Add support defining Availability with annotated method

- This is for new annotation model
- @CommandAvailability which takes names of
  AvailabilityProvider beans supplying Availability info.
- Relates #663

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

@@ -0,0 +1,27 @@
+/*
+ * 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.util.function.Supplier;
+
+/**
+ * Interface resolving {@link Availability}.
+ *
+ * @author Janne Valkealahti
+ */
+@FunctionalInterface
+public interface AvailabilityProvider extends Supplier<Availability> {
+}

spring-shell-core/src/main/java/org/springframework/shell/command/annotation/CommandAvailability.java

@@ -0,0 +1,42 @@
+/*
+ * 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.command.annotation;
+
+import java.lang.annotation.Documented;
+import java.lang.annotation.ElementType;
+import java.lang.annotation.Retention;
+import java.lang.annotation.RetentionPolicy;
+import java.lang.annotation.Target;
+
+import org.springframework.shell.Availability;
+
+/**
+ * Annotation marking a method having {@link Availability}.
+ *
+ * @author Janne Valkealahti
+ */
+@Retention(RetentionPolicy.RUNTIME)
+@Target(ElementType.METHOD)
+@Documented
+public @interface CommandAvailability {
+
+	/**
+	 * Names of supplier beans for {@link Availability}.
+	 *
+	 * @return names of supplier beans
+	 */
+	String[] name() default {};
+}

spring-shell-core/src/main/java/org/springframework/shell/command/annotation/support/CommandRegistrationFactoryBean.java

@@ -18,6 +18,8 @@ package org.springframework.shell.command.annotation.support;
 import java.lang.reflect.Method;
 import java.util.ArrayList;
 import java.util.List;
+import java.util.stream.Collectors;
+import java.util.stream.Stream;
 
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
@@ -34,6 +36,8 @@ import org.springframework.core.annotation.MergedAnnotation;
 import org.springframework.core.annotation.MergedAnnotations;
 import org.springframework.core.annotation.MergedAnnotations.SearchStrategy;
 import org.springframework.messaging.handler.invocation.InvocableHandlerMethod;
+import org.springframework.shell.Availability;
+import org.springframework.shell.AvailabilityProvider;
 import org.springframework.shell.Utils;
 import org.springframework.shell.command.CommandExceptionResolver;
 import org.springframework.shell.command.CommandHandlingResult;
@@ -42,6 +46,7 @@ import org.springframework.shell.command.CommandRegistration.Builder;
 import org.springframework.shell.command.CommandRegistration.OptionArity;
 import org.springframework.shell.command.CommandRegistration.OptionSpec;
 import org.springframework.shell.command.annotation.Command;
+import org.springframework.shell.command.annotation.CommandAvailability;
 import org.springframework.shell.command.annotation.ExceptionResolverMethodResolver;
 import org.springframework.shell.command.annotation.Option;
 import org.springframework.shell.command.annotation.OptionValues;
@@ -159,6 +164,29 @@ class CommandRegistrationFactoryBean implements FactoryBean<CommandRegistration>
 		InteractionMode deduceInteractionMode = CommandAnnotationUtils.deduceInteractionMode(classAnn, methodAnn);
 		builder.interactionMode(deduceInteractionMode);
 
+		// availability
+		MergedAnnotation<CommandAvailability> caAnn = MergedAnnotations.from(method, SearchStrategy.TYPE_HIERARCHY)
+				.get(CommandAvailability.class);
+		if (caAnn.isPresent()) {
+			String[] refs = caAnn.getStringArray("name");
+			List<AvailabilityProvider> avails = Stream.of(refs)
+				.map(r -> {
+					return this.applicationContext.getBean(r, AvailabilityProvider.class);
+				})
+				.collect(Collectors.toList());
+			if (!avails.isEmpty()) {
+				builder.availability(() -> {
+					for (AvailabilityProvider avail : avails) {
+						Availability a = avail.get();
+						if (!a.isAvailable()) {
+							return a;
+						}
+					}
+					return Availability.available();
+				});
+			}
+		}
+
 		// alias
 		String[] deduceAlias = CommandAnnotationUtils.deduceAlias(classAnn, methodAnn);
 		if (deduceAlias.length > 0) {