suggest to add a constraint except asyn-fn without explicit output

src/librustc/infer/error_reporting/nice_region_error/different_lifetimes.rs

@@ -43,7 +43,7 @@ impl<'a, 'tcx> NiceRegionError<'a, 'tcx> {
     ///
     /// It will later be extended to trait objects.
     pub(super) fn try_report_anon_anon_conflict(&self) -> Option<ErrorReported> {
-        let (span, sub, sup) = self.get_regions();
+        let (span, sub, sup) = self.regions();
 
         // Determine whether the sub and sup consist of both anonymous (elided) regions.
         let anon_reg_sup = self.tcx().is_suitable_region(sup)?;

src/librustc/infer/error_reporting/nice_region_error/mod.rs

@@ -77,7 +77,7 @@ impl<'cx, 'tcx> NiceRegionError<'cx, 'tcx> {
             .or_else(|| self.try_report_impl_not_conforming_to_trait())
     }
 
-    pub fn get_regions(&self) -> (Span, ty::Region<'tcx>, ty::Region<'tcx>) {
+    pub fn regions(&self) -> (Span, ty::Region<'tcx>, ty::Region<'tcx>) {
         match (&self.error, self.regions) {
             (Some(ConcreteFailure(origin, sub, sup)), None) => (origin.span(), sub, sup),
             (Some(SubSupConflict(_, _, origin, sub, _, sup)), None) => (origin.span(), sub, sup),

src/librustc/infer/error_reporting/nice_region_error/named_anon_conflict.rs

@@ -9,7 +9,7 @@ impl<'a, 'tcx> NiceRegionError<'a, 'tcx> {
     /// When given a `ConcreteFailure` for a function with parameters containing a named region and
     /// an anonymous region, emit an descriptive diagnostic error.
     pub(super) fn try_report_named_anon_conflict(&self) -> Option<DiagnosticBuilder<'a>> {
-        let (span, sub, sup) = self.get_regions();
+        let (span, sub, sup) = self.regions();
 
         debug!(
             "try_report_named_anon_conflict(sub={:?}, sup={:?}, error={:?})",

src/librustc/infer/error_reporting/nice_region_error/static_impl_trait.rs

@@ -20,8 +20,9 @@ impl<'a, 'tcx> NiceRegionError<'a, 'tcx> {
                 ) = error.clone()
             {
                 let anon_reg_sup = self.tcx().is_suitable_region(sup_r)?;
+                let return_ty = self.tcx().return_type_impl_trait(anon_reg_sup.def_id);
                 if sub_r == &RegionKind::ReStatic &&
-                    self.tcx().return_type_impl_trait(anon_reg_sup.def_id).is_some()
+                    return_ty.is_some()
                 {
                     let sp = var_origin.span();
                     let return_sp = sub_origin.span();
@@ -53,16 +54,19 @@ impl<'a, 'tcx> NiceRegionError<'a, 'tcx> {
                         _ => "'_".to_owned(),
                     };
                     if let Ok(snippet) = self.tcx().sess.source_map().span_to_snippet(return_sp) {
-                        err.span_suggestion(
-                            return_sp,
-                            &format!(
-                                "you can add a constraint to the return type to make it last \
+                        // only apply this suggestion onto non-async fnunctions
+                        if !return_ty.unwrap().1 {
+                            err.span_suggestion(
+                                return_sp,
+                                &format!(
+                                    "you can add a constraint to the return type to make it last \
                                  less than `'static` and match {}",
-                                lifetime,
-                            ),
-                            format!("{} + {}", snippet, lifetime_name),
-                            Applicability::Unspecified,
-                        );
+                                 lifetime,
+                                ),
+                                format!("{} + {}", snippet, lifetime_name),
+                                Applicability::Unspecified,
+                            );
+                        }
                     }
                     err.emit();
                     return Some(ErrorReported);

src/librustc/ty/context.rs

@@ -1546,14 +1546,14 @@ impl<'tcx> TyCtxt<'tcx> {
         return Some(FreeRegionInfo {
             def_id: suitable_region_binding_scope,
             boundregion: bound_region,
-            is_impl_item: is_impl_item,
+            is_impl_item,
         });
     }
 
     pub fn return_type_impl_trait(
         &self,
         scope_def_id: DefId,
-    ) -> Option<Ty<'tcx>> {
+    ) -> Option<(Ty<'tcx>, bool)> {
         // HACK: `type_of_def_id()` will fail on these (#55796), so return `None`.
         let hir_id = self.hir().as_local_hir_id(scope_def_id).unwrap();
         match self.hir().get(hir_id) {
@@ -1573,8 +1573,10 @@ impl<'tcx> TyCtxt<'tcx> {
             ty::FnDef(_, _) => {
                 let sig = ret_ty.fn_sig(*self);
                 let output = self.erase_late_bound_regions(&sig.output());
+                let is_async_fn =
+                    hir::IsAsync::Async == self.asyncness(scope_def_id);
                 if output.is_impl_trait() {
-                    Some(output)
+                    Some((output, is_async_fn))
                 } else {
                     None
                 }

src/librustc_mir/borrow_check/nll/region_infer/error_reporting/mod.rs

@@ -698,10 +698,10 @@ impl<'tcx> RegionInferenceContext<'tcx> {
         if let (Some(f), Some(ty::RegionKind::ReStatic)) =
             (self.to_error_region(fr), self.to_error_region(outlived_fr))
         {
-            if let Some(ty::TyS {
+            if let Some((ty::TyS {
                 kind: ty::Opaque(did, substs),
                 ..
-            }) = infcx
+            }, _)) = infcx
                 .tcx
                 .is_suitable_region(f)
                 .map(|r| r.def_id)