From 73c92a0bc1499f02092a7425c45d4992f4e573a1 Mon Sep 17 00:00:00 2001
From: Blaž Hrastnik
Date: Mon, 22 Mar 2021 17:58:49 +0900
Subject: Implement m / match_brackets (using tree sitter).

---
 helix-core/src/auto_pairs.rs     |  2 ++
 helix-core/src/lib.rs            |  1 +
 helix-core/src/match_brackets.rs | 34 ++++++++++++++++++++++++++++++++++
 helix-term/src/commands.rs       | 14 +++++++++++++-
 helix-term/src/keymap.rs         |  3 +++
 5 files changed, 53 insertions(+), 1 deletion(-)
 create mode 100644 helix-core/src/match_brackets.rs

diff --git a/helix-core/src/auto_pairs.rs b/helix-core/src/auto_pairs.rs
index 52a45075..e6b8f667 100644
--- a/helix-core/src/auto_pairs.rs
+++ b/helix-core/src/auto_pairs.rs
@@ -1,6 +1,8 @@
 use crate::{Range, Rope, Selection, Tendril, Transaction};
 use smallvec::SmallVec;
 
+// Heavily based on https://github.com/codemirror/closebrackets/
+
 const PAIRS: &[(char, char)] = &[
     ('(', ')'),
     ('{', '}'),
diff --git a/helix-core/src/lib.rs b/helix-core/src/lib.rs
index a8a449ca..30b3d37f 100644
--- a/helix-core/src/lib.rs
+++ b/helix-core/src/lib.rs
@@ -6,6 +6,7 @@ pub mod graphemes;
 mod history;
 pub mod indent;
 pub mod macros;
+pub mod match_brackets;
 pub mod movement;
 pub mod object;
 mod position;
diff --git a/helix-core/src/match_brackets.rs b/helix-core/src/match_brackets.rs
new file mode 100644
index 00000000..bacd764f
--- /dev/null
+++ b/helix-core/src/match_brackets.rs
@@ -0,0 +1,34 @@
+use crate::{Range, Rope, Selection, Syntax};
+
+// const PAIRS: &[(char, char)] = &[('(', ')'), ('{', '}'), ('[', ']')];
+// limit matching pairs to only ( ) { } [ ] < >
+
+pub fn find(syntax: &Syntax, doc: &Rope, pos: usize) -> Option<usize> {
+    let tree = syntax.root_layer.tree.as_ref().unwrap();
+
+    let byte_pos = doc.char_to_byte(pos);
+
+    // most naive implementation: find the innermost syntax node, if we're at the edge of a node,
+    // return the other edge.
+
+    let mut node = match tree
+        .root_node()
+        .named_descendant_for_byte_range(byte_pos, byte_pos)
+    {
+        Some(node) => node,
+        None => return None,
+    };
+
+    let start_byte = node.start_byte();
+    let end_byte = node.end_byte() - 1; // it's end exclusive
+
+    if start_byte == byte_pos {
+        return Some(doc.byte_to_char(end_byte));
+    }
+
+    if end_byte == byte_pos {
+        return Some(doc.byte_to_char(start_byte));
+    }
+
+    None
+}
diff --git a/helix-term/src/commands.rs b/helix-term/src/commands.rs
index b9ee933d..3f0e32a0 100644
--- a/helix-term/src/commands.rs
+++ b/helix-term/src/commands.rs
@@ -1,5 +1,5 @@
 use helix_core::{
-    comment, coords_at_pos, graphemes,
+    comment, coords_at_pos, graphemes, match_brackets,
     movement::{self, Direction},
     object, pos_at_coords,
     regex::{self, Regex},
@@ -1592,3 +1592,15 @@ pub fn expand_selection(cx: &mut Context) {
         doc.set_selection(selection);
     }
 }
+
+pub fn match_brackets(cx: &mut Context) {
+    let mut doc = cx.doc();
+
+    if let Some(syntax) = doc.syntax() {
+        let pos = doc.selection().cursor();
+        if let Some(pos) = match_brackets::find(syntax, doc.text(), pos) {
+            let selection = Selection::point(pos);
+            doc.set_selection(selection);
+        };
+    }
+}
diff --git a/helix-term/src/keymap.rs b/helix-term/src/keymap.rs
index 1f34aa9e..bd1b31ef 100644
--- a/helix-term/src/keymap.rs
+++ b/helix-term/src/keymap.rs
@@ -182,6 +182,9 @@ pub fn default() -> Keymaps {
         // or select mode X?
         // extend_to_whole_line, crop_to_whole_line
 
+
+        key!('m') => commands::match_brackets,
+        // TODO: refactor into
         // key!('m') => commands::select_to_matching,
         // key!('M') => commands::back_select_to_matching,
         // select mode extend equivalents
-- 
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