Parse 'async unsafe fn' instead of 'unsafe async fn'.

src/libsyntax/parse/parser.rs

@@ -7205,20 +7205,16 @@ impl<'a> Parser<'a> {
             return Ok(Some(item));
         }
 
-        // `unsafe async fn` or `async fn`
+        // Parse `async unsafe? fn`.
-        if (
+        if self.check_keyword(kw::Async) {
-            self.check_keyword(kw::Unsafe) &&
+            let async_span = self.span;
-            self.is_keyword_ahead(1, &[kw::Async])
+            if self.is_keyword_ahead(1, &[kw::Fn])
-        ) || (
+                || self.is_keyword_ahead(2, &[kw::Fn])
-            self.check_keyword(kw::Async) &&
-            self.is_keyword_ahead(1, &[kw::Fn])
-        )
             {
                 // ASYNC FUNCTION ITEM
-            let unsafety = self.parse_unsafety();
+                self.bump(); // `async`
-            self.expect_keyword(kw::Async)?;
+                let unsafety = self.parse_unsafety(); // `unsafe`?
-            let async_span = self.prev_span;
+                self.expect_keyword(kw::Fn)?; // `fn`
-            self.expect_keyword(kw::Fn)?;
                 let fn_span = self.prev_span;
                 let (ident, item_, extra_attrs) =
                     self.parse_item_fn(unsafety,
@@ -7244,6 +7240,7 @@ impl<'a> Parser<'a> {
                 }
                 return Ok(Some(item));
             }
+        }
         if self.check_keyword(kw::Unsafe) &&
             self.is_keyword_ahead(1, &[kw::Trait, kw::Auto])
         {

src/test/ui/async-await/async-await.rs

@@ -122,7 +122,7 @@ fn async_fn_with_internal_borrow(y: u8) -> impl Future<Output = u8> {
     }
 }
 
-unsafe async fn unsafe_async_fn(x: u8) -> u8 {
+async unsafe fn unsafe_async_fn(x: u8) -> u8 {
     wake_and_yield_once().await;
     x
 }

src/test/ui/async-await/await-macro.rs

@@ -122,7 +122,7 @@ fn async_fn_with_internal_borrow(y: u8) -> impl Future<Output = u8> {
     }
 }
 
-unsafe async fn unsafe_async_fn(x: u8) -> u8 {
+async unsafe fn unsafe_async_fn(x: u8) -> u8 {
     await!(wake_and_yield_once());
     x
 }