Revise ResolvableType equality

ResolvableTypes are only considered equal if of the very same class now.
As a consequence, a forRawClass result is not equal to forClass anymore.
The new equalsType method is available for plain type equality checks.

Closes gh-28608
Closes gh-27748

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

@@ -101,22 +101,22 @@ public class ResolvableType implements Serializable {
 	private final Type type;
 
 	/**
-	 * Optional provider for the type.
+	 * The component type for an array or {@code null} if the type should be deduced.
 	 */
 	@Nullable
-	private final TypeProvider typeProvider;
+	private final ResolvableType componentType;
 
 	/**
-	 * The {@code VariableResolver} to use or {@code null} if no resolver is available.
+	 * Optional provider for the type.
 	 */
 	@Nullable
-	private final VariableResolver variableResolver;
+	private final TypeProvider typeProvider;
 
 	/**
-	 * The component type for an array or {@code null} if the type should be deduced.
+	 * The {@code VariableResolver} to use or {@code null} if no resolver is available.
 	 */
 	@Nullable
-	private final ResolvableType componentType;
+	private final VariableResolver variableResolver;
 
 	@Nullable
 	private final Integer hash;
@@ -138,22 +138,22 @@ public class ResolvableType implements Serializable {
 
 
 	/**
-	 * Private constructor used to create a new {@link ResolvableType} for cache key purposes,
+	 * Private constructor used to create a new {@code ResolvableType} for cache key purposes,
 	 * with no upfront resolution.
 	 */
 	private ResolvableType(
 			Type type, @Nullable TypeProvider typeProvider, @Nullable VariableResolver variableResolver) {
 
 		this.type = type;
+		this.componentType = null;
 		this.typeProvider = typeProvider;
 		this.variableResolver = variableResolver;
-		this.componentType = null;
 		this.hash = calculateHashCode();
 		this.resolved = null;
 	}
 
 	/**
-	 * Private constructor used to create a new {@link ResolvableType} for cache value purposes,
+	 * Private constructor used to create a new {@code ResolvableType} for cache value purposes,
 	 * with upfront resolution and a pre-calculated hash.
 	 * @since 4.2
 	 */
@@ -161,39 +161,39 @@ public class ResolvableType implements Serializable {
 			@Nullable VariableResolver variableResolver, @Nullable Integer hash) {
 
 		this.type = type;
+		this.componentType = null;
 		this.typeProvider = typeProvider;
 		this.variableResolver = variableResolver;
-		this.componentType = null;
 		this.hash = hash;
 		this.resolved = resolveClass();
 	}
 
 	/**
-	 * Private constructor used to create a new {@link ResolvableType} for uncached purposes,
+	 * Private constructor used to create a new {@code ResolvableType} for uncached purposes,
 	 * with upfront resolution but lazily calculated hash.
 	 */
-	private ResolvableType(Type type, @Nullable TypeProvider typeProvider,
-			@Nullable VariableResolver variableResolver, @Nullable ResolvableType componentType) {
+	private ResolvableType(Type type, @Nullable ResolvableType componentType,
+			@Nullable TypeProvider typeProvider, @Nullable VariableResolver variableResolver) {
 
 		this.type = type;
+		this.componentType = componentType;
 		this.typeProvider = typeProvider;
 		this.variableResolver = variableResolver;
-		this.componentType = componentType;
 		this.hash = null;
 		this.resolved = resolveClass();
 	}
 
 	/**
-	 * Private constructor used to create a new {@link ResolvableType} on a {@link Class} basis.
+	 * Private constructor used to create a new {@code ResolvableType} on a {@link Class} basis.
 	 * <p>Avoids all {@code instanceof} checks in order to create a straight {@link Class} wrapper.
 	 * @since 4.2
 	 */
 	private ResolvableType(@Nullable Class<?> clazz) {
 		this.resolved = (clazz != null ? clazz : Object.class);
 		this.type = this.resolved;
+		this.componentType = null;
 		this.typeProvider = null;
 		this.variableResolver = null;
-		this.componentType = null;
 		this.hash = null;
 	}
 
@@ -223,7 +223,7 @@ public class ResolvableType implements Serializable {
 
 	/**
 	 * Return the underlying source of the resolvable type. Will return a {@link Field},
-	 * {@link MethodParameter} or {@link Type} depending on how the {@link ResolvableType}
+	 * {@link MethodParameter} or {@link Type} depending on how the {@code ResolvableType}
 	 * was constructed. This method is primarily to provide access to additional type
 	 * information or meta-data that alternative JVM languages may provide.
 	 */
@@ -428,12 +428,12 @@ public class ResolvableType implements Serializable {
 	}
 
 	/**
-	 * Return this type as a {@link ResolvableType} of the specified class. Searches
+	 * Return this type as a {@code ResolvableType} of the specified class. Searches
 	 * {@link #getSuperType() supertype} and {@link #getInterfaces() interface}
 	 * hierarchies to find a match, returning {@link #NONE} if this type does not
 	 * implement or extend the specified class.
 	 * @param type the required type (typically narrowed)
-	 * @return a {@link ResolvableType} representing this object as the specified
+	 * @return a {@code ResolvableType} representing this object as the specified
 	 * type, or {@link #NONE} if not resolvable as that type
 	 * @see #asCollection()
 	 * @see #asMap()
@@ -458,9 +458,9 @@ public class ResolvableType implements Serializable {
 	}
 
 	/**
-	 * Return a {@link ResolvableType} representing the direct supertype of this type.
+	 * Return a {@code ResolvableType} representing the direct supertype of this type.
 	 * <p>If no supertype is available this method returns {@link #NONE}.
-	 * <p>Note: The resulting {@link ResolvableType} instance may not be {@link Serializable}.
+	 * <p>Note: The resulting {@code ResolvableType} instance may not be {@link Serializable}.
 	 * @see #getInterfaces()
 	 */
 	public ResolvableType getSuperType() {
@@ -487,10 +487,10 @@ public class ResolvableType implements Serializable {
 	}
 
 	/**
-	 * Return a {@link ResolvableType} array representing the direct interfaces
+	 * Return a {@code ResolvableType} array representing the direct interfaces
 	 * implemented by this type. If this type does not implement any interfaces an
 	 * empty array is returned.
-	 * <p>Note: The resulting {@link ResolvableType} instances may not be {@link Serializable}.
+	 * <p>Note: The resulting {@code ResolvableType} instances may not be {@link Serializable}.
 	 * @see #getSuperType()
 	 */
 	public ResolvableType[] getInterfaces() {
@@ -618,17 +618,17 @@ public class ResolvableType implements Serializable {
 	}
 
 	/**
-	 * Return a {@link ResolvableType} for the specified nesting level.
+	 * Return a {@code ResolvableType} for the specified nesting level.
 	 * <p>See {@link #getNested(int, Map)} for details.
 	 * @param nestingLevel the nesting level
-	 * @return the {@link ResolvableType} type, or {@code #NONE}
+	 * @return the {@code ResolvableType} type, or {@code #NONE}
 	 */
 	public ResolvableType getNested(int nestingLevel) {
 		return getNested(nestingLevel, null);
 	}
 
 	/**
-	 * Return a {@link ResolvableType} for the specified nesting level.
+	 * Return a {@code ResolvableType} for the specified nesting level.
 	 * <p>The nesting level refers to the specific generic parameter that should be returned.
 	 * A nesting level of 1 indicates this type; 2 indicates the first nested generic;
 	 * 3 the second; and so on. For example, given {@code List<Set<Integer>>} level 1 refers
@@ -645,7 +645,7 @@ public class ResolvableType implements Serializable {
 	 * current type, 2 for the first nested generic, 3 for the second and so on
 	 * @param typeIndexesPerLevel a map containing the generic index for a given
 	 * nesting level (may be {@code null})
-	 * @return a {@link ResolvableType} for the nested level, or {@link #NONE}
+	 * @return a {@code ResolvableType} for the nested level, or {@link #NONE}
 	 */
 	public ResolvableType getNested(int nestingLevel, @Nullable Map<Integer, Integer> typeIndexesPerLevel) {
 		ResolvableType result = this;
@@ -667,7 +667,7 @@ public class ResolvableType implements Serializable {
 	}
 
 	/**
-	 * Return a {@link ResolvableType} representing the generic parameter for the
+	 * Return a {@code ResolvableType} representing the generic parameter for the
 	 * given indexes. Indexes are zero based; for example given the type
 	 * {@code Map<Integer, List<String>>}, {@code getGeneric(0)} will access the
 	 * {@code Integer}. Nested generics can be accessed by specifying multiple indexes;
@@ -677,7 +677,7 @@ public class ResolvableType implements Serializable {
 	 * <p>If no generic is available at the specified indexes {@link #NONE} is returned.
 	 * @param indexes the indexes that refer to the generic parameter
 	 * (may be omitted to return the first generic)
-	 * @return a {@link ResolvableType} for the specified generic, or {@link #NONE}
+	 * @return a {@code ResolvableType} for the specified generic, or {@link #NONE}
 	 * @see #hasGenerics()
 	 * @see #getGenerics()
 	 * @see #resolveGeneric(int...)
@@ -839,7 +839,7 @@ public class ResolvableType implements Serializable {
 
 	/**
 	 * Resolve this type by a single level, returning the resolved value or {@link #NONE}.
-	 * <p>Note: The returned {@link ResolvableType} should only be used as an intermediary
+	 * <p>Note: The returned {@code ResolvableType} should only be used as an intermediary
 	 * as it cannot be serialized.
 	 */
 	ResolvableType resolveType() {
@@ -910,16 +910,22 @@ public class ResolvableType implements Serializable {
 	}
 
 
+	/**
+	 * Check for full equality of all type resolution artifacts:
+	 * type as well as {@code TypeProvider} and {@code VariableResolver}.
+	 * @see #equalsType(ResolvableType)
+	 */
 	@Override
 	public boolean equals(@Nullable Object other) {
 		if (this == other) {
 			return true;
 		}
-		if (!(other instanceof ResolvableType otherType)) {
+		if (other == null || other.getClass() != getClass()) {
 			return false;
 		}
+		ResolvableType otherType = (ResolvableType) other;
 
-		if (!ObjectUtils.nullSafeEquals(this.type, otherType.type)) {
+		if (!equalsType(otherType)) {
 			return false;
 		}
 		if (this.typeProvider != otherType.typeProvider &&
@@ -932,12 +938,22 @@ public class ResolvableType implements Serializable {
 				!ObjectUtils.nullSafeEquals(this.variableResolver.getSource(), otherType.variableResolver.getSource()))) {
 			return false;
 		}
-		if (!ObjectUtils.nullSafeEquals(this.componentType, otherType.componentType)) {
-			return false;
-		}
 		return true;
 	}
 
+	/**
+	 * Check for type-level equality with another {@code ResolvableType}.
+	 * <p>In contrast to {@link #equals(Object)} or {@link #isAssignableFrom(ResolvableType)},
+	 * this works between different sources as well, e.g. method parameters and return types.
+	 * @param otherType the {@code ResolvableType} to match against
+	 * @return whether the declared type and type variables match
+	 * @since 6.1
+	 */
+	public boolean equalsType(ResolvableType otherType) {
+		return (ObjectUtils.nullSafeEquals(this.type, otherType.type) &&
+				ObjectUtils.nullSafeEquals(this.componentType, otherType.componentType));
+	}
+
 	@Override
 	public int hashCode() {
 		return (this.hash != null ? this.hash : calculateHashCode());
@@ -945,20 +961,20 @@ public class ResolvableType implements Serializable {
 
 	private int calculateHashCode() {
 		int hashCode = ObjectUtils.nullSafeHashCode(this.type);
+		if (this.componentType != null) {
+			hashCode = 31 * hashCode + ObjectUtils.nullSafeHashCode(this.componentType);
+		}
 		if (this.typeProvider != null) {
 			hashCode = 31 * hashCode + ObjectUtils.nullSafeHashCode(this.typeProvider.getType());
 		}
 		if (this.variableResolver != null) {
 			hashCode = 31 * hashCode + ObjectUtils.nullSafeHashCode(this.variableResolver.getSource());
 		}
-		if (this.componentType != null) {
-			hashCode = 31 * hashCode + ObjectUtils.nullSafeHashCode(this.componentType);
-		}
 		return hashCode;
 	}
 
 	/**
-	 * Adapts this {@link ResolvableType} to a {@link VariableResolver}.
+	 * Adapts this {@code ResolvableType} to a {@link VariableResolver}.
 	 */
 	@Nullable
 	VariableResolver asVariableResolver() {
@@ -1004,12 +1020,12 @@ public class ResolvableType implements Serializable {
 	// Factory methods
 
 	/**
-	 * Return a {@link ResolvableType} for the specified {@link Class},
+	 * Return a {@code ResolvableType} for the specified {@link Class},
 	 * using the full generic type information for assignability checks.
 	 * <p>For example: {@code ResolvableType.forClass(MyArrayList.class)}.
 	 * @param clazz the class to introspect ({@code null} is semantically
 	 * equivalent to {@code Object.class} for typical use cases here)
-	 * @return a {@link ResolvableType} for the specified class
+	 * @return a {@code ResolvableType} for the specified class
 	 * @see #forClass(Class, Class)
 	 * @see #forClassWithGenerics(Class, Class...)
 	 */
@@ -1018,13 +1034,13 @@ public class ResolvableType implements Serializable {
 	}
 
 	/**
-	 * Return a {@link ResolvableType} for the specified {@link Class},
+	 * Return a {@code ResolvableType} for the specified {@link Class},
 	 * doing assignability checks against the raw class only (analogous to
 	 * {@link Class#isAssignableFrom}, which this serves as a wrapper for).
 	 * <p>For example: {@code ResolvableType.forRawClass(List.class)}.
 	 * @param clazz the class to introspect ({@code null} is semantically
 	 * equivalent to {@code Object.class} for typical use cases here)
-	 * @return a {@link ResolvableType} for the specified class
+	 * @return a {@code ResolvableType} for the specified class
 	 * @since 4.2
 	 * @see #forClass(Class)
 	 * @see #getRawClass()
@@ -1048,12 +1064,12 @@ public class ResolvableType implements Serializable {
 	}
 
 	/**
-	 * Return a {@link ResolvableType} for the specified base type
+	 * Return a {@code ResolvableType} for the specified base type
 	 * (interface or base class) with a given implementation class.
 	 * <p>For example: {@code ResolvableType.forClass(List.class, MyArrayList.class)}.
 	 * @param baseType the base type (must not be {@code null})
 	 * @param implementationClass the implementation class
-	 * @return a {@link ResolvableType} for the specified base type backed by the
+	 * @return a {@code ResolvableType} for the specified base type backed by the
 	 * given implementation class
 	 * @see #forClass(Class)
 	 * @see #forClassWithGenerics(Class, Class...)
@@ -1065,10 +1081,10 @@ public class ResolvableType implements Serializable {
 	}
 
 	/**
-	 * Return a {@link ResolvableType} for the specified {@link Class} with pre-declared generics.
+	 * Return a {@code ResolvableType} for the specified {@link Class} with pre-declared generics.
 	 * @param clazz the class (or interface) to introspect
 	 * @param generics the generics of the class
-	 * @return a {@link ResolvableType} for the specific class and generics
+	 * @return a {@code ResolvableType} for the specific class and generics
 	 * @see #forClassWithGenerics(Class, ResolvableType...)
 	 */
 	public static ResolvableType forClassWithGenerics(Class<?> clazz, Class<?>... generics) {
@@ -1082,10 +1098,10 @@ public class ResolvableType implements Serializable {
 	}
 
 	/**
-	 * Return a {@link ResolvableType} for the specified {@link Class} with pre-declared generics.
+	 * Return a {@code ResolvableType} for the specified {@link Class} with pre-declared generics.
 	 * @param clazz the class (or interface) to introspect
 	 * @param generics the generics of the class
-	 * @return a {@link ResolvableType} for the specific class and generics
+	 * @return a {@code ResolvableType} for the specific class and generics
 	 * @see #forClassWithGenerics(Class, Class...)
 	 */
 	public static ResolvableType forClassWithGenerics(Class<?> clazz, ResolvableType... generics) {
@@ -1106,12 +1122,12 @@ public class ResolvableType implements Serializable {
 	}
 
 	/**
-	 * Return a {@link ResolvableType} for the specified instance. The instance does not
+	 * Return a {@code ResolvableType} for the specified instance. The instance does not
 	 * convey generic information but if it implements {@link ResolvableTypeProvider} a
-	 * more precise {@link ResolvableType} can be used than the simple one based on
+	 * more precise {@code ResolvableType} can be used than the simple one based on
 	 * the {@link #forClass(Class) Class instance}.
 	 * @param instance the instance (possibly {@code null})
-	 * @return a {@link ResolvableType} for the specified instance,
+	 * @return a {@code ResolvableType} for the specified instance,
 	 * or {@code NONE} for {@code null}
 	 * @since 4.2
 	 * @see ResolvableTypeProvider
@@ -1127,9 +1143,9 @@ public class ResolvableType implements Serializable {
 	}
 
 	/**
-	 * Return a {@link ResolvableType} for the specified {@link Field}.
+	 * Return a {@code ResolvableType} for the specified {@link Field}.
 	 * @param field the source field
-	 * @return a {@link ResolvableType} for the specified field
+	 * @return a {@code ResolvableType} for the specified field
 	 * @see #forField(Field, Class)
 	 */
 	public static ResolvableType forField(Field field) {
@@ -1138,13 +1154,13 @@ public class ResolvableType implements Serializable {
 	}
 
 	/**
-	 * Return a {@link ResolvableType} for the specified {@link Field} with a given
+	 * Return a {@code ResolvableType} for the specified {@link Field} with a given
 	 * implementation.
 	 * <p>Use this variant when the class that declares the field includes generic
 	 * parameter variables that are satisfied by the implementation class.
 	 * @param field the source field
 	 * @param implementationClass the implementation class
-	 * @return a {@link ResolvableType} for the specified field
+	 * @return a {@code ResolvableType} for the specified field
 	 * @see #forField(Field)
 	 */
 	public static ResolvableType forField(Field field, Class<?> implementationClass) {
@@ -1154,13 +1170,13 @@ public class ResolvableType implements Serializable {
 	}
 
 	/**
-	 * Return a {@link ResolvableType} for the specified {@link Field} with a given
+	 * Return a {@code ResolvableType} for the specified {@link Field} with a given
 	 * implementation.
 	 * <p>Use this variant when the class that declares the field includes generic
 	 * parameter variables that are satisfied by the implementation type.
 	 * @param field the source field
 	 * @param implementationType the implementation type
-	 * @return a {@link ResolvableType} for the specified field
+	 * @return a {@code ResolvableType} for the specified field
 	 * @see #forField(Field)
 	 */
 	public static ResolvableType forField(Field field, @Nullable ResolvableType implementationType) {
@@ -1171,7 +1187,7 @@ public class ResolvableType implements Serializable {
 	}
 
 	/**
-	 * Return a {@link ResolvableType} for the specified {@link Field} with the
+	 * Return a {@code ResolvableType} for the specified {@link Field} with the
 	 * given nesting level.
 	 * @param field the source field
 	 * @param nestingLevel the nesting level (1 for the outer level; 2 for a nested
@@ -1184,7 +1200,7 @@ public class ResolvableType implements Serializable {
 	}
 
 	/**
-	 * Return a {@link ResolvableType} for the specified {@link Field} with a given
+	 * Return a {@code ResolvableType} for the specified {@link Field} with a given
 	 * implementation and the given nesting level.
 	 * <p>Use this variant when the class that declares the field includes generic
 	 * parameter variables that are satisfied by the implementation class.
@@ -1192,7 +1208,7 @@ public class ResolvableType implements Serializable {
 	 * @param nestingLevel the nesting level (1 for the outer level; 2 for a nested
 	 * generic type; etc)
 	 * @param implementationClass the implementation class
-	 * @return a {@link ResolvableType} for the specified field
+	 * @return a {@code ResolvableType} for the specified field
 	 * @see #forField(Field)
 	 */
 	public static ResolvableType forField(Field field, int nestingLevel, @Nullable Class<?> implementationClass) {
@@ -1202,10 +1218,10 @@ public class ResolvableType implements Serializable {
 	}
 
 	/**
-	 * Return a {@link ResolvableType} for the specified {@link Constructor} parameter.
+	 * Return a {@code ResolvableType} for the specified {@link Constructor} parameter.
 	 * @param constructor the source constructor (must not be {@code null})
 	 * @param parameterIndex the parameter index
-	 * @return a {@link ResolvableType} for the specified constructor parameter
+	 * @return a {@code ResolvableType} for the specified constructor parameter
 	 * @see #forConstructorParameter(Constructor, int, Class)
 	 */
 	public static ResolvableType forConstructorParameter(Constructor<?> constructor, int parameterIndex) {
@@ -1214,14 +1230,14 @@ public class ResolvableType implements Serializable {
 	}
 
 	/**
-	 * Return a {@link ResolvableType} for the specified {@link Constructor} parameter
+	 * Return a {@code ResolvableType} for the specified {@link Constructor} parameter
 	 * with a given implementation. Use this variant when the class that declares the
 	 * constructor includes generic parameter variables that are satisfied by the
 	 * implementation class.
 	 * @param constructor the source constructor (must not be {@code null})
 	 * @param parameterIndex the parameter index
 	 * @param implementationClass the implementation class
-	 * @return a {@link ResolvableType} for the specified constructor parameter
+	 * @return a {@code ResolvableType} for the specified constructor parameter
 	 * @see #forConstructorParameter(Constructor, int)
 	 */
 	public static ResolvableType forConstructorParameter(Constructor<?> constructor, int parameterIndex,
@@ -1233,9 +1249,9 @@ public class ResolvableType implements Serializable {
 	}
 
 	/**
-	 * Return a {@link ResolvableType} for the specified {@link Method} return type.
+	 * Return a {@code ResolvableType} for the specified {@link Method} return type.
 	 * @param method the source for the method return type
-	 * @return a {@link ResolvableType} for the specified method return
+	 * @return a {@code ResolvableType} for the specified method return
 	 * @see #forMethodReturnType(Method, Class)
 	 */
 	public static ResolvableType forMethodReturnType(Method method) {
@@ -1244,12 +1260,12 @@ public class ResolvableType implements Serializable {
 	}
 
 	/**
-	 * Return a {@link ResolvableType} for the specified {@link Method} return type.
+	 * Return a {@code ResolvableType} for the specified {@link Method} return type.
 	 * <p>Use this variant when the class that declares the method includes generic
 	 * parameter variables that are satisfied by the implementation class.
 	 * @param method the source for the method return type
 	 * @param implementationClass the implementation class
-	 * @return a {@link ResolvableType} for the specified method return
+	 * @return a {@code ResolvableType} for the specified method return
 	 * @see #forMethodReturnType(Method)
 	 */
 	public static ResolvableType forMethodReturnType(Method method, Class<?> implementationClass) {
@@ -1259,10 +1275,10 @@ public class ResolvableType implements Serializable {
 	}
 
 	/**
-	 * Return a {@link ResolvableType} for the specified {@link Method} parameter.
+	 * Return a {@code ResolvableType} for the specified {@link Method} parameter.
 	 * @param method the source method (must not be {@code null})
 	 * @param parameterIndex the parameter index
-	 * @return a {@link ResolvableType} for the specified method parameter
+	 * @return a {@code ResolvableType} for the specified method parameter
 	 * @see #forMethodParameter(Method, int, Class)
 	 * @see #forMethodParameter(MethodParameter)
 	 */
@@ -1272,13 +1288,13 @@ public class ResolvableType implements Serializable {
 	}
 
 	/**
-	 * Return a {@link ResolvableType} for the specified {@link Method} parameter with a
+	 * Return a {@code ResolvableType} for the specified {@link Method} parameter with a
 	 * given implementation. Use this variant when the class that declares the method
 	 * includes generic parameter variables that are satisfied by the implementation class.
 	 * @param method the source method (must not be {@code null})
 	 * @param parameterIndex the parameter index
 	 * @param implementationClass the implementation class
-	 * @return a {@link ResolvableType} for the specified method parameter
+	 * @return a {@code ResolvableType} for the specified method parameter
 	 * @see #forMethodParameter(Method, int, Class)
 	 * @see #forMethodParameter(MethodParameter)
 	 */
@@ -1289,9 +1305,9 @@ public class ResolvableType implements Serializable {
 	}
 
 	/**
-	 * Return a {@link ResolvableType} for the specified {@link MethodParameter}.
+	 * Return a {@code ResolvableType} for the specified {@link MethodParameter}.
 	 * @param methodParameter the source method parameter (must not be {@code null})
-	 * @return a {@link ResolvableType} for the specified method parameter
+	 * @return a {@code ResolvableType} for the specified method parameter
 	 * @see #forMethodParameter(Method, int)
 	 */
 	public static ResolvableType forMethodParameter(MethodParameter methodParameter) {
@@ -1299,12 +1315,12 @@ public class ResolvableType implements Serializable {
 	}
 
 	/**
-	 * Return a {@link ResolvableType} for the specified {@link MethodParameter} with a
+	 * Return a {@code ResolvableType} for the specified {@link MethodParameter} with a
 	 * given implementation type. Use this variant when the class that declares the method
 	 * includes generic parameter variables that are satisfied by the implementation type.
 	 * @param methodParameter the source method parameter (must not be {@code null})
 	 * @param implementationType the implementation type
-	 * @return a {@link ResolvableType} for the specified method parameter
+	 * @return a {@code ResolvableType} for the specified method parameter
 	 * @see #forMethodParameter(MethodParameter)
 	 */
 	public static ResolvableType forMethodParameter(MethodParameter methodParameter,
@@ -1319,11 +1335,11 @@ public class ResolvableType implements Serializable {
 	}
 
 	/**
-	 * Return a {@link ResolvableType} for the specified {@link MethodParameter},
+	 * Return a {@code ResolvableType} for the specified {@link MethodParameter},
 	 * overriding the target type to resolve with a specific given type.
 	 * @param methodParameter the source method parameter (must not be {@code null})
 	 * @param targetType the type to resolve (a part of the method parameter's type)
-	 * @return a {@link ResolvableType} for the specified method parameter
+	 * @return a {@code ResolvableType} for the specified method parameter
 	 * @see #forMethodParameter(Method, int)
 	 */
 	public static ResolvableType forMethodParameter(MethodParameter methodParameter, @Nullable Type targetType) {
@@ -1332,13 +1348,13 @@ public class ResolvableType implements Serializable {
 	}
 
 	/**
-	 * Return a {@link ResolvableType} for the specified {@link MethodParameter} at
+	 * Return a {@code ResolvableType} for the specified {@link MethodParameter} at
 	 * a specific nesting level, overriding the target type to resolve with a specific
 	 * given type.
 	 * @param methodParameter the source method parameter (must not be {@code null})
 	 * @param targetType the type to resolve (a part of the method parameter's type)
 	 * @param nestingLevel the nesting level to use
-	 * @return a {@link ResolvableType} for the specified method parameter
+	 * @return a {@code ResolvableType} for the specified method parameter
 	 * @since 5.2
 	 * @see #forMethodParameter(Method, int)
 	 */
@@ -1351,21 +1367,21 @@ public class ResolvableType implements Serializable {
 	}
 
 	/**
-	 * Return a {@link ResolvableType} as an array of the specified {@code componentType}.
+	 * Return a {@code ResolvableType} as an array of the specified {@code componentType}.
 	 * @param componentType the component type
-	 * @return a {@link ResolvableType} as an array of the specified component type
+	 * @return a {@code ResolvableType} as an array of the specified component type
 	 */
 	public static ResolvableType forArrayComponent(ResolvableType componentType) {
 		Assert.notNull(componentType, "Component type must not be null");
 		Class<?> arrayClass = Array.newInstance(componentType.resolve(), 0).getClass();
-		return new ResolvableType(arrayClass, null, null, componentType);
+		return new ResolvableType(arrayClass, componentType, null, null);
 	}
 
 	/**
-	 * Return a {@link ResolvableType} for the specified {@link Type}.
-	 * <p>Note: The resulting {@link ResolvableType} instance may not be {@link Serializable}.
+	 * Return a {@code ResolvableType} for the specified {@link Type}.
+	 * <p>Note: The resulting {@code ResolvableType} instance may not be {@link Serializable}.
 	 * @param type the source type (potentially {@code null})
-	 * @return a {@link ResolvableType} for the specified {@link Type}
+	 * @return a {@code ResolvableType} for the specified {@link Type}
 	 * @see #forType(Type, ResolvableType)
 	 */
 	public static ResolvableType forType(@Nullable Type type) {
@@ -1373,12 +1389,12 @@ public class ResolvableType implements Serializable {
 	}
 
 	/**
-	 * Return a {@link ResolvableType} for the specified {@link Type} backed by the given
+	 * Return a {@code ResolvableType} for the specified {@link Type} backed by the given
 	 * owner type.
-	 * <p>Note: The resulting {@link ResolvableType} instance may not be {@link Serializable}.
+	 * <p>Note: The resulting {@code ResolvableType} instance may not be {@link Serializable}.
 	 * @param type the source type or {@code null}
 	 * @param owner the owner type used to resolve variables
-	 * @return a {@link ResolvableType} for the specified {@link Type} and owner
+	 * @return a {@code ResolvableType} for the specified {@link Type} and owner
 	 * @see #forType(Type)
 	 */
 	public static ResolvableType forType(@Nullable Type type, @Nullable ResolvableType owner) {
@@ -1391,10 +1407,10 @@ public class ResolvableType implements Serializable {
 
 
 	/**
-	 * Return a {@link ResolvableType} for the specified {@link ParameterizedTypeReference}.
-	 * <p>Note: The resulting {@link ResolvableType} instance may not be {@link Serializable}.
+	 * Return a {@code ResolvableType} for the specified {@link ParameterizedTypeReference}.
+	 * <p>Note: The resulting {@code ResolvableType} instance may not be {@link Serializable}.
 	 * @param typeReference the reference to obtain the source type from
-	 * @return a {@link ResolvableType} for the specified {@link ParameterizedTypeReference}
+	 * @return a {@code ResolvableType} for the specified {@link ParameterizedTypeReference}
 	 * @since 4.3.12
 	 * @see #forType(Type)
 	 */
@@ -1403,23 +1419,23 @@ public class ResolvableType implements Serializable {
 	}
 
 	/**
-	 * Return a {@link ResolvableType} for the specified {@link Type} backed by a given
+	 * Return a {@code ResolvableType} for the specified {@link Type} backed by a given
 	 * {@link VariableResolver}.
 	 * @param type the source type or {@code null}
 	 * @param variableResolver the variable resolver or {@code null}
-	 * @return a {@link ResolvableType} for the specified {@link Type} and {@link VariableResolver}
+	 * @return a {@code ResolvableType} for the specified {@link Type} and {@link VariableResolver}
 	 */
 	static ResolvableType forType(@Nullable Type type, @Nullable VariableResolver variableResolver) {
 		return forType(type, null, variableResolver);
 	}
 
 	/**
-	 * Return a {@link ResolvableType} for the specified {@link Type} backed by a given
+	 * Return a {@code ResolvableType} for the specified {@link Type} backed by a given
 	 * {@link VariableResolver}.
 	 * @param type the source type or {@code null}
 	 * @param typeProvider the type provider or {@code null}
 	 * @param variableResolver the variable resolver or {@code null}
-	 * @return a {@link ResolvableType} for the specified {@link Type} and {@link VariableResolver}
+	 * @return a {@code ResolvableType} for the specified {@link Type} and {@link VariableResolver}
 	 */
 	static ResolvableType forType(
 			@Nullable Type type, @Nullable TypeProvider typeProvider, @Nullable VariableResolver variableResolver) {
@@ -1434,7 +1450,7 @@ public class ResolvableType implements Serializable {
 		// For simple Class references, build the wrapper right away -
 		// no expensive resolution necessary, so not worth caching...
 		if (type instanceof Class) {
-			return new ResolvableType(type, typeProvider, variableResolver, (ResolvableType) null);
+			return new ResolvableType(type, null, typeProvider, variableResolver);
 		}
 
 		// Purge empty entries on access since we don't have a clean-up thread or the like.

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

@@ -123,6 +123,7 @@ class ResolvableTypeTests {
 		assertThat(type.getRawClass()).isEqualTo(ExtendsList.class);
 		assertThat(type.isAssignableFrom(ExtendsList.class)).isTrue();
 		assertThat(type.isAssignableFrom(ArrayList.class)).isFalse();
+		assertThat(type).isNotEqualTo(ResolvableType.forClass(ExtendsList.class));
 	}
 
 	@Test
@@ -132,6 +133,7 @@ class ResolvableTypeTests {
 		assertThat(type.getRawClass()).isEqualTo(Object.class);
 		assertThat(type.isAssignableFrom(Object.class)).isTrue();
 		assertThat(type.isAssignableFrom(String.class)).isTrue();
+		assertThat(type).isNotEqualTo(ResolvableType.forClass(null));
 	}
 
 	@Test  // gh-23321
@@ -200,8 +202,8 @@ class ResolvableTypeTests {
 	@Test
 	void forFieldMustNotBeNull() throws Exception {
 		assertThatIllegalArgumentException()
-			.isThrownBy(() -> ResolvableType.forField(null))
-			.withMessage("Field must not be null");
+				.isThrownBy(() -> ResolvableType.forField(null))
+				.withMessage("Field must not be null");
 	}
 
 	@Test
@@ -214,8 +216,8 @@ class ResolvableTypeTests {
 	@Test
 	void forConstructorParameterMustNotBeNull() throws Exception {
 		assertThatIllegalArgumentException()
-			.isThrownBy(() -> ResolvableType.forConstructorParameter(null, 0))
-			.withMessage("Constructor must not be null");
+				.isThrownBy(() -> ResolvableType.forConstructorParameter(null, 0))
+				.withMessage("Constructor must not be null");
 	}
 
 	@Test
@@ -228,8 +230,8 @@ class ResolvableTypeTests {
 	@Test
 	void forMethodParameterByIndexMustNotBeNull() throws Exception {
 		assertThatIllegalArgumentException()
-			.isThrownBy(() -> ResolvableType.forMethodParameter(null, 0))
-			.withMessage("Method must not be null");
+				.isThrownBy(() -> ResolvableType.forMethodParameter(null, 0))
+				.withMessage("Method must not be null");
 	}
 
 	@Test
@@ -268,8 +270,8 @@ class ResolvableTypeTests {
 	@Test
 	void forMethodParameterMustNotBeNull() throws Exception {
 		assertThatIllegalArgumentException()
-			.isThrownBy(() -> ResolvableType.forMethodParameter(null))
-			.withMessage("MethodParameter must not be null");
+				.isThrownBy(() -> ResolvableType.forMethodParameter(null))
+				.withMessage("MethodParameter must not be null");
 	}
 
 	@Test  // SPR-16210
@@ -295,8 +297,23 @@ class ResolvableTypeTests {
 	@Test
 	void forMethodReturnMustNotBeNull() throws Exception {
 		assertThatIllegalArgumentException()
-			.isThrownBy(() -> ResolvableType.forMethodReturnType(null))
-			.withMessage("Method must not be null");
+				.isThrownBy(() -> ResolvableType.forMethodReturnType(null))
+				.withMessage("Method must not be null");
+	}
+
+	@Test  // gh-27748
+	void genericMatchesReturnType() throws Exception {
+		Method method = SomeRepository.class.getMethod("someMethod", Class.class, Class.class, Class.class);
+
+		ResolvableType returnType = ResolvableType.forMethodReturnType(method, SomeRepository.class);
+
+		ResolvableType arg0 = ResolvableType.forMethodParameter(method, 0, SomeRepository.class); // generic[0]=T
+		ResolvableType arg1 = ResolvableType.forMethodParameter(method, 1, SomeRepository.class); // generic[0]=?
+		ResolvableType arg2 = ResolvableType.forMethodParameter(method, 2, SomeRepository.class); // generic[0]=java.lang.Object
+
+		assertThat(returnType.equalsType(arg0.as(Class.class).getGeneric(0))).isTrue();
+		assertThat(returnType.equalsType(arg1.as(Class.class).getGeneric(0))).isFalse();
+		assertThat(returnType.equalsType(arg2.as(Class.class).getGeneric(0))).isFalse();
 	}
 
 	@Test
@@ -964,8 +981,8 @@ class ResolvableTypeTests {
 	@Test
 	void isAssignableFromMustNotBeNull() throws Exception {
 		assertThatIllegalArgumentException()
-			.isThrownBy(() -> ResolvableType.forClass(Object.class).isAssignableFrom((ResolvableType) null))
-			.withMessage("ResolvableType must not be null");
+				.isThrownBy(() -> ResolvableType.forClass(Object.class).isAssignableFrom((ResolvableType) null))
+				.withMessage("ResolvableType must not be null");
 	}
 
 	@Test
@@ -1220,9 +1237,9 @@ class ResolvableTypeTests {
 	@Test
 	void forClassWithMismatchedGenerics() throws Exception {
 		assertThatIllegalArgumentException()
-			.isThrownBy(() -> ResolvableType.forClassWithGenerics(Map.class, Integer.class))
-			.withMessageContaining("Mismatched number of generics specified for")
-			.withMessageContaining("java.util.Map<K,V>");
+				.isThrownBy(() -> ResolvableType.forClassWithGenerics(Map.class, Integer.class))
+				.withMessageContaining("Mismatched number of generics specified for")
+				.withMessageContaining("java.util.Map<K,V>");
 	}
 
 	@Test
@@ -1368,6 +1385,12 @@ class ResolvableTypeTests {
 	}
 
 
+	interface SomeRepository {
+
+		<T> T someMethod(Class<T> arg0, Class<?> arg1, Class<Object> arg2);
+	}
+
+
 	static class Fields<T> {
 
 		public List classType;