[GHC] #10152: Testsuite diffs can be misleading when normalisers are in use

10 Mar 2015

      #10152: Testsuite diffs can be misleading when normalisers are in use
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              Reporter:  ezyang      |             Owner:
                  Type:  task        |            Status:  new
              Priority:  low         |         Milestone:
             Component:  Test Suite  |           Version:  7.11
              Keywords:              |  Operating System:  Unknown/Multiple
          Architecture:              |   Type of failure:  None/Unknown
  Unknown/Multiple                   |        Blocked By:
             Test Case:              |   Related Tickets:
              Blocking:              |
Differential Revisions:              |
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 When output fails to match, GHC will output the diff based on the original
 outputs.  However, this is misleading: some "differences" will actually
 have been normalised by the whitespace and more substantive normalisers we
 apply. So you really have to compare the normalised output to see what the
 /real/ difference is.

 Unfortunately, the real normalised output is missing newlines, so it's not
 really suitable for diffing. So it's not really clear what an improved
 algorithm would be.

 This seems to not actually be a problem in practice, since SOP for
 messages which need heavy normalizing is that when the new message looks
 good, it's just 'make accept'ed. Can be a little confusing when you're
 developing normalisers.

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Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/10152
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