[GHC] #14522: GHC recompilation checker doesn't take account of deprecated pragmas

24 Nov 2017

      #14522: GHC recompilation checker doesn't take account of deprecated pragmas
-------------------------------------+-------------------------------------
           Reporter:  NeilMitchell   |             Owner:  (none)
               Type:  bug            |            Status:  new
           Priority:  normal         |         Milestone:
          Component:  Compiler       |           Version:  8.2.1
           Keywords:                 |  Operating System:  Unknown/Multiple
       Architecture:                 |   Type of failure:  Incorrect
  Unknown/Multiple                   |  error/warning at compile-time
          Test Case:                 |        Blocked By:
           Blocking:                 |   Related Tickets:
Differential Rev(s):                 |         Wiki Page:
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 Given the sources:

 {{{#!hs
 -- A.hs --------------------
 module A
 --  {-# DEPRECATED "bad" #-}
     where
 a = 1
 }}}

 {{{#!hs
 -- B.hs --------------------
 module B where
 import A
 }}}

 I get the interactions:

 {{{
 $ ghc B
 [1 of 2] Compiling A                ( A.hs, A.o )
 [2 of 2] Compiling B                ( B.hs, B.o )

 $ manually edit A.hs to uncomment the deprecated line

 $ ghc B
 [1 of 2] Compiling A                ( A.hs, A.o )

 $ touch B.hs

 $ ghc B
 [2 of 2] Compiling B                ( B.hs, B.o )

 B.hs:2:1: warning: [-Wdeprecations] Module `A' is deprecated: bad
   |
 2 | import A
   | ^^^^^^^^
 }}}

 Observe that after editing the deprecated pragma in {{{A.hs}}} GHC didn't
 recompile {{{B.hs}}}, meaning that the warning only appeared after I
 touch'd {{{B.hs}}}. Turning on {{{-Werror}}} turns the problem from one of
 incorrectly missing warnings to one of incorrect compilation results.

 I was also got the same results when adding a deprecated pragma to an
 individual function.

 My guess is whatever {{{.hi}}} hash you take for recompilation checking
 should include deprecated pragmas.

-- 
Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/14522
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