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traversal.rs
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traversal.rs
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//! # Traverse Node AST
//!
//! ast-grep supports common tree traversal algorithms, including
//! * Pre order traversal
//! * Post order traversal
//! * Level order traversal
//!
//! Note tree traversal can also be used with Matcher. A traversal with Matcher will
//! produce a [`NodeMatch`] sequence where all items satisfies the Matcher.
//!
//! It is also possible to specify the reentrancy of a traversal.
//! That is, we can control whether a matching node should be visited when it is nested within another match.
//! For example, suppose we want to find all usages of calling `foo` in the source `foo(foo())`.
//! The code has two matching calls and we can configure a traversal
//! to report only the inner one, only the outer one or both.
//!
//! Pre and Post order traversals in this module are implemented using tree-sitter's cursor API without extra heap allocation.
//! It is recommended to use traversal instead of tree recursion to avoid stack overflow and memory overhead.
//! Level order is also included for completeness and should be used sparingly.
use crate::matcher::Matcher;
use crate::{Doc, Node, NodeMatch, Root};
use tree_sitter as ts;
use std::collections::VecDeque;
use std::iter::FusedIterator;
use std::marker::PhantomData;
pub struct Visitor<M, A = PreOrder> {
/// Whether a node will match if it contains or is contained in another match.
reentrant: bool,
/// Whether visit named node only
named_only: bool,
/// optional matcher to filter nodes
matcher: M,
/// The algorithm to traverse the tree, can be pre/post/level order
algorithm: PhantomData<A>,
}
impl<M> Visitor<M> {
pub fn new(matcher: M) -> Visitor<M> {
Visitor {
reentrant: true,
named_only: false,
matcher,
algorithm: PhantomData,
}
}
}
impl<M, A> Visitor<M, A> {
pub fn algorithm<Algo>(self) -> Visitor<M, Algo> {
Visitor {
reentrant: self.reentrant,
named_only: self.named_only,
matcher: self.matcher,
algorithm: PhantomData,
}
}
pub fn reentrant(self, reentrant: bool) -> Self {
Self { reentrant, ..self }
}
pub fn named_only(self, named_only: bool) -> Self {
Self { named_only, ..self }
}
}
impl<M, A> Visitor<M, A>
where
A: Algorithm,
{
pub fn visit<D: Doc>(self, node: Node<D>) -> Visit<'_, D, A::Traversal<'_, D>, M>
where
M: Matcher<D::Lang>,
{
let traversal = A::traverse(node);
Visit {
reentrant: self.reentrant,
named: self.named_only,
matcher: self.matcher,
traversal,
lang: PhantomData,
}
}
}
pub struct Visit<'t, D, T, M> {
reentrant: bool,
named: bool,
matcher: M,
traversal: T,
lang: PhantomData<&'t D>,
}
impl<'t, D, T, M> Visit<'t, D, T, M>
where
D: Doc + 't,
T: Traversal<'t, D>,
M: Matcher<D::Lang>,
{
#[inline]
fn mark_match(&mut self, depth: Option<usize>) {
if !self.reentrant {
self.traversal.calibrate_for_match(depth);
}
}
}
impl<'t, D, T, M> Iterator for Visit<'t, D, T, M>
where
D: Doc + 't,
T: Traversal<'t, D>,
M: Matcher<D::Lang>,
{
type Item = NodeMatch<'t, D>;
fn next(&mut self) -> Option<Self::Item> {
loop {
let match_depth = self.traversal.get_current_depth();
let node = self.traversal.next()?;
let pass_named = !self.named || node.is_named();
if let Some(node_match) = pass_named.then(|| self.matcher.match_node(node)).flatten() {
self.mark_match(Some(match_depth));
return Some(node_match);
} else {
self.mark_match(None);
}
}
}
}
pub trait Algorithm {
type Traversal<'t, D: 't + Doc>: Traversal<'t, D>;
fn traverse<D: Doc>(node: Node<D>) -> Self::Traversal<'_, D>;
}
pub struct PreOrder;
impl Algorithm for PreOrder {
type Traversal<'t, D: 't + Doc> = Pre<'t, D>;
fn traverse<D: Doc>(node: Node<D>) -> Self::Traversal<'_, D> {
Pre::new(&node)
}
}
pub struct PostOrder;
impl Algorithm for PostOrder {
type Traversal<'t, D: 't + Doc> = Post<'t, D>;
fn traverse<D: Doc>(node: Node<D>) -> Self::Traversal<'_, D> {
Post::new(&node)
}
}
/// Traversal can iterate over node by using traversal algorithm.
/// The `next` method should only handle normal, reentrant iteration.
/// If reentrancy is not desired, traversal should mutate cursor in `calibrate_for_match`.
/// Visit will maintain the matched node depth so traversal does not need to use extra field.
pub trait Traversal<'t, D: Doc + 't>: Iterator<Item = Node<'t, D>> {
/// Calibrate cursor position to skip overlapping matches.
/// node depth will be passed if matched, otherwise None.
fn calibrate_for_match(&mut self, depth: Option<usize>);
/// Returns the current depth of cursor depth.
/// Cursor depth is incremented by 1 when moving from parent to child.
/// Cursor depth at Root node is 0.
fn get_current_depth(&self) -> usize;
}
/// Represents a pre-order traversal
pub struct Pre<'tree, D: Doc> {
cursor: ts::TreeCursor<'tree>,
root: &'tree Root<D>,
// record the starting node, if we return back to starting point
// we should terminate the dfs.
start_id: Option<usize>,
current_depth: usize,
}
impl<'tree, D: Doc> Pre<'tree, D> {
pub fn new(node: &Node<'tree, D>) -> Self {
Self {
cursor: node.inner.walk(),
root: node.root,
start_id: Some(node.inner.id()),
current_depth: 0,
}
}
fn step_down(&mut self) -> bool {
if self.cursor.goto_first_child() {
self.current_depth += 1;
true
} else {
false
}
}
// retrace back to ancestors and find next node to explore
fn trace_up(&mut self, start: usize) {
let cursor = &mut self.cursor;
while cursor.node().id() != start {
// try visit sibling nodes
if cursor.goto_next_sibling() {
return;
}
self.current_depth -= 1;
// go back to parent node
if !cursor.goto_parent() {
// it should never fail here. However, tree-sitter has bad parsing bugs
// stop to avoid panic. https://github.com/ast-grep/ast-grep/issues/713
break;
}
}
// terminate traversal here
self.start_id = None;
}
}
/// Amortized time complexity is O(NlgN), depending on branching factor.
impl<'tree, D: Doc> Iterator for Pre<'tree, D> {
type Item = Node<'tree, D>;
// 1. Yield the node itself
// 2. Try visit the child node until no child available
// 3. Try visit next sibling after going back to parent
// 4. Repeat step 3 until returning to the starting node
fn next(&mut self) -> Option<Self::Item> {
// start_id will always be Some until the dfs terminates
let start = self.start_id?;
let cursor = &mut self.cursor;
let inner = cursor.node(); // get current node
let ret = Some(self.root.adopt(inner));
// try going to children first
if self.step_down() {
return ret;
}
// if no child available, go to ancestor nodes
// until we get to the starting point
self.trace_up(start);
ret
}
}
impl<'tree, D: Doc> FusedIterator for Pre<'tree, D> {}
impl<'t, D: Doc> Traversal<'t, D> for Pre<'t, D> {
fn calibrate_for_match(&mut self, depth: Option<usize>) {
// not entering the node, ignore
let Some(depth) = depth else {
return;
};
// if already entering sibling or traced up, ignore
if self.current_depth <= depth {
return;
}
debug_assert!(self.current_depth > depth);
if let Some(start) = self.start_id {
// revert the step down
self.cursor.goto_parent();
self.trace_up(start);
}
}
#[inline]
fn get_current_depth(&self) -> usize {
self.current_depth
}
}
/// Represents a post-order traversal
pub struct Post<'tree, D: Doc> {
cursor: ts::TreeCursor<'tree>,
root: &'tree Root<D>,
start_id: Option<usize>,
current_depth: usize,
match_depth: usize,
}
/// Amortized time complexity is O(NlgN), depending on branching factor.
impl<'tree, D: Doc> Post<'tree, D> {
pub fn new(node: &Node<'tree, D>) -> Self {
let mut ret = Self {
cursor: node.inner.walk(),
root: node.root,
start_id: Some(node.inner.id()),
current_depth: 0,
match_depth: 0,
};
ret.trace_down();
ret
}
fn trace_down(&mut self) {
while self.cursor.goto_first_child() {
self.current_depth += 1;
}
}
fn step_up(&mut self) {
self.current_depth -= 1;
self.cursor.goto_parent();
}
}
/// Amortized time complexity is O(NlgN), depending on branching factor.
impl<'tree, D: Doc> Iterator for Post<'tree, D> {
type Item = Node<'tree, D>;
fn next(&mut self) -> Option<Self::Item> {
// start_id will always be Some until the dfs terminates
let start = self.start_id?;
let cursor = &mut self.cursor;
let node = self.root.adopt(cursor.node());
// return to start
if node.inner.id() == start {
self.start_id = None
} else if cursor.goto_next_sibling() {
// try visit sibling
self.trace_down();
} else {
self.step_up();
}
Some(node)
}
}
impl<'tree, D: Doc> FusedIterator for Post<'tree, D> {}
impl<'t, D: Doc> Traversal<'t, D> for Post<'t, D> {
fn calibrate_for_match(&mut self, depth: Option<usize>) {
if let Some(depth) = depth {
// Later matches' depth should always be greater than former matches.
// because we bump match_depth in `step_up` during traversal.
debug_assert!(depth >= self.match_depth);
self.match_depth = depth;
return;
}
// found new nodes to explore in trace_down, skip calibration.
if self.current_depth >= self.match_depth {
return;
}
let Some(start) = self.start_id else {
return;
};
while self.cursor.node().id() != start {
self.match_depth = self.current_depth;
if self.cursor.goto_next_sibling() {
// try visit sibling
self.trace_down();
return;
}
self.step_up();
}
// terminate because all ancestors are skipped
self.start_id = None;
}
#[inline]
fn get_current_depth(&self) -> usize {
self.current_depth
}
}
/// Represents a level-order traversal.
/// It is implemented with [`VecDeque`] since quadratic backtracking is too time consuming.
/// Though level-order is not used as frequently as other DFS traversals,
/// traversing a big AST with level-order should be done with caution since it might increase the memory usage.
pub struct Level<'tree, D: Doc> {
deque: VecDeque<ts::Node<'tree>>,
cursor: ts::TreeCursor<'tree>,
root: &'tree Root<D>,
}
impl<'tree, D: Doc> Level<'tree, D> {
pub fn new(node: &Node<'tree, D>) -> Self {
let mut deque = VecDeque::new();
deque.push_back(node.inner.clone());
let cursor = node.inner.walk();
Self {
deque,
cursor,
root: node.root,
}
}
}
/// Time complexity is O(N). Space complexity is O(N)
impl<'tree, D: Doc> Iterator for Level<'tree, D> {
type Item = Node<'tree, D>;
fn next(&mut self) -> Option<Self::Item> {
let inner = self.deque.pop_front()?;
let children = inner.children(&mut self.cursor);
self.deque.extend(children);
Some(self.root.adopt(inner))
}
}
impl<'tree, D: Doc> FusedIterator for Level<'tree, D> {}
#[cfg(test)]
mod test {
use super::*;
use crate::language::{Language, Tsx};
use crate::StrDoc;
use std::ops::Range;
// recursive pre order as baseline
fn pre_order(node: Node<StrDoc<Tsx>>) -> Vec<Range<usize>> {
let mut ret = vec![node.range()];
ret.extend(node.children().flat_map(pre_order));
ret
}
// recursion baseline
fn post_order(node: Node<StrDoc<Tsx>>) -> Vec<Range<usize>> {
let mut ret: Vec<_> = node.children().flat_map(post_order).collect();
ret.push(node.range());
ret
}
fn pre_order_equivalent(source: &str) {
let grep = Tsx.ast_grep(source);
let node = grep.root();
let iterative: Vec<_> = Pre::new(&node).map(|n| n.range()).collect();
let recursive = pre_order(node);
assert_eq!(iterative, recursive);
}
fn post_order_equivalent(source: &str) {
let grep = Tsx.ast_grep(source);
let node = grep.root();
let iterative: Vec<_> = Post::new(&node).map(|n| n.range()).collect();
let recursive = post_order(node);
assert_eq!(iterative, recursive);
}
const CASES: &[&str] = &[
"console.log('hello world')",
"let a = (a, b, c)",
"function test() { let a = 1; let b = 2; a === b}",
"[[[[[[]]]]], 1 , 2 ,3]",
"class A { test() { class B {} } }",
];
#[test]
fn tes_pre_order() {
for case in CASES {
pre_order_equivalent(case);
}
}
#[test]
fn test_post_order() {
for case in CASES {
post_order_equivalent(case);
}
}
#[test]
fn test_different_order() {
for case in CASES {
let grep = Tsx.ast_grep(case);
let node = grep.root();
let pre: Vec<_> = Pre::new(&node).map(|n| n.range()).collect();
let post: Vec<_> = Post::new(&node).map(|n| n.range()).collect();
let level: Vec<_> = Level::new(&node).map(|n| n.range()).collect();
assert_ne!(pre, post);
assert_ne!(pre, level);
assert_ne!(post, level);
}
}
#[test]
fn test_fused_traversal() {
for case in CASES {
let grep = Tsx.ast_grep(case);
let node = grep.root();
let mut pre = Pre::new(&node);
let mut post = Post::new(&node);
while pre.next().is_some() {}
while post.next().is_some() {}
assert!(pre.next().is_none());
assert!(pre.next().is_none());
assert!(post.next().is_none());
assert!(post.next().is_none());
}
}
#[test]
fn test_non_root_traverse() {
let grep = Tsx.ast_grep("let a = 123; let b = 123;");
let node = grep.root();
let pre: Vec<_> = Pre::new(&node).map(|n| n.range()).collect();
let post: Vec<_> = Post::new(&node).map(|n| n.range()).collect();
let node2 = node.child(0).unwrap();
let pre2: Vec<_> = Pre::new(&node2).map(|n| n.range()).collect();
let post2: Vec<_> = Post::new(&node2).map(|n| n.range()).collect();
// traversal should stop at node
assert_ne!(pre, pre2);
assert_ne!(post, post2);
// child traversal should be a part of parent traversal
assert!(pre[1..].starts_with(&pre2));
assert!(post.starts_with(&post2));
}
fn pre_order_with_matcher(node: Node<StrDoc<Tsx>>, matcher: &str) -> Vec<Range<usize>> {
if node.matches(matcher) {
vec![node.range()]
} else {
node
.children()
.flat_map(|n| pre_order_with_matcher(n, matcher))
.collect()
}
}
fn post_order_with_matcher(node: Node<StrDoc<Tsx>>, matcher: &str) -> Vec<Range<usize>> {
let mut ret: Vec<_> = node
.children()
.flat_map(|n| post_order_with_matcher(n, matcher))
.collect();
if ret.is_empty() && node.matches(matcher) {
ret.push(node.range());
}
ret
}
const MATCHER_CASES: &[&str] = &[
"Some(123)",
"Some(1, 2, Some(2))",
"NoMatch",
"NoMatch(Some(123))",
"Some(1, Some(2), Some(3))",
"Some(1, Some(2), Some(Some(3)))",
];
#[test]
fn test_pre_order_visitor() {
let matcher = "Some($$$)";
for case in MATCHER_CASES {
let grep = Tsx.ast_grep(case);
let node = grep.root();
let recur = pre_order_with_matcher(grep.root(), matcher);
let visit: Vec<_> = Visitor::new(matcher)
.reentrant(false)
.visit(node)
.map(|n| n.range())
.collect();
assert_eq!(recur, visit);
}
}
#[test]
fn test_post_order_visitor() {
let matcher = "Some($$$)";
for case in MATCHER_CASES {
let grep = Tsx.ast_grep(case);
let node = grep.root();
let recur = post_order_with_matcher(grep.root(), matcher);
let visit: Vec<_> = Visitor::new(matcher)
.algorithm::<PostOrder>()
.reentrant(false)
.visit(node)
.map(|n| n.range())
.collect();
assert_eq!(recur, visit);
}
}
// match a leaf node will trace_up the cursor
#[test]
fn test_traversal_leaf() {
let matcher = "true";
let case = "((((true))));true";
let grep = Tsx.ast_grep(case);
let recur = pre_order_with_matcher(grep.root(), matcher);
let visit: Vec<_> = Visitor::new(matcher)
.reentrant(false)
.visit(grep.root())
.map(|n| n.range())
.collect();
assert_eq!(recur, visit);
let recur = post_order_with_matcher(grep.root(), matcher);
let visit: Vec<_> = Visitor::new(matcher)
.algorithm::<PostOrder>()
.reentrant(false)
.visit(grep.root())
.map(|n| n.range())
.collect();
assert_eq!(recur, visit);
}
}