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-docs/src/main/asciidoc/using-shell-commands-helpoptions.adoc

@@ -0,0 +1,41 @@
+[[commands-helpoptions]]
+=== Help Options
+ifndef::snippets[:snippets: ../../test/java/org/springframework/shell/docs]
+
+_Spring Shell_ has a build-in `help` command but not all favour getting command help
+from it as you always need to call it with arguments for target command. It's
+common in many cli frameworks for every command having options _--help_ and _-h_
+to print out command help.
+
+Default functionality is that every command will get modified to have options
+_--help_ and _-h_, which if present in a given command will automatically
+short circuit command execution into a existing `help` command regardless
+what other command-line options is typed.
+
+Below example shows its default settings.
+
+====
+[source, java, indent=0]
+----
+include::{snippets}/CommandRegistrationHelpOptionsSnippets.java[tag=defaults]
+----
+====
+
+It is possible to change default behaviour via configuration options.
+
+====
+[source, yaml]
+----
+spring:
+  shell:
+    help:
+      enabled: true
+      long-names: help
+      short-names: h
+      command: help
+----
+====
+
+NOTE: Commands defined programmationally or via annotations will automatically add
+help options. With annotation model you can only turn things off globally, programmatic
+model gives option to modify settings per command.

spring-shell-docs/src/main/asciidoc/using-shell-commands-programmaticmodel.adoc

@@ -1,11 +1,40 @@
 ==== Programmatic Model
 ifndef::snippets[:snippets: ../../test/java/org/springframework/shell/docs]
 
-In the programmatic model, `CommandRegistration` is defined as a `@Bean`, and it is automatically registered:
+In the programmatic model, `CommandRegistration` can be defined as a `@Bean`
+and it will be automatically registered.
 
 ====
 [source, java, indent=0]
 ----
-include::{snippets}/CommandRegistrationBeanSnippets.java[tag=snippet1]
+include::{snippets}/CommandRegistrationBeanSnippets.java[tag=plain]
+----
+====
+
+If all your commands have something in common, an instance of
+a _Supplier<CommandRegistration.Builder>_ is created which can
+be autowired. Default implementation of this supplier returns
+a new builder so you don't need to worry about its internal state.
+
+IMPORTANT: Commands registered programmatically automatically
+add _help options_ mentioned in <<commands-helpoptions>>.
+
+If bean of this supplier type is defined then auto-configuration
+will back off giving you an option to redefine default functionality.
+
+====
+[source, java, indent=0]
+----
+include::{snippets}/CommandRegistrationBeanSnippets.java[tag=fromsupplier]
+----
+====
+
+`CommandRegistrationCustomizer` beans can be defined if you want to centrally
+modify builder instance given you by supplier mentioned above.
+
+====
+[source, java, indent=0]
+----
+include::{snippets}/CommandRegistrationBeanSnippets.java[tag=customizer]
 ----
 ====

spring-shell-docs/src/main/asciidoc/using-shell-commands.adoc

@@ -15,6 +15,8 @@ include::using-shell-commands-exceptionhandling.adoc[]
 
 include::using-shell-commands-hidden.adoc[]
 
+include::using-shell-commands-helpoptions.adoc[]
+
 include::using-shell-commands-interactionmode.adoc[]
 
 include::using-shell-commands-builtin.adoc[]

spring-shell-docs/src/test/java/org/springframework/shell/docs/CommandRegistrationBeanSnippets.java

@@ -15,17 +15,44 @@
  */
 package org.springframework.shell.docs;
 
+import java.util.function.Supplier;
+
 import org.springframework.context.annotation.Bean;
+import org.springframework.shell.boot.CommandRegistrationCustomizer;
 import org.springframework.shell.command.CommandRegistration;
 
 public class CommandRegistrationBeanSnippets {
 
-	// tag::snippet1[]
-	@Bean
-	CommandRegistration commandRegistration() {
-		return CommandRegistration.builder()
-			.command("mycommand")
-			.build();
+	class Dump1 {
+		// tag::plain[]
+		@Bean
+		CommandRegistration commandRegistration() {
+			return CommandRegistration.builder()
+				.command("mycommand")
+				.build();
+		}
+		// end::plain[]
+	}
+
+	class Dump2 {
+		// tag::fromsupplier[]
+		@Bean
+		CommandRegistration commandRegistration(Supplier<CommandRegistration.Builder> builder) {
+			return builder.get()
+				.command("mycommand")
+				.build();
+		}
+		// end::fromsupplier[]
+	}
+
+	class Dump3 {
+		// tag::customizer[]
+		@Bean
+		CommandRegistrationCustomizer commandRegistrationCustomizerExample() {
+			return builder -> {
+				// customize instance of CommandRegistration.Builder
+			};
+		}
+		// end::customizer[]
 	}
-	// end::snippet1[]
 }

spring-shell-docs/src/test/java/org/springframework/shell/docs/CommandRegistrationHelpOptionsSnippets.java

@@ -0,0 +1,40 @@
+/*
+ * 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.docs;
+
+import org.springframework.context.annotation.Bean;
+import org.springframework.shell.command.CommandRegistration;
+
+class CommandRegistrationHelpOptionsSnippets {
+
+	class Dump1 {
+		// tag::defaults[]
+		@Bean
+		CommandRegistration commandRegistration() {
+			return CommandRegistration.builder()
+				.command("mycommand")
+				.withHelpOptions()
+					.enabled(true)
+					.longNames("help")
+					.shortNames('h')
+					.command("help")
+					.and()
+				.build();
+		}
+		// end::defaults[]
+	}
+
+}