Jump to end char of surrounding pair from any cursor pos (#1121)

* Jump to end char of surrounding pair from any cursor pos

* Separate bracket matching into exact and fuzzy search

* Add constants for bracket chars

* Abort early if char under cursor is not a bracket

* Simplify bracket char validation

* Refactor node search and unify find methods

* Remove bracket constants

1 files changed, 66 insertions, 29 deletions

diff --git a/helix-core/src/match_brackets.rs b/helix-core/src/match_brackets.rs
index 136ce320..cd554005 100644
--- a/helix-core/src/match_brackets.rs
+++ b/helix-core/src/match_brackets.rs
@@ -1,3 +1,5 @@
+use tree_sitter::Node;
+
 use crate::{Rope, Syntax};
 
 const PAIRS: &[(char, char)] = &[
@@ -6,50 +8,85 @@ const PAIRS: &[(char, char)] = &[
     ('[', ']'),
     ('<', '>'),
     ('\'', '\''),
-    ('"', '"'),
+    ('\"', '\"'),
 ];
+
 // limit matching pairs to only ( ) { } [ ] < >
 
+// Returns the position of the matching bracket under cursor.
+//
+// If the cursor is one the opening bracket, the position of
+// the closing bracket is returned. If the cursor in the closing
+// bracket, the position of the opening bracket is returned.
+//
+// If the cursor is not on a bracket, `None` is returned.
+#[must_use]
+pub fn find_matching_bracket(syntax: &Syntax, doc: &Rope, pos: usize) -> Option<usize> {
+    if pos >= doc.len_chars() || !is_valid_bracket(doc.char(pos)) {
+        return None;
+    }
+    find_pair(syntax, doc, pos, false)
+}
+
+// Returns the position of the bracket that is closing the current scope.
+//
+// If the cursor is on an opening or closing bracket, the function
+// behaves equivalent to [`find_matching_bracket`].
+//
+// If the cursor position is within a scope, the function searches
+// for the surrounding scope that is surrounded by brackets and
+// returns the position of the closing bracket for that scope.
+//
+// If no surrounding scope is found, the function returns `None`.
 #[must_use]
-pub fn find(syntax: &Syntax, doc: &Rope, pos: usize) -> Option<usize> {
+pub fn find_matching_bracket_fuzzy(syntax: &Syntax, doc: &Rope, pos: usize) -> Option<usize> {
+    find_pair(syntax, doc, pos, true)
+}
+
+fn find_pair(syntax: &Syntax, doc: &Rope, pos: usize, traverse_parents: bool) -> Option<usize> {
     let tree = syntax.tree();
+    let pos = doc.char_to_byte(pos);
 
-    let byte_pos = doc.char_to_byte(pos);
+    let mut node = tree.root_node().named_descendant_for_byte_range(pos, pos)?;
 
-    // most naive implementation: find the innermost syntax node, if we're at the edge of a node,
-    // return the other edge.
+    loop {
+        let (start_byte, end_byte) = surrounding_bytes(doc, &node)?;
+        let (start_char, end_char) = (doc.byte_to_char(start_byte), doc.byte_to_char(end_byte));
 
-    let node = match tree
-        .root_node()
-        .named_descendant_for_byte_range(byte_pos, byte_pos)
-    {
-        Some(node) => node,
-        None => return None,
-    };
+        if is_valid_pair(doc, start_char, end_char) {
+            if end_byte == pos {
+                return Some(start_char);
+            }
+            // We return the end char if the cursor is either on the start char
+            // or at some arbitrary position between start and end char.
+            return Some(end_char);
+        }
 
-    if node.is_error() {
-        return None;
+        if traverse_parents {
+            node = node.parent()?;
+        } else {
+            return None;
+        }
     }
+}
 
+fn is_valid_bracket(c: char) -> bool {
+    PAIRS.iter().any(|(l, r)| *l == c || *r == c)
+}
+
+fn is_valid_pair(doc: &Rope, start_char: usize, end_char: usize) -> bool {
+    PAIRS.contains(&(doc.char(start_char), doc.char(end_char)))
+}
+
+fn surrounding_bytes(doc: &Rope, node: &Node) -> Option<(usize, usize)> {
     let len = doc.len_bytes();
+
     let start_byte = node.start_byte();
-    let end_byte = node.end_byte().saturating_sub(1); // it's end exclusive
+    let end_byte = node.end_byte().saturating_sub(1);
+
     if start_byte >= len || end_byte >= len {
         return None;
     }
 
-    let start_char = doc.byte_to_char(start_byte);
-    let end_char = doc.byte_to_char(end_byte);
-
-    if PAIRS.contains(&(doc.char(start_char), doc.char(end_char))) {
-        if start_byte == byte_pos {
-            return Some(end_char);
-        }
-
-        if end_byte == byte_pos {
-            return Some(start_char);
-        }
-    }
-
-    None
+    Some((start_byte, end_byte))
 }