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use darling::FromMeta;
use proc_macro::TokenStream;
use quote::{format_ident, quote};
use syn::{
parse_macro_input, spanned::Spanned, AttributeArgs, Error, Expr, ItemConst, Type,
Type::Reference,
};
type TokenStream2 = proc_macro2::TokenStream;
#[derive(Debug, FromMeta)]
struct Metadata {
#[darling(default)]
min: Option<f64>,
#[darling(default)]
max: Option<f64>,
#[darling(default)]
step: Option<f64>,
}
impl Metadata {
pub fn from_attributes(args: AttributeArgs) -> Result<Self, TokenStream> {
match Metadata::from_list(&args) {
Ok(v) => Ok(v),
Err(e) => Err(TokenStream::from(e.write_errors())),
}
}
}
fn field_init(
ty: &Type,
metadata: Metadata,
default_value: Expr,
) -> Result<TokenStream2, TokenStream> {
if let Type::Path(type_path) = &*ty {
match type_path.path.get_ident() {
Some(type_ident) => {
let min = metadata.min.unwrap_or(-1.0);
let max = metadata.max.unwrap_or(1.0);
let step = metadata.step.unwrap_or(0.1);
match &*(type_ident.to_string()) {
"f64" => Ok(quote! {
const_tweaker::Field::F64 {
value: #default_value,
min: #min,
max: #max,
step: #step,
}
}),
"bool" => Ok(quote! {
const_tweaker::Field::Bool {
value: #default_value,
}
}),
"str" => Ok(quote! {
const_tweaker::Field::String {
value: #default_value.to_string(),
}
}),
_ => mismatching_type_error(&ty),
}
}
None => mismatching_type_error(&ty),
}
} else {
mismatching_type_error(&ty)
}
}
fn field_name(ty: &Type) -> Result<TokenStream2, TokenStream> {
if let Type::Path(type_path) = &*ty {
match type_path.path.get_ident() {
Some(type_ident) => match &*(type_ident.to_string()) {
"f64" => Ok(quote! { const_tweaker::Field::F64 }),
"bool" => Ok(quote! { const_tweaker::Field::Bool }),
"str" => Ok(quote! { const_tweaker::Field::String }),
_ => mismatching_type_error(&ty),
},
None => mismatching_type_error(&ty),
}
} else {
mismatching_type_error(&ty)
}
}
fn mismatching_type_error<T>(ty: &Type) -> Result<T, TokenStream> {
Err(TokenStream::from(
Error::new(
ty.span(),
"expected bool, &str or f64, other types are not supported in const_tweaker (yet)",
)
.to_compile_error(),
))
}
fn tweak_impl(args: AttributeArgs, input: ItemConst) -> Result<TokenStream, TokenStream> {
let name = input.ident;
let init_name = format_ident!("{}_INIT", name);
let ty = if let Reference(type_ref) = *input.ty {
type_ref.elem
} else {
input.ty
};
let field_init = field_init(&*ty, Metadata::from_attributes(args)?, *input.expr)?;
let field_name = field_name(&*ty)?;
let result = quote! {
#[allow(non_camel_case_types)]
#[doc(hidden)]
#[derive(Copy, Clone)]
pub struct #name {
__private_field: ()
}
impl #name {
pub fn get(&self) -> &'static #ty {
#init_name.call_once(|| {
const_tweaker::DATA.insert(stringify!(#name), #field_init);
});
match const_tweaker::DATA.get(stringify!(#name)).expect("Value should have been added already").value() {
#field_name { ref value, .. } => unsafe {
std::mem::transmute::<&#ty, &'static #ty>(value as &#ty)
},
_ => panic!("Type mismatch, this probably means there's a duplicate value in the map, please report an issue")
}
}
}
impl std::ops::Deref for #name {
type Target = #ty;
fn deref(&self) -> &'static #ty {
self.get()
}
}
impl std::fmt::Debug for #name {
fn fmt(&self, f: &mut std::fmt::Formatter) -> std::fmt::Result {
write!(f, "{:?}", self.get())
}
}
impl std::fmt::Display for #name {
fn fmt(&self, f: &mut std::fmt::Formatter) -> std::fmt::Result {
write!(f, "{:?}", self.get())
}
}
static #init_name: std::sync::Once = std::sync::Once::new();
static #name: #name = #name { __private_field: () };
};
Ok(result.into())
}
#[proc_macro_attribute]
pub fn tweak(args: TokenStream, input: TokenStream) -> TokenStream {
let args = parse_macro_input!(args as AttributeArgs);
let input = parse_macro_input!(input as ItemConst);
match tweak_impl(args, input) {
Ok(result) => result,
Err(err) => err,
}
}