[GHC] #11204: Recompilation checking stochastically broken on Darwin

[GHC]

#11204: Recompilation checking stochastically broken on Darwin
----------------------------------------+----------------------------
           Reporter:  bgamari           |             Owner:
               Type:  bug               |            Status:  new
           Priority:  normal            |         Milestone:  8.2.1
          Component:  Compiler          |           Version:  7.11
           Keywords:                    |  Operating System:  MacOS X
       Architecture:  Unknown/Multiple  |   Type of failure:  Other
          Test Case:                    |        Blocked By:
           Blocking:                    |   Related Tickets:
Differential Rev(s):                    |         Wiki Page:
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 The `retc001` test usually fails on Darwin. Unfortunately, it also
 sometimes passes.

 Failures look like this,
 {{{
 =====> retc001(normal) 1 of 1 [0, 0, 0]
 cd . && $MAKE -s --no-print-directory retc001    </dev/null >
 retc001.run.stdout 2> retc001.run.stderr
 Actual stderr output differs from expected:
 --- ./retc001.stderr.normalised 2015-12-11 23:02:23.000000000 +0200
 +++ ./retc001.run.stderr.normalised     2015-12-11 23:02:23.000000000
 +0200
 @@ -1,2 +0,0 @@
 -
 -C.hs:3:11: Module ‘B’ does not export ‘foo’
 \ No newline at end of file
 Actual stdout output differs from expected:
 --- ./retc001.stdout.normalised 2015-12-11 23:02:23.000000000 +0200
 +++ ./retc001.run.stdout.normalised     2015-12-11 23:02:23.000000000
 +0200
 @@ -3,5 +3,3 @@
  [3 of 3] Compiling Main             ( C.hs, nothing )
  Middle
  End
 -[2 of 3] Compiling B                ( B.hs, nothing )
 -[3 of 3] Compiling Main             ( C.hs, nothing ) [B changed]
 \ No newline at end of file
 *** unexpected failure for retc001(normal)
 }}}

 I suspect the problem is mtime resolution as if I apply the following
 patch it almost always passes,
 {{{
 diff --git a/testsuite/tests/driver/retc001/Makefile
 b/testsuite/tests/driver/retc001/Makefile
 index a3cf6eb..bb1eca8 100644
 --- a/testsuite/tests/driver/retc001/Makefile
 +++ b/testsuite/tests/driver/retc001/Makefile
 @@ -20,5 +20,6 @@ retc001: clean
         echo 'Middle'
         '$(TEST_HC)' $(TEST_HC_OPTS_NO_RECOMP) -fno-code -fwrite-interface
 --make C.hs
         echo 'End'
 +       sleep 1
         cp B2.hs B.hs
         -'$(TEST_HC)' $(TEST_HC_OPTS_NO_RECOMP) -fno-code -fwrite-
 interface --make C.hs
 }}}

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/11204>
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