Re: [GHC] #13043: GHC 7.10->8.0 regression: GHC code-generates duplicate _closures

#13043: GHC 7.10->8.0 regression: GHC code-generates duplicate _closures -------------------------------------+------------------------------------- Reporter: hvr | Owner: Type: bug | Status: new Priority: normal | Milestone: 8.0.3 Component: Compiler | Version: 8.0.2-rc2 Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: Type of failure: Compile-time | Unknown/Multiple crash or panic | Test Case: Blocked By: | Blocking: Related Tickets: #12595 | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Comment (by Simon Peyton Jones ): In [changeset:"baf9ebe55a51827c0511b3a670e60b9bb3617ab5/ghc" baf9ebe5/ghc]: {{{ #!CommitTicketReference repository="ghc" revision="baf9ebe55a51827c0511b3a670e60b9bb3617ab5" Ensure nested binders have Internal Names This is a long-standing bug. A nested (non-top-level) binder in Core should not have an External Name, like M.x. But - Lint was not checking this invariant - The desugarer could generate programs that failed the invariant. An example is in tests/deSugar/should_compile/T13043, which had let !_ = M.scState in ... This desugared to let ds = case M.scSate of M.scState { DEFAULT -> () } in case ds of () -> ... We were wrongly re-using that scrutinee as a case binder. And Trac #13043 showed that could ultimately lead to two top-level bindings with the same closure name. Alas! - The desugarer had one other place (in DsUtils.mkCoreAppDs) that could generate bogus code This patch fixes all three bugs, and adds a regression test. }}} -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/13043#comment:7 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler