New "-V" flag behavour not reverse compatible when combined with "--end" flag

[trevorld]

In particular in hledger the "-V" when combined with the "--end" flag used to only use price directives up to the end date to determine market value but now it also uses price directives after the end flag.

Example:

$ cat error.hledger 

P 2016/01/01 00:00:00 SP                        250 USD
P 2017/01/01 00:00:00 SP                        500 USD

2016-01-01 * Brokerage | Buy Stock
  Assets:Checking  4 SP @ 250 USD
  Equity:Opening  -1000 USD
$ hledger -f error.hledger register -V --end=2016-12-31
2016/01/01 Brokerage | Buy Stock                                                 Assets:Checking                                                           2000 USD      2000 USD
                                                                                 Equity:Opening                                                           -1000 USD      1000 USD
$ hledger -f error.hledger register -V --end=2017-12-31
2016/01/01 Brokerage | Buy Stock                                                 Assets:Checking                                                           2000 USD      2000 USD
                                                                                 Equity:Opening                                                           -1000 USD      1000 USD

The old behaviour used to be equivalent to the new "--value=END-DATE" behaviour:

$ hledger -f error.hledger register --value=2016-12-31
2016/01/01 Brokerage | Buy Stock                                                 Assets:Checking                                                           1000 USD      1000 USD
                                                                                 Equity:Opening                                                           -1000 USD             0

Is this new "-V" combined with "--end=YYYY-MM-DD" behaviour considered a bug that will be fixed? Or do I need to update r-ledger to detect which version of hledger is being used and if the version is new enough use the -value=END-DATE and if older instead use -V --end=END-DATE?

[simonmichael]

That's interesting, thanks. Reviewing what you've found, old behaviour first:

$ hledger-1.14 print
2016/01/01 * Brokerage | Buy Stock
    Assets:Checking    4 SP @ 250 USD
    Equity:Opening          -1000 USD

-V shows the SP amount in USD, using the market price on today's date by default. (Ignore the fact that print with -V looks unbalanced, that's expected.):

$ hledger-1.14 print -V
2016/01/01 * Brokerage | Buy Stock
    Assets:Checking        2000 USD
    Equity:Opening        -1000 USD

With a report end date specified, -V uses the market price on that date:

$ hledger-1.14 print -V -e 2016/12/31
2016/01/01 * Brokerage | Buy Stock
    Assets:Checking        1000 USD
    Equity:Opening        -1000 USD

Now the new behaviour - print -V still uses today's market price by default:

$ hledger print -V
2016/01/01 * Brokerage | Buy Stock
    Assets:Checking        2000 USD
    Equity:Opening        -1000 USD

It no longer pays attention to the report end date:

$ hledger print -V -e 2016/12/31
2016/01/01 * Brokerage | Buy Stock
    Assets:Checking        2000 USD
    Equity:Opening        -1000 USD

Unless you set the valuation date explicitly, to "end":

$ hledger print  --value=end -e 2016/12/31
2016/01/01 * Brokerage | Buy Stock
    Assets:Checking        1000 USD
    Equity:Opening        -1000 USD

Is this a bug ? Well, report end date and valuation date are independent concepts; you should be able to see any period's data, valued using the prices on any date. So should a report end date also set the valuation date ? I don't think so.

https://hledger.org/hledger.html#effect-of-value-on-reports is supposed to document how print is affected, and seems a bit unclear.

https://github.com/simonmichael/hledger/blob/master/hledger-lib/Hledger/Reports/EntriesReport.hs#L47 helps determine the default valuation date used by print. In this case I can see it's being used only with --value=end (evaluating to 2016-01-02); it's not used with -V.

https://github.com/simonmichael/hledger/blob/master/hledger-lib/Hledger/Data/Posting.hs#L337 shows why: --value=end executes the AtEnd case. -V executes the second AtDefault case, which uses today's date (same as --value=now).

Is this a bug ? Is there a better default valuation date for -V when valuing postings, affecting print and register ? Still not sure, I'll need a fresh mind.

[simonmichael]

https://hledger.org/hledger.html#valuation docs updated a bit.

[trevorld]

Well I reported it as a bug since the release notes claim "There is a new valuation option --value=TYPE[,COMM], with backwards-compatible -B/--cost, -V/--market, -X/--exchange=COMM variants" but there is actually new non-backwards-compatible behaviour that breaks how r-ledger calculates historical net worth in hledger files.

If you want to keep the new behaviour I can first figure out which version of hledger the user has and then use different flags based on whether it is hledger (>= 1.15) or hledger (< 1.15) (which does not have the new --value=DATE option).

I suspect that using the reporting end date as the default valuation date for "--market" is the most useful default market valuation date (which it seems you continue to use as the default for multiperiod reports) instead of --value=now (the new default for single period reports). If users really want the valuation date to differ from the reporting end date couldn't they now set different dates to --value and -end?

[simonmichael]

I had a weaker notion of backwards-compatible in mind there, but you're right. And as you say, "-V == --value=end, always" would seem both more compatible and simpler, and at least as useful, I think. And I think we could do this in a bugfix release quite soon.

[simonmichael]

"-V == --value=end" isn't fully compatible either:

P 2000/01/01 A  2 B
P 2002/01/01 A  3 B

2000/01/01
  (a)      1 A

Old -V uses prices on -e date, otherwise today's date:

$ hledger-1.14 reg -V -e2001; hledger-1.14 reg -V
2000/01/01                      (a)                            2 B           2 B
2000/01/01                      (a)                            3 B           3 B

1.15 single-period -V uses prices on today's date, ignoring -e date:

$ hledger-1.15 reg -V -e2001; hledger-1.15 reg -V
2000/01/01                      (a)                            3 B           3 B
2000/01/01                      (a)                            3 B           3 B

-V equivalent to --value=end uses prices on -e date, otherwise journal end date:

$ hledger-1083 reg -V -e2001; hledger-1083 reg -V
2000/01/01                      (a)                            2 B           2 B
2000/01/01                      (a)                            2 B           2 B

[simonmichael]

I think that last behaviour might be ok from a usability perspective, even though it's a change. How would it affect your usage ?

[simonmichael]

Whether -V (with no report end date specified) should be changed to use the journal end date instead of today as default valuation date.

Pro:

• When reviewing finances from the babylonian cuneiform tablets, or from last year, -V would show the contemporary value from (end of) that period. Perhaps a more useful default ? (To see value at today's prices, you'd have to say -V -e today, or --value=now.)
• It would remove the difference between -V's behaviour in single-period and multi-period reports, making it simpler to document and understand. (Currently bal -V shows today's value, while bal -V -Y shows values at each year end.)

Con:

• It would be different from past hledger.
• It would be different from Ledger.

[trevorld]

When importing in an hledger register (without the user specifying an end-date) r-ledger adds a market value column to the imported register constructed by just using the -V flag. So theoretically it seems the market value column in the imported register r-ledger presents could be affected for a subset of r-ledger's hledger users:

1. Users with both future transactions and future price directives
2. Users with price directives before today recorded after their last transaction.

Neither the r-ledger unit tests nor my personal ledgers should be affected since they have neither future price directives nor do they lack any transactions after any price directives and I suspect the majority of users wouldn't be impacted either way but I think (if you don't want to use the reverse-compatible today as the default) then the slightly more useful default if no end date is given would be to use both the price directive dates and the transaction dates in the calculation of the "journal end date" - this would then be equivalent to the current behaviour if there are no future price directives (which are probably rare).

One use case would be someone keeping track of an inventory or investments in a separate ledger that they are holding long-term and while they are keeping the price directives up to date they don't have any new transactions to record but they are still interested in knowing what their current market values are in that separate ledger. Not sure how many such users with that use case exist, if you keep everything (including checking account and credit card) in one ledger and don't have future price directives then you aren't likely to be impacted either way.

[simonmichael]

For the record, price directive dates is something we don't currently consider at all when choosing valuation date. I don't know if Ledger does.

There are are a lot of dates and cases to keep track of. Tricky! And this is reflected a bit in the code right now. So this might take a little longer to bake.

Currently I lean towards just fixing the issue you reported (make -V use -e) and maximising compatibility.