[GHC] #12931: tc_infer_args does not set in-scope set correctly

[GHC]

#12931: tc_infer_args does not set in-scope set correctly
-------------------------------------+-------------------------------------
           Reporter:  johnleo        |             Owner:  goldfire
               Type:  bug            |            Status:  new
           Priority:  normal         |         Milestone:
          Component:  Compiler       |           Version:  8.0.1
           Keywords:                 |  Operating System:  Unknown/Multiple
       Architecture:                 |   Type of failure:  None/Unknown
  Unknown/Multiple                   |
          Test Case:                 |        Blocked By:
           Blocking:                 |   Related Tickets:  #12549 #11371
                                     |  #12785
Differential Rev(s):                 |         Wiki Page:
-------------------------------------+-------------------------------------
 As noted in https://ghc.haskell.org/trac/ghc/ticket/12785#comment:6,
 `TcHsType.tc_infer_args` does not set its in-scope set correctly, which
 means the call to `TcMType.new_meta_tv_x` will fail if `substTyUnchecked`
 is replaced by `substTy` in the line
 {{{
 kind   = substTyUnchecked subst (tyVarKind tv)
 }}}

 This is the only known caller of `new_meta_tv_x` to not set the in-scope
 set, now that #12549 has been fixed.  Once this bug is fixed, change
 `substTyUnchecked` back to `substTy` in the line noted above.

 Note that other calls to `substTyUnchecked` that need to be converted to
 `substTy` are covered in the general ticket #11371.

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/12931>
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