[18.0][IMP] web_form_banner: client-side fast path for simple rules

[dnplkndll]

Why

Every banner rule today fires a server RPC (compute_message) per trigger-field change. For typical conditions — state == 'draft' and amount_total > 1000 — Odoo's view compiler already evaluates exactly that kind of expression purely client-side via py.js in invisible= attributes. The round-trip isn't needed for the 80% case.

What

Per-rule client_side opt-in. When enabled:

• Visibility is evaluated by Odoo's view compiler against the in-memory record. Zero RPC.
• Message text uses inline <field name="..."/> tags (Odoo-native, reactive) plus the existing ${field_name} sugar that rewrites to those tags at get_view time.
• The existing JS RPC machinery is untouched and continues to drive server-side rules.

Generated arch

For a rule with client_condition: not email and name, message Contact <strong>${name}</strong> has no email., target xpath //sheet, on res.partner form:

<form>
  <!-- ...standard partner header... -->
  <field name="email" invisible="True"/>   <!-- auto-injected so py.js can resolve -->
  <div class="alert alert-warning"
       invisible="not (not email and name)"
       role="status"
       data-rule-id="123"
       data-model="res.partner"
       data-client="1">
    Contact <strong><field name="name"/></strong> has no email.
  </div>
  <sheet>...</sheet>
</form>

Toggle email on/off in the form → banner appears/disappears instantly. Zero Network-tab activity, zero compute_message RPC.

Defensive auto-injection

If client_condition references a field that the form view doesn't declare, py.js raises Name 'X' is not defined at render time and crashes any browser test that opens the form. The get_view override parses the condition via ast.parse, extracts every leftmost-Name reference, filters out py.js reserved names + names not on the model + names already declared, and auto-injects the remaining as <field name="X" invisible="True"/> siblings. Any admin-defined rule referencing a non-loaded field now Just Works.

What works in client_condition

Comparisons, boolean ops, in/not in, attribute access (partner_id.email), built-ins (len, bool, min, max, set), ternary x if cond else y.

What does NOT work — keep server-side mode

Arbitrary method calls (.filtered(), .mapped()), slicing, lambdas, comprehensions, ORM searches, per-record severity overrides, ${X.Y} dotted interpolation.

Files

File	Change
models/web_form_banner_rule.py	client_side + client_condition fields, _check_client_condition constraint via ast.parse, _to_client_arch for ${var} → <field/>
models/ir_model.py	get_view branches on rule.client_side; _client_rule_missing_fields returns hidden field shims; banner built via lxml element API
static/src/js/web_form_banner.esm.js	One-line filter in bannersIn() skips data-client="1" divs
views/web_form_banner_rule_views.xml	New fields exposed, notebook page toggles between server- and client-side help
tests/test_web_form_banner.py	11 new test cases — arch emission, ${var} sugar, HTML escaping, missing/malformed condition rejection, hidden-field auto-injection with dedup, py.js-reserved-name skipping, dotted-${} rejection, quote-bearing conditions, position=after, multi-rule field sharing
demo/web_form_banner_rule_demo.xml	One extra fast-path demo using base-only fields (not email and name)
readme/USAGE.md + ROADMAP.md + CONTRIBUTORS.md	Client-side section, limitations, follow-ups, Ledoweb co-author
__manifest__.py	Bump to 18.0.1.2.0, add Ledoweb co-author + maintainers=["dnplkndll"]

Notable correctness details

• Banner element built via lxml's etree.Element API rather than f-string XML — single quotes in conditions like state == 'draft' would otherwise terminate the invisible='...' attribute mid-expression. Caught during review; covered by test_client_side_handles_quoted_string_literals.
• ${var} sugar restricted to bare field names. Dotted paths like ${partner_id.email} would rewrite to invalid form arch. Covered by test_client_side_rejects_dotted_var_sugar. Documented in USAGE.

Verification

Local fresh-DB --test-enable: 20 tests, 0 failures.

Fork CI on ledoent self-hosted runners (hetzner-k3s-ledoent): all 5 jobs green (commit effeea0 on 18.0-imp-web_form_banner-client-side).

Practice run scope

PR opened against the fork (not OCA upstream) to exercise the review workflow. Will close after squashing/promoting to OCA/web.

Test plan

• All 20 unit tests pass on a fresh DB
• All 5 CI jobs pass on the fork (Detect deps, test with Odoo, test with OCB, both rebel variants)
• Client-side rule with quoted string literal serializes correctly
• Hidden-field auto-injection works for missing references
• Server-driven rules continue to work unchanged
• Pre-flight strip of >>> FORK-LOCAL BLOCK <<< before promoting upstream