Hierarchical commands easy setup

[adibacco]

Setting up a Completer is very flexible but sometimes it generates a long piece of code that is also quite difficult to read. It would be really nice to have a Completer that can be setup with a tree-like structure whose nodes contain a List of Candidates. This approach doesn't cover all possible scenarios but it is very useful in most cases. Consider a Cisco-like CLI for example.

I think the same approach is used in https://github.com/dparrish/libcli

[gnodet]

I see the use case. I haven't run into yet though, mostly because most of the commands I define take options, so that a strict hierarchical completion does not really help.
What could be interesting also is a slightly more complicate completer that you could configure using a syntax such as:

(C1 | C2 | C3)* C4? C5+

which would mean : 0 or more occurrences of c1 or c2 or c3, eventually followed by c4, followed by one or more c5, where c[1-9] would be keys into a Map<String, Completer>.

[gnodet]

See

jline3/builtins/src/test/java/org/jline/example/Example.java

Lines 163 to 180 in 104a5eb

	case "tree":
	completer = new TreeCompleter(
	node("Command1",
	node("Option1",
	node("Param1", "Param2")),
	node("Option2"),
	node("Option3")));
	break label;
	case "regexp":
	Map<String, Completer> comp = new HashMap<>();
	comp.put("C1", new StringsCompleter("cmd1"));
	comp.put("C11", new StringsCompleter("--opt11", "--opt12"));
	comp.put("C12", new StringsCompleter("arg11", "arg12", "arg13"));
	comp.put("C2", new StringsCompleter("cmd2"));
	comp.put("C21", new StringsCompleter("--opt21", "--opt22"));
	comp.put("C22", new StringsCompleter("arg21", "arg22", "arg23"));
	completer = new Completers.RegexCompleter("C1 C11* C12+ | C2 C21* C22+", comp::get);
	break label;

[adibacco]

Really neat way to specify a tree-like commands structure. Just for people that would need "hint" for certain values to insert I created a class like this:

package org.jline.reader;

import java.util.Objects;

public class Hint extends Candidate {

	public Hint(String suggestion) {
		super("", suggestion, null, "", null, null, false);
	}
	public Hint(String suggestion, String description) {
		super("", suggestion, null, description, null, null, false);
	}
}

and then I modified Completer.java like this:

                    if (res instanceof Candidate) {
                        candidates.add((Candidate) res);
                    } else if (res instanceof Hint) {
                        candidates.add((Hint) res);
                    } else if (res instanceof String) {