Add support for command completion

Author: fmbenhassine

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

@@ -48,6 +48,7 @@
 import org.springframework.shell.core.command.Command;
 import org.springframework.shell.core.command.CommandRegistry;
 import org.springframework.shell.core.config.UserConfigPathProvider;
+import org.springframework.shell.jline.CommandCompleter;
 import org.springframework.shell.jline.ExtendedDefaultParser;
 import org.springframework.shell.jline.JLineInputProvider;
 import org.springframework.shell.jline.PromptProvider;
@@ -88,10 +89,12 @@ public void onContextClosedEvent(ContextClosedEvent event) throws IOException {
 	}
 
 	@Bean
-	public LineReader lineReader(Terminal terminal, Parser parser, CommandRegistry commandRegistry) {
+	public LineReader lineReader(Terminal terminal, Parser parser, CommandCompleter commandCompleter,
+			CommandRegistry commandRegistry) {
 		LineReaderBuilder lineReaderBuilder = LineReaderBuilder.builder()
 			.terminal(terminal)
 			.appName("Spring Shell")
+			.completer(commandCompleter)
 			.history(jLineHistory)
 			.highlighter(new Highlighter() {
 
@@ -179,6 +182,12 @@ public Parser parser() {
 		return parser;
 	}
 
+	@Bean
+	@ConditionalOnMissingBean
+	public CommandCompleter commandCompleter(CommandRegistry commandRegistry) {
+		return new CommandCompleter(commandRegistry);
+	}
+
 	@Configuration
 	@ConditionalOnMissingBean(org.jline.reader.History.class)
 	public static class JLineHistoryConfiguration {

spring-shell-jline/src/main/java/org/springframework/shell/jline/CommandCompleter.java

@@ -0,0 +1,41 @@
+package org.springframework.shell.jline;
+
+import java.util.List;
+import java.util.Set;
+
+import org.jline.reader.Candidate;
+import org.jline.reader.Completer;
+import org.jline.reader.LineReader;
+import org.jline.reader.ParsedLine;
+
+import org.springframework.shell.core.command.Command;
+import org.springframework.shell.core.command.CommandRegistry;
+
+/**
+ * A JLine {@link Completer} that completes command names from a {@link CommandRegistry}.
+ *
+ * @author Mahmoud Ben Hassine
+ * @since 4.0.0
+ */
+public class CommandCompleter implements Completer {
+
+	private final CommandRegistry commandRegistry;
+
+	/**
+	 * Create a new {@link CommandCompleter} instance.
+	 * @param commandRegistry the command registry
+	 */
+	public CommandCompleter(CommandRegistry commandRegistry) {
+		this.commandRegistry = commandRegistry;
+	}
+
+	@Override
+	public void complete(LineReader reader, ParsedLine line, List<Candidate> candidates) {
+		Set<Command> commands = this.commandRegistry.getCommands();
+		for (Command command : commands) {
+			candidates.add(new Candidate(command.getName(), command.getName() + ": " + command.getDescription(),
+					command.getGroup(), command.getHelp(), null, null, true));
+		}
+	}
+
+}

spring-shell-jline/src/main/java/org/springframework/shell/jline/DefaultJLineShellConfiguration.java

@@ -28,8 +28,13 @@ public JLineInputProvider inputProvider(LineReader lineReader) {
 	}
 
 	@Bean
-	public LineReader lineReader(Terminal terminal) {
-		return LineReaderBuilder.builder().terminal(terminal).build();
+	public LineReader lineReader(Terminal terminal, CommandCompleter commandCompleter) {
+		return LineReaderBuilder.builder().terminal(terminal).completer(commandCompleter).build();
+	}
+
+	@Bean
+	public CommandCompleter commandCompleter(CommandRegistry commandRegistry) {
+		return new CommandCompleter(commandRegistry);
 	}
 
 	@Bean