Avoid cloning Rows during Galley::concat (#7649)

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Moves `ends_with_newline` into `PlacedRow` to avoid clones during
layout.
I don't think there was a rationale stronger than "don't change too
much" for not doing this in #5411, so
I should've just done this from the start.
This was a significant part of the profile for text layout (as it cloned
almost every `Row`, even though it only needed to change a single
boolean).

Before:
<img width="757" height="250" alt="image"
src="https://github.com/user-attachments/assets/d1c2afd1-f1ec-4cf5-9d05-f5a5a78052df"
/>

After:
<img width="615" height="249" alt="image"
src="https://github.com/user-attachments/assets/c70966da-c892-4e84-adba-494d0f37f263"
/>

(note that these profiles focus solely on the top-level
`Galley::layout_inline` subtree, also don't compare sample count as the
duration of these tests was completely arbitrary)

egui_demo_lib `*text_layout*` benches:
<img width="791" height="461" alt="image"
src="https://github.com/user-attachments/assets/4f97ce84-2768-4876-9488-d42f8f358ed1"
/>

* [X] I have followed the instructions in the PR template

(As usual, the tests fail for me even on master but the failures on
master and with these changes seem the same :))

Author: afishhh

crates/egui/src/text_selection/visuals.rs

@@ -31,7 +31,8 @@ pub fn paint_text_selection(
     let max = galley.layout_from_cursor(max);
 
     for ri in min.row..=max.row {
-        let row = Arc::make_mut(&mut galley.rows[ri].row);
+        let placed_row = &mut galley.rows[ri];
+        let row = Arc::make_mut(&mut placed_row.row);
 
         let left = if ri == min.row {
             row.x_offset(min.column)
@@ -41,7 +42,7 @@ pub fn paint_text_selection(
         let right = if ri == max.row {
             row.x_offset(max.column)
         } else {
-            let newline_size = if row.ends_with_newline {
+            let newline_size = if placed_row.ends_with_newline {
                 row.height() / 2.0 // visualize that we select the newline
             } else {
                 0.0

crates/epaint/src/shapes/text_shape.rs

@@ -137,15 +137,19 @@ impl TextShape {
         *mesh_bounds = transform.scaling * *mesh_bounds;
         *intrinsic_size = transform.scaling * *intrinsic_size;
 
-        for text::PlacedRow { pos, row } in rows {
+        for text::PlacedRow {
+            pos,
+            row,
+            ends_with_newline: _,
+        } in rows
+        {
             *pos *= transform.scaling;
 
             let text::Row {
                 section_index_at_start: _,
                 glyphs: _, // TODO(emilk): would it make sense to transform these?
                 size,
                 visuals,
-                ends_with_newline: _,
             } = Arc::make_mut(row);
 
             *size *= transform.scaling;

crates/epaint/src/text/text_layout.rs

@@ -296,8 +296,8 @@ fn rows_from_paragraphs(
                     glyphs: vec![],
                     visuals: Default::default(),
                     size: vec2(0.0, paragraph.empty_paragraph_height),
-                    ends_with_newline: !is_last_paragraph,
                 }),
+                ends_with_newline: !is_last_paragraph,
             });
         } else {
             let paragraph_max_x = paragraph.glyphs.last().unwrap().max_x();
@@ -310,14 +310,13 @@ fn rows_from_paragraphs(
                         glyphs: paragraph.glyphs,
                         visuals: Default::default(),
                         size: vec2(paragraph_max_x, 0.0),
-                        ends_with_newline: !is_last_paragraph,
                     }),
+                    ends_with_newline: !is_last_paragraph,
                 });
             } else {
                 line_break(&paragraph, job, &mut rows, elided);
                 let placed_row = rows.last_mut().unwrap();
-                let row = Arc::make_mut(&mut placed_row.row);
-                row.ends_with_newline = !is_last_paragraph;
+                placed_row.ends_with_newline = !is_last_paragraph;
             }
         }
     }
@@ -363,8 +362,8 @@ fn line_break(
                         glyphs: vec![],
                         visuals: Default::default(),
                         size: Vec2::ZERO,
-                        ends_with_newline: false,
                     }),
+                    ends_with_newline: false,
                 });
                 row_start_x += first_row_indentation;
                 first_row_indentation = 0.0;
@@ -389,8 +388,8 @@ fn line_break(
                         glyphs,
                         visuals: Default::default(),
                         size: vec2(paragraph_max_x, 0.0),
-                        ends_with_newline: false,
                     }),
+                    ends_with_newline: false,
                 });
 
                 // Start a new row:
@@ -431,8 +430,8 @@ fn line_break(
                     glyphs,
                     visuals: Default::default(),
                     size: vec2(paragraph_max_x - paragraph_min_x, 0.0),
-                    ends_with_newline: false,
                 }),
+                ends_with_newline: false,
             });
         }
     }

crates/epaint/src/text/text_layout_types.rs

@@ -572,6 +572,13 @@ pub struct PlacedRow {
 
     /// The underlying unpositioned [`Row`].
     pub row: Arc<Row>,
+
+    /// If true, this [`PlacedRow`] came from a paragraph ending with a `\n`.
+    /// The `\n` itself is omitted from row's [`Row::glyphs`].
+    /// A `\n` in the input text always creates a new [`PlacedRow`] below it,
+    /// so that text that ends with `\n` has an empty [`PlacedRow`] last.
+    /// This also implies that the last [`PlacedRow`] in a [`Galley`] always has `ends_with_newline == false`.
+    pub ends_with_newline: bool,
 }
 
 impl PlacedRow {
@@ -617,13 +624,6 @@ pub struct Row {
 
     /// The mesh, ready to be rendered.
     pub visuals: RowVisuals,
-
-    /// If true, this [`Row`] came from a paragraph ending with a `\n`.
-    /// The `\n` itself is omitted from [`Self::glyphs`].
-    /// A `\n` in the input text always creates a new [`Row`] below it,
-    /// so that text that ends with `\n` has an empty [`Row`] last.
-    /// This also implies that the last [`Row`] in a [`Galley`] always has `ends_with_newline == false`.
-    pub ends_with_newline: bool,
 }
 
 /// The tessellated output of a row.
@@ -735,12 +735,6 @@ impl Row {
         self.glyphs.len()
     }
 
-    /// Includes the implicit `\n` after the [`Row`], if any.
-    #[inline]
-    pub fn char_count_including_newline(&self) -> usize {
-        self.glyphs.len() + (self.ends_with_newline as usize)
-    }
-
     /// Closest char at the desired x coordinate in row-relative coordinates.
     /// Returns something in the range `[0, char_count_excluding_newline()]`.
     pub fn char_at(&self, desired_x: f32) -> usize {
@@ -776,6 +770,12 @@ impl PlacedRow {
     pub fn max_y(&self) -> f32 {
         self.rect().bottom()
     }
+
+    /// Includes the implicit `\n` after the [`PlacedRow`], if any.
+    #[inline]
+    pub fn char_count_including_newline(&self) -> usize {
+        self.row.glyphs.len() + (self.ends_with_newline as usize)
+    }
 }
 
 impl Galley {
@@ -867,13 +867,15 @@ impl Galley {
                         placed_row.visuals.mesh_bounds.translate(new_pos.to_vec2());
                     merged_galley.rect |= Rect::from_min_size(new_pos, placed_row.size);
 
-                    let mut row = placed_row.row.clone();
+                    let mut ends_with_newline = placed_row.ends_with_newline;
                     let is_last_row_in_galley = row_idx + 1 == galley.rows.len();
-                    if !is_last_galley && is_last_row_in_galley {
-                        // Since we remove the `\n` when splitting rows, we need to add it back here
-                        Arc::make_mut(&mut row).ends_with_newline = true;
+                    // Since we remove the `\n` when splitting rows, we need to add it back here
+                    ends_with_newline |= !is_last_galley && is_last_row_in_galley;
+                    super::PlacedRow {
+                        pos: new_pos,
+                        row: placed_row.row.clone(),
+                        ends_with_newline,
                     }
-                    super::PlacedRow { pos: new_pos, row }
                 }));
 
             merged_galley.num_vertices += galley.num_vertices;