Support hidden commands

- CommandRegistration now has a structure to define
  it beind hidden
- Modify relevant parts to filter out hidden commands
- Essentially command is hidden from all other than
  command execution
- Sample in e2e tests
- Fixes #416

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

@@ -18,7 +18,9 @@ package org.springframework.shell;
 import java.lang.reflect.UndeclaredThrowableException;
 import java.nio.channels.ClosedByInterruptException;
 import java.util.ArrayList;
+import java.util.Iterator;
 import java.util.List;
+import java.util.Map;
 import java.util.Optional;
 import java.util.function.Function;
 import java.util.stream.Collectors;
@@ -196,7 +198,7 @@ public class Shell {
 
 		List<String> words = input.words();
 		String line = words.stream().collect(Collectors.joining(" ")).trim();
-		String command = findLongestCommand(line);
+		String command = findLongestCommand(line, false);
 
 		if (command == null) {
 			return new CommandNotFound(words);
@@ -349,7 +351,7 @@ public class Shell {
 		List<CompletionProposal> candidates = new ArrayList<>();
 		candidates.addAll(commandsStartingWith(prefix));
 
-		String best = findLongestCommand(prefix);
+		String best = findLongestCommand(prefix, true);
 		if (best != null) {
 			context = context.drop(best.split(" ").length);
 			CommandRegistration registration = commandRegistry.getRegistrations().get(best);
@@ -434,7 +436,7 @@ public class Shell {
 		// Workaround for https://github.com/spring-projects/spring-shell/issues/150
 		// (sadly, this ties this class to JLine somehow)
 		int lastWordStart = prefix.lastIndexOf(' ') + 1;
-		return commandRegistry.getRegistrations().entrySet().stream()
+		return Utils.removeHiddenCommands(commandRegistry.getRegistrations()).entrySet().stream()
 			.filter(e -> e.getKey().startsWith(prefix))
 			.map(e -> {
 				String c = e.getKey();
@@ -456,8 +458,12 @@ public class Shell {
 	 *
 	 * @return a valid command name, or {@literal null} if none matched
 	 */
-	private String findLongestCommand(String prefix) {
-		String result = commandRegistry.getRegistrations().keySet().stream()
+	private String findLongestCommand(String prefix, boolean filterHidden) {
+		Map<String, CommandRegistration> registrations = commandRegistry.getRegistrations();
+		if (filterHidden) {
+			registrations = Utils.removeHiddenCommands(registrations);
+		}
+		String result = registrations.keySet().stream()
 				.filter(command -> prefix.equals(command) || prefix.startsWith(command + " "))
 				.reduce("", (c1, c2) -> c1.length() > c2.length() ? c1 : c2);
 		return "".equals(result) ? null : result;

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

@@ -1,5 +1,5 @@
 /*
- * Copyright 2015-2021 the original author or authors.
+ * Copyright 2015-2022 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.
@@ -22,7 +22,9 @@ import java.lang.reflect.Method;
 import java.lang.reflect.Parameter;
 import java.util.ArrayList;
 import java.util.Arrays;
+import java.util.Iterator;
 import java.util.List;
+import java.util.Map;
 import java.util.function.Predicate;
 import java.util.stream.Collectors;
 import java.util.stream.IntStream;
@@ -34,6 +36,7 @@ import jakarta.validation.ValidatorFactory;
 
 import org.springframework.core.DefaultParameterNameDiscoverer;
 import org.springframework.core.MethodParameter;
+import org.springframework.shell.command.CommandRegistration;
 
 /**
  * Some text utilities.
@@ -166,4 +169,21 @@ public class Utils {
 
 		return split;
 	}
+
+	/**
+	 * Takes a map of command registrations and removes hidden commands from it.
+	 *
+	 * @param registrations a command registrations
+	 * @return same map with removed hidden commands
+	 */
+	public static Map<String, CommandRegistration> removeHiddenCommands(Map<String, CommandRegistration> registrations) {
+		Iterator<Map.Entry<String, CommandRegistration>> iter = registrations.entrySet().iterator();
+		while (iter.hasNext()) {
+			Map.Entry<String, CommandRegistration> entry = iter.next();
+			if (entry.getValue().isHidden()) {
+				iter.remove();
+			}
+		}
+		return registrations;
+	}
 }

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

@@ -65,6 +65,13 @@ public interface CommandRegistration {
 	 */
 	String getGroup();
 
+	/**
+	 * Returns if command is hidden.
+	 *
+	 * @return true if command is hidden
+	 */
+	boolean isHidden();
+
 	/**
 	 * Get description for a command.
 	 *
@@ -516,6 +523,22 @@ public interface CommandRegistration {
 		 */
 		Builder group(String group);
 
+		/**
+		 * Define a command to be hidden.
+		 *
+		 * @return builder for chaining
+		 * @see #hidden(boolean)
+		 */
+		Builder hidden();
+
+		/**
+		 * Define a command to be hidden by a given flag.
+		 *
+		 * @param hidden the hidden flag
+		 * @return builder for chaining
+		 */
+		Builder hidden(boolean hidden);
+
 		/**
 		 * Define an option what this command should user for. Can be used multiple
 		 * times.
@@ -866,6 +889,7 @@ public interface CommandRegistration {
 		private String command;
 		private InteractionMode interactionMode;
 		private String group;
+		private boolean hidden;
 		private String description;
 		private Supplier<Availability> availability;
 		private List<DefaultOptionSpec> optionSpecs;
@@ -875,12 +899,13 @@ public interface CommandRegistration {
 		private DefaultErrorHandlingSpec errorHandlingSpec;
 
 		public DefaultCommandRegistration(String[] commands, InteractionMode interactionMode, String group,
-				String description, Supplier<Availability> availability, List<DefaultOptionSpec> optionSpecs,
-				DefaultTargetSpec targetSpec, List<DefaultAliasSpec> aliasSpecs, DefaultExitCodeSpec exitCodeSpec,
-				DefaultErrorHandlingSpec errorHandlingSpec) {
+				boolean hidden,	String description, Supplier<Availability> availability,
+				List<DefaultOptionSpec> optionSpecs, DefaultTargetSpec targetSpec, List<DefaultAliasSpec> aliasSpecs,
+				DefaultExitCodeSpec exitCodeSpec, DefaultErrorHandlingSpec errorHandlingSpec) {
 			this.command = commandArrayToName(commands);
 			this.interactionMode = interactionMode;
 			this.group = group;
+			this.hidden = hidden;
 			this.description = description;
 			this.availability = availability;
 			this.optionSpecs = optionSpecs;
@@ -905,6 +930,11 @@ public interface CommandRegistration {
 			return group;
 		}
 
+		@Override
+		public boolean isHidden() {
+			return hidden;
+		}
+
 		@Override
 		public String getDescription() {
 			return description;
@@ -985,6 +1015,7 @@ public interface CommandRegistration {
 		private String[] commands;
 		private InteractionMode interactionMode = InteractionMode.ALL;
 		private String group;
+		private boolean hidden;
 		private String description;
 		private Supplier<Availability> availability;
 		private List<DefaultOptionSpec> optionSpecs = new ArrayList<>();
@@ -1023,6 +1054,17 @@ public interface CommandRegistration {
 			return this;
 		}
 
+		@Override
+		public Builder hidden() {
+			return hidden(true);
+		}
+
+		@Override
+		public Builder hidden(boolean hidden) {
+			this.hidden = hidden;
+			return this;
+		}
+
 		@Override
 		public Builder availability(Supplier<Availability> availability) {
 			this.availability = availability;
@@ -1069,7 +1111,7 @@ public interface CommandRegistration {
 			Assert.notNull(commands, "command cannot be empty");
 			Assert.notNull(targetSpec, "target cannot be empty");
 			Assert.state(!(targetSpec.bean != null && targetSpec.function != null), "only one target can exist");
-			return new DefaultCommandRegistration(commands, interactionMode, group, description, availability,
+			return new DefaultCommandRegistration(commands, interactionMode, group, hidden, description, availability,
 					optionSpecs, targetSpec, aliasSpecs, exitCodeSpec, errorHandlingSpec);
 		}
 	}

spring-shell-core/src/test/java/org/springframework/shell/command/CommandRegistrationTests.java

@@ -485,4 +485,42 @@ public class CommandRegistrationTests extends AbstractCommandTests {
 			.build();
 		assertThat(registration.getExceptionResolvers()).hasSize(0);
 	}
+
+	@Test
+	public void testHidden() {
+		CommandRegistration registration = CommandRegistration.builder()
+			.command("command1")
+			.withTarget()
+				.function(function1)
+				.and()
+			.build();
+		assertThat(registration.isHidden()).isFalse();
+
+		registration = CommandRegistration.builder()
+			.command("command1")
+			.hidden()
+			.withTarget()
+				.function(function1)
+				.and()
+			.build();
+		assertThat(registration.isHidden()).isTrue();
+
+		registration = CommandRegistration.builder()
+			.command("command1")
+			.hidden(false)
+			.withTarget()
+				.function(function1)
+				.and()
+			.build();
+		assertThat(registration.isHidden()).isFalse();
+
+		registration = CommandRegistration.builder()
+			.command("command1")
+			.hidden(true)
+			.withTarget()
+				.function(function1)
+				.and()
+			.build();
+		assertThat(registration.isHidden()).isTrue();
+	}
 }