上次我们聊到 CLI 的领域交互模式。在领域交互模式中，可能存在多层次的子命令。在使用过程中如果全评记忆的话，命令少还好，多了真心记不住。频繁 --help 也是个很麻烦的事情。如果每次按 'tab' 键就可以提示或补齐命令是不是很方便呢。这一节我们就来说说 'autocommplete' 如何实现。我们还是以 interactcli-rs 中的实现来解说实现过程

实现过程

其实，rustyline 已经为我们提供了基本的 helper 功能框架，其中包括了 completer。我们来看代码，文件位置 src/interact/cli.rs

[derive(Helper)]

struct MyHelper {
completer: CommandCompleter,
highlighter: MatchingBracketHighlighter,
validator: MatchingBracketValidator,
hinter: HistoryHinter,
colored_prompt: String,
}

pub fn run() {
let config = Config::builder()
.history_ignore_space(true)
.completion_type(CompletionType::List)
.output_stream(OutputStreamType::Stdout)
.build();

let h = MyHelper {
    completer: get_command_completer(),
    highlighter: MatchingBracketHighlighter::new(),
    hinter: HistoryHinter {},
    colored_prompt: "".to_owned(),
    validator: MatchingBracketValidator::new(),
};

let mut rl = Editor::with_config(config);
// let mut rl = Editor::<()>::new();
rl.set_helper(Some(h));

......

}

首先定义 MyHelper 结构体， 需要实现 Completer + Hinter + Highlighter + Validator trait。然后通过 rustyline 的 set_helper 函数加载我们定义好的 helper。在 MyHelper 结构体中，需要我们自己来实现 completer 的逻辑。

Sub command autocompleter 实现详解

SubCmd 结构体

[derive(Debug, Clone)]

pub struct SubCmd {
pub level: usize,
pub command_name: String,
pub subcommands: Vec,
}

SubCmd 结构体包含：命令级别，命令名称，以及该命令包含的子命令信息，以便在实现实现 autocomplete 时定位命令和子命令的范围

在程序启动时遍历所有的 command，src/cmd/rootcmd.rs 中的 all_subcommand 函数负责收集所有命令并转换为 Vec
pub fn all_subcommand(app: &clap_Command, beginlevel: usize, input: &mut Vec) {
let nextlevel = beginlevel + 1;
let mut subcmds = vec![];
for iterm in app.get_subcommands() {
subcmds.push(iterm.get_name().to_string());
if iterm.has_subcommands() {
all_subcommand(iterm, nextlevel, input);
} else {
if beginlevel == 0 {
all_subcommand(iterm, nextlevel, input);
}
}
}
let subcommand = SubCmd {
level: beginlevel,
command_name: app.get_name().to_string(),
subcommands: subcmds,
};
input.push(subcommand);
}

CommandCompleter 子命令自动补充功能的核心部分

[derive(Debug, Clone)]

pub struct CommandCompleter {
subcommands: Vec,
}

impl CommandCompleter {
pub fn new(subcmds: Vec) -> Self {
Self {
subcommands: subcmds,
}
}

//获取level下所有可能的子命令
pub fn level_possible_cmd(&self, level: usize) ->   Vec<String> {
    let mut subcmds = vec![];
    let cmds = self.subcommands.clone();
    for iterm in cmds {
        if iterm.level == level {
            subcmds.push(iterm.command_name.clone());
        }
    }
    return subcmds;
}
//获取level下某字符串开头的子命令
pub fn level_prefix_possible_cmd(&self, level: usize,   prefix: &str) -> Vec<String> {
    let mut subcmds = vec![];
    let cmds = self.subcommands.clone();
    for iterm in cmds {
        if iterm.level == level && iterm.command_name.  starts_with(prefix) {
            subcmds.push(iterm.command_name);
        }
    }
    return subcmds;
}

//获取某level 下某subcommand的所有子命令
pub fn level_cmd_possible_sub_cmd(&self, level:   usize, cmd: String) -> Vec<String> {
    let mut subcmds = vec![];
    let cmds = self.subcommands.clone();
    for iterm in cmds {
        if iterm.level == level && iterm.command_name   == cmd {
            subcmds = iterm.subcommands.clone();
        }
    }
    return subcmds;
}

//获取某level 下某subcommand的所有prefix子命令
pub fn level_cmd_possible_prefix_sub_cmd(
    &self,
    level: usize,
    cmd: String,
    prefix: &str,
) -> Vec<String> {
    let mut subcmds = vec![];
    let cmds = self.subcommands.clone();
    for iterm in cmds {
        if iterm.level == level && iterm.command_name   == cmd {
            for i in iterm.subcommands {
                if i.starts_with(prefix) {
                    subcmds.push(i);
                }
            }
        }
    }
    return subcmds;
}

pub fn complete_cmd(&self, line: &str, pos: usize) ->   Result<(usize, Vec<Pair>)> {
    let mut entries: Vec<Pair> = Vec::new();
    let d: Vec<_> = line.split(' ').collect();

    if d.len() == 1 {
        if d.last() == Some(&"") {
            for str in self.level_possible_cmd(1) {
                let mut replace = str.clone();
                replace.push_str(" ");
                entries.push(Pair {
                    display: str.clone(),
                    replacement: replace,
                });
            }
            return Ok((pos, entries));
        }

        if let Some(last) = d.last() {
            for str in self.level_prefix_possible_cmd  (1, *last) {
                let mut replace = str.clone();
                replace.push_str(" ");
                entries.push(Pair {
                    display: str.clone(),
                    replacement: replace,
                });
            }
            return Ok((pos - last.len(), entries));
        }
    }

    if d.last() == Some(&"") {
        for str in self
            .level_cmd_possible_sub_cmd(d.len() - 1,   d.get(d.len() - 2).unwrap().to_string())
        {
            let mut replace = str.clone();
            replace.push_str(" ");
            entries.push(Pair {
                display: str.clone(),
                replacement: replace,
            });
        }
        return Ok((pos, entries));
    }

    if let Some(last) = d.last() {
        for str in self.  level_cmd_possible_prefix_sub_cmd(
            d.len() - 1,
            d.get(d.len() - 2).unwrap().to_string(),
            *last,
        ) {
            let mut replace = str.clone();
            replace.push_str(" ");
            entries.push(Pair {
                display: str.clone(),
                replacement: replace,
            });
        }
        return Ok((pos - last.len(), entries));
    }

    Ok((pos, entries))
}

}

impl Completer for CommandCompleter {
type Candidate = Pair;

fn complete(&self, line: &str, pos: usize, _ctx: &  Context<'_>) -> Result<(usize, Vec<Pair>)> {
    self.complete_cmd(line, pos)
}

}

CommandCompleter 的实现部分比较多，大致包括两个部分，前一部分包括：获取某一级别下所有可能的子命令、获取某级别下某字符串开头的子命令、获取某级别下某个命令的所有子命令，等基本功能。这部分代码中有注释就不一一累述。

函数 complete_cmd 用来计算行中的位置以及在该位置的替换内容。

输入项是命令行的内容以及光标所在位置，输出项为在该位置需要替换的内容。比如，我们在提示符下输入 "root cm" root 下包含 cmd1、cmd2 两个子命令，此时如果按 'tab' 键，complete_cmd 函数就会返回 (7,[cmd1,cmd2])。