved us
                  -- from generating many of these usages (at least in
                  -- one-shot mode), but that's even more bogus!
\end{code}

\begin{code}
mkIfaceAnnotations :: [Annotation] -> [IfaceAnnotation]
mkIfaceAnnotations = map mkIfaceAnnotation

mkIfaceAnnotation :: Annotation -> IfaceAnnotation
mkIfaceAnnotation (Annotation { ann_target = target, ann_value = serialized }) = IfaceAnnotation { 
        ifAnnotatedTarget = fmap nameOccName target,
        ifAnnotatedValue = serialized
    }
\end{code}

\begin{code}
mkIfaceExports :: [AvailInfo]
               -> [(Module, [GenAvailInfo OccName])]
                  -- Group by module and sort by occurrence
mkIfaceExports exports
  = [ (mod, Map.elems avails)
    | (mod, avails) <- sortBy (stableModuleCmp `on` fst)
                              (moduleEnvToList groupFM)
                       -- NB. the Map.toList is in a random order,
                       -- because Ord Module is not a predictable
                       -- ordering.  Hence we perform a final sort
                       -- using the stable Module ordering.
    ]
  where
	-- Group by the module where the exported entities are defined
	-- (which may not be the same for all Names in an Avail)
	-- Deliberately use Map rather than UniqFM so we
	-- get a canonical ordering
    groupFM :: ModuleEnv (Map FastString (GenAvailInfo OccName))
    groupFM = foldl add emptyModuleEnv exports

    add_one :: ModuleEnv (Map FastString (GenAvailInfo OccName))
	    -> Module -> GenAvailInfo OccName
	    -> ModuleEnv (Map FastString (GenAvailInfo OccName))
    add_one env mod avail 
      -- XXX Is there a need to flip Map.union here?
      =  extendModuleEnvWith (flip Map.union) env mod 
		(Map.singleton (occNameFS (availName avail)) avail)

	-- NB: we should not get T(X) and T(Y) in the export list
	--     else the Map.union will simply discard one!  They
	--     should have been combined by now.
    add env (Avail n)
      = ASSERT( isExternalName n ) 
        add_one env (nameModule n) (Avail (nameOccName n))

    add env (AvailTC tc ns)
      = ASSERT( all isExternalName ns ) 
	foldl add_for_mod env mods
      where
	tc_occ = nameOccName tc
	mods   = nub (map nameModule ns)
		-- Usually just one, but see Note [Original module]

	add_for_mod env mod
	    = add_one env mod (AvailTC tc_occ (sort names_from_mod))
              -- NB. sort the children, we need a canonical order
	    where
	      names_from_mod = [nameOccName n | n <- ns, nameModule n == mod]
\end{code}

Note [Orignal module]
~~~~~~~~~~~~~~~~~~~~~
Consider this:
	module X where { data family T }
	module Y( T(..) ) where { import X; data instance T Int = MkT Int }
The exported Avail from Y will look like
	X.T{X.T, Y.MkT}
That is, in Y, 
  - only MkT is brought into scope by the data instance;
  - but the parent (used for grouping and naming in T(..) exports) is X.T
  - and in this case we export X.T too

In the result of MkIfaceExports, the names are grouped by defining module,
so we may need to split up a single Avail into multiple ones.


%************************************************************************
%*									*
	Load the old interface file for this module (unless
	we have it aleady), and check whether it is up to date
	
%*									*
%************************************************************************

\begin{code}
checkOldIface :: HscEnv
	      -> ModSummary
	      -> Bool 			-- Source unchanged
	      -> Maybe ModIface 	-- Old interface from compilation manager, if any
	      -> IO (RecompileRequired, Maybe ModIface)

checkOldIface hsc_env mod_summary source_unchanged maybe_iface
  = do	{ showPass (hsc_dflags hsc_env) 
	           ("Checking old interface for " ++ 
			showSDoc (ppr (ms_mod mod_summary))) ;

	; initIfaceCheck hsc_env $
	  check_old_iface hsc_env mod_summary source_unchanged maybe_iface
     }

check_old_iface :: HscEnv -> ModSummary -> Bool -> Maybe ModIface
                -> IfG (Bool, Maybe ModIface)
check_old_iface hsc_env mod_summary source_unchanged maybe_iface
 =  do 	-- CHECK WHETHER THE SOURCE HAS CHANGED
    { when (not source_unchanged)
	   (traceHiDiffs (nest 4 (text "Source file changed or recompilation check turned off")))

     -- If the source has changed and we're in interactive mode, avoid reading
     -- an interface; just return the one we might have been supplied with.
    ; let dflags = hsc_dflags hsc_env
    ; if not (isObjectTarget (hscTarget dflags)) && not source_unchanged then
         return (outOfDate, maybe_iface)
      else
      case maybe_iface of {
        Just old_iface -> do -- Use the one we already have
	  { traceIf (text "We already have the old interface for" <+> ppr (ms_mod mod_summary))
	  ; recomp <- checkVersions hsc_env source_unchanged mod_summary old_iface
	  ; return (recomp, Just old_iface) }

      ; Nothing -> do

	-- Try and read the old interface for the current module
	-- from the .hi file left from the last time we compiled it
    { let iface_path = msHiFilePath mod_summary
    ; read_result <- readIface (ms_mod mod_summary) iface_path False
    ; case read_result of {
         Failed err -> do	-- Old interface file not found, or garbled; give up
		{ traceIf (text "FYI: cannot read old interface file:"
			   	 $$ nest 4 err)
	        ; return (outOfDate, Nothing) }

      ;  Succeeded iface -> do

	-- We have got the old iface; check its versions
    { traceIf (text "Read the interface file" <+> text iface_path)
    ; recomp <- checkVersions hsc_env source_unchanged mod_summary iface
    ; return (recomp, Just iface)
    }}}}}

\end{code}

@recompileRequired@ is called from the HscMain.   It checks whether
a recompilation is required.  It needs access to the persistent state,
finder, etc, because it may have to load lots of interface files to
check their versions.

\begin{code}
type RecompileRequired = Bool
upToDate, outOfDate :: Bool
upToDate  = False	-- Recompile not required
outOfDate = True	-- Recompile required

checkVersions :: HscEnv
	      -> Bool		-- True <=> source unchanged
              -> ModSummary
	      -> ModIface 	-- Old interface
	      -> IfG RecompileRequired
checkVersions hsc_env source_unchanged mod_summary iface
  | not source_unchanged
  = return outOfDate
  | otherwise
  = do	{ traceHiDiffs (text "Considering whether compilation is required for" <+> 
		        ppr (mi_module iface) <> colon)

        ; recomp <- checkDependencies hsc_env mod_summary iface
        ; if recomp then return outOfDate else do {

	-- Source code unchanged and no errors yet... carry on 
        --
	-- First put the dependent-module info, read from the old
	-- interface, into the envt, so that when we look for
	-- interfaces we look for the right one (.hi or .hi-boot)
	-- 
	-- It's just temporary because either the usage check will succeed 
	-- (in which case we are done with this module) or it'll fail (in which
	-- case we'll compile the module from scratch anyhow).
	--	
	-- We do this regardless of compilation mode, although in --make mode
	-- all the dependent modules should be in the HPT already, so it's
	-- quite redundant
	  updateEps_ $ \eps  -> eps { eps_is_boot = mod_deps }

	; let this_pkg = thisPackage (hsc_dflags hsc_env)
	; checkList [checkModUsage this_pkg u | u <- mi_usages iface]
    }}
  where
	-- This is a bit of a hack really
    mod_deps :: ModuleNameEnv (ModuleName, IsBootInterface)
    mod_deps = mkModDeps (dep_mods (mi_deps iface))


-- If the direct imports of this module are resolved to targets that
-- are not among the dependencies of the previous interface file,
-- then we definitely need to recompile.  This catches cases like
--   - an exposed package has been upgraded
--   - we are compiling with different package flags
--   - a home module that was shadowing a package module has been removed
--   - a new home module has been added that shadows a package module
-- See bug #1372.
--
-- Returns True if recompilation is required.
checkDependencies :: HscEnv -> ModSummary -> ModIface -> IfG RecompileRequired
checkDependencies hsc_env summary iface
 = orM (map dep_missing (ms_imps summary ++ ms_srcimps summary))
  where
   prev_dep_mods = dep_mods (mi_deps iface)
   prev_dep_pkgs = dep_pkgs (mi_deps iface)

   this_pkg = thisPackage (hsc_dflags hsc_env)

   orM = foldr f (return False)
    where f m rest = do b <- m; if b then return True else rest

   dep_missing (L _ (ImportDecl (L _ mod) pkg _ _ _ _)) = do
     find_res <- liftIO $ findImportedModule hsc_env mod pkg
     case find_res of
        Found _ mod
          | pkg == this_pkg
           -> if moduleName mod `notElem` map fst prev_dep_mods
                 then do traceHiDiffs $
                           text "imported module " <> quotes (ppr mod) <>
                           text " not among previous dependencies"
                         return outOfDate
                 else
                         return upToDate
          | otherwise
           -> if pkg `notElem` prev_dep_pkgs
                 then do traceHiDiffs $
                           text "imported module " <> quotes (ppr mod) <>
                           text " is from package " <> quotes (ppr pkg) <>
                           text ", which is not among previous dependencies"
                         return outOfDate
                 else
                         return upToDate
           where pkg = modulePackageId mod
        _otherwise  -> return outOfDate

needInterface :: Module -> (ModIface -> IfG RecompileRequired)
              -> IfG RecompileRequired
needInterface mod continue
  = do	-- Load the imported interface if possible
    let doc_str = sep [ptext (sLit "need version info for"), ppr mod]
    traceHiDiffs (text "Checking usages for module" <+> ppr mod)

    mb_iface <- loadInterface doc_str mod ImportBySystem
	-- Load the interface, but don't complain on failure;
	-- Instead, get an Either back which we can test

    case mb_iface of
      Failed _ ->  (out_of_date (sep [ptext (sLit "Couldn't load interface for module"),
                                      ppr mod]))
                  -- 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
      Succeeded iface -> continue iface


checkModUsage :: PackageId ->Usage -> IfG RecompileRequired
-- Given the usage information extracted from the old
-- M.hi file for the module being compiled, figure out
-- whether M needs to be recompiled.

checkModUsage _this_pkg UsagePackageModule{
                                usg_mod = mod,
                                usg_mod_hash = old_mod_hash }
  = needInterface mod $ \iface -> do
    checkModuleFingerprint old_mod_hash (mi_mod_hash iface)
        -- We only track the ABI hash of package modules, rather than
        -- individual entity usages, so if the ABI hash changes we must
        -- recompile.  This is safe but may entail more recompilation when
        -- a dependent package has changed.

checkModUsage this_pkg UsageHomeModule{ 
                                usg_mod_name = mod_name, 
                                usg_mod_hash = old_mod_hash,
		       		usg_exports = maybe_old_export_hash,
		       		usg_entities = old_decl_hash }
  = do
    let mod = mkModule this_pkg mod_name
    needInterface mod $ \iface -> do

    let
	new_mod_hash    = mi_mod_hash    iface
	new_decl_hash 	= mi_hash_fn     iface
	new_export_hash = mi_exp_hash    iface

	-- CHECK MODULE
    recompile <- checkModuleFingerprint old_mod_hash new_mod_hash
    if not recompile then return upToDate else do
				 
	-- CHECK EXPORT LIST
    checkMaybeHash maybe_old_export_hash new_export_hash
        (ptext (sLit "  Export list changed")) $ do

	-- CHECK ITEMS ONE BY ONE
    recompile <- checkList [ checkEntityUsage new_decl_hash u 
                           | u <- old_decl_hash]
    if recompile 
      then return outOfDate	-- This one failed, so just bail out now
      else up_to_date (ptext (sLit "  Great!  The bits I use are up to date"))

------------------------
checkModuleFingerprint :: Fingerprint -> Fingerprint -> IfG Bool
checkModuleFingerprint old_mod_hash new_mod_hash
  | new_mod_hash == old_mod_hash
  = up_to_date (ptext (sLit "Module fingerprint unchanged"))

  | otherwise
  = out_of_date_hash (ptext (sLit "  Module fingerprint has changed"))
		     old_mod_hash new_mod_hash

------------------------
checkMaybeHash :: Maybe Fingerprint -> Fingerprint -> SDoc
               -> IfG RecompileRequired -> IfG RecompileRequired
checkMaybeHash maybe_old_hash new_hash doc continue
  | Just hash <- maybe_old_hash, hash /= new_hash
  = out_of_date_hash doc hash new_hash
  | otherwise
  = continue

------------------------
checkEntityUsage :: (OccName -> Maybe (OccName, Fingerprint))
                 -> (OccName, Fingerprint)
                 -> IfG Bool
checkEntityUsage new_hash (name,old_hash)
  = case new_hash name of

	Nothing       -> 	-- We used it before, but it ain't there now
			  out_of_date (sep [ptext (sLit "No longer exported:"), ppr name])

	Just (_, new_hash) 	-- It's there, but is it up to date?
	  | new_hash == old_hash -> do traceHiDiffs (text "  Up to date" <+> ppr name <+> parens (ppr new_hash))
			  	       retur…