#16261: Mysterious rule shadowing warning -------------------------------------+------------------------------------- Reporter: dfeuer | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: 8.10.1 Component: Compiler | Version: 8.6.3 Keywords: | Operating System: Unknown/Multiple Architecture: | Type of failure: Incorrect Unknown/Multiple | error/warning at compile-time Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- Compiling `Data.Set.Internal` produces the following: {{{ Data/Set/Internal.hs:958:11: warning: [-Winline-rule-shadowing] Rule "Set.toAscListBack" may never fire because rule "Class op fromListN" for ‘GHCExts.fromListN’ might fire first Probable fix: add phase [n] or [~n] to the competing rule | 958 | {-# RULES "Set.toAscListBack" [1] foldrFB (:) [] = toAscList #-} | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ Data/Set/Internal.hs:960:11: warning: [-Winline-rule-shadowing] Rule "Set.toDescListBack" may never fire because rule "Class op fromListN" for ‘GHCExts.fromListN’ might fire first Probable fix: add phase [n] or [~n] to the competing rule | 960 | {-# RULES "Set.toDescListBack" [1] foldlFB (\xs x -> x : xs) [] = toDescList #-} | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ }}} What the heck does the class op rule for `fromListN` have to do with anything anywhere near here? -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/16261 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler