1use proc_macro::TokenStream;
 2use quote::quote;
 3use syn::{parse_macro_input, parse_quote, DeriveInput};
 4
 5pub fn derive_render_once(input: TokenStream) -> TokenStream {
 6    let ast = parse_macro_input!(input as DeriveInput);
 7    let type_name = &ast.ident;
 8
 9    let mut trait_generics = ast.generics.clone();
10    let view_type = if let Some(view_type) = specified_view_type(&ast) {
11        quote! { #view_type }
12    } else {
13        if let Some(first_type_param) = ast.generics.params.iter().find_map(|param| {
14            if let syn::GenericParam::Type(type_param) = param {
15                Some(type_param.ident.clone())
16            } else {
17                None
18            }
19        }) {
20            quote! { #first_type_param }
21        } else {
22            trait_generics.params.push(parse_quote! { V: 'static });
23            quote! { V }
24        }
25    };
26
27    let (impl_generics, _, where_clause) = trait_generics.split_for_impl();
28    let (_, type_generics, _) = ast.generics.split_for_impl();
29
30    let gen = quote! {
31        impl #impl_generics gpui::RenderOnce<#view_type> for #type_name #type_generics
32        #where_clause
33        {
34            type Element = gpui::CompositeElement<#view_type, Self>;
35
36            fn element_id(&self) -> Option<ElementId> {
37                None
38            }
39
40            fn render_once(self) -> Self::Element {
41                gpui::CompositeElement::new(self)
42            }
43        }
44    };
45
46    gen.into()
47}
48
49fn specified_view_type(ast: &DeriveInput) -> Option<proc_macro2::Ident> {
50    ast.attrs.iter().find_map(|attr| {
51        if attr.path.is_ident("view") {
52            if let Ok(syn::Meta::NameValue(meta_name_value)) = attr.parse_meta() {
53                if let syn::Lit::Str(lit_str) = meta_name_value.lit {
54                    return Some(
55                        lit_str
56                            .parse::<syn::Ident>()
57                            .expect("Failed to parse view_type"),
58                    );
59                }
60            }
61        }
62        None
63    })
64}