[peholmst]

Review risk: two-way door. Docs and examples only: one new reference page, one removed page with a redirect, a new section on Shared Signals, and link updates. Reverting brings the old page back.

Summary

Moves full-stack signals from the Hilla guides to the Flow UI State section, as the new page Shared Signals in React Views (flow/ui-state/full-stack-signals). This is the seventh step of dissolving the Hilla section, after #6611, #6616, #6618, #6620, #6621 and #6622.

The page is a reference: which shared signal types a service can return, the client API of the signals, how they connect and synchronize, and how the access annotations apply. It's rewritten for 25.4, because most of the old page described an API that no longer exists. Every statement is checked against main of vaadin/hilla and vaadin/flow, and the behavior is checked in a scratch 25.4.0-alpha5 application with two browser tabs. This pull request targets main only, so it gets no target/v25.3 label.

What changed

• New page flow/ui-state/full-stack-signals.adoc, marked as a preview feature behind the fullstackSignals feature flag:
  • the supported types (SharedValueSignal, SharedNumberSignal, SharedListSignal) and their TypeScript counterparts;
  • returning one instance from the service, and service methods with parameters;
  • creating, connecting and reading the signals in a view, and default values;
  • the members of ValueSignal, NumberSignal and ListSignal, and operation results;
  • changes made on the server;
  • access control.
• Shared Signals: a new Validating Changes section for withValidator() and CommandValidator, which the Flow page didn't cover. The UI State index links to the new page.
• Feature Flags: fullstackSignals moves to the list of experimental flags, and the Hilla Feature Flags heading goes away.
• Examples: a compiled MeetingService and a view that uses a value, number and list signal, replacing the inline examples.
• Removed page, with a redirect: hilla/guides/full-stack-signals → flow/ui-state/full-stack-signals.
• Links: Type Conversion now links to the new page.
• Corrections compared with the old page, each checked in the scratch application:
  • ValueSignal has no replace() or update() anymore (feat!: integrate Vaadin signals library in Hilla (ValueSignal) hilla#3500), and ListSignal has insertFirst() as well.
  • The operation-validator API (withOperationValidator, ValidationResult, IncrementOperation, …) no longer exists. Flow's shared signals use withValidator(CommandValidator), which is now on the Shared Signals page.
  • new SharedValueSignal<>(false, Boolean.class) doesn't compile. The constructors take an initial value, a type, or both as a TypeReference.
  • The list example used the index as the React key. Each item signal has a stable id.
  • SharedMapSignal and SharedNodeSignal aren't supported. The generator produces a plain method for them.

Test summary

• npm run check-redirects passes.
• mvn spotless:apply and mvn compile pass. npx eslint frontend/demo/fusion/signals passes.
• The example service and view type-check in the scratch 25.4.0-alpha5 application. Two tabs share the topic, the votes, and the agenda items: adding, checking and removing items all sync.
• Checked with the browser and the generated client:
  • the generated types and default values;
  • write before read;
  • access denied on connecting and on changing;
  • result and error of a failed change;
  • a server-side change, which the connected browsers don't get and a new connection does (Full-stack signal subscription emits null after server-side SharedNumberSignal.set hilla#5722);
  • assigning the value of a list signal.
• withValidator(), chained validators, child signals, transactions and asReadonly() checked with a small program against the 25.4.0-alpha5 classpath.
• Every cross reference in the new and changed lines resolves.
• Vale: no errors or warnings on the added and changed lines with the pull request configuration.
• Asciidoctor renders the new and changed pages, with all includes and tags resolved.
• I didn't run a full dspublisher build locally.

Behaviors that came up during testing, which the page describes as they are:

• Changes that server-side code makes to a shared signal don't reach the connected browsers, only new connections (Full-stack signal subscription emits null after server-side SharedNumberSignal.set hilla#5722).
• When a change fails, its result promise doesn't settle; the signal's error holds the error. Related to [Full-Stack Signals] command rejection is ignored hilla#3967.

🤖 Generated with Claude Code

[vaadin-review-bot]

Reviewed the changes — left 3 comments.

	Finding
⚠️	The default-value statement and the examples only hold when the service package is @NullMarked, and the page never says so.
💬	Access Control doesn't say that validators on the returned signal don't apply to changes from the browser.
⚠️	When a change to a list item fails, the error goes to the list signal, not to the item signal the page tells readers to change.

[github-actions]

Preview Deployment

This PR has been deployed for preview.

URL: https://docs-preview-pr-6624.fly.dev

Changed pages

Added content is highlighted in green; removed content is marked in red on each page.

• flow/configuration/feature-flags — modified, +3/-6 lines, 1 removal marker(s)
• flow/react-views/browser-callable-services/type-conversion — modified, +1/-1 lines, 1 removal marker(s)
• flow/ui-state — modified, +2/-0 lines
• flow/ui-state/full-stack-signals — added, +159/-0 lines
• flow/ui-state/shared-signals — modified, +24/-0 lines

Other changed files

• articles/hilla/guides/full-stack-signals.adoc (deleted)
• frontend/demo/services/react-signals.ts (added)
• src/main/java/com/vaadin/demo/fusion/signals/package-info.java (added)

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