Parsing precise strings into less precise time points rounds rather than floors

[DavisVaughan]

library(clock)

naive_time_parse("2019-01-01 23:00:00", format = "%Y-%m-%d %H:%M:%S")
#> <time_point<naive><second>[1]>
#> [1] "2019-01-01 23:00:00"

# rounds up
naive_time_parse("2019-01-01 23:00:00", format = "%Y-%m-%d %H:%M:%S", precision = "day")
#> <time_point<naive><day>[1]>
#> [1] "2019-01-02"

# ^ this is essentially what date_parse() does
date_parse("2019-01-01 23:00:00", format = "%Y-%m-%d %H:%M:%S")
#> [1] "2019-01-02"

^{Created on 2021-04-07 by the reprex package (v1.0.0)}

See HowardHinnant/date#657 for rationale of why date does this. Since we don't allow user defined precisions (like 1/3 of a second), it might be possible for us to replace round_i() with floor(). We already have custom clock_from_stream() operators, so it wouldn't be too invasive.

[DavisVaughan]

Another less technical reason in favor of keeping this behavior might be: Since you asked it to parse the time components, when it converts to day precision it might as well use that information, so it rounds

library(clock)

# - you've asked it to parse the HMS components
# - it needs to convert to day precision somehow
# - since you have the HMS info, you might as well use it and round
sys_time_parse("2019-12-31 22:59:59", format = "%Y-%m-%d %H:%M:%S", precision = "day")
#> <time_point<sys><day>[1]>
#> [1] "2020-01-01"

# - you didn't ask it to parse the HMS components
# - it needs to convert to day precision somehow
# - straightforward since that HMS information isn't available
sys_time_parse("2019-12-31 22:59:59", format = "%Y-%m-%d", precision = "day")
#> <time_point<sys><day>[1]>
#> [1] "2019-12-31"


# similar idea here
sys_time_parse("2019-01-01 01:01:01.1238", format = "%Y-%m-%d %H:%M:%6S", precision = "millisecond")
#> <time_point<sys><millisecond>[1]>
#> [1] "2019-01-01 01:01:01.123"

sys_time_parse("2019-01-01 01:01:01.1238", format = "%Y-%m-%d %H:%M:%7S", precision = "millisecond")
#> <time_point<sys><millisecond>[1]>
#> [1] "2019-01-01 01:01:01.124"

^{Created on 2021-04-07 by the reprex package (v1.0.0)}