[GHC] #9150: libraries/time: parseTime barfs on leading space in format string

[GHC]

#9150: libraries/time: parseTime barfs on leading space in format string
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              Reporter:  mjo         |             Owner:  Ashley Yakeley
                  Type:  bug         |            Status:  new
              Priority:  normal      |         Milestone:
             Component:  libraries   |           Version:  7.8.2
  (other)                            |          Keywords:
            Resolution:              |  Operating System:  Unknown/Multiple
Differential Revisions:              |   Type of failure:  Incorrect result
          Architecture:              |  at runtime
  Unknown/Multiple                   |         Test Case:
            Difficulty:  Unknown     |          Blocking:
            Blocked By:              |
       Related Tickets:              |
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Comment (by mjo):

 Replying to [comment:2 Ashley Yakeley]:
 > Another alternative would be to drop skipping of leading and trailing
 spaces. This would make the behaviour of the parsing functions more
 predictable. However, the current behaviour has been there since time-1.1
 from 2007, so programs that depend on it will fail with stricter
 functions.

 I assumed this was a bug because the behaviour changed between
 time-1.4.0.1 and time-1.4.2. I've narrowed down the change to time-1.4.0.1
 -> time-1.4.0.2. Maybe I'm misunderstanding what you wrote, but your
 examples at least seem to parse fine with the older library.

 {{{
 $ ghc-pkg list | grep time
     old-time-1.1.0.1
     time-1.4.0.1

 $ ghci
 ...
 > parseTime defaultTimeLocale "%Q " " " :: Maybe LocalTime
 Just 1970-01-01 00:00:00
 > parseTime defaultTimeLocale "%k" " 8" :: Maybe LocalTime
 Just 1970-01-01 08:00:00
 }}}

 The two examples in the description also both worked in earlier versions:

 {{{
 > parseTime defaultTimeLocale "%M " "15 " :: Maybe UTCTime
 Just 1970-01-01 00:15:00 UTC
 > parseTime defaultTimeLocale " %M" " 15" :: Maybe UTCTime
 Just 1970-01-01 00:15:00 UTC
 }}}

 Maybe there was a bug in time <= 1.4.0.1 that prevented the spaces from
 being skipped?

 For what it's worth, my use case is in pickling/unpickling XML. The
 package is now public at http://hackage.haskell.org/package/htsn-import. I
 have a test case that basically says, if we unpickle some XML and then
 repickle it, we should get what we started with. For that to work, the
 leading/trailing space needs to be preserved (I don't control the XML so
 I'm stuck with the spaces). I have a test case ensuring that, and with
 time-1.4.0.1 it passes. Once I upgraded the time library along with ghc, I
 noticed the failure.

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/9150#comment:3>
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