Add TypeReference implementation for generated code

This commit adds a TypeReference implementation that is suitable for
creating a reference to generated code.

Closes gh-28148

Author: snicoll

spring-core/src/main/java/org/springframework/aot/generator/GeneratedTypeReference.java

@@ -0,0 +1,70 @@
+/*
+ * Copyright 2002-2022 the original author or authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.springframework.aot.generator;
+
+import org.springframework.aot.hint.AbstractTypeReference;
+import org.springframework.aot.hint.TypeReference;
+import org.springframework.javapoet.ClassName;
+import org.springframework.lang.Nullable;
+import org.springframework.util.Assert;
+
+/**
+ * A {@link TypeReference} for a generated {@linkplain ClassName type}.
+ *
+ * @author Stephane Nicoll
+ * @since 6.0
+ */
+public final class GeneratedTypeReference extends AbstractTypeReference {
+
+	private final ClassName className;
+
+	@Nullable
+	private final TypeReference enclosingType;
+
+	private GeneratedTypeReference(ClassName className) {
+		this.className = className;
+		this.enclosingType = (className.enclosingClassName() != null
+				? new GeneratedTypeReference(className.enclosingClassName())
+				: null);
+	}
+
+	public static GeneratedTypeReference of(ClassName className) {
+		Assert.notNull(className, "ClassName must not be null");
+		return new GeneratedTypeReference(className);
+	}
+
+	@Override
+	public String getCanonicalName() {
+		return this.className.canonicalName();
+	}
+
+	@Override
+	public String getPackageName() {
+		return this.className.packageName();
+	}
+
+	@Override
+	public String getSimpleName() {
+		return this.className.simpleName();
+	}
+
+	@Override
+	public TypeReference getEnclosingType() {
+		return this.enclosingType;
+	}
+
+}

spring-core/src/test/java/org/springframework/aot/generator/GeneratedTypeReferenceTests.java

@@ -0,0 +1,64 @@
+/*
+ * Copyright 2002-2022 the original author or authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.springframework.aot.generator;
+
+import org.junit.jupiter.api.Test;
+
+import org.springframework.aot.hint.TypeReference;
+import org.springframework.javapoet.ClassName;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+/**
+ * Tests for {@link GeneratedTypeReference}.
+ *
+ * @author Stephane Nicoll
+ */
+class GeneratedTypeReferenceTests {
+
+	@Test
+	void createWithClassName() {
+		GeneratedTypeReference typeReference = GeneratedTypeReference.of(
+				ClassName.get("com.example", "Test"));
+		assertThat(typeReference.getPackageName()).isEqualTo("com.example");
+		assertThat(typeReference.getSimpleName()).isEqualTo("Test");
+		assertThat(typeReference.getCanonicalName()).isEqualTo("com.example.Test");
+		assertThat(typeReference.getEnclosingType()).isNull();
+	}
+
+	@Test
+	void createWithClassNameAndParent() {
+		GeneratedTypeReference typeReference = GeneratedTypeReference.of(
+				ClassName.get("com.example", "Test").nestedClass("Nested"));
+		assertThat(typeReference.getPackageName()).isEqualTo("com.example");
+		assertThat(typeReference.getSimpleName()).isEqualTo("Nested");
+		assertThat(typeReference.getCanonicalName()).isEqualTo("com.example.Test.Nested");
+		assertThat(typeReference.getEnclosingType()).satisfies(parentTypeReference -> {
+			assertThat(parentTypeReference.getPackageName()).isEqualTo("com.example");
+			assertThat(parentTypeReference.getSimpleName()).isEqualTo("Test");
+			assertThat(parentTypeReference.getCanonicalName()).isEqualTo("com.example.Test");
+			assertThat(parentTypeReference.getEnclosingType()).isNull();
+		});
+	}
+
+	@Test
+	void equalsWithIdenticalCanonicalNameIsTrue() {
+		assertThat(GeneratedTypeReference.of(ClassName.get("java.lang", "String")))
+				.isEqualTo(TypeReference.of(String.class));
+	}
+
+}