derive(FromRepr)

sub/_macros/src/from_repr.rs

@@ -0,0 +1,64 @@
+use proc_macro::TokenStream;
+
+const VALID: &[&'static str] = &[
+    "u8", "u16", "u32", "u64", "u128",
+    "i8", "i16", "i32", "i64", "i128",
+];
+
+pub fn derive_from_repr(input: TokenStream) -> TokenStream {
+    let syn::DeriveInput { attrs, ident, data, .. } = syn::parse_macro_input!(input);
+    let edata = match data {
+        syn::Data::Enum(edata) => edata,
+        _invalid => return TokenStream::from(quote::quote! { compile_error!("The identifier should not be empty"); }),
+    };
+
+    let repr_type = attrs.iter()
+        .filter_map(|attribute| {
+            // verify it is a repr type
+            attribute.path().get_ident()?
+                .to_string().eq("repr")
+                .then_some(())?;
+            let mut repr_type: Option<syn::Path> = None;
+            let _ = attribute.parse_nested_meta(|meta| {
+                for &v in VALID {
+                    if meta.path.is_ident(v) {
+                        repr_type = Some(meta.path);
+                        return Ok(())
+                    }
+                }
+                Err(meta.error("unrecognized repr"))
+            });
+            repr_type
+        }).next();
+
+    let repr = match repr_type {
+        Some(repr) => repr,
+        None => {
+            return TokenStream::from(quote::quote! {
+                compile_error!("PrimitiveEnum requires the #[repr(u/i*)] attribute");
+            })
+        }
+    };
+
+    let values = edata.variants.iter().filter_map(|variant| {
+        if let Some((_, desc)) = &variant.discriminant {
+            let variant = &variant.ident;
+            Some(quote::quote! {
+                #desc => Some(Self::#variant),
+            })
+        } else { None }
+    });
+
+    let name = &ident;
+    TokenStream::from(quote::quote! {
+        impl x::FromRepr for #name {
+            type Repr = #repr;
+            fn from_repr(repr: #repr) -> Option<Self>  {
+                match repr {
+                    #(#values)*
+                    _ => None
+                }
+            }
+        }
+    })
+}

sub/_macros/src/lib.rs

@@ -0,0 +1,14 @@
+
+mod from_repr;
+
+
+#[proc_macro_derive(FromRepr)]
+pub fn derive_from_repr(input: proc_macro::TokenStream) -> proc_macro::TokenStream {
+    from_repr::derive_from_repr(input)
+}
+
+
+
+
+
+