Use parenthetical notation for Fn traits

Always use the `Fn(T) -> R` format when printing closure traits instead of `Fn<(T,), Output = R>`.

Fix #67100:

```
error[E0277]: expected a `Fn()` closure, found `F`
 --> file.rs:6:13
  |
6 |     call_fn(f)
  |     ------- ^ expected an `Fn()` closure, found `F`
  |     |
  |     required by a bound introduced by this call
  |
  = note: wrap the `F` in a closure with no arguments: `|| { /* code */ }`
note: required by a bound in `call_fn`
 --> file.rs:1:15
  |
1 | fn call_fn<F: Fn() -> ()>(f: &F) {
  |               ^^^^^^^^^^ required by this bound in `call_fn`
help: consider further restricting this bound
  |
5 | fn call_any<F: std::any::Any + Fn()>(f: &F) {
  |                              ++++++
```

Author: estebank

compiler/rustc_borrowck/src/diagnostics/conflict_errors.rs

@@ -1362,7 +1362,7 @@ impl<'cx, 'tcx> MirBorrowckCtxt<'cx, 'tcx> {
                     match *predicate.self_ty().kind() {
                         ty::Param(param_ty) => Ok((
                             generics.type_param(param_ty, tcx),
-                            predicate.trait_ref.print_only_trait_path().to_string(),
+                            predicate.trait_ref.print_trait_sugared().to_string(),
                         )),
                         _ => Err(()),
                     }

compiler/rustc_const_eval/src/check_consts/ops.rs

@@ -113,7 +113,7 @@ impl<'tcx> NonConstOp<'tcx> for FnCallNonConst<'tcx> {
                     if let Some(generics) = tcx.hir_node_by_def_id(caller).generics() {
                         let constraint = with_no_trimmed_paths!(format!(
                             "~const {}",
-                            trait_ref.print_only_trait_path()
+                            trait_ref.print_trait_sugared(),
                         ));
                         suggest_constraining_type_param(
                             tcx,

compiler/rustc_hir_analysis/src/coherence/builtin.rs

@@ -554,7 +554,7 @@ fn infringing_fields_error(
                         if let ty::Param(_) = ty.kind() {
                             bounds.push((
                                 format!("{ty}"),
-                                trait_ref.print_only_trait_path().to_string(),
+                                trait_ref.print_trait_sugared().to_string(),
                                 Some(trait_ref.def_id),
                             ));
                         }

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

@@ -3197,7 +3197,7 @@ define_print_and_forward_display! {
         if let ty::PredicatePolarity::Negative = self.0.polarity {
             p!("!")
         }
-        p!(print(self.0.trait_ref.print_only_trait_path()));
+        p!(print(self.0.trait_ref.print_trait_sugared()));
     }
 
     PrintClosureAsImpl<'tcx> {

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

@@ -29,10 +29,11 @@ use rustc_macros::extension;
 use rustc_middle::hir::map;
 use rustc_middle::traits::IsConstable;
 use rustc_middle::ty::error::TypeError::{self, Sorts};
+use rustc_middle::ty::print::PrintPolyTraitRefExt;
 use rustc_middle::ty::{
     self, suggest_arbitrary_trait_bound, suggest_constraining_type_param, AdtKind, GenericArgs,
-    InferTy, IsSuggestable, Ty, TyCtxt, TypeFoldable, TypeFolder, TypeSuperFoldable,
-    TypeVisitableExt, TypeckResults, Upcast,
+    InferTy, IsSuggestable, ToPolyTraitRef, Ty, TyCtxt, TypeFoldable, TypeFolder,
+    TypeSuperFoldable, TypeVisitableExt, TypeckResults, Upcast,
 };
 use rustc_middle::{bug, span_bug};
 use rustc_span::def_id::LocalDefId;
@@ -219,15 +220,15 @@ pub fn suggest_restriction<'tcx, G: EmissionGuarantee>(
             (_, None) => predicate_constraint(hir_generics, trait_pred.upcast(tcx)),
             (None, Some((ident, []))) => (
                 ident.span.shrink_to_hi(),
-                format!(": {}", trait_pred.print_modifiers_and_trait_path()),
+                format!(": {}", trait_pred.to_poly_trait_ref().print_trait_sugared()),
             ),
             (_, Some((_, [.., bounds]))) => (
                 bounds.span().shrink_to_hi(),
-                format!(" + {}", trait_pred.print_modifiers_and_trait_path()),
+                format!(" + {}", trait_pred.to_poly_trait_ref().print_trait_sugared()),
             ),
             (Some(_), Some((_, []))) => (
                 hir_generics.span.shrink_to_hi(),
-                format!(": {}", trait_pred.print_modifiers_and_trait_path()),
+                format!(": {}", trait_pred.to_poly_trait_ref().print_trait_sugared()),
             ),
         };
 

tests/ui/async-await/async-fn/impl-header.stderr

@@ -28,7 +28,7 @@ error[E0277]: expected a `FnMut()` closure, found `F`
 LL | impl async Fn<()> for F {}
    |                       ^ expected an `FnMut()` closure, found `F`
    |
-   = help: the trait `FnMut<()>` is not implemented for `F`
+   = help: the trait `FnMut()` is not implemented for `F`
    = note: wrap the `F` in a closure with no arguments: `|| { /* code */ }`
 note: required by a bound in `Fn`
   --> $SRC_DIR/core/src/ops/function.rs:LL:COL

tests/ui/closures/closure-expected.stderr

@@ -6,7 +6,7 @@ LL |     let y = x.or_else(4);
    |               |
    |               required by a bound introduced by this call
    |
-   = help: the trait `FnOnce<()>` is not implemented for `{integer}`
+   = help: the trait `FnOnce()` is not implemented for `{integer}`
    = note: wrap the `{integer}` in a closure with no arguments: `|| { /* code */ }`
 note: required by a bound in `Option::<T>::or_else`
   --> $SRC_DIR/core/src/option.rs:LL:COL

tests/ui/closures/coerce-unsafe-to-closure.stderr

@@ -6,7 +6,7 @@ LL |     let x: Option<&[u8]> = Some("foo").map(std::mem::transmute);
    |                                        |
    |                                        required by a bound introduced by this call
    |
-   = help: the trait `FnOnce<(&str,)>` is not implemented for fn item `unsafe extern "rust-intrinsic" fn(_) -> _ {transmute::<_, _>}`
+   = help: the trait `FnOnce(&str)` is not implemented for fn item `unsafe extern "rust-intrinsic" fn(_) -> _ {transmute::<_, _>}`
    = note: unsafe function cannot be called generically without an unsafe block
 note: required by a bound in `Option::<T>::map`
   --> $SRC_DIR/core/src/option.rs:LL:COL

tests/ui/consts/fn_trait_refs.stderr

@@ -107,8 +107,8 @@ LL |     f()
    = note: calls in constant functions are limited to constant functions, tuple structs and tuple variants
 help: consider further restricting this bound
    |
-LL |     T: ~const Fn<()> + ~const Destruct + ~const std::ops::Fn<()>,
-   |                                        +++++++++++++++++++++++++
+LL |     T: ~const Fn<()> + ~const Destruct + ~const Fn(),
+   |                                        +++++++++++++
 help: add `#![feature(effects)]` to the crate attributes to enable
    |
 LL + #![feature(effects)]
@@ -132,8 +132,8 @@ LL |     f()
    = note: calls in constant functions are limited to constant functions, tuple structs and tuple variants
 help: consider further restricting this bound
    |
-LL |     T: ~const FnMut<()> + ~const Destruct + ~const std::ops::FnMut<()>,
-   |                                           ++++++++++++++++++++++++++++
+LL |     T: ~const FnMut<()> + ~const Destruct + ~const FnMut(),
+   |                                           ++++++++++++++++
 help: add `#![feature(effects)]` to the crate attributes to enable
    |
 LL + #![feature(effects)]
@@ -157,8 +157,8 @@ LL |     f()
    = note: calls in constant functions are limited to constant functions, tuple structs and tuple variants
 help: consider further restricting this bound
    |
-LL |     T: ~const FnOnce<()> + ~const std::ops::FnOnce<()>,
-   |                          +++++++++++++++++++++++++++++
+LL |     T: ~const FnOnce<()> + ~const FnOnce(),
+   |                          +++++++++++++++++
 help: add `#![feature(effects)]` to the crate attributes to enable
    |
 LL + #![feature(effects)]

tests/ui/consts/unstable-const-fn-in-libcore.stderr

@@ -13,8 +13,8 @@ LL |             Opt::None => f(),
    = note: calls in constant functions are limited to constant functions, tuple structs and tuple variants
 help: consider further restricting this bound
    |
-LL |     const fn unwrap_or_else<F: ~const FnOnce() -> T + ~const std::ops::FnOnce<()>>(self, f: F) -> T {
-   |                                                     +++++++++++++++++++++++++++++
+LL |     const fn unwrap_or_else<F: ~const FnOnce() -> T + ~const FnOnce()>(self, f: F) -> T {
+   |                                                     +++++++++++++++++
 help: add `#![feature(effects)]` to the crate attributes to enable
    |
 LL + #![feature(effects)]