Derive Completer, Highlighter, Hinter, Validator from struct fields

[AlephAlpha]

This improves the derive macros.

Instead of:

#[derive(Helper)]
struct MyHelper {
    completer: FilenameCompleter,
    highlighter: MatchingBracketHighlighter,
    validator: MatchingBracketValidator,
    hinter: HistoryHinter,
}

impl Completer for MyHelper {
    type Candidate = Pair;

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

impl Hinter for MyHelper {
    type Hint = String;

    fn hint(&self, line: &str, pos: usize, ctx: &Context<'_>) -> Option<String> {
        self.hinter.hint(line, pos, ctx)
    }
}

impl Highlighter for MyHelper {
    fn highlight<'l>(&self, line: &'l str, pos: usize) -> Cow<'l, str> {
        self.highlighter.highlight(line, pos)
    }

    fn highlight_char(&self, line: &str, pos: usize) -> bool {
        self.highlighter.highlight_char(line, pos)
    }
}

impl Validator for MyHelper {
    fn validate(
        &self,
        ctx: &mut validate::ValidationContext,
    ) -> rustyline::Result<validate::ValidationResult> {
        self.validator.validate(ctx)
    }

    fn validate_while_typing(&self) -> bool {
        self.validator.validate_while_typing()
    }
}

Now you can write:

#[derive(Helper, Completer, Highlighter, Validator, Hinter)]
struct MyHelper {
    #[rustyline(Completer)]
    completer: FilenameCompleter,
    #[rustyline(Highlighter)]
    highlighter: MatchingBracketHighlighter,
    #[rustyline(Validator)]
    validator: MatchingBracketValidator,
    #[rustyline(Hinter)]
    hinter: HistoryHinter,
}

This also works for tuple structs. So instead of:

#[derive(Completer, Helper, Highlighter, Validator)]
struct MyHelper(HistoryHinter);

impl Hinter for MyHelper {
    type Hint = String;

    fn hint(&self, line: &str, pos: usize, ctx: &Context<'_>) -> Option<String> {
        self.0.hint(line, pos, ctx)
    }
}

Now you can write:

#[derive(Helper, Completer, Highlighter, Hinter, Validator)]
struct MyHelper(#[rustyline(Hinter)] HistoryHinter)

[gwenn]

Thanks.