period expressions: support quarterly on a custom day

[simonmichael]

From @zino23 [1]:

hledger support specifying a custom day on a week, month and year, but not on a quarter.

E.g. we can specify a recurring transaction every 1st day of the month:

~ every 1st day of month from 2025-07-31 to 2026-07-30
  expenses:rent  7,875 CNY
  assets:bank:cmb

Output of hl reg expenses:rent --forecast

2025-09-01                                                              expenses:rent                                                  7875.00 CNY   7875.00 CNY
2025-10-01                                                              expenses:rent                                                  7875.00 CNY  15750.00 CNY
2025-11-01                                                              expenses:rent                                                  7875.00 CNY  23625.00 CNY
2025-12-01                                                              expenses:rent                                                  7875.00 CNY  31500.00 CNY
2026-01-01                                                              expenses:rent                                                  7875.00 CNY  39375.00 CNY

But specify every 1st day of the quarter fails:

~ every 1st day of quarter from 2025-07-31 to 2026-07-30
  expenses:rent  7,875 CNY
  assets:bank:cmb

Error output:

    |
161 | ~ every 1st day of quarter from 2025-07-31 to 2026-07-30
    |                ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

remainder of period expression cannot be parsed
perhaps you need to terminate the period expression with a double space?
a double space is required between period expression and description/comment

We can only specify a transaction takes place every quarter with this:

~ every quarter from 2025-07-31 to 2026-07-30
  expenses:rent  7,875 CNY
  assets:bank:cmb

and the transaction will take place at the last day of the quarter:

hl reg expenses:rent --forecast

2025-10-31                                                              expenses:rent                                                  7875.00 CNY   7875.00 CNY

But in reality the transaction takes place on 2025-07-31, so assets:bank:cmb's money is incorrect from 2025-07-31 to 2025-10-30, with a deficit of 7875 CNY. After 2025-10-31, it will be corrected.

Is there a good reason specifying a custom day is not supported on quarter?

[simonmichael]

No reason we can't add this. If you are a programmer, would you be interested in researching it ?

[zino-34]

No reason we can't add this. If you are a programmer, would you be interested in researching it ?

Yeah I would love to contribute to hledger! Although I've never written one line of haskell, I think it would be fun to learn it while reading the code:) Can you assign this issue to me?