macros: forward input arguments in #[tokio::test] (#3691)

Fixes #2388

Previously `#[tokio::test]` would error on functions that took
arguments. That meant other attribute macros couldn't do further
transformations on them. This changes that so arguments are forwarded as
is.

Whatever else might be included on the function is forwarded as well.
For example return type, generics, etc.

Worth noting that this is only for compatibility with other macros.
`#[test]`s that take arguments will still fail to compile.

A bit odd that [trybuild] tests don't fail `#[test]` functions with
arguments which is why the new tests are run with `t.pass(...)`. They do
actually fail if part of a real crate.

[trybuild]: https://crates.io/crates/trybuild

tokio-macros/src/entry.rs

@@ -190,18 +190,11 @@ fn parse_knobs(
     is_test: bool,
     rt_multi_thread: bool,
 ) -> Result<TokenStream, syn::Error> {
-    let sig = &mut input.sig;
-    let body = &input.block;
-    let attrs = &input.attrs;
-    let vis = input.vis;
-
-    if sig.asyncness.is_none() {
+    if input.sig.asyncness.take().is_none() {
         let msg = "the `async` keyword is missing from the function declaration";
-        return Err(syn::Error::new_spanned(sig.fn_token, msg));
+        return Err(syn::Error::new_spanned(input.sig.fn_token, msg));
     }
 
-    sig.asyncness = None;
-
     let mut config = Configuration::new(is_test, rt_multi_thread);
     let macro_name = config.macro_name();
 
@@ -300,20 +293,17 @@ fn parse_knobs(
         rt = quote! { #rt.start_paused(#v) };
     }
 
-    let header = {
-        if is_test {
-            quote! {
-                #[::core::prelude::v1::test]
-            }
-        } else {
-            quote! {}
+    let header = if is_test {
+        quote! {
+            #[::core::prelude::v1::test]
         }
+    } else {
+        quote! {}
     };
 
-    let result = quote! {
-        #header
-        #(#attrs)*
-        #vis #sig {
+    let body = &input.block;
+    input.block = syn::parse_quote! {
+        {
             #rt
                 .enable_all()
                 .build()
@@ -322,6 +312,11 @@ fn parse_knobs(
         }
     };
 
+    let result = quote! {
+        #header
+        #input
+    };
+
     Ok(result.into())
 }
 
@@ -353,12 +348,5 @@ pub(crate) fn test(args: TokenStream, item: TokenStream, rt_multi_thread: bool)
         }
     }
 
-    if !input.sig.inputs.is_empty() {
-        let msg = "the test function cannot accept arguments";
-        return syn::Error::new_spanned(&input.sig.inputs, msg)
-            .to_compile_error()
-            .into();
-    }
-
     parse_knobs(input, args, true, rt_multi_thread).unwrap_or_else(|e| e.to_compile_error().into())
 }