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extern crate proc_macro; use proc_macro2::TokenStream; use quote::quote; use syn::spanned::Spanned; #[proc_macro_attribute] pub fn wasmtime( _attr: proc_macro::TokenStream, item: proc_macro::TokenStream, ) -> proc_macro::TokenStream { let item = syn::parse_macro_input!(item as syn::ItemTrait); expand(item).unwrap_or_else(|e| e.to_compile_error()).into() } fn expand(item: syn::ItemTrait) -> syn::Result<TokenStream> { let definition = generate_struct(&item)?; let load = generate_load(&item)?; let methods = generate_methods(&item)?; let name = &item.ident; Ok(quote! { #definition impl #name { #load #methods } }) } fn generate_struct(item: &syn::ItemTrait) -> syn::Result<TokenStream> { let vis = &item.vis; let name = &item.ident; let root = root(); Ok(quote! { #vis struct #name { instance: #root::wasmtime::Instance, data: #root::wasmtime_interface_types::ModuleData, } }) } fn generate_load(item: &syn::ItemTrait) -> syn::Result<TokenStream> { let vis = &item.vis; let name = &item.ident; let root = root(); Ok(quote! { #vis fn load_file(path: impl AsRef<std::path::Path>) -> #root::anyhow::Result<#name> { Self::load_bytes(std::fs::read(path)?) } #vis fn load_bytes(bytes: impl AsRef<[u8]>) -> #root::anyhow::Result<#name> { use #root::wasmtime::{Config, Extern, Engine, Store, Instance, Module}; use #root::anyhow::{bail, format_err}; let store = Store::default(); let data = #root::wasmtime_interface_types::ModuleData::new(bytes.as_ref())?; let module = Module::new(&engine, bytes.as_ref())?; let mut imports: Vec<Extern> = Vec::new(); if let Some(module_name) = data.find_wasi_module_name() { let wasi_cx = #root::wasmtime_wasi::WasiCtxBuilder::new().build()?; let wasi = #root::wasmtime_wasi::Wasi::new(&store, wasi_cx); for i in module.imports().iter() { if i.module() != module_name { bail!("unknown import module {}", i.module()); } if let Some(export) = wasi.get_export(i.name()) { imports.push(export.clone().into()); } else { bail!("unknown import {}:{}", i.module(), i.name()) } } } let instance = Instance::new(&store, &module, &imports).map_err(|t| format_err!("instantiation trap: {:?}", t))?; Ok(#name { instance, data }) } }) } fn generate_methods(item: &syn::ItemTrait) -> syn::Result<TokenStream> { macro_rules! bail { ($e:expr, $($fmt:tt)*) => ( return Err(syn::Error::new($e.span(), format!($($fmt)*))); ) } let mut result = TokenStream::new(); let root = root(); let vis = &item.vis; for item in item.items.iter() { let method = match item { syn::TraitItem::Method(f) => f, other => bail!(other, "only methods are allowed"), }; if let Some(e) = &method.default { bail!(e, "cannot specify an implementation of methods"); } if let Some(t) = &method.sig.constness { bail!(t, "cannot be `const`"); } if let Some(t) = &method.sig.asyncness { bail!(t, "cannot be `async`"); } match &method.sig.inputs.first() { Some(syn::FnArg::Receiver(_)) => {} Some(t) => bail!(t, "first arugment needs to be \"self\""), None => bail!( method.sig, "trait method requires at least one argument which needs to be \"self\"" ), } let mut args = Vec::new(); for arg in method.sig.inputs.iter() { let arg = match arg { syn::FnArg::Receiver(_) => continue, syn::FnArg::Typed(arg) => arg, }; let ident = match &*arg.pat { syn::Pat::Ident(i) => i, other => bail!(other, "must use bare idents for arguments"), }; if let Some(t) = &ident.by_ref { bail!(t, "arguments cannot bind by reference"); } if let Some(t) = &ident.mutability { bail!(t, "arguments cannot be mutable"); } if let Some((_, t)) = &ident.subpat { bail!(t, "arguments cannot have sub-bindings"); } let ident = &ident.ident; args.push(quote! { #root::wasmtime_interface_types::Value::from(#ident) }); } let convert_ret = match &method.sig.output { syn::ReturnType::Default => { quote! { <() as #root::FromVecValue>::from(results) } } syn::ReturnType::Type(_, ty) => match &**ty { syn::Type::Tuple(..) => { quote! { <#ty as #root::FromVecValue>::from(results) } } _ => { quote! { <(#ty,) as #root::FromVecValue>::from(results).map(|t| t.0) } } }, }; let sig = &method.sig; let attrs = &method.attrs; let name = &method.sig.ident; result.extend(quote! { #(#attrs)* #vis #sig { let args = [ #(#args),* ]; let results = self.data.invoke_export( &self.instance, stringify!(#name), &args, ).expect("wasm execution failed"); #convert_ret.expect("failed to convert return type") } }); } Ok(result) } fn root() -> TokenStream { quote! { wasmtime_rust::__rt } }