Optimize lsp_pos_to_pos (#1423)

lines().count() is slow compared to len_lines()

helix-lsp/src/lib.rs

@@ -66,39 +66,26 @@ pub mod util {
         pos: lsp::Position,
         offset_encoding: OffsetEncoding,
     ) -> Option<usize> {
-        let max_line = doc.lines().count().saturating_sub(1);
         let pos_line = pos.line as usize;
-        let pos_line = if pos_line > max_line {
+        if pos_line > doc.len_lines() - 1 {
             return None;
-        } else {
-            pos_line
-        };
+        }
+
         match offset_encoding {
             OffsetEncoding::Utf8 => {
-                let max_char = doc
-                    .line_to_char(max_line)
-                    .checked_add(doc.line(max_line).len_chars())?;
                 let line = doc.line_to_char(pos_line);
                 let pos = line.checked_add(pos.character as usize)?;
-                if pos <= max_char {
+                if pos <= doc.len_chars() {
                     Some(pos)
                 } else {
                     None
                 }
             }
             OffsetEncoding::Utf16 => {
-                let max_char = doc
-                    .line_to_char(max_line)
-                    .checked_add(doc.line(max_line).len_chars())?;
-                let max_cu = doc.char_to_utf16_cu(max_char);
                 let line = doc.line_to_char(pos_line);
                 let line_start = doc.char_to_utf16_cu(line);
                 let pos = line_start.checked_add(pos.character as usize)?;
-                if pos <= max_cu {
-                    Some(doc.utf16_cu_to_char(pos))
-                } else {
-                    None
-                }
+                doc.try_utf16_cu_to_char(pos).ok()
             }
         }
     }