Replace the GWT client engine with a TypeScript implementation

[totally-not-ai]

What

Removes the GWT-based Flow client engine and replaces it with a TypeScript port that ships as part of the frontend bundle.

• New engine — 79 modules under flow-client/src/main/frontend/internal/, a module-for-module port of the Java client: bootstrap (Bootstrapper, ApplicationConfiguration, ApplicationConnection), the reactive core and node features (StateNode, StateTree, NodeMap, NodeList, MapProperty, TreeChangeProcessor), the binding layer (Binder, SimpleElementBindingStrategy, TextBindingStrategy, Debouncer, ServerEventObject), networking (MessageSender, MessageHandler, XhrConnection, AtmospherePushConnection, Heartbeat, Poller, reconnect/loading-indicator state handling), and the support services (DependencyLoader, ResourceLoader, Profiler, PolymerUtils, LitUtils, ReactUtils, WidgetUtil, URIResolver, …).
• Removed — all 105 Java classes of com.vaadin.client.**, the GWT linker com.vaadin.flow.linker.ClientEngineLinker, the *.gwt.xml modules and the single-script template, the src/test-gwt HtmlUnit suite, and the corresponding Java unit tests. flow-client/pom.xml drops the gwt-maven-plugin, the gwt-user/gwt-dev/gwt-elemental dependencies, the sdm profile, and the GWT-specific surefire/spotless/build-helper configuration. BootstrapHandler no longer resolves and injects a client.nocache.js / compiled client-engine <script> tag.
• Build — scripts/client.js no longer inlines the compiled GWT bundle into FlowClient.js; it emits a small entry point that calls onModuleLoad() from the TypeScript bootstrap.
• Tests — 85 web-test-runner suites under src/test/frontend/ covering the ported modules, replacing the deleted Java/GWT tests.

Why

The GWT toolchain was the last piece of the client that could not be built, linted, debugged, or tested with the same tooling as the rest of the frontend. Porting it removes a separate compiler and dependency stack, drops the extra client-engine script request from bootstrap, and makes the client engine ordinary TypeScript that ships through the existing bundler.

Behavior fixes made during the port

• Native DOM throughout — the DomApi abstraction and the Polymer/HTML-import DOM path are gone; the binding layer, ApplicationConnection, and dependency loading use native DOM directly, and the HTML-imports-ready bootstrap gate is removed (chore: remove Polymer 1 DOM API and HTML import loading #25145, refactor: use the elemental DOM API directly in the client engine #25146).
• Container refills no longer flash empty — when the server clears and refills a container in one change set, old children are kept until the replacements are inserted, preserving scroll position (mirrors GWT fix fix: keep replaced children until the new ones are in place #25147).
• client.getNodeInfo(nodeId).javaClass works again — the engine read node property "class" instead of the "jc" the server writes. JAVA_CLASS now lives in the NodeProperties table with the other wire names mirrored from com.vaadin.flow.internal.nodefeature.NodeProperties; the test fixture that hardcoded the wrong key now uses real wire names.
• Production-mode log gating restored — the port had dropped Console.setProductionMode, so all 64 log statements across 21 engine modules logged unconditionally (including the raw session-resynchronization response body). Logging is routed through the ported Console again, and an eslint no-console rule over src/main/frontend/internal keeps it that way; two deliberately ungated sites are marked.
• Synchronous startup — the bootstrap imports the engine statically instead of via a dynamic import(), matching the old Java bootstrap and removing an always-fetched 105 kB chunk from the startup critical path.

API Changes

API Changes: flow-server-remove-client-engine vs origin/main

105 public classes/interfaces removed (all of com.vaadin.client.** plus com.vaadin.flow.linker.ClientEngineLinker); no additions and no signature changes. All public/protected members of these types are removed with them. The only other Java edits (BootstrapHandler, ClassesSerializableTest) touch private members and test configuration only.

com.vaadin.client

// Removed
public class ApplicationConfiguration
public class ApplicationConnection
public class BrowserInfo
public interface Command
public class ConnectionIndicator
public final class Console
public class DefaultRegistry extends Registry
public class DependencyLoader
public class ElementUtil
public final class ExecuteJavaScriptElementUtils
public class ExistingElementMap
public class InitialPropertiesHandler
public final class LitUtils
public final class PolymerUtils
public class Profiler
public final class ReactUtils
public class Registry
public class ResourceLoader
public class StorageUtil
public class SystemErrorHandler
public class TrackingScheduler extends SchedulerImpl
public class UILifecycle
public class URIResolver extends VaadinUriResolver
public final class ValueMap extends JavaScriptObject
public class WidgetUtil

com.vaadin.client.bootstrap

// Removed
public class Bootstrapper implements EntryPoint
public final class ErrorMessage extends JavaScriptObject
public final class JsoConfiguration extends JavaScriptObject
public class LocationParser

com.vaadin.client.communication

// Removed
public class AtmospherePushConnection implements PushConnection
public interface ConnectionStateHandler
public class DefaultConnectionStateHandler implements ConnectionStateHandler
public class Heartbeat
public class LoadingIndicatorConfigurator
public class LoadingIndicatorStateHandler
public class MessageHandler
public class MessageSender
public class PollConfigurator
public class Poller
public class PushConfiguration
public interface PushConnection
public interface PushConnectionFactory
public class ReconnectConfiguration
public class ReconnectionAttemptEvent
public class RequestResponseTracker
public class RequestStartingEvent extends Event<RequestStartingEvent.Handler>
public class ResponseHandlingEndedEvent
public class ResponseHandlingStartedEvent
public class ServerConnector
public class ServerRpcQueue
public class XhrConnection
public class XhrConnectionError

com.vaadin.client.flow

// Removed
public class ConstantPool
public class ExecuteJavaScriptProcessor
public class NodeUnregisterEvent
public interface NodeUnregisterListener
public class StateNode
public class StateTree
public class TreeChangeProcessor

com.vaadin.client.flow.binding

// Removed
public final class Binder
public interface BinderContext
public interface BindingStrategy<T extends Node>
public class Debouncer
public class ServerEventHandlerBinder
public final class ServerEventObject extends JavaScriptObject
public class SimpleElementBindingStrategy implements BindingStrategy<Element>
public class TextBindingStrategy implements BindingStrategy<Text>

com.vaadin.client.flow.collection

// Removed
public class JsArray<T>
public class JsCollections
public class JsMap<K, V>
public class JsSet<V>
public interface JsWeakMap<K, V>
public class JreJsArray<T> extends JsArray<T>       // com.vaadin.client.flow.collection.jre
public class JreJsMap<K, V> extends JsMap<K, V>     // com.vaadin.client.flow.collection.jre
public class JreJsSet<V> extends JsSet<V>           // com.vaadin.client.flow.collection.jre
public class JreJsWeakMap<K, V> implements JsWeakMap<K, V> // com.vaadin.client.flow.collection.jre

com.vaadin.client.flow.dom

// Removed
public class DomApi
public interface DomElement extends DomNode
public interface DomNode

com.vaadin.client.flow.model

// Removed
public class UpdatableModelProperties

com.vaadin.client.flow.nodefeature

// Removed
public class ListSpliceEvent extends ReactiveValueChangeEvent
public interface ListSpliceListener
public class MapProperty implements ReactiveValue
public class MapPropertyAddEvent extends ReactiveValueChangeEvent
public interface MapPropertyAddListener
public class MapPropertyChangeEvent extends ReactiveValueChangeEvent
public interface MapPropertyChangeListener
public abstract class NodeFeature
public class NodeList extends NodeFeature implements ReactiveValue
public class NodeMap extends NodeFeature implements ReactiveValue

com.vaadin.client.flow.reactive

// Removed
public abstract class Computation implements ReactiveValueChangeListener
public interface FlushListener
public class InvalidateEvent
public interface InvalidateListener
public class Reactive
public abstract class ReactiveEventRouter<L, E extends ReactiveValueChangeEvent>
public interface ReactiveValue
public abstract class ReactiveValueChangeEvent
public interface ReactiveValueChangeListener

com.vaadin.client.flow.util

// Removed
public class ClientJsonCodec
public class JsObject
public class NativeFunction

com.vaadin.client.gwt

// Removed
public class SimpleEventBus extends EventBus  // com.vaadin.client.gwt.com.google.web.bindery.event.shared
public class Xhr                              // com.vaadin.client.gwt.elemental.js.util

com.vaadin.flow.linker.ClientEngineLinker

// Removed
public class ClientEngineLinker extends SingleScriptLinker

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud

[github-actions]

Test Results

 1 424 files   -  26   1 509 suites  +58   1h 27m 59s ⏱️ +42s
10 578 tests +169  10 511 ✅ +169  67 💤 ±0  0 ❌ ±0 
11 014 runs  +169  10 946 ✅ +169  68 💤 ±0  0 ❌ ±0 

Results for commit 3c839b9. ± Comparison against base commit d306eb5.

[Artur-]

Commits distributed into the PRs that introduced the code they fix.