Handle ResponseStatusException thrown by MVC functional endpoints

Prior to this commit, exceptions thrown by MVC functional handlers would
not be considered by `ExceptionHandlerExceptionResolver`. This means
that common exceptions would not be handled consistently between
annotated and functional handlers. This is true, for example, for all
`ProblemDetails`-related exception handling.

While MVC functional and annotation models are separate concepts,
WebFlux has a different error handling model that processes all
exceptions in a central place.

This commit ensures that `ExceptionHandlerExceptionResolver` considers
exceptions thrown by handlers of type `HandlerFunction<?>` and processes
them accordingly.

Closes gh-32689

spring-webmvc/src/main/java/org/springframework/web/servlet/handler/AbstractHandlerMethodExceptionResolver.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2023 the original author or authors.
+ * Copyright 2002-2024 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -22,6 +22,7 @@ import jakarta.servlet.http.HttpServletResponse;
 import org.springframework.lang.Nullable;
 import org.springframework.web.method.HandlerMethod;
 import org.springframework.web.servlet.ModelAndView;
+import org.springframework.web.servlet.function.HandlerFunction;
 
 /**
  * Abstract base class for
@@ -34,9 +35,9 @@ import org.springframework.web.servlet.ModelAndView;
 public abstract class AbstractHandlerMethodExceptionResolver extends AbstractHandlerExceptionResolver {
 
 	/**
-	 * Checks if the handler is a {@link HandlerMethod} and then delegates to the
+	 * Checks if the handler is a {@link HandlerMethod} or a {@link HandlerFunction}
-	 * base class implementation of {@code #shouldApplyTo(HttpServletRequest, Object)}
+	 * and then delegates to the base class implementation of {@code #shouldApplyTo(HttpServletRequest, Object)}
-	 * passing the bean of the {@code HandlerMethod}. Otherwise returns {@code false}.
+	 * passing the bean of the {@code HandlerMethod}. Otherwise, returns {@code false}.
 	 */
 	@Override
 	protected boolean shouldApplyTo(HttpServletRequest request, @Nullable Object handler) {
@@ -47,6 +48,9 @@ public abstract class AbstractHandlerMethodExceptionResolver extends AbstractHan
 			handler = handlerMethod.getBean();
 			return super.shouldApplyTo(request, handler);
 		}
+		else if (handler instanceof HandlerFunction<?> handlerFunction) {
+			return super.shouldApplyTo(request, handlerFunction);
+		}
 		else if (hasGlobalExceptionHandlers() && hasHandlerMappings()) {
 			return super.shouldApplyTo(request, handler);
 		}

spring-webmvc/src/test/java/org/springframework/web/servlet/mvc/method/annotation/ExceptionHandlerExceptionResolverTests.java

@@ -60,6 +60,8 @@ import org.springframework.web.method.support.HandlerMethodReturnValueHandler;
 import org.springframework.web.servlet.DispatcherServlet;
 import org.springframework.web.servlet.FlashMap;
 import org.springframework.web.servlet.ModelAndView;
+import org.springframework.web.servlet.function.HandlerFunction;
+import org.springframework.web.servlet.function.ServerResponse;
 import org.springframework.web.servlet.mvc.support.RedirectAttributes;
 import org.springframework.web.servlet.resource.ResourceHttpRequestHandler;
 import org.springframework.web.testfixture.servlet.MockHttpServletRequest;
@@ -82,6 +84,8 @@ import static org.mockito.Mockito.mock;
 @SuppressWarnings("unused")
 class ExceptionHandlerExceptionResolverTests {
 
+	//TODO
+
 	private static int DEFAULT_RESOLVER_COUNT;
 
 	private static int DEFAULT_HANDLER_COUNT;
@@ -255,6 +259,19 @@ class ExceptionHandlerExceptionResolverTests {
 		assertExceptionHandledAsBody(mav, "AnotherTestExceptionResolver: IllegalAccessException");
 	}
 
+	@Test
+	void resolveExceptionGlobalHandlerForHandlerFunction() throws Exception {
+		loadConfiguration(MyConfig.class);
+
+		IllegalAccessException ex = new IllegalAccessException();
+		HandlerFunction<ServerResponse> handlerFunction = req -> {
+			throw new IllegalAccessException();
+		};
+		ModelAndView mav = this.resolver.resolveException(this.request, this.response, handlerFunction, ex);
+
+		assertExceptionHandledAsBody(mav, "AnotherTestExceptionResolver: IllegalAccessException");
+	}
+
 	@Test
 	void resolveExceptionGlobalHandlerOrdered() throws Exception {
 		loadConfiguration(MyConfig.class);