Use new type Estring to avoid cloning &'static str

`ui.label("static string")` is a very common use case,
and currently egui clones the string in these cases.

This PR introduces a new type:

``` rust
pub enum Estring {
    Static(&'static str),
    Owned(Arc<str>),
}
```

which is used everywhere text is needed, with
`impl Into<Estring>` in the API for e.g. `ui.label`.

This reduces the number of copies drastically and speeds up
the benchmark demo_with_tessellate__realistic by 17%.

This hurts the ergonomics of egui a bit, and this is a breaking change.

For instance, this used to work:

``` rust
fn my_label(ui: &mut egui::Ui, text: &str) {
    ui.label(text);
}
```

This must now either be changed to

``` rust
fn my_label(ui: &mut egui::Ui, text: &str) {
    ui.label(text.to_string());
}
```

(or the argument must be changed to either
`text: &'static str` or `text: String`)

egui/src/containers/collapsing_header.rs

@@ -152,7 +152,7 @@ impl CollapsingHeader {
     /// If the label is unique and static this is fine,
     /// but if it changes or there are several `CollapsingHeader` with the same title
     /// you need to provide a unique id source with [`Self::id_source`].
-    pub fn new(label: impl ToString) -> Self {
+    pub fn new(label: impl Into<Estring>) -> Self {
         let label = Label::new(label).wrap(false);
         let id_source = Id::new(label.text());
         Self {

egui/src/containers/combo_box.rs

@@ -23,7 +23,7 @@ use epaint::Shape;
 pub struct ComboBox {
     id_source: Id,
     label: Option<Label>,
-    selected_text: String,
+    selected_text: Estring,
     width: Option<f32>,
 }
 
@@ -56,9 +56,8 @@ impl ComboBox {
     }
 
     /// What we show as the currently selected value
-    #[allow(clippy::needless_pass_by_value)]
-    pub fn selected_text(mut self, selected_text: impl ToString) -> Self {
-        self.selected_text = selected_text.to_string();
+    pub fn selected_text(mut self, selected_text: impl Into<Estring>) -> Self {
+        self.selected_text = selected_text.into();
         self
     }
 
@@ -143,11 +142,10 @@ impl ComboBox {
     }
 }
 
-#[allow(clippy::needless_pass_by_value)]
 fn combo_box<R>(
     ui: &mut Ui,
     button_id: Id,
-    selected: impl ToString,
+    selected: impl Into<Estring>,
     menu_contents: impl FnOnce(&mut Ui) -> R,
 ) -> InnerResponse<Option<R>> {
     let popup_id = button_id.with("popup");
@@ -158,9 +156,9 @@ fn combo_box<R>(
         let full_minimum_width = ui.spacing().slider_width;
         let icon_size = Vec2::splat(ui.spacing().icon_width);
 
-        let galley =
-            ui.fonts()
-                .layout_delayed_color(selected.to_string(), TextStyle::Button, f32::INFINITY);
+        let galley = ui
+            .fonts()
+            .layout_delayed_color(selected, TextStyle::Button, f32::INFINITY);
 
         let width = galley.size.x + ui.spacing().item_spacing.x + icon_size.x;
         let width = width.at_least(full_minimum_width);

egui/src/containers/popup.rs

@@ -194,7 +194,7 @@ fn show_tooltip_at_avoid<R>(
 ///     egui::show_tooltip_text(ui.ctx(), egui::Id::new("my_tooltip"), "Helpful text");
 /// }
 /// ```
-pub fn show_tooltip_text(ctx: &CtxRef, id: Id, text: impl ToString) -> Option<()> {
+pub fn show_tooltip_text(ctx: &CtxRef, id: Id, text: impl Into<Estring>) -> Option<()> {
     show_tooltip(ctx, id, |ui| {
         ui.add(crate::widgets::Label::new(text));
     })

egui/src/containers/window.rs

@@ -37,9 +37,8 @@ impl<'open> Window<'open> {
     /// The window title is used as a unique [`Id`] and must be unique, and should not change.
     /// This is true even if you disable the title bar with `.title_bar(false)`.
     /// If you need a changing title, you must call `window.id(…)` with a fixed id.
-    #[allow(clippy::needless_pass_by_value)]
-    pub fn new(title: impl ToString) -> Self {
-        let title = title.to_string();
+    pub fn new(title: impl Into<Estring>) -> Self {
+        let title = title.into();
         let area = Area::new(&title);
         let title_label = Label::new(title).text_style(TextStyle::Heading).wrap(false);
         Self {

egui/src/layout.rs

@@ -1,4 +1,4 @@
-use crate::{egui_assert, emath::*, Align};
+use crate::{egui_assert, emath::*, Align, Estring};
 use std::f32::INFINITY;
 
 // ----------------------------------------------------------------------------
@@ -737,7 +737,7 @@ impl Layout {
         painter: &crate::Painter,
         region: &Region,
         stroke: epaint::Stroke,
-        text: impl ToString,
+        text: impl Into<Estring>,
     ) {
         let cursor = region.cursor;
         let next_pos = self.next_widget_position(region);

egui/src/lib.rs

@@ -352,7 +352,7 @@ pub use emath as math; // historical reasons
 pub use emath::{lerp, pos2, remap, remap_clamp, vec2, Align, Align2, NumExt, Pos2, Rect, Vec2};
 pub use epaint::{
     color, mutex,
-    text::{FontDefinitions, FontFamily, TextStyle},
+    text::{Estring, FontDefinitions, FontFamily, TextStyle},
     ClippedMesh, Color32, Rgba, Shape, Stroke, Texture, TextureId,
 };
 
@@ -378,7 +378,9 @@ pub use {
 };
 
 pub mod text {
-    pub use epaint::text::{Galley, LayoutJob, LayoutSection, TextFormat, TAB_SIZE};
+    pub use epaint::text::{
+        Galley, LayoutJob, LayoutJobBuilder, LayoutSection, TextFormat, TAB_SIZE,
+    };
 }
 
 // ----------------------------------------------------------------------------

egui/src/menu.rs

@@ -64,7 +64,7 @@ pub fn bar<R>(ui: &mut Ui, add_contents: impl FnOnce(&mut Ui) -> R) -> InnerResp
 /// Returns `None` if the menu is not open.
 pub fn menu<R>(
     ui: &mut Ui,
-    title: impl ToString,
+    title: impl Into<Estring>,
     add_contents: impl FnOnce(&mut Ui) -> R,
 ) -> Option<R> {
     menu_impl(ui, title, Box::new(add_contents))
@@ -104,13 +104,12 @@ pub(crate) fn menu_ui<'c, R>(
     })
 }
 
-#[allow(clippy::needless_pass_by_value)]
 fn menu_impl<'c, R>(
     ui: &mut Ui,
-    title: impl ToString,
+    title: impl Into<Estring>,
     add_contents: Box<dyn FnOnce(&mut Ui) -> R + 'c>,
 ) -> Option<R> {
-    let title = title.to_string();
+    let title = title.into();
     let bar_id = ui.id();
     let menu_id = bar_id.with(&title);
 

egui/src/painter.rs

@@ -5,7 +5,7 @@ use crate::{
 };
 use epaint::{
     mutex::Mutex,
-    text::{Fonts, Galley, TextStyle},
+    text::{Estring, Fonts, Galley, TextStyle},
     Shape, Stroke,
 };
 
@@ -193,33 +193,25 @@ impl Painter {
 
 /// ## Debug painting
 impl Painter {
-    #[allow(clippy::needless_pass_by_value)]
-    pub fn debug_rect(&mut self, rect: Rect, color: Color32, text: impl ToString) {
+    pub fn debug_rect(&mut self, rect: Rect, color: Color32, text: impl Into<Estring>) {
         self.rect_stroke(rect, 0.0, (1.0, color));
         let text_style = TextStyle::Monospace;
-        self.text(
-            rect.min,
-            Align2::LEFT_TOP,
-            text.to_string(),
-            text_style,
-            color,
-        );
+        self.text(rect.min, Align2::LEFT_TOP, text.into(), text_style, color);
     }
 
     pub fn error(&self, pos: Pos2, text: impl std::fmt::Display) -> Rect {
         self.debug_text(pos, Align2::LEFT_TOP, Color32::RED, format!("🔥 {}", text))
     }
 
     /// text with a background
-    #[allow(clippy::needless_pass_by_value)]
     pub fn debug_text(
         &self,
         pos: Pos2,
         anchor: Align2,
         color: Color32,
-        text: impl ToString,
+        text: impl Into<Estring>,
     ) -> Rect {
-        let galley = self.layout_no_wrap(text.to_string(), TextStyle::Monospace, color);
+        let galley = self.layout_no_wrap(text, TextStyle::Monospace, color);
         let rect = anchor.anchor_rect(Rect::from_min_size(pos, galley.size));
         let frame_rect = rect.expand(2.0);
         self.add(Shape::Rect {
@@ -332,16 +324,15 @@ impl Painter {
     /// [`Self::layout`] or [`Self::layout_no_wrap`].
     ///
     /// Returns where the text ended up.
-    #[allow(clippy::needless_pass_by_value)]
     pub fn text(
         &self,
         pos: Pos2,
         anchor: Align2,
-        text: impl ToString,
+        text: impl Into<Estring>,
         text_style: TextStyle,
         text_color: Color32,
     ) -> Rect {
-        let galley = self.layout_no_wrap(text.to_string(), text_style, text_color);
+        let galley = self.layout_no_wrap(text, text_style, text_color);
         let rect = anchor.anchor_rect(Rect::from_min_size(pos, galley.size));
         self.galley(rect.min, galley);
         rect
@@ -353,7 +344,7 @@ impl Painter {
     #[inline(always)]
     pub fn layout(
         &self,
-        text: String,
+        text: impl Into<Estring>,
         text_style: TextStyle,
         color: crate::Color32,
         wrap_width: f32,
@@ -367,7 +358,7 @@ impl Painter {
     #[inline(always)]
     pub fn layout_no_wrap(
         &self,
-        text: String,
+        text: impl Into<Estring>,
         text_style: TextStyle,
         color: crate::Color32,
     ) -> std::sync::Arc<Galley> {

egui/src/placer.rs

@@ -262,7 +262,7 @@ impl Placer {
 }
 
 impl Placer {
-    pub(crate) fn debug_paint_cursor(&self, painter: &crate::Painter, text: impl ToString) {
+    pub(crate) fn debug_paint_cursor(&self, painter: &crate::Painter, text: impl Into<Estring>) {
         let stroke = Stroke::new(1.0, Color32::DEBUG_COLOR);
 
         if let Some(grid) = &self.grid {

egui/src/response.rs

@@ -1,8 +1,7 @@
 use crate::{
     emath::{lerp, Align, Pos2, Rect, Vec2},
-    CursorIcon, PointerButton, NUM_POINTER_BUTTONS,
+    CtxRef, CursorIcon, Estring, Id, LayerId, PointerButton, Sense, Ui, NUM_POINTER_BUTTONS,
 };
-use crate::{CtxRef, Id, LayerId, Sense, Ui};
 
 // ----------------------------------------------------------------------------
 
@@ -373,14 +372,14 @@ impl Response {
     /// For that, use [`Self::on_disabled_hover_text`] instead.
     ///
     /// If you call this multiple times the tooltips will stack underneath the previous ones.
-    pub fn on_hover_text(self, text: impl ToString) -> Self {
+    pub fn on_hover_text(self, text: impl Into<Estring>) -> Self {
         self.on_hover_ui(|ui| {
             ui.add(crate::widgets::Label::new(text));
         })
     }
 
     /// Show this text when hovering if the widget is disabled.
-    pub fn on_disabled_hover_text(self, text: impl ToString) -> Self {
+    pub fn on_disabled_hover_text(self, text: impl Into<Estring>) -> Self {
         self.on_disabled_hover_ui(|ui| {
             ui.add(crate::widgets::Label::new(text));
         })

egui/src/style.rs

@@ -919,7 +919,7 @@ impl DebugOptions {
 fn slider_vec2<'a>(
     value: &'a mut Vec2,
     range: std::ops::RangeInclusive<f32>,
-    text: &'a str,
+    text: &'static str,
 ) -> impl Widget + 'a {
     move |ui: &mut crate::Ui| {
         ui.horizontal(|ui| {

egui/src/ui.rs

@@ -979,7 +979,7 @@ impl Ui {
     /// Shortcut for `add(Hyperlink::new(url))`
     ///
     /// See also [`Hyperlink`].
-    pub fn hyperlink(&mut self, url: impl ToString) -> Response {
+    pub fn hyperlink(&mut self, url: impl Into<Estring>) -> Response {
         Hyperlink::new(url).ui(self)
     }
 
@@ -991,7 +991,7 @@ impl Ui {
     /// ```
     ///
     /// See also [`Hyperlink`].
-    pub fn hyperlink_to(&mut self, label: impl ToString, url: impl ToString) -> Response {
+    pub fn hyperlink_to(&mut self, label: impl Into<Estring>, url: impl Into<Estring>) -> Response {
         Hyperlink::new(url).text(label).ui(self)
     }
 
@@ -1031,7 +1031,7 @@ impl Ui {
     /// See also [`Button`].
     #[must_use = "You should check if the user clicked this with `if ui.button(…).clicked() { … } "]
     #[inline(always)]
-    pub fn button(&mut self, text: impl ToString) -> Response {
+    pub fn button(&mut self, text: impl Into<Estring>) -> Response {
         Button::new(text).ui(self)
     }
 
@@ -1041,19 +1041,19 @@ impl Ui {
     ///
     /// Shortcut for `add(Button::new(text).small())`
     #[must_use = "You should check if the user clicked this with `if ui.small_button(…).clicked() { … } "]
-    pub fn small_button(&mut self, text: impl ToString) -> Response {
+    pub fn small_button(&mut self, text: impl Into<Estring>) -> Response {
         Button::new(text).small().ui(self)
     }
 
     /// Show a checkbox.
-    pub fn checkbox(&mut self, checked: &mut bool, text: impl ToString) -> Response {
+    pub fn checkbox(&mut self, checked: &mut bool, text: impl Into<Estring>) -> Response {
         Checkbox::new(checked, text).ui(self)
     }
 
     /// Show a [`RadioButton`].
     /// Often you want to use [`Self::radio_value`] instead.
     #[must_use = "You should check if the user clicked this with `if ui.radio(…).clicked() { … } "]
-    pub fn radio(&mut self, selected: bool, text: impl ToString) -> Response {
+    pub fn radio(&mut self, selected: bool, text: impl Into<Estring>) -> Response {
         RadioButton::new(selected, text).ui(self)
     }
 
@@ -1078,7 +1078,7 @@ impl Ui {
         &mut self,
         current_value: &mut Value,
         selected_value: Value,
-        text: impl ToString,
+        text: impl Into<Estring>,
     ) -> Response {
         let mut response = self.radio(*current_value == selected_value, text);
         if response.clicked() {
@@ -1092,7 +1092,7 @@ impl Ui {
     ///
     /// See also [`SelectableLabel`].
     #[must_use = "You should check if the user clicked this with `if ui.selectable_label(…).clicked() { … } "]
-    pub fn selectable_label(&mut self, checked: bool, text: impl ToString) -> Response {
+    pub fn selectable_label(&mut self, checked: bool, text: impl Into<Estring>) -> Response {
         SelectableLabel::new(checked, text).ui(self)
     }
 
@@ -1106,7 +1106,7 @@ impl Ui {
         &mut self,
         current_value: &mut Value,
         selected_value: Value,
-        text: impl ToString,
+        text: impl Into<Estring>,
     ) -> Response {
         let mut response = self.selectable_label(*current_value == selected_value, text);
         if response.clicked() {
@@ -1303,7 +1303,7 @@ impl Ui {
     /// A [`CollapsingHeader`] that starts out collapsed.
     pub fn collapsing<R>(
         &mut self,
-        heading: impl ToString,
+        heading: impl Into<Estring>,
         add_contents: impl FnOnce(&mut Ui) -> R,
     ) -> CollapsingResponse<R> {
         CollapsingHeader::new(heading).show(self, add_contents)
@@ -1644,7 +1644,7 @@ impl Ui {
 
     /// Shows the given text where the next widget is to be placed
     /// if when [`Context::set_debug_on_hover`] has been turned on and the mouse is hovering the Ui.
-    pub fn trace_location(&self, text: impl ToString) {
+    pub fn trace_location(&self, text: impl Into<Estring>) {
         let rect = self.max_rect();
         if self.style().debug.debug_on_hover && self.rect_contains_pointer(rect) {
             self.placer