[ghc-hetmet.git] / ghc / compiler / iface / MkIface.lhs

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

\begin{code}
module MkIface ( 
        showIface,      -- Print the iface in Foo.hi

        mkUsageInfo,    -- Construct the usage info for a module

        mkIface,        -- Build a ModIface from a ModGuts, 
                        -- including computing version information

        checkOldIface   -- See if recompilation is required, by
                        -- comparing version information
 ) where
\end{code}

        -----------------------------------------------
                MkIface.lhs deals with versioning
        -----------------------------------------------

Here's the version-related info in an interface file

  module Foo 8          -- module-version 
             3          -- export-list-version
             2          -- rule-version
    Usages:     -- Version info for what this compilation of Foo imported
        Baz 3           -- Module version
            [4]         -- The export-list version if Foo depended on it
            (g,2)       -- Function and its version
            (T,1)       -- Type and its version

    <version> f :: Int -> Int {- Unfolding: \x -> Wib.t[2] x -}
                -- The [2] says that f's unfolding 
                -- mentions verison 2 of Wib.t
        
        -----------------------------------------------
                        Basic idea
        -----------------------------------------------

Basic idea: 
  * In the mi_usages information in an interface, we record the 
    version number of each free variable of the module

  * In mkIface, we compute the version number of each exported thing A.f
    by comparing its A.f's info with its new info, and bumping its 
    version number if it differs.  If A.f mentions B.g, and B.g's version
    number has changed, then we count A.f as having changed too.

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


Fixities
~~~~~~~~
We count A.f as changing if its fixity changes

Rules
~~~~~
If a rule changes, we want to recompile any module that might be
affected by that rule.  For non-orphan rules, this is relatively easy.
If module M defines f, and a rule for f, just arrange that the version
number for M.f changes if any of the rules for M.f change.  Any module
that does not depend on M.f can't be affected by the rule-change
either.

Orphan rules (ones whose 'head function' is not defined in M) are
harder.  Here's what we do.

  * We have a per-module orphan-rule version number which changes if 
    any orphan rule changes. (It's unaffected by non-orphan rules.)

  * We record usage info for any orphan module 'below' this one,
    giving the orphan-rule version number.  We recompile if this 
    changes. 

The net effect is that if an orphan rule changes, we recompile every
module above it.  That's very conservative, but it's devilishly hard
to know what it might affect, so we just have to be conservative.

Instance decls
~~~~~~~~~~~~~~
In an iface file we have
     module A where
        instance Eq a => Eq [a]  =  dfun29
        dfun29 :: ... 

We have a version number for dfun29, covering its unfolding
etc. Suppose we are compiling a module M that imports A only
indirectly.  If typechecking M uses this instance decl, we record the
dependency on A.dfun29 as if it were a free variable of the module
(via the tcg_inst_usages accumulator).  That means that A will appear
in M's usage list.  If the shape of the instance declaration changes,
then so will dfun29's version, triggering a recompilation.

Adding an instance declaration, or changing an instance decl that is
not currently used, is more tricky.  (This really only makes a
difference when we have overlapping instance decls, because then the
new instance decl might kick in to override the old one.)  We handle
this in a very similar way that we handle rules above.

  * For non-orphan instance decls, identify one locally-defined tycon/class
    mentioned in the decl.  Treat the instance decl as part of the defn of that
    tycon/class, so that if the shape of the instance decl changes, so does the
    tycon/class; that in turn will force recompilation of anything that uses
    that tycon/class.

  * For orphan instance decls, act the same way as for orphan rules.
    Indeed, we use the same global orphan-rule version number.

mkUsageInfo
~~~~~~~~~~~
mkUsageInfo 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.  

We produce a line for every module B below the module, A, currently being
compiled:
        import B <n> ;
to record the fact that A does import B indirectly.  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.

The usage information records:

\begin{itemize}
\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
\end{itemize}

Why (b)?  Because if @Foo@ changes then this module's export list
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.

Why (c)?  Consider this:
\begin{verbatim}
        module A( f, g ) where  |       module B( f ) where
          import B( f )         |         f = h 3
          g = ...               |         h = ...
\end{verbatim}

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.

        *** Conclusion: if A mentions B.f in its export list,
            behave just as if A mentioned B.f in its source code,
            and slurp in B.f and all its transitive closure ***

[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.]


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

import HsSyn
import IfaceSyn         ( IfaceDecl(..), IfaceClassOp(..), IfaceConDecl(..),
                          IfaceRule(..), IfaceInst(..), IfaceExtName(..), IfaceTyCon(..),
                          eqIfDecl, eqIfRule, eqIfInst, IfaceEq(..), (&&&), bool, 
                          eqMaybeBy, eqListBy, visibleIfConDecls,
                          tyThingToIfaceDecl, dfunToIfaceInst, coreRuleToIfaceRule )
import LoadIface        ( readIface, loadInterface, ifaceInstGates )
import BasicTypes       ( Version, initialVersion, bumpVersion )
import TcRnMonad
import TcRnTypes        ( ImportAvails(..), mkModDeps )
import TcType           ( isFFITy )
import HscTypes         ( ModIface(..), TyThing(..),
                          ModGuts(..), ModGuts, IfaceExport,
                          GhciMode(..), isOneShot,
                          HscEnv(..), hscEPS,
                          Dependencies(..), FixItem(..), 
                          mkIfaceDepCache, mkIfaceFixCache, mkIfaceVerCache,
                          typeEnvElts, 
                          GenAvailInfo(..), availName, 
                          ExternalPackageState(..),
                          Usage(..), IsBootInterface,
                          Deprecs(..), IfaceDeprecs, Deprecations,
                          lookupIfaceByModName
                        )


import CmdLineOpts
import Name             ( Name, nameModule, nameOccName, nameParent, isExternalName,
                          nameParent_maybe, isWiredInName, NamedThing(..), nameModuleName )
import NameEnv
import NameSet
import OccName          ( OccName, OccEnv, mkOccEnv, lookupOccEnv, emptyOccEnv, extendOccEnv_C,
                          OccSet, emptyOccSet, elemOccSet, occSetElts, 
                          extendOccSet, extendOccSetList,
                          isEmptyOccSet, intersectOccSet, intersectsOccSet,
                          occNameFS, isTcOcc )
import TyCon            ( tyConDataCons, isNewTyCon, newTyConRep )
import Class            ( classSelIds )
import DataCon          ( dataConName, dataConFieldLabels )
import Module           ( Module, ModuleName, moduleNameFS, moduleName, isHomeModule,
                          ModLocation(..), mkSysModuleNameFS, moduleUserString,
                          ModuleEnv, emptyModuleEnv, lookupModuleEnv,
                          extendModuleEnv_C, moduleEnvElts
                        )
import Outputable
import DriverUtil       ( createDirectoryHierarchy, directoryOf )
import Util             ( sortLe, seqList )
import Binary           ( getBinFileWithDict )
import BinIface         ( writeBinIface, v_IgnoreHiWay )
import Unique           ( Unique, Uniquable(..) )
import ErrUtils         ( dumpIfSet_dyn, showPass )
import Digraph          ( stronglyConnComp, SCC(..) )
import FiniteMap
import FastString

import DATA_IOREF       ( writeIORef )
import Monad            ( when )
import List             ( insert )
import Maybes           ( orElse, mapCatMaybes, isNothing, fromJust, expectJust )
\end{code}



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

\begin{code}
mkIface :: HscEnv
        -> ModLocation
        -> Maybe ModIface       -- The old interface, if we have it
        -> ModGuts              -- The compiled, tidied module
        -> IO ModIface          -- The new one, complete with decls and versions
-- mkFinalIface 
--      a) completes the interface
--      b) writes it out to a file if necessary

mkIface hsc_env location maybe_old_iface 
        guts@ModGuts{ mg_module = this_mod,
                      mg_usages = usages,
                      mg_deps   = deps,
                      mg_exports = exports,
                      mg_fix_env = fix_env,
                      mg_deprecs = src_deprecs,
                      mg_insts = insts, 
                      mg_rules = rules,
                      mg_types = type_env }
  = do  { eps <- hscEPS hsc_env
        ; let   { this_mod_name = moduleName this_mod
                ; ext_nm = mkExtNameFn hsc_env eps this_mod_name
                ; local_things = [thing | thing <- typeEnvElts type_env,
                                          not (isWiredInName (getName thing)) ]
                        -- Do not export anything about wired-in things
                        --  (GHC knows about them already)

                ; abstract_tcs :: NameSet -- TyCons and Classes whose representation is not exposed
                ; abstract_tcs
                    | not omit_prags = emptyNameSet             -- In the -O case, nothing is abstract
                    | otherwise      = mkNameSet [ getName thing 
                                                 | thing <- local_things
                                                 , not (mustExposeThing exports thing)]

                ; decls  = [ tyThingToIfaceDecl omit_prags abstract_tcs ext_nm thing 
                           | thing <- local_things, wantDeclFor exports abstract_tcs thing ]
                                -- Don't put implicit Ids and class tycons in the interface file

                ; fixities = [(occ,fix) | FixItem occ fix _ <- nameEnvElts fix_env]
                ; deprecs  = mkIfaceDeprec src_deprecs
                ; iface_rules 
                     | omit_prags = []
                     | otherwise  = sortLe le_rule $
                                    map (coreRuleToIfaceRule this_mod_name ext_nm) rules
                ; iface_insts = sortLe le_inst (map dfunToIfaceInst insts)

                ; intermediate_iface = ModIface { 
                        mi_module   = this_mod,
                        mi_package  = opt_InPackage,
                        mi_boot     = False,
                        mi_deps     = deps,
                        mi_usages   = usages,
                        mi_exports  = mkIfaceExports exports,
                        mi_insts    = iface_insts,
                        mi_rules    = iface_rules,
                        mi_fixities = fixities,
                        mi_deprecs  = deprecs,
        
                        -- Left out deliberately: filled in by addVersionInfo
                        mi_mod_vers  = initialVersion,
                        mi_exp_vers  = initialVersion,
                        mi_rule_vers = initialVersion,
                        mi_orphan    = False,   -- Always set by addVersionInfo, but
                                                -- it's a strict field, so we can't omit it.
                        mi_decls     = deliberatelyOmitted "decls",
                        mi_ver_fn    = deliberatelyOmitted "ver_fn",

                        -- And build the cached values
                        mi_dep_fn = mkIfaceDepCache deprecs,
                        mi_fix_fn = mkIfaceFixCache fixities }

                -- Add version information
                ; (new_iface, no_change_at_all, pp_diffs) 
                        = _scc_ "versioninfo" 
                         addVersionInfo maybe_old_iface intermediate_iface decls
                }

                -- Write the interface file, if necessary
        ; when (not no_change_at_all && ghci_mode /= Interactive) $ do
                createDirectoryHierarchy (directoryOf hi_file_path)
                writeBinIface hi_file_path new_iface

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

        ; return new_iface }
  where
     r1 `le_rule` r2 = ifRuleName r1 <= ifRuleName r2
     i1 `le_inst` i2 = ifDFun     i1 <= ifDFun     i2

     dflags    = hsc_dflags hsc_env
     ghci_mode = hsc_mode hsc_env
     hi_file_path = ml_hi_file location
     omit_prags = dopt Opt_OmitInterfacePragmas dflags

                                              
mustExposeThing :: NameSet -> TyThing -> Bool
-- We are compiling without -O, and thus trying to write as little as 
-- possible into the interface file.  But we must expose the details of
-- any data types and classes whose constructors, fields, methods are 
-- visible to an importing module
mustExposeThing exports (ATyCon tc) 
  =  any exported_data_con (tyConDataCons tc)
        -- Expose rep if any datacon or field is exported

  || (isNewTyCon tc && isFFITy (snd (newTyConRep tc)))
        -- Expose the rep for newtypes if the rep is an FFI type.  
        -- For a very annoying reason.  'Foreign import' is meant to
        -- be able to look through newtypes transparently, but it
        -- can only do that if it can "see" the newtype representation
  where         
     exported_data_con con 
        = any (`elemNameSet` exports) (dataConName con : dataConFieldLabels con)
                
mustExposeThing exports (AClass cls) 
  = any exported_class_op (classSelIds cls)
  where         -- Expose rep if any classs op is exported
     exported_class_op op = getName op `elemNameSet` exports

mustExposeThing exports other = False


wantDeclFor :: NameSet  -- User-exported things
            -> NameSet  -- Abstract things
            -> TyThing -> Bool
wantDeclFor exports abstracts thing
  | Just parent <- nameParent_maybe name        -- An implicit thing
  = parent `elemNameSet` abstracts && name `elemNameSet` exports
  | otherwise
  = True
  where
    name = getName thing
  

deliberatelyOmitted x = panic ("Deliberately omitted: " ++ x)

-----------------------------
mkExtNameFn :: HscEnv -> ExternalPackageState -> ModuleName -> Name -> IfaceExtName
mkExtNameFn hsc_env eps this_mod
  = ext_nm
  where
    hpt = hsc_HPT hsc_env
    pit = eps_PIT eps

    ext_nm name 
      | mod_nm == this_mod = case nameParent_maybe name of
                                Nothing  -> LocalTop occ
                                Just par -> LocalTopSub occ (nameOccName par)
      | isWiredInName name = ExtPkg  mod_nm occ
      | isHomeModule mod   = HomePkg mod_nm occ vers
      | otherwise          = ExtPkg  mod_nm occ
      where
        mod      = nameModule name
        mod_nm   = moduleName mod
        occ      = nameOccName name
        par_occ  = nameOccName (nameParent name)
                -- The version of the *parent* is the one want
        vers     = lookupVersion mod_nm par_occ
              
    lookupVersion :: ModuleName -> OccName -> Version
        -- Even though we're looking up a home-package thing, in
        -- one-shot mode the imported interfaces may be in the PIT
    lookupVersion mod occ
      = mi_ver_fn iface occ `orElse` 
        pprPanic "lookupVers1" (ppr mod <+> ppr occ)
      where
        iface = lookupIfaceByModName hpt pit mod `orElse` 
                pprPanic "lookupVers2" (ppr mod <+> ppr occ)

-----------------------------
-- Compute version numbers for local decls

addVersionInfo :: Maybe ModIface        -- The old interface, read from M.hi
               -> ModIface              -- The new interface decls (lacking decls)
               -> [IfaceDecl]           -- The new decls
               -> (ModIface, 
                   Bool,                -- True <=> no changes at all; no need to write new Iface
                   SDoc)                -- Differences

addVersionInfo Nothing new_iface new_decls
-- No old interface, so definitely write a new one!
  = (new_iface { mi_orphan = anyNothing getInstKey (mi_insts new_iface)
                          || anyNothing getRuleKey (mi_rules new_iface),
                 mi_decls  = [(initialVersion, decl) | decl <- new_decls],
                 mi_ver_fn = \n -> Just initialVersion },
     False, ptext SLIT("No old interface file") $$ 
            pprOrphans orph_insts orph_rules)
  where
    orph_insts = filter (isNothing . getInstKey) (mi_insts new_iface)
    orph_rules = filter (isNothing . getRuleKey) (mi_rules new_iface)

addVersionInfo (Just old_iface@(ModIface { mi_mod_vers  = old_mod_vers, 
                                           mi_exp_vers  = old_exp_vers, 
                                           mi_rule_vers = old_rule_vers, 
                                           mi_decls     = old_decls,
                                           mi_ver_fn    = old_decl_vers,
                                           mi_fix_fn    = old_fixities }))
               new_iface@(ModIface { mi_fix_fn = new_fixities })
               new_decls

  | no_change_at_all = (old_iface,   True,  ptext SLIT("Interface file unchanged") $$ pp_orphs)
  | otherwise        = (final_iface, False, vcat [ptext SLIT("Interface file has changed"),
                                                  nest 2 pp_diffs,
                                                  text "" $$ pp_orphs])
  where
    final_iface = new_iface { mi_mod_vers  = bump_unless no_output_change old_mod_vers,
                              mi_exp_vers  = bump_unless no_export_change old_exp_vers,
                              mi_rule_vers = bump_unless no_rule_change   old_rule_vers,
                              mi_orphan    = not (null new_orph_rules && null new_orph_insts),
                              mi_decls     = decls_w_vers,
                              mi_ver_fn    = mkIfaceVerCache decls_w_vers }

    decls_w_vers = [(add_vers decl, decl) | decl <- new_decls]

    -------------------
    (old_non_orph_insts, old_orph_insts) = mkRuleMap getInstKey (mi_insts old_iface)
    (new_non_orph_insts, new_orph_insts) = mkRuleMap getInstKey (mi_insts new_iface)
    same_insts occ = eqMaybeBy  (eqListBy eqIfInst) 
                                (lookupOccEnv old_non_orph_insts occ)
                                (lookupOccEnv new_non_orph_insts occ)
  
    (old_non_orph_rules, old_orph_rules) = mkRuleMap getRuleKey (mi_rules old_iface)
    (new_non_orph_rules, new_orph_rules) = mkRuleMap getRuleKey (mi_rules new_iface)
    same_rules occ = eqMaybeBy  (eqListBy eqIfRule)
                                (lookupOccEnv old_non_orph_rules occ)
                                (lookupOccEnv new_non_orph_rules occ)
    -------------------
    -- Computing what changed
    no_output_change = no_decl_change   && no_rule_change && 
                       no_export_change && no_deprec_change
    no_export_change = mi_exports new_iface == mi_exports old_iface     -- Kept sorted
    no_decl_change   = isEmptyOccSet changed_occs
    no_rule_change   = not (changedWrt changed_occs (eqListBy eqIfRule old_orph_rules new_orph_rules)
                         || changedWrt changed_occs (eqListBy eqIfInst old_orph_insts new_orph_insts))
    no_deprec_change = mi_deprecs new_iface == mi_deprecs old_iface

        -- If the usages havn't changed either, we don't need to write the interface file
    no_other_changes = mi_usages new_iface == mi_usages old_iface && 
                       mi_deps new_iface == mi_deps old_iface
    no_change_at_all = no_output_change && no_other_changes
 
    pp_diffs = vcat [pp_change no_export_change "Export list" 
                        (ppr old_exp_vers <+> arrow <+> ppr (mi_exp_vers final_iface)),
                     pp_change no_rule_change "Rules"
                        (ppr old_rule_vers <+> arrow <+> ppr (mi_rule_vers final_iface)),
                     pp_change no_deprec_change "Deprecations" empty,
                     pp_change no_other_changes  "Usages" empty,
                     pp_decl_diffs]
    pp_change True  what info = empty
    pp_change False what info = text what <+> ptext SLIT("changed") <+> info

    -------------------
    old_decl_env = mkOccEnv [(ifName decl, decl) | (_,decl) <- old_decls]
    same_fixity n = bool (old_fixities n == new_fixities n)

    -------------------
    -- Adding version info
    new_version     = bumpVersion old_mod_vers
    add_vers decl | occ `elemOccSet` changed_occs = new_version
                  | otherwise = expectJust "add_vers" (old_decl_vers occ)
                                -- If it's unchanged, there jolly well 
                  where         -- should be an old version number
                    occ = ifName decl

    -------------------
    changed_occs :: OccSet
    changed_occs = computeChangedOccs eq_info

    eq_info :: [(OccName, IfaceEq)]
    eq_info = map check_eq new_decls
    check_eq new_decl | Just old_decl <- lookupOccEnv old_decl_env occ 
                      = (occ, new_decl `eqIfDecl` old_decl &&&
                              eq_indirects new_decl)
                      | otherwise {- No corresponding old decl -}      
                      = (occ, NotEqual) 
                      where
                        occ = ifName new_decl

    eq_indirects :: IfaceDecl -> IfaceEq
                -- When seeing if two decls are the same, remember to
                -- check whether any relevant fixity or rules have changed
    eq_indirects (IfaceId {ifName = occ}) = eq_ind_occ occ
    eq_indirects (IfaceClass {ifName = cls_occ, ifSigs = sigs})
        = same_insts cls_occ &&& 
          eq_ind_occs [op | IfaceClassOp op _ _ <- sigs] 
    eq_indirects (IfaceData {ifName = tc_occ, ifCons = cons})
        = same_insts tc_occ &&& same_fixity tc_occ &&&  -- The TyCon can have a fixity too
          eq_ind_occs (map ifConOcc (visibleIfConDecls cons))
    eq_indirects other = Equal  -- Synonyms and foreign declarations

    eq_ind_occ :: OccName -> IfaceEq    -- For class ops and Ids; check fixity and rules
    eq_ind_occ occ = same_fixity occ &&& same_rules occ
    eq_ind_occs = foldr ((&&&) . eq_ind_occ) Equal 
   
    -------------------
    -- Diffs
    pp_decl_diffs :: SDoc       -- Nothing => no changes
    pp_decl_diffs 
        | isEmptyOccSet changed_occs = empty
        | otherwise 
        = vcat [ptext SLIT("Changed occs:") <+> ppr (occSetElts changed_occs),
                ptext SLIT("Version change for these decls:"),
                nest 2 (vcat (map show_change new_decls))]

    eq_env = mkOccEnv eq_info
    show_change new_decl
        | not (occ `elemOccSet` changed_occs) = empty
        | otherwise
        = vcat [ppr occ <+> ppr (old_decl_vers occ) <+> arrow <+> ppr new_version, 
                nest 2 why]
        where
          occ = ifName new_decl
          why = case lookupOccEnv eq_env occ of
                    Just (EqBut occs) -> sep [ppr occ <> colon, ptext SLIT("Free vars (only) changed:"),
                                              nest 2 (braces (fsep (map ppr (occSetElts 
                                                (occs `intersectOccSet` changed_occs)))))]
                    Just NotEqual  
                        | Just old_decl <- lookupOccEnv old_decl_env occ 
                        -> vcat [ptext SLIT("Old:") <+> ppr old_decl,
                         ptext SLIT("New:") <+> ppr new_decl]
                        | otherwise 
                        -> ppr occ <+> ptext SLIT("only in new interface")
                    other -> pprPanic "MkIface.show_change" (ppr occ)
        
    pp_orphs = pprOrphans new_orph_insts new_orph_rules

pprOrphans insts rules
  = vcat [if null insts then empty else
             ptext SLIT("Orphan instances:") <+> vcat (map ppr insts),
          if null rules then empty else
             ptext SLIT("Orphan rules:") <+> vcat (map ppr rules)]

computeChangedOccs :: [(OccName, IfaceEq)] -> OccSet
computeChangedOccs eq_info
  = foldl add_changes emptyOccSet (stronglyConnComp edges)
  where
    edges :: [((OccName,IfaceEq), Unique, [Unique])]
    edges = [ (node, getUnique occ, map getUnique occs)
            | node@(occ, iface_eq) <- eq_info
            , let occs = case iface_eq of
                           EqBut occ_set -> occSetElts occ_set
                           other -> [] ]

    -- Changes in declarations
    add_changes :: OccSet -> SCC (OccName, IfaceEq) -> OccSet
    add_changes so_far (AcyclicSCC (occ, iface_eq)) 
        | changedWrt so_far iface_eq                            -- This one has changed
        = extendOccSet so_far occ
    add_changes so_far (CyclicSCC pairs)
        | changedWrt so_far (foldr1 (&&&) (map snd pairs))      -- One of this group has changed
        = extendOccSetList so_far (map fst pairs)
    add_changes so_far other = so_far

changedWrt :: OccSet -> IfaceEq -> Bool
changedWrt so_far Equal        = False
changedWrt so_far NotEqual     = True
changedWrt so_far (EqBut kids) = so_far `intersectsOccSet` kids

----------------------
-- mkRuleMap 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
mkRuleMap :: (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
mkRuleMap get_key decls
  = foldl go (emptyOccEnv, []) decls
  where
    go (non_orphs, orphs) d
        | Just occ <- get_key d
        = (extendOccEnv_C (\ ds _ -> d:ds) non_orphs occ [d], orphs)
        | otherwise = (non_orphs, d:orphs)

-- getXxKey: find at least one local OccName that belongs to this decl

getInstKey :: IfaceInst -> Maybe OccName
getInstKey (IfaceInst {ifInstHead = inst_ty})
  = case [occ | LocalTop occ <- cls_ext : tc_exts] of
        []      -> Nothing
        (occ:_) -> Just occ
  where
    (cls_ext, tcs) = ifaceInstGates inst_ty
    tc_exts = [tc | IfaceTc tc <- tcs]
        -- Ignore the wired-in IfaceTyCons; the class will do as the key

getRuleKey :: IfaceRule -> Maybe OccName
getRuleKey (IfaceRule {ifRuleHead = LocalTop occ}) = Just occ
getRuleKey other                                   = Nothing

anyNothing :: (a -> Maybe b) -> [a] -> Bool
anyNothing p []     = False
anyNothing p (x:xs) = isNothing (p x) || anyNothing p xs

----------------------
mkIfaceDeprec :: Deprecations -> IfaceDeprecs
mkIfaceDeprec NoDeprecs        = NoDeprecs
mkIfaceDeprec (DeprecAll t)    = DeprecAll t
mkIfaceDeprec (DeprecSome env) = DeprecSome (sortLe (<=) (nameEnvElts env))

----------------------
bump_unless :: Bool -> Version -> Version
bump_unless True  v = v -- True <=> no change
bump_unless False v = bumpVersion v
\end{code}


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


\begin{code}
mkUsageInfo :: HscEnv -> ImportAvails -> NameSet -> IO [Usage]
mkUsageInfo hsc_env
            (ImportAvails { imp_mods = dir_imp_mods,
                            imp_dep_mods = dep_mods })
            used_names
  = do  { eps <- hscEPS hsc_env
        ; return (mk_usage_info (eps_PIT eps) (hsc_HPT hsc_env) 
                                dir_imp_mods dep_mods used_names) }

mk_usage_info pit hpt dir_imp_mods dep_mods proto_used_names
  = -- 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.
    usages `seqList` usages
  where
    used_names = mkNameSet $                    -- Eliminate duplicates
                 [ nameParent n                 -- Just record usage on the 'main' names
                 | n <- nameSetToList proto_used_names
                 , not (isWiredInName n)        -- Don't record usages for wired-in names
                 , isExternalName n             -- Ignore internal names
                 ]

    -- ent_map groups together all the things imported and used
    -- from a particular module in this package
    ent_map :: ModuleEnv [OccName]
    ent_map  = foldNameSet add_mv emptyModuleEnv used_names
    add_mv name mv_map = extendModuleEnv_C add_item mv_map mod [occ]
                   where
                     occ = nameOccName name
                     mod = nameModule name
                     add_item occs _ = occ:occs
    
    usages = mapCatMaybes mkUsage (moduleEnvElts dep_mods)
        -- ToDo: do we need to sort into canonical order?

    import_all mod = case lookupModuleEnv dir_imp_mods mod of
                        Just (_,imp_all,_) -> isNothing imp_all
                        Nothing            -> False
    
    -- We want to create a Usage for a home module if 
    --  a) we used something from; has something in used_names
    --  b) we imported all of it, even if we used nothing from it
    --          (need to recompile if its export list changes: export_vers)
    --  c) is a home-package orphan module (need to recompile if its
    --          instance decls change: rules_vers)
    mkUsage :: (ModuleName, Bool) -> Maybe Usage
    mkUsage (mod_name, _)
      |  isNothing maybe_iface  -- We can't depend on it if we didn't
      || not (isHomeModule mod) -- even open the interface!
      || (null used_occs
          && not all_imported
          && not orphan_mod)
      = Nothing                 -- Record no usage info
    
      | otherwise       
      = Just (Usage { usg_name     = moduleName mod,
                      usg_mod      = mod_vers,
                      usg_exports  = export_vers,
                      usg_entities = ent_vers,
                      usg_rules    = rules_vers })
      where
        maybe_iface  = lookupIfaceByModName hpt pit mod_name
                -- In one-shot mode, the interfaces for home-package 
                -- modules accumulate in the PIT not HPT.  Sigh.

        Just iface   = maybe_iface
        mod          = mi_module    iface
        orphan_mod   = mi_orphan    iface
        version_env  = mi_ver_fn    iface
        mod_vers     = mi_mod_vers  iface
        rules_vers   = mi_rule_vers iface
        all_imported = import_all mod 
        export_vers | all_imported = Just (mi_exp_vers iface)
                    | otherwise    = Nothing
    
        -- The sort is to put them into canonical order
        used_occs = lookupModuleEnv ent_map mod `orElse` []
        ent_vers :: [(OccName,Version)]
        ent_vers = [ (occ, version_env occ `orElse` initialVersion) 
                   | occ <- sortLe (<=) used_occs]
\end{code}

\begin{code}
mkIfaceExports :: NameSet -> [(ModuleName, [GenAvailInfo OccName])]
  -- Group by module and sort by occurrence
  -- This keeps the list in canonical order
mkIfaceExports exports 
  = [ (mkSysModuleNameFS fs, eltsFM avails)
    | (fs, avails) <- fmToList groupFM
    ]
  where
    groupFM :: FiniteMap FastString (FiniteMap FastString (GenAvailInfo OccName))
        -- Deliberately use the FastString so we
        -- get a canonical ordering
    groupFM = foldl add emptyFM (nameSetToList exports)

    add env name = addToFM_C add_avail env mod_fs 
                             (unitFM avail_fs avail)
      where
        occ    = nameOccName name
        mod_fs = moduleNameFS (nameModuleName name)
        avail | Just p <- nameParent_maybe name = AvailTC (nameOccName p) [occ]
              | isTcOcc occ                     = AvailTC occ [occ]
              | otherwise                       = Avail occ
        avail_fs = occNameFS (availName avail)      
        add_avail avail_fm _ = addToFM_C add_item avail_fm avail_fs avail

        add_item (AvailTC p occs) _ = AvailTC p (insert occ occs)
        add_item (Avail n)         _ = pprPanic "MkIface.addAvail" (ppr n <+> ppr name)
\end{code}


%************************************************************************
%*                                                                      *
        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
              -> Module
              -> FilePath               -- Where the interface file is
              -> Bool                   -- Source unchanged
              -> Maybe ModIface         -- Old interface from compilation manager, if any
              -> IO (RecompileRequired, Maybe ModIface)

checkOldIface hsc_env mod iface_path source_unchanged maybe_iface
  = do  { showPass (hsc_dflags hsc_env) 
                   ("Checking old interface for " ++ moduleUserString mod) ;

        ; initIfaceCheck hsc_env $
          check_old_iface mod iface_path source_unchanged maybe_iface
     }

check_old_iface this_mod iface_path source_unchanged maybe_iface
 =      -- CHECK WHETHER THE SOURCE HAS CHANGED
    ifM (not source_unchanged)
        (traceHiDiffs (nest 4 (text "Source file changed or recompilation check turned off")))
                                                `thenM_`

     -- 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.
    getGhciMode                                 `thenM` \ ghci_mode ->
    if (ghci_mode == Interactive) && not source_unchanged then
         returnM (outOfDate, maybe_iface)
    else

    case maybe_iface of {
       Just old_iface -> -- Use the one we already have
                         checkVersions source_unchanged old_iface       `thenM` \ recomp ->
                         returnM (recomp, Just old_iface)

    ;  Nothing ->

        -- Try and read the old interface for the current module
        -- from the .hi file left from the last time we compiled it
    readIface (moduleName this_mod) iface_path False            `thenM` \ read_result ->
    case read_result of {
       Left err ->      -- Old interface file not found, or garbled; give up
                   traceIf (text "FYI: cannot read old interface file:"
                                 $$ nest 4 err)         `thenM_`
                   returnM (outOfDate, Nothing)

    ;  Right iface ->   

        -- We have got the old iface; check its versions
    checkVersions source_unchanged iface        `thenM` \ recomp ->
    returnM (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  = False       -- Recompile not required
outOfDate = True        -- Recompile required

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

        -- 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
        ; updateEps_ $ \eps  -> eps { eps_is_boot = mod_deps }

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

checkModUsage :: 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 (Usage { usg_name = mod_name, usg_mod = old_mod_vers,
                       usg_rules = old_rule_vers,
                       usg_exports = maybe_old_export_vers, 
                       usg_entities = old_decl_vers })
  =     -- Load the imported interface is possible
    let
        doc_str = sep [ptext SLIT("need version info for"), ppr mod_name]
    in
    traceHiDiffs (text "Checking usages for module" <+> ppr mod_name) `thenM_`

    loadInterface doc_str mod_name ImportBySystem       `thenM` \ mb_iface ->
        -- Load the interface, but don't complain on failure;
        -- Instead, get an Either back which we can test

    case mb_iface of {
        Left exn ->  (out_of_date (sep [ptext SLIT("Can't find version number for module"), 
                                       ppr mod_name]));
                -- 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

        Right iface -> 
    let
        new_mod_vers    = mi_mod_vers  iface
        new_decl_vers   = mi_ver_fn    iface
        new_export_vers = mi_exp_vers  iface
        new_rule_vers   = mi_rule_vers iface
    in
        -- CHECK MODULE
    checkModuleVersion old_mod_vers new_mod_vers        `thenM` \ recompile ->
    if not recompile then
        returnM upToDate
    else
                                 
        -- CHECK EXPORT LIST
    if checkExportList maybe_old_export_vers new_export_vers then
        out_of_date_vers (ptext SLIT("  Export list changed"))
                         (fromJust maybe_old_export_vers) 
                         new_export_vers
    else

        -- CHECK RULES
    if old_rule_vers /= new_rule_vers then
        out_of_date_vers (ptext SLIT("  Rules changed")) 
                         old_rule_vers new_rule_vers
    else

        -- CHECK ITEMS ONE BY ONE
    checkList [checkEntityUsage new_decl_vers u | u <- old_decl_vers]   `thenM` \ recompile ->
    if recompile then
        returnM outOfDate       -- This one failed, so just bail out now
    else
        up_to_date (ptext SLIT("  Great!  The bits I use are up to date"))
    }

------------------------
checkModuleVersion old_mod_vers new_mod_vers
  | new_mod_vers == old_mod_vers
  = up_to_date (ptext SLIT("Module version unchanged"))

  | otherwise
  = out_of_date_vers (ptext SLIT("  Module version has changed"))
                     old_mod_vers new_mod_vers

------------------------
checkExportList Nothing  new_vers = upToDate
checkExportList (Just v) new_vers = v /= new_vers

------------------------
checkEntityUsage new_vers (name,old_vers)
  = case new_vers 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_vers   -- It's there, but is it up to date?
          | new_vers == old_vers -> traceHiDiffs (text "  Up to date" <+> ppr name <+> parens (ppr new_vers)) `thenM_`
                                    returnM upToDate
          | otherwise            -> out_of_date_vers (ptext SLIT("  Out of date:") <+> ppr name)
                                                     old_vers new_vers

up_to_date  msg = traceHiDiffs msg `thenM_` returnM upToDate
out_of_date msg = traceHiDiffs msg `thenM_` returnM outOfDate
out_of_date_vers msg old_vers new_vers 
  = out_of_date (hsep [msg, ppr old_vers, ptext SLIT("->"), ppr new_vers])

----------------------
checkList :: [IfG RecompileRequired] -> IfG RecompileRequired
-- This helper is used in two places
checkList []             = returnM upToDate
checkList (check:checks) = check        `thenM` \ recompile ->
                           if recompile then 
                                returnM outOfDate
                           else
                                checkList checks
\end{code}

%************************************************************************
%*                                                                      *
                Printing interfaces
%*                                                                      *
%************************************************************************

\begin{code}
showIface :: FilePath -> IO ()
-- Raad binary interface, and print it out
showIface filename = do
   -- skip the version check; we don't want to worry about profiled vs.
   -- non-profiled interfaces, for example.
   writeIORef v_IgnoreHiWay True
   iface <- Binary.getBinFileWithDict filename
   printDump (pprModIface iface)
 where
\end{code}


\begin{code}
pprModIface :: ModIface -> SDoc
-- Show a ModIface
pprModIface iface
 = vcat [ ptext SLIT("interface")
                <+> doubleQuotes (ftext (mi_package iface))
                <+> ppr (mi_module iface) <+> ppr (mi_mod_vers iface)
                <+> pp_sub_vers
                <+> (if mi_orphan iface then ptext SLIT("[orphan module]") else empty)
                <+> int opt_HiVersion
                <+> ptext SLIT("where")
        , vcat (map pprExport (mi_exports iface))
        , pprDeps (mi_deps iface)
        , vcat (map pprUsage (mi_usages iface))
        , pprFixities (mi_fixities iface)
        , vcat (map pprIfaceDecl (mi_decls iface))
        , vcat (map ppr (mi_insts iface))
        , vcat (map ppr (mi_rules iface))
        , pprDeprecs (mi_deprecs iface)
        ]
  where
    exp_vers  = mi_exp_vers iface
    rule_vers = mi_rule_vers iface

    pp_sub_vers | exp_vers == initialVersion && rule_vers == initialVersion = empty
                | otherwise = brackets (ppr exp_vers <+> ppr rule_vers)
\end{code}

When printing export lists, we print like this:
        Avail   f               f
        AvailTC C [C, x, y]     C(x,y)
        AvailTC C [x, y]        C!(x,y)         -- Exporting x, y but not C

\begin{code}
pprExport :: IfaceExport -> SDoc
pprExport (mod, items)
 = hsep [ ptext SLIT("export"), ppr mod, hsep (map pp_avail items) ]
  where
    pp_avail :: GenAvailInfo OccName -> SDoc
    pp_avail (Avail occ)    = ppr occ
    pp_avail (AvailTC _ []) = empty
    pp_avail (AvailTC n (n':ns)) 
        | n==n'     = ppr n <> pp_export ns
        | otherwise = ppr n <> char '|' <> pp_export (n':ns)
    
    pp_export []    = empty
    pp_export names = braces (hsep (map ppr names))

pprUsage :: Usage -> SDoc
pprUsage usage
  = hsep [ptext SLIT("import"), ppr (usg_name usage), 
          int (usg_mod usage), 
          pp_export_version (usg_exports usage),
          int (usg_rules usage),
          pp_versions (usg_entities usage) ]
  where
    pp_versions nvs = hsep [ ppr n <+> int v | (n,v) <- nvs ]
    pp_export_version Nothing  = empty
    pp_export_version (Just v) = int v

pprDeps :: Dependencies -> SDoc
pprDeps (Deps { dep_mods = mods, dep_pkgs = pkgs, dep_orphs = orphs})
  = vcat [ptext SLIT("module dependencies:") <+> fsep (map ppr_mod mods),
          ptext SLIT("package dependencies:") <+> fsep (map ppr pkgs), 
          ptext SLIT("orphans:") <+> fsep (map ppr orphs)
        ]
  where
    ppr_mod (mod_name, boot) = ppr mod_name <+> ppr_boot boot
    ppr_boot True  = text "[boot]"
    ppr_boot False = empty

pprIfaceDecl :: (Version, IfaceDecl) -> SDoc
pprIfaceDecl (ver, decl)
  = ppr_vers ver <+> ppr decl
  where
        -- Print the version for the decl
    ppr_vers v | v == initialVersion = empty
               | otherwise           = int v

pprFixities :: [(OccName, Fixity)] -> SDoc
pprFixities []    = empty
pprFixities fixes = ptext SLIT("fixities") <+> pprWithCommas pprFix fixes
                  where
                    pprFix (occ,fix) = ppr fix <+> ppr occ 

pprDeprecs NoDeprecs        = empty
pprDeprecs (DeprecAll txt)  = ptext SLIT("Deprecate all") <+> doubleQuotes (ftext txt)
pprDeprecs (DeprecSome prs) = ptext SLIT("Deprecate") <+> vcat (map pprDeprec prs)
                            where
                              pprDeprec (name, txt) = ppr name <+> doubleQuotes (ftext txt)
\end{code}