Rollup merge of #62241 - Centril:fix-async-unsafe-order, r=petrochenkov

Always parse 'async unsafe fn' + properly ban in 2015

Parse `async unsafe fn` not `unsafe async fn` in implementations. We also take the opportunity to properly ban `async fn` in Rust 2015 when they are inside implementations.

Closes https://github.com/rust-lang/rust/issues/62232.

cc https://github.com/rust-lang/rust/pull/61319, https://github.com/rust-lang/rust/issues/62121, and https://github.com/rust-lang/rust/issues/62149.

r? @petrochenkov

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

@@ -134,11 +134,15 @@ trait Bar {
 }
 
 impl Foo {
-    async fn async_method(x: u8) -> u8 {
+    async fn async_assoc_item(x: u8) -> u8 {
         unsafe {
             unsafe_async_fn(x).await
         }
     }
+
+    async unsafe fn async_unsafe_assoc_item(x: u8) -> u8 {
+        unsafe_async_fn(x).await
+    }
 }
 
 fn test_future_yields_once_then_returns<F, Fut>(f: F)
@@ -180,12 +184,17 @@ fn main() {
         async_fn,
         generic_async_fn,
         async_fn_with_internal_borrow,
-        Foo::async_method,
+        Foo::async_assoc_item,
         |x| {
             async move {
                 unsafe { unsafe_async_fn(x).await }
             }
         },
+        |x| {
+            async move {
+                unsafe { Foo::async_unsafe_assoc_item(x).await }
+            }
+        },
     }
     test_with_borrow! {
         async_block_with_borrow_named_lifetime,

src/test/ui/async-await/edition-deny-async-fns-2015.rs

@@ -28,6 +28,12 @@ fn main() {
         async fn foo() {} //~ ERROR `async fn` is not permitted in the 2015 edition
     }
 
+    accept_item! {
+        impl Foo {
+            async fn bar() {} //~ ERROR `async fn` is not permitted in the 2015 edition
+        }
+    }
+
     let inside_closure = || {
         async fn bar() {} //~ ERROR `async fn` is not permitted in the 2015 edition
     };

src/test/ui/async-await/edition-deny-async-fns-2015.stderr

@@ -23,7 +23,19 @@ LL | async fn async_baz() {
    | ^^^^^
 
 error[E0670]: `async fn` is not permitted in the 2015 edition
-  --> $DIR/edition-deny-async-fns-2015.rs:32:9
+  --> $DIR/edition-deny-async-fns-2015.rs:16:5
+   |
+LL |     async fn foo() {}
+   |     ^^^^^
+
+error[E0670]: `async fn` is not permitted in the 2015 edition
+  --> $DIR/edition-deny-async-fns-2015.rs:20:5
+   |
+LL |     async fn foo() {}
+   |     ^^^^^
+
+error[E0670]: `async fn` is not permitted in the 2015 edition
+  --> $DIR/edition-deny-async-fns-2015.rs:38:9
    |
 LL |         async fn bar() {}
    |         ^^^^^
@@ -35,10 +47,10 @@ LL |         async fn foo() {}
    |         ^^^^^
 
 error[E0670]: `async fn` is not permitted in the 2015 edition
-  --> $DIR/edition-deny-async-fns-2015.rs:16:5
+  --> $DIR/edition-deny-async-fns-2015.rs:33:13
    |
-LL |     async fn foo() {}
-   |     ^^^^^
+LL |             async fn bar() {}
+   |             ^^^^^
 
 error[E0706]: trait fns cannot be declared `async`
   --> $DIR/edition-deny-async-fns-2015.rs:20:5
@@ -46,12 +58,6 @@ error[E0706]: trait fns cannot be declared `async`
 LL |     async fn foo() {}
    |     ^^^^^^^^^^^^^^^^^
 
-error[E0670]: `async fn` is not permitted in the 2015 edition
-  --> $DIR/edition-deny-async-fns-2015.rs:20:5
-   |
-LL |     async fn foo() {}
-   |     ^^^^^
-
-error: aborting due to 9 previous errors
+error: aborting due to 10 previous errors
 
 For more information about this error, try `rustc --explain E0670`.

src/test/ui/async-await/no-unsafe-async.rs

@@ -0,0 +1,11 @@
+// edition:2018
+
+struct S;
+
+impl S {
+    #[cfg(FALSE)]
+    unsafe async fn g() {} //~ ERROR expected one of `extern` or `fn`, found `async`
+}
+
+#[cfg(FALSE)]
+unsafe async fn f() {} //~ ERROR expected one of `extern`, `fn`, or `{`, found `async`

src/test/ui/async-await/no-unsafe-async.stderr

@@ -0,0 +1,14 @@
+error: expected one of `extern` or `fn`, found `async`
+  --> $DIR/no-unsafe-async.rs:7:12
+   |
+LL |     unsafe async fn g() {}
+   |            ^^^^^ expected one of `extern` or `fn` here
+
+error: expected one of `extern`, `fn`, or `{`, found `async`
+  --> $DIR/no-unsafe-async.rs:11:8
+   |
+LL | unsafe async fn f() {}
+   |        ^^^^^ expected one of `extern`, `fn`, or `{` here
+
+error: aborting due to 2 previous errors
+