[GHC] #15867: STG scope error

[GHC]

#15867: STG scope error
-------------------------------------+-------------------------------------
           Reporter:  csabahruska    |             Owner:  (none)
               Type:  bug            |            Status:  new
           Priority:  normal         |         Milestone:
          Component:  Compiler       |           Version:  8.7
           Keywords:                 |  Operating System:  Unknown/Multiple
       Architecture:                 |   Type of failure:  None/Unknown
  Unknown/Multiple                   |
          Test Case:                 |        Blocked By:
           Blocking:                 |   Related Tickets:
Differential Rev(s):                 |         Wiki Page:
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 StgRhsClosure can contain duplicated names in its free variable and
 argument list.

 Example bug: libraries/integer-gmp/src/GHC/Integer/Type.hs

 GHC HEAD and 8.2.2 has this issue.

 I have not checked with other versions.

 I've extended the STG linter to do scope checking. See the patch attached.

 To reproduce:
  * patch GHC head: `git apply StgScopeCheck.patch`
  * make sure every compiled stg is linted: add `-dstg-lint` to
 GhcStage2HcOpts GhcLibHcOpts GhcRtsHcOpts config vars
  * compile GHC HEAD

 Background info:
  I've found this issue because I'm using GHC as a Haskell fronted for my
 whole program compiler project. I work on The GRIN Compiler
 (https://github.com/grin-tech) where GHC/GRIN compiles STG to GRIN.

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/15867>
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