Pass the Padding by value in the layout data struct

It can simply be a Copy type anyway.
So there is no more special code needed in the rust (and also in C++) generator for it

sixtyfps_compiler/generator/rust.rs

@@ -1529,18 +1529,8 @@ fn compile_expression(expr: &Expression, ctx: &EvaluationContext) -> TokenStream
             }
         }
         Expression::Struct { ty, values } => {
-            if let Type::Struct { fields, name, node } = ty {
-                let elem = fields.keys().map(|k| {
-                    values.get(k).map(|e| {
-                        let e = compile_expression(e, ctx);
-                        if node.is_none() && k == "padding" {
-                            // FIXME: it would be nice if we didn't have to handle this field specially
-                            quote!(&#e)
-                        } else {
-                            e
-                        }
-                    })
-                });
+            if let Type::Struct { fields, name, .. } = ty {
+                let elem = fields.keys().map(|k| values.get(k).map(|e| compile_expression(e, ctx)));
                 if let Some(name) = name {
                     let name_tokens: TokenStream = struct_name_to_tokens(name.as_str());
                     let keys = fields.keys().map(|k| ident(k));

sixtyfps_runtime/corelib/layout.rs

@@ -334,7 +334,7 @@ impl Default for Constraint {
 }
 
 #[repr(C)]
-#[derive(Debug, Default)]
+#[derive(Copy, Clone, Debug, Default)]
 pub struct Padding {
     pub begin: Coord,
     pub end: Coord,
@@ -345,7 +345,7 @@ pub struct Padding {
 pub struct GridLayoutData<'a> {
     pub size: Coord,
     pub spacing: Coord,
-    pub padding: &'a Padding,
+    pub padding: Padding,
     pub cells: Slice<'a, GridLayoutCellData>,
 }
 
@@ -432,7 +432,7 @@ impl Default for LayoutAlignment {
 pub struct BoxLayoutData<'a> {
     pub size: Coord,
     pub spacing: Coord,
-    pub padding: &'a Padding,
+    pub padding: Padding,
     pub alignment: LayoutAlignment,
     pub cells: Slice<'a, BoxLayoutCellData>,
 }

sixtyfps_runtime/interpreter/eval_layout.rs

@@ -104,7 +104,7 @@ pub(crate) fn solve_layout(
             core_layout::solve_grid_layout(&core_layout::GridLayoutData {
                 size: size_ref.map(expr_eval).unwrap_or(0.),
                 spacing,
-                padding: &padding,
+                padding,
                 cells: Slice::from(cells.as_slice()),
             })
             .into()
@@ -128,7 +128,7 @@ pub(crate) fn solve_layout(
                 &core_layout::BoxLayoutData {
                     size: size_ref.as_ref().map(expr_eval).unwrap_or(0.),
                     spacing,
-                    padding: &padding,
+                    padding,
                     alignment,
                     cells: Slice::from(cells.as_slice()),
                 },