introduce workspace

crates/macros/src/register.rs

@@ -0,0 +1,114 @@
+use proc_macro::TokenStream;
+use quote::quote;
+use syn::DeriveInput;
+use syn::__private::TokenStream2;
+
+pub fn register(input: TokenStream) -> TokenStream {
+    let input = syn::parse::<DeriveInput>(input).unwrap();
+
+    let name = &input.ident;
+
+    let enum_data = if let syn::Data::Enum(enum_data) = &input.data {
+        enum_data
+    } else {
+        panic!("`Register` can only be used on enums");
+    };
+
+    let first_variant = &enum_data.variants[0].ident;
+
+    let variant_matches_backend = generate_variant_backend(enum_data);
+    let variant_matches_next = generate_variant_matches_next(enum_data);
+    let variant_imports = generate_variant_imports(enum_data);
+
+    let expanded = compile_output(
+        name,
+        first_variant,
+        variant_matches_backend,
+        variant_matches_next,
+        variant_imports,
+    );
+
+    TokenStream::from(expanded)
+}
+
+fn compile_output<T, U, V>(
+    name: &syn::Ident,
+    first_variant: &syn::Ident,
+    variant_backend: T,
+    variant_next: U,
+    variant_imports: V,
+) -> TokenStream2
+where
+    T: Iterator<Item = TokenStream2>,
+    U: Iterator<Item = TokenStream2>,
+    V: Iterator<Item = TokenStream2>,
+{
+    let expanded = quote! {
+        #(#variant_imports)*
+
+        impl #name {
+            pub fn iter() -> BackendIter {
+                BackendIter {
+                    next: Some(Self::#first_variant),
+                }
+            }
+            fn get_backend(&self) -> Box<dyn Backend> {
+                match self {
+                    #(#variant_backend)*
+                }
+            }
+            fn next(&self) -> Option<Self> {
+                match self {
+                    #(#variant_next)*
+                }
+            }
+        }
+    };
+    expanded
+}
+
+fn generate_variant_imports(enum_data: &syn::DataEnum) -> impl Iterator<Item = TokenStream2> + '_ {
+    let variant_imports = enum_data.variants.iter().map(|variant| {
+        let variant_name = &variant.ident;
+
+        let variant_module = proc_macro2::Ident::new(
+            &variant_name.to_string().to_lowercase(),
+            proc_macro2::Span::call_site(),
+        );
+
+        quote! {
+            pub(crate) use actual::#variant_module::#variant_name;
+
+        }
+    });
+    variant_imports
+}
+
+fn generate_variant_matches_next(
+    enum_data: &syn::DataEnum,
+) -> impl Iterator<Item = TokenStream2> + '_ {
+    let variant_matches_next = enum_data.variants.iter().enumerate().map(|(i, variant)| {
+        let variant_name = &variant.ident;
+        if i == enum_data.variants.len() - 1 {
+            quote! {
+                Self::#variant_name => None,
+            }
+        } else {
+            let next_variant = &enum_data.variants[i + 1].ident;
+            quote! {
+                Self::#variant_name => Some(Self::#next_variant),
+            }
+        }
+    });
+    variant_matches_next
+}
+
+fn generate_variant_backend(enum_data: &syn::DataEnum) -> impl Iterator<Item = TokenStream2> + '_ {
+    let variant_matches_backend = enum_data.variants.iter().map(|variant| {
+        let variant_name = &variant.ident;
+        quote! {
+            Self::#variant_name => Box::new(#variant_name::new()),
+        }
+    });
+    variant_matches_backend
+}