[proposal] reports: user-set parameters - a period, a threshold, a name the reader chooses

[delchev]

A report is rarely read once. It is read for a period, for amounts above a threshold, for a counterparty whose name someone half-remembers - inputs the reader chooses at the moment of reading.

The format has no way to say so. filter is fixed when the report is generated, and the only runtime narrowing a reader gets is whatever per-column filtering the surface offers over the columns the report already displays. Two consequences, both routine:

• A period is not a column. "This quarter" over an invoice date means two bounds the reader sets. The model can express either every row or one hard-coded window, so an application carries one report per period, or none.
• The interesting filter is often on a field the report does not show. A receivables list displays customer, number and balance; the reader wants only the ones whose internal owner is themselves. Filtering over displayed columns cannot reach that field, so the report grows a column nobody wanted in order to be filterable by it.

One report kind already escapes this, by hardwiring: the balance report declares its own From/To window, because its opening/period/closing shape cannot be specified without one. That is the argument that the mechanism belongs to reports in general.

Proposed shape:

reports:
  - name: Revenue
    source: Invoice
    dimensions: [date, customer.name]
    measures: ["sum(total)"]
    parameters:
      - { name: fromDate, target: date, op: ge }
      - { name: toDate, target: date, op: le }
      - { name: minTotal, target: total, op: ge, initial: "0" }
      - { name: customer, target: customer.name, op: like }

The load-bearing decision is that a parameter is bound on every read, so the unset case is carried by a value (initial) rather than by a vanishing predicate - a report whose query shape depends on which inputs were touched is one no surface can present or cache. initial is therefore required unless the comparison has a neutral "any value" default (a date bound, a like search).

Proposal document and the full normative text: PR to follow. Reference implementation: eclipse-dirigible/dirigible#6357 / eclipse-dirigible/dirigible#6911.