Handle more SCALE attributes: skip, index

derive/src/lib.rs

@@ -18,6 +18,7 @@ extern crate alloc;
 extern crate proc_macro;
 
 mod trait_bounds;
+mod utils;
 
 use alloc::{
     string::{
@@ -41,21 +42,14 @@ use syn::{
     punctuated::Punctuated,
     token::Comma,
     visit_mut::VisitMut,
-    AttrStyle,
     Data,
     DataEnum,
     DataStruct,
     DeriveInput,
-    Expr,
-    ExprLit,
     Field,
     Fields,
     Ident,
     Lifetime,
-    Lit,
-    Meta,
-    MetaList,
-    NestedMeta,
     Variant,
 };
 
@@ -140,6 +134,7 @@ type FieldsList = Punctuated<Field, Comma>;
 fn generate_fields(fields: &FieldsList) -> Vec<TokenStream2> {
     fields
         .iter()
+        .filter(|f| !utils::should_skip(&f.attrs))
         .map(|f| {
             let (ty, ident) = (&f.ty, &f.ident);
             // Replace any field lifetime params with `static to prevent "unnecessary lifetime parameter"
@@ -154,7 +149,7 @@ fn generate_fields(fields: &FieldsList) -> Vec<TokenStream2> {
             StaticLifetimesReplace.visit_type_mut(&mut ty);
 
             let type_name = clean_type_string(&quote!(#ty).to_string());
-            let method_call = if is_compact(f) {
+            let method_call = if utils::is_compact(f) {
                 quote!(.compact_of::<#ty>)
             } else {
                 quote!(.field_of::<#ty>)
@@ -168,23 +163,6 @@ fn generate_fields(fields: &FieldsList) -> Vec<TokenStream2> {
         .collect()
 }
 
-/// Look for a `#[codec(compact)]` outer attribute.
-fn is_compact(f: &Field) -> bool {
-    f.attrs.iter().any(|attr| {
-        let mut is_compact = false;
-        if attr.style == AttrStyle::Outer && attr.path.is_ident("codec") {
-            if let Ok(Meta::List(MetaList { nested, .. })) = attr.parse_meta() {
-                if let Some(NestedMeta::Meta(Meta::Path(path))) = nested.iter().next() {
-                    if path.is_ident("compact") {
-                        is_compact = true;
-                    }
-                }
-            }
-        }
-        is_compact
-    })
-}
-
 fn clean_type_string(input: &str) -> String {
     input
         .replace(" ::", "::")
@@ -229,27 +207,17 @@ fn generate_composite_type(data_struct: &DataStruct, scale_info: &Ident) -> Toke
 type VariantList = Punctuated<Variant, Comma>;
 
 fn generate_c_like_enum_def(variants: &VariantList, scale_info: &Ident) -> TokenStream2 {
-    let variants = variants.into_iter().enumerate().map(|(i, v)| {
-        let name = &v.ident;
-        let discriminant = if let Some((
-            _,
-            Expr::Lit(ExprLit {
-                lit: Lit::Int(lit_int),
-                ..
-            }),
-        )) = &v.discriminant
-        {
-            match lit_int.base10_parse::<u64>() {
-                Ok(i) => i,
-                Err(err) => return err.to_compile_error(),
+    let variants = variants
+        .into_iter()
+        .enumerate()
+        .filter(|(_, v)| !utils::should_skip(&v.attrs))
+        .map(|(i, v)| {
+            let name = &v.ident;
+            let discriminant = utils::variant_index(v, i);
+            quote! {
+                .variant(stringify!(#name), #discriminant as u64)
             }
-        } else {
-            i as u64
-        };
-        quote! {
-            .variant(stringify!(#name), #discriminant)
-        }
-    });
+        });
     quote! {
         variant(
             :: #scale_info ::build::Variants::fieldless()
@@ -259,9 +227,9 @@ fn generate_c_like_enum_def(variants: &VariantList, scale_info: &Ident) -> Token
 }
 
 fn is_c_like_enum(variants: &VariantList) -> bool {
-    // any variant has an explicit discriminant
+    // One of the variants has an explicit discriminant, or…
     variants.iter().any(|v| v.discriminant.is_some()) ||
-        // all variants are unit
+        // …all variants are unit
         variants.iter().all(|v| matches!(v.fields, Fields::Unit))
 }
 
@@ -272,37 +240,40 @@ fn generate_variant_type(data_enum: &DataEnum, scale_info: &Ident) -> TokenStrea
         return generate_c_like_enum_def(variants, scale_info)
     }
 
-    let variants = variants.into_iter().map(|v| {
-        let ident = &v.ident;
-        let v_name = quote! {stringify!(#ident) };
-        match v.fields {
-            Fields::Named(ref fs) => {
-                let fields = generate_fields(&fs.named);
-                quote! {
-                    .variant(
-                        #v_name,
-                        :: #scale_info ::build::Fields::named()
-                            #( #fields)*
-                    )
+    let variants = variants
+        .into_iter()
+        .filter(|v| !utils::should_skip(&v.attrs))
+        .map(|v| {
+            let ident = &v.ident;
+            let v_name = quote! {stringify!(#ident) };
+            match v.fields {
+                Fields::Named(ref fs) => {
+                    let fields = generate_fields(&fs.named);
+                    quote! {
+                        .variant(
+                            #v_name,
+                            :: #scale_info::build::Fields::named()
+                                #( #fields)*
+                        )
+                    }
                 }
-            }
-            Fields::Unnamed(ref fs) => {
-                let fields = generate_fields(&fs.unnamed);
-                quote! {
-                    .variant(
-                        #v_name,
-                        :: #scale_info ::build::Fields::unnamed()
-                            #( #fields)*
-                    )
+                Fields::Unnamed(ref fs) => {
+                    let fields = generate_fields(&fs.unnamed);
+                    quote! {
+                        .variant(
+                            #v_name,
+                            :: #scale_info::build::Fields::unnamed()
+                                #( #fields)*
+                        )
+                    }
                 }
-            }
-            Fields::Unit => {
-                quote! {
-                    .variant_unit(#v_name)
+                Fields::Unit => {
+                    quote! {
+                        .variant_unit(#v_name)
+                    }
                 }
             }
-        }
-    });
+        });
     quote! {
         variant(
             :: #scale_info ::build::Variants::with_fields()

derive/src/trait_bounds.rs

@@ -29,6 +29,8 @@ use syn::{
     WhereClause,
 };
 
+use crate::utils;
+
 /// Generates a where clause for a `TypeInfo` impl, adding `TypeInfo + 'static` bounds to all
 /// relevant generic types including associated types (e.g. `T::A: TypeInfo`), correctly dealing
 /// with self-referential types.
@@ -164,7 +166,7 @@ fn collect_types_to_bind(
                 // to not have them in the where clause.
                 !type_or_sub_type_path_starts_with_ident(&field.ty, &input_ident)
             })
-            .map(|f| (f.ty.clone(), super::is_compact(f)))
+            .map(|f| (f.ty.clone(), utils::is_compact(f)))
             .collect()
     };
 

derive/src/utils.rs

@@ -0,0 +1,109 @@
+// Copyright 2019-2021 Parity Technologies (UK) Ltd.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+//! Utility methods to work with `SCALE` attributes relevant for the `TypeInfo` derive..
+//!
+//! NOTE: The code here is copied verbatim from `parity-scale-codec-derive`.
+
+use proc_macro2::TokenStream;
+use quote::quote;
+use syn::{
+    spanned::Spanned,
+    AttrStyle,
+    Attribute,
+    Lit,
+    Meta,
+    NestedMeta,
+    Variant,
+};
+
+/// Look for a `#[codec(index = $int)]` attribute on a variant. If no attribute
+/// is found, fall back to the discriminant or just the variant index.
+pub fn variant_index(v: &Variant, i: usize) -> TokenStream {
+    // first look for an attribute
+    let index = find_meta_item(v.attrs.iter(), |meta| {
+        if let NestedMeta::Meta(Meta::NameValue(ref nv)) = meta {
+            if nv.path.is_ident("index") {
+                if let Lit::Int(ref v) = nv.lit {
+                    let byte = v
+                        .base10_parse::<u8>()
+                        .expect("Internal error. `#[codec(index = …)]` attribute syntax must be checked in `parity-scale-codec`. This is a bug.");
+                    return Some(byte)
+                }
+            }
+        }
+
+        None
+    });
+
+    // then fallback to discriminant or just index
+    index.map(|i| quote! { #i }).unwrap_or_else(|| {
+        v.discriminant
+            .as_ref()
+            .map(|&(_, ref expr)| quote! { #expr })
+            .unwrap_or_else(|| quote! { #i })
+    })
+}
+
+/// Look for a `#[codec(compact)]` outer attribute on the given `Field`.
+pub fn is_compact(field: &syn::Field) -> bool {
+    let outer_attrs = field
+        .attrs
+        .iter()
+        .filter(|attr| attr.style == AttrStyle::Outer);
+    find_meta_item(outer_attrs, |meta| {
+        if let NestedMeta::Meta(Meta::Path(ref path)) = meta {
+            if path.is_ident("compact") {
+                return Some(())
+            }
+        }
+
+        None
+    })
+    .is_some()
+}
+
+/// Look for a `#[codec(skip)]` in the given attributes.
+pub fn should_skip(attrs: &[Attribute]) -> bool {
+    find_meta_item(attrs.iter(), |meta| {
+        if let NestedMeta::Meta(Meta::Path(ref path)) = meta {
+            if path.is_ident("skip") {
+                return Some(path.span())
+            }
+        }
+
+        None
+    })
+    .is_some()
+}
+
+fn find_meta_item<'a, F, R, I>(itr: I, pred: F) -> Option<R>
+where
+    F: Fn(&NestedMeta) -> Option<R> + Clone,
+    I: Iterator<Item = &'a Attribute>,
+{
+    itr.filter_map(|attr| {
+        if attr.path.is_ident("codec") {
+            if let Meta::List(ref meta_list) = attr
+                .parse_meta()
+                .expect("Internal error. `#[codec(…)]` attributes must be checked in `parity-scale-codec`. This is a bug.")
+            {
+                return meta_list.nested.iter().filter_map(pred.clone()).next()
+            }
+        }
+
+        None
+    })
+    .next()
+}

src/ty/variant.rs

@@ -60,7 +60,7 @@ use serde::{
 ///     Monday,
 ///     Tuesday,
 ///     Wednesday,
-///     Thursday = 42, // Also allows to manually set the discriminant!
+///     Thursday = 42, // Allows setting the discriminant explicitly
 ///     Friday,
 ///     Saturday,
 ///     Sunday,