Minimize allocation when converting table rows to string

helix-term/src/ui/picker.rs

@@ -733,7 +733,11 @@ fn render(&mut self, area: Rect, surface: &mut Surface, cx: &mut Context) {
             .map(|mut row| {
                 const TEMP_CELL_SEP: &str = " ";
 
-                let line = row.cell_text().join(TEMP_CELL_SEP);
+                let line = row.cell_text().fold(String::new(), |mut s, frag| {
+                    s.push_str(&frag);
+                    s.push_str(TEMP_CELL_SEP);
+                    s
+                });
 
                 // Items are filtered by using the text returned by menu::Item::filter_text
                 // but we do highlighting here using the text in Row and therefore there

helix-tui/src/text.rs

@@ -438,17 +438,30 @@ fn from(lines: Vec<Spans<'a>>) -> Text<'a> {
 
 impl<'a> From<Text<'a>> for String {
     fn from(text: Text<'a>) -> String {
-        let lines: Vec<String> = text.lines.iter().map(String::from).collect();
-        lines.join("\n")
+        String::from(&text)
     }
 }
 
 impl<'a> From<&Text<'a>> for String {
     fn from(text: &Text<'a>) -> String {
-        let lines: Vec<String> = text.lines.iter().map(String::from).collect();
-        lines.join("\n")
+        let size = text
+            .lines
+            .iter()
+            .flat_map(|spans| spans.0.iter().map(|span| span.content.len()))
+            .sum::<usize>()
+            + text.lines.len().saturating_sub(1); // for newline after each line
+        let mut output = String::with_capacity(size);
+
+        for spans in &text.lines {
+            for span in &spans.0 {
+                output.push_str(&span.content);
+            }
+            output.push('\n');
+        }
+        output
     }
 }
+
 impl<'a> IntoIterator for Text<'a> {
     type Item = Spans<'a>;
     type IntoIter = std::vec::IntoIter<Self::Item>;

helix-tui/src/widgets/table.rs

@@ -122,11 +122,8 @@ fn total_height(&self) -> u16 {
     }
 
     /// Returns the contents of cells as plain text, without styles and colors.
-    pub fn cell_text(&self) -> Vec<String> {
-        self.cells
-            .iter()
-            .map(|cell| String::from(&cell.content))
-            .collect()
+    pub fn cell_text(&self) -> impl Iterator<Item = String> + '_ {
+        self.cells.iter().map(|cell| String::from(&cell.content))
     }
 }