Optimize rendering by using Ropey::byte_slice

This avoids costly conversions via byte_to_char (which are then
reversed back into bytes internally in Ropey).

Reduces time spent in slice/byte_to_char from ~24% to ~5%.

Cargo.lock

@@ -862,10 +862,10 @@ checksum = "8c31b5c4033f8fdde8700e4657be2c497e7288f01515be52168c631e2e4d4086"
 [[package]]
 name = "ropey"
 version = "1.3.2"
-source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "e6b9aa65bcd9f308d37c7158b4a1afaaa32b8450213e20c9b98e7d5b3cc2fec3"
+source = "git+https://github.com/cessen/ropey#38531e083f8cf5c5b1aeb328361895fb5a9b867c"
 dependencies = [
  "smallvec",
+ "str_indices",
 ]
 
 [[package]]
@@ -1031,6 +1031,12 @@ version = "1.0.5"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "d44a3643b4ff9caf57abcee9c2c621d6c03d9135e0d8b589bd9afb5992cb176a"
 
+[[package]]
+name = "str_indices"
+version = "0.3.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "283baa48c486e4c5e27b4d92c435db9eaceac236a74dab5e3293570e2c3fa4aa"
+
 [[package]]
 name = "syn"
 version = "1.0.88"

helix-core/Cargo.toml

@@ -15,7 +15,8 @@ include = ["src/**/*", "README.md"]
 [dependencies]
 helix-loader = { version = "0.6", path = "../helix-loader" }
 
-ropey = "1.3"
+# ropey = "1.3"
+ropey = { git = "https://github.com/cessen/ropey" }
 smallvec = "1.8"
 smartstring = "1.0.0"
 unicode-segmentation = "1.9"

helix-core/src/graphemes.rs

@@ -333,10 +333,7 @@ impl<'a> Iterator for RopeGraphemes<'a> {
         }
 
         if a < self.cur_chunk_start {
-            let a_char = self.text.byte_to_char(a);
-            let b_char = self.text.byte_to_char(b);
-
-            Some(self.text.slice(a_char..b_char))
+            Some(self.text.byte_slice(a..b))
         } else {
             let a2 = a - self.cur_chunk_start;
             let b2 = b - self.cur_chunk_start;

helix-core/src/syntax.rs

@@ -576,9 +576,7 @@ pub struct Syntax {
 }
 
 fn byte_range_to_str(range: std::ops::Range<usize>, source: RopeSlice) -> Cow<str> {
-    let start_char = source.byte_to_char(range.start);
-    let end_char = source.byte_to_char(range.end);
-    Cow::from(source.slice(start_char..end_char))
+    Cow::from(source.byte_slice(range))
 }
 
 impl Syntax {
@@ -1197,9 +1195,7 @@ impl<'a> TextProvider<'a> for RopeProvider<'a> {
     type I = ChunksBytes<'a>;
 
     fn text(&mut self, node: Node) -> Self::I {
-        let start_char = self.0.byte_to_char(node.start_byte());
-        let end_char = self.0.byte_to_char(node.end_byte());
-        let fragment = self.0.slice(start_char..end_char);
+        let fragment = self.0.byte_slice(node.start_byte()..node.end_byte());
         ChunksBytes {
             chunks: fragment.chunks(),
         }

helix-term/src/ui/editor.rs

@@ -183,6 +183,7 @@ impl EditorView {
                     .highlight_iter(text.slice(..), Some(range), None)
                     .map(|event| event.unwrap())
                     .map(move |event| match event {
+                        // TODO: use byte slices directly
                         // convert byte offsets to char offset
                         HighlightEvent::Source { start, end } => {
                             let start =
@@ -317,6 +318,8 @@ impl EditorView {
         theme: &Theme,
         highlights: H,
     ) {
+        // It's slightly more efficient to produce a full RopeSlice from the Rope, then slice that a bunch
+        // of times than it is to always call Rope::slice/get_slice (it will internally always hit RSEnum::Light).
         let text = doc.text().slice(..);
 
         let mut spans = Vec::new();
@@ -327,10 +330,6 @@ impl EditorView {
 
         let text_style = theme.get("ui.text");
 
-        // It's slightly more efficient to produce a full RopeSlice from the Rope, then slice that a bunch
-        // of times than it is to always call Rope::slice/get_slice (it will internally always hit RSEnum::Light).
-        let text = text.slice(..);
-
         'outer: for event in highlights {
             match event {
                 HighlightEvent::HighlightStart(span) => {