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use proc_macro2::Span;
use quote::quote;
use syn::Attribute;
use syn::Data;
use syn::DataEnum;
use syn::DataStruct;
use syn::DeriveInput;
use syn::Field;
use syn::Fields;
use syn::Ident;
use syn::LitStr;
use syn::Type;
use syn::parse_macro_input;
#[proc_macro_derive(ExperimentalApi, attributes(experimental))]
pub fn derive_experimental_api(input: TokenStream) -> TokenStream {
let input = parse_macro_input!(input as DeriveInput);
match &input.data {
Data::Struct(data) => derive_for_struct(&input, data),
Data::Enum(data) => derive_for_enum(&input, data),
Data::Union(_) => {
syn::Error::new_spanned(&input.ident, "ExperimentalApi does not support unions")
.to_compile_error()
.into()
}
}
}
fn derive_for_struct(input: &DeriveInput, data: &DataStruct) -> TokenStream {
let name = &input.ident;
let type_name_lit = LitStr::new(&name.to_string(), Span::call_site());
let (checks, experimental_fields, registrations) = match &data.fields {
Fields::Named(named) => {
let mut checks = Vec::new();
let mut experimental_fields = Vec::new();
let mut registrations = Vec::new();
for field in &named.named {
if let Some(reason) = experimental_reason(&field.attrs) {
let expr = experimental_presence_expr(field, /*tuple_struct*/ false);
checks.push(quote! {
if #expr {
return Some(#reason);
}
});
if let Some(field_name) = field_serialized_name(field) {
let field_name_lit = LitStr::new(&field_name, Span::call_site());
experimental_fields.push(quote! {
crate::experimental_api::ExperimentalField {
type_name: #type_name_lit,
field_name: #field_name_lit,
reason: #reason,
}
});
registrations.push(quote! {
::inventory::submit! {
crate::experimental_api::ExperimentalField {
type_name: #type_name_lit,
field_name: #field_name_lit,
reason: #reason,
}
}
});
}
} else if has_nested_experimental(field) {
let Some(ident) = field.ident.as_ref() else {
continue;
};
checks.push(quote! {
if let Some(reason) =
crate::experimental_api::ExperimentalApi::experimental_reason(&self.#ident)
{
return Some(reason);
}
});
}
}
(checks, experimental_fields, registrations)
}
Fields::Unnamed(unnamed) => {
let mut checks = Vec::new();
let mut experimental_fields = Vec::new();
let mut registrations = Vec::new();
for (index, field) in unnamed.unnamed.iter().enumerate() {
if let Some(reason) = experimental_reason(&field.attrs) {
let expr = index_presence_expr(index, &field.ty);
checks.push(quote! {
if #expr {
return Some(#reason);
}
});
let field_name_lit = LitStr::new(&index.to_string(), Span::call_site());
experimental_fields.push(quote! {
crate::experimental_api::ExperimentalField {
type_name: #type_name_lit,
field_name: #field_name_lit,
reason: #reason,
}
});
registrations.push(quote! {
::inventory::submit! {
crate::experimental_api::ExperimentalField {
type_name: #type_name_lit,
field_name: #field_name_lit,
reason: #reason,
}
}
});
} else if has_nested_experimental(field) {
let index = syn::Index::from(index);
checks.push(quote! {
if let Some(reason) =
crate::experimental_api::ExperimentalApi::experimental_reason(&self.#index)
{
return Some(reason);
}
});
}
}
(checks, experimental_fields, registrations)
}
Fields::Unit => (Vec::new(), Vec::new(), Vec::new()),
};
let checks = if checks.is_empty() {
quote! { None }
} else {
quote! {
#(#checks)*
None
}
};
let experimental_fields = if experimental_fields.is_empty() {
quote! { &[] }
} else {
quote! { &[ #(#experimental_fields,)* ] }
};
let expanded = quote! {
#(#registrations)*
impl #name {
pub(crate) const EXPERIMENTAL_FIELDS: &'static [crate::experimental_api::ExperimentalField] =
#experimental_fields;
}
impl crate::experimental_api::ExperimentalApi for #name {
fn experimental_reason(&self) -> Option<&'static str> {
#checks
}
}
};
expanded.into()
}
fn derive_for_enum(input: &DeriveInput, data: &DataEnum) -> TokenStream {
let name = &input.ident;
let mut match_arms = Vec::new();
for variant in &data.variants {
let variant_name = &variant.ident;
let pattern = match &variant.fields {
Fields::Named(_) => quote!(Self::#variant_name { .. }),
Fields::Unnamed(_) => quote!(Self::#variant_name ( .. )),
Fields::Unit => quote!(Self::#variant_name),
};
let reason = experimental_reason(&variant.attrs);
if let Some(reason) = reason {
match_arms.push(quote! {
#pattern => Some(#reason),
});
} else {
match_arms.push(quote! {
#pattern => None,
});
}
}
let expanded = quote! {
impl crate::experimental_api::ExperimentalApi for #name {
fn experimental_reason(&self) -> Option<&'static str> {
match self {
#(#match_arms)*
}
}
}
};
expanded.into()
}
fn experimental_reason(attrs: &[Attribute]) -> Option<LitStr> {
attrs.iter().find_map(experimental_reason_attr)
}
fn experimental_reason_attr(attr: &Attribute) -> Option<LitStr> {
if !attr.path().is_ident("experimental") {
return None;
}
attr.parse_args::<LitStr>().ok()
}
fn has_nested_experimental(field: &Field) -> bool {
field.attrs.iter().any(experimental_nested_attr)
}
fn experimental_nested_attr(attr: &Attribute) -> bool {
if !attr.path().is_ident("experimental") {
return false;
}
attr.parse_args::<Ident>()
.is_ok_and(|ident| ident == "nested")
}
fn field_serialized_name(field: &Field) -> Option<String> {
let ident = field.ident.as_ref()?;
let name = ident.to_string();
Some(snake_to_camel(&name))
}
fn snake_to_camel(s: &str) -> String {
let mut out = String::with_capacity(s.len());
let mut upper = false;
for ch in s.chars() {
if ch == '_' {
upper = true;
continue;
}
if upper {
out.push(ch.to_ascii_uppercase());
upper = false;
} else {
out.push(ch);
}
}
out
}
fn experimental_presence_expr(
field: &Field,
tuple_struct: bool,
) -> Option<proc_macro2::TokenStream> {
if tuple_struct {
return None;
}
let ident = field.ident.as_ref()?;
Some(presence_expr_for_access(quote!(self.#ident), &field.ty))
}
fn index_presence_expr(index: usize, ty: &Type) -> proc_macro2::TokenStream {
let index = syn::Index::from(index);
presence_expr_for_access(quote!(self.#index), ty)
}
fn presence_expr_for_access(
access: proc_macro2::TokenStream,
ty: &Type,
) -> proc_macro2::TokenStream {
if option_inner(ty).is_some() {
return quote! { #access.is_some() };
}
if is_vec_like(ty) || is_map_like(ty) {
return quote! { !#access.is_empty() };
}
if is_bool(ty) {
return quote! { #access };
}
quote! { true }
}
fn option_inner(ty: &Type) -> Option<&Type> {
let Type::Path(type_path) = ty else {
return None;
};
let segment = type_path.path.segments.last()?;
if segment.ident != "Option" {
return None;
}
let syn::PathArguments::AngleBracketed(args) = &segment.arguments else {
return None;
};
args.args.iter().find_map(|arg| match arg {
syn::GenericArgument::Type(inner) => Some(inner),
_ => None,
})
}
fn is_vec_like(ty: &Type) -> bool {
type_last_ident(ty).is_some_and(|ident| ident == "Vec")
}
fn is_map_like(ty: &Type) -> bool {
type_last_ident(ty).is_some_and(|ident| ident == "HashMap" || ident == "BTreeMap")
}
fn is_bool(ty: &Type) -> bool {
type_last_ident(ty).is_some_and(|ident| ident == "bool")
}
fn type_last_ident(ty: &Type) -> Option<Ident> {
let Type::Path(type_path) = ty else {
return None;
};
type_path.path.segments.last().map(|seg| seg.ident.clone())
}
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