Add support for global help options

- Essentially this commit registeres on default `--help` and
  `-h` options to every command and execution short circuits
  in presense of help options to help command.
- Add Supplier<CommandRegistration.Builder> as a bean which
  can be autowired registration beans.
- Make this common bean customisable via CommandRegistrationCustomizer.
- Change StandardMethodTargetRegistrar to use supplier so that
  annotated commands gets common customizations.
- Change sample commands to use supplier.
- Add new group, spring.shell.help to config props.
- Docs changes
- Fixes #582
- Fixes #585

spring-shell-autoconfigure/src/main/java/org/springframework/shell/boot/CommandCatalogAutoConfiguration.java

@@ -16,19 +16,23 @@
 package org.springframework.shell.boot;
 
 import java.util.List;
+import java.util.function.Supplier;
 import java.util.stream.Collectors;
 
 import org.springframework.beans.factory.ObjectProvider;
 import org.springframework.boot.autoconfigure.AutoConfiguration;
 import org.springframework.boot.autoconfigure.condition.ConditionalOnMissingBean;
+import org.springframework.boot.context.properties.EnableConfigurationProperties;
 import org.springframework.context.annotation.Bean;
 import org.springframework.shell.MethodTargetRegistrar;
+import org.springframework.shell.boot.SpringShellProperties.Help;
 import org.springframework.shell.command.CommandCatalog;
 import org.springframework.shell.command.CommandCatalogCustomizer;
 import org.springframework.shell.command.CommandRegistration;
 import org.springframework.shell.command.CommandResolver;
 
 @AutoConfiguration
+@EnableConfigurationProperties(SpringShellProperties.class)
 public class CommandCatalogAutoConfiguration {
 
 	@Bean
@@ -55,4 +59,29 @@ public class CommandCatalogAutoConfiguration {
 			});
 		};
 	}
+
+	@Bean
+	public CommandRegistrationCustomizer helpOptionsCommandRegistrationCustomizer(SpringShellProperties properties) {
+		return registration -> {
+			Help help = properties.getHelp();
+			if (help.isEnabled()) {
+				registration.withHelpOptions()
+					.enabled(true)
+					.longNames(help.getLongNames())
+					.shortNames(help.getShortNames())
+					.command(help.getCommand());
+			}
+		};
+	}
+
+	@Bean
+	@ConditionalOnMissingBean
+	public Supplier<CommandRegistration.Builder> commandRegistrationBuilderSupplier(
+			ObjectProvider<CommandRegistrationCustomizer> customizerProvider) {
+		return () -> {
+			CommandRegistration.Builder builder = CommandRegistration.builder();
+			customizerProvider.orderedStream().forEach((customizer) -> customizer.customize(builder));
+			return builder;
+		};
+	}
 }

spring-shell-autoconfigure/src/main/java/org/springframework/shell/boot/CommandRegistrationCustomizer.java

@@ -0,0 +1,34 @@
+/*
+ * Copyright 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.shell.boot;
+
+import org.springframework.shell.command.CommandRegistration;
+
+/**
+ * Callback interface that can be used to customize a {@link CommandRegistration.Builder}.
+ *
+ * @author Janne Valkealahti
+ */
+@FunctionalInterface
+public interface CommandRegistrationCustomizer {
+
+	/**
+	 * Callback to customize a {@link CommandRegistration.Builder} instance.
+	 *
+	 * @param commandRegistrationBuilder the command registration builder to customize
+	 */
+	void customize(CommandRegistration.Builder commandRegistrationBuilder);
+}

spring-shell-autoconfigure/src/main/java/org/springframework/shell/boot/SpringShellProperties.java

@@ -32,6 +32,7 @@ public class SpringShellProperties {
 	private Noninteractive noninteractive = new Noninteractive();
 	private Theme theme = new Theme();
 	private Command command = new Command();
+	private Help help = new Help();
 
 	public void setConfig(Config config) {
 		this.config = config;
@@ -89,6 +90,14 @@ public class SpringShellProperties {
 		this.command = command;
 	}
 
+	public void setHelp(Help help) {
+		this.help = help;
+	}
+
+	public Help getHelp() {
+		return help;
+	}
+
 	public static class Config {
 
 		private String env;
@@ -495,4 +504,59 @@ public class SpringShellProperties {
 			this.showGitCommitTime = showGitCommitTime;
 		}
 	}
+
+	public static class Help {
+
+		/**
+		 * Command to call when presense of help option is detected.
+		 */
+		private String command = "help";
+
+		/**
+		 * Long style help option, without a prefix "--".
+		 */
+		private String[] longNames = new String[] { "help" };
+
+		/**
+		 * Short style help option, without a prefix "-".
+		 */
+		private Character[] shortNames = new Character[] { 'h' };
+
+		/**
+		 * Whether to enable help options for commands.
+		 */
+		private boolean enabled = true;
+
+		public String getCommand() {
+			return command;
+		}
+
+		public void setCommand(String command) {
+			this.command = command;
+		}
+
+		public String[] getLongNames() {
+			return longNames;
+		}
+
+		public void setLongNames(String[] longNames) {
+			this.longNames = longNames;
+		}
+
+		public Character[] getShortNames() {
+			return shortNames;
+		}
+
+		public void setShortNames(Character[] shortNames) {
+			this.shortNames = shortNames;
+		}
+
+		public boolean isEnabled() {
+			return enabled;
+		}
+
+		public void setEnabled(boolean enabled) {
+			this.enabled = enabled;
+		}
+	}
 }

spring-shell-autoconfigure/src/main/java/org/springframework/shell/boot/StandardAPIAutoConfiguration.java

@@ -16,10 +16,14 @@
 
 package org.springframework.shell.boot;
 
+import java.util.function.Supplier;
+
 import org.springframework.boot.autoconfigure.AutoConfiguration;
+import org.springframework.context.ApplicationContext;
 import org.springframework.context.annotation.Bean;
 import org.springframework.shell.MethodTargetRegistrar;
 import org.springframework.shell.command.CommandCatalog;
+import org.springframework.shell.command.CommandRegistration;
 import org.springframework.shell.standard.CommandValueProvider;
 import org.springframework.shell.standard.EnumValueProvider;
 import org.springframework.shell.standard.FileValueProvider;
@@ -50,7 +54,8 @@ public class StandardAPIAutoConfiguration {
 	}
 
 	@Bean
-	public MethodTargetRegistrar standardMethodTargetResolver() {
-		return new StandardMethodTargetRegistrar();
+	public MethodTargetRegistrar standardMethodTargetResolver(ApplicationContext applicationContext,
+			Supplier<CommandRegistration.Builder> builder) {
+		return new StandardMethodTargetRegistrar(applicationContext, builder);
 	}
 }

spring-shell-autoconfigure/src/test/java/org/springframework/shell/boot/SpringShellPropertiesTests.java

@@ -63,6 +63,10 @@ public class SpringShellPropertiesTests {
 					assertThat(properties.getCommand().getVersion().isShowGitCommitId()).isFalse();
 					assertThat(properties.getCommand().getVersion().isShowGitShortCommitId()).isFalse();
 					assertThat(properties.getCommand().getVersion().isShowGitCommitTime()).isFalse();
+					assertThat(properties.getHelp().isEnabled()).isTrue();
+					assertThat(properties.getHelp().getCommand()).isEqualTo("help");
+					assertThat(properties.getHelp().getLongNames()).containsExactly("help");
+					assertThat(properties.getHelp().getShortNames()).containsExactly('h');
 				});
 	}
 
@@ -99,6 +103,10 @@ public class SpringShellPropertiesTests {
 				.withPropertyValues("spring.shell.command.version.show-git-commit-id=true")
 				.withPropertyValues("spring.shell.command.version.show-git-short-commit-id=true")
 				.withPropertyValues("spring.shell.command.version.show-git-commit-time=true")
+				.withPropertyValues("spring.shell.help.enabled=false")
+				.withPropertyValues("spring.shell.help.command=fake")
+				.withPropertyValues("spring.shell.help.long-names=fake")
+				.withPropertyValues("spring.shell.help.short-names=f")
 				.withUserConfiguration(Config1.class)
 				.run((context) -> {
 					SpringShellProperties properties = context.getBean(SpringShellProperties.class);
@@ -132,6 +140,24 @@ public class SpringShellPropertiesTests {
 					assertThat(properties.getCommand().getVersion().isShowGitCommitId()).isTrue();
 					assertThat(properties.getCommand().getVersion().isShowGitShortCommitId()).isTrue();
 					assertThat(properties.getCommand().getVersion().isShowGitCommitTime()).isTrue();
+					assertThat(properties.getHelp().isEnabled()).isFalse();
+					assertThat(properties.getHelp().getCommand()).isEqualTo("fake");
+					assertThat(properties.getHelp().getLongNames()).containsExactly("fake");
+					assertThat(properties.getHelp().getShortNames()).containsExactly('f');
+				});
+	}
+
+
+	@Test
+	public void essentiallyUnset() {
+		this.contextRunner
+				.withPropertyValues("spring.shell.help.long-names=")
+				.withPropertyValues("spring.shell.help.short-names=")
+				.withUserConfiguration(Config1.class)
+				.run((context) -> {
+					SpringShellProperties properties = context.getBean(SpringShellProperties.class);
+					assertThat(properties.getHelp().getLongNames()).isEmpty();
+					assertThat(properties.getHelp().getShortNames()).isEmpty();
 				});
 	}