2 files changed, 431 insertions, 0 deletions

diff --git a/crates/tt/src/buffer.rs b/crates/tt/src/buffer.rs
new file mode 100644
index 000000000..02c771f70
--- /dev/null
+++ b/crates/tt/src/buffer.rs
@@ -0,0 +1,185 @@
+//! FIXME: write short doc here
+
+use crate::{Subtree, TokenTree};
+
+#[derive(Copy, Clone, Debug, Eq, PartialEq)]
+struct EntryId(usize);
+
+#[derive(Copy, Clone, Debug, Eq, PartialEq)]
+struct EntryPtr(EntryId, usize);
+
+/// Internal type which is used instead of `TokenTree` to represent a token tree
+/// within a `TokenBuffer`.
+#[derive(Debug)]
+enum Entry<'t> {
+    // Mimicking types from proc-macro.
+    Subtree(&'t TokenTree, EntryId),
+    Leaf(&'t TokenTree),
+    // End entries contain a pointer to the entry from the containing
+    // token tree, or None if this is the outermost level.
+    End(Option<EntryPtr>),
+}
+
+/// A token tree buffer
+/// The safe version of `syn` [`TokenBuffer`](https://github.com/dtolnay/syn/blob/6533607f91686545cb034d2838beea338d9d0742/src/buffer.rs#L41)
+#[derive(Debug)]
+pub struct TokenBuffer<'t> {
+    buffers: Vec<Box<[Entry<'t>]>>,
+}
+
+impl<'t> TokenBuffer<'t> {
+    pub fn new(tokens: &'t [TokenTree]) -> TokenBuffer<'t> {
+        let mut buffers = vec![];
+
+        let idx = TokenBuffer::new_inner(tokens, &mut buffers, None);
+        assert_eq!(idx, 0);
+
+        TokenBuffer { buffers }
+    }
+
+    fn new_inner(
+        tokens: &'t [TokenTree],
+        buffers: &mut Vec<Box<[Entry<'t>]>>,
+        next: Option<EntryPtr>,
+    ) -> usize {
+        // Must contain everything in tokens and then the Entry::End
+        let start_capacity = tokens.len() + 1;
+        let mut entries = Vec::with_capacity(start_capacity);
+        let mut children = vec![];
+
+        for (idx, tt) in tokens.iter().enumerate() {
+            match tt {
+                TokenTree::Leaf(_) => {
+                    entries.push(Entry::Leaf(tt));
+                }
+                TokenTree::Subtree(subtree) => {
+                    entries.push(Entry::End(None));
+                    children.push((idx, (subtree, tt)));
+                }
+            }
+        }
+
+        entries.push(Entry::End(next));
+        let res = buffers.len();
+        buffers.push(entries.into_boxed_slice());
+
+        for (child_idx, (subtree, tt)) in children {
+            let idx = TokenBuffer::new_inner(
+                &subtree.token_trees,
+                buffers,
+                Some(EntryPtr(EntryId(res), child_idx + 1)),
+            );
+            buffers[res].as_mut()[child_idx] = Entry::Subtree(tt, EntryId(idx));
+        }
+
+        res
+    }
+
+    /// Creates a cursor referencing the first token in the buffer and able to
+    /// traverse until the end of the buffer.
+    pub fn begin(&self) -> Cursor {
+        Cursor::create(self, EntryPtr(EntryId(0), 0))
+    }
+
+    fn entry(&self, ptr: &EntryPtr) -> Option<&Entry> {
+        let id = ptr.0;
+        self.buffers[id.0].get(ptr.1)
+    }
+}
+
+/// A safe version of `Cursor` from `syn` crate https://github.com/dtolnay/syn/blob/6533607f91686545cb034d2838beea338d9d0742/src/buffer.rs#L125
+#[derive(Copy, Clone, Debug)]
+pub struct Cursor<'a> {
+    buffer: &'a TokenBuffer<'a>,
+    ptr: EntryPtr,
+}
+
+impl<'a> PartialEq for Cursor<'a> {
+    fn eq(&self, other: &Cursor) -> bool {
+        self.ptr == other.ptr && std::ptr::eq(self.buffer, other.buffer)
+    }
+}
+
+impl<'a> Eq for Cursor<'a> {}
+
+impl<'a> Cursor<'a> {
+    /// Check whether it is eof
+    pub fn eof(self) -> bool {
+        matches!(self.buffer.entry(&self.ptr), None | Some(Entry::End(None)))
+    }
+
+    /// If the cursor is pointing at the end of a subtree, returns
+    /// the parent subtree
+    pub fn end(self) -> Option<&'a Subtree> {
+        match self.entry() {
+            Some(Entry::End(Some(ptr))) => {
+                let idx = ptr.1;
+                if let Some(Entry::Subtree(TokenTree::Subtree(subtree), _)) =
+                    self.buffer.entry(&EntryPtr(ptr.0, idx - 1))
+                {
+                    return Some(subtree);
+                }
+
+                None
+            }
+            _ => None,
+        }
+    }
+
+    fn entry(self) -> Option<&'a Entry<'a>> {
+        self.buffer.entry(&self.ptr)
+    }
+
+    /// If the cursor is pointing at a `Subtree`, returns
+    /// a cursor into that subtree
+    pub fn subtree(self) -> Option<Cursor<'a>> {
+        match self.entry() {
+            Some(Entry::Subtree(_, entry_id)) => {
+                Some(Cursor::create(self.buffer, EntryPtr(*entry_id, 0)))
+            }
+            _ => None,
+        }
+    }
+
+    /// If the cursor is pointing at a `TokenTree`, returns it
+    pub fn token_tree(self) -> Option<&'a TokenTree> {
+        match self.entry() {
+            Some(Entry::Leaf(tt)) => Some(tt),
+            Some(Entry::Subtree(tt, _)) => Some(tt),
+            Some(Entry::End(_)) => None,
+            None => None,
+        }
+    }
+
+    fn create(buffer: &'a TokenBuffer, ptr: EntryPtr) -> Cursor<'a> {
+        Cursor { buffer, ptr }
+    }
+
+    /// Bump the cursor
+    pub fn bump(self) -> Cursor<'a> {
+        if let Some(Entry::End(exit)) = self.buffer.entry(&self.ptr) {
+            if let Some(exit) = exit {
+                Cursor::create(self.buffer, *exit)
+            } else {
+                self
+            }
+        } else {
+            Cursor::create(self.buffer, EntryPtr(self.ptr.0, self.ptr.1 + 1))
+        }
+    }
+
+    /// Bump the cursor, if it is a subtree, returns
+    /// a cursor into that subtree
+    pub fn bump_subtree(self) -> Cursor<'a> {
+        match self.entry() {
+            Some(Entry::Subtree(_, _)) => self.subtree().unwrap(),
+            _ => self.bump(),
+        }
+    }
+
+    /// Check whether it is a top level
+    pub fn is_root(&self) -> bool {
+        let entry_id = self.ptr.0;
+        entry_id.0 == 0
+    }
+}
diff --git a/crates/tt/src/lib.rs b/crates/tt/src/lib.rs
new file mode 100644
index 000000000..20c3f5eab
--- /dev/null
+++ b/crates/tt/src/lib.rs
@@ -0,0 +1,246 @@
+//! `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`.
+use std::{
+    fmt::{self, Debug},
+    panic::RefUnwindSafe,
+};
+
+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,
+}
+
+fn print_debug_subtree(f: &mut fmt::Formatter<'_>, subtree: &Subtree, level: usize) -> fmt::Result {
+    let align = std::iter::repeat("  ").take(level).collect::<String>();
+
+    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 = std::iter::repeat("  ").take(level).collect::<String>();
+
+    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 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.iter() {
+            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(),
+                _ => 0,
+            })
+            .sum::<usize>();
+
+        self.token_trees.len() + children_count
+    }
+
+    pub fn delimiter_kind(&self) -> Option<DelimiterKind> {
+        self.delimiter.map(|it| it.kind)
+    }
+}
+
+pub mod buffer;
+
+#[derive(Debug, PartialEq, Eq, Clone)]
+pub enum ExpansionError {
+    IOError(String),
+    JsonError(String),
+    Unknown(String),
+    ExpansionError(String),
+}
+
+pub trait TokenExpander: Debug + Send + Sync + RefUnwindSafe {
+    fn expand(&self, subtree: &Subtree, attrs: Option<&Subtree>)
+        -> Result<Subtree, ExpansionError>;
+}