#14817: GHC 8.4.1 pretty-prints data family instances with redundant kind signatures using -ddump-splices -------------------------------------+------------------------------------- Reporter: RyanGlScott | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.4.1-alpha3 Keywords: | Operating System: Unknown/Multiple Architecture: | Type of failure: None/Unknown Unknown/Multiple | Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- Consider this program: {{{#!hs {-# LANGUAGE TemplateHaskell #-} {-# LANGUAGE TypeFamilies #-} {-# OPTIONS_GHC -ddump-splices #-} module Bug where $([d| data family Foo :: * data instance Foo :: * |]) }}} On GHC 8.2.2, this gives the following `-ddump-splices` output: {{{ $ /opt/ghc/8.2.2/bin/ghci Bug.hs GHCi, version 8.2.2: http://www.haskell.org/ghc/ :? for help Loaded GHCi configuration from /home/rgscott/.ghci [1 of 1] Compiling Bug ( Bug.hs, interpreted ) Bug.hs:(6,3)-(7,31): Splicing declarations [d| data family Foo_a1sB :: * data instance :: * |] ======> data family Foo_a494 :: GHC.Types.Type data instance :: GHC.Types.Type }}} But on GHC 8.4.1, we have: {{{ $ /opt/ghc/8.4.1/bin/ghci Bug.hs GHCi, version 8.4.0.20180209: http://www.haskell.org/ghc/ :? for help Loaded GHCi configuration from /home/rgscott/.ghci [1 of 1] Compiling Bug ( Bug.hs, interpreted ) Bug.hs:(6,3)-(7,31): Splicing declarations [d| data family Foo_a1xd :: * data instance Foo_a1xd :: * :: * |] ======> data family Foo_a487 :: GHC.Types.Type data instance Foo_a487 :: GHC.Types.Type :: GHC.Types.Type }}} Notice how there is a redundant kind signature in `data instance Foo_a1xd :: * :: *`. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/14817 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler