+
+-- 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 _ mod) = do
+ find_res <- ioToIOEnv $ findImportedModule hsc_env mod Nothing
+ 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
+