Re: [GHC] #11608: Possible type-checker regression in GHC 8.0 when compiling `microlens`

#11608: Possible type-checker regression in GHC 8.0 when compiling `microlens` -------------------------------------+------------------------------------- Reporter: hvr | Owner: simonpj Type: bug | Status: merge Priority: highest | Milestone: 8.0.1 Component: Compiler (Type | Version: 8.0.1-rc2 checker) | Resolution: fixed | Keywords: Operating System: Unknown/Multiple | Architecture: | Unknown/Multiple Type of failure: GHC rejects | Test Case: valid program | typecheck/should_compile/T11608 Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Changes (by simonpj): * status: closed => merge Comment: Here's the patch for the other three {{{ commit 3c29c770be7a8c7268dcb8d8624853428aa42071 Author: Simon Peyton Jones Date: Mon Feb 29 14:12:28 2016 +0000 Do not check synonym RHS for ambiguity With this patch we no longer check the RHS of a type synonym declaration for ambiguity. It only affects type synonyms with foralls on the RHS (which are rare in the first place), and it's arguably over-aggressive to check them for ambiguity. See TcValidity Note [When we don't check for ambiguity] This fixes the ASSERT failures in th T3100 typecheck/should_compile T3692 typecheck/should_fail T3592 }}} Just about worth merging. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/11608#comment:18 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler