132. A model wires itself

Date: 2026-08-19

Status

Accepted. Finishes what ADR-0129 started.

Context

After ADR-0129 the application still said this:

Widgets.inflater(
        Showcase.actions(model, this::toggleMenu, this::toggleHud),
        icons,
        Models.bindings(model));

Three registries handed to a call that could have worked out two of them. A model already declares its @Bind paths and its @Action names — fetching both and passing them back is ceremony around a fact the object carries.

Showcase.actions(model, openMenu, toggleHud) is the other half of the problem. Two of the window’s actions are not the model’s: “open the menu” needs a Host, which a view model must not have. So the application wrote a static that took the model’s registry and added two handlers to it, and a test that wanted the same document had to call the same static or pass while the application refused to start.

Decision

Hand over the models. The toolkit reads them.

Widgets.inflater(icons, model, this);

Wiring.of(icons, models…) merges what each model publishes. Icons stay explicit, and only icons: an Icon owns native memory and has to be closed, so markup may name one and must never be able to build one — that registry is a decision the application makes and the toolkit cannot.

More than one model, which is what makes the window’s own actions ordinary. Showcase is itself a @Model now, with @Action("app.open-menu") on the method that opens the menu. The list is List.of(model, this), and a document writes press="app.open-menu" beside press="app.click" without knowing they came from two objects.

The same list is [Application#models()], so the toolkit also uses it to wire repainting (ADR-0128) and restyling (ADR-0133). One declaration answers three questions.

Names may not collide across models

Wiring.of refuses two models claiming one path. Two features quietly sharing one name is a bug that presents as a value changing by itself, and it is no less a bug for the two being in different classes — the check that already existed within a model now spans them.

Consequences

Showcase.start lost the three-registry call, the Models.onChange line, the two restyle subscriptions and the Showcase.actions static. What is left is one Widgets.inflater(icons, model, this) and a models() returning two objects.

Models.bindings and Models.actions still exist, and are still public. They are what Wiring.of calls, and what an application building its registries some other way needs. They are no longer on the path an ordinary application walks, which was the ask; deleting them would have left the escape hatch nailed shut.

The merge has to tell the two halves of the action registry apart. Actions keeps plain and valued handlers in separate maps for a reason — adapting a valued one down to a Runnable would call it with a value it was never given — so the merge inspects each and re-binds it into the right half. There is a test for it, because the failure would be a slider that reports nothing.

A test that wants the real document now constructs the real Showcase. That is better than the static it replaced: the names come from the object the application uses, so a test cannot pass against a list the application does not have.