96 lines
2.5 KiB
Rust
96 lines
2.5 KiB
Rust
use proc_macro::TokenStream;
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use quote::quote;
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use syn::{FnArg, Item, ItemConst, ItemFn, parse_macro_input};
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#[proc_macro_attribute]
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pub fn export(_attr: TokenStream, item: TokenStream) -> TokenStream {
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match parse_macro_input!(item as Item) {
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Item::Fn(function) => export_fn(function),
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Item::Const(constant) => export_const(constant),
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other => syn::Error::new_spanned(other, "#[export] only supports fn and const items")
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.to_compile_error()
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.into(),
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}
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}
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fn export_fn(function: ItemFn) -> TokenStream {
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let param_count = function
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.sig
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.inputs
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.iter()
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.filter(|arg| matches!(arg, FnArg::Typed(_)))
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.count();
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if param_count > 1 {
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return syn::Error::new_spanned(
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&function.sig.inputs,
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"#[export] functions must accept a single options struct, not positional arguments. \
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Wrap parameters in a struct: `fn foo(FooOptions { a, b }: FooOptions)`",
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)
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.to_compile_error()
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.into();
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}
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let js_name = snake_to_camel(&function.sig.ident.to_string());
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quote! {
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#[cfg_attr(feature = "wasm", ::wasm_bindgen::prelude::wasm_bindgen(js_name = #js_name))]
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#function
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}
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.into()
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}
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fn export_const(constant: ItemConst) -> TokenStream {
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let js_name = constant.ident.to_string();
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let const_ident = &constant.ident;
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let getter_ident = syn::Ident::new(
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&format!("__const_{}", constant.ident.to_string().to_lowercase()),
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constant.ident.span(),
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);
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quote! {
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#constant
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#[cfg(feature = "wasm")]
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#[::wasm_bindgen::prelude::wasm_bindgen(js_name = #js_name)]
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pub fn #getter_ident() -> f64 {
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#const_ident as f64
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}
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}
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.into()
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}
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fn snake_to_camel(name: &str) -> String {
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let mut camel = String::with_capacity(name.len());
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let mut should_uppercase_next = false;
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for character in name.chars() {
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if character == '_' {
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should_uppercase_next = true;
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continue;
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}
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if should_uppercase_next {
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camel.push(character.to_ascii_uppercase());
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should_uppercase_next = false;
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continue;
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}
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camel.push(character);
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}
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camel
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}
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#[cfg(test)]
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mod tests {
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use super::snake_to_camel;
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#[test]
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fn converts_snake_case_to_camel_case() {
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assert_eq!(snake_to_camel("do_something"), "doSomething");
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assert_eq!(snake_to_camel("a_b_c"), "aBC");
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assert_eq!(snake_to_camel("already"), "already");
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}
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}
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