Introduce Parameter.getRequiredName() method.

Add getRequiredName to shortcut parameter name discovery and fast-fail in cases where the parameter name is required.

Closes #3124

src/main/java/org/springframework/data/repository/query/Parameter.java

@@ -24,6 +24,7 @@
 import java.util.Optional;
 
 import org.springframework.core.MethodParameter;
+import org.springframework.core.ParameterNameDiscoverer;
 import org.springframework.core.ResolvableType;
 import org.springframework.data.domain.Limit;
 import org.springframework.data.domain.Pageable;
@@ -59,7 +60,8 @@ public class Parameter {
 
 	static {
 
-		List<Class<?>> types = new ArrayList<>(Arrays.asList(ScrollPosition.class, Pageable.class, Sort.class, Limit.class));
+		List<Class<?>> types = new ArrayList<>(
+				Arrays.asList(ScrollPosition.class, Pageable.class, Sort.class, Limit.class));
 
 		// consider Kotlin Coroutines Continuation a special parameter. That parameter is synthetic and should not get
 		// bound to any query.
@@ -153,23 +155,39 @@ public int getIndex() {
 	}
 
 	/**
-	 * Returns whether the parameter is annotated with {@link Param}.
+	 * Returns whether the parameter is annotated with {@link Param} or has a method parameter name.
 	 *
 	 * @return
+	 * @see Param
+	 * @see ParameterNameDiscoverer
 	 */
 	public boolean isNamedParameter() {
 		return !isSpecialParameter() && getName().isPresent();
 	}
 
 	/**
-	 * Returns the name of the parameter (through {@link Param} annotation).
+	 * Returns the name of the parameter (through {@link Param} annotation or method parameter naming).
 	 *
-	 * @return
+	 * @return the optional name of the parameter.
 	 */
 	public Optional<String> getName() {
 		return this.name.get();
 	}
 
+	/**
+	 * Returns the required name of the parameter (through {@link Param} annotation or method parameter naming) or throws
+	 * {@link IllegalStateException} if the parameter has no name.
+	 *
+	 * @return the required parameter name.
+	 * @throws IllegalStateException if the parameter has no name.
+	 * @since 3.4
+	 */
+	public String getRequiredName() {
+
+		return getName().orElseThrow(() -> new IllegalStateException("Parameter " + parameter
+				+ " is not named. For queries with named parameters you need to provide names for method parameters; Use @Param for query method parameters, or use the javac flag -parameters."));
+	}
+
 	/**
 	 * Returns the type of the {@link Parameter}.
 	 *

src/test/java/org/springframework/data/repository/query/ParametersUnitTests.java

@@ -128,12 +128,13 @@ void doesNotRejectParameterIfPageableComesFirst() throws Exception {
 		getParametersFor("validWithPageableFirst", Pageable.class, String.class);
 	}
 
-	@Test // DATACMNS-731
+	@Test // DATACMNS-731, GH-3124
 	void detectsExplicitlyNamedParameter() throws Exception {
 
 		var parameter = getParametersFor("valid", String.class).getBindableParameter(0);
 
-		assertThat(parameter.getName()).isNotNull();
+		assertThat(parameter.getName()).isNotEmpty();
+		assertThat(parameter.getRequiredName()).isNotNull();
 		assertThat(parameter.isExplicitlyNamed()).isTrue();
 	}
 
@@ -145,7 +146,7 @@ void doesNotConsiderParameterExplicitlyNamedEvenIfNamePresent() throws Exception
 		var methodParameter = ReflectionTestUtils.getField(parameter, "parameter");
 		ReflectionTestUtils.setField(methodParameter, "parameterName", "name");
 
-		assertThat(parameter.getName()).isNotNull();
+		assertThat(parameter.getName()).isNotEmpty();
 		assertThat(parameter.isExplicitlyNamed()).isFalse();
 	}