1 files changed, 129 insertions, 0 deletions

diff --git a/crates/ra_syntax/src/algo/mod.rs b/crates/ra_syntax/src/algo/mod.rs
new file mode 100644
index 000000000..7287f5bb2
--- /dev/null
+++ b/crates/ra_syntax/src/algo/mod.rs
@@ -0,0 +1,129 @@
+pub mod walk;
+pub mod visit;
+
+use {
+    SyntaxNodeRef, TextUnit, TextRange,
+    text_utils::{contains_offset_nonstrict, is_subrange},
+};
+
+pub fn find_leaf_at_offset(node: SyntaxNodeRef, offset: TextUnit) -> LeafAtOffset {
+    let range = node.range();
+    assert!(
+        contains_offset_nonstrict(range, offset),
+        "Bad offset: range {:?} offset {:?}", range, offset
+    );
+    if range.is_empty() {
+        return LeafAtOffset::None;
+    }
+
+    if node.is_leaf() {
+        return LeafAtOffset::Single(node);
+    }
+
+    let mut children = node.children()
+        .filter(|child| {
+            let child_range = child.range();
+            !child_range.is_empty() && contains_offset_nonstrict(child_range, offset)
+        });
+
+    let left = children.next().unwrap();
+    let right = children.next();
+    assert!(children.next().is_none());
+    return if let Some(right) = right {
+        match (find_leaf_at_offset(left, offset), find_leaf_at_offset(right, offset)) {
+            (LeafAtOffset::Single(left), LeafAtOffset::Single(right)) =>
+                LeafAtOffset::Between(left, right),
+            _ => unreachable!()
+        }
+    } else {
+        find_leaf_at_offset(left, offset)
+    };
+}
+
+#[derive(Clone, Copy, Debug)]
+pub enum LeafAtOffset<'a> {
+    None,
+    Single(SyntaxNodeRef<'a>),
+    Between(SyntaxNodeRef<'a>, SyntaxNodeRef<'a>)
+}
+
+impl<'a> LeafAtOffset<'a> {
+    pub fn right_biased(self) -> Option<SyntaxNodeRef<'a>> {
+        match self {
+            LeafAtOffset::None => None,
+            LeafAtOffset::Single(node) => Some(node),
+            LeafAtOffset::Between(_, right) => Some(right)
+        }
+    }
+
+    pub fn left_biased(self) -> Option<SyntaxNodeRef<'a>> {
+        match self {
+            LeafAtOffset::None => None,
+            LeafAtOffset::Single(node) => Some(node),
+            LeafAtOffset::Between(left, _) => Some(left)
+        }
+    }
+}
+
+impl<'f> Iterator for LeafAtOffset<'f> {
+    type Item = SyntaxNodeRef<'f>;
+
+    fn next(&mut self) -> Option<SyntaxNodeRef<'f>> {
+        match *self {
+            LeafAtOffset::None => None,
+            LeafAtOffset::Single(node) => { *self = LeafAtOffset::None; Some(node) }
+            LeafAtOffset::Between(left, right) => { *self = LeafAtOffset::Single(right); Some(left) }
+        }
+    }
+}
+
+pub fn find_covering_node(root: SyntaxNodeRef, range: TextRange) -> SyntaxNodeRef {
+    assert!(is_subrange(root.range(), range));
+    let (left, right) = match (
+        find_leaf_at_offset(root, range.start()).right_biased(),
+        find_leaf_at_offset(root, range.end()).left_biased()
+    ) {
+        (Some(l), Some(r)) => (l, r),
+        _ => return root
+    };
+
+    common_ancestor(left, right)
+}
+
+pub fn ancestors<'a>(node: SyntaxNodeRef<'a>) -> impl Iterator<Item=SyntaxNodeRef<'a>> {
+    generate(Some(node), |&node| node.parent())
+}
+
+#[derive(Debug)]
+pub enum Direction {
+    Forward,
+    Backward,
+}
+
+pub fn siblings<'a>(
+    node: SyntaxNodeRef<'a>,
+    direction: Direction
+) -> impl Iterator<Item=SyntaxNodeRef<'a>> {
+    generate(Some(node), move |&node| match direction {
+        Direction::Forward => node.next_sibling(),
+        Direction::Backward => node.prev_sibling(),
+    })
+}
+
+fn common_ancestor<'a>(n1: SyntaxNodeRef<'a>, n2: SyntaxNodeRef<'a>) -> SyntaxNodeRef<'a> {
+    for p in ancestors(n1) {
+        if ancestors(n2).any(|a| a == p) {
+            return p;
+        }
+    }
+    panic!("Can't find common ancestor of {:?} and {:?}", n1, n2)
+}
+
+pub fn generate<T>(seed: Option<T>, step: impl Fn(&T) -> Option<T>) -> impl Iterator<Item=T> {
+    ::itertools::unfold(seed, move |slot| {
+        slot.take().map(|curr| {
+            *slot = step(&curr);
+            curr
+        })
+    })
+}