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

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

@@ -40,8 +40,11 @@ import org.springframework.lang.Nullable;
 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 @@ import org.springframework.web.servlet.ModelAndView;
  */
 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 @@ final class DefaultAsyncServerResponse extends ErrorHandlingServerResponse imple
 		WebAsyncManager asyncManager = WebAsyncUtils.getAsyncManager(request);
 		AsyncWebRequest asyncWebRequest = WebAsyncUtils.createAsyncWebRequest(request, response);
 		asyncManager.setAsyncWebRequest(asyncWebRequest);
+		asyncManager.registerDeferredResultInterceptors(CLEAR_PATTERN_ATTRIBUTE_INTERCEPTOR);
 		try {
 			asyncManager.startDeferredResultProcessing(deferredResult);
 		}