@@ -421,6 +421,8 @@ impl EditorView {
421421 .map(|range| range.cursor_line(text))
422422 .collect();
423423
424+ use std::fmt::Write;
425+
424426 fn diagnostic<'doc>(
425427 doc: &'doc Document,
426428 _view: &View,
@@ -435,18 +437,16 @@ impl EditorView {
435437 let hint = theme.get("hint");
436438 let diagnostics = doc.diagnostics();
437439
438− Box::new(move |line: usize, _selected: bool| {
440+ Box::new(move |line: usize, _selected: bool, out: &mut String| {
439441 use helix_core::diagnostic::Severity;
440442 if let Some(diagnostic) = diagnostics.iter().find(|d| d.line == line) {
441− return Some((
442− "●".to_string(),
443− match diagnostic.severity {
444− Some(Severity::Error) => error,
445− Some(Severity::Warning) | None => warning,
446− Some(Severity::Info) => info,
447− Some(Severity::Hint) => hint,
448− },
449− ));
443+ write!(out, "●").unwrap();
444+ return Some(match diagnostic.severity {
445+ Some(Severity::Error) => error,
446+ Some(Severity::Warning) | None => warning,
447+ Some(Severity::Info) => info,
448+ Some(Severity::Hint) => hint,
449+ });
450450 }
451451 None
452452 })
@@ -475,9 +475,10 @@ impl EditorView {
475475
476476 let config = config.line_number;
477477
478− Box::new(move |line: usize, selected: bool| {
478+ Box::new(move |line: usize, selected: bool, out: &mut String| {
479479 if line == last_line && !draw_last {
480− Some((format!("{:>1$}", '~', width), linenr))
480+ write!(out, "{:>1$}", '~', width).unwrap();
481+ Some(linenr)
481482 } else {
482483 let line = match config {
483484 LineNumber::Absolute => line + 1,
@@ -494,25 +495,38 @@ impl EditorView {
494495 } else {
495496 linenr
496497 };
497− Some((format!("{:>1$}", line, width), style))
498+ write!(out, "{:>1$}", line, width).unwrap();
499+ Some(style)
498500 }
499501 })
500502 }
501503
502− type GutterFn<'doc> = Box<dyn Fn(usize, bool) -> Option<(String, Style)> + 'doc>;
504+ type GutterFn<'doc> = Box<dyn Fn(usize, bool, &mut String) -> Option<Style> + 'doc>;
503505 type Gutter =
504506 for<'doc> fn(&'doc Document, &View, &Theme, &Config, bool, usize) -> GutterFn<'doc>;
505507 let gutters: &[(Gutter, usize)] = &[(diagnostic, 1), (line_number, 5)];
506508
507509 let mut offset = 0;
510+
511+ // avoid lots of small allocations by reusing a text buffer for each line
512+ let mut text = String::with_capacity(8);
513+
508514 for (constructor, width) in gutters {
509515 let gutter = constructor(doc, view, theme, config, is_focused, *width);
516+ text.reserve(*width); // ensure there's enough space for the gutter
510517 for (i, line) in (view.offset.row..(last_line + 1)).enumerate() {
511518 let selected = cursors.contains(&line);
512519
513− if let Some((text, style)) = gutter(line, selected) {
514− surface.set_stringn(viewport.x + offset, viewport.y + i as u16, text, 5, style);
520+ if let Some(style) = gutter(line, selected, &mut text) {
521+ surface.set_stringn(
522+ viewport.x + offset,
523+ viewport.y + i as u16,
524+ &text,
525+ *width,
526+ style,
527+ );
515528 }
529+ text.clear();
516530 }
517531 offset += *width as u16;
518532 }