Crate synthez[−][src]
Expand description
synthez
Steroids for syn
, quote
and proc_macro2
crates.
Cargo features
full
Same as full
feature of syn
crate.
Enables support of data structures for representing the syntax tree of all valid Rust source code, including items and expressions.
Example of writing proc_macro_derive
This is an example of how this library can be used to write a simplified proc_macro_derive
for deriving a From
implementations.
use synthez::{DataExt as _, ParseAttrs, ToTokens};
pub fn derive(input: syn::DeriveInput) -> syn::Result<TokenStream> {
let attrs = Attrs::parse_attrs("from", &input)?;
match (attrs.forward.is_some(), !attrs.custom.is_empty()) {
(true, true) => Err(syn::Error::new_spanned(
input,
"`forward` and `on` arguments are mutually exclusive",
)),
(false, false) => Err(syn::Error::new_spanned(
input,
"either `forward` or `on` argument is expected",
)),
// #[from(forward)]
(true, _) => {
if !matches!(&input.data, syn::Data::Struct(_)) {
return Err(syn::Error::new_spanned(
input,
"only tuple structs can forward-derive From",
));
}
let fields = input.data.unnamed_fields()?;
if fields.len() > 1 {
return Err(syn::Error::new_spanned(
fields,
"only single-field tuple structs can forward-derive \
From",
));
}
let definition = ForwardDefinition {
ty: input.ident,
inner_ty: fields.into_iter().last().unwrap().ty,
};
Ok(quote! {
#definition
})
}
// #[from(on <type> = <func>)]
(_, true) => {
let definitions =
CustomDefinitions { ty: input.ident, funcs: attrs.custom };
Ok(quote! {
#definitions
})
}
}
}
#[derive(Default, ParseAttrs)]
struct Attrs {
#[parse(ident)]
forward: Option<syn::Ident>,
#[parse(map, arg = on)]
custom: HashMap<syn::Type, syn::Expr>,
}
#[derive(ToTokens)]
#[to_tokens(append(impl_from))]
struct ForwardDefinition {
ty: syn::Ident,
inner_ty: syn::Type,
}
impl ForwardDefinition {
fn impl_from(&self) -> TokenStream {
let (ty, inner_ty) = (&self.ty, &self.inner_ty);
quote! {
impl<T> From<T> for #ty where #inner_ty: From<T> {
fn from(v: T) -> Self {
Self(v.into())
}
}
}
}
}
#[derive(ToTokens)]
#[to_tokens(append(impl_froms))]
struct CustomDefinitions {
ty: syn::Ident,
funcs: HashMap<syn::Type, syn::Expr>,
}
impl CustomDefinitions {
fn impl_froms(&self) -> TokenStream {
let ty = &self.ty;
// We sort here for tests below not failing due to undetermined
// order only. Real implementation may omit this.
let mut sorted = self.funcs.iter().collect::<Vec<_>>();
sorted.sort_unstable_by(|(ty1, _), (ty2, _)| {
quote!(#ty1).to_string().cmp("e!(#ty2).to_string())
});
let impls = sorted.into_iter().map(move |(from_ty, func)| {
quote! {
impl From<#from_ty> for #ty {
fn from(v: #from_ty) -> Self {
#func(v)
}
}
}
});
quote! { #( #impls )* }
}
}
let input = syn::parse_quote! {
#[derive(From)]
#[from(forward)]
struct Id(u64);
};
let output = quote! {
impl<T> From<T> for Id where u64: From<T> {
fn from(v: T) -> Self {
Self(v.into())
}
}
};
assert_eq!(derive(input).unwrap().to_string(), output.to_string());
let input = syn::parse_quote! {
#[derive(From)]
#[from(on bool = Self::parse_bool)]
#[from(on u8 = from_u8_to_maybe)]
enum Maybe {
Yes,
No,
}
};
let output = quote! {
impl From<bool> for Maybe {
fn from(v: bool) -> Self {
Self::parse_bool(v)
}
}
impl From<u8> for Maybe {
fn from(v: u8) -> Self {
from_u8_to_maybe(v)
}
}
};
assert_eq!(derive(input).unwrap().to_string(), output.to_string());
License
This software is subject to the terms of the Blue Oak Model License 1.0.0. If a copy of the BlueOak-1.0.0 license was not distributed with this file, You can obtain one at https://blueoakcouncil.org/license/1.0.0.
Re-exports
Modules
Batteries for working with struct fields.
Batteries for syn::parse
.
Batteries for Span
and syn::spanned
.
Structs
Traits
Extension of a syn::Ident
.
Parse
ing of syn::Attribute
s into a custom defined struct.
Extension of a syn::parse::ParseBuffer
providing common function widely
used by this crate for parsing.
Types that can be interpolated inside a quote!
invocation.
Derive Macros
Deriving of synthez::ParseAttrs
along with a syn::parse::Parse
implementation to parse syn::Attribute
s into a custom defined struct.
Deriving of a quote::ToTokens
implementation.