[GHC] #14476: Keep source locations in Core (optionally)

[GHC]

#14476: Keep source locations in Core (optionally)
-------------------------------------+-------------------------------------
           Reporter:  nomeata        |             Owner:  (none)
               Type:  feature        |            Status:  new
  request                            |
           Priority:  normal         |         Milestone:
          Component:  Compiler       |           Version:  8.3
           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:
-------------------------------------+-------------------------------------
 The people working on liquid haskell have to maintain their own copy of
 the desugarer because of one little change they have to do: Add lots and
 lots of `CC`s to keep source spans around. Their current patch is

 {{{
 diff --git a/src/Language/Haskell/Liquid/Desugar/DsExpr.hs
 b/src/Language/Haskell/Liquid/Desugar/DsExpr.hs
 index 396095e9a..9ba60c56f 100644
 --- a/src/Language/Haskell/Liquid/Desugar/DsExpr.hs
 +++ b/src/Language/Haskell/Liquid/Desugar/DsExpr.hs
 @@ -221,14 +221,13 @@ dsUnliftedBind bind body = pprPanic "dsLet:
 unlifted" (ppr bind $$ ppr body)
  dsLExpr :: LHsExpr Id -> DsM CoreExpr

  dsLExpr (L loc e)
 -  = putSrcSpanDs loc $
 -    do { core_expr <- dsExpr e
 -   -- uncomment this check to test the hsExprType function in TcHsSyn
 -   --    ; MASSERT2( exprType core_expr `eqType` hsExprType e
 -   --              , ppr e <+> dcolon <+> ppr (hsExprType e) $$
 -   --                ppr core_expr <+> dcolon <+> ppr (exprType
 core_expr) )
 -       ; return core_expr }
 +  = do ce <- putSrcSpanDs loc $ dsExpr e
 +       m <- getModule
 +       return $ Tick (srcSpanTick m loc) ce

 +srcSpanTick :: Module -> SrcSpan -> Tickish a
 +srcSpanTick m loc
 +  = ProfNote (AllCafsCC m loc) False True
  -- | Variant of 'dsLExpr' that ensures that the result is not levity
  -- polymorphic. This should be used when the resulting expression will
  -- be an argument to some other function.
 }}}

 It would make their live easier if they could just use GHC’s desugarer,
 and it might open the path to making Liquid Haskell a proper GHC plugin
 instead of a separate program, which could facilitate adoption.

 Would it be ok to add a flag to GHC that enables this behaviour? Or is
 there another way of doing this?

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/14476>
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