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//! 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
}
}
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