Fix missing self subst when rendering impl Fn*<T> with no output type

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

@@ -232,7 +232,7 @@ pub trait PrettyPrinter<'tcx>: Printer<'tcx> + fmt::Write {
         f: F,
     ) -> Result<(), PrintError>
     where
-        T: Print<'tcx, Self> + TypeFoldable<TyCtxt<'tcx>>,
+        T: TypeFoldable<TyCtxt<'tcx>>,
     {
         f(value.as_ref().skip_binder(), self)
     }
@@ -1056,7 +1056,7 @@ pub trait PrettyPrinter<'tcx>: Printer<'tcx> + fmt::Write {
         // Insert parenthesis around (Fn(A, B) -> C) if the opaque ty has more than one other trait
         let paren_needed = fn_traits.len() > 1 || traits.len() > 0 || !has_sized_bound;
 
-        for ((bound_args, is_async), entry) in fn_traits {
+        for ((bound_args_and_self_ty, is_async), entry) in fn_traits {
             write!(self, "{}", if first { "" } else { " + " })?;
             write!(self, "{}", if paren_needed { "(" } else { "" })?;
 
@@ -1067,7 +1067,7 @@ pub trait PrettyPrinter<'tcx>: Printer<'tcx> + fmt::Write {
             };
 
             if let Some(return_ty) = entry.return_ty {
-                self.wrap_binder(&bound_args, |args, cx| {
+                self.wrap_binder(&bound_args_and_self_ty, |(args, _), cx| {
                     define_scoped_cx!(cx);
                     p!(write("{}", tcx.item_name(trait_def_id)));
                     p!("(");
@@ -1093,9 +1093,13 @@ pub trait PrettyPrinter<'tcx>: Printer<'tcx> + fmt::Write {
             } else {
                 // Otherwise, render this like a regular trait.
                 traits.insert(
-                    bound_args.map_bound(|args| ty::TraitPredicate {
+                    bound_args_and_self_ty.map_bound(|(args, self_ty)| ty::TraitPredicate {
                         polarity: ty::PredicatePolarity::Positive,
-                        trait_ref: ty::TraitRef::new(tcx, trait_def_id, [Ty::new_tup(tcx, args)]),
+                        trait_ref: ty::TraitRef::new(
+                            tcx,
+                            trait_def_id,
+                            [self_ty, Ty::new_tup(tcx, args)],
+                        ),
                     }),
                     FxIndexMap::default(),
                 );
@@ -1229,7 +1233,7 @@ pub trait PrettyPrinter<'tcx>: Printer<'tcx> + fmt::Write {
             FxIndexMap<DefId, ty::Binder<'tcx, Term<'tcx>>>,
         >,
         fn_traits: &mut FxIndexMap<
-            (ty::Binder<'tcx, &'tcx ty::List<Ty<'tcx>>>, bool),
+            (ty::Binder<'tcx, (&'tcx ty::List<Ty<'tcx>>, Ty<'tcx>)>, bool),
             OpaqueFnEntry<'tcx>,
         >,
     ) {
@@ -1249,7 +1253,7 @@ pub trait PrettyPrinter<'tcx>: Printer<'tcx> + fmt::Write {
             && let ty::Tuple(types) = *trait_pred.skip_binder().trait_ref.args.type_at(1).kind()
         {
             let entry = fn_traits
-                .entry((trait_pred.rebind(types), is_async))
+                .entry((trait_pred.rebind((types, trait_pred.skip_binder().self_ty())), is_async))
                 .or_insert_with(|| OpaqueFnEntry { kind, return_ty: None });
             if kind.extends(entry.kind) {
                 entry.kind = kind;
@@ -2379,7 +2383,7 @@ impl<'tcx> PrettyPrinter<'tcx> for FmtPrinter<'_, 'tcx> {
         f: C,
     ) -> Result<(), PrintError>
     where
-        T: Print<'tcx, Self> + TypeFoldable<TyCtxt<'tcx>>,
+        T: TypeFoldable<TyCtxt<'tcx>>,
     {
         self.pretty_wrap_binder(value, f)
     }
@@ -2633,7 +2637,7 @@ impl<'tcx> FmtPrinter<'_, 'tcx> {
         value: &ty::Binder<'tcx, T>,
     ) -> Result<(T, UnordMap<ty::BoundRegion, ty::Region<'tcx>>), fmt::Error>
     where
-        T: Print<'tcx, Self> + TypeFoldable<TyCtxt<'tcx>>,
+        T: TypeFoldable<TyCtxt<'tcx>>,
     {
         fn name_by_region_index(
             index: usize,
@@ -2814,7 +2818,7 @@ impl<'tcx> FmtPrinter<'_, 'tcx> {
         f: C,
     ) -> Result<(), fmt::Error>
     where
-        T: Print<'tcx, Self> + TypeFoldable<TyCtxt<'tcx>>,
+        T: TypeFoldable<TyCtxt<'tcx>>,
     {
         let old_region_index = self.region_index;
         let (new_value, _) = self.name_all_regions(value)?;

tests/ui/unboxed-closures/existential-printing.rs

@@ -0,0 +1,8 @@
+// Make sure we don't ICE printing `impl AsyncFnOnce<()>`.
+
+#![feature(unboxed_closures, fn_traits)]
+
+fn f() -> impl FnOnce<()> { || () }
+
+fn main() { () = f(); }
+//~^ ERROR mismatched types

tests/ui/unboxed-closures/existential-printing.stderr

@@ -0,0 +1,17 @@
+error[E0308]: mismatched types
+  --> $DIR/existential-printing.rs:7:13
+   |
+LL | fn f() -> impl FnOnce<()> { || () }
+   |           --------------- the expected opaque type
+LL |
+LL | fn main() { () = f(); }
+   |             ^^   --- this expression has type `impl FnOnce<()>`
+   |             |
+   |             expected opaque type, found `()`
+   |
+   = note: expected opaque type `impl FnOnce<()>`
+                found unit type `()`
+
+error: aborting due to 1 previous error
+
+For more information about this error, try `rustc --explain E0308`.