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//! Implementation of [`fmt::Display`]-like derive macros.
#[cfg(doc)]
use std::fmt;
use proc_macro2::{Ident, TokenStream};
use quote::{format_ident, quote};
use syn::{
parse::{Parse, ParseStream},
parse_quote,
spanned::Spanned as _,
};
use super::{BoundsAttribute, FmtAttribute};
/// Expands a [`fmt::Display`]-like derive macro.
///
/// Available macros:
/// - [`Binary`](fmt::Binary)
/// - [`Display`](fmt::Display)
/// - [`LowerExp`](fmt::LowerExp)
/// - [`LowerHex`](fmt::LowerHex)
/// - [`Octal`](fmt::Octal)
/// - [`Pointer`](fmt::Pointer)
/// - [`UpperExp`](fmt::UpperExp)
/// - [`UpperHex`](fmt::UpperHex)
pub fn expand(input: &syn::DeriveInput, trait_name: &str) -> syn::Result<TokenStream> {
let trait_name = normalize_trait_name(trait_name);
let attrs = Attributes::parse_attrs(&input.attrs, trait_name)?;
let trait_ident = format_ident!("{trait_name}");
let ident = &input.ident;
let ctx = (&attrs, ident, &trait_ident, trait_name);
let (bounds, body) = match &input.data {
syn::Data::Struct(s) => expand_struct(s, ctx),
syn::Data::Enum(e) => expand_enum(e, ctx),
syn::Data::Union(u) => expand_union(u, ctx),
}?;
let (impl_gens, ty_gens, where_clause) = {
let (impl_gens, ty_gens, where_clause) = input.generics.split_for_impl();
let mut where_clause = where_clause
.cloned()
.unwrap_or_else(|| parse_quote! { where });
where_clause.predicates.extend(bounds);
(impl_gens, ty_gens, where_clause)
};
Ok(quote! {
#[automatically_derived]
impl #impl_gens ::core::fmt::#trait_ident for #ident #ty_gens
#where_clause
{
fn fmt(
&self, __derive_more_f: &mut ::core::fmt::Formatter<'_>
) -> ::core::fmt::Result {
#body
}
}
})
}
/// Type alias for an expansion context:
/// - [`Attributes`].
/// - Struct/enum/union [`Ident`].
/// - Derived trait [`Ident`].
/// - Derived trait `&`[`str`].
type ExpansionCtx<'a> = (&'a Attributes, &'a Ident, &'a Ident, &'a str);
/// Expands a [`fmt::Display`]-like derive macro for the provided struct.
fn expand_struct(
s: &syn::DataStruct,
(attrs, ident, trait_ident, _): ExpansionCtx<'_>,
) -> syn::Result<(Vec<syn::WherePredicate>, TokenStream)> {
let s = Expansion {
attrs,
fields: &s.fields,
trait_ident,
ident,
};
let bounds = s.generate_bounds();
let body = s.generate_body()?;
let vars = s.fields.iter().enumerate().map(|(i, f)| {
let var = f.ident.clone().unwrap_or_else(|| format_ident!("_{i}"));
let member = f
.ident
.clone()
.map_or_else(|| syn::Member::Unnamed(i.into()), syn::Member::Named);
quote! {
let #var = &self.#member;
}
});
let body = quote! {
#( #vars )*
#body
};
Ok((bounds, body))
}
/// Expands a [`fmt`]-like derive macro for the provided enum.
fn expand_enum(
e: &syn::DataEnum,
(attrs, _, trait_ident, trait_name): ExpansionCtx<'_>,
) -> syn::Result<(Vec<syn::WherePredicate>, TokenStream)> {
if attrs.fmt.is_some() {
}
let (bounds, match_arms) = e.variants.iter().try_fold(
(Vec::new(), TokenStream::new()),
|(mut bounds, mut arms), variant| {
let attrs = Attributes::parse_attrs(&variant.attrs, trait_name)?;
let ident = &variant.ident;
if attrs.fmt.is_none()
&& variant.fields.is_empty()
&& trait_name != "Display"
{
return Err(syn::Error::new(
e.variants.span(),
format!(
"implicit formatting of unit enum variant is supported \
only for `Display` macro, use `#[{}(\"...\")]` to \
explicitly specify the formatting",
trait_name_to_attribute_name(trait_name),
),
));
}
let v = Expansion {
attrs: &attrs,
fields: &variant.fields,
trait_ident,
ident,
};
let arm_body = v.generate_body()?;
bounds.extend(v.generate_bounds());
let fields_idents =
variant.fields.iter().enumerate().map(|(i, f)| {
f.ident.clone().unwrap_or_else(|| format_ident!("_{i}"))
});
let matcher = match variant.fields {
syn::Fields::Named(_) => {
quote! { Self::#ident { #( #fields_idents ),* } }
}
syn::Fields::Unnamed(_) => {
quote! { Self::#ident ( #( #fields_idents ),* ) }
}
syn::Fields::Unit => quote! { Self::#ident },
};
arms.extend([quote! { #matcher => { #arm_body }, }]);
Ok::<_, syn::Error>((bounds, arms))
},
)?;
let body = match_arms
.is_empty()
.then(|| quote! { match *self {} })
.unwrap_or_else(|| quote! { match self { #match_arms } });
Ok((bounds, body))
}
/// Expands a [`fmt::Display`]-like derive macro for the provided union.
fn expand_union(
u: &syn::DataUnion,
(attrs, _, _, trait_name): ExpansionCtx<'_>,
) -> syn::Result<(Vec<syn::WherePredicate>, TokenStream)> {
let fmt = &attrs.fmt.as_ref().ok_or_else(|| {
syn::Error::new(
u.fields.span(),
format!(
"unions must have `#[{}(\"...\", ...)]` attribute",
trait_name_to_attribute_name(trait_name),
),
)
})?;
Ok((
attrs.bounds.0.clone().into_iter().collect(),
quote! { ::core::write!(__derive_more_f, #fmt) },
))
}
/// Representation of a [`fmt::Display`]-like derive macro attribute.
///
/// ```rust,ignore
/// #[<fmt_trait>("<fmt_literal>", <fmt_args>)]
/// #[bound(<bounds>)]
/// ```
///
/// `#[<fmt_trait>(...)]` can be specified only once, while multiple
/// `#[<fmt_trait>(bound(...))]` are allowed.
#[derive(Debug, Default)]
struct Attributes {
/// Interpolation [`FmtAttribute`].
fmt: Option<FmtAttribute>,
/// Addition trait bounds.
bounds: BoundsAttribute,
}
impl Attributes {
/// Parses [`Attributes`] from the provided [`syn::Attribute`]s.
fn parse_attrs(
attrs: impl AsRef<[syn::Attribute]>,
trait_name: &str,
) -> syn::Result<Self> {
attrs
.as_ref()
.iter()
.filter(|attr| attr.path().is_ident(trait_name_to_attribute_name(trait_name)))
.try_fold(Attributes::default(), |mut attrs, attr| {
let attr = attr.parse_args::<Attribute>()?;
match attr {
Attribute::Bounds(more) => {
attrs.bounds.0.extend(more.0);
}
Attribute::Fmt(fmt) => {
attrs.fmt.replace(fmt).map_or(Ok(()), |dup| Err(syn::Error::new(
dup.span(),
format!(
"multiple `#[{}(\"...\", ...)]` attributes aren't allowed",
trait_name_to_attribute_name(trait_name),
))))?;
}
};
Ok(attrs)
})
}
}
/// Representation of a single [`fmt::Display`]-like derive macro attribute.
#[derive(Debug)]
enum Attribute {
/// [`fmt`] attribute.
Fmt(FmtAttribute),
/// Addition trait bounds.
Bounds(BoundsAttribute),
}
impl Parse for Attribute {
fn parse(input: ParseStream<'_>) -> syn::Result<Self> {
BoundsAttribute::check_legacy_fmt(input)?;
FmtAttribute::check_legacy_fmt(input)?;
if input.peek(syn::LitStr) {
input.parse().map(Attribute::Fmt)
} else {
input.parse().map(Attribute::Bounds)
}
}
}
/// Helper struct to generate [`Display::fmt()`] implementation body and trait
/// bounds for a struct or an enum variant.
///
/// [`Display::fmt()`]: fmt::Display::fmt()
#[derive(Debug)]
struct Expansion<'a> {
/// Derive macro [`Attributes`].
attrs: &'a Attributes,
/// Struct or enum [`Ident`].
ident: &'a Ident,
/// Struct or enum [`syn::Fields`].
fields: &'a syn::Fields,
/// [`fmt`] trait [`Ident`].
trait_ident: &'a Ident,
}
impl<'a> Expansion<'a> {
/// Generates [`Display::fmt()`] implementation for a struct or an enum variant.
///
/// # Errors
///
/// In case [`FmtAttribute`] is [`None`] and [`syn::Fields`] length is
/// greater than 1.
///
/// [`Display::fmt()`]: fmt::Display::fmt()
fn generate_body(&self) -> syn::Result<TokenStream> {
match &self.attrs.fmt {
Some(fmt) => Ok(quote! { ::core::write!(__derive_more_f, #fmt) }),
None if self.fields.is_empty() => {
let ident_str = self.ident.to_string();
Ok(quote! { ::core::write!(__derive_more_f, #ident_str) })
}
None if self.fields.len() == 1 => {
let field = self
.fields
.iter()
.next()
.unwrap_or_else(|| unreachable!("count() == 1"));
let ident = field.ident.clone().unwrap_or_else(|| format_ident!("_0"));
let trait_ident = self.trait_ident;
Ok(quote! {
::core::fmt::#trait_ident::fmt(#ident, __derive_more_f)
})
}
_ => Err(syn::Error::new(
self.fields.span(),
format!(
"struct or enum variant with more than 1 field must have \
`#[{}(\"...\", ...)]` attribute",
trait_name_to_attribute_name(self.trait_ident),
),
)),
}
}
/// Generates trait bounds for a struct or an enum variant.
fn generate_bounds(&self) -> Vec<syn::WherePredicate> {
let Some(fmt) = &self.attrs.fmt else {
return self
.fields
.iter()
.next()
.map(|f| {
let ty = &f.ty;
let trait_ident = &self.trait_ident;
vec![parse_quote! { #ty: ::core::fmt::#trait_ident }]
})
.unwrap_or_default();
};
fmt.bounded_types(self.fields)
.map(|(ty, trait_name)| {
let tr = format_ident!("{}", trait_name);
parse_quote! { #ty: ::core::fmt::#tr }
})
.chain(self.attrs.bounds.0.clone())
.collect()
}
}
/// Matches the provided `trait_name` to appropriate [`Attribute::Fmt`] argument name.
fn trait_name_to_attribute_name<T>(trait_name: T) -> &'static str
where
T: for<'a> PartialEq<&'a str>,
{
match () {
_ if trait_name == "Binary" => "binary",
_ if trait_name == "Display" => "display",
_ if trait_name == "LowerExp" => "lower_exp",
_ if trait_name == "LowerHex" => "lower_hex",
_ if trait_name == "Octal" => "octal",
_ if trait_name == "Pointer" => "pointer",
_ if trait_name == "UpperExp" => "upper_exp",
_ if trait_name == "UpperHex" => "upper_hex",
_ => unimplemented!(),
}
}
/// Matches the provided derive macro `name` to appropriate actual trait name.
fn normalize_trait_name(name: &str) -> &'static str {
match name {
"Binary" => "Binary",
"Display" => "Display",
"LowerExp" => "LowerExp",
"LowerHex" => "LowerHex",
"Octal" => "Octal",
"Pointer" => "Pointer",
"UpperExp" => "UpperExp",
"UpperHex" => "UpperHex",
_ => unimplemented!(),
}
}