Fix repr on DateTime

[sam0410]

An Attempt to fix #29909
Thanks.

[StefanKarpinski]

Looks good to me. Could probably use another pair of eyes that's more familiar with the dates code.

[fredrikekre]

These changes seems like an unintended consequence? At least to me it is a step back in readability.

[StefanKarpinski]

No, the idea is to show dates and times in a format that is valid input syntax. The fact that the step doesn't quite use valid input syntax is the remaining issue here—if that was shown as Day(1) instead then this whole output would be valid input syntax. Printing date ranges could use a more human-readable format instead of a valid input syntax.

[fredrikekre]

Ok, placed the comment on the wrong line; do we want the new printing from the collect on the next lines?

[StefanKarpinski]

Not sure, I guess we can use either format there. This seems fine to me though.

[omus]

I noticed with this PR Dates in DataFrames display the valid input syntax and not the human readable form:

julia> DataFrame(:date => today(), :value => rand())
1×2 DataFrame
│ Row │ date              │ value    │
│     │ Date              │ Float64  │
├─────┼───────────────────┼──────────┤
│ 1   │ Date(2018, 12, 4) │ 0.615755 │

If we make the :compact version of show call print then would get the terse 2018-12-04 version in the DataFrame.

[omus]

Changes look good to me. I'd like someone to chime in on if the :compact behavioural differences make sense (I think they do). The current behaviour of this PR:

julia> using Dates, DataFrames

julia> d = today()
2018-12-07

julia> print(d)
2018-12-07
julia> show(d)
Date(2018, 12, 7)

julia> fill(d, 2)
2-element Array{Date,1}:
 Date(2018, 12, 7)
 Date(2018, 12, 7)

julia> fill(d, 2, 2)
2×2 Array{Date,2}:
 2018-12-07  2018-12-07
 2018-12-07  2018-12-07

julia> DataFrame(:date => today(), :value => rand())
1×2 DataFrame
│ Row │ date       │ value    │
│     │ Date       │ Float64  │
├─────┼────────────┼──────────┤
│ 1   │ 2018-12-07 │ 0.657502 │

[sam0410]

Thanks @omus

[sam0410]

Hi everyone, Is this ready for merge now?

[ararslan]

The changes look okay to me, but this will need an entry in NEWS.md.

[sam0410]

Thanks for your review @ararslan. I added the news entry.

[omus]

@sam0410 thanks for the contribution! 👍