macros: preserve none-delimiters in function body

.github/workflows/ci.yml

@@ -10,7 +10,7 @@ env:
   RUSTFLAGS: -Dwarnings
   RUST_BACKTRACE: 1
   nightly: nightly-2020-09-21
-  minrust: 1.45.2
+  minrust: 1.47.0
 
 jobs:
   # Depends on all action sthat are required for a "successful" CI run.

README.md

@@ -156,7 +156,7 @@ several other libraries, including:
 
 ## Supported Rust Versions
 
-Tokio is built against the latest stable release. The minimum supported version is 1.45.
+Tokio is built against the latest stable release. The minimum supported version is 1.47.
 The current Tokio version is not guaranteed to build on Rust versions earlier than the
 minimum supported version.
 

tests-integration/tests/macros_main.rs

@@ -26,3 +26,25 @@ fn shell() {
     assert_eq!(1, basic_main());
     assert_eq!(bool::default(), generic_fun::<bool>())
 }
+
+macro_rules! generate_preserve_none_delimiters_tests {
+    ($e:expr) => {
+        #[test]
+        #[allow(clippy::redundant_closure_call)]
+        fn preserve_none_delimiters_in_main() {
+            #[tokio::main]
+            async fn f() -> i32 {
+                $e()
+            }
+
+            assert_eq!(f(), ($e)());
+        }
+
+        #[tokio::test]
+        #[allow(clippy::redundant_closure_call)]
+        async fn preserve_none_delimiters_in_test() {
+            assert_eq!($e(), ($e)());
+        }
+    };
+}
+generate_preserve_none_delimiters_tests!(|| 5);

tokio-macros/src/entry.rs

@@ -174,13 +174,29 @@ fn parse_bool(bool: syn::Lit, span: Span, field: &str) -> Result<bool, syn::Erro
 }
 
 fn parse_knobs(
-    mut input: syn::ItemFn,
+    input_tokens: TokenStream,
     args: syn::AttributeArgs,
     is_test: bool,
     rt_multi_thread: bool,
 ) -> Result<TokenStream, syn::Error> {
+    let mut input: syn::ItemFn = syn::parse(input_tokens.clone())?;
+
+    if (is_test || input.sig.ident == "main") && !input.sig.inputs.is_empty() {
+        let function = if is_test { "test" } else { "main" };
+
+        return Err(syn::Error::new_spanned(
+            &input.sig.inputs,
+            format_args!("the {} function cannot accept arguments", function),
+        ));
+    }
+    if is_test {
+        if let Some(attr) = input.attrs.iter().find(|attr| attr.path.is_ident("test")) {
+            let msg = "second test attribute is supplied";
+            return Err(syn::Error::new_spanned(attr, msg));
+        }
+    }
+
     let sig = &mut input.sig;
-    let body = &input.block;
     let attrs = &input.attrs;
     let vis = input.vis;
 
@@ -291,6 +307,12 @@ fn parse_knobs(
         }
     };
 
+    // The last token of a function item is always its body. We use the input token stream directly
+    // instead of printing the parsed function to make sure that Rust preserves None-delimited
+    // groups inside the function body; see <https://github.com/tokio-rs/tokio/issues/3579>.
+    let body =
+        proc_macro2::TokenStream::from(TokenStream::from(input_tokens.into_iter().last().unwrap()));
+
     let result = quote! {
         #header
         #(#attrs)*
@@ -308,38 +330,11 @@ fn parse_knobs(
 
 #[cfg(not(test))] // Work around for rust-lang/rust#62127
 pub(crate) fn main(args: TokenStream, item: TokenStream, rt_multi_thread: bool) -> TokenStream {
-    let input = syn::parse_macro_input!(item as syn::ItemFn);
     let args = syn::parse_macro_input!(args as syn::AttributeArgs);
-
-    if input.sig.ident == "main" && !input.sig.inputs.is_empty() {
-        let msg = "the main function cannot accept arguments";
-        return syn::Error::new_spanned(&input.sig.ident, msg)
-            .to_compile_error()
-            .into();
-    }
-
-    parse_knobs(input, args, false, rt_multi_thread).unwrap_or_else(|e| e.to_compile_error().into())
+    parse_knobs(item, args, false, rt_multi_thread).unwrap_or_else(|e| e.to_compile_error().into())
 }
 
 pub(crate) fn test(args: TokenStream, item: TokenStream, rt_multi_thread: bool) -> TokenStream {
-    let input = syn::parse_macro_input!(item as syn::ItemFn);
     let args = syn::parse_macro_input!(args as syn::AttributeArgs);
-
-    for attr in &input.attrs {
-        if attr.path.is_ident("test") {
-            let msg = "second test attribute is supplied";
-            return syn::Error::new_spanned(&attr, msg)
-                .to_compile_error()
-                .into();
-        }
-    }
-
-    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())
+    parse_knobs(item, args, true, rt_multi_thread).unwrap_or_else(|e| e.to_compile_error().into())
 }

tokio/README.md

@@ -155,7 +155,7 @@ several other libraries, including:
 
 ## Supported Rust Versions
 
-Tokio is built against the latest stable release. The minimum supported version is 1.45.
+Tokio is built against the latest stable release. The minimum supported version is 1.47.
 The current Tokio version is not guaranteed to build on Rust versions earlier than the
 minimum supported version.