rowan/
ast.rs

1//! Working with abstract syntax trees.
2//!
3//! In rowan, syntax trees are transient objects. That means that we create
4//! trees when we need them, and tear them down to save memory. In this
5//! architecture, hanging on to a particular syntax node for a long time is
6//! ill-advisable, as that keeps the whole tree resident.
7//!
8//! Instead, we provide a [`SyntaxNodePtr`] type, which stores information about
9//! the _location_ of a particular syntax node in a tree. It's a small type
10//! which can be cheaply stored, and which can be resolved to a real
11//! [`SyntaxNode`] when necessary.
12//!
13//! We also provide an [`AstNode`] trait for typed AST wrapper APIs over rowan
14//! nodes.
15
16use std::{
17    fmt,
18    hash::{Hash, Hasher},
19    iter::successors,
20    marker::PhantomData,
21};
22
23use crate::{Language, SyntaxNode, SyntaxNodeChildren, TextRange};
24
25/// The main trait to go from untyped [`SyntaxNode`] to a typed AST. The
26/// conversion itself has zero runtime cost: AST and syntax nodes have exactly
27/// the same representation: a pointer to the tree root and a pointer to the
28/// node itself.
29pub trait AstNode {
30    type Language: Language;
31
32    fn can_cast(kind: <Self::Language as Language>::Kind) -> bool
33    where
34        Self: Sized;
35
36    fn cast(node: SyntaxNode<Self::Language>) -> Option<Self>
37    where
38        Self: Sized;
39
40    fn syntax(&self) -> &SyntaxNode<Self::Language>;
41
42    fn clone_for_update(&self) -> Self
43    where
44        Self: Sized,
45    {
46        Self::cast(self.syntax().clone_for_update()).unwrap()
47    }
48
49    fn clone_subtree(&self) -> Self
50    where
51        Self: Sized,
52    {
53        Self::cast(self.syntax().clone_subtree()).unwrap()
54    }
55}
56
57/// A "pointer" to a [`SyntaxNode`], via location in the source code.
58///
59/// ## Note
60/// Since the location is source code dependent, this must not be used
61/// with mutable syntax trees. Any changes made in such trees causes
62/// the pointed node's source location to change, invalidating the pointer.
63#[derive(Debug, Copy, Clone, PartialEq, Eq, Hash)]
64pub struct SyntaxNodePtr<L: Language> {
65    kind: L::Kind,
66    range: TextRange,
67}
68
69impl<L: Language> SyntaxNodePtr<L> {
70    /// Returns a [`SyntaxNodePtr`] for the node.
71    ///
72    /// Panics if the provided node is mutable
73    pub fn new(node: &SyntaxNode<L>) -> Self {
74        assert!(!node.is_mutable(), "tree is mutable");
75        Self { kind: node.kind(), range: node.text_range() }
76    }
77
78    /// Like [`Self::try_to_node`] but panics instead of returning `None` on
79    /// failure.
80    pub fn to_node(&self, root: &SyntaxNode<L>) -> SyntaxNode<L> {
81        self.try_to_node(root).unwrap_or_else(|| panic!("can't resolve {self:?} with {root:?}"))
82    }
83
84    /// "Dereferences" the pointer to get the [`SyntaxNode`] it points to.
85    ///
86    /// Returns `None` if the node is not found, so make sure that the `root`
87    /// syntax tree is equivalent to (i.e. is build from the same text from) the
88    /// tree which was originally used to get this [`SyntaxNodePtr`].
89    ///
90    /// Also returns `None` if `root` is not actually a root (i.e. it has a
91    /// parent).
92    ///
93    /// NOTE: If this function is called on a mutable tree, it will panic
94    ///
95    /// The complexity is linear in the depth of the tree and logarithmic in
96    /// tree width. As most trees are shallow, thinking about this as
97    /// `O(log(N))` in the size of the tree is not too wrong!
98    pub fn try_to_node(&self, root: &SyntaxNode<L>) -> Option<SyntaxNode<L>> {
99        assert!(!root.is_mutable(), "tree is mutable");
100        if root.parent().is_some() {
101            return None;
102        }
103        successors(Some(root.clone()), |node| node.child_or_token_at_range(self.range)?.into_node())
104            .find(|it| it.text_range() == self.range && it.kind() == self.kind)
105    }
106
107    /// Casts this to an [`AstPtr`] to the given node type if possible.
108    pub fn cast<N: AstNode<Language = L>>(self) -> Option<AstPtr<N>> {
109        if !N::can_cast(self.kind) {
110            return None;
111        }
112        Some(AstPtr { raw: self })
113    }
114
115    /// Returns the kind of the syntax node this points to.
116    pub fn kind(&self) -> L::Kind {
117        self.kind
118    }
119
120    /// Returns the range of the syntax node this points to.
121    pub fn text_range(&self) -> TextRange {
122        self.range
123    }
124}
125
126/// Like [`SyntaxNodePtr`], but remembers the type of node.
127///
128/// ## Note
129/// As with [`SyntaxNodePtr`], this must not be used on mutable
130/// syntax trees, since any mutation can cause the pointed node's
131/// source location to change, invalidating the pointer
132pub struct AstPtr<N: AstNode> {
133    raw: SyntaxNodePtr<N::Language>,
134}
135
136impl<N: AstNode> AstPtr<N> {
137    /// Returns an [`AstPtr`] for the node.
138    ///
139    /// Panics if the provided node is mutable
140    pub fn new(node: &N) -> Self {
141        // The above mentioned panic is handled by SyntaxNodePtr
142        Self { raw: SyntaxNodePtr::new(node.syntax()) }
143    }
144
145    /// Like `Self::try_to_node` but panics on failure.
146    pub fn to_node(&self, root: &SyntaxNode<N::Language>) -> N {
147        self.try_to_node(root).unwrap_or_else(|| panic!("can't resolve {self:?} with {root:?}"))
148    }
149
150    /// Given the root node containing the node `n` that `self` is a pointer to,
151    /// returns `n` if possible. Panics if `root` is mutable. See [`SyntaxNodePtr::try_to_node`].
152    pub fn try_to_node(&self, root: &SyntaxNode<N::Language>) -> Option<N> {
153        // The above mentioned panic is handled by SyntaxNodePtr
154        N::cast(self.raw.try_to_node(root)?)
155    }
156
157    /// Returns the underlying [`SyntaxNodePtr`].
158    pub fn syntax_node_ptr(&self) -> SyntaxNodePtr<N::Language> {
159        self.raw.clone()
160    }
161
162    /// Casts this to an [`AstPtr`] to the given node type if possible.
163    pub fn cast<U: AstNode<Language = N::Language>>(self) -> Option<AstPtr<U>> {
164        if !U::can_cast(self.raw.kind) {
165            return None;
166        }
167        Some(AstPtr { raw: self.raw })
168    }
169}
170
171impl<N: AstNode> fmt::Debug for AstPtr<N> {
172    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
173        f.debug_struct("AstPtr").field("raw", &self.raw).finish()
174    }
175}
176
177impl<N: AstNode> Clone for AstPtr<N> {
178    fn clone(&self) -> Self {
179        Self { raw: self.raw.clone() }
180    }
181}
182
183impl<N: AstNode> PartialEq for AstPtr<N> {
184    fn eq(&self, other: &AstPtr<N>) -> bool {
185        self.raw == other.raw
186    }
187}
188
189impl<N: AstNode> Eq for AstPtr<N> {}
190
191impl<N: AstNode> Hash for AstPtr<N> {
192    fn hash<H: Hasher>(&self, state: &mut H) {
193        self.raw.hash(state)
194    }
195}
196
197impl<N: AstNode> From<AstPtr<N>> for SyntaxNodePtr<N::Language> {
198    fn from(ptr: AstPtr<N>) -> SyntaxNodePtr<N::Language> {
199        ptr.raw
200    }
201}
202
203#[derive(Debug, Clone)]
204pub struct AstChildren<N: AstNode> {
205    inner: SyntaxNodeChildren<N::Language>,
206    ph: PhantomData<N>,
207}
208
209impl<N: AstNode> AstChildren<N> {
210    fn new(parent: &SyntaxNode<N::Language>) -> Self {
211        AstChildren { inner: parent.children(), ph: PhantomData }
212    }
213}
214
215impl<N: AstNode> Iterator for AstChildren<N> {
216    type Item = N;
217    fn next(&mut self) -> Option<N> {
218        self.inner.find_map(N::cast)
219    }
220}
221
222pub mod support {
223    use super::{AstChildren, AstNode};
224    use crate::{Language, SyntaxNode, SyntaxToken};
225
226    pub fn child<N: AstNode>(parent: &SyntaxNode<N::Language>) -> Option<N> {
227        parent.children().find_map(N::cast)
228    }
229
230    pub fn children<N: AstNode>(parent: &SyntaxNode<N::Language>) -> AstChildren<N> {
231        AstChildren::new(parent)
232    }
233
234    pub fn token<L: Language>(parent: &SyntaxNode<L>, kind: L::Kind) -> Option<SyntaxToken<L>> {
235        parent.children_with_tokens().filter_map(|it| it.into_token()).find(|it| it.kind() == kind)
236    }
237}
238
239#[cfg(test)]
240mod tests {
241    use crate::{GreenNodeBuilder, Language, SyntaxKind, SyntaxNode};
242
243    use super::SyntaxNodePtr;
244
245    #[derive(Debug, Clone, Copy, PartialEq, Eq, PartialOrd, Ord, Hash)]
246    struct TestLanguage;
247    impl Language for TestLanguage {
248        type Kind = SyntaxKind;
249
250        fn kind_from_raw(raw: SyntaxKind) -> Self::Kind {
251            raw
252        }
253
254        fn kind_to_raw(kind: Self::Kind) -> SyntaxKind {
255            kind
256        }
257    }
258
259    fn build_immut_tree() -> SyntaxNode<TestLanguage> {
260        // Creates a single-node tree
261        let mut builder = GreenNodeBuilder::new();
262        builder.start_node(SyntaxKind(0));
263        builder.finish_node();
264
265        SyntaxNode::<TestLanguage>::new_root(builder.finish())
266    }
267
268    #[test]
269    #[should_panic = "tree is mutable"]
270    fn ensure_mut_panic_on_create() {
271        // Make a mutable version
272        let tree = build_immut_tree().clone_for_update();
273
274        SyntaxNodePtr::new(&tree);
275    }
276
277    #[test]
278    #[should_panic = "tree is mutable"]
279    fn ensure_mut_panic_on_deref() {
280        let tree = build_immut_tree();
281        let tree_mut = tree.clone_for_update();
282
283        // Create on immutable, convert on mutable
284        let syn_ptr = SyntaxNodePtr::new(&tree);
285        syn_ptr.to_node(&tree_mut);
286    }
287}
rowan/ast.rs

rowan/
ast.rs
