[commit: ghc] wip/T15449, wip/T16188, wip/llvm-configure-opts: Fix optSemi type in Parser.y (071bef1)

[git at git.haskell.org]

Repository : ssh://git@git.haskell.org/ghc

On branches: wip/T15449,wip/T16188,wip/llvm-configure-opts
Link       : http://ghc.haskell.org/trac/ghc/changeset/071bef18ccafb134ab886da9e362689b9f092dd3/ghc

>---------------------------------------------------------------

commit 071bef18ccafb134ab886da9e362689b9f092dd3
Author: Vladislav Zavialov <vlad.z.4096 at gmail.com>
Date:   Tue Feb 5 20:01:36 2019 -0500

    Fix optSemi type in Parser.y
    
    The definition of 'optSemi' claimed it had type
    
    ([Located a],Bool)
    
    Note that its production actually returns ([Located Token],Bool):
    
      : ';' { ([$1],True) }   -- $1 :: Located Token
    
    Due to an infelicity in the implementation of 'happy -c', it effectively
    resulted in 'unsafeCoerce :: Token -> a'.
    See https://github.com/simonmar/happy/pull/134
    
    If any consumer of 'optSemi' tried to instantiate 'a' to something not
    representationally equal to 'Token', they would experience a segfault.
    
    In addition to that, this definition made it impossible to compile Parser.y
    without the -c flag (as it's reliant on this bug to cast 'Token' to 'forall
    a. a').


>---------------------------------------------------------------

071bef18ccafb134ab886da9e362689b9f092dd3
 compiler/parser/Parser.y | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/compiler/parser/Parser.y b/compiler/parser/Parser.y
index c5b5c5f..820144d 100644
--- a/compiler/parser/Parser.y
+++ b/compiler/parser/Parser.y
@@ -1,4 +1,3 @@
-
 --                                                              -*-haskell-*-
 -- ---------------------------------------------------------------------------
 -- (c) The University of Glasgow 1997-2003
@@ -2581,7 +2580,7 @@ exp10 :: { LHsExpr GhcPs }
         | scc_annot exp        {% ams (sLL $1 $> $ HsSCC noExt (snd $ fst $ unLoc $1) (snd $ unLoc $1) $2)
                                       (fst $ fst $ unLoc $1) }
 
-optSemi :: { ([Located a],Bool) }
+optSemi :: { ([Located Token],Bool) }
         : ';'         { ([$1],True) }
         | {- empty -} { ([],False) }