1 files changed, 55 insertions, 0 deletions
diff --git a/third_party/rust/futures-macro/src/executor.rs b/third_party/rust/futures-macro/src/executor.rs
new file mode 100644
index 0000000000..40a091f94c
--- /dev/null
+++ b/third_party/rust/futures-macro/src/executor.rs
@@ -0,0 +1,55 @@
+use proc_macro::TokenStream;
+use proc_macro2::Span;
+use quote::{quote, quote_spanned, ToTokens};
+
+pub(crate) fn test(args: TokenStream, item: TokenStream) -> TokenStream {
+    if !args.is_empty() {
+        return syn::Error::new_spanned(proc_macro2::TokenStream::from(args), "invalid argument")
+            .to_compile_error()
+            .into();
+    }
+
+    let mut input = syn::parse_macro_input!(item as syn::ItemFn);
+
+    if input.sig.asyncness.take().is_none() {
+        return syn::Error::new_spanned(input.sig.fn_token, "Only async functions are supported")
+            .to_compile_error()
+            .into();
+    }
+
+    // If type mismatch occurs, the current rustc points to the last statement.
+    let (last_stmt_start_span, last_stmt_end_span) = {
+        let mut last_stmt = input
+            .block
+            .stmts
+            .last()
+            .map(ToTokens::into_token_stream)
+            .unwrap_or_default()
+            .into_iter();
+        // `Span` on stable Rust has a limitation that only points to the first
+        // token, not the whole tokens. We can work around this limitation by
+        // using the first/last span of the tokens like
+        // `syn::Error::new_spanned` does.
+        let start = last_stmt.next().map_or_else(Span::call_site, |t| t.span());
+        let end = last_stmt.last().map_or(start, |t| t.span());
+        (start, end)
+    };
+
+    let path = quote_spanned! {last_stmt_start_span=>
+        ::futures_test::__private
+    };
+    let body = &input.block;
+    input.block.stmts = vec![syn::Stmt::Expr(
+        syn::parse2(quote_spanned! {last_stmt_end_span=>
+            #path::block_on(async #body)
+        })
+        .unwrap(),
+    )];
+
+    let gen = quote! {
+        #[::core::prelude::v1::test]
+        #input
+    };
+
+    gen.into()
+}