Clear path pattern after async result

This commit makes sure that the matching pattern attributes is cleared
when an async result has been obtained, so that the subsequent
dispatch starts from scratch.

Closes gh-26239

Author: poutsma

spring-webmvc/src/main/java/org/springframework/web/servlet/function/DefaultAsyncServerResponse.java

@@ -40,8 +40,11 @@
 import org.springframework.util.Assert;
 import org.springframework.util.ClassUtils;
 import org.springframework.util.MultiValueMap;
+import org.springframework.web.context.request.NativeWebRequest;
+import org.springframework.web.context.request.RequestAttributes;
 import org.springframework.web.context.request.async.AsyncWebRequest;
 import org.springframework.web.context.request.async.DeferredResult;
+import org.springframework.web.context.request.async.DeferredResultProcessingInterceptor;
 import org.springframework.web.context.request.async.WebAsyncManager;
 import org.springframework.web.context.request.async.WebAsyncUtils;
 import org.springframework.web.servlet.ModelAndView;
@@ -54,6 +57,16 @@
  */
 final class DefaultAsyncServerResponse extends ErrorHandlingServerResponse implements AsyncServerResponse {
 
+	private static final DeferredResultProcessingInterceptor CLEAR_PATTERN_ATTRIBUTE_INTERCEPTOR =
+			new DeferredResultProcessingInterceptor() {
+				@Override
+				public <T> void postProcess(NativeWebRequest request, DeferredResult<T> deferredResult,
+						Object concurrentResult) {
+					request.removeAttribute(RouterFunctions.MATCHING_PATTERN_ATTRIBUTE,
+							RequestAttributes.SCOPE_REQUEST);
+				}
+			};
+
 	static final boolean reactiveStreamsPresent = ClassUtils.isPresent(
 			"org.reactivestreams.Publisher", DefaultAsyncServerResponse.class.getClassLoader());
 
@@ -128,6 +141,7 @@ static void writeAsync(HttpServletRequest request, HttpServletResponse response,
 		WebAsyncManager asyncManager = WebAsyncUtils.getAsyncManager(request);
 		AsyncWebRequest asyncWebRequest = WebAsyncUtils.createAsyncWebRequest(request, response);
 		asyncManager.setAsyncWebRequest(asyncWebRequest);
+		asyncManager.registerDeferredResultInterceptors(CLEAR_PATTERN_ATTRIBUTE_INTERCEPTOR);
 		try {
 			asyncManager.startDeferredResultProcessing(deferredResult);
 		}