Replace parents statement stack with a Nodes abstraction (#4233)

crates/ruff_python_semantic/src/node.rs

@@ -0,0 +1,112 @@
+use std::num::{NonZeroU32, TryFromIntError};
+use std::ops::{Index, IndexMut};
+
+use rustc_hash::FxHashMap;
+use rustpython_parser::ast::Stmt;
+
+use ruff_python_ast::types::RefEquality;
+
+/// Id uniquely identifying a statement in a program.
+///
+/// Using a `u32` is sufficient because Ruff only supports parsing documents with a size of max `u32::max`
+/// and it is impossible to have more statements than characters in the file. We use a `NonZeroU32` to
+/// take advantage of memory layout optimizations.
+#[derive(Debug, Copy, Clone, Eq, PartialEq, Hash, Ord, PartialOrd)]
+pub struct NodeId(NonZeroU32);
+
+/// Convert a `usize` to a `NodeId` (by adding 1 to the value, and casting to `NonZeroU32`).
+impl TryFrom<usize> for NodeId {
+    type Error = TryFromIntError;
+
+    fn try_from(value: usize) -> Result<Self, Self::Error> {
+        Ok(Self(NonZeroU32::try_from(u32::try_from(value)? + 1)?))
+    }
+}
+
+/// Convert a `NodeId` to a `usize` (by subtracting 1 from the value, and casting to `usize`).
+impl From<NodeId> for usize {
+    fn from(value: NodeId) -> Self {
+        value.0.get() as usize - 1
+    }
+}
+
+#[derive(Debug)]
+struct Node<'a> {
+    /// The statement this node represents.
+    stmt: &'a Stmt,
+    /// The ID of the parent of this node, if any.
+    parent: Option<NodeId>,
+    /// The depth of this node in the tree.
+    depth: u32,
+}
+
+/// The nodes of a program indexed by [`NodeId`]
+#[derive(Debug, Default)]
+pub struct Nodes<'a> {
+    nodes: Vec<Node<'a>>,
+    node_to_id: FxHashMap<RefEquality<'a, Stmt>, NodeId>,
+}
+
+impl<'a> Nodes<'a> {
+    /// Inserts a new node into the node tree and returns its unique id.
+    ///
+    /// Panics if a node with the same pointer already exists.
+    pub fn insert(&mut self, stmt: &'a Stmt, parent: Option<NodeId>) -> NodeId {
+        let next_id = NodeId::try_from(self.nodes.len()).unwrap();
+        if let Some(existing_id) = self.node_to_id.insert(RefEquality(stmt), next_id) {
+            panic!("Node already exists with id {existing_id:?}");
+        }
+        self.nodes.push(Node {
+            stmt,
+            parent,
+            depth: parent.map_or(0, |parent| self.nodes[usize::from(parent)].depth + 1),
+        });
+        next_id
+    }
+
+    /// Returns the [`NodeId`] of the given node.
+    #[inline]
+    pub fn node_id(&self, node: &'a Stmt) -> Option<NodeId> {
+        self.node_to_id.get(&RefEquality(node)).copied()
+    }
+
+    /// Return the [`NodeId`] of the parent node.
+    #[inline]
+    pub fn parent_id(&self, node_id: NodeId) -> Option<NodeId> {
+        self.nodes[usize::from(node_id)].parent
+    }
+
+    /// Return the depth of the node.
+    #[inline]
+    pub fn depth(&self, node_id: NodeId) -> u32 {
+        self.nodes[usize::from(node_id)].depth
+    }
+
+    /// Returns an iterator over all [`NodeId`] ancestors, starting from the given [`NodeId`].
+    pub fn ancestor_ids(&self, node_id: NodeId) -> impl Iterator<Item = NodeId> + '_ {
+        std::iter::successors(Some(node_id), |&node_id| {
+            self.nodes[usize::from(node_id)].parent
+        })
+    }
+
+    /// Return the parent of the given node.
+    pub fn parent(&self, node: &'a Stmt) -> Option<&'a Stmt> {
+        let node_id = self.node_to_id.get(&RefEquality(node))?;
+        let parent_id = self.nodes[usize::from(*node_id)].parent?;
+        Some(self[parent_id])
+    }
+}
+
+impl<'a> Index<NodeId> for Nodes<'a> {
+    type Output = &'a Stmt;
+
+    fn index(&self, index: NodeId) -> &Self::Output {
+        &self.nodes[usize::from(index)].stmt
+    }
+}
+
+impl<'a> IndexMut<NodeId> for Nodes<'a> {
+    fn index_mut(&mut self, index: NodeId) -> &mut Self::Output {
+        &mut self.nodes[usize::from(index)].stmt
+    }
+}