Add `m` textobject to select closest surround pair

2 files changed, 64 insertions, 1 deletions

diff --git a/helix-core/src/surround.rs b/helix-core/src/surround.rs
index c14456b7..4cba81bf 100644
--- a/helix-core/src/surround.rs
+++ b/helix-core/src/surround.rs
@@ -52,6 +52,45 @@ pub fn get_pair(ch: char) -> (char, char) {
         .unwrap_or((ch, ch))
 }
 
+pub fn find_nth_closest_pairs_pos(
+    text: RopeSlice,
+    range: Range,
+    n: usize,
+) -> Result<(usize, usize)> {
+    let is_open_pair = |ch| PAIRS.iter().any(|(open, _)| *open == ch);
+    let is_close_pair = |ch| PAIRS.iter().any(|(_, close)| *close == ch);
+
+    let mut stack = Vec::with_capacity(2);
+    let pos = range.cursor(text);
+
+    for ch in text.chars_at(pos) {
+        if is_open_pair(ch) {
+            // Track open pairs encountered so that we can step over
+            // the correspoding close pairs that will come up further
+            // down the loop. We want to find a lone close pair whose
+            // open pair is before the cursor position.
+            stack.push(ch);
+            continue;
+        } else if is_close_pair(ch) {
+            let (open, _) = get_pair(ch);
+            if stack.last() == Some(&open) {
+                stack.pop();
+                continue;
+            } else {
+                // In the ideal case the stack would be empty here and the
+                // current character would be the close pair that we are
+                // looking for. It could also be the case that the pairs
+                // are unbalanced and we encounter a close pair that doesn't
+                // close the last seen open pair. In either case use this
+                // char as the auto-detected closest pair.
+                return find_nth_pairs_pos(text, ch, range, n);
+            }
+        }
+    }
+
+    Err(Error::PairNotFound)
+}
+
 /// Find the position of surround pairs of `ch` which can be either a closing
 /// or opening pair. `n` will skip n - 1 pairs (eg. n=2 will discard (only)
 /// the first pair found and keep looking)
diff --git a/helix-core/src/textobject.rs b/helix-core/src/textobject.rs
index ab418792..ee06bf47 100644
--- a/helix-core/src/textobject.rs
+++ b/helix-core/src/textobject.rs
@@ -205,7 +205,31 @@ pub fn textobject_surround(
     ch: char,
     count: usize,
 ) -> Range {
-    surround::find_nth_pairs_pos(slice, ch, range, count)
+    textobject_surround_impl(slice, range, textobject, Some(ch), count)
+}
+
+pub fn textobject_surround_closest(
+    slice: RopeSlice,
+    range: Range,
+    textobject: TextObject,
+    count: usize,
+) -> Range {
+    textobject_surround_impl(slice, range, textobject, None, count)
+}
+
+fn textobject_surround_impl(
+    slice: RopeSlice,
+    range: Range,
+    textobject: TextObject,
+    ch: Option<char>,
+    count: usize,
+) -> Range {
+    let pair_pos = match ch {
+        Some(ch) => surround::find_nth_pairs_pos(slice, ch, range, count),
+        // Automatically find the closest surround pairs
+        None => surround::find_nth_closest_pairs_pos(slice, range, count),
+    };
+    pair_pos
         .map(|(anchor, head)| match textobject {
             TextObject::Inside => Range::new(next_grapheme_boundary(slice, anchor), head),
             TextObject::Around => Range::new(anchor, next_grapheme_boundary(slice, head)),