[FIX] models: do less snapshots in onchange()

As snapshots are costly to compute, we now create exactly two snapshots:
one initial snapshot and one final snapshot.  All intermediate checks
are done with respect to the initial snapshot.

Note also that checks are costly for x2many fields.  Therefore, once a
field has changed, it will never be checked again.  This optimization is
correct since, by contract, the onchanges of a field are processed at
most once.  This guarantees the absence of cycles in onchange.

For instance, assume that field A modifies fields B and C, and that
field C modifies fields D, E and F:
- before: 7 snapshots (snapshot, process A, snapshot, process B,
snapshot, process C, snapshot, process D, snapshot, process E,
snapshot, process F, snapshot)
- after: 2 snapshots (snapshot, process A, process B, process C,
process D, process E, process F, snapshot)

closes odoo/odoo#31872

Signed-off-by: Raphael Collet (rco) <rco@openerp.com>

0 files changed, 0 insertions, 0 deletions