85 lines
2.9 KiB
Rust
85 lines
2.9 KiB
Rust
use proc_macro2::{Span, TokenStream};
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use quote::{quote, ToTokens};
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use syn::{Fields, FieldsNamed, FieldsUnnamed, ItemEnum};
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use crate::util::{get_rename, get_rename_rule};
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pub fn expand_enum_from_string(input: &ItemEnum) -> syn::Result<TokenStream> {
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let enum_name = &input.ident;
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let rename_rule = get_rename_rule(input)?;
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let mut fallback = None;
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let mut fallback_ty = None;
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let branches: Vec<_> = input
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.variants
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.iter()
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.map(|v| {
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let variant_name = &v.ident;
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let variant_str = match (get_rename(v)?, &v.fields) {
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(None, Fields::Unit) => Some(
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rename_rule.apply_to_variant(&variant_name.to_string()).into_token_stream(),
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),
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(Some(rename), Fields::Unit) => Some(rename.into_token_stream()),
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(None, Fields::Named(FieldsNamed { named: fields, .. }))
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| (None, Fields::Unnamed(FieldsUnnamed { unnamed: fields, .. })) => {
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if fields.len() != 1 {
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return Err(syn::Error::new_spanned(
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v,
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"multiple data fields are not supported",
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));
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}
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if fallback.is_some() {
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return Err(syn::Error::new_spanned(
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v,
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"multiple data-carrying variants are not supported",
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));
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}
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let member = match &fields[0].ident {
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Some(name) => name.into_token_stream(),
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None => quote! { 0 },
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};
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fallback = Some(quote! {
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_ => #enum_name :: #variant_name { #member: s.into() }
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});
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fallback_ty = Some(&fields[0].ty);
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None
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}
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(Some(_), _) => {
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return Err(syn::Error::new_spanned(
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v,
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"ruma_enum(rename) is only allowed on unit variants",
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));
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}
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};
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Ok(variant_str.map(|s| quote! { #s => #enum_name :: #variant_name }))
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})
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.collect::<syn::Result<_>>()?;
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// Remove `None` from the iterator to avoid emitting consecutive commas in repetition
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let branches = branches.iter().flatten();
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if fallback.is_none() {
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return Err(syn::Error::new(Span::call_site(), "required fallback variant not found"));
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}
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Ok(quote! {
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impl<T> ::std::convert::From<T> for #enum_name
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where
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T: ::std::convert::AsRef<::std::primitive::str>
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+ ::std::convert::Into<#fallback_ty>
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{
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fn from(s: T) -> Self {
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match s.as_ref() {
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#( #branches, )*
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#fallback
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}
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}
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}
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})
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}
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