[Libreoffice] [REVIEW][3-4] date change regression fdo#44385

[Noel Power]

Hi Andrew,

> My primary concerns
>
> 1. Change in behavior that may break existing code.
the intent of the patch is to restore the previous behaviour ( by 
previous behaviour I mean before integration of the feature that 
erroneously removed the 'special' processing for '+' for dates ). 
Additionally the intent of the patch is to make the behaviour for '-' 
similar for'+' e.g. if Date + 1 gives a Date then surely Date - 1 should 
additionally give back at Date. Hopefully that makes sense :-)
>
> 2. Previous behavior was never flagged as an issue, and may arguably 
> be considered logical to some. for example, storing a "delta" in the 
> native type.
I don't think we should be afraid to change present behaviour if we 
think it is wrong and especially if the impact is probably going to be 
very minor ( as I think is the case here ). I would bet that the 
behaviour we have at the moment is an incomplete attempt to behave in a 
compatible way with vba. Where we can, I think if the cost is low we 
should try to be compatible ( should actually look at what vba does 
[*]). But... I take it that you are unhappy with changing the treatment 
of '-' ? and wouldn't be in favour of the change right? ( funny somehow 
I thought in the previous mail thread that you were in favour of even 
letting the Date type be set for all those numeric operations, sorry I 
misunderstood you )
>
> 3. The rules are more complicated now and require complex examples to 
> explain; for example, time_1 + time_2 + time_3 returns a date but 
> time_1 + time_2 does not. We cannot simply state that math done with 
> dates or including a date returns a date.
yeah that doesn't sound right :-/  should remain a Date I would think

[*] table of behaviour in vba, pre the bug being introduced and post patch

                                mso    old behaviour  present
                             --------------------------------
date + num                    Date      Date          Date
date - num                    Date      Double        Date
date * num                    Double    Double        Double
date / num                    Double    Double        Double
date + date                   Date      Double        Double [1]
date - date                   Double    Double        Double
date * date                   Double    Double        Double

[1] the date + date is clearly wrong (fixing that would address '3.' 
above. )

personally I am all for fixing this to be compatible

Noel