#8128: Standalone deriving fails for GADTs due to inaccessible code -------------------------------------+------------------------------------- Reporter: adamgundry | Owner: (none) Type: bug | Status: closed Priority: normal | Milestone: 8.6.1 Component: Compiler (Type | Version: 7.7 checker) | Keywords: GADTs, Resolution: fixed | deriving Operating System: Unknown/Multiple | Architecture: | Unknown/Multiple Type of failure: GHC rejects | Test Case: valid program | deriving/should_compile/T8128 Blocked By: | Blocking: Related Tickets: #8740, #11066 | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Comment (by Krzysztof Gogolewski <krz.gogolewski@…>): In [changeset:"44a7b9baa45c4ab939c7d996519b5e3de3e13c5a/ghc" 44a7b9b/ghc]: {{{ #!CommitTicketReference repository="ghc" revision="44a7b9baa45c4ab939c7d996519b5e3de3e13c5a" Suppress -Winaccessible-code in derived code Summary: It's rather unfortunate that derived code can produce inaccessible code warnings (as demonstrated in #8128, #8740, and #15398), since the programmer has no control over the generated code. This patch aims to suppress `-Winaccessible-code` in all derived code. It accomplishes this by doing the following: * Generalize the `ic_env :: TcLclEnv` field of `Implication` to be of type `Env TcGblEnc TcLclEnv` instead. This way, it also captures `DynFlags`, which record the flag state at the time the `Implication` was created. * When typechecking derived code, turn off `-Winaccessible-code`. This way, any insoluble given `Implication`s that are created when typechecking this derived code will remember that `-Winaccessible-code` was disabled. * During error reporting, consult the `DynFlags` of an `Implication` before making the decision to report an inaccessible code warning. Test Plan: make test TEST="T8128 T8740 T15398" Reviewers: simonpj, bgamari Reviewed By: simonpj Subscribers: monoidal, rwbarton, thomie, carter GHC Trac Issues: #8128, #8740, #15398 Differential Revision: https://phabricator.haskell.org/D4993 }}} -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/8128#comment:16> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler