Empty path mapping behaves consistently

An empty path mapping in an @RequestMapping now consistently matches to
empty paths regardless of whether there are both type and method level,
annotations, or method-level only.

Closes gh-22543

spring-webflux/src/main/java/org/springframework/web/reactive/result/condition/PatternsRequestCondition.java

@@ -16,9 +16,9 @@
 
 package org.springframework.web.reactive.result.condition;
 
-import java.util.ArrayList;
 import java.util.Arrays;
 import java.util.Collection;
+import java.util.Collections;
 import java.util.Iterator;
 import java.util.List;
 import java.util.Set;
@@ -29,6 +29,7 @@ import org.springframework.http.server.PathContainer;
 import org.springframework.lang.Nullable;
 import org.springframework.web.server.ServerWebExchange;
 import org.springframework.web.util.pattern.PathPattern;
+import org.springframework.web.util.pattern.PathPatternParser;
 
 /**
  * A logical disjunction (' || ') request condition that matches a request
@@ -40,6 +41,10 @@ import org.springframework.web.util.pattern.PathPattern;
  */
 public final class PatternsRequestCondition extends AbstractRequestCondition<PatternsRequestCondition> {
 
+	private static final SortedSet<PathPattern> EMPTY_PATTERNS =
+			new TreeSet<>(Collections.singleton(new PathPatternParser().parse("")));
+
+
 	private final SortedSet<PathPattern> patterns;
 
 
@@ -55,7 +60,7 @@ public final class PatternsRequestCondition extends AbstractRequestCondition<Pat
 	 * Creates a new instance with the given URL patterns.
 	 */
 	public PatternsRequestCondition(List<PathPattern> patterns) {
-		this(new TreeSet<>(patterns));
+		this(patterns.isEmpty() ? EMPTY_PATTERNS : new TreeSet<>(patterns));
 	}
 
 
@@ -89,8 +94,9 @@ public final class PatternsRequestCondition extends AbstractRequestCondition<Pat
 	 */
 	@Override
 	public PatternsRequestCondition combine(PatternsRequestCondition other) {
-		List<PathPattern> combined = new ArrayList<>();
+		SortedSet<PathPattern> combined;
 		if (!this.patterns.isEmpty() && !other.patterns.isEmpty()) {
+			combined = new TreeSet<>();
 			for (PathPattern pattern1 : this.patterns) {
 				for (PathPattern pattern2 : other.patterns) {
 					combined.add(pattern1.combine(pattern2));
@@ -98,10 +104,13 @@ public final class PatternsRequestCondition extends AbstractRequestCondition<Pat
 			}
 		}
 		else if (!this.patterns.isEmpty()) {
-			combined.addAll(this.patterns);
+			combined = this.patterns;
 		}
 		else if (!other.patterns.isEmpty()) {
-			combined.addAll(other.patterns);
+			combined = other.patterns;
+		}
+		else {
+			combined = EMPTY_PATTERNS;
 		}
 		return new PatternsRequestCondition(combined);
 	}

spring-webflux/src/test/java/org/springframework/web/reactive/result/condition/PatternsRequestConditionTests.java

@@ -140,6 +140,19 @@ public class PatternsRequestConditionTests {
 		assertNull(match);
 	}
 
+	@Test // gh-22543
+	public void matchWithEmptyPatterns() {
+		PatternsRequestCondition condition = new PatternsRequestCondition();
+		assertEquals(new PatternsRequestCondition(this.parser.parse("")), condition);
+		assertNotNull(condition.getMatchingCondition(MockServerWebExchange.from(get(""))));
+		assertNull(condition.getMatchingCondition(MockServerWebExchange.from(get("/anything"))));
+
+		condition = condition.combine(new PatternsRequestCondition());
+		assertEquals(new PatternsRequestCondition(this.parser.parse("")), condition);
+		assertNotNull(condition.getMatchingCondition(MockServerWebExchange.from(get(""))));
+		assertNull(condition.getMatchingCondition(MockServerWebExchange.from(get("/anything"))));
+	}
+
 	@Test
 	public void compareToConsistentWithEquals() throws Exception {
 		PatternsRequestCondition c1 = createPatternsCondition("/foo*");

spring-webflux/src/test/java/org/springframework/web/reactive/result/condition/RequestMappingInfoTests.java

@@ -34,6 +34,7 @@ import org.springframework.web.bind.annotation.RequestMethod;
 import org.springframework.web.reactive.result.method.RequestMappingInfo;
 import org.springframework.web.server.ServerWebExchange;
 import org.springframework.web.util.pattern.PathPattern;
+import org.springframework.web.util.pattern.PathPatternParser;
 import org.springframework.web.util.pattern.PatternParseException;
 
 import static java.util.Arrays.asList;
@@ -61,7 +62,8 @@ public class RequestMappingInfoTests {
 	public void createEmpty() {
 		RequestMappingInfo info = paths().build();
 
-		assertEquals(0, info.getPatternsCondition().getPatterns().size());
+		PathPattern emptyPattern = (new PathPatternParser()).parse("");
+		assertEquals(Collections.singleton(emptyPattern), info.getPatternsCondition().getPatterns());
 		assertEquals(0, info.getMethodsCondition().getMethods().size());
 		assertEquals(true, info.getConsumesCondition().isEmpty());
 		assertEquals(true, info.getProducesCondition().isEmpty());

spring-webflux/src/test/java/org/springframework/web/reactive/result/method/RequestMappingInfoHandlerMappingTests.java

@@ -253,14 +253,12 @@ public class RequestMappingInfoHandlerMappingTests {
 		assertSame(handlerMethod, mapped);
 	}
 
-	@Test
+	@Test // gh-22543
 	public void handleMatchBestMatchingPatternAttributeNoPatternsDefined() {
-		RequestMappingInfo key = paths().build();
-		ServerWebExchange exchange = MockServerWebExchange.from(get("/1/2"));
-		this.handlerMapping.handleMatch(key, handlerMethod, exchange);
-
-		PathPattern bestMatch = (PathPattern) exchange.getAttributes().get(BEST_MATCHING_PATTERN_ATTRIBUTE);
-		assertEquals("/1/2", bestMatch.getPatternString());
+		ServerWebExchange exchange = MockServerWebExchange.from(get(""));
+		this.handlerMapping.handleMatch(paths().build(), handlerMethod, exchange);
+		PathPattern pattern = (PathPattern) exchange.getAttributes().get(BEST_MATCHING_PATTERN_ATTRIBUTE);
+		assertEquals("", pattern.getPatternString());
 	}
 
 	@Test