Re: [GHC] #16348: GHC HEAD regression: tyConAppArgs

#16348: GHC HEAD regression: tyConAppArgs -------------------------------------+------------------------------------- Reporter: RyanGlScott | Owner: (none) Type: bug | Status: closed Priority: highest | Milestone: 8.10.1 Component: Compiler | Version: 8.7 Resolution: fixed | Keywords: Operating System: Unknown/Multiple | Architecture: | Unknown/Multiple Type of failure: Compile-time | Test Case: crash or panic | simplCore/should_compile/T16348 Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | https://gitlab.haskell.org/ghc/ghc/merge_requests/416 -------------------------------------+------------------------------------- Comment (by Matthew Pickering ): In [changeset:"c25b135ff5b9c69a90df0ccf51b04952c2dc6ee1/ghc" c25b135f/ghc]: {{{ #!CommitTicketReference repository="ghc" revision="c25b135ff5b9c69a90df0ccf51b04952c2dc6ee1" Fix exprIsConApp_maybe In this commit commit 7833cf407d1f608bebb1d38bb99d3035d8d735e6 Date: Thu Jan 24 17:58:50 2019 +0100 Look through newtype wrappers (Trac #16254) we made exprIsConApp_maybe quite a bit cleverer. But I had not paid enough attention to keeping exactly the correct substitution and in-scope set, which led to Trac #16348. There were several buglets (like applying the substitution twice in exprIsConApp_maybe, but the proximate source of the bug was that we were calling addNewInScopeIds, which deleted things from the substitution as well as adding them to the in-scope set. That's usually right, but not here! This was quite tricky to track down. But it is nicer now. }}} -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/16348#comment:7 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler