Add primitive type support to Nullness

See gh-34261

framework-docs/modules/ROOT/pages/core/null-safety.adoc

@@ -13,8 +13,9 @@ annotations such as IntelliJ IDEA or Eclipse) and Kotlin where JSpecify annotati
 {kotlin-docs}/null-safety.html[Kotlin's null safety].
 
 The {spring-framework-api}/core/Nullness.html[`Nullness` Spring API] can be used at runtime to detect the nullness of a
-type usage, a field, a method return type or a parameter. It provides full support for JSpecify annotations and
+type usage, a field, a method return type or a parameter. It provides full support for JSpecify annotations,
-Kotlin null safety, as well as a pragmatic check on any `@Nullable` annotation (regardless of the package).
+Kotlin null safety, Java primitive types, as well as a pragmatic check on any `@Nullable` annotation (regardless of the
+package).
 
 [[null-safety-libraries]]
 == Annotating libraries with JSpecify annotations

spring-core/src/main/java/org/springframework/core/Nullness.java

@@ -41,8 +41,9 @@ import org.jspecify.annotations.Nullable;
  *
  * <p>The nullness applies to a type usage, a field, a method return type or a parameter.
  * <a href="https://jspecify.dev/docs/user-guide/">JSpecify annotations</a> are fully supported, as well as
- * <a href="https://kotlinlang.org/docs/null-safety.html">Kotlin null safety</a> and {@code @Nullable} annotations
+ * <a href="https://kotlinlang.org/docs/null-safety.html">Kotlin null safety</a>, {@code @Nullable} annotations
- * regardless of their package (from Spring, JSR-305 or Jakarta set of annotations for example).
+ * regardless of their package (from Spring, JSR-305 or Jakarta set of annotations for example) and Java primitive
+ * types.
  *
  * @author Sebastien Deleuze
  * @since 7.0
@@ -50,7 +51,7 @@ import org.jspecify.annotations.Nullable;
 public enum Nullness {
 
 	/**
-	 * Unspecified nullness (Java and JSpecify {@code @NullUnmarked} defaults).
+	 * Unspecified nullness (Java default for non-primitive types and JSpecify {@code @NullUnmarked} code).
 	 */
 	UNSPECIFIED,
 
@@ -60,7 +61,7 @@ public enum Nullness {
 	NULLABLE,
 
 	/**
-	 * Will not include null (Kotlin and JSpecify {@code @NullMarked} defaults).
+	 * Will not include null (Kotlin default and JSpecify {@code @NullMarked} code).
 	 */
 	NON_NULL;
 
@@ -130,6 +131,9 @@ public enum Nullness {
 	}
 
 	private static Nullness jSpecifyNullness(AnnotatedElement annotatedElement, Class<?> declaringClass, AnnotatedType annotatedType) {
+		if (annotatedType.getType() instanceof Class<?> clazz && clazz.isPrimitive()) {
+			return (clazz != void.class ? Nullness.NON_NULL : Nullness.UNSPECIFIED);
+		}
 		if (annotatedType.isAnnotationPresent(Nullable.class)) {
 			return Nullness.NULLABLE;
 		}

spring-core/src/test/java/org/springframework/core/NullnessTests.java

@@ -377,4 +377,20 @@ public class NullnessTests {
 		Assertions.assertThat(nullness).isEqualTo(Nullness.NULLABLE);
 	}
 
+	// Primitive types
+
+	@Test
+	void primitiveField() throws NoSuchFieldException {
+		var field = NullnessFields.class.getDeclaredField("primitiveField");
+		var nullness = Nullness.forField(field);
+		Assertions.assertThat(nullness).isEqualTo(Nullness.NON_NULL);
+	}
+
+	@Test
+	void voidMethod() throws NoSuchMethodException {
+		var method = JSpecifyProcessor.class.getMethod("voidProcess");
+		var nullness = Nullness.forMethodReturnType(method);
+		Assertions.assertThat(nullness).isEqualTo(Nullness.UNSPECIFIED);
+	}
+
 }

spring-core/src/testFixtures/java/org/springframework/core/testfixture/nullness/JSpecifyProcessor.java

@@ -36,4 +36,6 @@ public interface JSpecifyProcessor {
 
 	@NullMarked
 	@NonNull String nonNullMarkedProcess();
+
+	void voidProcess();
 }

spring-core/src/testFixtures/java/org/springframework/core/testfixture/nullness/NullnessFields.java

@@ -26,4 +26,6 @@ public class NullnessFields {
 
 	@org.springframework.core.testfixture.nullness.custom.Nullable
 	public String customNullableField;
+
+	public int primitiveField = 0;
 }