+%*********************************************************
+%* *
+\subsection{Keeping track of what we've slurped, and version numbers}
+%* *
+%*********************************************************
+
+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}
+mkUsageInfo :: HscEnv -> ExternalPackageState
+ -> ImportAvails -> EntityUsage
+ -> [Usage Name]
+
+mkUsageInfo hsc_env eps
+ (ImportAvails { imp_mods = dir_imp_mods,
+ imp_dep_mods = dep_mods })
+ 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
+ usages = catMaybes [ mkUsage mod_name
+ | (mod_name,_) <- moduleEnvElts dep_mods]
+
+ hpt = hsc_HPT hsc_env
+ pit = eps_PIT eps
+
+ import_all mod = case lookupModuleEnv dir_imp_mods mod of
+ Just (_,imp_all) -> imp_all
+ Nothing -> False
+
+ -- ent_map groups together all the things imported and used
+ -- from a particular module in this package
+ ent_map :: ModuleEnv [Name]
+ ent_map = foldNameSet add_mv emptyModuleEnv used_names
+ add_mv name mv_map = extendModuleEnv_C add_item mv_map mod [name]
+ where
+ mod = nameModule name
+ add_item names _ = name:names
+
+ -- 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 -> Maybe (Usage Name)
+ 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_names
+ && 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
+ version_info = mi_version iface
+ orphan_mod = mi_orphan iface
+ version_env = vers_decls version_info
+ mod_vers = vers_module version_info
+ rules_vers = vers_rules version_info
+ all_imported = import_all mod
+ export_vers | all_imported = Just (vers_exports version_info)
+ | otherwise = Nothing
+
+ -- The sort is to put them into canonical order
+ used_names = lookupModuleEnv ent_map mod `orElse` []
+ ent_vers = [(n, lookupVersion version_env n)
+ | n <- sortLt lt_occ used_names ]
+ lt_occ n1 n2 = nameOccName n1 < nameOccName n2
+\end{code}
+
+\begin{code}
+groupAvails :: Module -> Avails -> [(ModuleName, Avails)]
+ -- Group by module and sort by occurrence
+ -- This keeps the list in canonical order
+groupAvails this_mod avails
+ = [ (mkSysModuleNameFS fs, sortLt lt avails)
+ | (fs,avails) <- fmToList groupFM
+ ]
+ where
+ groupFM :: FiniteMap FastString Avails
+ -- Deliberately use the FastString so we
+ -- get a canonical ordering
+ groupFM = foldl add emptyFM avails
+
+ add env avail = addToFM_C combine env mod_fs [avail']
+ where
+ mod_fs = moduleNameFS (moduleName avail_mod)
+ avail_mod = case nameModule_maybe (availName avail) of
+ Just m -> m
+ Nothing -> this_mod
+ combine old _ = avail':old
+ avail' = sortAvail avail
+
+ a1 `lt` a2 = occ1 < occ2
+ where
+ occ1 = nameOccName (availName a1)
+ occ2 = nameOccName (availName a2)
+
+sortAvail :: AvailInfo -> AvailInfo
+-- Sort the sub-names into canonical order.
+-- The canonical order has the "main name" at the beginning
+-- (if it's there at all)
+sortAvail (Avail n) = Avail n
+sortAvail (AvailTC n ns) | n `elem` ns = AvailTC n (n : sortLt lt (filter (/= n) ns))
+ | otherwise = AvailTC n ( sortLt lt ns)
+ where
+ n1 `lt` n2 = nameOccName n1 < nameOccName n2
+\end{code}
+