[GHC] #11556: GHC recompiles unchanged hs-boot files

[GHC]

#11556: GHC recompiles unchanged hs-boot files
-------------------------------------+-------------------------------------
           Reporter:  thomie         |             Owner:
               Type:  bug            |            Status:  new
           Priority:  normal         |         Milestone:
          Component:  Driver         |           Version:  7.10.3
           Keywords:                 |  Operating System:  Unknown/Multiple
       Architecture:                 |   Type of failure:  None/Unknown
  Unknown/Multiple                   |
          Test Case:                 |        Blocked By:
           Blocking:                 |   Related Tickets:  #11013, #10333
Differential Rev(s):                 |         Wiki Page:
-------------------------------------+-------------------------------------
 A.hs:
 {{{#!hs
 module A where

 import B

 f = someError
 }}}

 A.hs-boot:
 {{{#!hs
 module A where
 }}}

 B.hs:
 {{{#!hs
 module B where

 import {-# SOURCE #-} A
 }}}

 {{{
 $ ghc-7.10.3 --make A.hs
 [1 of 3] Compiling A[boot]          ( A.hs-boot, A.o-boot )
 [2 of 3] Compiling B                ( B.hs, B.o )
 [3 of 3] Compiling A                ( A.hs, A.o )

 A.hs:5:5: Not in scope: ‘someError’


 $ ghc-7.10.3 --make A.hs
 [1 of 3] Compiling A[boot]          ( A.hs-boot, A.o-boot )
 [3 of 3] Compiling A                ( A.hs, A.o )

 A.hs:5:5: Not in scope: ‘someError’
 }}}

 Why does `ghc --make` recompile `B.hs-boot`?

 Note that recompilation avoidance does work when using `ghc -c`:
 {{{
 $ ghc -c A.hs-boot
 compilation IS NOT required
 }}}

 (found while trying to reduce the testcase for #11532, which contains 644
 .hs and 642 .hs-boot files)

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/11556>
GHC <http://www.haskell.org/ghc/>
The Glasgow Haskell Compiler