diff --git a/compiler/rustc_span/src/symbol.rs b/compiler/rustc_span/src/symbol.rs
index e4fafbc12d355..f815be573de6e 100644
--- a/compiler/rustc_span/src/symbol.rs
+++ b/compiler/rustc_span/src/symbol.rs
@@ -295,6 +295,7 @@ symbols! {
         ToOwned,
         ToString,
         TokenStream,
+        Trait,
         Try,
         TryCaptureGeneric,
         TryCapturePrintable,
diff --git a/compiler/rustc_trait_selection/src/traits/error_reporting/on_unimplemented.rs b/compiler/rustc_trait_selection/src/traits/error_reporting/on_unimplemented.rs
index d645dc033b811..c24ade57926bf 100644
--- a/compiler/rustc_trait_selection/src/traits/error_reporting/on_unimplemented.rs
+++ b/compiler/rustc_trait_selection/src/traits/error_reporting/on_unimplemented.rs
@@ -50,6 +50,7 @@ static ALLOWED_FORMAT_SYMBOLS: &[Symbol] = &[
     sym::float,
     sym::_Self,
     sym::crate_local,
+    sym::Trait,
 ];
 
 impl<'tcx> TypeErrCtxtExt<'tcx> for TypeErrCtxt<'_, 'tcx> {
@@ -180,6 +181,19 @@ impl<'tcx> TypeErrCtxtExt<'tcx> for TypeErrCtxt<'_, 'tcx> {
             flags.push((sym::cause, Some("MainFunctionType".to_string())));
         }
 
+        if let Some(kind) = self.tcx.fn_trait_kind_from_def_id(trait_ref.def_id)
+            && let ty::Tuple(args) = trait_ref.args.type_at(1).kind()
+        {
+            let args = args
+                .iter()
+                .map(|ty| ty.to_string())
+                .collect::<Vec<_>>()
+                .join(", ");
+            flags.push((sym::Trait, Some(format!("{}({args})", kind.as_str()))));
+        } else {
+            flags.push((sym::Trait, Some(trait_ref.print_only_trait_path().to_string())));
+        }
+
         // Add all types without trimmed paths.
         ty::print::with_no_trimmed_paths!({
             let generics = self.tcx.generics_of(def_id);
diff --git a/library/core/src/ops/function.rs b/library/core/src/ops/function.rs
index 20f0bba4c13b6..51e304dd7c247 100644
--- a/library/core/src/ops/function.rs
+++ b/library/core/src/ops/function.rs
@@ -56,7 +56,7 @@ use crate::marker::Tuple;
 #[lang = "fn"]
 #[stable(feature = "rust1", since = "1.0.0")]
 #[rustc_paren_sugar]
-#[rustc_on_unimplemented(
+#[cfg_attr(not(bootstrap), rustc_on_unimplemented(
     on(
         Args = "()",
         note = "wrap the `{Self}` in a closure with no arguments: `|| {{ /* code */ }}`"
@@ -67,9 +67,9 @@ use crate::marker::Tuple;
         // SAFETY: tidy is not smart enough to tell that the below unsafe block is a string
         label = "call the function in a closure: `|| unsafe {{ /* code */ }}`"
     ),
-    message = "expected a `{Fn}<{Args}>` closure, found `{Self}`",
-    label = "expected an `Fn<{Args}>` closure, found `{Self}`"
-)]
+    message = "expected a `{Trait}` closure, found `{Self}`",
+    label = "expected an `{Trait}` closure, found `{Self}`"
+))]
 #[fundamental] // so that regex can rely that `&str: !FnMut`
 #[must_use = "closures are lazy and do nothing unless called"]
 // FIXME(effects) #[const_trait]
@@ -143,7 +143,7 @@ pub trait Fn<Args: Tuple>: FnMut<Args> {
 #[lang = "fn_mut"]
 #[stable(feature = "rust1", since = "1.0.0")]
 #[rustc_paren_sugar]
-#[rustc_on_unimplemented(
+#[cfg_attr(not(bootstrap), rustc_on_unimplemented(
     on(
         Args = "()",
         note = "wrap the `{Self}` in a closure with no arguments: `|| {{ /* code */ }}`"
@@ -154,9 +154,9 @@ pub trait Fn<Args: Tuple>: FnMut<Args> {
         // SAFETY: tidy is not smart enough to tell that the below unsafe block is a string
         label = "call the function in a closure: `|| unsafe {{ /* code */ }}`"
     ),
-    message = "expected a `{FnMut}<{Args}>` closure, found `{Self}`",
-    label = "expected an `FnMut<{Args}>` closure, found `{Self}`"
-)]
+    message = "expected a `{Trait}` closure, found `{Self}`",
+    label = "expected an `{Trait}` closure, found `{Self}`"
+))]
 #[fundamental] // so that regex can rely that `&str: !FnMut`
 #[must_use = "closures are lazy and do nothing unless called"]
 // FIXME(effects) #[const_trait]
@@ -222,7 +222,7 @@ pub trait FnMut<Args: Tuple>: FnOnce<Args> {
 #[lang = "fn_once"]
 #[stable(feature = "rust1", since = "1.0.0")]
 #[rustc_paren_sugar]
-#[rustc_on_unimplemented(
+#[cfg_attr(not(bootstrap), rustc_on_unimplemented(
     on(
         Args = "()",
         note = "wrap the `{Self}` in a closure with no arguments: `|| {{ /* code */ }}`"
@@ -233,9 +233,9 @@ pub trait FnMut<Args: Tuple>: FnOnce<Args> {
         // SAFETY: tidy is not smart enough to tell that the below unsafe block is a string
         label = "call the function in a closure: `|| unsafe {{ /* code */ }}`"
     ),
-    message = "expected a `{FnOnce}<{Args}>` closure, found `{Self}`",
-    label = "expected an `FnOnce<{Args}>` closure, found `{Self}`"
-)]
+    message = "expected a `{Trait}` closure, found `{Self}`",
+    label = "expected an `{Trait}` closure, found `{Self}`"
+))]
 #[fundamental] // so that regex can rely that `&str: !FnMut`
 #[must_use = "closures are lazy and do nothing unless called"]
 // FIXME(effects) #[const_trait]
diff --git a/tests/ui/closures/closure-expected.rs b/tests/ui/closures/closure-expected.rs
index 68cac3dd85edf..d730bcd1faf51 100644
--- a/tests/ui/closures/closure-expected.rs
+++ b/tests/ui/closures/closure-expected.rs
@@ -1,5 +1,5 @@
 fn main() {
     let x = Some(1);
     let y = x.or_else(4);
-    //~^ ERROR expected a `FnOnce<()>` closure, found `{integer}`
+    //~^ ERROR expected a `FnOnce()` closure, found `{integer}`
 }
diff --git a/tests/ui/closures/closure-expected.stderr b/tests/ui/closures/closure-expected.stderr
index 87a5d67a420c4..565038f5144e1 100644
--- a/tests/ui/closures/closure-expected.stderr
+++ b/tests/ui/closures/closure-expected.stderr
@@ -1,8 +1,8 @@
-error[E0277]: expected a `FnOnce<()>` closure, found `{integer}`
+error[E0277]: expected a `FnOnce()` closure, found `{integer}`
   --> $DIR/closure-expected.rs:3:23
    |
 LL |     let y = x.or_else(4);
-   |               ------- ^ expected an `FnOnce<()>` closure, found `{integer}`
+   |               ------- ^ expected an `FnOnce()` closure, found `{integer}`
    |               |
    |               required by a bound introduced by this call
    |
diff --git a/tests/ui/closures/coerce-unsafe-to-closure.stderr b/tests/ui/closures/coerce-unsafe-to-closure.stderr
index 449cd0b317757..bd4ab13a205f2 100644
--- a/tests/ui/closures/coerce-unsafe-to-closure.stderr
+++ b/tests/ui/closures/coerce-unsafe-to-closure.stderr
@@ -1,4 +1,4 @@
-error[E0277]: expected a `FnOnce<(&str,)>` closure, found `unsafe extern "rust-intrinsic" fn(_) -> _ {transmute::<_, _>}`
+error[E0277]: expected a `FnOnce(&str)` closure, found `unsafe extern "rust-intrinsic" fn(_) -> _ {transmute::<_, _>}`
   --> $DIR/coerce-unsafe-to-closure.rs:2:44
    |
 LL |     let x: Option<&[u8]> = Some("foo").map(std::mem::transmute);
diff --git a/tests/ui/extern/extern-wrong-value-type.rs b/tests/ui/extern/extern-wrong-value-type.rs
index 337865ec18d51..56c6cf1dfaba7 100644
--- a/tests/ui/extern/extern-wrong-value-type.rs
+++ b/tests/ui/extern/extern-wrong-value-type.rs
@@ -7,5 +7,5 @@ fn main() {
     // extern functions are extern "C" fn
     let _x: extern "C" fn() = f; // OK
     is_fn(f);
-    //~^ ERROR expected a `Fn<()>` closure, found `extern "C" fn() {f}`
+    //~^ ERROR expected a `Fn()` closure, found `extern "C" fn() {f}`
 }
diff --git a/tests/ui/extern/extern-wrong-value-type.stderr b/tests/ui/extern/extern-wrong-value-type.stderr
index ff2934a2ba883..463cee83169d3 100644
--- a/tests/ui/extern/extern-wrong-value-type.stderr
+++ b/tests/ui/extern/extern-wrong-value-type.stderr
@@ -1,8 +1,8 @@
-error[E0277]: expected a `Fn<()>` closure, found `extern "C" fn() {f}`
+error[E0277]: expected a `Fn()` closure, found `extern "C" fn() {f}`
   --> $DIR/extern-wrong-value-type.rs:9:11
    |
 LL |     is_fn(f);
-   |     ----- ^ expected an `Fn<()>` closure, found `extern "C" fn() {f}`
+   |     ----- ^ expected an `Fn()` closure, found `extern "C" fn() {f}`
    |     |
    |     required by a bound introduced by this call
    |
diff --git a/tests/ui/fn/fn-trait-formatting.rs b/tests/ui/fn/fn-trait-formatting.rs
index 636ac7107e62a..61a8791ab1f3e 100644
--- a/tests/ui/fn/fn-trait-formatting.rs
+++ b/tests/ui/fn/fn-trait-formatting.rs
@@ -17,5 +17,5 @@ fn main() {
     //~| found struct `Box<dyn FnMut() -> isize>`
 
     needs_fn(1);
-    //~^ ERROR expected a `Fn<(isize,)>` closure, found `{integer}`
+    //~^ ERROR expected a `Fn(isize)` closure, found `{integer}`
 }
diff --git a/tests/ui/fn/fn-trait-formatting.stderr b/tests/ui/fn/fn-trait-formatting.stderr
index 45d543bda5323..c5e2f41691faa 100644
--- a/tests/ui/fn/fn-trait-formatting.stderr
+++ b/tests/ui/fn/fn-trait-formatting.stderr
@@ -39,11 +39,11 @@ LL |     let _: () = Box::new(|| -> isize { unimplemented!() }) as Box<dyn FnMut
    = note: expected unit type `()`
                  found struct `Box<dyn FnMut() -> isize>`
 
-error[E0277]: expected a `Fn<(isize,)>` closure, found `{integer}`
+error[E0277]: expected a `Fn(isize)` closure, found `{integer}`
   --> $DIR/fn-trait-formatting.rs:19:14
    |
 LL |     needs_fn(1);
-   |     -------- ^ expected an `Fn<(isize,)>` closure, found `{integer}`
+   |     -------- ^ expected an `Fn(isize)` closure, found `{integer}`
    |     |
    |     required by a bound introduced by this call
    |
diff --git a/tests/ui/generic-associated-types/issue-68642-broken-llvm-ir.rs b/tests/ui/generic-associated-types/issue-68642-broken-llvm-ir.rs
index f5502adee4263..c444ee9e1cdb4 100644
--- a/tests/ui/generic-associated-types/issue-68642-broken-llvm-ir.rs
+++ b/tests/ui/generic-associated-types/issue-68642-broken-llvm-ir.rs
@@ -10,7 +10,7 @@ trait Fun {
 
 impl<T> Fun for T {
     type F<'a> = Self;
-    //~^ ERROR expected a `Fn<()>` closure, found `T`
+    //~^ ERROR expected a `Fn()` closure, found `T`
 }
 
 fn main() {
diff --git a/tests/ui/generic-associated-types/issue-68642-broken-llvm-ir.stderr b/tests/ui/generic-associated-types/issue-68642-broken-llvm-ir.stderr
index 07452137b5bd6..2376bda8190d0 100644
--- a/tests/ui/generic-associated-types/issue-68642-broken-llvm-ir.stderr
+++ b/tests/ui/generic-associated-types/issue-68642-broken-llvm-ir.stderr
@@ -1,8 +1,8 @@
-error[E0277]: expected a `Fn<()>` closure, found `T`
+error[E0277]: expected a `Fn()` closure, found `T`
   --> $DIR/issue-68642-broken-llvm-ir.rs:12:18
    |
 LL |     type F<'a> = Self;
-   |                  ^^^^ expected an `Fn<()>` closure, found `T`
+   |                  ^^^^ expected an `Fn()` closure, found `T`
    |
    = note: wrap the `T` in a closure with no arguments: `|| { /* code */ }`
 note: required by a bound in `Fun::F`
diff --git a/tests/ui/generic-associated-types/issue-68643-broken-mir.rs b/tests/ui/generic-associated-types/issue-68643-broken-mir.rs
index 6050a8bf56181..39db51c0e2a21 100644
--- a/tests/ui/generic-associated-types/issue-68643-broken-mir.rs
+++ b/tests/ui/generic-associated-types/issue-68643-broken-mir.rs
@@ -10,7 +10,7 @@ trait Fun {
 
 impl<T> Fun for T {
     type F<'a> = Self;
-    //~^ ERROR expected a `Fn<()>` closure, found `T`
+    //~^ ERROR expected a `Fn()` closure, found `T`
 }
 
 pub fn main() {
diff --git a/tests/ui/generic-associated-types/issue-68643-broken-mir.stderr b/tests/ui/generic-associated-types/issue-68643-broken-mir.stderr
index 31ded5dab95b6..2429531e4e5ab 100644
--- a/tests/ui/generic-associated-types/issue-68643-broken-mir.stderr
+++ b/tests/ui/generic-associated-types/issue-68643-broken-mir.stderr
@@ -1,8 +1,8 @@
-error[E0277]: expected a `Fn<()>` closure, found `T`
+error[E0277]: expected a `Fn()` closure, found `T`
   --> $DIR/issue-68643-broken-mir.rs:12:18
    |
 LL |     type F<'a> = Self;
-   |                  ^^^^ expected an `Fn<()>` closure, found `T`
+   |                  ^^^^ expected an `Fn()` closure, found `T`
    |
    = note: wrap the `T` in a closure with no arguments: `|| { /* code */ }`
 note: required by a bound in `Fun::F`
diff --git a/tests/ui/generic-associated-types/issue-68644-codegen-selection.rs b/tests/ui/generic-associated-types/issue-68644-codegen-selection.rs
index 898cfa1e744cf..e379bce07d313 100644
--- a/tests/ui/generic-associated-types/issue-68644-codegen-selection.rs
+++ b/tests/ui/generic-associated-types/issue-68644-codegen-selection.rs
@@ -10,7 +10,7 @@ trait Fun {
 
 impl<T> Fun for T {
     type F<'a> = Self;
-    //~^ ERROR expected a `Fn<()>` closure, found `T`
+    //~^ ERROR expected a `Fn()` closure, found `T`
 }
 
 fn main() {
diff --git a/tests/ui/generic-associated-types/issue-68644-codegen-selection.stderr b/tests/ui/generic-associated-types/issue-68644-codegen-selection.stderr
index e2f9930cc67fd..11221353a92d4 100644
--- a/tests/ui/generic-associated-types/issue-68644-codegen-selection.stderr
+++ b/tests/ui/generic-associated-types/issue-68644-codegen-selection.stderr
@@ -1,8 +1,8 @@
-error[E0277]: expected a `Fn<()>` closure, found `T`
+error[E0277]: expected a `Fn()` closure, found `T`
   --> $DIR/issue-68644-codegen-selection.rs:12:18
    |
 LL |     type F<'a> = Self;
-   |                  ^^^^ expected an `Fn<()>` closure, found `T`
+   |                  ^^^^ expected an `Fn()` closure, found `T`
    |
    = note: wrap the `T` in a closure with no arguments: `|| { /* code */ }`
 note: required by a bound in `Fun::F`
diff --git a/tests/ui/generic-associated-types/issue-68645-codegen-fulfillment.rs b/tests/ui/generic-associated-types/issue-68645-codegen-fulfillment.rs
index 60b065bfc3171..e69a08b0a3991 100644
--- a/tests/ui/generic-associated-types/issue-68645-codegen-fulfillment.rs
+++ b/tests/ui/generic-associated-types/issue-68645-codegen-fulfillment.rs
@@ -10,7 +10,7 @@ trait Fun {
 
 impl<T> Fun for T {
     type F<'a> = Self;
-    //~^ ERROR expected a `Fn<()>` closure, found `T`
+    //~^ ERROR expected a `Fn()` closure, found `T`
 }
 
 fn main() {
diff --git a/tests/ui/generic-associated-types/issue-68645-codegen-fulfillment.stderr b/tests/ui/generic-associated-types/issue-68645-codegen-fulfillment.stderr
index 0065368ad31d9..52300efc2d8ca 100644
--- a/tests/ui/generic-associated-types/issue-68645-codegen-fulfillment.stderr
+++ b/tests/ui/generic-associated-types/issue-68645-codegen-fulfillment.stderr
@@ -1,8 +1,8 @@
-error[E0277]: expected a `Fn<()>` closure, found `T`
+error[E0277]: expected a `Fn()` closure, found `T`
   --> $DIR/issue-68645-codegen-fulfillment.rs:12:18
    |
 LL |     type F<'a> = Self;
-   |                  ^^^^ expected an `Fn<()>` closure, found `T`
+   |                  ^^^^ expected an `Fn()` closure, found `T`
    |
    = note: wrap the `T` in a closure with no arguments: `|| { /* code */ }`
 note: required by a bound in `Fun::F`
diff --git a/tests/ui/higher-ranked/trait-bounds/fn-ptr.classic.stderr b/tests/ui/higher-ranked/trait-bounds/fn-ptr.classic.stderr
index 9af6bc45c7a06..8ab88c580755b 100644
--- a/tests/ui/higher-ranked/trait-bounds/fn-ptr.classic.stderr
+++ b/tests/ui/higher-ranked/trait-bounds/fn-ptr.classic.stderr
@@ -1,8 +1,8 @@
-error[E0277]: expected a `Fn<(&'w (),)>` closure, found `fn(&'w ())`
+error[E0277]: expected a `Fn(&'w ())` closure, found `fn(&'w ())`
   --> $DIR/fn-ptr.rs:12:5
    |
 LL |     ice();
-   |     ^^^ expected an `Fn<(&'w (),)>` closure, found `fn(&'w ())`
+   |     ^^^ expected an `Fn(&'w ())` closure, found `fn(&'w ())`
    |
    = help: the trait `for<'w> Fn<(&'w (),)>` is not implemented for `fn(&'w ())`
 note: required by a bound in `ice`
diff --git a/tests/ui/higher-ranked/trait-bounds/fn-ptr.rs b/tests/ui/higher-ranked/trait-bounds/fn-ptr.rs
index 853160f961245..adb19c035bce6 100644
--- a/tests/ui/higher-ranked/trait-bounds/fn-ptr.rs
+++ b/tests/ui/higher-ranked/trait-bounds/fn-ptr.rs
@@ -10,5 +10,5 @@ where
 
 fn main() {
     ice();
-    //[classic]~^ ERROR expected a `Fn<(&'w (),)>` closure, found `fn(&'w ())`
+    //[classic]~^ ERROR expected a `Fn(&'w ())` closure, found `fn(&'w ())`
 }
diff --git a/tests/ui/higher-ranked/trait-bounds/normalize-under-binder/issue-62529-3.stderr b/tests/ui/higher-ranked/trait-bounds/normalize-under-binder/issue-62529-3.stderr
index 2cc2bb2bbc3c9..7b0743cc7c5ce 100644
--- a/tests/ui/higher-ranked/trait-bounds/normalize-under-binder/issue-62529-3.stderr
+++ b/tests/ui/higher-ranked/trait-bounds/normalize-under-binder/issue-62529-3.stderr
@@ -1,8 +1,8 @@
-error[E0277]: expected a `Fn<(<_ as ATC<'a>>::Type,)>` closure, found `F`
+error[E0277]: expected a `Fn(<_ as ATC<'a>>::Type)` closure, found `F`
   --> $DIR/issue-62529-3.rs:25:14
    |
 LL |         call(f, ());
-   |         ---- ^ expected an `Fn<(<_ as ATC<'a>>::Type,)>` closure, found `F`
+   |         ---- ^ expected an `Fn(<_ as ATC<'a>>::Type)` closure, found `F`
    |         |
    |         required by a bound introduced by this call
    |
diff --git a/tests/ui/implied-bounds/issue-100690.rs b/tests/ui/implied-bounds/issue-100690.rs
index 5599cd410baad..ea33c9f423b77 100644
--- a/tests/ui/implied-bounds/issue-100690.rs
+++ b/tests/ui/implied-bounds/issue-100690.rs
@@ -35,8 +35,8 @@ impl<'a, T: 'a> Handle<'a, T, UIView<'a, T>, Result<(), io::Error>> for TUIHandl
         F: FnOnce(&mut UIView<'a, T>) -> Result<(), io::Error> + Send + 'static,
     {
         real_dispatch(f)
-        //~^ ERROR expected a `FnOnce<(&mut UIView<'_, T>,)>` closure, found `F`
-        //~| NOTE expected an `FnOnce<(&mut UIView<'_, T>,)>` closure, found `F`
+        //~^ ERROR expected a `FnOnce(&mut UIView<'_, T>)` closure, found `F`
+        //~| NOTE expected an `FnOnce(&mut UIView<'_, T>)` closure, found `F`
         //~| NOTE expected a closure with arguments
         //~| NOTE required by a bound introduced by this call
     }
diff --git a/tests/ui/implied-bounds/issue-100690.stderr b/tests/ui/implied-bounds/issue-100690.stderr
index dba0353377fa2..ac9f7ab252968 100644
--- a/tests/ui/implied-bounds/issue-100690.stderr
+++ b/tests/ui/implied-bounds/issue-100690.stderr
@@ -1,8 +1,8 @@
-error[E0277]: expected a `FnOnce<(&mut UIView<'_, T>,)>` closure, found `F`
+error[E0277]: expected a `FnOnce(&mut UIView<'_, T>)` closure, found `F`
   --> $DIR/issue-100690.rs:37:23
    |
 LL |         real_dispatch(f)
-   |         ------------- ^ expected an `FnOnce<(&mut UIView<'_, T>,)>` closure, found `F`
+   |         ------------- ^ expected an `FnOnce(&mut UIView<'_, T>)` closure, found `F`
    |         |
    |         required by a bound introduced by this call
    |
diff --git a/tests/ui/intrinsics/const-eval-select-bad.rs b/tests/ui/intrinsics/const-eval-select-bad.rs
index 991d1450aff99..7e75de88d2926 100644
--- a/tests/ui/intrinsics/const-eval-select-bad.rs
+++ b/tests/ui/intrinsics/const-eval-select-bad.rs
@@ -8,8 +8,8 @@ const fn not_fn_items() {
     //~^ ERROR this argument must be a function item
     //~| ERROR this argument must be a function item
     const_eval_select((), 42, 0xDEADBEEF);
-    //~^ ERROR expected a `FnOnce<()>` closure
-    //~| ERROR expected a `FnOnce<()>` closure
+    //~^ ERROR expected a `FnOnce()` closure
+    //~| ERROR expected a `FnOnce()` closure
     //~| ERROR this argument must be a function item
     //~| ERROR this argument must be a function item
 }
diff --git a/tests/ui/intrinsics/const-eval-select-bad.stderr b/tests/ui/intrinsics/const-eval-select-bad.stderr
index ecd08e3cdfd29..e6ff9d5a0df7d 100644
--- a/tests/ui/intrinsics/const-eval-select-bad.stderr
+++ b/tests/ui/intrinsics/const-eval-select-bad.stderr
@@ -25,11 +25,11 @@ LL |     const_eval_select((), 42, 0xDEADBEEF);
    = note: expected a function item, found {integer}
    = help: consult the documentation on `const_eval_select` for more information
 
-error[E0277]: expected a `FnOnce<()>` closure, found `{integer}`
+error[E0277]: expected a `FnOnce()` closure, found `{integer}`
   --> $DIR/const-eval-select-bad.rs:10:27
    |
 LL |     const_eval_select((), 42, 0xDEADBEEF);
-   |     -----------------     ^^ expected an `FnOnce<()>` closure, found `{integer}`
+   |     -----------------     ^^ expected an `FnOnce()` closure, found `{integer}`
    |     |
    |     required by a bound introduced by this call
    |
@@ -47,11 +47,11 @@ LL |     const_eval_select((), 42, 0xDEADBEEF);
    = note: expected a function item, found {integer}
    = help: consult the documentation on `const_eval_select` for more information
 
-error[E0277]: expected a `FnOnce<()>` closure, found `{integer}`
+error[E0277]: expected a `FnOnce()` closure, found `{integer}`
   --> $DIR/const-eval-select-bad.rs:10:31
    |
 LL |     const_eval_select((), 42, 0xDEADBEEF);
-   |     -----------------         ^^^^^^^^^^ expected an `FnOnce<()>` closure, found `{integer}`
+   |     -----------------         ^^^^^^^^^^ expected an `FnOnce()` closure, found `{integer}`
    |     |
    |     required by a bound introduced by this call
    |
diff --git a/tests/ui/issues/issue-22034.rs b/tests/ui/issues/issue-22034.rs
index 405ffd089c245..ed741779f6807 100644
--- a/tests/ui/issues/issue-22034.rs
+++ b/tests/ui/issues/issue-22034.rs
@@ -6,6 +6,6 @@ fn main() {
     let ptr: *mut () = core::ptr::null_mut();
     let _: &mut dyn Fn() = unsafe {
         &mut *(ptr as *mut dyn Fn())
-        //~^ ERROR expected a `Fn<()>` closure, found `()`
+        //~^ ERROR expected a `Fn()` closure, found `()`
     };
 }
diff --git a/tests/ui/issues/issue-22034.stderr b/tests/ui/issues/issue-22034.stderr
index 9833e559cbcdb..d64b024098c9b 100644
--- a/tests/ui/issues/issue-22034.stderr
+++ b/tests/ui/issues/issue-22034.stderr
@@ -1,8 +1,8 @@
-error[E0277]: expected a `Fn<()>` closure, found `()`
+error[E0277]: expected a `Fn()` closure, found `()`
   --> $DIR/issue-22034.rs:8:16
    |
 LL |         &mut *(ptr as *mut dyn Fn())
-   |                ^^^ expected an `Fn<()>` closure, found `()`
+   |                ^^^ expected an `Fn()` closure, found `()`
    |
    = help: the trait `Fn<()>` is not implemented for `()`
    = note: wrap the `()` in a closure with no arguments: `|| { /* code */ }`
diff --git a/tests/ui/issues/issue-23966.stderr b/tests/ui/issues/issue-23966.stderr
index 8f934481d85db..542aed0eb2618 100644
--- a/tests/ui/issues/issue-23966.stderr
+++ b/tests/ui/issues/issue-23966.stderr
@@ -1,8 +1,8 @@
-error[E0277]: expected a `FnMut<(_, char)>` closure, found `()`
+error[E0277]: expected a `FnMut(_, char)` closure, found `()`
   --> $DIR/issue-23966.rs:2:32
    |
 LL |     "".chars().fold(|_, _| (), ());
-   |                ----            ^^ expected an `FnMut<(_, char)>` closure, found `()`
+   |                ----            ^^ expected an `FnMut(_, char)` closure, found `()`
    |                |
    |                required by a bound introduced by this call
    |
diff --git a/tests/ui/issues/issue-59494.rs b/tests/ui/issues/issue-59494.rs
index a53e28f7246e6..8dcdd88c618c7 100644
--- a/tests/ui/issues/issue-59494.rs
+++ b/tests/ui/issues/issue-59494.rs
@@ -19,5 +19,5 @@ fn main() {
     let g = |(a, _)| a;
     let t7 = |env| |a| |b| t7p(f, g)(((env, a), b));
     let t8 = t8n(t7, t7p(f, g));
-    //~^ ERROR: expected a `Fn<(_,)>` closure, found `impl Fn(((_, _), _))` [E0277]
+    //~^ ERROR: expected a `Fn(_)` closure, found `impl Fn(((_, _), _))` [E0277]
 }
diff --git a/tests/ui/issues/issue-59494.stderr b/tests/ui/issues/issue-59494.stderr
index a9284535e4dc4..e9a4bf96741e6 100644
--- a/tests/ui/issues/issue-59494.stderr
+++ b/tests/ui/issues/issue-59494.stderr
@@ -1,8 +1,8 @@
-error[E0277]: expected a `Fn<(_,)>` closure, found `impl Fn(((_, _), _))`
+error[E0277]: expected a `Fn(_)` closure, found `impl Fn(((_, _), _))`
   --> $DIR/issue-59494.rs:21:22
    |
 LL |     let t8 = t8n(t7, t7p(f, g));
-   |              ---     ^^^^^^^^^ expected an `Fn<(_,)>` closure, found `impl Fn(((_, _), _))`
+   |              ---     ^^^^^^^^^ expected an `Fn(_)` closure, found `impl Fn(((_, _), _))`
    |              |
    |              required by a bound introduced by this call
    |
diff --git a/tests/ui/mismatched_types/suggest-option-asderef-unfixable.rs b/tests/ui/mismatched_types/suggest-option-asderef-unfixable.rs
index ac0831ce65508..42adff43a58f2 100644
--- a/tests/ui/mismatched_types/suggest-option-asderef-unfixable.rs
+++ b/tests/ui/mismatched_types/suggest-option-asderef-unfixable.rs
@@ -24,9 +24,9 @@ fn main() {
     let _ = produces_string().and_then(takes_str_but_too_many_refs);
     //~^ ERROR type mismatch in function arguments
     let _ = produces_string().and_then(takes_str_but_wrong_abi);
-    //~^ ERROR expected a `FnOnce<(String,)>` closure, found `for<'a> extern "C" fn(&'a str) -> Option<()> {takes_str_but_wrong_abi}`
+    //~^ ERROR expected a `FnOnce(String)` closure, found `for<'a> extern "C" fn(&'a str) -> Option<()> {takes_str_but_wrong_abi}`
     let _ = produces_string().and_then(takes_str_but_unsafe);
-    //~^ ERROR expected a `FnOnce<(String,)>` closure, found `for<'a> unsafe fn(&'a str) -> Option<()> {takes_str_but_unsafe}`
+    //~^ ERROR expected a `FnOnce(String)` closure, found `for<'a> unsafe fn(&'a str) -> Option<()> {takes_str_but_unsafe}`
     let _ = produces_string().and_then(no_args);
     //~^ ERROR function is expected to take 1 argument, but it takes 0 arguments
     let _ = Some(TypeWithoutDeref).and_then(takes_str_but_too_many_refs);
diff --git a/tests/ui/mismatched_types/suggest-option-asderef-unfixable.stderr b/tests/ui/mismatched_types/suggest-option-asderef-unfixable.stderr
index ecfbd27b180e6..3175a258906fe 100644
--- a/tests/ui/mismatched_types/suggest-option-asderef-unfixable.stderr
+++ b/tests/ui/mismatched_types/suggest-option-asderef-unfixable.stderr
@@ -14,11 +14,11 @@ LL |     let _ = produces_string().and_then(takes_str_but_too_many_refs);
 note: required by a bound in `Option::<T>::and_then`
   --> $SRC_DIR/core/src/option.rs:LL:COL
 
-error[E0277]: expected a `FnOnce<(String,)>` closure, found `for<'a> extern "C" fn(&'a str) -> Option<()> {takes_str_but_wrong_abi}`
+error[E0277]: expected a `FnOnce(String)` closure, found `for<'a> extern "C" fn(&'a str) -> Option<()> {takes_str_but_wrong_abi}`
   --> $DIR/suggest-option-asderef-unfixable.rs:26:40
    |
 LL |     let _ = produces_string().and_then(takes_str_but_wrong_abi);
-   |                               -------- ^^^^^^^^^^^^^^^^^^^^^^^ expected an `FnOnce<(String,)>` closure, found `for<'a> extern "C" fn(&'a str) -> Option<()> {takes_str_but_wrong_abi}`
+   |                               -------- ^^^^^^^^^^^^^^^^^^^^^^^ expected an `FnOnce(String)` closure, found `for<'a> extern "C" fn(&'a str) -> Option<()> {takes_str_but_wrong_abi}`
    |                               |
    |                               required by a bound introduced by this call
    |
@@ -26,7 +26,7 @@ LL |     let _ = produces_string().and_then(takes_str_but_wrong_abi);
 note: required by a bound in `Option::<T>::and_then`
   --> $SRC_DIR/core/src/option.rs:LL:COL
 
-error[E0277]: expected a `FnOnce<(String,)>` closure, found `for<'a> unsafe fn(&'a str) -> Option<()> {takes_str_but_unsafe}`
+error[E0277]: expected a `FnOnce(String)` closure, found `for<'a> unsafe fn(&'a str) -> Option<()> {takes_str_but_unsafe}`
   --> $DIR/suggest-option-asderef-unfixable.rs:28:40
    |
 LL |     let _ = produces_string().and_then(takes_str_but_unsafe);
diff --git a/tests/ui/rfcs/rfc-2396-target_feature-11/fn-traits.rs b/tests/ui/rfcs/rfc-2396-target_feature-11/fn-traits.rs
index 43bda49624e96..1374ad935a388 100644
--- a/tests/ui/rfcs/rfc-2396-target_feature-11/fn-traits.rs
+++ b/tests/ui/rfcs/rfc-2396-target_feature-11/fn-traits.rs
@@ -21,14 +21,14 @@ fn call_once(f: impl FnOnce()) {
 }
 
 fn main() {
-    call(foo); //~ ERROR expected a `Fn<()>` closure, found `fn() {foo}`
-    call_mut(foo); //~ ERROR expected a `FnMut<()>` closure, found `fn() {foo}`
-    call_once(foo); //~ ERROR expected a `FnOnce<()>` closure, found `fn() {foo}`
+    call(foo); //~ ERROR expected a `Fn()` closure, found `fn() {foo}`
+    call_mut(foo); //~ ERROR expected a `FnMut()` closure, found `fn() {foo}`
+    call_once(foo); //~ ERROR expected a `FnOnce()` closure, found `fn() {foo}`
 
     call(foo_unsafe);
-    //~^ ERROR expected a `Fn<()>` closure, found `unsafe fn() {foo_unsafe}`
+    //~^ ERROR expected a `Fn()` closure, found `unsafe fn() {foo_unsafe}`
     call_mut(foo_unsafe);
-    //~^ ERROR expected a `FnMut<()>` closure, found `unsafe fn() {foo_unsafe}`
+    //~^ ERROR expected a `FnMut()` closure, found `unsafe fn() {foo_unsafe}`
     call_once(foo_unsafe);
-    //~^ ERROR expected a `FnOnce<()>` closure, found `unsafe fn() {foo_unsafe}`
+    //~^ ERROR expected a `FnOnce()` closure, found `unsafe fn() {foo_unsafe}`
 }
diff --git a/tests/ui/rfcs/rfc-2396-target_feature-11/fn-traits.stderr b/tests/ui/rfcs/rfc-2396-target_feature-11/fn-traits.stderr
index fc7bf22775dd7..a8164297bd58d 100644
--- a/tests/ui/rfcs/rfc-2396-target_feature-11/fn-traits.stderr
+++ b/tests/ui/rfcs/rfc-2396-target_feature-11/fn-traits.stderr
@@ -1,8 +1,8 @@
-error[E0277]: expected a `Fn<()>` closure, found `fn() {foo}`
+error[E0277]: expected a `Fn()` closure, found `fn() {foo}`
   --> $DIR/fn-traits.rs:24:10
    |
 LL |     call(foo);
-   |     ---- ^^^ expected an `Fn<()>` closure, found `fn() {foo}`
+   |     ---- ^^^ expected an `Fn()` closure, found `fn() {foo}`
    |     |
    |     required by a bound introduced by this call
    |
@@ -15,11 +15,11 @@ note: required by a bound in `call`
 LL | fn call(f: impl Fn()) {
    |                 ^^^^ required by this bound in `call`
 
-error[E0277]: expected a `FnMut<()>` closure, found `fn() {foo}`
+error[E0277]: expected a `FnMut()` closure, found `fn() {foo}`
   --> $DIR/fn-traits.rs:25:14
    |
 LL |     call_mut(foo);
-   |     -------- ^^^ expected an `FnMut<()>` closure, found `fn() {foo}`
+   |     -------- ^^^ expected an `FnMut()` closure, found `fn() {foo}`
    |     |
    |     required by a bound introduced by this call
    |
@@ -32,11 +32,11 @@ note: required by a bound in `call_mut`
 LL | fn call_mut(f: impl FnMut()) {
    |                     ^^^^^^^ required by this bound in `call_mut`
 
-error[E0277]: expected a `FnOnce<()>` closure, found `fn() {foo}`
+error[E0277]: expected a `FnOnce()` closure, found `fn() {foo}`
   --> $DIR/fn-traits.rs:26:15
    |
 LL |     call_once(foo);
-   |     --------- ^^^ expected an `FnOnce<()>` closure, found `fn() {foo}`
+   |     --------- ^^^ expected an `FnOnce()` closure, found `fn() {foo}`
    |     |
    |     required by a bound introduced by this call
    |
@@ -49,7 +49,7 @@ note: required by a bound in `call_once`
 LL | fn call_once(f: impl FnOnce()) {
    |                      ^^^^^^^^ required by this bound in `call_once`
 
-error[E0277]: expected a `Fn<()>` closure, found `unsafe fn() {foo_unsafe}`
+error[E0277]: expected a `Fn()` closure, found `unsafe fn() {foo_unsafe}`
   --> $DIR/fn-traits.rs:28:10
    |
 LL |     call(foo_unsafe);
@@ -66,7 +66,7 @@ note: required by a bound in `call`
 LL | fn call(f: impl Fn()) {
    |                 ^^^^ required by this bound in `call`
 
-error[E0277]: expected a `FnMut<()>` closure, found `unsafe fn() {foo_unsafe}`
+error[E0277]: expected a `FnMut()` closure, found `unsafe fn() {foo_unsafe}`
   --> $DIR/fn-traits.rs:30:14
    |
 LL |     call_mut(foo_unsafe);
@@ -83,7 +83,7 @@ note: required by a bound in `call_mut`
 LL | fn call_mut(f: impl FnMut()) {
    |                     ^^^^^^^ required by this bound in `call_mut`
 
-error[E0277]: expected a `FnOnce<()>` closure, found `unsafe fn() {foo_unsafe}`
+error[E0277]: expected a `FnOnce()` closure, found `unsafe fn() {foo_unsafe}`
   --> $DIR/fn-traits.rs:32:15
    |
 LL |     call_once(foo_unsafe);
diff --git a/tests/ui/suggestions/issue-104961.fixed b/tests/ui/suggestions/issue-104961.fixed
index 520d638b1748f..36917cf339548 100644
--- a/tests/ui/suggestions/issue-104961.fixed
+++ b/tests/ui/suggestions/issue-104961.fixed
@@ -2,12 +2,12 @@
 
 fn foo(x: &str) -> bool {
     x.starts_with(&("hi".to_string() + " you"))
-    //~^ ERROR expected a `FnMut<(char,)>` closure, found `String`
+    //~^ ERROR expected a `FnMut(char)` closure, found `String`
 }
 
 fn foo2(x: &str) -> bool {
     x.starts_with(&"hi".to_string())
-    //~^ ERROR expected a `FnMut<(char,)>` closure, found `String`
+    //~^ ERROR expected a `FnMut(char)` closure, found `String`
 }
 
 fn main() {
diff --git a/tests/ui/suggestions/issue-104961.rs b/tests/ui/suggestions/issue-104961.rs
index aeb787abb6fc8..25a8e0c45e827 100644
--- a/tests/ui/suggestions/issue-104961.rs
+++ b/tests/ui/suggestions/issue-104961.rs
@@ -2,12 +2,12 @@
 
 fn foo(x: &str) -> bool {
     x.starts_with("hi".to_string() + " you")
-    //~^ ERROR expected a `FnMut<(char,)>` closure, found `String`
+    //~^ ERROR expected a `FnMut(char)` closure, found `String`
 }
 
 fn foo2(x: &str) -> bool {
     x.starts_with("hi".to_string())
-    //~^ ERROR expected a `FnMut<(char,)>` closure, found `String`
+    //~^ ERROR expected a `FnMut(char)` closure, found `String`
 }
 
 fn main() {
diff --git a/tests/ui/suggestions/issue-104961.stderr b/tests/ui/suggestions/issue-104961.stderr
index 8cec6a3f8270a..7e795a74c9000 100644
--- a/tests/ui/suggestions/issue-104961.stderr
+++ b/tests/ui/suggestions/issue-104961.stderr
@@ -1,4 +1,4 @@
-error[E0277]: expected a `FnMut<(char,)>` closure, found `String`
+error[E0277]: expected a `FnMut(char)` closure, found `String`
   --> $DIR/issue-104961.rs:4:19
    |
 LL |     x.starts_with("hi".to_string() + " you")
@@ -15,7 +15,7 @@ help: consider borrowing here
 LL |     x.starts_with(&("hi".to_string() + " you"))
    |                   ++                         +
 
-error[E0277]: expected a `FnMut<(char,)>` closure, found `String`
+error[E0277]: expected a `FnMut(char)` closure, found `String`
   --> $DIR/issue-104961.rs:9:19
    |
 LL |     x.starts_with("hi".to_string())
diff --git a/tests/ui/suggestions/issue-62843.stderr b/tests/ui/suggestions/issue-62843.stderr
index b6e271de8076c..ead8f18547b67 100644
--- a/tests/ui/suggestions/issue-62843.stderr
+++ b/tests/ui/suggestions/issue-62843.stderr
@@ -1,4 +1,4 @@
-error[E0277]: expected a `FnMut<(char,)>` closure, found `String`
+error[E0277]: expected a `FnMut(char)` closure, found `String`
   --> $DIR/issue-62843.rs:4:32
    |
 LL |     println!("{:?}", line.find(pattern));
diff --git a/tests/ui/trait-bounds/mismatch-fn-trait.stderr b/tests/ui/trait-bounds/mismatch-fn-trait.stderr
index 961e6d88fbef4..519aa9ea3f3bc 100644
--- a/tests/ui/trait-bounds/mismatch-fn-trait.stderr
+++ b/tests/ui/trait-bounds/mismatch-fn-trait.stderr
@@ -1,8 +1,8 @@
-error[E0277]: expected a `FnMut<(i32,)>` closure, found `impl FnMut(u32)`
+error[E0277]: expected a `FnMut(i32)` closure, found `impl FnMut(u32)`
   --> $DIR/mismatch-fn-trait.rs:4:10
    |
 LL |     take(f)
-   |     ---- ^ expected an `FnMut<(i32,)>` closure, found `impl FnMut(u32)`
+   |     ---- ^ expected an `FnMut(i32)` closure, found `impl FnMut(u32)`
    |     |
    |     required by a bound introduced by this call
    |
@@ -14,11 +14,11 @@ note: required by a bound in `take`
 LL | fn take(_f: impl FnMut(i32)) {}
    |                  ^^^^^^^^^^ required by this bound in `take`
 
-error[E0277]: expected a `FnMut<(i32,)>` closure, found `impl FnMut(i32, i32)`
+error[E0277]: expected a `FnMut(i32)` closure, found `impl FnMut(i32, i32)`
   --> $DIR/mismatch-fn-trait.rs:9:10
    |
 LL |     take(f)
-   |     ---- ^ expected an `FnMut<(i32,)>` closure, found `impl FnMut(i32, i32)`
+   |     ---- ^ expected an `FnMut(i32)` closure, found `impl FnMut(i32, i32)`
    |     |
    |     required by a bound introduced by this call
    |
@@ -29,11 +29,11 @@ note: required by a bound in `take`
 LL | fn take(_f: impl FnMut(i32)) {}
    |                  ^^^^^^^^^^ required by this bound in `take`
 
-error[E0277]: expected a `FnMut<(i32,)>` closure, found `impl FnMut()`
+error[E0277]: expected a `FnMut(i32)` closure, found `impl FnMut()`
   --> $DIR/mismatch-fn-trait.rs:14:10
    |
 LL |     take(f)
-   |     ---- ^ expected an `FnMut<(i32,)>` closure, found `impl FnMut()`
+   |     ---- ^ expected an `FnMut(i32)` closure, found `impl FnMut()`
    |     |
    |     required by a bound introduced by this call
    |
@@ -44,11 +44,11 @@ note: required by a bound in `take`
 LL | fn take(_f: impl FnMut(i32)) {}
    |                  ^^^^^^^^^^ required by this bound in `take`
 
-error[E0277]: expected a `FnMut<(i32,)>` closure, found `impl FnOnce(i32)`
+error[E0277]: expected a `FnMut(i32)` closure, found `impl FnOnce(i32)`
   --> $DIR/mismatch-fn-trait.rs:19:10
    |
 LL |     take(f)
-   |     ---- ^ expected an `FnMut<(i32,)>` closure, found `impl FnOnce(i32)`
+   |     ---- ^ expected an `FnMut(i32)` closure, found `impl FnOnce(i32)`
    |     |
    |     required by a bound introduced by this call
    |
@@ -59,11 +59,11 @@ note: required by a bound in `take`
 LL | fn take(_f: impl FnMut(i32)) {}
    |                  ^^^^^^^^^^ required by this bound in `take`
 
-error[E0277]: expected a `FnMut<(i32,)>` closure, found `impl FnOnce(u32)`
+error[E0277]: expected a `FnMut(i32)` closure, found `impl FnOnce(u32)`
   --> $DIR/mismatch-fn-trait.rs:24:10
    |
 LL |     take(f)
-   |     ---- ^ expected an `FnMut<(i32,)>` closure, found `impl FnOnce(u32)`
+   |     ---- ^ expected an `FnMut(i32)` closure, found `impl FnOnce(u32)`
    |     |
    |     required by a bound introduced by this call
    |
diff --git a/tests/ui/traits/associated_type_bound/check-trait-object-bounds-2.rs b/tests/ui/traits/associated_type_bound/check-trait-object-bounds-2.rs
index eb2fb6e841bce..1359eb6cb87a4 100644
--- a/tests/ui/traits/associated_type_bound/check-trait-object-bounds-2.rs
+++ b/tests/ui/traits/associated_type_bound/check-trait-object-bounds-2.rs
@@ -11,5 +11,5 @@ fn f<T: for<'r> X<'r> + ?Sized>() {
 
 fn main() {
     f::<dyn for<'x> X<'x, F = i32>>();
-    //~^ expected a `FnOnce<(&i32,)>` closure, found `i32`
+    //~^ expected a `FnOnce(&i32)` closure, found `i32`
 }
diff --git a/tests/ui/traits/associated_type_bound/check-trait-object-bounds-2.stderr b/tests/ui/traits/associated_type_bound/check-trait-object-bounds-2.stderr
index 10e82c54e0f2b..68b9319d65c76 100644
--- a/tests/ui/traits/associated_type_bound/check-trait-object-bounds-2.stderr
+++ b/tests/ui/traits/associated_type_bound/check-trait-object-bounds-2.stderr
@@ -1,8 +1,8 @@
-error[E0277]: expected a `FnOnce<(&i32,)>` closure, found `i32`
+error[E0277]: expected a `FnOnce(&i32)` closure, found `i32`
   --> $DIR/check-trait-object-bounds-2.rs:13:9
    |
 LL |     f::<dyn for<'x> X<'x, F = i32>>();
-   |         ^^^^^^^^^^^^^^^^^^^^^^^^^^ expected an `FnOnce<(&i32,)>` closure, found `i32`
+   |         ^^^^^^^^^^^^^^^^^^^^^^^^^^ expected an `FnOnce(&i32)` closure, found `i32`
    |
    = help: the trait `for<'a> FnOnce<(&'a i32,)>` is not implemented for `i32`
 note: required by a bound in `f`
diff --git a/tests/ui/traits/bound/assoc-fn-bound-root-obligation.rs b/tests/ui/traits/bound/assoc-fn-bound-root-obligation.rs
index f9a9347641143..f8e3f8e968e11 100644
--- a/tests/ui/traits/bound/assoc-fn-bound-root-obligation.rs
+++ b/tests/ui/traits/bound/assoc-fn-bound-root-obligation.rs
@@ -1,7 +1,7 @@
 fn strip_lf(s: &str) -> &str {
     s.strip_suffix(b'\n').unwrap_or(s)
-    //~^ ERROR expected a `FnMut<(char,)>` closure, found `u8`
-    //~| NOTE expected an `FnMut<(char,)>` closure, found `u8`
+    //~^ ERROR expected a `FnMut(char)` closure, found `u8`
+    //~| NOTE expected an `FnMut(char)` closure, found `u8`
     //~| HELP the trait `FnMut<(char,)>` is not implemented for `u8`
     //~| HELP the following other types implement trait `Pattern<'a>`:
     //~| NOTE required for `u8` to implement `Pattern<'_>`
diff --git a/tests/ui/traits/bound/assoc-fn-bound-root-obligation.stderr b/tests/ui/traits/bound/assoc-fn-bound-root-obligation.stderr
index b1c683e4729ea..f30fe12b216d6 100644
--- a/tests/ui/traits/bound/assoc-fn-bound-root-obligation.stderr
+++ b/tests/ui/traits/bound/assoc-fn-bound-root-obligation.stderr
@@ -1,8 +1,8 @@
-error[E0277]: expected a `FnMut<(char,)>` closure, found `u8`
+error[E0277]: expected a `FnMut(char)` closure, found `u8`
   --> $DIR/assoc-fn-bound-root-obligation.rs:2:7
    |
 LL |     s.strip_suffix(b'\n').unwrap_or(s)
-   |       ^^^^^^^^^^^^ expected an `FnMut<(char,)>` closure, found `u8`
+   |       ^^^^^^^^^^^^ expected an `FnMut(char)` closure, found `u8`
    |
    = help: the trait `FnMut<(char,)>` is not implemented for `u8`
    = help: the following other types implement trait `Pattern<'a>`:
diff --git a/tests/ui/traits/new-solver/fn-trait.rs b/tests/ui/traits/new-solver/fn-trait.rs
index 0599e51d7ad8c..0a19e62655348 100644
--- a/tests/ui/traits/new-solver/fn-trait.rs
+++ b/tests/ui/traits/new-solver/fn-trait.rs
@@ -18,15 +18,15 @@ fn main() {
     require_fn(f);
     require_fn(f as fn() -> i32);
     require_fn(f as unsafe fn() -> i32);
-    //~^ ERROR: expected a `Fn<()>` closure, found `unsafe fn() -> i32`
+    //~^ ERROR: expected a `Fn()` closure, found `unsafe fn() -> i32`
     //~| ERROR: type mismatch resolving `<unsafe fn() -> i32 as FnOnce<()>>::Output == i32`
     require_fn(g);
-    //~^ ERROR: expected a `Fn<()>` closure, found `extern "C" fn() -> i32 {g}`
+    //~^ ERROR: expected a `Fn()` closure, found `extern "C" fn() -> i32 {g}`
     //~| ERROR: type mismatch resolving `<extern "C" fn() -> i32 {g} as FnOnce<()>>::Output == i32`
     require_fn(g as extern "C" fn() -> i32);
-    //~^ ERROR: expected a `Fn<()>` closure, found `extern "C" fn() -> i32`
+    //~^ ERROR: expected a `Fn()` closure, found `extern "C" fn() -> i32`
     //~| ERROR: type mismatch resolving `<extern "C" fn() -> i32 as FnOnce<()>>::Output == i32`
     require_fn(h);
-    //~^ ERROR: expected a `Fn<()>` closure, found `unsafe fn() -> i32 {h}`
+    //~^ ERROR: expected a `Fn()` closure, found `unsafe fn() -> i32 {h}`
     //~| ERROR: type mismatch resolving `<unsafe fn() -> i32 {h} as FnOnce<()>>::Output == i32`
 }
diff --git a/tests/ui/traits/new-solver/fn-trait.stderr b/tests/ui/traits/new-solver/fn-trait.stderr
index d52bcaf25b87c..4a42f08a7fb63 100644
--- a/tests/ui/traits/new-solver/fn-trait.stderr
+++ b/tests/ui/traits/new-solver/fn-trait.stderr
@@ -1,4 +1,4 @@
-error[E0277]: expected a `Fn<()>` closure, found `unsafe fn() -> i32`
+error[E0277]: expected a `Fn()` closure, found `unsafe fn() -> i32`
   --> $DIR/fn-trait.rs:20:16
    |
 LL |     require_fn(f as unsafe fn() -> i32);
@@ -28,11 +28,11 @@ note: required by a bound in `require_fn`
 LL | fn require_fn(_: impl Fn() -> i32) {}
    |                               ^^^ required by this bound in `require_fn`
 
-error[E0277]: expected a `Fn<()>` closure, found `extern "C" fn() -> i32 {g}`
+error[E0277]: expected a `Fn()` closure, found `extern "C" fn() -> i32 {g}`
   --> $DIR/fn-trait.rs:23:16
    |
 LL |     require_fn(g);
-   |     ---------- ^ expected an `Fn<()>` closure, found `extern "C" fn() -> i32 {g}`
+   |     ---------- ^ expected an `Fn()` closure, found `extern "C" fn() -> i32 {g}`
    |     |
    |     required by a bound introduced by this call
    |
@@ -58,11 +58,11 @@ note: required by a bound in `require_fn`
 LL | fn require_fn(_: impl Fn() -> i32) {}
    |                               ^^^ required by this bound in `require_fn`
 
-error[E0277]: expected a `Fn<()>` closure, found `extern "C" fn() -> i32`
+error[E0277]: expected a `Fn()` closure, found `extern "C" fn() -> i32`
   --> $DIR/fn-trait.rs:26:16
    |
 LL |     require_fn(g as extern "C" fn() -> i32);
-   |     ---------- ^^^^^^^^^^^^^^^^^^^^^^^^^^^ expected an `Fn<()>` closure, found `extern "C" fn() -> i32`
+   |     ---------- ^^^^^^^^^^^^^^^^^^^^^^^^^^^ expected an `Fn()` closure, found `extern "C" fn() -> i32`
    |     |
    |     required by a bound introduced by this call
    |
@@ -88,7 +88,7 @@ note: required by a bound in `require_fn`
 LL | fn require_fn(_: impl Fn() -> i32) {}
    |                               ^^^ required by this bound in `require_fn`
 
-error[E0277]: expected a `Fn<()>` closure, found `unsafe fn() -> i32 {h}`
+error[E0277]: expected a `Fn()` closure, found `unsafe fn() -> i32 {h}`
   --> $DIR/fn-trait.rs:29:16
    |
 LL |     require_fn(h);
diff --git a/tests/ui/traits/suggest-dereferences/root-obligation.fixed b/tests/ui/traits/suggest-dereferences/root-obligation.fixed
index 7a8433f90572e..d03d733c76d0c 100644
--- a/tests/ui/traits/suggest-dereferences/root-obligation.fixed
+++ b/tests/ui/traits/suggest-dereferences/root-obligation.fixed
@@ -4,7 +4,7 @@ fn get_vowel_count(string: &str) -> usize {
     string
         .chars()
         .filter(|c| "aeiou".contains(*c))
-        //~^ ERROR expected a `Fn<(char,)>` closure, found `char`
+        //~^ ERROR expected a `Fn(char)` closure, found `char`
         .count()
 }
 
diff --git a/tests/ui/traits/suggest-dereferences/root-obligation.rs b/tests/ui/traits/suggest-dereferences/root-obligation.rs
index 51bac2107e3b4..9d9ffb3f55ef0 100644
--- a/tests/ui/traits/suggest-dereferences/root-obligation.rs
+++ b/tests/ui/traits/suggest-dereferences/root-obligation.rs
@@ -4,7 +4,7 @@ fn get_vowel_count(string: &str) -> usize {
     string
         .chars()
         .filter(|c| "aeiou".contains(c))
-        //~^ ERROR expected a `Fn<(char,)>` closure, found `char`
+        //~^ ERROR expected a `Fn(char)` closure, found `char`
         .count()
 }
 
diff --git a/tests/ui/traits/suggest-dereferences/root-obligation.stderr b/tests/ui/traits/suggest-dereferences/root-obligation.stderr
index 1363fb8c47af8..a19708e46bb1a 100644
--- a/tests/ui/traits/suggest-dereferences/root-obligation.stderr
+++ b/tests/ui/traits/suggest-dereferences/root-obligation.stderr
@@ -1,8 +1,8 @@
-error[E0277]: expected a `Fn<(char,)>` closure, found `char`
+error[E0277]: expected a `Fn(char)` closure, found `char`
   --> $DIR/root-obligation.rs:6:38
    |
 LL |         .filter(|c| "aeiou".contains(c))
-   |                             -------- ^ expected an `Fn<(char,)>` closure, found `char`
+   |                             -------- ^ expected an `Fn(char)` closure, found `char`
    |                             |
    |                             required by a bound introduced by this call
    |
diff --git a/tests/ui/type-alias-impl-trait/issue-63279.rs b/tests/ui/type-alias-impl-trait/issue-63279.rs
index 0e46745c65cd6..02f2111468a25 100644
--- a/tests/ui/type-alias-impl-trait/issue-63279.rs
+++ b/tests/ui/type-alias-impl-trait/issue-63279.rs
@@ -3,11 +3,11 @@
 type Closure = impl FnOnce();
 
 fn c() -> Closure {
-    //~^ ERROR: expected a `FnOnce<()>` closure, found `()`
+    //~^ ERROR: expected a `FnOnce()` closure, found `()`
     || -> Closure { || () }
     //~^ ERROR: mismatched types
     //~| ERROR: mismatched types
-    //~| ERROR: expected a `FnOnce<()>` closure, found `()`
+    //~| ERROR: expected a `FnOnce()` closure, found `()`
 }
 
 fn main() {}
diff --git a/tests/ui/type-alias-impl-trait/issue-63279.stderr b/tests/ui/type-alias-impl-trait/issue-63279.stderr
index a868562479e8b..58cafd21ca872 100644
--- a/tests/ui/type-alias-impl-trait/issue-63279.stderr
+++ b/tests/ui/type-alias-impl-trait/issue-63279.stderr
@@ -1,17 +1,17 @@
-error[E0277]: expected a `FnOnce<()>` closure, found `()`
+error[E0277]: expected a `FnOnce()` closure, found `()`
   --> $DIR/issue-63279.rs:5:11
    |
 LL | fn c() -> Closure {
-   |           ^^^^^^^ expected an `FnOnce<()>` closure, found `()`
+   |           ^^^^^^^ expected an `FnOnce()` closure, found `()`
    |
    = help: the trait `FnOnce<()>` is not implemented for `()`
    = note: wrap the `()` in a closure with no arguments: `|| { /* code */ }`
 
-error[E0277]: expected a `FnOnce<()>` closure, found `()`
+error[E0277]: expected a `FnOnce()` closure, found `()`
   --> $DIR/issue-63279.rs:7:11
    |
 LL |     || -> Closure { || () }
-   |           ^^^^^^^ expected an `FnOnce<()>` closure, found `()`
+   |           ^^^^^^^ expected an `FnOnce()` closure, found `()`
    |
    = help: the trait `FnOnce<()>` is not implemented for `()`
    = note: wrap the `()` in a closure with no arguments: `|| { /* code */ }`
diff --git a/tests/ui/unboxed-closures/unboxed-closures-fnmut-as-fn.stderr b/tests/ui/unboxed-closures/unboxed-closures-fnmut-as-fn.stderr
index 0ea1c1dcd5bde..ce4d0fe25f51d 100644
--- a/tests/ui/unboxed-closures/unboxed-closures-fnmut-as-fn.stderr
+++ b/tests/ui/unboxed-closures/unboxed-closures-fnmut-as-fn.stderr
@@ -1,8 +1,8 @@
-error[E0277]: expected a `Fn<(isize,)>` closure, found `S`
+error[E0277]: expected a `Fn(isize)` closure, found `S`
   --> $DIR/unboxed-closures-fnmut-as-fn.rs:27:21
    |
 LL |     let x = call_it(&S, 22);
-   |             ------- ^^ expected an `Fn<(isize,)>` closure, found `S`
+   |             ------- ^^ expected an `Fn(isize)` closure, found `S`
    |             |
    |             required by a bound introduced by this call
    |
diff --git a/tests/ui/unboxed-closures/unboxed-closures-unsafe-extern-fn.stderr b/tests/ui/unboxed-closures/unboxed-closures-unsafe-extern-fn.stderr
index 802696e1b2f94..d836af2b01495 100644
--- a/tests/ui/unboxed-closures/unboxed-closures-unsafe-extern-fn.stderr
+++ b/tests/ui/unboxed-closures/unboxed-closures-unsafe-extern-fn.stderr
@@ -1,4 +1,4 @@
-error[E0277]: expected a `Fn<(&isize,)>` closure, found `for<'a> unsafe fn(&'a isize) -> isize {square}`
+error[E0277]: expected a `Fn(&isize)` closure, found `for<'a> unsafe fn(&'a isize) -> isize {square}`
   --> $DIR/unboxed-closures-unsafe-extern-fn.rs:20:21
    |
 LL |     let x = call_it(&square, 22);
@@ -14,7 +14,7 @@ note: required by a bound in `call_it`
 LL | fn call_it<F: Fn(&isize) -> isize>(_: &F, _: isize) -> isize {
    |               ^^^^^^^^^^^^^^^^^^^ required by this bound in `call_it`
 
-error[E0277]: expected a `FnMut<(&isize,)>` closure, found `for<'a> unsafe fn(&'a isize) -> isize {square}`
+error[E0277]: expected a `FnMut(&isize)` closure, found `for<'a> unsafe fn(&'a isize) -> isize {square}`
   --> $DIR/unboxed-closures-unsafe-extern-fn.rs:25:25
    |
 LL |     let y = call_it_mut(&mut square, 22);
@@ -30,7 +30,7 @@ note: required by a bound in `call_it_mut`
 LL | fn call_it_mut<F: FnMut(&isize) -> isize>(_: &mut F, _: isize) -> isize {
    |                   ^^^^^^^^^^^^^^^^^^^^^^ required by this bound in `call_it_mut`
 
-error[E0277]: expected a `FnOnce<(&isize,)>` closure, found `for<'a> unsafe fn(&'a isize) -> isize {square}`
+error[E0277]: expected a `FnOnce(&isize)` closure, found `for<'a> unsafe fn(&'a isize) -> isize {square}`
   --> $DIR/unboxed-closures-unsafe-extern-fn.rs:30:26
    |
 LL |     let z = call_it_once(square, 22);
diff --git a/tests/ui/unboxed-closures/unboxed-closures-wrong-abi.stderr b/tests/ui/unboxed-closures/unboxed-closures-wrong-abi.stderr
index 0bbb9836c5840..c0dcf83a5bb06 100644
--- a/tests/ui/unboxed-closures/unboxed-closures-wrong-abi.stderr
+++ b/tests/ui/unboxed-closures/unboxed-closures-wrong-abi.stderr
@@ -1,8 +1,8 @@
-error[E0277]: expected a `Fn<(&isize,)>` closure, found `for<'a> extern "C" fn(&'a isize) -> isize {square}`
+error[E0277]: expected a `Fn(&isize)` closure, found `for<'a> extern "C" fn(&'a isize) -> isize {square}`
   --> $DIR/unboxed-closures-wrong-abi.rs:20:21
    |
 LL |     let x = call_it(&square, 22);
-   |             ------- ^^^^^^^ expected an `Fn<(&isize,)>` closure, found `for<'a> extern "C" fn(&'a isize) -> isize {square}`
+   |             ------- ^^^^^^^ expected an `Fn(&isize)` closure, found `for<'a> extern "C" fn(&'a isize) -> isize {square}`
    |             |
    |             required by a bound introduced by this call
    |
@@ -13,11 +13,11 @@ note: required by a bound in `call_it`
 LL | fn call_it<F: Fn(&isize) -> isize>(_: &F, _: isize) -> isize {
    |               ^^^^^^^^^^^^^^^^^^^ required by this bound in `call_it`
 
-error[E0277]: expected a `FnMut<(&isize,)>` closure, found `for<'a> extern "C" fn(&'a isize) -> isize {square}`
+error[E0277]: expected a `FnMut(&isize)` closure, found `for<'a> extern "C" fn(&'a isize) -> isize {square}`
   --> $DIR/unboxed-closures-wrong-abi.rs:25:25
    |
 LL |     let y = call_it_mut(&mut square, 22);
-   |             ----------- ^^^^^^^^^^^ expected an `FnMut<(&isize,)>` closure, found `for<'a> extern "C" fn(&'a isize) -> isize {square}`
+   |             ----------- ^^^^^^^^^^^ expected an `FnMut(&isize)` closure, found `for<'a> extern "C" fn(&'a isize) -> isize {square}`
    |             |
    |             required by a bound introduced by this call
    |
@@ -28,11 +28,11 @@ note: required by a bound in `call_it_mut`
 LL | fn call_it_mut<F: FnMut(&isize) -> isize>(_: &mut F, _: isize) -> isize {
    |                   ^^^^^^^^^^^^^^^^^^^^^^ required by this bound in `call_it_mut`
 
-error[E0277]: expected a `FnOnce<(&isize,)>` closure, found `for<'a> extern "C" fn(&'a isize) -> isize {square}`
+error[E0277]: expected a `FnOnce(&isize)` closure, found `for<'a> extern "C" fn(&'a isize) -> isize {square}`
   --> $DIR/unboxed-closures-wrong-abi.rs:30:26
    |
 LL |     let z = call_it_once(square, 22);
-   |             ------------ ^^^^^^ expected an `FnOnce<(&isize,)>` closure, found `for<'a> extern "C" fn(&'a isize) -> isize {square}`
+   |             ------------ ^^^^^^ expected an `FnOnce(&isize)` closure, found `for<'a> extern "C" fn(&'a isize) -> isize {square}`
    |             |
    |             required by a bound introduced by this call
    |
diff --git a/tests/ui/unboxed-closures/unboxed-closures-wrong-arg-type-extern-fn.stderr b/tests/ui/unboxed-closures/unboxed-closures-wrong-arg-type-extern-fn.stderr
index 31a66790ce089..d261c38f50c29 100644
--- a/tests/ui/unboxed-closures/unboxed-closures-wrong-arg-type-extern-fn.stderr
+++ b/tests/ui/unboxed-closures/unboxed-closures-wrong-arg-type-extern-fn.stderr
@@ -1,4 +1,4 @@
-error[E0277]: expected a `Fn<(&isize,)>` closure, found `unsafe fn(isize) -> isize {square}`
+error[E0277]: expected a `Fn(&isize)` closure, found `unsafe fn(isize) -> isize {square}`
   --> $DIR/unboxed-closures-wrong-arg-type-extern-fn.rs:21:21
    |
 LL |     let x = call_it(&square, 22);
@@ -14,7 +14,7 @@ note: required by a bound in `call_it`
 LL | fn call_it<F: Fn(&isize) -> isize>(_: &F, _: isize) -> isize {
    |               ^^^^^^^^^^^^^^^^^^^ required by this bound in `call_it`
 
-error[E0277]: expected a `FnMut<(&isize,)>` closure, found `unsafe fn(isize) -> isize {square}`
+error[E0277]: expected a `FnMut(&isize)` closure, found `unsafe fn(isize) -> isize {square}`
   --> $DIR/unboxed-closures-wrong-arg-type-extern-fn.rs:26:25
    |
 LL |     let y = call_it_mut(&mut square, 22);
@@ -30,7 +30,7 @@ note: required by a bound in `call_it_mut`
 LL | fn call_it_mut<F: FnMut(&isize) -> isize>(_: &mut F, _: isize) -> isize {
    |                   ^^^^^^^^^^^^^^^^^^^^^^ required by this bound in `call_it_mut`
 
-error[E0277]: expected a `FnOnce<(&isize,)>` closure, found `unsafe fn(isize) -> isize {square}`
+error[E0277]: expected a `FnOnce(&isize)` closure, found `unsafe fn(isize) -> isize {square}`
   --> $DIR/unboxed-closures-wrong-arg-type-extern-fn.rs:31:26
    |
 LL |     let z = call_it_once(square, 22);
diff --git a/tests/ui/unsafe/initializing-ranged-via-ctor.stderr b/tests/ui/unsafe/initializing-ranged-via-ctor.stderr
index d34554c6641a9..13438fd31d0a9 100644
--- a/tests/ui/unsafe/initializing-ranged-via-ctor.stderr
+++ b/tests/ui/unsafe/initializing-ranged-via-ctor.stderr
@@ -1,4 +1,4 @@
-error[E0277]: expected a `FnOnce<({integer},)>` closure, found `unsafe fn(u8) -> NonZeroAndOneU8 {NonZeroAndOneU8}`
+error[E0277]: expected a `FnOnce({integer})` closure, found `unsafe fn(u8) -> NonZeroAndOneU8 {NonZeroAndOneU8}`
   --> $DIR/initializing-ranged-via-ctor.rs:9:34
    |
 LL |     println!("{:?}", Some(1).map(NonZeroAndOneU8).unwrap());