From b351dbbcbb199cf1b6135130e679a83198b23a29 Mon Sep 17 00:00:00 2001
From: mars <mars@tebibyte.media>
Date: Wed, 12 Apr 2023 18:24:06 -0400
Subject: [PATCH] Faster syntax highlighting with a style stack

---
 src/buffer.rs | 31 +++++++++++++++++++------------
 1 file changed, 19 insertions(+), 12 deletions(-)

diff --git a/src/buffer.rs b/src/buffer.rs
index 4e94f65..95926ab 100644
--- a/src/buffer.rs
+++ b/src/buffer.rs
@@ -25,7 +25,7 @@ use crossterm::{cursor, ExecutableCommand, QueueableCommand};
 use parking_lot::Mutex;
 use ropey::Rope;
 use syntect::easy::ScopeRangeIterator;
-use syntect::parsing::{ParseState, Scope, ScopeStack, SyntaxSet};
+use syntect::parsing::{BasicScopeStackOp, ParseState, Scope, ScopeStack, SyntaxSet};
 
 use crate::theme::{Style, StyleStore};
 use crate::{Cursor, Direction};
@@ -150,6 +150,8 @@ impl Buffer {
         let mut parser = self.parser.clone();
         let mut line_buf = String::new();
         let mut stack = ScopeStack::new();
+        let mut style_stack = Vec::<Style>::new();
+        let mut styled_buf = Vec::new();
         for line in self.text.lines() {
             // display line to a pre-allocated buffer for fast parsing
             line_buf.clear();
@@ -161,26 +163,31 @@ impl Buffer {
             let stack_ops = parser.parse_line(&line_buf, &self.syntax_set).unwrap();
 
             // queue the operations on the stack
-            let mut line = Vec::new();
             let range_iter = ScopeRangeIterator::new(&stack_ops, &line_buf);
+            styled_buf.clear();
             for (range, op) in range_iter {
-                stack.apply(&op).unwrap();
+                stack
+                    .apply_with_hook(&op, |op, _scopes| match op {
+                        BasicScopeStackOp::Push(scope) => {
+                            let scope = scope.build_string();
+                            let style = styles.get_scope(&scope);
+                            style_stack.push(style);
+                        }
+                        BasicScopeStackOp::Pop => {
+                            style_stack.pop();
+                        }
+                    })
+                    .unwrap();
 
                 if range.start == range.end {
                     continue;
                 }
 
-                let mut style = Style::default();
-                for scope in stack.scopes.clone() {
-                    // TODO docs say that build_string "shouldn't be done frequently"
-                    let scope = scope.build_string();
-                    style.apply(&styles.get_scope(&scope));
-                }
-
-                line.push((style, range));
+                let style = style_stack.last().cloned().unwrap_or_default();
+                styled_buf.push((style, range));
             }
 
-            self.styled.push(line);
+            self.styled.push(styled_buf.clone());
         }
 
         self.style_dirty = false;