warning on undefined controller or action

src/core/application.ts

@@ -15,6 +15,7 @@ export class Application implements ErrorHandler {
   readonly actionDescriptorFilters: ActionDescriptorFilters
   logger: Logger = console
   debug = false
+  warnings = true
 
   static start(element?: Element, schema?: Schema): Application {
     const application = new this(element, schema)
@@ -90,6 +91,12 @@ export class Application implements ErrorHandler {
     window.onerror?.(message, "", 0, 0, error)
   }
 
+  handleWarning(warning: string, message: string, detail: object) {
+    if (this.warnings) {
+      this.logger.warn(`%s\n\n%s\n\n%o`, message, warning, detail)
+    }
+  }
+
   // Debug logging
 
   logDebugActivity = (identifier: string, functionName: string, detail: object = {}): void => {

src/core/binding_observer.ts

@@ -92,4 +92,13 @@ export class BindingObserver implements ValueListObserverDelegate<Action> {
   elementUnmatchedValue(element: Element, action: Action) {
     this.disconnectAction(action)
   }
+
+  elementMatchedNoValue(element: Element, token: Token) {
+    const { content } = token
+    this.context.handleWarning(
+      `Element references an undefined action "${content}"`,
+      `Warning connecting action ${content}`,
+      { element, action: content }
+    )
+  }
 }

src/core/context.ts

@@ -101,6 +101,12 @@ export class Context implements ErrorHandler, TargetObserverDelegate, OutletObse
     this.application.handleError(error, `Error ${message}`, detail)
   }
 
+  handleWarning(warning: string, message: string, detail: object = {}) {
+    const { identifier, controller, element } = this
+    detail = Object.assign({ identifier, controller, element }, detail)
+    this.application.handleWarning(warning, `Warning ${message}`, detail)
+  }
+
   // Debug logging
 
   logDebugActivity = (functionName: string, detail: object = {}): void => {

src/core/router.ts

@@ -88,10 +88,17 @@ export class Router implements ScopeObserverDelegate {
   }
 
   scopeConnected(scope: Scope) {
-    this.scopesByIdentifier.add(scope.identifier, scope)
-    const module = this.modulesByIdentifier.get(scope.identifier)
+    const { element, identifier } = scope
+    this.scopesByIdentifier.add(identifier, scope)
+    const module = this.modulesByIdentifier.get(identifier)
     if (module) {
       module.connectContextForScope(scope)
+    } else {
+      this.application.handleWarning(
+        `Element references undefined controller ${identifier}`,
+        `Warning connecting controller ${identifier}`,
+        { identifier, element }
+      )
     }
   }
 

src/core/scope_observer.ts

@@ -61,6 +61,8 @@ export class ScopeObserver implements ValueListObserverDelegate<Scope> {
     }
   }
 
+  elementMatchedNoValue(element: Element, token: Token) {}
+
   elementUnmatchedValue(element: Element, value: Scope) {
     const referenceCount = this.scopeReferenceCounts.get(value)
     if (referenceCount) {

src/mutation-observers/value_list_observer.ts

@@ -3,6 +3,7 @@ import { Token, TokenListObserver, TokenListObserverDelegate } from "./token_lis
 export interface ValueListObserverDelegate<T> {
   parseValueForToken(token: Token): T | undefined
   elementMatchedValue(element: Element, value: T): void
+  elementMatchedNoValue(element: Element, token: Token): void
   elementUnmatchedValue(element: Element, value: T): void
 }
 
@@ -50,10 +51,12 @@ export class ValueListObserver<T> implements TokenListObserverDelegate {
 
   tokenMatched(token: Token) {
     const { element } = token
-    const { value } = this.fetchParseResultForToken(token)
+    const { error, value } = this.fetchParseResultForToken(token)
     if (value) {
       this.fetchValuesByTokenForElement(element).set(token, value)
       this.delegate.elementMatchedValue(element, value)
+    } else if (error) {
+      this.delegate.elementMatchedNoValue(element, token)
     }
   }
 

src/tests/modules/mutation-observers/value_list_observer_tests.ts

@@ -100,4 +100,8 @@ export default class ValueListObserverTests extends ObserverTestCase implements
   elementUnmatchedValue(element: Element, value: Value) {
     this.recordCall("elementUnmatchedValue", element, value.id, value.token.content)
   }
+
+  elementMatchedNoValue(element: Element, token: Token) {
+    this.recordCall("elementMatchedNoValue", element, token)
+  }
 }