strum_macros/macros/
enum_count.rs

1use proc_macro2::TokenStream;
2use quote::quote;
3use syn::{Data, DeriveInput};
4
5use crate::helpers::variant_props::HasStrumVariantProperties;
6use crate::helpers::{non_enum_error, HasTypeProperties};
7
8pub(crate) fn enum_count_inner(ast: &DeriveInput) -> syn::Result<TokenStream> {
9    let n = match &ast.data {
10        Data::Enum(v) => v.variants.iter().try_fold(0usize, |acc, v| {
11            if v.get_variant_properties()?.disabled.is_none() {
12                Ok::<usize, syn::Error>(acc + 1usize)
13            } else {
14                Ok::<usize, syn::Error>(acc)
15            }
16        })?,
17        _ => return Err(non_enum_error()),
18    };
19    let type_properties = ast.get_type_properties()?;
20    let strum_module_path = type_properties.crate_module_path();
21
22    // Used in the quasi-quotation below as `#name`
23    let name = &ast.ident;
24
25    // Helper is provided for handling complex generic types correctly and effortlessly
26    let (impl_generics, ty_generics, where_clause) = ast.generics.split_for_impl();
27
28    Ok(quote! {
29        // Implementation
30        impl #impl_generics #strum_module_path::EnumCount for #name #ty_generics #where_clause {
31            const COUNT: usize = #n;
32        }
33    })
34}