1use proc_macro::TokenStream;
 2use quote::quote;
 3use syn::{parse_macro_input, DeriveInput, GenericParam};
 4
 5pub fn derive_element(input: TokenStream) -> TokenStream {
 6    let ast = parse_macro_input!(input as DeriveInput);
 7    let type_name = ast.ident;
 8
 9    let mut view_state_ty = quote! { V };
10
11    for param in &ast.generics.params {
12        if let GenericParam::Type(type_param) = param {
13            let type_ident = &type_param.ident;
14            view_state_ty = quote! {#type_ident};
15            break;
16        }
17    }
18
19    let attrs = &ast.attrs;
20    for attr in attrs {
21        if attr.path.is_ident("element") {
22            match attr.parse_meta() {
23                Ok(syn::Meta::List(i)) => {
24                    for nested_meta in i.nested {
25                        if let syn::NestedMeta::Meta(syn::Meta::NameValue(nv)) = nested_meta {
26                            if nv.path.is_ident("view_state") {
27                                if let syn::Lit::Str(lit_str) = nv.lit {
28                                    view_state_ty = lit_str.value().parse().unwrap();
29                                }
30                            }
31                        }
32                    }
33                }
34                _ => (),
35            }
36        }
37    }
38
39    let (impl_generics, ty_generics, where_clause) = ast.generics.split_for_impl();
40
41    let gen = quote! {
42        impl #impl_generics gpui::Element<#view_state_ty> for #type_name #ty_generics
43        #where_clause
44        {
45            type State = Option<gpui::AnyElement<#view_state_ty>>;
46
47            fn element_id(&self) -> Option<gpui::ElementId> {
48                None
49            }
50
51            fn layout(
52                &mut self,
53                view_state: &mut #view_state_ty,
54                _element_state: Option<Self::State>,
55                cx: &mut gpui::ViewContext<#view_state_ty>,
56            ) -> (gpui::LayoutId, Self::State) {
57                let mut element = self.render(view_state, cx).into_any();
58                let layout_id = element.layout(view_state, cx);
59                (layout_id, Some(element))
60            }
61
62            fn paint(
63                self,
64                _bounds: gpui::Bounds<gpui::Pixels>,
65                view_state: &mut #view_state_ty,
66                rendered_element: &mut Self::State,
67                cx: &mut gpui::ViewContext<#view_state_ty>,
68            ) {
69                rendered_element.take().unwrap().paint(view_state, cx)
70            }
71        }
72    };
73
74    gen.into()
75}