Rename rest to leftover

The length kind that asks for a part of what is left once the fixed
lengths are taken is called leftover: Len::leftover(2), Len::LEFTOVER,
Size::LEFTOVER, Len::leftover the field, and apply_leftover. It says
what it is where "rest" reads as "the remainder of the list" as often as
"the remaining space", and every agent who has touched this has reached
for a third word for it.

Locals called rest that meant a region or a widget are renamed with it,
since the word now names something else.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

Cargo.toml

@@ -25,6 +25,9 @@ tokio = { workspace = true, features = ["sync", "rt", "rt-multi-thread", "time"]
 [workspace]
 members = ["core", "macro", "rig-input"]
 
+[profile.dev]
+debug = 1
+
 [workspace.package]
 version = "0.1.0"
 edition = "2024"

core/src/orientation/len.rs

@@ -11,7 +11,7 @@ pub struct Size {
 pub struct Len {
     pub px: f32,
     pub rel: f32,
-    pub rest: f32,
+    pub leftover: f32,
 }
 
 impl<N: UiNum> From<N> for Len {
@@ -41,9 +41,9 @@ impl Size {
         y: Len::ZERO,
     };
 
-    pub const REST: Self = Self {
-        x: Len::REST,
-        y: Len::REST,
+    pub const LEFTOVER: Self = Self {
+        x: Len::LEFTOVER,
+        y: Len::LEFTOVER,
     };
 
     pub fn px(v: Vec2) -> Self {
@@ -60,17 +60,17 @@ impl Size {
         }
     }
 
-    pub fn rest(v: Vec2) -> Self {
+    pub fn leftover(v: Vec2) -> Self {
         Self {
-            x: Len::rest(v.x),
-            y: Len::rest(v.y),
+            x: Len::leftover(v.x),
+            y: Len::leftover(v.y),
         }
     }
 
     pub fn to_uivec2(self) -> UiVec2 {
         UiVec2 {
-            x: self.x.apply_rest(),
-            y: self.y.apply_rest(),
+            x: self.x.apply_leftover(),
+            y: self.y.apply_leftover(),
         }
     }
 
@@ -99,18 +99,18 @@ impl Len {
     pub const ZERO: Self = Self {
         px: 0.0,
         rel: 0.0,
-        rest: 0.0,
+        leftover: 0.0,
     };
 
-    pub const REST: Self = Self {
+    pub const LEFTOVER: Self = Self {
         px: 0.0,
         rel: 0.0,
-        rest: 1.0,
+        leftover: 1.0,
     };
 
-    pub fn apply_rest(&self) -> UiScalar {
+    pub fn apply_leftover(&self) -> UiScalar {
         UiScalar {
-            rel: self.rel + if self.rest > 0.0 { 1.0 } else { 0.0 },
+            rel: self.rel + if self.leftover > 0.0 { 1.0 } else { 0.0 },
             px: self.px,
         }
     }
@@ -119,21 +119,21 @@ impl Len {
         Self {
             px: px.to_f32(),
             rel: 0.0,
-            rest: 0.0,
+            leftover: 0.0,
         }
     }
     pub fn rel(rel: impl UiNum) -> Self {
         Self {
             px: 0.0,
             rel: rel.to_f32(),
-            rest: 0.0,
+            leftover: 0.0,
         }
     }
-    pub fn rest(ratio: impl UiNum) -> Self {
+    pub fn leftover(ratio: impl UiNum) -> Self {
         Self {
             px: 0.0,
             rel: 0.0,
-            rest: ratio.to_f32(),
+            leftover: ratio.to_f32(),
         }
     }
 }
@@ -145,34 +145,34 @@ pub mod len_fns {
         Len {
             px: px.to_f32(),
             rel: 0.0,
-            rest: 0.0,
+            leftover: 0.0,
         }
     }
     pub fn rel(rel: impl UiNum) -> Len {
         Len {
             px: 0.0,
             rel: rel.to_f32(),
-            rest: 0.0,
+            leftover: 0.0,
         }
     }
-    pub fn rest(ratio: impl UiNum) -> Len {
+    pub fn leftover(ratio: impl UiNum) -> Len {
         Len {
             px: 0.0,
             rel: 0.0,
-            rest: ratio.to_f32(),
+            leftover: ratio.to_f32(),
         }
     }
 }
 
-impl_op!(Len Add add; px rel rest);
-impl_op!(Len Sub sub; px rel rest);
+impl_op!(Len Add add; px rel leftover);
+impl_op!(Len Sub sub; px rel leftover);
 
 impl_op!(Size Add add; x y);
 impl_op!(Size Sub sub; x y);
 
 impl Default for Len {
     fn default() -> Self {
-        Self::rest(1.0)
+        Self::leftover(1.0)
     }
 }
 
@@ -190,8 +190,8 @@ impl std::fmt::Display for Len {
         if self.rel != 0.0 {
             write!(f, "{} rel;", self.rel)?;
         }
-        if self.rest != 0.0 {
-            write!(f, "{} rest;", self.rest)?;
+        if self.leftover != 0.0 {
+            write!(f, "{} leftover;", self.leftover)?;
         }
         Ok(())
     }

core/src/ui/painter.rs

@@ -112,7 +112,7 @@ impl<'a> Painter<'a> {
     }
 
     /// What a widget declares its lengths to be, which whoever draws it
-    /// resolves into its box. `rest` is not among them: a share of what is
+    /// resolves into its box. `leftover` is not among them: a part of what is
     /// left over is only a length to the widget dividing one, so it passes
     /// up in the size instead. Reading it depends on nothing -- the box that
     /// comes of it is kept on the child, and `redraw` compares it there.
@@ -439,11 +439,11 @@ impl PrimitiveLike for &TextureHandle {
     }
 }
 
-/// What a widget declares a length of its box to be. `rest` is not one: a
+/// What a widget declares a length of its box to be. `leftover` is not one: a
 /// share of what is left over is only a length to the widget dividing one,
 /// so it passes up in the size instead.
 pub(crate) fn declared_len(widget: &dyn Widget, axis: Axis) -> Option<Len> {
-    widget.size_hint(axis).filter(|len| len.rest == 0.0)
+    widget.size_hint(axis).filter(|len| len.leftover == 0.0)
 }
 
 /// Takes a widget's declared lengths in the box `region` is given in, since a

examples/tabs/main.rs

@@ -24,18 +24,18 @@ impl DefaultAppState for Client {
                     .color(Color::RED)
                     .sized((100, 100))
                     .center()
-                    .width(rest(2)),
+                    .width(leftover(2)),
                 (
                     rrect.color(Color::ORANGE),
                     rrect.color(Color::LIME).pad(10.0),
                 )
                     .span(Dir::RIGHT)
-                    .width(rest(2)),
+                    .width(leftover(2)),
                 rrect.color(Color::YELLOW),
             )
                 .span(Dir::RIGHT)
                 .pad(10)
-                .width(rest(3)),
+                .width(leftover(3)),
         )
             .span(Dir::RIGHT)
             .add(rsc);
@@ -121,11 +121,11 @@ impl DefaultAppState for Client {
             .add(rsc);
 
         let text_edit_scroll = (
-            msg_area.height(rest(1)),
+            msg_area.height(leftover(1)),
             (
                 Rect::new(Color::WHITE.darker(0.9)),
                 (
-                    add_text.width(rest(1)),
+                    add_text.width(leftover(1)),
                     Rect::new(Color::GREEN)
                         .on(CursorSense::click(), move |ctx, rsc: &mut ClientRsc| {
                             rsc.run_event::<Submit>(add_text, (), ctx.state);

src/random.rs

@@ -101,15 +101,15 @@ impl Widget for Branch {
         let mut top = UiRegion::FULL;
         top.y.end = top.y.start.offset(40.0);
         let measured = painter.place(&self.probe, top).len(Axis::X);
-        let px = measured.apply_rest().to_px(painter.px_len(Axis::X));
+        let px = measured.apply_leftover().to_px(painter.px_len(Axis::X));
 
-        let mut rest = UiRegion::FULL;
-        rest.y.start = rest.y.start.offset(40.0);
+        let mut below = UiRegion::FULL;
+        below.y.start = below.y.start.offset(40.0);
         match px > self.threshold {
-            true => painter.place(&self.wide, rest),
-            false => painter.place(&self.narrow, rest),
+            true => painter.place(&self.wide, below),
+            false => painter.place(&self.narrow, below),
         };
-        Size::REST
+        Size::LEFTOVER
     }
 }
 
@@ -172,7 +172,7 @@ impl<Rsc: UiRsc + 'static> Grow<'_, Rsc> {
     fn len(&mut self) -> Option<Len> {
         match self.rng.below(4) {
             0 => Some(Len::px(20.0 + self.rng.below(180) as f32)),
-            1 => Some(Len::REST),
+            1 => Some(Len::LEFTOVER),
             _ => None,
         }
     }

src/widget/position/align.rs

@@ -14,11 +14,17 @@ impl Widget for Aligned {
                 .map(|(x, y)| Size { x, y }),
             (Some(_), None) => painter
                 .known_len(&self.inner, Axis::X, UiRegion::FULL)
-                .map(|x| Size { x, y: Len::REST }),
+                .map(|x| Size {
+                    x,
+                    y: Len::LEFTOVER,
+                }),
             (None, Some(_)) => painter
                 .known_len(&self.inner, Axis::Y, UiRegion::FULL)
-                .map(|y| Size { x: Len::REST, y }),
-            (None, None) => Some(Size::REST),
+                .map(|y| Size {
+                    x: Len::LEFTOVER,
+                    y,
+                }),
+            (None, None) => Some(Size::LEFTOVER),
         };
         // Drawn where it may be too big only when the aligned axes are not
         // already known, then given its aligned box once its size is known.
@@ -26,8 +32,8 @@ impl Widget for Aligned {
         let size = known.unwrap_or_else(|| painter.place(&self.inner, UiRegion::FULL).size());
         let region = match self.align.tuple() {
             (Some(x), Some(y)) => size.to_uivec2().align(RegionAlign { x, y }),
-            (Some(x), None) => UiRegion::new(size.x.apply_rest().align(x), UiSpan::FULL),
-            (None, Some(y)) => UiRegion::new(UiSpan::FULL, size.y.apply_rest().align(y)),
+            (Some(x), None) => UiRegion::new(size.x.apply_leftover().align(x), UiSpan::FULL),
+            (None, Some(y)) => UiRegion::new(UiSpan::FULL, size.y.apply_leftover().align(y)),
             (None, None) => UiRegion::FULL,
         };
         let placed = painter.place(&self.inner, region).size();

src/widget/position/max_size.rs

@@ -19,7 +19,7 @@ impl Widget for MaxSize {
 
 fn capped(len: Len, max: Option<Len>, output: f32) -> Len {
     match max {
-        Some(max) if len.apply_rest().to_px(output) > max.apply_rest().to_px(output) => max,
+        Some(max) if len.apply_leftover().to_px(output) > max.apply_leftover().to_px(output) => max,
         _ => len,
     }
 }

src/widget/position/pad.rs

@@ -23,7 +23,7 @@ impl Widget for Pad {
     }
 
     /// The padding is an offset from each edge, so a longer box pads the same
-    /// amount and the child takes the rest.
+    /// amount and the child takes what is left over.
     fn on_resize(&self, _: Axis) -> OnResize {
         OnResize::Scale
     }

src/widget/position/scroll.rs

@@ -21,7 +21,7 @@ impl Widget for Scroll {
         let child = measured.then(|| painter.place(&self.inner, UiRegion::FULL).size());
         let content_len = known_len
             .unwrap_or_else(|| child.unwrap().axis(self.axis))
-            .apply_rest()
+            .apply_leftover()
             .within_len(container_len)
             .to_px(output_len);
         self.container_len = container_len.to_px(output_len);

src/widget/position/set_size.rs

@@ -9,7 +9,7 @@ pub struct SetSize {
 impl Widget for SetSize {
     fn draw(&mut self, painter: &mut Painter) -> Size {
         // Nothing to apply: a declared length is taken where this widget is
-        // drawn, so the box it has already is that length, and `rest` is a
+        // drawn, so the box it has already is that length, and `leftover` is a
         // share only whoever divides a length can work out. Both reach them
         // through `size_hint`.
         let child = painter.widget(&self.inner).size();
@@ -20,7 +20,7 @@ impl Widget for SetSize {
     }
 
     /// A declared axis is known without looking at the child, which is what
-    /// lets a span lay out around `.height(rest(1))` without drawing it.
+    /// lets a span lay out around `.height(leftover(1))` without drawing it.
     fn size_hint(&self, axis: Axis) -> Option<Len> {
         match axis {
             Axis::X => self.x,

src/widget/position/span.rs

@@ -37,9 +37,9 @@ impl Widget for Span {
         for (child, len) in self.children.iter().zip(&lens) {
             let mut span = UiSpan::FULL;
             span.start = start;
-            if len.rest > 0.0 {
+            if len.leftover > 0.0 {
                 let offset = UiScalar::new(total.rel, total.px);
-                let rel_end = UiScalar::rel(len.rest / total.rest);
+                let rel_end = UiScalar::rel(len.leftover / total.leftover);
                 let end = (UiScalar::rel_max() + start) - offset;
                 start = rel_end.within(&start.to(end));
             }
@@ -52,19 +52,19 @@ impl Widget for Span {
             }
             let used = painter.place(child, region).size().axis(!axis);
             // TODO: rel shouldn't do this, but no easy way before actually calculating pixels
-            if used.rel > 0.0 || used.rest > 0.0 {
-                ortho = Len::REST;
-            } else if ortho.rest == 0.0 {
+            if used.rel > 0.0 || used.leftover > 0.0 {
+                ortho = Len::LEFTOVER;
+            } else if ortho.leftover == 0.0 {
                 ortho.px = ortho.px.max(used.px);
             }
             start.px += self.gap;
         }
 
         // Carried whole rather than collapsed to one share: a span that sizes
-        // from its children does not resolve `rest`, it passes the weight up,
+        // from its children does not resolve `leftover`, it passes the weight up,
         // so nesting spans divides the same space rather than re-dividing a
-        // share of it. Four `rest(1)` children under two spans under one span
-        // get a quarter each, which collapsing to `rest(1)` per level does
+        // share of it. Four `leftover(1)` children under two spans under one span
+        // get a quarter each, which collapsing to `leftover(1)` per level does
         // not give. Resolution happens at the nearest ancestor with a length,
         // and the root always has one.
         let along = total;

src/widget/rect.rs

@@ -35,11 +35,11 @@ impl Widget for Rect {
             thickness: self.thickness,
             inner_radius: self.inner_radius,
         });
-        Size::REST
+        Size::LEFTOVER
     }
 
     fn size_hint(&self, _: Axis) -> Option<Len> {
-        Some(Len::REST)
+        Some(Len::LEFTOVER)
     }
 
     /// Its box is its primitive's own region, so a new one is written there.

tests/determinism.rs

@@ -24,15 +24,15 @@ impl Widget for BranchesOnMeasurement {
         let mut top = UiRegion::FULL;
         top.y.end = top.y.start.offset(40.0);
         let measured = painter.place(&self.probe, top).len(Axis::X);
-        let px = measured.apply_rest().to_px(painter.px_len(Axis::X));
+        let px = measured.apply_leftover().to_px(painter.px_len(Axis::X));
 
-        let mut rest = UiRegion::FULL;
-        rest.y.start = rest.y.start.offset(40.0);
+        let mut below = UiRegion::FULL;
+        below.y.start = below.y.start.offset(40.0);
         match px > self.threshold {
-            true => painter.place(&self.wide, rest),
-            false => painter.place(&self.narrow, rest),
+            true => painter.place(&self.wide, below),
+            false => painter.place(&self.narrow, below),
         };
-        Size::REST
+        Size::LEFTOVER
     }
 }
 

tests/layout.rs

@@ -131,22 +131,22 @@ fn a_moved_subtree_takes_its_children_with_it() {
 fn a_fixed_length_child_keeps_it_when_the_box_around_it_grows() {
     let mut h = Harness::new((400, 200));
     let fixed = rect(Color::BLUE).width(50).add(&mut h.rsc);
-    let rest = rect(Color::GREEN).add(&mut h.rsc);
-    let panel = (fixed, rest).span(Dir::RIGHT).add(&mut h.rsc);
+    let leftover = rect(Color::GREEN).add(&mut h.rsc);
+    let panel = (fixed, leftover).span(Dir::RIGHT).add(&mut h.rsc);
     // Changing the bar's width is the only thing that changes the box the
     // panel and everything under it was drawn for.
     let bar = rect(Color::RED).width(100).add(&mut h.rsc);
     h.set_root((bar, panel).span(Dir::RIGHT));
     assert_corners!(h, fixed, (100, 0), (150, 200));
-    assert_corners!(h, rest, (150, 0), (400, 200));
+    assert_corners!(h, leftover, (150, 0), (400, 200));
 
     h.rsc[bar].x = Some(Len::px(200));
     h.frame();
 
     // The panel's box is 100 shorter, so the fixed child is the same 50 wide
-    // against its new start and the one taking the rest absorbs the change.
+    // against its new start and the one taking what is left absorbs the change.
     assert_corners!(h, fixed, (200, 0), (250, 200));
-    assert_corners!(h, rest, (250, 0), (400, 200));
+    assert_corners!(h, leftover, (250, 0), (400, 200));
 }
 
 #[test]
@@ -187,7 +187,7 @@ fn only_a_container_that_places_its_children_lengthens_the_chain() {
     );
 }
 
-/// A span that sizes from its children passes their `rest` weight up rather
+/// A span that sizes from its children passes their `leftover` weight up
 /// than collapsing it to one share, so nesting divides the same space instead
 /// of re-dividing a share of it.
 #[test]
@@ -256,7 +256,7 @@ fn hairline(h: &mut Harness, marks: &mut Vec<WidgetId>) -> StrongWidget {
 fn share(h: &mut Harness, inner: StrongWidget, ratio: f32) -> StrongWidget {
     SetSize {
         inner,
-        x: Some(Len::rest(ratio)),
+        x: Some(Len::leftover(ratio)),
         y: None,
     }
     .add_strong(&mut h.rsc)

tests/retained.rs

@@ -43,11 +43,11 @@ fn counted(h: &mut Harness, size: Size, dependence: OnResize) -> (WeakWidget<Cou
     (id, Counts(draws))
 }
 
-/// A fixed-width leaf beside one that takes the rest, so changing the first
-/// hands the second a different box without the output changing.
-fn pair(h: &mut Harness, rest: OnResize) -> (WeakWidget<Counted>, Counts, WidgetId) {
+/// A fixed-width leaf beside one that takes what is left over, so changing
+/// the first hands the second a different box without the output changing.
+fn pair(h: &mut Harness, leftover: OnResize) -> (WeakWidget<Counted>, Counts, WidgetId) {
     let (first, _) = counted(h, Size::from((100, 200)), OnResize::Translate);
-    let (second, draws) = counted(h, Size::REST, rest);
+    let (second, draws) = counted(h, Size::LEFTOVER, leftover);
     h.set_root((first, second).span(Dir::RIGHT));
     (first, draws, second.id())
 }
@@ -119,7 +119,7 @@ fn a_span_relays_out_when_a_child_it_measured_changes() {
 fn a_repaint_that_keeps_its_size_does_not_relay_out() {
     let mut h = Harness::new((400, 200));
     let (first, draws) = counted(&mut h, Size::from((100, 200)), OnResize::Translate);
-    let (second, _) = counted(&mut h, Size::REST, OnResize::Translate);
+    let (second, _) = counted(&mut h, Size::LEFTOVER, OnResize::Translate);
     h.set_root((first, second).span(Dir::RIGHT));
     let settled = draws.get();
 
@@ -158,7 +158,7 @@ impl Widget for FromHint {
         let mut region = UiRegion::FULL;
         region.y.end = region.y.start.offset(len.px);
         painter.widget_within(&self.inner, region);
-        Size::REST
+        Size::LEFTOVER
     }
 }
 
@@ -214,7 +214,7 @@ impl Widget for ReadsWidth {
 #[test]
 fn a_resize_does_not_redraw_what_the_shader_can_move() {
     let mut h = Harness::new((400, 200));
-    let (leaf, draws) = counted(&mut h, Size::REST, OnResize::Scale);
+    let (leaf, draws) = counted(&mut h, Size::LEFTOVER, OnResize::Scale);
     h.set_root(leaf);
     let settled = draws.get();
 
@@ -236,7 +236,7 @@ fn a_resize_does_not_redraw_what_the_shader_can_move() {
 #[test]
 fn a_resize_redraws_what_does_not_scale() {
     let mut h = Harness::new((400, 200));
-    let (leaf, draws) = counted(&mut h, Size::REST, OnResize::Redraw);
+    let (leaf, draws) = counted(&mut h, Size::LEFTOVER, OnResize::Redraw);
     h.set_root(leaf);
     let settled = draws.get();
 
@@ -430,8 +430,8 @@ fn a_widened_row_redraws_what_reads_its_length_and_nothing_else() {
     let mut h = Harness::new((400, 200));
     // What a transcript row is: something whose shaping depends on the width
     // it is given, beside something that only has to be the right shape.
-    let (wraps, wrap_draws) = counted(&mut h, Size::REST, OnResize::Redraw);
-    let (backing, back_draws) = counted(&mut h, Size::REST, OnResize::Scale);
+    let (wraps, wrap_draws) = counted(&mut h, Size::LEFTOVER, OnResize::Redraw);
+    let (backing, back_draws) = counted(&mut h, Size::LEFTOVER, OnResize::Scale);
     let row = (backing, wraps).span(Dir::RIGHT).add(&mut h.rsc);
     let bar = rect(Color::RED).width(100).add(&mut h.rsc);
     h.set_root((bar, row).span(Dir::RIGHT));
@@ -457,8 +457,8 @@ fn a_declared_length_child_is_not_redrawn_when_the_box_around_it_grows() {
     // drawing the child in its own box is only an answer for that box.
     let (counter, draws) = counted(&mut h, Size::from((80, 200)), OnResize::Redraw);
     let fixed = counter.width(80).add(&mut h.rsc);
-    let (rest, _) = counted(&mut h, Size::REST, OnResize::Scale);
-    let row = (fixed, rest).span(Dir::RIGHT).add(&mut h.rsc);
+    let (leftover, _) = counted(&mut h, Size::LEFTOVER, OnResize::Scale);
+    let row = (fixed, leftover).span(Dir::RIGHT).add(&mut h.rsc);
     let bar = rect(Color::RED).width(100).add(&mut h.rsc);
     h.set_root((bar, row).span(Dir::RIGHT));
     let settled = draws.get();

tests/shrink.rs

@@ -327,7 +327,7 @@ fn sized(rng: &mut Rng, inner: Node) -> Node {
     }
     let len = |rng: &mut Rng| match rng.below(4) {
         0 => Some(Len::px(20.0 + rng.below(180) as f32)),
-        1 => Some(Len::REST),
+        1 => Some(Len::LEFTOVER),
         _ => None,
     };
     Node::Sized(len(rng), len(rng), Box::new(inner))
@@ -343,7 +343,7 @@ fn grow(rng: &mut Rng, depth: usize) -> Node {
     }
     let len = |rng: &mut Rng| match rng.below(4) {
         0 => Some(Len::px(20.0 + rng.below(180) as f32)),
-        1 => Some(Len::REST),
+        1 => Some(Len::LEFTOVER),
         2 => Some(Len::rel(0.25 + rng.below(3) as f32 * 0.25)),
         _ => None,
     };