Give a length with no share in it its own type again

`UiScalar` was `Len` without the `leftover` weight, which is the separation
canonical `main` already had as `Len` beside `LayoutLen` and this branch
collapsed. It is needed back for the queued clamp: a cap may not contain a
share, because a cap has to read the report a rule otherwise makes moot, and
a share puts the container's division into the same equation -- two
self-consistent assignments, which is the multiple-fixed-point failure
generated seed 13 punished for orthogonal sizing. `min(report, cap)` is not
a `LayoutLen` either: it is a sum of parts, and the smaller of two of them
is not one.

So `UiScalar` is `Len`, what was `Len` is `LayoutLen`, and the two say in
their docs which is which: a `Len` is pixels plus a fraction of a box -- a
position being the length from the box's start, which is why a span is two
of them -- and a `LayoutLen` is a `Len` plus a claim only a container
dividing its room can answer. `From<Len> for LayoutLen` is the one-way step
between them.

Names only; the shader's `UiScalar` is renamed with them. Checked: fmt,
clippy, 105 tests, and `tabs`, `minimal`, `view`, `text` and `random`
byte-identical at 1920x1200.

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

tests/cases/layout.rs

@@ -27,7 +27,7 @@ fn a_span_ruled_across_itself_does_not_measure_its_children_there() {
     let span = (child,).span(Dir::RIGHT).height(rel(1.0)).add(&mut h.rsc);
     h.set_root(span);
 
-    assert_eq!(h.render.active[&span.id()].size.y, Len::rel(1.0));
+    assert_eq!(h.render.active[&span.id()].size.y, LayoutLen::rel(1.0));
 }
 
 #[test]
@@ -38,7 +38,7 @@ fn a_span_reports_its_tallest_fixed_child() {
     let span = (short, tall).span(Dir::RIGHT).add(&mut h.rsc);
     h.set_root(span);
 
-    assert_eq!(h.render.active[&span.id()].size.y, Len::px(70.0));
+    assert_eq!(h.render.active[&span.id()].size.y, LayoutLen::px(70.0));
 }
 
 #[test]
@@ -331,7 +331,7 @@ fn drawn_edges(h: &Harness, id: WidgetId, axis: Axis) -> (f32, f32) {
     let region = h.render.moves.resolve(active.parent_move, active.region);
     let dim = h.size().axis(axis);
     let snap = |v: f32| (v + Px::STEP.to_f32() * 0.5).floor();
-    let edge = |s: UiScalar| snap(s.rel.to_f32() * dim) + snap(s.px.to_f32());
+    let edge = |s: Len| snap(s.rel.to_f32() * dim) + snap(s.px.to_f32());
     let span = region.axis(axis);
     (edge(span.start), edge(span.end))
 }
@@ -343,7 +343,7 @@ fn hairline(h: &mut Harness, marks: &mut Vec<WidgetId>) -> StrongWidget {
 }
 
 fn share(h: &mut Harness, inner: StrongWidget, ratio: f32) -> StrongWidget {
-    h.set_len(&inner, Axis::X, Len::leftover(ratio));
+    h.set_len(&inner, Axis::X, LayoutLen::leftover(ratio));
     inner
 }
 
@@ -454,7 +454,7 @@ fn only_a_pure_leftover_child_disappears_when_nothing_is_left() {
     let mut h = Harness::new((100, 20));
     let fixed = rect(Color::RED).width(100).add(&mut h.rsc);
     let mixed = rect(Color::BLUE)
-        .width(Len::px(20) + Len::LEFTOVER)
+        .width(LayoutLen::px(20) + LayoutLen::LEFTOVER)
         .add(&mut h.rsc);
     h.set_root((fixed, mixed).span(Dir::RIGHT));
 

tests/cases/retained.rs

@@ -125,10 +125,7 @@ fn moving_an_ordinary_subtree_remaps_its_mask() {
     let active = &h.render.active[&masked.id()];
     assert_eq!(
         h.rsc.ui().masks[active.mask.idx()].region,
-        UiRegion::new(
-            UiSpan::new(UiScalar::px(150.0), UiScalar::rel_max()),
-            UiSpan::FULL,
-        )
+        UiRegion::new(UiSpan::new(Len::px(150.0), Len::rel_max()), UiSpan::FULL,)
     );
     assert_corners!(h, inner, (150, 0), (400, 200));
 }
@@ -312,7 +309,7 @@ fn a_span_ruled_across_itself_moves_its_child_without_redrawing_it() {
 
     assert_eq!(draws.get(), settled);
     assert_corners!(h, leaf, (0, 0), (400, 100));
-    assert_eq!(h.render.active[&span.id()].size.y, Len::rel(1.0));
+    assert_eq!(h.render.active[&span.id()].size.y, LayoutLen::rel(1.0));
 }
 
 /// The output is the root of the box chain, so a resize is a box that changed
@@ -407,12 +404,12 @@ fn a_box_change_within_one_step_is_not_a_change() {
 
     let step = Px::STEP.to_f32();
     for part in [0.1, 0.2, 0.3] {
-        h.rsc[first].size.x = Len::px(100.0 + step * part);
+        h.rsc[first].size.x = LayoutLen::px(100.0 + step * part);
         h.frame();
         assert_eq!(draws.get(), settled);
     }
 
-    h.rsc[first].size.x = Len::px(100.0 + step);
+    h.rsc[first].size.x = LayoutLen::px(100.0 + step);
     h.frame();
     assert_eq!(draws.get(), settled + 1);
 }

tests/cases/unsettled.rs

@@ -281,11 +281,11 @@ struct Wider {
 impl Widget for Wider {
     fn draw(&mut self, painter: &mut Painter) -> Size {
         Size {
-            x: Len {
+            x: LayoutLen {
                 px: painter.px_len(Axis::X) + Px::from_f32(self.extra),
-                ..Len::ZERO
+                ..LayoutLen::ZERO
             },
-            y: Len::LEFTOVER,
+            y: LayoutLen::LEFTOVER,
         }
     }
 }
@@ -341,7 +341,7 @@ fn plant_boundary(h: &mut Harness, swapped: bool) -> (Vec<WidgetId>, [WeakWidget
     let whole = rect(Color::RED).add(&mut h.rsc);
     h.rsc
         .widgets_mut()
-        .set_size_rules(whole, None, Some(Len::rel(1.0)));
+        .set_size_rules(whole, None, Some(LayoutLen::rel(1.0)));
     let mut inner_children: Vec<StrongWidget> = vec![
         measured.add_strong(&mut h.rsc),
         whole.add_strong(&mut h.rsc),
@@ -357,7 +357,7 @@ fn plant_boundary(h: &mut Harness, swapped: bool) -> (Vec<WidgetId>, [WeakWidget
     .add(&mut h.rsc);
     h.rsc
         .widgets_mut()
-        .set_size_rules(inner, None, Some(Len::px(198.0)));
+        .set_size_rules(inner, None, Some(LayoutLen::px(198.0)));
     // One more span above it: without a box composed through it, both trees
     // round the same way and the boundary is never crossed.
     let outer = (inner,).span(Dir::DOWN).add(&mut h.rsc);