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Support #[from] on an Option field

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David Tolnay 2021-08-28 15:47:05 -07:00
parent 6159aba3b7
commit 2a2d1725e7
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1 changed files with 32 additions and 9 deletions
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41
impl/src/expand.rs
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@ -2,7 +2,7 @@ use crate::ast::{Enum, Field, Input, Struct};
use proc_macro2::TokenStream;
use quote::{format_ident, quote, quote_spanned, ToTokens};
use syn::spanned::Spanned;
use syn::{Data, DeriveInput, Member, PathArguments, Result, Type, Visibility};
use syn::{Data, DeriveInput, GenericArgument, Member, PathArguments, Result, Type, Visibility};
pub fn derive(node: &DeriveInput) -> Result<TokenStream> {
let input = Input::from_syn(node)?;
@ -131,7 +131,7 @@ fn impl_struct(input: Struct) -> TokenStream {
let from_impl = input.from_field().map(|from_field| {
let backtrace_field = input.distinct_backtrace_field();
let from = from_field.ty;
let from = unoptional_type(from_field.ty);
let body = from_initializer(from_field, backtrace_field);
quote! {
#[allow(unused_qualifications)]
@ -351,7 +351,7 @@ fn impl_enum(input: Enum) -> TokenStream {
let from_field = variant.from_field()?;
let backtrace_field = variant.distinct_backtrace_field();
let variant = &variant.ident;
let from = from_field.ty;
let from = unoptional_type(from_field.ty);
let body = from_initializer(from_field, backtrace_field);
Some(quote! {
#[allow(unused_qualifications)]
@ -394,6 +394,11 @@ fn fields_pat(fields: &[Field]) -> TokenStream {
fn from_initializer(from_field: &Field, backtrace_field: Option<&Field>) -> TokenStream {
let from_member = &from_field.member;
let some_source = if type_is_option(from_field.ty) {
quote!(std::option::Option::Some(source))
} else {
quote!(source)
};
let backtrace = backtrace_field.map(|backtrace_field| {
let backtrace_member = &backtrace_field.member;
if type_is_option(backtrace_field.ty) {
@ -407,25 +412,43 @@ fn from_initializer(from_field: &Field, backtrace_field: Option<&Field>) -> Toke
}
});
quote!({
#from_member: source,
#from_member: #some_source,
#backtrace
})
}
fn type_is_option(ty: &Type) -> bool {
type_parameter_of_option(ty).is_some()
}
fn unoptional_type(ty: &Type) -> TokenStream {
let unoptional = type_parameter_of_option(ty).unwrap_or(ty);
quote!(#unoptional)
}
fn type_parameter_of_option(ty: &Type) -> Option<&Type> {
let path = match ty {
Type::Path(ty) => &ty.path,
_ => return false,
_ => return None,
};
let last = path.segments.last().unwrap();
if last.ident != "Option" {
return false;
return None;
}
match &last.arguments {
PathArguments::AngleBracketed(bracketed) => bracketed.args.len() == 1,
_ => false,
let bracketed = match &last.arguments {
PathArguments::AngleBracketed(bracketed) => bracketed,
_ => return None,
};
if bracketed.args.len() != 1 {
return None;
}
match &bracketed.args[0] {
GenericArgument::Type(arg) => Some(arg),
_ => None,
}
}