Field Refactoring

This is a development scratch pad to outline a few of the requirements and ideas about how to better handle the ticket fields.

For now, this puts aside the generalization of such fields to other objects/resources than Tickets (see GenericTrac for that, 0.12 material).

Goals

Get an "adapted" rendering of standard and custom fields, in the following situations:

1. Display of the field's value in the Ticket Box and other similar places (e.g. query and report results)
2. Display of the field's value changes, in the Change History and other similar places (e.g. timeline, notification)
3. Display of a field editor in the "Properties" fieldset and other similar places (e.g. bulk editor)
4. Display of a field selector in the Query view

Some points to consider:

• the distinction between regular and custom types should become fairly transparent at the web UI level (leave the door open for unification later in GenericTrac) — this is (was, even) already the case
• a rendering flexibility similar to the one of "Browser" properties should be reached (see source:trunk/trac/versioncontrol/web_ui/browser.py​ and source:trunk/trac/versioncontrol/web_ui/changeset.py​)

Proposal

A new API for dealing with fields according to the 4 points detailed above should be introduced. The old 0.9 - 0.11 API should be preserved, as there's a bunch of scripts all over the Trac world that probably depend on it, so ideally no existing method should be modified (I'm thinking in particular to TicketSystem.get_ticket_fields).

Instead, a new set of methods and objects should be introduced. In order to avoid any confusion between the old and new ways, I propose to use the term property instead of field. This matches the user-visible Properties label displayed in the ticket UI.

There will be a Property class and a set of basic subclasses that correspond to the main types of fields. A resource (tickets only for now) will define the set of properties that it provides (first in TicketSystem.get_ticket_properties(), but preferably later in TicketDescriptor.get_properties(), with TicketDescriptor a subclass of ResourceDescriptor, the generic handle for resources).

A Property subclass will have methods and attributes for answering the needs enumerated above.

1. render(context, name, mode, value) - similar to the render_property of the trac.versioncontrol.browser.IPropertyRenderer (probably some kind of unification is in order)
   • multiple other methods checking for the 'visibility' status of the field, 'row' display mode, etc. Each time with a given 'mode', which would be one of: 'ticket', 'ticket_preview', 'query'
2. render_change(old_context, new_context, name, mode, old_value, new_value) - similar to the render_property_diff of the trac.versioncontrol.changeset.IPropertyDiffRenderer
3. render_editor(context, name, mode, value). There could also be a validation method supporting validation requests that would be handled by a generic property module.
4. render_selector(context, name, mode, values), for e.g. the query module.

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See: log:sandbox/field-refactoring-tmp