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from_repr.rs
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from_repr.rs
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use heck::ToShoutySnakeCase;
use proc_macro2::{Span, TokenStream};
use quote::{format_ident, quote};
use syn::{Data, DeriveInput, Fields, PathArguments, Type, TypeParen};
use crate::helpers::{non_enum_error, HasStrumVariantProperties, HasTypeProperties};
pub fn from_repr_inner(ast: &DeriveInput) -> syn::Result<TokenStream> {
let name = &ast.ident;
let gen = &ast.generics;
let (impl_generics, ty_generics, where_clause) = gen.split_for_impl();
let vis = &ast.vis;
let attrs = &ast.attrs;
let type_properties = ast.get_type_properties()?;
let strum_module_path = type_properties.crate_module_path();
let mut discriminant_type: Type = syn::parse("usize".parse().unwrap()).unwrap();
for attr in attrs {
let path = &attr.path;
let tokens = &attr.tokens;
if path.leading_colon.is_some() {
continue;
}
if path.segments.len() != 1 {
continue;
}
let segment = path.segments.first().unwrap();
if segment.ident != "repr" {
continue;
}
if segment.arguments != PathArguments::None {
continue;
}
let typ_paren = match syn::parse2::<Type>(tokens.clone()) {
Ok(Type::Paren(TypeParen { elem, .. })) => *elem,
_ => continue,
};
let inner_path = match &typ_paren {
Type::Path(t) => t,
_ => continue,
};
if let Some(seg) = inner_path.path.segments.last() {
for t in &[
"u8", "u16", "u32", "u64", "usize", "i8", "i16", "i32", "i64", "isize",
] {
if seg.ident == t {
discriminant_type = typ_paren;
break;
}
}
}
}
if gen.lifetimes().count() > 0 {
return Err(syn::Error::new(
Span::call_site(),
"This macro doesn't support enums with lifetimes. \
The resulting enums would be unbounded.",
));
}
let variants = match &ast.data {
Data::Enum(v) => &v.variants,
_ => return Err(non_enum_error()),
};
let mut arms = Vec::new();
let mut constant_defs = Vec::new();
let mut has_additional_data = false;
let mut prev_const_var_ident = None;
for variant in variants {
if variant.get_variant_properties()?.disabled.is_some() {
continue;
}
let ident = &variant.ident;
let params = match &variant.fields {
Fields::Unit => quote! {},
Fields::Unnamed(fields) => {
has_additional_data = true;
let defaults = ::core::iter::repeat(quote!(::core::default::Default::default()))
.take(fields.unnamed.len());
quote! { (#(#defaults),*) }
}
Fields::Named(fields) => {
has_additional_data = true;
let fields = fields
.named
.iter()
.map(|field| field.ident.as_ref().unwrap());
quote! { {#(#fields: ::core::default::Default::default()),*} }
}
};
let const_var_str = format!("{}_DISCRIMINANT", variant.ident).to_shouty_snake_case();
let const_var_ident = format_ident!("{}", const_var_str);
let const_val_expr = match &variant.discriminant {
Some((_, expr)) => quote! { #expr },
None => match &prev_const_var_ident {
Some(prev) => quote! { #prev + 1 },
None => quote! { 0 },
},
};
constant_defs.push(quote! {const #const_var_ident: #discriminant_type = #const_val_expr;});
arms.push(quote! {v if v == #const_var_ident => ::core::option::Option::Some(#name::#ident #params)});
prev_const_var_ident = Some(const_var_ident);
}
arms.push(quote! { _ => ::core::option::Option::None });
let const_if_possible = if has_additional_data {
quote! {}
} else {
#[rustversion::before(1.46)]
fn filter_by_rust_version(_: TokenStream) -> TokenStream {
quote! {}
}
#[rustversion::since(1.46)]
fn filter_by_rust_version(s: TokenStream) -> TokenStream {
s
}
filter_by_rust_version(quote! { const })
};
let from_repr = quote! {
#[allow(clippy::use_self)]
impl #impl_generics #name #ty_generics #where_clause {
#[doc = "Try to create [Self] from the raw representation"]
#vis #const_if_possible fn from_repr(discriminant: #discriminant_type) -> Option<#name #ty_generics> {
#(#constant_defs)*
match discriminant {
#(#arms),*
}
}
}
};
let try_from_repr = try_from_repr(
name,
&discriminant_type,
&impl_generics,
&ty_generics,
where_clause,
&strum_module_path,
);
Ok(quote! {
#from_repr
#try_from_repr
})
}
#[rustversion::before(1.34)]
fn try_from_repr(
_name: &proc_macro2::Ident,
_discriminant_type: &Type,
_impl_generics: &syn::ImplGenerics,
_ty_generics: &syn::TypeGenerics,
_where_clause: Option<&syn::WhereClause>,
_strum_module_path: &syn::Path,
) -> TokenStream {
Default::default()
}
#[rustversion::since(1.34)]
fn try_from_repr(
name: &proc_macro2::Ident,
discriminant_type: &Type,
impl_generics: &syn::ImplGenerics,
ty_generics: &syn::TypeGenerics,
where_clause: Option<&syn::WhereClause>,
strum_module_path: &syn::Path,
) -> TokenStream {
quote! {
#[allow(clippy::use_self)]
impl #impl_generics ::core::convert::TryFrom<#discriminant_type> for #name #ty_generics #where_clause {
type Error = #strum_module_path::ParseError;
fn try_from(s: #discriminant_type) -> ::core::result::Result< #name #ty_generics , <Self as ::core::convert::TryFrom<#discriminant_type>>::Error> {
Self::from_repr(s).ok_or(#strum_module_path::ParseError::VariantNotFound)
}
}
}
}