Add hints for Availability targets

- Annotate ShellComponent with @Reflective and use custom
  AvailabilityReflectiveProcessor to find possible method
  targets returning Availability.
- Backport #747
- Fixes #758

spring-shell-core/src/main/java/org/springframework/shell/AvailabilityReflectiveProcessor.java

@@ -0,0 +1,56 @@
+/*
+ * Copyright 2023 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.shell;
+
+import java.lang.reflect.AnnotatedElement;
+import java.lang.reflect.Method;
+
+import org.springframework.aot.hint.ExecutableMode;
+import org.springframework.aot.hint.ReflectionHints;
+import org.springframework.aot.hint.annotation.ReflectiveProcessor;
+import org.springframework.util.ClassUtils;
+import org.springframework.util.ReflectionUtils;
+
+/**
+ * A {@link ReflectiveProcessor} implementation that registers methods of a
+ * return type {@link Availability} from a target which is a class.
+ *
+ * @author Janne Valkealahti
+ */
+public final class AvailabilityReflectiveProcessor implements ReflectiveProcessor {
+
+	@Override
+	public void registerReflectionHints(ReflectionHints hints, AnnotatedElement element) {
+		if (element instanceof Class<?> type) {
+			ReflectionUtils.doWithMethods(type, method -> {
+				registerMethodHint(hints, method);
+			}, mf -> {
+				return ClassUtils.isAssignable(mf.getReturnType(), Availability.class)
+						&& mf.getDeclaringClass() != Object.class;
+			});
+		}
+	}
+
+	/**
+	 * Register {@link ReflectionHints} against the specified {@link Method}.
+	 *
+	 * @param hints the reflection hints instance to use
+	 * @param method the method to process
+	 */
+	protected void registerMethodHint(ReflectionHints hints, Method method) {
+		hints.registerMethod(method, ExecutableMode.INVOKE);
+	}
+}

spring-shell-core/src/test/java/org/springframework/shell/AvailabilityReflectiveProcessorTests.java

@@ -0,0 +1,55 @@
+/*
+ * Copyright 2023 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.shell;
+
+import org.junit.jupiter.api.Test;
+
+import org.springframework.aot.hint.ExecutableMode;
+import org.springframework.aot.hint.ReflectionHints;
+import org.springframework.aot.hint.TypeReference;
+import org.springframework.aot.hint.annotation.Reflective;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+class AvailabilityReflectiveProcessorTests {
+
+	private final AvailabilityReflectiveProcessor processor = new AvailabilityReflectiveProcessor();
+
+	private final ReflectionHints hints = new ReflectionHints();
+
+	@Test
+	void registerReflectiveHintsForMethod() throws NoSuchMethodException {
+			processor.registerReflectionHints(hints, SampleBean.class);
+			assertThat(hints.typeHints()).singleElement().satisfies(typeHint -> {
+					assertThat(typeHint.getType()).isEqualTo(TypeReference.of(SampleBean.class));
+					assertThat(typeHint.getMemberCategories()).isEmpty();
+					assertThat(typeHint.constructors()).isEmpty();
+					assertThat(typeHint.fields()).isEmpty();
+					assertThat(typeHint.methods()).singleElement().satisfies(methodHint -> {
+							assertThat(methodHint.getName()).isEqualTo("test");
+							assertThat(methodHint.getMode()).isEqualTo(ExecutableMode.INVOKE);
+					});
+			});
+	}
+
+	@Reflective(AvailabilityReflectiveProcessor.class)
+	static class SampleBean {
+
+		public Availability test() {
+			return null;
+		}
+	}
+}

spring-shell-standard/src/main/java/org/springframework/shell/standard/ShellComponent.java

@@ -22,6 +22,8 @@ import java.lang.annotation.Retention;
 import java.lang.annotation.RetentionPolicy;
 import java.lang.annotation.Target;
 
+import org.springframework.aot.hint.annotation.Reflective;
+import org.springframework.shell.AvailabilityReflectiveProcessor;
 import org.springframework.stereotype.Component;
 
 /**
@@ -38,6 +40,7 @@ import org.springframework.stereotype.Component;
 @Target(ElementType.TYPE)
 @Documented
 @Component
+@Reflective(AvailabilityReflectiveProcessor.class)
 public @interface ShellComponent {
 
 	/**