2 files changed, 23 insertions, 12 deletions

diff --git a/compiler/rustc_hir_analysis/src/astconv/mod.rs b/compiler/rustc_hir_analysis/src/astconv/mod.rs
index 9ad1d2bc542..8b1cc50a3a1 100644
--- a/compiler/rustc_hir_analysis/src/astconv/mod.rs
+++ b/compiler/rustc_hir_analysis/src/astconv/mod.rs
@@ -274,7 +274,7 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
             item_segment.args(),
             item_segment.infer_args,
             None,
-            None,
+            ty::BoundConstness::NotConst,
         );
         if let Some(b) = item_segment.args().bindings.first() {
             Self::prohibit_assoc_ty_binding(self.tcx(), b.span);
@@ -324,7 +324,7 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
         generic_args: &'a hir::GenericArgs<'_>,
         infer_args: bool,
         self_ty: Option<Ty<'tcx>>,
-        constness: Option<ty::BoundConstness>,
+        constness: ty::BoundConstness,
     ) -> (SubstsRef<'tcx>, GenericArgCountResult) {
         // If the type is parameterized by this region, then replace this
         // region with the current anon region binding (in other words,
@@ -538,7 +538,7 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
             &mut substs_ctx,
         );
 
-        if let Some(ty::BoundConstness::ConstIfConst) = constness
+        if let ty::BoundConstness::ConstIfConst = constness
             && generics.has_self && !tcx.has_attr(def_id, sym::const_trait)
         {
             tcx.sess.emit_err(crate::errors::ConstBoundForNonConstTrait { span } );
@@ -611,7 +611,7 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
             item_segment.args(),
             item_segment.infer_args,
             None,
-            None,
+            ty::BoundConstness::NotConst,
         );
 
         if let Some(b) = item_segment.args().bindings.first() {
@@ -641,7 +641,7 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
             self_ty,
             trait_ref.path.segments.last().unwrap(),
             true,
-            Some(constness),
+            constness,
         )
     }
 
@@ -668,7 +668,7 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
             args,
             infer_args,
             Some(self_ty),
-            Some(constness),
+            constness,
         );
 
         let tcx = self.tcx();
@@ -798,7 +798,7 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
         self_ty: Ty<'tcx>,
         trait_segment: &hir::PathSegment<'_>,
         is_impl: bool,
-        constness: Option<ty::BoundConstness>,
+        constness: ty::BoundConstness,
     ) -> ty::TraitRef<'tcx> {
         let (substs, _) = self.create_substs_for_ast_trait_ref(
             span,
@@ -822,7 +822,7 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
         self_ty: Ty<'tcx>,
         trait_segment: &'a hir::PathSegment<'a>,
         is_impl: bool,
-        constness: Option<ty::BoundConstness>,
+        constness: ty::BoundConstness,
     ) -> (SubstsRef<'tcx>, GenericArgCountResult) {
         self.complain_about_internal_fn_trait(span, trait_def_id, trait_segment, is_impl);
 
@@ -2129,7 +2129,7 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
             self_ty,
             trait_segment,
             false,
-            Some(constness),
+            constness,
         );
 
         let item_substs = self.create_substs_for_associated_item(
@@ -2700,7 +2700,7 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
                     &GenericArgs::none(),
                     true,
                     None,
-                    None,
+                    ty::BoundConstness::NotConst,
                 );
                 EarlyBinder(self.normalize_ty(span, tcx.at(span).type_of(def_id)))
                     .subst(tcx, substs)
diff --git a/compiler/rustc_resolve/src/late/diagnostics.rs b/compiler/rustc_resolve/src/late/diagnostics.rs
index 103187b00d1..a1338dcd477 100644
--- a/compiler/rustc_resolve/src/late/diagnostics.rs
+++ b/compiler/rustc_resolve/src/late/diagnostics.rs
@@ -322,7 +322,12 @@ impl<'a: 'ast, 'ast> LateResolutionVisitor<'a, '_, 'ast> {
         }
 
         self.suggest_bare_struct_literal(&mut err);
-        self.suggest_pattern_match_with_let(&mut err, source, span);
+
+        if self.suggest_pattern_match_with_let(&mut err, source, span) {
+            // Fallback label.
+            err.span_label(base_error.span, &base_error.fallback_label);
+            return (err, Vec::new());
+        }
 
         self.suggest_self_or_self_ref(&mut err, path, span);
         self.detect_assoct_type_constraint_meant_as_path(&mut err, &base_error);
@@ -341,7 +346,11 @@ impl<'a: 'ast, 'ast> LateResolutionVisitor<'a, '_, 'ast> {
         if !self.type_ascription_suggestion(&mut err, base_error.span) {
             let mut fallback =
                 self.suggest_trait_and_bounds(&mut err, source, res, span, &base_error);
+
+            // if we have suggested using pattern matching, then don't add needless suggestions
+            // for typos.
             fallback |= self.suggest_typo(&mut err, source, path, span, &base_error);
+
             if fallback {
                 // Fallback label.
                 err.span_label(base_error.span, &base_error.fallback_label);
@@ -937,7 +946,7 @@ impl<'a: 'ast, 'ast> LateResolutionVisitor<'a, '_, 'ast> {
         err: &mut Diagnostic,
         source: PathSource<'_>,
         span: Span,
-    ) {
+    ) -> bool {
         if let PathSource::Expr(_) = source &&
         let Some(Expr {
                     span: expr_span,
@@ -954,8 +963,10 @@ impl<'a: 'ast, 'ast> LateResolutionVisitor<'a, '_, 'ast> {
                     "let ",
                     Applicability::MaybeIncorrect,
                 );
+                return true;
             }
         }
+        false
     }
 
     fn get_single_associated_item(