[GHC] #11624: Cannot declare hs-boot declaration if there is already a value in scope

[GHC]

#11624: Cannot declare hs-boot declaration if there is already a value in scope
-------------------------------------+-------------------------------------
        Reporter:  ezyang            |                Owner:  ezyang
            Type:  bug               |               Status:  closed
        Priority:  highest           |            Milestone:  8.0.1
       Component:  Compiler (Type    |              Version:  8.0.1-rc2
  checker)                           |
      Resolution:  fixed             |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:
 Type of failure:  GHC rejects       |  Unknown/Multiple
  valid program                      |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:  #10472            |  Differential Rev(s):  Phab:D1963
       Wiki Page:                    |
-------------------------------------+-------------------------------------
Changes (by bgamari):

 * status:  merge => closed
 * resolution:   => fixed


@@ -3,1 +3,1 @@
- {{{
+ {{{#!hs
@@ -49,1 +49,1 @@
- Is a regression from 7.10. The dodginess is proximal to renameSig but I
+ Is a regression from 7.10. The dodginess is proximal to `renameSig` but I

New description:

 This code no longer works:

 {{{#!hs
 -- A.hs-boot
 module A where
 concat :: Int -> Int -- overlaps with Prelude's concat

 -- B.hs
 module B where
 import Prelude ()
 import {-# SOURCE #-} A
 x = concat 3

 -- A.hs
 module A where
 import B
 concat n = n + 2
 }}}

 Building `ghc --make A`, this crashes with:

 {{{
 [1 of 3] Compiling A[boot]          ( A.hs-boot, A.o-boot )
 [2 of 3] Compiling B                ( B.hs, B.o )

 B.hs:4:5: error:
     • Can't find interface-file declaration for variable concat
         Probable cause: bug in .hi-boot file, or inconsistent .hi file
         Use -ddump-if-trace to get an idea of which file caused the error
     • In the expression: concat 3
       In an equation for ‘x’: x = concat 3
 }}}

 The trouble is that renaming has botched up the top-level declaration for
 boot:

 {{{
 ezyang at sabre:~$ ghc-8.0 -c A.hs-boot -ddump-rn -dppr-debug
 A.hs-boot:1:1:

     ==================== Renamer ====================
     {A.hs-boot:2:1-20}
     base-4.9.0.0:Data.Foldable.concat{v r2S} ::
       {A.hs-boot:2:11-20}
       ghc-prim-0.5.0.0:GHC.Types.Int{(w) tc 3J}
       -> ghc-prim-0.5.0.0:GHC.Types.Int{(w) tc 3J}
 }}}

 Is a regression from 7.10. The dodginess is proximal to `renameSig` but I
 haven't quite narrowed it down yet.

--

Comment:

 Merged to `ghc-8.0` as 88a86f126f0fb2439b832927d51fd6d6445135b7.

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/11624#comment:9>
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