libraries/time: parseTime barfs on leading space in format string
This used to work around 1.4.0, one of my test suites caught it:
module Main
where
import Data.Time.Clock
import Data.Time.Format
import System.Locale
main :: IO ()
main = do
putStrLn "Trailing space is handled:"
print $ (parseTime defaultTimeLocale "%M " "15 " :: Maybe UTCTime)
putStrLn "\nBut leading space isn't:"
print $ (parseTime defaultTimeLocale " %M" " 15" :: Maybe UTCTime)Trac metadata
| Trac field | Value |
|---|---|
| Version | 7.8.2 |
| Type | Bug |
| TypeOfFailure | OtherFailure |
| Priority | normal |
| Resolution | Unresolved |
| Component | libraries (other) |
| Test case | |
| Differential revisions | |
| BlockedBy | |
| Related | |
| Blocking | |
| CC | |
| Operating system | |
| Architecture |
Activity
added Tbug Trac import labels
This is awkward. The problem is that
parseTimediscards leading and trailing spaces in the input string when formatting. The obvious solution is to discard leading spaces in the format string. But here's a more difficult case:parseTime defaultTimeLocale "%Q " " " :: Maybe LocalTime%Qmatches the empty string, so one would expect this to match. However,parseTimediscards leading spaces,%Qmatches the empty string, and the following space can't be matched.Alternatively, instead of skipping initial spaces with
skipSpaces, one can parse them withskipMany (satisfy isSpace). But now this givesNothing:parseTime defaultTimeLocale "%k" " 8" :: Maybe LocalTimeThis ends up parsing two ways: the first when initial skipping grabs the space, and the second when
%kgrabs the space. They end up with the same value, but currently we need exactly one parse forparseTimeto give aJustvalue.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.
Replying to [ticket:9150#comment:86096 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 08:00:00The 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 UTCMaybe 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.
Fixed in HEAD for time-1.5.
Prelude Data.Time> parseTime defaultTimeLocale "%Q " " " :: Maybe LocalTime Just 1970-01-01 00:00:00 Prelude Data.Time> parseTime defaultTimeLocale "%k" " 8" :: Maybe LocalTime Just 1970-01-01 08:00:00 Prelude Data.Time> parseTime defaultTimeLocale "%M " "15 " :: Maybe UTCTime Just 1970-01-01 00:15:00 UTC Prelude Data.Time> parseTime defaultTimeLocale " %M" " 15" :: Maybe UTCTime Just 1970-01-01 00:15:00 UTCTrac metadata
Trac field Value Resolution Unresolved → ResolvedFixed Replying to [ticket:9150#comment:87135 Ashley Yakeley]:
Fixed in HEAD for time-1.5.
Awesome, thank you.
added incorrect runtime result label
added Pnormal label
