navigation: federation — contracts, mount, and capabilities by aurindam · Pull Request #12569 · slint-ui/slint

aurindam · 2026-07-21T14:31:27Z

Adds the federation layer to the navigator (built on #12554): an app can be assembled from independently-authored, independently-released parts, composed by an integration layer without editing any part's internals.

This supersedes #12565, re-implemented on master's current interface/implement model. The only user-visible change from that earlier draft: a part declares conformance with the body statement implement <Contract> <=> self; instead of the removed implements header. Contracts, needs, and both mount forms are unchanged.

Multi-team composition

A navigation contract (an interface of routes) is the boundary. A part conforms with implement Contract <=> self, declares the capabilities it needs, and runs its own navigator; the integration shell mounts each part at a route and binds those needs.

Runnable: examples/navigation-federated models this with separate owners.

File	Owner	Role
`ui/contract.slint`	platform	the `FeatureNav` contract + `HostServices`
`ui/media.slint`	Media team	`MediaFeature`, `implement FeatureNav <=> self`, `needs HostServices`
`ui/settings.slint`	Settings team	`SettingsFeature`, same contract
`ui/app.slint`	integration	mounts both features + an external plugin, binds the capabilities

// contract (shared, owned by the platform team)
export interface FeatureNav {
    @version(1)
    @uri("app://feature") route Main;
}
export interface HostServices { callback log(string); callback go-home(); }

// a feature (Media team): conforms + states what it needs, runs its own navigator
export component MediaFeature inherits Rectangle {
    implement FeatureNav <=> self;
    needs HostServices;
    in-out property <MediaRoute> current-route: MediaRoute.Main;
    navigator (current-route) { MediaRoute.Main: Library { home => { root.go-home(); } } }
}

// the integration shell composes features without editing them
export component App inherits Window {
    navigator (current) {
        Shell.Home:    HomeScreen { }
        Shell.Media:   mount MediaFeature via FeatureNav {
            log(message) => { debug(message); }
            go-home => { root.navigate(Shell.Home); }
        }
        Shell.Plugin:  mount extern via FeatureNav { component-factory: root.plugin-factory; }
    }
}

What's in it

Contracts — an interface carries a navigation contract; route attributes
@version(n) / @uri("…") make it versioned and deep-linkable. Routes live in a
side-car on the component, off the interface member lists, so interface member
projection never sees them.
Conformance — implement Contract <=> self requires the component's navigator to
cover every contract route by name (checked at build time).
Capabilities — needs Capability; declares the interface's callbacks as unbound
members, bound by the integrator at the mount site; an unbound need is a compile error.
Build-time mount — mount Impl via Contract { … }, a direct instantiation checked
against the contract.
Cross-process mount — mount extern via Contract { component-factory: … } via
ComponentContainer + ComponentFactory, for parts shipped as their own binary.
examples/navigation-federated demonstrates it end to end: the host builds the plugin
in main.rs and passes it in as a slint::ComponentFactory.
Public factory API — slint_interpreter::ComponentDefinition::create_embedded is now
public (was #[doc(hidden)] + #[cfg(feature = "internal")]), so a real app can supply
the factory for an external mount without reaching into internal API.
Docs — a new Federated Navigation guide
(docs/…/guide/development/navigation-federation.mdx).

Notes

Experimental: SLINT_ENABLE_EXPERIMENTAL_FEATURES=1.
Base: stacked on navigation: experimental declarative navigator construct #12554 (auri/upstream/nav-a5); the diff shows only the federation delta.
Tests: interpreter tests for contract conformance, the build-time mount + capability
binding, and the external factory seam; cross-language driver case
tests/cases/navigation/mount.slint (Rust/C++/JS/Python).
Deferred (follow-ups): route-parameter payloads (parsed and typed, not yet threaded
through navigate), cross-process capability binding over the extern seam,
route param-type conformance, and <=> child contracts.

…rmance Re-implements the navigation-contract slice on master's redesigned interface model, where conformance is the body statement `implement I <=> self;` (the old `implements` header was removed). - grammar: `route` members (RouteDeclaration) with `@version`/`@uri` attributes on an `interface`, parsed unconditionally, gated at lowering. - object tree: an interface's routes collect into a side-car `Component.navigation_contract`, kept off the member lists so interface member projection never sees routes; `route` outside an interface is rejected. - conformance: `validate_navigation_contract_conformance` walks the self- implemented interfaces from master's `get_implemented_interfaces` and requires the component's navigator to cover every contract route by name. Test `navigation_contract_conformance` covers both the passing and the missing-route cases. Mount, `needs`, and external mount are later steps. Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

- needs: `needs Capability;` declares the interface's callbacks as unbound members, bound by the integrator at the mount site (get_needed_interfaces/apply_needs; verify_mount_capabilities). - local mount: `Route.X: mount Impl via Contract { bindings }` desugars to a direct instantiation, conformance-checked against the contract (from_navigator_node + verify_federated_mount/resolve_mount_contract/ validate_mount_conformance). - external mount: `mount extern via Contract { component-factory: … }` builds a ComponentContainer the host fills at runtime (from_external_mount_node/ verify_external_mount); FederatedMount.impl_name is None for external. - route-set fix: lower_navigator marks the route property set so a mounted module's internal navigator isn't classified constant (would panic on navigate). Tests: navigation_federated_mount (mount + unbound-capability + external), and navigation_internal_route_is_writable (runtime navigate/back on an internal route). 30 interpreter + 325 compiler tests pass. Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

- example: port examples/navigation-federated to the new conformance syntax (`implement <Contract> <=> self;` instead of the removed `implements` header); registered in the examples workspace. Builds end to end, including the external plugin mounted via `mount extern via` whose factory main.rs builds from interpreter-loaded source. - api: make `slint_interpreter::ComponentDefinition::create_embedded` public so a host can supply the factory for an external mount without internal API. - docs: add the Federated Navigation guide (contracts, implement/needs, mount, extern), registered in the sidebar after Navigation. Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

…al route - tests/cases/navigation/mount.slint: a mounted feature (implement <=> self) driven through the outer navigator, in Rust/C++/JS/Python. - tests/cases/navigation/internal_route.slint: navigate()/back() on a non-root component's internal route (the mark_as_set regression). Green in the Rust driver (LLR codegen) and the interpreter driver. Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

Compress the wordier inline/doc comments added by the federation slices to match the repository convention (why, not what). No behavior change. Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

0x6e

Cool!

0x6e · 2026-07-21T15:51:00Z

+
+/// Resolve the `needs` specifiers on `node` to capability interfaces.
+pub(super) fn get_needed_interfaces(
+    e: &Element,


Please spell out variable names in this file (e -> element, tr -> type_register) etc. Here an below.

0x6e · 2026-07-21T15:56:18Z

+    for NeededInterface { needs_specifier, interface, interface_name } in needed {
+        let mut members = Vec::new();
+        for (name, prop_decl) in interface.borrow().property_declarations.iter().filter(|(_, d)| {
+            matches!(d.property_type, Type::Callback { .. } | Type::Function { .. })


Can a capability provide a property? An interface can provide one, yet they are not applied.

0x6e · 2026-07-21T16:00:26Z

+}
+
+export component MediaFeature inherits Rectangle {
+    implement FeatureNav <=> self;


Note that once #12566 lands the interface must be fully implemented here. I haven't understood what that means for your @version and @uri yet.

0x6e · 2026-07-21T16:03:44Z

+            home => { root.go-home(); }
+        }
+        MediaRoute.Player: Player {
+            can-go-back: root.can-go-back;


Where does root.can-go-back come from? Or is root here no longer the MediaFeature?

0x6e · 2026-07-21T16:07:24Z

+        }
+        all_bound
+    }
+


I wonder if some of the stuff added to object_tree.rs and interfaces.rs should be moved to object_tree/navigation.rs?

aurindam and others added 5 commits July 21, 2026 14:52

navigation: trim federation comments to the repo's terse style

1759c32

Compress the wordier inline/doc comments added by the federation slices to match the repository convention (why, not what). No behavior change. Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

0x6e reviewed Jul 21, 2026

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navigation: federation — contracts, mount, and capabilities - #12569

navigation: federation — contracts, mount, and capabilities#12569
aurindam wants to merge 5 commits into
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aurindam commented Jul 21, 2026

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aurindam commented Jul 21, 2026

Multi-team composition

What's in it

Notes

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