Macro impl_merge 

macro_rules! impl_merge {
    (
        $struct_name:ident {
            $(option { $($opt_field:ident),* $(,)? })?
            $(nested { $($nest_field:ident),* $(,)? })?
        }
    ) => { ... };
}

Generates merge() and is_empty() methods for theme structs.

Two field categories:

• option { field1, field2, ... } – Option<T> leaf fields
• nested { field1, field2, ... } – nested struct fields with their own merge()

For option fields, Some values in the overlay replace the corresponding fields in self; None fields are left unchanged. For nested fields, merge is called recursively.

Examples

use native_theme::impl_merge;

#[derive(Clone, Debug, Default)]
struct MyColors {
    accent: Option<String>,
    background: Option<String>,
}

impl_merge!(MyColors {
    option { accent, background }
});

let mut base = MyColors { accent: Some("blue".into()), background: None };
let overlay = MyColors { accent: None, background: Some("white".into()) };
base.merge(&overlay);
assert_eq!(base.accent.as_deref(), Some("blue"));
assert_eq!(base.background.as_deref(), Some("white"));