+-- Module cycles
+-----------------------------------------------------------------
+
+dumpModCycles :: DynFlags -> [ModSummary] -> IO ()
+dumpModCycles dflags mod_summaries
+ | not (dopt Opt_D_dump_mod_cycles dflags)
+ = return ()
+
+ | null cycles
+ = putMsg dflags (ptext SLIT("No module cycles"))
+
+ | otherwise
+ = putMsg dflags (hang (ptext SLIT("Module cycles found:")) 2 pp_cycles)
+ where
+
+ cycles :: [[ModSummary]]
+ cycles = [ c | CyclicSCC c <- GHC.topSortModuleGraph True mod_summaries Nothing ]
+
+ pp_cycles = vcat [ (ptext SLIT("---------- Cycle") <+> int n <+> ptext SLIT("----------"))
+ $$ pprCycle c $$ text ""
+ | (n,c) <- [1..] `zip` cycles ]
+
+pprCycle :: [ModSummary] -> SDoc
+-- Print a cycle, but show only the imports within the cycle
+pprCycle summaries = pp_group (CyclicSCC summaries)
+ where
+ cycle_mods :: [ModuleName] -- The modules in this cycle
+ cycle_mods = map (moduleName . ms_mod) summaries
+
+ pp_group (AcyclicSCC ms) = pp_ms ms
+ pp_group (CyclicSCC mss)
+ = ASSERT( not (null boot_only) )
+ -- The boot-only list must be non-empty, else there would
+ -- be an infinite chain of non-boot imoprts, and we've
+ -- already checked for that in processModDeps
+ pp_ms loop_breaker $$ vcat (map pp_group groups)
+ where
+ (boot_only, others) = partition is_boot_only mss
+ is_boot_only ms = not (any in_group (ms_imps ms))
+ in_group (L _ m) = m `elem` group_mods
+ group_mods = map (moduleName . ms_mod) mss
+
+ loop_breaker = head boot_only
+ all_others = tail boot_only ++ others
+ groups = GHC.topSortModuleGraph True all_others Nothing
+
+ pp_ms summary = text mod_str <> text (take (20 - length mod_str) (repeat ' '))
+ <+> (pp_imps empty (ms_imps summary) $$
+ pp_imps (ptext SLIT("{-# SOURCE #-}")) (ms_srcimps summary))
+ where
+ mod_str = moduleNameString (moduleName (ms_mod summary))
+
+ pp_imps :: SDoc -> [Located ModuleName] -> SDoc
+ pp_imps what [] = empty
+ pp_imps what lms
+ = case [m | L _ m <- lms, m `elem` cycle_mods] of
+ [] -> empty
+ ms -> what <+> ptext SLIT("imports") <+>
+ pprWithCommas ppr ms
+
+-----------------------------------------------------------------