Add print_trait_sugared

compiler/rustc_middle/src/ty/print/pretty.rs

@@ -2640,6 +2640,23 @@ impl<'tcx> fmt::Debug for TraitRefPrintOnlyTraitPath<'tcx> {
     }
 }
 
+/// Wrapper type for `ty::TraitRef` which opts-in to pretty printing only
+/// the trait path, and additionally tries to "sugar" `Fn(...)` trait bounds.
+#[derive(Copy, Clone, TypeFoldable, TypeVisitable, Lift)]
+pub struct TraitRefPrintSugared<'tcx>(ty::TraitRef<'tcx>);
+
+impl<'tcx> rustc_errors::IntoDiagnosticArg for TraitRefPrintSugared<'tcx> {
+    fn into_diagnostic_arg(self) -> rustc_errors::DiagnosticArgValue<'static> {
+        self.to_string().into_diagnostic_arg()
+    }
+}
+
+impl<'tcx> fmt::Debug for TraitRefPrintSugared<'tcx> {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        fmt::Display::fmt(self, f)
+    }
+}
+
 /// Wrapper type for `ty::TraitRef` which opts-in to pretty printing only
 /// the trait name. That is, it will print `Trait` instead of
 /// `<T as Trait<U>>`.
@@ -2657,6 +2674,10 @@ impl<'tcx> ty::TraitRef<'tcx> {
         TraitRefPrintOnlyTraitPath(self)
     }
 
+    pub fn print_trait_sugared(self) -> TraitRefPrintSugared<'tcx> {
+        TraitRefPrintSugared(self)
+    }
+
     pub fn print_only_trait_name(self) -> TraitRefPrintOnlyTraitName<'tcx> {
         TraitRefPrintOnlyTraitName(self)
     }
@@ -2666,6 +2687,10 @@ impl<'tcx> ty::Binder<'tcx, ty::TraitRef<'tcx>> {
     pub fn print_only_trait_path(self) -> ty::Binder<'tcx, TraitRefPrintOnlyTraitPath<'tcx>> {
         self.map_bound(|tr| tr.print_only_trait_path())
     }
+
+    pub fn print_trait_sugared(self) -> ty::Binder<'tcx, TraitRefPrintSugared<'tcx>> {
+        self.map_bound(|tr| tr.print_trait_sugared())
+    }
 }
 
 #[derive(Copy, Clone, TypeFoldable, TypeVisitable, Lift)]
@@ -2745,6 +2770,7 @@ forward_display_to_print! {
     ty::PolyExistentialTraitRef<'tcx>,
     ty::Binder<'tcx, ty::TraitRef<'tcx>>,
     ty::Binder<'tcx, TraitRefPrintOnlyTraitPath<'tcx>>,
+    ty::Binder<'tcx, TraitRefPrintSugared<'tcx>>,
     ty::Binder<'tcx, ty::FnSig<'tcx>>,
     ty::Binder<'tcx, ty::TraitPredicate<'tcx>>,
     ty::Binder<'tcx, TraitPredPrintModifiersAndPath<'tcx>>,
@@ -2844,6 +2870,24 @@ define_print_and_forward_display! {
         p!(print_def_path(self.0.def_id, self.0.args));
     }
 
+    TraitRefPrintSugared<'tcx> {
+        if !with_no_queries()
+            && let Some(kind) = cx.tcx().fn_trait_kind_from_def_id(self.0.def_id)
+            && let ty::Tuple(args) = self.0.args.type_at(1).kind()
+        {
+            p!(write("{}", kind.as_str()), "(");
+            for (i, arg) in args.iter().enumerate() {
+                if i > 0 {
+                    p!(", ");
+                }
+                p!(print(arg));
+            }
+            p!(")");
+        } else {
+            p!(print_def_path(self.0.def_id, self.0.args));
+        }
+    }
+
     TraitRefPrintOnlyTraitName<'tcx> {
         p!(print_def_path(self.0.def_id, &[]));
     }
@@ -2892,7 +2936,7 @@ define_print_and_forward_display! {
         if let ty::ImplPolarity::Negative = self.polarity {
             p!("!");
         }
-        p!(print(self.trait_ref.print_only_trait_path()))
+        p!(print(self.trait_ref.print_trait_sugared()))
     }
 
     ty::ProjectionPredicate<'tcx> {