Impove diagnostic for .awaiting non-futures

compiler/rustc_ast_lowering/src/expr.rs

@@ -146,13 +146,19 @@ impl<'hir> LoweringContext<'_, 'hir> {
                         |this| this.with_new_scopes(|this| this.lower_block_expr(block)),
                     ),
                 ExprKind::Await(ref expr) => {
-                    let span = if expr.span.hi() < e.span.hi() {
-                        expr.span.shrink_to_hi().with_hi(e.span.hi())
+                    let dot_await_span = if expr.span.hi() < e.span.hi() {
+                        let span_with_whitespace = self
+                            .tcx
+                            .sess
+                            .source_map()
+                            .span_extend_while(expr.span, char::is_whitespace)
+                            .unwrap_or(expr.span);
+                        span_with_whitespace.shrink_to_hi().with_hi(e.span.hi())
                     } else {
                         // this is a recovered `await expr`
                         e.span
                     };
-                    self.lower_expr_await(span, expr)
+                    self.lower_expr_await(dot_await_span, expr)
                 }
                 ExprKind::Closure(
                     ref binder,

compiler/rustc_trait_selection/src/traits/error_reporting/suggestions.rs

@@ -1160,8 +1160,8 @@ impl<'a, 'tcx> InferCtxtExt<'tcx> for InferCtxt<'a, 'tcx> {
                     // and if not maybe suggest doing something else? If we kept the expression around we
                     // could also check if it is an fn call (very likely) and suggest changing *that*, if
                     // it is from the local crate.
-                    err.span_suggestion_verbose(
-                        expr.span.shrink_to_hi().with_hi(span.hi()),
+                    err.span_suggestion(
+                        span,
                         "remove the `.await`",
                         "",
                         Applicability::MachineApplicable,

src/test/ui/async-await/issue-101715.rs

@@ -0,0 +1,17 @@
+// edition:2018
+
+struct S;
+
+impl S {
+    fn very_long_method_name_the_longest_method_name_in_the_whole_universe(self) {}
+}
+
+async fn foo() {
+    S.very_long_method_name_the_longest_method_name_in_the_whole_universe()
+        .await
+        //~^ error: `()` is not a future
+        //~| help: remove the `.await`
+        //~| help: the trait `Future` is not implemented for `()`
+}
+
+fn main() {}

src/test/ui/async-await/issue-101715.stderr

@@ -0,0 +1,16 @@
+error[E0277]: `()` is not a future
+  --> $DIR/issue-101715.rs:11:9
+   |
+LL |         .await
+   |         ^^^^^^
+   |         |
+   |         `()` is not a future
+   |         help: remove the `.await`
+   |
+   = help: the trait `Future` is not implemented for `()`
+   = note: () must be a future or must implement `IntoFuture` to be awaited
+   = note: required for `()` to implement `IntoFuture`
+
+error: aborting due to previous error
+
+For more information about this error, try `rustc --explain E0277`.

src/test/ui/async-await/issue-70594.stderr

@@ -22,16 +22,14 @@ error[E0277]: `()` is not a future
   --> $DIR/issue-70594.rs:4:11
    |
 LL |     [1; ().await];
-   |           ^^^^^^ `()` is not a future
+   |           ^^^^^^
+   |           |
+   |           `()` is not a future
+   |           help: remove the `.await`
    |
    = help: the trait `Future` is not implemented for `()`
    = note: () must be a future or must implement `IntoFuture` to be awaited
    = note: required for `()` to implement `IntoFuture`
-help: remove the `.await`
-   |
-LL -     [1; ().await];
-LL +     [1; ()];
-   |
 
 error: aborting due to 4 previous errors
 

src/test/ui/async-await/issues/issue-62009-1.stderr

@@ -28,16 +28,14 @@ error[E0277]: `[closure@$DIR/issue-62009-1.rs:12:6: 12:9]` is not a future
   --> $DIR/issue-62009-1.rs:12:15
    |
 LL |     (|_| 2333).await;
-   |               ^^^^^^ `[closure@$DIR/issue-62009-1.rs:12:6: 12:9]` is not a future
+   |               ^^^^^^
+   |               |
+   |               `[closure@$DIR/issue-62009-1.rs:12:6: 12:9]` is not a future
+   |               help: remove the `.await`
    |
    = help: the trait `Future` is not implemented for closure `[closure@$DIR/issue-62009-1.rs:12:6: 12:9]`
    = note: [closure@$DIR/issue-62009-1.rs:12:6: 12:9] must be a future or must implement `IntoFuture` to be awaited
    = note: required for `[closure@$DIR/issue-62009-1.rs:12:6: 12:9]` to implement `IntoFuture`
-help: remove the `.await`
-   |
-LL -     (|_| 2333).await;
-LL +     (|_| 2333);
-   |
 
 error: aborting due to 4 previous errors