Ask a value a question through a reference

A method taking `self` can only be called on a value, so anywhere the caller
holds a reference it has to dereference to ask -- which costs the caller
whether or not the type is `Copy` (Bryan, 2026-09-20, correcting the opposite
change made in 7502176).

So every method that answers a question about a value takes `&self`:
`Holds`'s four, `AxisHolds` and `LayoutHolds`'s three each, `LayoutLen`'s
`is_px`, `is_only_leftover`, `declared` and `fills`, and `Size::within_box`.
The two callers passing `LayoutLen::declared` as a function value say the
closure instead.

Builders that return a changed copy, and methods on a handle that is meant to
be given up, still take `self`.

core/src/orientation/len.rs

@@ -148,20 +148,20 @@ impl LayoutLen {
     /// Only pixels: the same number of them whatever box it lands in, and
     /// whatever anyone else in the row asks for. A length that is any part
     /// of a box or of what is left over is not one.
-    pub fn is_px(self) -> bool {
+    pub fn is_px(&self) -> bool {
         self.rel == Rel::ZERO && self.leftover == Weight::ZERO
     }
 
     /// Nothing but a claim on what is left over, so there is no length here
     /// at all where nothing is.
-    pub fn is_only_leftover(self) -> bool {
+    pub fn is_only_leftover(&self) -> bool {
         self.leftover > Weight::ZERO && self.without_leftover() == Len::ZERO
     }
 
     /// This as a length of a box, where it is one. `leftover` is not: a
     /// share of what is left over is a length only to whoever divides one,
     /// so it passes up in the reported size instead and is resolved there.
-    pub fn declared(self) -> Option<Len> {
+    pub fn declared(&self) -> Option<Len> {
         (self.leftover == Weight::ZERO).then(|| self.without_leftover())
     }
 

core/src/ui/holds.rs

@@ -29,17 +29,17 @@ impl Holds {
         Self { lo: len, hi: len }
     }
 
-    pub const fn contains(self, len: Px) -> bool {
+    pub const fn contains(&self, len: Px) -> bool {
         len.raw() >= self.lo.raw() && len.raw() <= self.hi.raw()
     }
 
     /// Every length `other` holds for is one this holds for, so a drawing
     /// made under this range is still good wherever `other` is.
-    pub const fn covers(self, other: Self) -> bool {
+    pub const fn covers(&self, other: Self) -> bool {
         self.lo.raw() <= other.lo.raw() && self.hi.raw() >= other.hi.raw()
     }
 
-    pub const fn and(self, other: Self) -> Self {
+    pub const fn and(&self, other: Self) -> Self {
         Self {
             lo: self.lo.max(other.lo),
             hi: self.hi.min(other.hi),
@@ -57,7 +57,7 @@ impl Holds {
     /// boxes therefore give one length. That is a floor rather than an
     /// allowance: inverting it is two divisions and nothing else, and the
     /// whole of a box maps back to itself.
-    pub const fn through(self, len: Len) -> Self {
+    pub const fn through(&self, len: Len) -> Self {
         if self.lo.raw() == Px::MIN.raw() && self.hi.raw() == Px::MAX.raw() {
             return Self::ANY;
         }

core/src/ui/layout_holds.rs

@@ -34,7 +34,7 @@ impl AxisHolds {
         region_len: None,
     };
 
-    pub fn and(self, other: Self) -> Self {
+    pub fn and(&self, other: Self) -> Self {
         // Two pins of the same length disagreeing would mean one drawing was
         // a fraction of two different lengths at once.
         debug_assert!(
@@ -53,7 +53,7 @@ impl AxisHolds {
         }
     }
 
-    pub fn covers(self, other: Self) -> bool {
+    pub fn covers(&self, other: Self) -> bool {
         self.window.covers(other.window)
             && self.region.covers(other.region)
             && self
@@ -64,7 +64,7 @@ impl AxisHolds {
 
     /// Whether a widget in a box `len` long, with that rel base, in that
     /// window, is one this drawing holds for.
-    pub fn contains(self, window: Px, rel_base: Len, len: Len) -> bool {
+    pub fn contains(&self, window: Px, rel_base: Len, len: Len) -> bool {
         self.window.contains(window)
             && self.rel_base.is_none_or(|pinned| pinned == rel_base)
             && self.region.contains(len.to_px(window))
@@ -87,18 +87,18 @@ impl LayoutHolds {
         y: AxisHolds::ANY,
     };
 
-    pub fn and(self, other: Self) -> Self {
+    pub fn and(&self, other: Self) -> Self {
         Self {
             x: self.x.and(other.x),
             y: self.y.and(other.y),
         }
     }
 
-    pub fn covers(self, other: Self) -> bool {
+    pub fn covers(&self, other: Self) -> bool {
         self.x.covers(other.x) && self.y.covers(other.y)
     }
 
-    pub fn contains(self, window: PxVec2, rel_base: UiVec2, region: UiRegion) -> bool {
+    pub fn contains(&self, window: PxVec2, rel_base: UiVec2, region: UiRegion) -> bool {
         Axis::BOTH
             .into_iter()
             .all(|axis| self[axis].contains(window[axis], rel_base[axis], region[axis].len()))

core/src/ui/painter.rs

@@ -665,7 +665,7 @@ impl Widgets {
                 // the box it was offered.
                 widget
                     .and_then(|widget| widget.size_hint(axis))
-                    .and_then(LayoutLen::declared)
+                    .and_then(|len| len.declared())
             })
         })
     }
@@ -679,7 +679,7 @@ impl LayoutLen {
     /// the rule already gave the region its length, and the rule's length is
     /// what the widget reports there. And an axis the parent decided from
     /// the answer is the answer already.
-    pub(super) fn fills(self, declared: Option<Len>, decided: bool) -> bool {
+    pub(super) fn fills(&self, declared: Option<Len>, decided: bool) -> bool {
         self.leftover != Weight::ZERO || declared.is_some() || decided
     }
 }

core/src/ui/render_state.rs

@@ -1167,7 +1167,7 @@ impl Size {
     /// in. Both are lengths of the window, so the comparison is in its
     /// pixels. A share is a length only to whoever divides one, so it is not
     /// a claim about this box and cannot exceed it.
-    fn within_box(self, region: UiRegion, window: PxVec2, axis: Axis) -> bool {
+    fn within_box(&self, region: UiRegion, window: PxVec2, axis: Axis) -> bool {
         let len = self[axis];
         let window = window[axis];
         len.leftover != Weight::ZERO

core/src/widget/size_rule.rs

@@ -22,7 +22,7 @@ impl SizeRule {
     /// The length this rule gives without the widget being drawn, if it can
     /// give one.
     pub fn declared(&self) -> Option<Len> {
-        self.exact().and_then(LayoutLen::declared)
+        self.exact().and_then(|len| len.declared())
     }
 
     /// The length this rule gives outright, whatever the widget reports --