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|
//! This module provides a way to construct a `File`.
//! It is intended to be completely decoupled from the
//! parser, so as to allow to evolve the tree representation
//! and the parser algorithm independently.
//!
//! The `Sink` trait is the bridge between the parser and the
//! tree builder: the parser produces a stream of events like
//! `start node`, `finish node`, and `FileBuilder` converts
//! this stream to a real tree.
use {
lexer::Token,
SyntaxKind::{self, TOMBSTONE},
TextUnit,
};
pub(crate) trait Sink {
type Tree;
fn new(text: String) -> Self;
fn leaf(&mut self, kind: SyntaxKind, len: TextUnit);
fn start_internal(&mut self, kind: SyntaxKind);
fn finish_internal(&mut self);
fn error(&mut self, err: String);
fn finish(self) -> Self::Tree;
}
/// `Parser` produces a flat list of `Event`s.
/// They are converted to a tree-structure in
/// a separate pass, via `TreeBuilder`.
#[derive(Debug)]
pub(crate) enum Event {
/// This event signifies the start of the node.
/// It should be either abandoned (in which case the
/// `kind` is `TOMBSTONE`, and the event is ignored),
/// or completed via a `Finish` event.
///
/// All tokens between a `Start` and a `Finish` would
/// become the children of the respective node.
///
/// For left-recursive syntactic constructs, the parser produces
/// a child node before it sees a parent. `forward_parent`
/// exists to allow to tweak parent-child relationships.
///
/// Consider this path
///
/// foo::bar
///
/// The events for it would look like this:
///
///
/// START(PATH) IDENT('foo') FINISH START(PATH) COLONCOLON IDENT('bar') FINISH
/// | /\
/// | |
/// +------forward-parent------+
///
/// And the tree would look like this
///
/// +--PATH---------+
/// | | |
/// | | |
/// | '::' 'bar'
/// |
/// PATH
/// |
/// 'foo'
///
/// See also `CompletedMarker::precede`.
Start {
kind: SyntaxKind,
forward_parent: Option<u32>,
},
/// Complete the previous `Start` event
Finish,
/// Produce a single leaf-element.
/// `n_raw_tokens` is used to glue complex contextual tokens.
/// For example, lexer tokenizes `>>` as `>`, `>`, and
/// `n_raw_tokens = 2` is used to produced a single `>>`.
Token {
kind: SyntaxKind,
n_raw_tokens: u8,
},
Error {
msg: String,
},
}
pub(super) fn process(builder: &mut impl Sink, tokens: &[Token], events: Vec<Event>) {
let mut idx = 0;
let mut holes = Vec::new();
let mut forward_parents = Vec::new();
for (i, event) in events.iter().enumerate() {
if holes.last() == Some(&i) {
holes.pop();
continue;
}
match event {
&Event::Start {
kind: TOMBSTONE, ..
} => (),
&Event::Start { .. } => {
forward_parents.clear();
let mut idx = i;
loop {
let (kind, fwd) = match events[idx] {
Event::Start {
kind,
forward_parent,
} => (kind, forward_parent),
_ => unreachable!(),
};
forward_parents.push((idx, kind));
if let Some(fwd) = fwd {
idx += fwd as usize;
} else {
break;
}
}
for &(idx, kind) in forward_parents.iter().into_iter().rev() {
builder.start_internal(kind);
holes.push(idx);
}
holes.pop();
}
&Event::Finish => {
while idx < tokens.len() {
let token = tokens[idx];
if token.kind.is_trivia() {
idx += 1;
builder.leaf(token.kind, token.len);
} else {
break;
}
}
builder.finish_internal()
}
&Event::Token {
kind,
mut n_raw_tokens,
} => {
// FIXME: currently, we attach whitespace to some random node
// this should be done in a sensible manner instead
loop {
let token = tokens[idx];
if !token.kind.is_trivia() {
break;
}
builder.leaf(token.kind, token.len);
idx += 1
}
let mut len = 0.into();
for _ in 0..n_raw_tokens {
len += tokens[idx].len;
idx += 1;
}
builder.leaf(kind, len);
}
&Event::Error { ref msg } => builder.error(msg.clone()),
}
}
}
|
