Re: [GHC] #12583: Deriving standalone Ix instance for GADT leads to GHC panic

#12583: Deriving standalone Ix instance for GADT leads to GHC panic -------------------------------------+------------------------------------- Reporter: RyanGlScott | Owner: Type: bug | Status: patch Priority: normal | Milestone: Component: Compiler | Version: 8.0.1 Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: Type of failure: Compile-time | Unknown/Multiple crash | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Phab:D2521 Wiki Page: | -------------------------------------+------------------------------------- Comment (by Ryan Scott ): In [changeset:"7b7ea8f40e7400b8c183595a85bb2c65c9f9bb29/ghc" 7b7ea8f/ghc]: {{{ #!CommitTicketReference repository="ghc" revision="7b7ea8f40e7400b8c183595a85bb2c65c9f9bb29" Fix derived Ix instances for one-constructor GADTs Summary: Standalone-derived `Ix` instances would panic on GADTs with exactly one constructor, since the list of fields was being passed to a function that uses `foldl1` in order to generate an implementation for `inRange`. This adds a simple check that makes `inRange` be `True` whenever a product type has no fields. Fixes #12583. Test Plan: make test TEST=12583 Reviewers: simonpj, austin, bgamari Reviewed By: bgamari Subscribers: thomie Differential Revision: https://phabricator.haskell.org/D2521 GHC Trac Issues: #12583 }}} -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/12583#comment:2 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler