rust/crates/tt/src/lib.rs

//! `tt` crate defines a `TokenTree` data structure: this is the interface (both
//! input and output) of macros. It closely mirrors `proc_macro` crate's
//! `TokenTree`.

#![warn(rust_2018_idioms, unused_lifetimes, semicolon_in_expressions_from_macros)]

use std::fmt;

use stdx::impl_from;

pub use smol_str::SmolStr;

/// Represents identity of the token.
///
/// For hygiene purposes, we need to track which expanded tokens originated from
/// which source tokens. We do it by assigning an distinct identity to each
/// source token and making sure that identities are preserved during macro
/// expansion.
#[derive(Debug, Clone, Copy, PartialEq, Eq, Hash)]
pub struct TokenId(pub u32);

impl TokenId {
    pub const fn unspecified() -> TokenId {
        TokenId(!0)
    }
}

#[derive(Debug, Clone, PartialEq, Eq, Hash)]
pub enum TokenTree {
    Leaf(Leaf),
    Subtree(Subtree),
}
impl_from!(Leaf, Subtree for TokenTree);

impl TokenTree {
    pub fn empty() -> Self {
        TokenTree::Subtree(Subtree::default())
    }
}

#[derive(Debug, Clone, PartialEq, Eq, Hash)]
pub enum Leaf {
    Literal(Literal),
    Punct(Punct),
    Ident(Ident),
}
impl_from!(Literal, Punct, Ident for Leaf);

#[derive(Clone, PartialEq, Eq, Hash, Default)]
pub struct Subtree {
    pub delimiter: Option<Delimiter>,
    pub token_trees: Vec<TokenTree>,
}

#[derive(Clone, Copy, Debug, PartialEq, Eq, Hash)]
pub struct Delimiter {
    pub id: TokenId,
    pub kind: DelimiterKind,
}

#[derive(Clone, Copy, Debug, PartialEq, Eq, Hash)]
pub enum DelimiterKind {
    Parenthesis,
    Brace,
    Bracket,
}

#[derive(Debug, Clone, PartialEq, Eq, Hash)]
pub struct Literal {
    pub text: SmolStr,
    pub id: TokenId,
}

#[derive(Debug, Clone, Copy, PartialEq, Eq, Hash)]
pub struct Punct {
    pub char: char,
    pub spacing: Spacing,
    pub id: TokenId,
}

#[derive(Debug, Clone, Copy, PartialEq, Eq, Hash)]
pub enum Spacing {
    Alone,
    Joint,
}

#[derive(Debug, Clone, PartialEq, Eq, Hash)]
pub struct Ident {
    pub text: SmolStr,
    pub id: TokenId,
}

impl Leaf {
    pub fn id(&self) -> TokenId {
        match self {
            Leaf::Literal(l) => l.id,
            Leaf::Punct(p) => p.id,
            Leaf::Ident(i) => i.id,
        }
    }
}

fn print_debug_subtree(f: &mut fmt::Formatter<'_>, subtree: &Subtree, level: usize) -> fmt::Result {
    let align = "  ".repeat(level);

    let aux = match subtree.delimiter.map(|it| (it.kind, it.id.0)) {
        None => "$".to_string(),
        Some((DelimiterKind::Parenthesis, id)) => format!("() {}", id),
        Some((DelimiterKind::Brace, id)) => format!("{{}} {}", id),
        Some((DelimiterKind::Bracket, id)) => format!("[] {}", id),
    };

    if subtree.token_trees.is_empty() {
        write!(f, "{}SUBTREE {}", align, aux)?;
    } else {
        writeln!(f, "{}SUBTREE {}", align, aux)?;
        for (idx, child) in subtree.token_trees.iter().enumerate() {
            print_debug_token(f, child, level + 1)?;
            if idx != subtree.token_trees.len() - 1 {
                writeln!(f)?;
            }
        }
    }

    Ok(())
}

fn print_debug_token(f: &mut fmt::Formatter<'_>, tkn: &TokenTree, level: usize) -> fmt::Result {
    let align = "  ".repeat(level);

    match tkn {
        TokenTree::Leaf(leaf) => match leaf {
            Leaf::Literal(lit) => write!(f, "{}LITERAL {} {}", align, lit.text, lit.id.0)?,
            Leaf::Punct(punct) => write!(
                f,
                "{}PUNCH   {} [{}] {}",
                align,
                punct.char,
                if punct.spacing == Spacing::Alone { "alone" } else { "joint" },
                punct.id.0
            )?,
            Leaf::Ident(ident) => write!(f, "{}IDENT   {} {}", align, ident.text, ident.id.0)?,
        },
        TokenTree::Subtree(subtree) => {
            print_debug_subtree(f, subtree, level)?;
        }
    }

    Ok(())
}

impl fmt::Debug for Subtree {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        print_debug_subtree(f, self, 0)
    }
}

impl fmt::Display for TokenTree {
    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
        match self {
            TokenTree::Leaf(it) => fmt::Display::fmt(it, f),
            TokenTree::Subtree(it) => fmt::Display::fmt(it, f),
        }
    }
}

impl fmt::Display for Subtree {
    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
        let (l, r) = match self.delimiter_kind() {
            Some(DelimiterKind::Parenthesis) => ("(", ")"),
            Some(DelimiterKind::Brace) => ("{", "}"),
            Some(DelimiterKind::Bracket) => ("[", "]"),
            None => ("", ""),
        };
        f.write_str(l)?;
        let mut needs_space = false;
        for tt in &self.token_trees {
            if needs_space {
                f.write_str(" ")?;
            }
            needs_space = true;
            match tt {
                TokenTree::Leaf(Leaf::Punct(p)) => {
                    needs_space = p.spacing == Spacing::Alone;
                    fmt::Display::fmt(p, f)?;
                }
                tt => fmt::Display::fmt(tt, f)?,
            }
        }
        f.write_str(r)?;
        Ok(())
    }
}

impl fmt::Display for Leaf {
    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
        match self {
            Leaf::Ident(it) => fmt::Display::fmt(it, f),
            Leaf::Literal(it) => fmt::Display::fmt(it, f),
            Leaf::Punct(it) => fmt::Display::fmt(it, f),
        }
    }
}

impl fmt::Display for Ident {
    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
        fmt::Display::fmt(&self.text, f)
    }
}

impl fmt::Display for Literal {
    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
        fmt::Display::fmt(&self.text, f)
    }
}

impl fmt::Display for Punct {
    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
        fmt::Display::fmt(&self.char, f)
    }
}

impl Subtree {
    /// Count the number of tokens recursively
    pub fn count(&self) -> usize {
        let children_count = self
            .token_trees
            .iter()
            .map(|c| match c {
                TokenTree::Subtree(c) => c.count(),
                TokenTree::Leaf(_) => 0,
            })
            .sum::<usize>();

        self.token_trees.len() + children_count
    }

    pub fn delimiter_kind(&self) -> Option<DelimiterKind> {
        self.delimiter.map(|it| it.kind)
    }
}

impl Subtree {
    /// A simple line string used for debugging
    pub fn as_debug_string(&self) -> String {
        let delim = match self.delimiter_kind() {
            Some(DelimiterKind::Brace) => ("{", "}"),
            Some(DelimiterKind::Bracket) => ("[", "]"),
            Some(DelimiterKind::Parenthesis) => ("(", ")"),
            None => (" ", " "),
        };

        let mut res = String::new();
        res.push_str(delim.0);
        let mut last = None;
        for child in &self.token_trees {
            let s = match child {
                TokenTree::Leaf(it) => {
                    let s = match it {
                        Leaf::Literal(it) => it.text.to_string(),
                        Leaf::Punct(it) => it.char.to_string(),
                        Leaf::Ident(it) => it.text.to_string(),
                    };
                    match (it, last) {
                        (Leaf::Ident(_), Some(&TokenTree::Leaf(Leaf::Ident(_)))) => {
                            " ".to_string() + &s
                        }
                        (Leaf::Punct(_), Some(&TokenTree::Leaf(Leaf::Punct(punct)))) => {
                            if punct.spacing == Spacing::Alone {
                                " ".to_string() + &s
                            } else {
                                s
                            }
                        }
                        _ => s,
                    }
                }
                TokenTree::Subtree(it) => it.as_debug_string(),
            };
            res.push_str(&s);
            last = Some(child);
        }

        res.push_str(delim.1);
        res
    }
}

pub mod buffer;

pub fn pretty(tkns: &[TokenTree]) -> String {
    fn tokentree_to_text(tkn: &TokenTree) -> String {
        match tkn {
            TokenTree::Leaf(Leaf::Ident(ident)) => ident.text.clone().into(),
            TokenTree::Leaf(Leaf::Literal(literal)) => literal.text.clone().into(),
            TokenTree::Leaf(Leaf::Punct(punct)) => format!("{}", punct.char),
            TokenTree::Subtree(subtree) => {
                let content = pretty(&subtree.token_trees);
                let (open, close) = match subtree.delimiter.map(|it| it.kind) {
                    None => ("", ""),
                    Some(DelimiterKind::Brace) => ("{", "}"),
                    Some(DelimiterKind::Parenthesis) => ("(", ")"),
                    Some(DelimiterKind::Bracket) => ("[", "]"),
                };
                format!("{}{}{}", open, content, close)
            }
        }
    }

    tkns.iter()
        .fold((String::new(), true), |(last, last_to_joint), tkn| {
            let s = [last, tokentree_to_text(tkn)].join(if last_to_joint { "" } else { " " });
            let mut is_joint = false;
            if let TokenTree::Leaf(Leaf::Punct(punct)) = tkn {
                if punct.spacing == Spacing::Joint {
                    is_joint = true;
                }
            }
            (s, is_joint)
        })
        .0
}