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//! Implementation of an [`Into`] derive macro.
use std::{borrow::Cow, iter};
use proc_macro2::{Span, TokenStream};
use quote::{quote, ToTokens as _};
use syn::{
ext::IdentExt as _,
parse::{discouraged::Speculative as _, Parse, ParseStream},
punctuated::Punctuated,
spanned::Spanned as _,
token, Ident,
};
use crate::{
parsing::Type,
utils::{polyfill, Either, FieldsExt as _},
};
/// Expands an [`Into`] derive macro.
pub fn expand(input: &syn::DeriveInput, _: &'static str) -> syn::Result<TokenStream> {
let data = match &input.data {
syn::Data::Struct(data) => Ok(data),
syn::Data::Enum(e) => Err(syn::Error::new(
e.enum_token.span(),
"`Into` cannot be derived for enums",
)),
syn::Data::Union(u) => Err(syn::Error::new(
u.union_token.span(),
"`Into` cannot be derived for unions",
)),
}?;
let attr = StructAttribute::parse_attrs(&input.attrs, &data.fields)?
.unwrap_or_else(|| StructAttribute {
owned: Some(Punctuated::new()),
r#ref: None,
ref_mut: None,
});
let ident = &input.ident;
let fields = data
.fields
.iter()
.enumerate()
.filter_map(|(i, f)| match SkipFieldAttribute::parse_attrs(&f.attrs) {
Ok(None) => Some(Ok((
&f.ty,
f.ident
.as_ref()
.map_or_else(|| Either::Right(syn::Index::from(i)), Either::Left),
))),
Ok(Some(_)) => None,
Err(e) => Some(Err(e)),
})
.collect::<syn::Result<Vec<_>>>()?;
let (fields_tys, fields_idents): (Vec<_>, Vec<_>) = fields.into_iter().unzip();
let (fields_tys, fields_idents) = (&fields_tys, &fields_idents);
let expand = |tys: Option<Punctuated<_, _>>, r: bool, m: bool| {
let Some(tys) = tys else {
return Either::Left(iter::empty());
};
let lf =
r.then(|| syn::Lifetime::new("'__derive_more_into", Span::call_site()));
let r = r.then(token::And::default);
let m = m.then(token::Mut::default);
let gens = if let Some(lf) = lf.clone() {
let mut gens = input.generics.clone();
gens.params.push(syn::LifetimeParam::new(lf).into());
Cow::Owned(gens)
} else {
Cow::Borrowed(&input.generics)
};
Either::Right(
if tys.is_empty() {
Either::Left(iter::once(Type::tuple(fields_tys.clone())))
} else {
Either::Right(tys.into_iter())
}
.map(move |ty| {
let tys = fields_tys.validate_type(&ty)?.collect::<Vec<_>>();
let (impl_gens, _, where_clause) = gens.split_for_impl();
let (_, ty_gens, _) = input.generics.split_for_impl();
Ok(quote! {
#[automatically_derived]
impl #impl_gens ::core::convert::From<#r #lf #m #ident #ty_gens>
for ( #( #r #lf #m #tys ),* ) #where_clause
{
#[inline]
fn from(value: #r #lf #m #ident #ty_gens) -> Self {
(#(
<#r #m #tys as ::core::convert::From<_>>::from(
#r #m value. #fields_idents
)
),*)
}
}
})
}),
)
};
[
expand(attr.owned, false, false),
expand(attr.r#ref, true, false),
expand(attr.ref_mut, true, true),
]
.into_iter()
.flatten()
.collect()
}
/// Representation of an [`Into`] derive macro struct container attribute.
///
/// ```rust,ignore
/// #[into(<types>)]
/// #[into(owned(<types>), ref(<types>), ref_mut(<types>))]
/// ```
#[derive(Debug, Default)]
struct StructAttribute {
/// [`Type`]s wrapped into `owned(...)` or simply `#[into(...)]`.
owned: Option<Punctuated<Type, token::Comma>>,
/// [`Type`]s wrapped into `ref(...)`.
r#ref: Option<Punctuated<Type, token::Comma>>,
/// [`Type`]s wrapped into `ref_mut(...)`.
ref_mut: Option<Punctuated<Type, token::Comma>>,
}
impl StructAttribute {
/// Parses a [`StructAttribute`] from the provided [`syn::Attribute`]s.
fn parse_attrs(
attrs: impl AsRef<[syn::Attribute]>,
fields: &syn::Fields,
) -> syn::Result<Option<Self>> {
fn infer<T>(v: T) -> T
where
T: for<'a> FnOnce(ParseStream<'a>) -> syn::Result<StructAttribute>,
{
v
}
attrs
.as_ref()
.iter()
.filter(|attr| attr.path().is_ident("into"))
.try_fold(None, |mut attrs, attr| {
let merge = |out: &mut Option<_>, tys| match (out.as_mut(), tys) {
(None, Some(tys)) => {
*out = Some::<Punctuated<_, _>>(tys);
}
(Some(out), Some(tys)) => out.extend(tys),
(Some(_), None) | (None, None) => {}
};
let field_attr =
attr.parse_args_with(infer(|stream| Self::parse(stream, fields)))?;
let out = attrs.get_or_insert_with(Self::default);
merge(&mut out.owned, field_attr.owned);
merge(&mut out.r#ref, field_attr.r#ref);
merge(&mut out.ref_mut, field_attr.ref_mut);
Ok(attrs)
})
}
/// Parses a single [`StructAttribute`].
fn parse(content: ParseStream<'_>, fields: &syn::Fields) -> syn::Result<Self> {
check_legacy_syntax(content, fields)?;
let mut out = Self::default();
let parse_inner = |ahead, types: &mut Option<_>| {
content.advance_to(&ahead);
let types = types.get_or_insert_with(Punctuated::new);
if content.peek(token::Paren) {
let inner;
syn::parenthesized!(inner in content);
types.extend(
inner
.parse_terminated(Type::parse, token::Comma)?
.into_pairs(),
);
}
if content.peek(token::Comma) {
let comma = content.parse::<token::Comma>()?;
if !types.empty_or_trailing() {
types.push_punct(comma);
}
}
Ok(())
};
let mut has_wrapped_type = false;
let mut top_level_type = None;
while !content.is_empty() {
let ahead = content.fork();
let res = if ahead.peek(Ident::peek_any) {
ahead.call(Ident::parse_any).map(Into::into)
} else {
ahead.parse::<syn::Path>()
};
match res {
Ok(p) if p.is_ident("owned") => {
has_wrapped_type = true;
parse_inner(ahead, &mut out.owned)?;
}
Ok(p) if p.is_ident("ref") => {
has_wrapped_type = true;
parse_inner(ahead, &mut out.r#ref)?;
}
Ok(p) if p.is_ident("ref_mut") => {
has_wrapped_type = true;
parse_inner(ahead, &mut out.ref_mut)?;
}
_ => {
let ty = content.parse::<Type>()?;
let _ = top_level_type.get_or_insert_with(|| ty.clone());
out.owned.get_or_insert_with(Punctuated::new).push_value(ty);
if content.peek(token::Comma) {
out.owned
.get_or_insert_with(Punctuated::new)
.push_punct(content.parse::<token::Comma>()?)
}
}
}
}
if let Some(ty) = top_level_type.filter(|_| has_wrapped_type) {
Err(syn::Error::new(
ty.span(),
format!(
"mixing regular types with wrapped into \
`owned`/`ref`/`ref_mut` is not allowed, try wrapping \
this type into `owned({ty}), ref({ty}), ref_mut({ty})`",
ty = ty.into_token_stream(),
),
))
} else {
Ok(out)
}
}
}
/// `#[into(skip)]` field attribute.
struct SkipFieldAttribute;
impl SkipFieldAttribute {
/// Parses a [`SkipFieldAttribute`] from the provided [`syn::Attribute`]s.
fn parse_attrs(attrs: impl AsRef<[syn::Attribute]>) -> syn::Result<Option<Self>> {
Ok(attrs
.as_ref()
.iter()
.filter(|attr| attr.path().is_ident("into"))
.try_fold(None, |mut attrs, attr| {
let field_attr = attr.parse_args::<SkipFieldAttribute>()?;
if let Some((path, _)) = attrs.replace((attr.path(), field_attr)) {
Err(syn::Error::new(
path.span(),
"only single `#[into(...)]` attribute is allowed here",
))
} else {
Ok(attrs)
}
})?
.map(|(_, attr)| attr))
}
}
impl Parse for SkipFieldAttribute {
fn parse(content: ParseStream) -> syn::Result<Self> {
match content.parse::<syn::Path>()? {
p if p.is_ident("skip") | p.is_ident("ignore") => Ok(Self),
p => Err(syn::Error::new(
p.span(),
format!("expected `skip`, found: `{}`", p.into_token_stream()),
)),
}
}
}
/// [`Error`]ors for legacy syntax: `#[into(types(i32, "&str"))]`.
fn check_legacy_syntax(
tokens: ParseStream<'_>,
fields: &syn::Fields,
) -> syn::Result<()> {
let span = tokens.span();
let tokens = tokens.fork();
let map_ty = |s: String| {
if fields.len() > 1 {
format!(
"({})",
(0..fields.len())
.map(|_| s.as_str())
.collect::<Vec<_>>()
.join(", ")
)
} else {
s
}
};
let field = match fields.len() {
0 => None,
1 => Some(
fields
.iter()
.next()
.unwrap_or_else(|| unreachable!("fields.len() == 1"))
.ty
.to_token_stream()
.to_string(),
),
_ => Some(format!(
"({})",
fields
.iter()
.map(|f| f.ty.to_token_stream().to_string())
.collect::<Vec<_>>()
.join(", ")
)),
};
let Ok(metas) = tokens.parse_terminated(polyfill::Meta::parse, token::Comma) else {
return Ok(());
};
let parse_list = |list: polyfill::MetaList, attrs: &mut Option<Vec<_>>| {
if !list.path.is_ident("types") {
return None;
}
for meta in list
.parse_args_with(Punctuated::<_, token::Comma>::parse_terminated)
.ok()?
{
attrs.get_or_insert_with(Vec::new).push(match meta {
polyfill::NestedMeta::Lit(syn::Lit::Str(str)) => str.value(),
polyfill::NestedMeta::Meta(polyfill::Meta::Path(path)) => {
path.into_token_stream().to_string()
}
_ => return None,
})
}
Some(())
};
let Some((top_level, owned, ref_, ref_mut)) = metas
.into_iter()
.try_fold(
(None, None, None, None),
|(mut top_level, mut owned, mut ref_, mut ref_mut), meta| {
let is = |name| {
matches!(&meta, polyfill::Meta::Path(p) if p.is_ident(name))
|| matches!(&meta, polyfill::Meta::List(list) if list.path.is_ident(name))
};
let parse_inner = |meta, attrs: &mut Option<_>| {
match meta {
polyfill::Meta::Path(_) => {
let _ = attrs.get_or_insert_with(Vec::new);
Some(())
}
polyfill::Meta::List(list) => {
if let polyfill::NestedMeta::Meta(polyfill::Meta::List(list)) = list
.parse_args_with(Punctuated::<_, token::Comma>::parse_terminated)
.ok()?
.pop()?
.into_value()
{
parse_list(list, attrs)
} else {
None
}
}
}
};
match meta {
meta if is("owned") => parse_inner(meta, &mut owned),
meta if is("ref") => parse_inner(meta, &mut ref_),
meta if is("ref_mut") => parse_inner(meta, &mut ref_mut),
polyfill::Meta::List(list) => parse_list(list, &mut top_level),
_ => None,
}
.map(|_| (top_level, owned, ref_, ref_mut))
},
)
.filter(|(top_level, owned, ref_, ref_mut)| {
[top_level, owned, ref_, ref_mut]
.into_iter()
.any(|l| l.as_ref().map_or(false, |l| !l.is_empty()))
})
else {
return Ok(());
};
if [&owned, &ref_, &ref_mut].into_iter().any(Option::is_some) {
let format = |list: Option<Vec<_>>, name: &str| match list {
Some(l)
if top_level.as_ref().map_or(true, Vec::is_empty) && l.is_empty() =>
{
Some(name.to_owned())
}
Some(l) => Some(format!(
"{}({})",
name,
l.into_iter()
.chain(top_level.clone().into_iter().flatten())
.map(map_ty)
.chain(field.clone())
.collect::<Vec<_>>()
.join(", "),
)),
None => None,
};
let format = [
format(owned, "owned"),
format(ref_, "ref"),
format(ref_mut, "ref_mut"),
]
.into_iter()
.flatten()
.collect::<Vec<_>>()
.join(", ");
Err(syn::Error::new(
span,
format!("legacy syntax, use `{format}` instead"),
))
} else {
Err(syn::Error::new(
span,
format!(
"legacy syntax, remove `types` and use `{}` instead",
top_level.unwrap_or_else(|| unreachable!()).join(", "),
),
))
}
}