Simplify proc-macro

There's no need to inspect the test case so deeply; all this macro wants
to do is insert a prelude - so do that and expand the rest as-is.

This removes the inner function `test_impl`, which is the suspected
cause of d-e-s-o#28.

Closes d-e-s-o#28.

src/lib.rs

@@ -16,14 +16,10 @@ use quote::quote;
 
 use syn::parse_macro_input;
 use syn::parse_quote;
-use syn::punctuated::Punctuated;
 use syn::AttributeArgs;
-use syn::FnArg;
 use syn::ItemFn;
 use syn::Meta;
 use syn::NestedMeta;
-use syn::ReturnType;
-use syn::Token;
 
 /// A procedural macro for the `test` attribute.
 ///
@@ -149,55 +145,22 @@ fn expand_tracing_init() -> Tokens {
     quote! {}
 }
 
-/// Extract the argument names from the inputs of a function signature.
-fn extract_args(inputs: &Punctuated<FnArg, Token![,]>) -> Punctuated<Tokens, Token![,]> {
-    inputs
-        .iter()
-        .map(|arg| match arg {
-            FnArg::Receiver(receiver) => {
-                let slf = receiver.self_token;
-                quote! { #slf }
-            }
-            FnArg::Typed(typed) => {
-                let pat = &typed.pat;
-                quote! { #pat }
-            }
-        })
-        .collect()
-}
-
 /// Emit code for a wrapper function around a test function.
 fn expand_wrapper(inner_test: &Tokens, wrappee: &ItemFn) -> TokenStream {
-    let attrs = &wrappee.attrs;
-    let async_ = &wrappee.sig.asyncness;
-    let await_ = if async_.is_some() {
-        quote! {.await}
-    } else {
-        quote! {}
-    };
-    let body = &wrappee.block;
-    let test_name = &wrappee.sig.ident;
-    let inputs = &wrappee.sig.inputs;
-    let args = extract_args(inputs);
-
-    // Note that Rust does not allow us to have a test function with
-    // #[should_panic] that has a non-unit return value.
-    let ret = match &wrappee.sig.output {
-        ReturnType::Default => quote! {},
-        ReturnType::Type(_, type_) => quote! {-> #type_},
-    };
+    let ItemFn {
+        attrs,
+        vis,
+        sig,
+        block,
+    } = wrappee;
 
     let logging_init = expand_logging_init();
     let tracing_init = expand_tracing_init();
 
     let result = quote! {
       #[#inner_test]
       #(#attrs)*
-      #async_ fn #test_name(#inputs) #ret {
-        #async_ fn test_impl(#inputs) #ret {
-          #body
-        }
-
+      #vis #sig {
         // We put all initialization code into a separate module here in
         // order to prevent potential ambiguities that could result in
         // compilation errors. E.g., client code could use traits that
@@ -216,7 +179,8 @@ fn expand_wrapper(inner_test: &Tokens, wrappee: &ItemFn) -> TokenStream {
         }
 
         init::init();
-        test_impl(#args)#await_
+
+        #block
       }
     };
     result.into()