作者： jiashiwen 原文来源： https://tidb.net/blog/ec09d93b

文盘Rust -- 子命令提示，提高用户体验

notice"Rust is a trademark of the Mozilla Foundation in the US and other countries."

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<String>,
}

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<SubCmd>) {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<SubCmd>,
}impl CommandCompleter {pub fn new(subcmds: Vec<SubCmd>) -> 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])。

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