Migrate types from a macro to a trait

crates/libm-macros/Cargo.toml

@@ -8,6 +8,7 @@ publish = false
 proc-macro = true
 
 [dependencies]
+heck = "0.5.0"
 proc-macro2 = "1.0.88"
 quote = "1.0.37"
 syn = { version = "2.0.79", features = ["full", "extra-traits", "visit-mut"] }

crates/libm-macros/src/enums.rs

@@ -0,0 +1,132 @@
+use heck::ToUpperCamelCase;
+use proc_macro2 as pm2;
+use proc_macro2::{Ident, Span};
+use quote::quote;
+use syn::spanned::Spanned;
+use syn::{Fields, ItemEnum, Variant};
+
+use crate::{ALL_FUNCTIONS_FLAT, base_name};
+
+/// Implement `#[function_enum]`, see documentation in `lib.rs`.
+pub fn function_enum(
+    mut item: ItemEnum,
+    attributes: pm2::TokenStream,
+) -> syn::Result<pm2::TokenStream> {
+    expect_empty_enum(&item)?;
+    let attr_span = attributes.span();
+    let mut attr = attributes.into_iter();
+
+    // Attribute should be the identifier of the `BaseName` enum.
+    let Some(tt) = attr.next() else {
+        return Err(syn::Error::new(attr_span, "expected one attribute"));
+    };
+
+    let pm2::TokenTree::Ident(base_enum) = tt else {
+        return Err(syn::Error::new(tt.span(), "expected an identifier"));
+    };
+
+    if let Some(tt) = attr.next() {
+        return Err(syn::Error::new(tt.span(), "unexpected token after identifier"));
+    }
+
+    let enum_name = &item.ident;
+    let mut as_str_arms = Vec::new();
+    let mut base_arms = Vec::new();
+
+    for func in ALL_FUNCTIONS_FLAT.iter() {
+        let fn_name = func.name;
+        let ident = Ident::new(&fn_name.to_upper_camel_case(), Span::call_site());
+        let bname_ident = Ident::new(&base_name(fn_name).to_upper_camel_case(), Span::call_site());
+
+        // Match arm for `fn as_str(self)` matcher
+        as_str_arms.push(quote! { Self::#ident => #fn_name });
+
+        // Match arm for `fn base_name(self)` matcher
+        base_arms.push(quote! { Self::#ident => #base_enum::#bname_ident });
+
+        let variant =
+            Variant { attrs: Vec::new(), ident, fields: Fields::Unit, discriminant: None };
+
+        item.variants.push(variant);
+    }
+
+    let res = quote! {
+        // Instantiate the enum
+        #item
+
+        impl #enum_name {
+            /// The stringified version of this function name.
+            const fn as_str(self) -> &'static str {
+                match self {
+                    #( #as_str_arms , )*
+                }
+            }
+
+            /// The base name enum for this function.
+            const fn base_name(self) -> #base_enum {
+                match self {
+                    #( #base_arms, )*
+                }
+            }
+        }
+    };
+
+    Ok(res)
+}
+
+/// Implement `#[base_name_enum]`, see documentation in `lib.rs`.
+pub fn base_name_enum(
+    mut item: ItemEnum,
+    attributes: pm2::TokenStream,
+) -> syn::Result<pm2::TokenStream> {
+    expect_empty_enum(&item)?;
+    if !attributes.is_empty() {
+        let sp = attributes.span();
+        return Err(syn::Error::new(sp.span(), "no attributes expected"));
+    }
+
+    let mut base_names: Vec<_> =
+        ALL_FUNCTIONS_FLAT.iter().map(|func| base_name(func.name)).collect();
+    base_names.sort_unstable();
+    base_names.dedup();
+
+    let item_name = &item.ident;
+    let mut as_str_arms = Vec::new();
+
+    for base_name in base_names {
+        let ident = Ident::new(&base_name.to_upper_camel_case(), Span::call_site());
+
+        // Match arm for `fn as_str(self)` matcher
+        as_str_arms.push(quote! { Self::#ident => #base_name });
+
+        let variant =
+            Variant { attrs: Vec::new(), ident, fields: Fields::Unit, discriminant: None };
+
+        item.variants.push(variant);
+    }
+
+    let res = quote! {
+        // Instantiate the enum
+        #item
+
+        impl #item_name {
+            /// The stringified version of this base name.
+            const fn as_str(self) -> &'static str {
+                match self {
+                    #( #as_str_arms ),*
+                }
+            }
+        }
+    };
+
+    Ok(res)
+}
+
+/// Verify that an enum is empty, otherwise return an error
+fn expect_empty_enum(item: &ItemEnum) -> syn::Result<()> {
+    if !item.variants.is_empty() {
+        Err(syn::Error::new(item.variants.span(), "expected an empty enum"))
+    } else {
+        Ok(())
+    }
+}