diff --git a/library/core/src/ops/function.rs b/library/core/src/ops/function.rs
index 25664a51a1d7b..15b54243c1eed 100644
--- a/library/core/src/ops/function.rs
+++ b/library/core/src/ops/function.rs
@@ -67,7 +67,7 @@ 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 `{This:resolved}` closure, found `{Self}`",
+    message = "expected an `{This:resolved}` closure, found `{Self}`",
     label = "expected an `{This:resolved}` closure, found `{Self}`"
 )]
 #[fundamental] // so that regex can rely that `&str: !FnMut`
@@ -154,7 +154,7 @@ pub const trait Fn<Args: Tuple>: [const] 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 `{This:resolved}` closure, found `{Self}`",
+    message = "expected an `{This:resolved}` closure, found `{Self}`",
     label = "expected an `{This:resolved}` closure, found `{Self}`"
 )]
 #[fundamental] // so that regex can rely that `&str: !FnMut`
@@ -233,7 +233,7 @@ pub const 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 `{This:resolved}` closure, found `{Self}`",
+    message = "expected an `{This:resolved}` closure, found `{Self}`",
     label = "expected an `{This:resolved}` closure, found `{Self}`"
 )]
 #[fundamental] // so that regex can rely that `&str: !FnMut`
diff --git a/library/std/src/sys/process/unix/unix.rs b/library/std/src/sys/process/unix/unix.rs
index 529cdaf72cc6c..b6ccc6b698fda 100644
--- a/library/std/src/sys/process/unix/unix.rs
+++ b/library/std/src/sys/process/unix/unix.rs
@@ -510,8 +510,8 @@ impl Command {
                                     support = SPAWN;
                                 }
                             }
-                            Err(e) if e.raw_os_error() == Some(libc::EMFILE) => {
-                                // We're temporarily(?) out of file descriptors. In this case pidfd_spawnp would also fail
+                            Err(e) if matches!(e.raw_os_error(), Some(libc::EMFILE | libc::ENFILE | libc::ENOMEM)) => {
+                                // We're temporarily(?) out of file descriptors or memory. In this case pidfd_spawnp would also fail
                                 // Don't update the support flag so we can probe again later.
                                 return Err(e)
                             }
diff --git a/tests/crashes/149748.rs b/tests/crashes/149748.rs
new file mode 100644
index 0000000000000..99e4a6ae15b80
--- /dev/null
+++ b/tests/crashes/149748.rs
@@ -0,0 +1,13 @@
+//@ known-bug: #149748
+//@ edition: 2024
+//@ compile-flags: -Zmir-enable-passes=+Inline -Zmir-enable-passes=+ReferencePropagation -Zlint-mir
+
+#![feature(gen_blocks)]
+gen fn foo(z: i32) -> i32 {
+    yield z;
+    z;
+}
+pub fn main() {
+    let mut iter = foo(3);
+    assert_eq!(iter.next(), Some(3))
+}
diff --git a/tests/crashes/150040.rs b/tests/crashes/150040.rs
new file mode 100644
index 0000000000000..bf5b7bbf9b536
--- /dev/null
+++ b/tests/crashes/150040.rs
@@ -0,0 +1,7 @@
+//@ known-bug: #150040
+
+fn main() {
+    let [(ref a, b), x];
+    a = "";
+    b = 5;
+}
diff --git a/tests/crashes/150049.rs b/tests/crashes/150049.rs
new file mode 100644
index 0000000000000..fa39785779c0f
--- /dev/null
+++ b/tests/crashes/150049.rs
@@ -0,0 +1,12 @@
+//@ known-bug: #150049
+#![feature(min_generic_const_args)]
+#![feature(inherent_associated_types)]
+struct Foo<'a> {
+    x: &'a (),
+}
+
+impl<'a> Foo<'a> {
+    fn foo(_: [u8; Foo::X]) { std::mem::transmute([4]) }
+}
+
+fn main() {}
diff --git a/tests/crashes/150128.rs b/tests/crashes/150128.rs
new file mode 100644
index 0000000000000..28372ee7935f7
--- /dev/null
+++ b/tests/crashes/150128.rs
@@ -0,0 +1,8 @@
+//@ known-bug: #150128
+fn main() {
+    match 0 {
+        _ => || (),
+        _ => || (),
+        _ => (|| ()) as unsafe fn,
+    };
+}
diff --git a/tests/crashes/150296.rs b/tests/crashes/150296.rs
new file mode 100644
index 0000000000000..f7d5a54ca9b65
--- /dev/null
+++ b/tests/crashes/150296.rs
@@ -0,0 +1,14 @@
+//@ known-bug: #150296
+#[derive(PartialEq)]
+pub struct Thing<const N: usize>;
+
+impl<const N: usize> Thing<N> {
+    const A: Self = Thing;
+}
+
+fn broken<const N: usize>(x: Thing<N>) {
+    match x {
+        <Thing<N>>::A => {}
+        _ => {}
+    }
+}
diff --git a/tests/crashes/150387.rs b/tests/crashes/150387.rs
new file mode 100644
index 0000000000000..b29ce143fb4ea
--- /dev/null
+++ b/tests/crashes/150387.rs
@@ -0,0 +1,13 @@
+//@ known-bug: #150387
+#![feature(min_specialization)]
+#![allow(dead_code)]
+
+struct Thing<T>(T) where [T]: Sized;
+
+impl<T> Drop for Thing<T> where [T]: Sized {
+    default fn drop(&mut self) {}
+}
+impl<T> Drop for Thing<T> where [T]: Sized {
+    fn drop(&mut self) {}
+}
+fn main() {}
diff --git a/tests/crashes/150403.rs b/tests/crashes/150403.rs
new file mode 100644
index 0000000000000..bc00fc32135fc
--- /dev/null
+++ b/tests/crashes/150403.rs
@@ -0,0 +1,26 @@
+//@ known-bug: #150403
+#![feature(non_lifetime_binders)]
+
+trait A {
+    type GAT<T>: A;
+    fn foo<T>(self, t: T) -> Self::GAT<T>
+    where
+        Self: Sized;
+}
+
+trait B: A where
+    for<T> Self::GAT<T>: B,
+{
+    fn bar<T>(self) -> Self::GAT<T>
+    where
+        Self: Sized;
+
+    fn baz<T>(self, t: T) -> Self::GAT<T>
+    where
+        Self: Sized,
+    {
+        self.foo(t).bar()
+    }
+}
+
+fn main() {}
diff --git a/tests/crashes/150517.rs b/tests/crashes/150517.rs
new file mode 100644
index 0000000000000..de14628547d28
--- /dev/null
+++ b/tests/crashes/150517.rs
@@ -0,0 +1,15 @@
+//@ known-bug: #150517
+trait Stream {
+    type Item;
+    fn next(self) -> ();
+}
+impl Stream for &'a () {}
+impl<'a, A> Stream for <&A as Stream>::Item {}
+trait StreamExt {
+    fn f(self) -> ()
+    where
+        for<'b> &'b A: Stream,
+    {
+        self.next()
+    }
+}
diff --git a/tests/crashes/150545.rs b/tests/crashes/150545.rs
new file mode 100644
index 0000000000000..04e084919d4f2
--- /dev/null
+++ b/tests/crashes/150545.rs
@@ -0,0 +1,8 @@
+//@ known-bug: #150545
+#![feature(non_lifetime_binders)]
+trait Foo: for<T> Bar<T> {
+    type Item;
+    fn next(self) -> Self::Item;
+}
+trait Bar<T> {}
+fn main() {}
diff --git a/tests/crashes/150749.rs b/tests/crashes/150749.rs
new file mode 100644
index 0000000000000..572dc67c27511
--- /dev/null
+++ b/tests/crashes/150749.rs
@@ -0,0 +1,12 @@
+//@ known-bug: #150749
+#![feature(min_generic_const_args)]
+
+trait CollectArray {
+    fn inner_array();
+}
+impl CollectArray for () {
+    fn inner_array() {
+        let temp_ptr: [(); Self];
+    }
+}
+fn main() {}
diff --git a/tests/crashes/150969.rs b/tests/crashes/150969.rs
new file mode 100644
index 0000000000000..daab977bce193
--- /dev/null
+++ b/tests/crashes/150969.rs
@@ -0,0 +1,7 @@
+//@ known-bug: #150969
+#![feature(generic_const_exprs)]
+#![feature(min_generic_const_args)]
+
+fn pass_enum<const N : usize, const M : usize = const {N}> {
+  pass_enum::<{None}>
+}
diff --git a/tests/crashes/151069.rs b/tests/crashes/151069.rs
new file mode 100644
index 0000000000000..ae6f4da5c6c70
--- /dev/null
+++ b/tests/crashes/151069.rs
@@ -0,0 +1,16 @@
+//@ known-bug: #151069
+trait Trait {
+    type Assoc2;
+}
+struct Bar;
+impl Trait for Bar
+where
+    <Bar as Trait>::Assoc2: Trait,
+{
+    type Assoc2 = ();
+}
+struct Foo {
+    field: <Bar as Trait>::Assoc2,
+}
+static FOO2: &Foo = 0;
+fn main() {}
diff --git a/tests/ui/abi/bad-custom.rs b/tests/ui/abi/bad-custom.rs
index 7c881134ccb4c..10e34fa19648a 100644
--- a/tests/ui/abi/bad-custom.rs
+++ b/tests/ui/abi/bad-custom.rs
@@ -100,7 +100,7 @@ async unsafe extern "custom" fn no_async_fn() {
 }
 
 fn no_promotion_to_fn_trait(f: unsafe extern "custom" fn()) -> impl Fn()  {
-    //~^ ERROR expected a `Fn()` closure, found `unsafe extern "custom" fn()`
+    //~^ ERROR expected an `Fn()` closure, found `unsafe extern "custom" fn()`
     f
 }
 
diff --git a/tests/ui/abi/bad-custom.stderr b/tests/ui/abi/bad-custom.stderr
index d7c9cae35c7b3..46da91d80c993 100644
--- a/tests/ui/abi/bad-custom.stderr
+++ b/tests/ui/abi/bad-custom.stderr
@@ -184,7 +184,7 @@ LL + #[unsafe(naked)]
 LL | async unsafe extern "custom" fn no_async_fn() {
    |
 
-error[E0277]: expected a `Fn()` closure, found `unsafe extern "custom" fn()`
+error[E0277]: expected an `Fn()` closure, found `unsafe extern "custom" fn()`
   --> $DIR/bad-custom.rs:102:64
    |
 LL | fn no_promotion_to_fn_trait(f: unsafe extern "custom" fn()) -> impl Fn()  {
diff --git a/tests/ui/associated-types/normalization-ice-issue-149746.rs b/tests/ui/associated-types/normalization-ice-issue-149746.rs
index 8932d321b7e5b..29661092b5751 100644
--- a/tests/ui/associated-types/normalization-ice-issue-149746.rs
+++ b/tests/ui/associated-types/normalization-ice-issue-149746.rs
@@ -4,14 +4,14 @@ trait Owner { type Ty<T: FnMut()>; }
 impl Owner for () { type Ty<T: FnMut()> = T; }
 pub struct Warns<T> {
     _significant_drop: <() as Owner>::Ty<T>,
-    //~^ ERROR expected a `FnMut()` closure, found `T`
+    //~^ ERROR expected an `FnMut()` closure, found `T`
     field: String,
 }
 pub fn test<T>(w: Warns<T>) {
-    //~^ ERROR expected a `FnMut()` closure, found `T`
+    //~^ ERROR expected an `FnMut()` closure, found `T`
     _ = || w.field
-    //~^ ERROR expected a `FnMut()` closure, found `T`
-    //~| ERROR expected a `FnMut()` closure, found `T`
+    //~^ ERROR expected an `FnMut()` closure, found `T`
+    //~| ERROR expected an `FnMut()` closure, found `T`
     //~| WARN: changes to closure capture in Rust 2021 will affect drop order
 }
 fn main() {}
diff --git a/tests/ui/associated-types/normalization-ice-issue-149746.stderr b/tests/ui/associated-types/normalization-ice-issue-149746.stderr
index 7f983d6e14ae2..ae6f6bbbb52c9 100644
--- a/tests/ui/associated-types/normalization-ice-issue-149746.stderr
+++ b/tests/ui/associated-types/normalization-ice-issue-149746.stderr
@@ -1,4 +1,4 @@
-error[E0277]: expected a `FnMut()` closure, found `T`
+error[E0277]: expected an `FnMut()` closure, found `T`
   --> $DIR/normalization-ice-issue-149746.rs:6:24
    |
 LL |     _significant_drop: <() as Owner>::Ty<T>,
@@ -35,7 +35,7 @@ help: add a dummy let to cause `w` to be fully captured
 LL |     _ = || { let _ = &w; w.field }
    |            +++++++++++++         +
 
-error[E0277]: expected a `FnMut()` closure, found `T`
+error[E0277]: expected an `FnMut()` closure, found `T`
   --> $DIR/normalization-ice-issue-149746.rs:12:9
    |
 LL |     _ = || w.field
@@ -48,7 +48,7 @@ note: required by a bound in `Owner::Ty`
 LL | trait Owner { type Ty<T: FnMut()>; }
    |                          ^^^^^^^ required by this bound in `Owner::Ty`
 
-error[E0277]: expected a `FnMut()` closure, found `T`
+error[E0277]: expected an `FnMut()` closure, found `T`
   --> $DIR/normalization-ice-issue-149746.rs:10:16
    |
 LL | pub fn test<T>(w: Warns<T>) {
@@ -61,7 +61,7 @@ note: required by a bound in `Owner::Ty`
 LL | trait Owner { type Ty<T: FnMut()>; }
    |                          ^^^^^^^ required by this bound in `Owner::Ty`
 
-error[E0277]: expected a `FnMut()` closure, found `T`
+error[E0277]: expected an `FnMut()` closure, found `T`
   --> $DIR/normalization-ice-issue-149746.rs:12:9
    |
 LL |     _ = || w.field
diff --git a/tests/ui/async-await/async-fn/impl-header.rs b/tests/ui/async-await/async-fn/impl-header.rs
index 9af5f1f42a957..349a875d4a6c4 100644
--- a/tests/ui/async-await/async-fn/impl-header.rs
+++ b/tests/ui/async-await/async-fn/impl-header.rs
@@ -6,7 +6,7 @@ impl async Fn<()> for F {}
 //~^ ERROR `async` trait implementations are unsupported
 //~| ERROR the precise format of `Fn`-family traits' type parameters is subject to change
 //~| ERROR manual implementations of `Fn` are experimental
-//~| ERROR expected a `FnMut()` closure, found `F`
+//~| ERROR expected an `FnMut()` closure, found `F`
 //~| ERROR not all trait items implemented, missing: `call`
 
 fn main() {}
diff --git a/tests/ui/async-await/async-fn/impl-header.stderr b/tests/ui/async-await/async-fn/impl-header.stderr
index d0cf0d822f254..d1e3f884d02b3 100644
--- a/tests/ui/async-await/async-fn/impl-header.stderr
+++ b/tests/ui/async-await/async-fn/impl-header.stderr
@@ -30,7 +30,7 @@ LL | impl async Fn<()> for F {}
    |
    = help: implement the missing item: `fn call(&self, _: ()) -> <Self as FnOnce<()>>::Output { todo!() }`
 
-error[E0277]: expected a `FnMut()` closure, found `F`
+error[E0277]: expected an `FnMut()` closure, found `F`
   --> $DIR/impl-header.rs:5:23
    |
 LL | impl async Fn<()> for F {}
diff --git a/tests/ui/cast/raw-ptr-to-dyn-fn-raw-ptr.rs b/tests/ui/cast/raw-ptr-to-dyn-fn-raw-ptr.rs
index 6572140786d2e..d966781f90d9f 100644
--- a/tests/ui/cast/raw-ptr-to-dyn-fn-raw-ptr.rs
+++ b/tests/ui/cast/raw-ptr-to-dyn-fn-raw-ptr.rs
@@ -4,6 +4,6 @@ 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 an `Fn()` closure, found `()`
     };
 }
diff --git a/tests/ui/cast/raw-ptr-to-dyn-fn-raw-ptr.stderr b/tests/ui/cast/raw-ptr-to-dyn-fn-raw-ptr.stderr
index d0f0bcb201425..a830ddc4468ff 100644
--- a/tests/ui/cast/raw-ptr-to-dyn-fn-raw-ptr.stderr
+++ b/tests/ui/cast/raw-ptr-to-dyn-fn-raw-ptr.stderr
@@ -1,4 +1,4 @@
-error[E0277]: expected a `Fn()` closure, found `()`
+error[E0277]: expected an `Fn()` closure, found `()`
   --> $DIR/raw-ptr-to-dyn-fn-raw-ptr.rs:6:16
    |
 LL |         &mut *(ptr as *mut dyn Fn())
diff --git a/tests/ui/closures/closure-expected.rs b/tests/ui/closures/closure-expected.rs
index d730bcd1faf51..4fc1b3a1fd006 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 an `FnOnce()` closure, found `{integer}`
 }
diff --git a/tests/ui/closures/closure-expected.stderr b/tests/ui/closures/closure-expected.stderr
index 53a93e1e84dd0..490988f247cdd 100644
--- a/tests/ui/closures/closure-expected.stderr
+++ b/tests/ui/closures/closure-expected.stderr
@@ -1,4 +1,4 @@
-error[E0277]: expected a `FnOnce()` closure, found `{integer}`
+error[E0277]: expected an `FnOnce()` closure, found `{integer}`
   --> $DIR/closure-expected.rs:3:23
    |
 LL |     let y = x.or_else(4);
diff --git a/tests/ui/closures/coerce-unsafe-to-closure.stderr b/tests/ui/closures/coerce-unsafe-to-closure.stderr
index 013b9009da406..2bf2739be52d6 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 fn(_) -> _ {std::intrinsics::transmute::<_, _>}`
+error[E0277]: expected an `FnOnce(&str)` closure, found `unsafe fn(_) -> _ {std::intrinsics::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/contracts/empty-ensures.rs b/tests/ui/contracts/empty-ensures.rs
index 0a52391117861..79e57df6eb984 100644
--- a/tests/ui/contracts/empty-ensures.rs
+++ b/tests/ui/contracts/empty-ensures.rs
@@ -6,7 +6,7 @@ extern crate core;
 use core::contracts::ensures;
 
 #[ensures()]
-//~^ ERROR expected a `Fn(&_)` closure, found `()` [E0277]
+//~^ ERROR expected an `Fn(&_)` closure, found `()` [E0277]
 fn foo(x: u32) -> u32 {
     x * 2
 }
diff --git a/tests/ui/contracts/empty-ensures.stderr b/tests/ui/contracts/empty-ensures.stderr
index 6a19d234b52c2..b87f709eeb7a4 100644
--- a/tests/ui/contracts/empty-ensures.stderr
+++ b/tests/ui/contracts/empty-ensures.stderr
@@ -1,4 +1,4 @@
-error[E0277]: expected a `Fn(&_)` closure, found `()`
+error[E0277]: expected an `Fn(&_)` closure, found `()`
   --> $DIR/empty-ensures.rs:8:1
    |
 LL | #[ensures()]
diff --git a/tests/ui/expr/malformed_closure/block_instead_of_closure_in_arg.rs b/tests/ui/expr/malformed_closure/block_instead_of_closure_in_arg.rs
index 5e64fd5d2af4a..94c6c85d28d27 100644
--- a/tests/ui/expr/malformed_closure/block_instead_of_closure_in_arg.rs
+++ b/tests/ui/expr/malformed_closure/block_instead_of_closure_in_arg.rs
@@ -1,6 +1,6 @@
 fn main() {
     let number = 2;
-    Some(true).filter({ //~ ERROR expected a `FnOnce(&bool)` closure, found `bool`
+    Some(true).filter({ //~ ERROR expected an `FnOnce(&bool)` closure, found `bool`
         if number % 2 == 0 {
             number == 0
         } else {
diff --git a/tests/ui/expr/malformed_closure/block_instead_of_closure_in_arg.stderr b/tests/ui/expr/malformed_closure/block_instead_of_closure_in_arg.stderr
index c4c1c830afa6e..b8b4a0a17bcf6 100644
--- a/tests/ui/expr/malformed_closure/block_instead_of_closure_in_arg.stderr
+++ b/tests/ui/expr/malformed_closure/block_instead_of_closure_in_arg.stderr
@@ -1,4 +1,4 @@
-error[E0277]: expected a `FnOnce(&bool)` closure, found `bool`
+error[E0277]: expected an `FnOnce(&bool)` closure, found `bool`
   --> $DIR/block_instead_of_closure_in_arg.rs:3:23
    |
 LL |        Some(true).filter({
diff --git a/tests/ui/expr/malformed_closure/ruby_style_closure_successful_parse.rs b/tests/ui/expr/malformed_closure/ruby_style_closure_successful_parse.rs
index bb2e9c0a63c75..faad88764bf98 100644
--- a/tests/ui/expr/malformed_closure/ruby_style_closure_successful_parse.rs
+++ b/tests/ui/expr/malformed_closure/ruby_style_closure_successful_parse.rs
@@ -1,6 +1,6 @@
 const x: usize =42;
 fn main() {
-    let p = Some(45).and_then({|x| //~ ERROR expected a `FnOnce({integer})` closure, found `Option<usize>`
+    let p = Some(45).and_then({|x| //~ ERROR expected an `FnOnce({integer})` closure, found `Option<usize>`
         1 + 1;
         Some(x * 2)
     });
diff --git a/tests/ui/expr/malformed_closure/ruby_style_closure_successful_parse.stderr b/tests/ui/expr/malformed_closure/ruby_style_closure_successful_parse.stderr
index 54d3c6727f77f..ea41e77952ff5 100644
--- a/tests/ui/expr/malformed_closure/ruby_style_closure_successful_parse.stderr
+++ b/tests/ui/expr/malformed_closure/ruby_style_closure_successful_parse.stderr
@@ -1,4 +1,4 @@
-error[E0277]: expected a `FnOnce({integer})` closure, found `Option<usize>`
+error[E0277]: expected an `FnOnce({integer})` closure, found `Option<usize>`
   --> $DIR/ruby_style_closure_successful_parse.rs:3:31
    |
 LL |       let p = Some(45).and_then({|x|
diff --git a/tests/ui/extern/extern-wrong-value-type.rs b/tests/ui/extern/extern-wrong-value-type.rs
index 56c6cf1dfaba7..ae07a721e83ee 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 an `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 692a660117112..e1686f8a3ab9b 100644
--- a/tests/ui/extern/extern-wrong-value-type.stderr
+++ b/tests/ui/extern/extern-wrong-value-type.stderr
@@ -1,4 +1,4 @@
-error[E0277]: expected a `Fn()` closure, found `extern "C" fn() {f}`
+error[E0277]: expected an `Fn()` closure, found `extern "C" fn() {f}`
   --> $DIR/extern-wrong-value-type.rs:9:11
    |
 LL |     is_fn(f);
diff --git a/tests/ui/feature-gates/feature-gate-unboxed-closures-manual-impls.rs b/tests/ui/feature-gates/feature-gate-unboxed-closures-manual-impls.rs
index 7b40c8760e368..d33625f06872e 100644
--- a/tests/ui/feature-gates/feature-gate-unboxed-closures-manual-impls.rs
+++ b/tests/ui/feature-gates/feature-gate-unboxed-closures-manual-impls.rs
@@ -9,7 +9,7 @@ struct Foo;
 impl Fn<()> for Foo {
     //~^ ERROR the precise format of `Fn`-family traits' type parameters is subject to change
     //~| ERROR manual implementations of `Fn` are experimental
-    //~| ERROR expected a `FnMut()` closure, found `Foo`
+    //~| ERROR expected an `FnMut()` closure, found `Foo`
     extern "rust-call" fn call(self, args: ()) -> () {}
     //~^ ERROR "rust-call" ABI is experimental and subject to change
     //~| ERROR `call` has an incompatible type for trait
@@ -26,7 +26,7 @@ struct Bar;
 impl FnMut<()> for Bar {
     //~^ ERROR the precise format of `Fn`-family traits' type parameters is subject to change
     //~| ERROR manual implementations of `FnMut` are experimental
-    //~| ERROR expected a `FnOnce()` closure, found `Bar`
+    //~| ERROR expected an `FnOnce()` closure, found `Bar`
     extern "rust-call" fn call_mut(&self, args: ()) -> () {}
     //~^ ERROR "rust-call" ABI is experimental and subject to change
     //~| ERROR incompatible type for trait
diff --git a/tests/ui/feature-gates/feature-gate-unboxed-closures-manual-impls.stderr b/tests/ui/feature-gates/feature-gate-unboxed-closures-manual-impls.stderr
index b2a2eba9ad1da..56cfd6d0c52b9 100644
--- a/tests/ui/feature-gates/feature-gate-unboxed-closures-manual-impls.stderr
+++ b/tests/ui/feature-gates/feature-gate-unboxed-closures-manual-impls.stderr
@@ -87,7 +87,7 @@ LL | impl FnMut<()> for Bar {
    |
    = help: add `#![feature(unboxed_closures)]` to the crate attributes to enable
 
-error[E0277]: expected a `FnMut()` closure, found `Foo`
+error[E0277]: expected an `FnMut()` closure, found `Foo`
   --> $DIR/feature-gate-unboxed-closures-manual-impls.rs:9:17
    |
 LL | impl Fn<()> for Foo {
@@ -161,7 +161,7 @@ help: change the self-receiver type to match the trait
 LL |     extern "rust-call" fn call_mut(&mut self, args: ()) -> () {}
    |                                     +++
 
-error[E0277]: expected a `FnOnce()` closure, found `Bar`
+error[E0277]: expected an `FnOnce()` closure, found `Bar`
   --> $DIR/feature-gate-unboxed-closures-manual-impls.rs:26:20
    |
 LL | impl FnMut<()> for Bar {
diff --git a/tests/ui/fn/fn-trait-formatting.rs b/tests/ui/fn/fn-trait-formatting.rs
index be74d1ca9be3c..a7b00491ade01 100644
--- a/tests/ui/fn/fn-trait-formatting.rs
+++ b/tests/ui/fn/fn-trait-formatting.rs
@@ -17,5 +17,5 @@ fn main() {
     //~| NOTE found struct `Box<dyn FnMut() -> isize>`
 
     needs_fn(1);
-    //~^ ERROR expected a `Fn(isize)` closure, found `{integer}`
+    //~^ ERROR expected an `Fn(isize)` closure, found `{integer}`
 }
diff --git a/tests/ui/fn/fn-trait-formatting.stderr b/tests/ui/fn/fn-trait-formatting.stderr
index bfd86106bf923..0b86634a52e56 100644
--- a/tests/ui/fn/fn-trait-formatting.stderr
+++ b/tests/ui/fn/fn-trait-formatting.stderr
@@ -39,7 +39,7 @@ 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 an `Fn(isize)` closure, found `{integer}`
   --> $DIR/fn-trait-formatting.rs:19:14
    |
 LL |     needs_fn(1);
diff --git a/tests/ui/fn/issue-39259.rs b/tests/ui/fn/issue-39259.rs
index d4569a9094b2f..d2b545e000b97 100644
--- a/tests/ui/fn/issue-39259.rs
+++ b/tests/ui/fn/issue-39259.rs
@@ -5,7 +5,7 @@ struct S;
 
 impl Fn(u32) -> u32 for S {
     //~^ ERROR associated item constraints are not allowed here [E0229]
-    //~| ERROR expected a `FnMut(u32)` closure, found `S`
+    //~| ERROR expected an `FnMut(u32)` closure, found `S`
     fn call(&self) -> u32 {
         //~^ ERROR method `call` has 1 parameter but the declaration in trait `call` has 2
         5
diff --git a/tests/ui/fn/issue-39259.stderr b/tests/ui/fn/issue-39259.stderr
index b932731b5275e..7f2f4ecdd8d9b 100644
--- a/tests/ui/fn/issue-39259.stderr
+++ b/tests/ui/fn/issue-39259.stderr
@@ -22,7 +22,7 @@ help: add the missing parameter from the trait
 LL |     fn call(&self, args: Args) -> u32 {
    |                  ++++++++++++
 
-error[E0277]: expected a `FnMut(u32)` closure, found `S`
+error[E0277]: expected an `FnMut(u32)` closure, found `S`
   --> $DIR/issue-39259.rs:6:25
    |
 LL | impl Fn(u32) -> u32 for S {
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 c444ee9e1cdb4..edd9ad11ae778 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 an `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 d98071efe8311..7821560d96090 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
@@ -1,4 +1,4 @@
-error[E0277]: expected a `Fn()` closure, found `T`
+error[E0277]: expected an `Fn()` closure, found `T`
   --> $DIR/issue-68642-broken-llvm-ir.rs:12:18
    |
 LL |     type F<'a> = Self;
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 39db51c0e2a21..23586f6af98bd 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 an `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 cd4c06a8660a8..99b56dd061933 100644
--- a/tests/ui/generic-associated-types/issue-68643-broken-mir.stderr
+++ b/tests/ui/generic-associated-types/issue-68643-broken-mir.stderr
@@ -1,4 +1,4 @@
-error[E0277]: expected a `Fn()` closure, found `T`
+error[E0277]: expected an `Fn()` closure, found `T`
   --> $DIR/issue-68643-broken-mir.rs:12:18
    |
 LL |     type F<'a> = Self;
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 e379bce07d313..85b932a063c14 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 an `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 12f9949a0d304..4537091a60915 100644
--- a/tests/ui/generic-associated-types/issue-68644-codegen-selection.stderr
+++ b/tests/ui/generic-associated-types/issue-68644-codegen-selection.stderr
@@ -1,4 +1,4 @@
-error[E0277]: expected a `Fn()` closure, found `T`
+error[E0277]: expected an `Fn()` closure, found `T`
   --> $DIR/issue-68644-codegen-selection.rs:12:18
    |
 LL |     type F<'a> = Self;
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 e69a08b0a3991..b8133148b1029 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 an `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 8b23f60953061..cc324f91d75eb 100644
--- a/tests/ui/generic-associated-types/issue-68645-codegen-fulfillment.stderr
+++ b/tests/ui/generic-associated-types/issue-68645-codegen-fulfillment.stderr
@@ -1,4 +1,4 @@
-error[E0277]: expected a `Fn()` closure, found `T`
+error[E0277]: expected an `Fn()` closure, found `T`
   --> $DIR/issue-68645-codegen-fulfillment.rs:12:18
    |
 LL |     type F<'a> = Self;
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 36264b0d997b2..96cef0a6a5c9e 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
@@ -1,4 +1,4 @@
-error[E0277]: expected a `Fn(<_ as ATC<'a>>::Type)` closure, found `F`
+error[E0277]: expected an `Fn(<_ as ATC<'a>>::Type)` closure, found `F`
   --> $DIR/issue-62529-3.rs:25:14
    |
 LL |         call(f, ());
diff --git a/tests/ui/implied-bounds/issue-100690.rs b/tests/ui/implied-bounds/issue-100690.rs
index b0dbf749c4670..4f8a2df9834f5 100644
--- a/tests/ui/implied-bounds/issue-100690.rs
+++ b/tests/ui/implied-bounds/issue-100690.rs
@@ -32,7 +32,7 @@ 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`
+        //~^ ERROR expected an `FnOnce(&mut UIView<'_, T>)` closure, found `F`
     }
 }
 
diff --git a/tests/ui/implied-bounds/issue-100690.stderr b/tests/ui/implied-bounds/issue-100690.stderr
index d00895d8fc9cc..b5465e2f3ce08 100644
--- a/tests/ui/implied-bounds/issue-100690.stderr
+++ b/tests/ui/implied-bounds/issue-100690.stderr
@@ -1,4 +1,4 @@
-error[E0277]: expected a `FnOnce(&mut UIView<'_, T>)` closure, found `F`
+error[E0277]: expected an `FnOnce(&mut UIView<'_, T>)` closure, found `F`
   --> $DIR/issue-100690.rs:34:23
    |
 LL |         real_dispatch(f)
diff --git a/tests/ui/intrinsics/const-eval-select-bad.rs b/tests/ui/intrinsics/const-eval-select-bad.rs
index f407125129921..23a7a4be7ff10 100644
--- a/tests/ui/intrinsics/const-eval-select-bad.rs
+++ b/tests/ui/intrinsics/const-eval-select-bad.rs
@@ -7,8 +7,8 @@ const fn not_fn_items() {
     const_eval_select((), || {}, || {});
     //~^ ERROR const FnOnce()` is not satisfied
     const_eval_select((), 42, 0xDEADBEEF);
-    //~^ ERROR expected a `FnOnce()` closure
-    //~| ERROR expected a `FnOnce()` closure
+    //~^ ERROR expected an `FnOnce()` closure
+    //~| ERROR expected an `FnOnce()` closure
 }
 
 const fn foo(n: i32) -> i32 {
diff --git a/tests/ui/intrinsics/const-eval-select-bad.stderr b/tests/ui/intrinsics/const-eval-select-bad.stderr
index d701f5ea90973..7880dfa36a8f4 100644
--- a/tests/ui/intrinsics/const-eval-select-bad.stderr
+++ b/tests/ui/intrinsics/const-eval-select-bad.stderr
@@ -9,7 +9,7 @@ LL |     const_eval_select((), || {}, || {});
 note: required by a bound in `const_eval_select`
   --> $SRC_DIR/core/src/intrinsics/mod.rs:LL:COL
 
-error[E0277]: expected a `FnOnce()` closure, found `{integer}`
+error[E0277]: expected an `FnOnce()` closure, found `{integer}`
   --> $DIR/const-eval-select-bad.rs:9:27
    |
 LL |     const_eval_select((), 42, 0xDEADBEEF);
@@ -22,7 +22,7 @@ LL |     const_eval_select((), 42, 0xDEADBEEF);
 note: required by a bound in `const_eval_select`
   --> $SRC_DIR/core/src/intrinsics/mod.rs:LL:COL
 
-error[E0277]: expected a `FnOnce()` closure, found `{integer}`
+error[E0277]: expected an `FnOnce()` closure, found `{integer}`
   --> $DIR/const-eval-select-bad.rs:9:31
    |
 LL |     const_eval_select((), 42, 0xDEADBEEF);
diff --git a/tests/ui/iterators/fold-iterator-error-23966.stderr b/tests/ui/iterators/fold-iterator-error-23966.stderr
index 15249a935972a..2e27108e6a483 100644
--- a/tests/ui/iterators/fold-iterator-error-23966.stderr
+++ b/tests/ui/iterators/fold-iterator-error-23966.stderr
@@ -1,4 +1,4 @@
-error[E0277]: expected a `FnMut(_, char)` closure, found `()`
+error[E0277]: expected an `FnMut(_, char)` closure, found `()`
   --> $DIR/fold-iterator-error-23966.rs:3:32
    |
 LL |     "".chars().fold(|_, _| (), ());
diff --git a/tests/ui/lifetimes/issue-76168-hr-outlives-3.rs b/tests/ui/lifetimes/issue-76168-hr-outlives-3.rs
index 77a1f0b4f25d6..ab3bf619f83b2 100644
--- a/tests/ui/lifetimes/issue-76168-hr-outlives-3.rs
+++ b/tests/ui/lifetimes/issue-76168-hr-outlives-3.rs
@@ -4,9 +4,9 @@
 use std::future::Future;
 
 async fn wrapper<F>(f: F)
-//~^ ERROR: expected a `FnOnce(&'a mut i32)` closure, found `i32`
-//~| ERROR: expected a `FnOnce(&'a mut i32)` closure, found `i32`
-//~| ERROR: expected a `FnOnce(&'a mut i32)` closure, found `i32`
+//~^ ERROR: expected an `FnOnce(&'a mut i32)` closure, found `i32`
+//~| ERROR: expected an `FnOnce(&'a mut i32)` closure, found `i32`
+//~| ERROR: expected an `FnOnce(&'a mut i32)` closure, found `i32`
 where
     F:,
     for<'a> <i32 as FnOnce<(&'a mut i32,)>>::Output: Future<Output = ()> + 'a,
diff --git a/tests/ui/lifetimes/issue-76168-hr-outlives-3.stderr b/tests/ui/lifetimes/issue-76168-hr-outlives-3.stderr
index bf70826165341..7a825b93461c0 100644
--- a/tests/ui/lifetimes/issue-76168-hr-outlives-3.stderr
+++ b/tests/ui/lifetimes/issue-76168-hr-outlives-3.stderr
@@ -1,4 +1,4 @@
-error[E0277]: expected a `FnOnce(&'a mut i32)` closure, found `i32`
+error[E0277]: expected an `FnOnce(&'a mut i32)` closure, found `i32`
   --> $DIR/issue-76168-hr-outlives-3.rs:6:1
    |
 LL | / async fn wrapper<F>(f: F)
@@ -9,7 +9,7 @@ LL | |     for<'a> <i32 as FnOnce<(&'a mut i32,)>>::Output: Future<Output = ()>
    |
    = help: the trait `for<'a> FnOnce(&'a mut i32)` is not implemented for `i32`
 
-error[E0277]: expected a `FnOnce(&'a mut i32)` closure, found `i32`
+error[E0277]: expected an `FnOnce(&'a mut i32)` closure, found `i32`
   --> $DIR/issue-76168-hr-outlives-3.rs:6:26
    |
 LL | async fn wrapper<F>(f: F)
@@ -17,7 +17,7 @@ LL | async fn wrapper<F>(f: F)
    |
    = help: the trait `for<'a> FnOnce(&'a mut i32)` is not implemented for `i32`
 
-error[E0277]: expected a `FnOnce(&'a mut i32)` closure, found `i32`
+error[E0277]: expected an `FnOnce(&'a mut i32)` closure, found `i32`
   --> $DIR/issue-76168-hr-outlives-3.rs:6:26
    |
 LL | async fn wrapper<F>(f: F)
diff --git a/tests/ui/lifetimes/issue-95023.rs b/tests/ui/lifetimes/issue-95023.rs
index 1faae50d9f158..d26317d2b9058 100644
--- a/tests/ui/lifetimes/issue-95023.rs
+++ b/tests/ui/lifetimes/issue-95023.rs
@@ -4,7 +4,7 @@ impl Fn(&isize) for Error {
     //~^ ERROR manual implementations of `Fn` are experimental [E0183]
     //~| ERROR associated item constraints are not allowed here [E0229]
     //~| ERROR not all trait items implemented
-    //~| ERROR expected a `FnMut(&isize)` closure, found `Error`
+    //~| ERROR expected an `FnMut(&isize)` closure, found `Error`
     fn foo<const N: usize>(&self) -> Self::B<{ N }>;
     //~^ ERROR associated function in `impl` without body
     //~| ERROR method `foo` is not a member of trait `Fn` [E0407]
diff --git a/tests/ui/lifetimes/issue-95023.stderr b/tests/ui/lifetimes/issue-95023.stderr
index 013bc51ff78a4..afb627de1c1bb 100644
--- a/tests/ui/lifetimes/issue-95023.stderr
+++ b/tests/ui/lifetimes/issue-95023.stderr
@@ -40,7 +40,7 @@ LL | impl Fn(&isize) for Error {
    |
    = help: implement the missing item: `fn call(&self, _: (&isize,)) -> <Self as FnOnce<(&isize,)>>::Output { todo!() }`
 
-error[E0277]: expected a `FnMut(&isize)` closure, found `Error`
+error[E0277]: expected an `FnMut(&isize)` closure, found `Error`
   --> $DIR/issue-95023.rs:3:21
    |
 LL | impl Fn(&isize) for Error {
diff --git a/tests/ui/macros/ice-in-tokenstream-for-contracts-issue-140683.rs b/tests/ui/macros/ice-in-tokenstream-for-contracts-issue-140683.rs
index 68346a00ae1a7..2b1bacf7e0c31 100644
--- a/tests/ui/macros/ice-in-tokenstream-for-contracts-issue-140683.rs
+++ b/tests/ui/macros/ice-in-tokenstream-for-contracts-issue-140683.rs
@@ -4,7 +4,7 @@
 struct T;
 
 impl T {
-    #[core::contracts::ensures] //~ ERROR expected a `Fn(&_)` closure, found `()`
+    #[core::contracts::ensures] //~ ERROR expected an `Fn(&_)` closure, found `()`
     fn b() {(loop)}
     //~^ ERROR expected `{`, found `)`
     //~| ERROR expected `{`, found `)`
diff --git a/tests/ui/macros/ice-in-tokenstream-for-contracts-issue-140683.stderr b/tests/ui/macros/ice-in-tokenstream-for-contracts-issue-140683.stderr
index f1ffda2a9bee6..56dbdae14189b 100644
--- a/tests/ui/macros/ice-in-tokenstream-for-contracts-issue-140683.stderr
+++ b/tests/ui/macros/ice-in-tokenstream-for-contracts-issue-140683.stderr
@@ -16,7 +16,7 @@ LL |     fn b() {(loop)}
    |
    = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
 
-error[E0277]: expected a `Fn(&_)` closure, found `()`
+error[E0277]: expected an `Fn(&_)` closure, found `()`
   --> $DIR/ice-in-tokenstream-for-contracts-issue-140683.rs:7:5
    |
 LL |     #[core::contracts::ensures]
diff --git a/tests/ui/methods/filter-relevant-fn-bounds.rs b/tests/ui/methods/filter-relevant-fn-bounds.rs
index 7945eaa0daa27..a23f4600d6d1b 100644
--- a/tests/ui/methods/filter-relevant-fn-bounds.rs
+++ b/tests/ui/methods/filter-relevant-fn-bounds.rs
@@ -16,5 +16,5 @@ impl Wrapper {
 fn main() {
     let mut wrapper = Wrapper;
     wrapper.do_something_wrapper(|value| ());
-    //~^ ERROR expected a `FnOnce
+    //~^ ERROR expected an `FnOnce
 }
diff --git a/tests/ui/methods/filter-relevant-fn-bounds.stderr b/tests/ui/methods/filter-relevant-fn-bounds.stderr
index 4efe40ae0903b..9ad0319440e9a 100644
--- a/tests/ui/methods/filter-relevant-fn-bounds.stderr
+++ b/tests/ui/methods/filter-relevant-fn-bounds.stderr
@@ -12,7 +12,7 @@ help: consider further restricting type parameter `F` with trait `Output`
 LL |         F: for<'a> FnOnce(<F as Output<'a>>::Type) + for<'a> Output<'a>,
    |                                                    ++++++++++++++++++++
 
-error[E0277]: expected a `FnOnce(<{closure@$DIR/filter-relevant-fn-bounds.rs:18:34: 18:41} as Output<'a>>::Type)` closure, found `{closure@$DIR/filter-relevant-fn-bounds.rs:18:34: 18:41}`
+error[E0277]: expected an `FnOnce(<{closure@$DIR/filter-relevant-fn-bounds.rs:18:34: 18:41} as Output<'a>>::Type)` closure, found `{closure@$DIR/filter-relevant-fn-bounds.rs:18:34: 18:41}`
   --> $DIR/filter-relevant-fn-bounds.rs:18:34
    |
 LL |     wrapper.do_something_wrapper(|value| ());
diff --git a/tests/ui/methods/method-suggestion-trait-with-extra-generics-no-ice.rs b/tests/ui/methods/method-suggestion-trait-with-extra-generics-no-ice.rs
index 0a98cdef5c923..f204e55f5a578 100644
--- a/tests/ui/methods/method-suggestion-trait-with-extra-generics-no-ice.rs
+++ b/tests/ui/methods/method-suggestion-trait-with-extra-generics-no-ice.rs
@@ -16,7 +16,7 @@ struct Bar;
 
 fn main() {
     let foo: Box<dyn Fn(bool) -> usize> = Box::new(Bar);
-    //~^ ERROR expected a `Fn(bool)` closure, found `Bar`
+    //~^ ERROR expected an `Fn(bool)` closure, found `Bar`
     foo.borrow();
     //~^ ERROR no method named `borrow` found
     foo.take()
diff --git a/tests/ui/methods/method-suggestion-trait-with-extra-generics-no-ice.stderr b/tests/ui/methods/method-suggestion-trait-with-extra-generics-no-ice.stderr
index aa46a41fa3378..73f5f441b3fef 100644
--- a/tests/ui/methods/method-suggestion-trait-with-extra-generics-no-ice.stderr
+++ b/tests/ui/methods/method-suggestion-trait-with-extra-generics-no-ice.stderr
@@ -22,7 +22,7 @@ help: there is a method `borrow_mut` with a similar name
 LL |     foo.borrow_mut();
    |               ++++
 
-error[E0277]: expected a `Fn(bool)` closure, found `Bar`
+error[E0277]: expected an `Fn(bool)` closure, found `Bar`
   --> $DIR/method-suggestion-trait-with-extra-generics-no-ice.rs:18:43
    |
 LL |     let foo: Box<dyn Fn(bool) -> usize> = Box::new(Bar);
diff --git a/tests/ui/mismatched_types/closure-arg-type-mismatch-issue-45727.current.fixed b/tests/ui/mismatched_types/closure-arg-type-mismatch-issue-45727.current.fixed
index c489b6e445dda..b1158e1cbffa7 100644
--- a/tests/ui/mismatched_types/closure-arg-type-mismatch-issue-45727.current.fixed
+++ b/tests/ui/mismatched_types/closure-arg-type-mismatch-issue-45727.current.fixed
@@ -5,10 +5,10 @@
 fn main() {
     let _ = (-10..=10).find(|x: &i32| x.signum() == 0);
     //[current]~^ ERROR type mismatch in closure arguments
-    //[next]~^^ ERROR: expected a `FnMut(&{integer})` closure, found
+    //[next]~^^ ERROR: expected an `FnMut(&{integer})` closure, found
     //[next]~| ERROR: type mismatch resolving `<{closure@closure-arg-type-mismatch-issue-45727.rs:6:29} as FnOnce<(&{integer},)>>::Output == bool`
     let _ = (-10..=10).find(|x: &i32| x.signum() == 0);
     //[current]~^ ERROR type mismatch in closure arguments
-    //[next]~^^ ERROR: expected a `FnMut(&{integer})` closure, found
+    //[next]~^^ ERROR: expected an `FnMut(&{integer})` closure, found
     //[next]~| ERROR: type mismatch resolving `<{closure@closure-arg-type-mismatch-issue-45727.rs:10:29} as FnOnce<(&{integer},)>>::Output == bool`
 }
diff --git a/tests/ui/mismatched_types/closure-arg-type-mismatch-issue-45727.next.stderr b/tests/ui/mismatched_types/closure-arg-type-mismatch-issue-45727.next.stderr
index 412fd53baeb37..eab9bf1ae34a8 100644
--- a/tests/ui/mismatched_types/closure-arg-type-mismatch-issue-45727.next.stderr
+++ b/tests/ui/mismatched_types/closure-arg-type-mismatch-issue-45727.next.stderr
@@ -1,4 +1,4 @@
-error[E0277]: expected a `FnMut(&{integer})` closure, found `{closure@$DIR/closure-arg-type-mismatch-issue-45727.rs:6:29: 6:37}`
+error[E0277]: expected an `FnMut(&{integer})` closure, found `{closure@$DIR/closure-arg-type-mismatch-issue-45727.rs:6:29: 6:37}`
   --> $DIR/closure-arg-type-mismatch-issue-45727.rs:6:29
    |
 LL |     let _ = (-10..=10).find(|x: i32| x.signum() == 0);
@@ -23,7 +23,7 @@ LL |     let _ = (-10..=10).find(|x: i32| x.signum() == 0);
 note: required by a bound in `find`
   --> $SRC_DIR/core/src/iter/traits/iterator.rs:LL:COL
 
-error[E0277]: expected a `FnMut(&{integer})` closure, found `{closure@$DIR/closure-arg-type-mismatch-issue-45727.rs:10:29: 10:40}`
+error[E0277]: expected an `FnMut(&{integer})` closure, found `{closure@$DIR/closure-arg-type-mismatch-issue-45727.rs:10:29: 10:40}`
   --> $DIR/closure-arg-type-mismatch-issue-45727.rs:10:29
    |
 LL |     let _ = (-10..=10).find(|x: &&&i32| x.signum() == 0);
diff --git a/tests/ui/mismatched_types/closure-arg-type-mismatch-issue-45727.rs b/tests/ui/mismatched_types/closure-arg-type-mismatch-issue-45727.rs
index 434b5d3d23110..09f7af7c0253e 100644
--- a/tests/ui/mismatched_types/closure-arg-type-mismatch-issue-45727.rs
+++ b/tests/ui/mismatched_types/closure-arg-type-mismatch-issue-45727.rs
@@ -5,10 +5,10 @@
 fn main() {
     let _ = (-10..=10).find(|x: i32| x.signum() == 0);
     //[current]~^ ERROR type mismatch in closure arguments
-    //[next]~^^ ERROR: expected a `FnMut(&{integer})` closure, found
+    //[next]~^^ ERROR: expected an `FnMut(&{integer})` closure, found
     //[next]~| ERROR: type mismatch resolving `<{closure@closure-arg-type-mismatch-issue-45727.rs:6:29} as FnOnce<(&{integer},)>>::Output == bool`
     let _ = (-10..=10).find(|x: &&&i32| x.signum() == 0);
     //[current]~^ ERROR type mismatch in closure arguments
-    //[next]~^^ ERROR: expected a `FnMut(&{integer})` closure, found
+    //[next]~^^ ERROR: expected an `FnMut(&{integer})` closure, found
     //[next]~| ERROR: type mismatch resolving `<{closure@closure-arg-type-mismatch-issue-45727.rs:10:29} as FnOnce<(&{integer},)>>::Output == bool`
 }
diff --git a/tests/ui/mismatched_types/suggest-option-asderef-unfixable.rs b/tests/ui/mismatched_types/suggest-option-asderef-unfixable.rs
index 42adff43a58f2..445a98cd49630 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 an `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 an `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 a657a65c426d4..14c821b260299 100644
--- a/tests/ui/mismatched_types/suggest-option-asderef-unfixable.stderr
+++ b/tests/ui/mismatched_types/suggest-option-asderef-unfixable.stderr
@@ -18,7 +18,7 @@ help: consider wrapping the function in a closure
 LL |     let _ = produces_string().and_then(|arg0: String| takes_str_but_too_many_refs(/* &&str */));
    |                                        ++++++++++++++                            +++++++++++++
 
-error[E0277]: expected a `FnOnce(String)` closure, found `for<'a> extern "C" fn(&'a str) -> Option<()> {takes_str_but_wrong_abi}`
+error[E0277]: expected an `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);
@@ -30,7 +30,7 @@ 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 an `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 82053a12b133f..b7eaabdf6ad3f 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
@@ -26,15 +26,15 @@ fn call_once_i32(f: impl FnOnce(i32)) {
 }
 
 fn main() {
-    call(foo); //~ ERROR expected a `Fn()` closure, found `#[target_features] fn() {foo}`
-    call_mut(foo); //~ ERROR expected a `FnMut()` closure, found `#[target_features] fn() {foo}`
-    call_once(foo); //~ ERROR expected a `FnOnce()` closure, found `#[target_features] fn() {foo}`
-    call_once_i32(bar); //~ ERROR expected a `FnOnce(i32)` closure, found `#[target_features] fn(i32) {bar}`
+    call(foo); //~ ERROR expected an `Fn()` closure, found `#[target_features] fn() {foo}`
+    call_mut(foo); //~ ERROR expected an `FnMut()` closure, found `#[target_features] fn() {foo}`
+    call_once(foo); //~ ERROR expected an `FnOnce()` closure, found `#[target_features] fn() {foo}`
+    call_once_i32(bar); //~ ERROR expected an `FnOnce(i32)` closure, found `#[target_features] fn(i32) {bar}`
 
     call(foo_unsafe);
-    //~^ ERROR expected a `Fn()` closure, found `unsafe fn() {foo_unsafe}`
+    //~^ ERROR expected an `Fn()` closure, found `unsafe fn() {foo_unsafe}`
     call_mut(foo_unsafe);
-    //~^ ERROR expected a `FnMut()` closure, found `unsafe fn() {foo_unsafe}`
+    //~^ ERROR expected an `FnMut()` closure, found `unsafe fn() {foo_unsafe}`
     call_once(foo_unsafe);
-    //~^ ERROR expected a `FnOnce()` closure, found `unsafe fn() {foo_unsafe}`
+    //~^ ERROR expected an `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 52543caad37db..5333307a59280 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
@@ -1,4 +1,4 @@
-error[E0277]: expected a `Fn()` closure, found `#[target_features] fn() {foo}`
+error[E0277]: expected an `Fn()` closure, found `#[target_features] fn() {foo}`
   --> $DIR/fn-traits.rs:29:10
    |
 LL |     call(foo);
@@ -16,7 +16,7 @@ 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 `#[target_features] fn() {foo}`
+error[E0277]: expected an `FnMut()` closure, found `#[target_features] fn() {foo}`
   --> $DIR/fn-traits.rs:30:14
    |
 LL |     call_mut(foo);
@@ -34,7 +34,7 @@ note: required by a bound in `call_mut`
 LL | fn call_mut(mut f: impl FnMut()) {
    |                         ^^^^^^^ required by this bound in `call_mut`
 
-error[E0277]: expected a `FnOnce()` closure, found `#[target_features] fn() {foo}`
+error[E0277]: expected an `FnOnce()` closure, found `#[target_features] fn() {foo}`
   --> $DIR/fn-traits.rs:31:15
    |
 LL |     call_once(foo);
@@ -52,7 +52,7 @@ 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 `FnOnce(i32)` closure, found `#[target_features] fn(i32) {bar}`
+error[E0277]: expected an `FnOnce(i32)` closure, found `#[target_features] fn(i32) {bar}`
   --> $DIR/fn-traits.rs:32:19
    |
 LL |     call_once_i32(bar);
@@ -69,7 +69,7 @@ note: required by a bound in `call_once_i32`
 LL | fn call_once_i32(f: impl FnOnce(i32)) {
    |                          ^^^^^^^^^^^ required by this bound in `call_once_i32`
 
-error[E0277]: expected a `Fn()` closure, found `unsafe fn() {foo_unsafe}`
+error[E0277]: expected an `Fn()` closure, found `unsafe fn() {foo_unsafe}`
   --> $DIR/fn-traits.rs:34:10
    |
 LL |     call(foo_unsafe);
@@ -88,7 +88,7 @@ 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 an `FnMut()` closure, found `unsafe fn() {foo_unsafe}`
   --> $DIR/fn-traits.rs:36:14
    |
 LL |     call_mut(foo_unsafe);
@@ -107,7 +107,7 @@ note: required by a bound in `call_mut`
 LL | fn call_mut(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 an `FnOnce()` closure, found `unsafe fn() {foo_unsafe}`
   --> $DIR/fn-traits.rs:38:15
    |
 LL |     call_once(foo_unsafe);
diff --git a/tests/ui/suggestions/restrict-bound-already-has-generic-args.rs b/tests/ui/suggestions/restrict-bound-already-has-generic-args.rs
new file mode 100644
index 0000000000000..0350ef50705d9
--- /dev/null
+++ b/tests/ui/suggestions/restrict-bound-already-has-generic-args.rs
@@ -0,0 +1,27 @@
+// Regression test for https://github.com/rust-lang/rust/issues/142803.
+
+trait Pair {
+    type Left;
+    type Right;
+
+    fn split(self) -> (Self::Left, Self::Right);
+}
+
+impl<A, B> Pair for (A, B) {
+    type Left = A;
+    type Right = B;
+
+    fn split(self) -> (Self::Left, Self::Right) {
+        self
+    }
+}
+
+fn frob<A, B>(pair: impl Pair<Left = A>) -> impl Pair<Left = A, Right = B> {
+    //~^ ERROR type mismatch
+    //~| HELP consider further restricting this bound
+    //~| SUGGESTION , Right = B
+    let (left, right) = pair.split();
+    (left, right)
+}
+
+fn main() {}
diff --git a/tests/ui/suggestions/restrict-bound-already-has-generic-args.stderr b/tests/ui/suggestions/restrict-bound-already-has-generic-args.stderr
new file mode 100644
index 0000000000000..a284f2adb366c
--- /dev/null
+++ b/tests/ui/suggestions/restrict-bound-already-has-generic-args.stderr
@@ -0,0 +1,24 @@
+error[E0271]: type mismatch resolving `<(A, <impl Pair<Left = A> as Pair>::Right) as Pair>::Right == B`
+  --> $DIR/restrict-bound-already-has-generic-args.rs:19:45
+   |
+LL | fn frob<A, B>(pair: impl Pair<Left = A>) -> impl Pair<Left = A, Right = B> {
+   |            - expected this type parameter   ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ type mismatch resolving `<(A, <impl Pair<Left = A> as Pair>::Right) as Pair>::Right == B`
+...
+LL |     (left, right)
+   |     ------------- return type was inferred to be `(A, <impl Pair<Left = A> as Pair>::Right)` here
+   |
+note: expected this to be `B`
+  --> $DIR/restrict-bound-already-has-generic-args.rs:12:18
+   |
+LL |     type Right = B;
+   |                  ^
+   = note: expected type parameter `B`
+             found associated type `<impl Pair<Left = A> as Pair>::Right`
+help: consider further restricting this bound
+   |
+LL | fn frob<A, B>(pair: impl Pair<Left = A, Right = B>) -> impl Pair<Left = A, Right = B> {
+   |                                       +++++++++++
+
+error: aborting due to 1 previous error
+
+For more information about this error, try `rustc --explain E0271`.
diff --git a/tests/ui/trait-bounds/mismatch-fn-trait.stderr b/tests/ui/trait-bounds/mismatch-fn-trait.stderr
index 051e660c2d106..a7805e25f651e 100644
--- a/tests/ui/trait-bounds/mismatch-fn-trait.stderr
+++ b/tests/ui/trait-bounds/mismatch-fn-trait.stderr
@@ -1,4 +1,4 @@
-error[E0277]: expected a `FnMut(i32)` closure, found `impl FnMut(u32)`
+error[E0277]: expected an `FnMut(i32)` closure, found `impl FnMut(u32)`
   --> $DIR/mismatch-fn-trait.rs:4:10
    |
 LL |     take(f)
@@ -14,7 +14,7 @@ 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 an `FnMut(i32)` closure, found `impl FnMut(i32, i32)`
   --> $DIR/mismatch-fn-trait.rs:9:10
    |
 LL |     take(f)
@@ -29,7 +29,7 @@ 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 an `FnMut(i32)` closure, found `impl FnMut()`
   --> $DIR/mismatch-fn-trait.rs:14:10
    |
 LL |     take(f)
@@ -44,7 +44,7 @@ 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 an `FnMut(i32)` closure, found `impl FnOnce(i32)`
   --> $DIR/mismatch-fn-trait.rs:19:10
    |
 LL |     take(f)
@@ -59,7 +59,7 @@ 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 an `FnMut(i32)` closure, found `impl FnOnce(u32)`
   --> $DIR/mismatch-fn-trait.rs:24:10
    |
 LL |     take(f)
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 891cc32e7b758..f19c9da7c5eb5 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>>();
-    //~^ ERROR expected a `FnOnce(&i32)` closure, found `i32`
+    //~^ ERROR expected an `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 ebd45b9dd9635..c4bc50746ebba 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
@@ -1,4 +1,4 @@
-error[E0277]: expected a `FnOnce(&i32)` closure, found `i32`
+error[E0277]: expected an `FnOnce(&i32)` closure, found `i32`
   --> $DIR/check-trait-object-bounds-2.rs:13:9
    |
 LL |     f::<dyn for<'x> X<'x, F = i32>>();
diff --git a/tests/ui/traits/issue-87558.stderr b/tests/ui/traits/issue-87558.stderr
index ca908a3062d33..b8b9ea57612b4 100644
--- a/tests/ui/traits/issue-87558.stderr
+++ b/tests/ui/traits/issue-87558.stderr
@@ -32,7 +32,7 @@ LL | impl Fn(&isize) for Error {
    |
    = help: implement the missing item: `fn call(&self, _: (&isize,)) -> <Self as FnOnce<(&isize,)>>::Output { todo!() }`
 
-error[E0277]: expected a `FnMut(&isize)` closure, found `Error`
+error[E0277]: expected an `FnMut(&isize)` closure, found `Error`
   --> $DIR/issue-87558.rs:3:21
    |
 LL | impl Fn(&isize) for Error {
diff --git a/tests/ui/traits/next-solver/diagnostics/const-host-effect-hrtb-no-ice.rs b/tests/ui/traits/next-solver/diagnostics/const-host-effect-hrtb-no-ice.rs
index 8463cb3f6ea1b..a0d1db3ff02b3 100644
--- a/tests/ui/traits/next-solver/diagnostics/const-host-effect-hrtb-no-ice.rs
+++ b/tests/ui/traits/next-solver/diagnostics/const-host-effect-hrtb-no-ice.rs
@@ -7,7 +7,7 @@ const fn with_positive<F: for<'a> [const] Fn(&'a ())>() {}
 
 const _: () = {
     with_positive::<()>();
-    //~^ ERROR expected a `Fn(&'a ())` closure, found `()`
+    //~^ ERROR expected an `Fn(&'a ())` closure, found `()`
     //~| ERROR type mismatch resolving `<() as FnOnce<(&(),)>>::Output == ()`
 };
 
diff --git a/tests/ui/traits/next-solver/diagnostics/const-host-effect-hrtb-no-ice.stderr b/tests/ui/traits/next-solver/diagnostics/const-host-effect-hrtb-no-ice.stderr
index 8ec772a3d7fa8..7b98ba618a727 100644
--- a/tests/ui/traits/next-solver/diagnostics/const-host-effect-hrtb-no-ice.stderr
+++ b/tests/ui/traits/next-solver/diagnostics/const-host-effect-hrtb-no-ice.stderr
@@ -1,4 +1,4 @@
-error[E0277]: expected a `Fn(&'a ())` closure, found `()`
+error[E0277]: expected an `Fn(&'a ())` closure, found `()`
   --> $DIR/const-host-effect-hrtb-no-ice.rs:9:21
    |
 LL |     with_positive::<()>();
diff --git a/tests/ui/traits/next-solver/fn-trait.rs b/tests/ui/traits/next-solver/fn-trait.rs
index 7994dd3052c40..e31d4d2b580a5 100644
--- a/tests/ui/traits/next-solver/fn-trait.rs
+++ b/tests/ui/traits/next-solver/fn-trait.rs
@@ -18,11 +18,11 @@ 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 an `Fn()` closure, found `unsafe fn() -> i32`
     require_fn(g);
-    //~^ ERROR: expected a `Fn()` closure, found `extern "C" fn() -> i32 {g}`
+    //~^ ERROR: expected an `Fn()` closure, found `extern "C" fn() -> i32 {g}`
     require_fn(g as extern "C" fn() -> i32);
-    //~^ ERROR: expected a `Fn()` closure, found `extern "C" fn() -> i32`
+    //~^ ERROR: expected an `Fn()` closure, found `extern "C" fn() -> i32`
     require_fn(h);
-    //~^ ERROR: expected a `Fn()` closure, found `unsafe fn() -> i32 {h}`
+    //~^ ERROR: expected an `Fn()` closure, found `unsafe fn() -> i32 {h}`
 }
diff --git a/tests/ui/traits/next-solver/fn-trait.stderr b/tests/ui/traits/next-solver/fn-trait.stderr
index 77c834f377852..6218928b309f7 100644
--- a/tests/ui/traits/next-solver/fn-trait.stderr
+++ b/tests/ui/traits/next-solver/fn-trait.stderr
@@ -1,4 +1,4 @@
-error[E0277]: expected a `Fn()` closure, found `unsafe fn() -> i32`
+error[E0277]: expected an `Fn()` closure, found `unsafe fn() -> i32`
   --> $DIR/fn-trait.rs:20:16
    |
 LL |     require_fn(f as unsafe fn() -> i32);
@@ -15,7 +15,7 @@ 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 `extern "C" fn() -> i32 {g}`
+error[E0277]: expected an `Fn()` closure, found `extern "C" fn() -> i32 {g}`
   --> $DIR/fn-trait.rs:22:16
    |
 LL |     require_fn(g);
@@ -31,7 +31,7 @@ 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 `extern "C" fn() -> i32`
+error[E0277]: expected an `Fn()` closure, found `extern "C" fn() -> i32`
   --> $DIR/fn-trait.rs:24:16
    |
 LL |     require_fn(g as extern "C" fn() -> i32);
@@ -47,7 +47,7 @@ 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 an `Fn()` closure, found `unsafe fn() -> i32 {h}`
   --> $DIR/fn-trait.rs:26:16
    |
 LL |     require_fn(h);
diff --git a/tests/ui/type-alias-impl-trait/issue-63279.rs b/tests/ui/type-alias-impl-trait/issue-63279.rs
index 10da40d2f90d2..50d4a42e1f355 100644
--- a/tests/ui/type-alias-impl-trait/issue-63279.rs
+++ b/tests/ui/type-alias-impl-trait/issue-63279.rs
@@ -4,11 +4,11 @@ type Closure = impl FnOnce();
 
 #[define_opaque(Closure)]
 fn c() -> Closure {
-    //~^ ERROR: expected a `FnOnce()` closure, found `()`
+    //~^ ERROR: expected an `FnOnce()` closure, found `()`
     || -> Closure { || () }
     //~^ ERROR: mismatched types
     //~| ERROR: mismatched types
-    //~| ERROR: expected a `FnOnce()` closure, found `()`
+    //~| ERROR: expected an `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 8f0e9c5fde04d..165c1c25280bd 100644
--- a/tests/ui/type-alias-impl-trait/issue-63279.stderr
+++ b/tests/ui/type-alias-impl-trait/issue-63279.stderr
@@ -1,4 +1,4 @@
-error[E0277]: expected a `FnOnce()` closure, found `()`
+error[E0277]: expected an `FnOnce()` closure, found `()`
   --> $DIR/issue-63279.rs:6:11
    |
 LL | fn c() -> Closure {
@@ -7,7 +7,7 @@ LL | fn c() -> Closure {
    = 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 an `FnOnce()` closure, found `()`
   --> $DIR/issue-63279.rs:8:11
    |
 LL |     || -> Closure { || () }
diff --git a/tests/ui/type-alias-impl-trait/lazy_subtyping_of_opaques.rs b/tests/ui/type-alias-impl-trait/lazy_subtyping_of_opaques.rs
index 075b0bd75fa53..aec311ede864f 100644
--- a/tests/ui/type-alias-impl-trait/lazy_subtyping_of_opaques.rs
+++ b/tests/ui/type-alias-impl-trait/lazy_subtyping_of_opaques.rs
@@ -8,10 +8,10 @@ type Tait = impl FnOnce() -> ();
 
 #[define_opaque(Tait)]
 fn reify_as_tait() -> Thunk<Tait> {
-    //~^ ERROR: expected a `FnOnce()` closure, found `()`
+    //~^ ERROR: expected an `FnOnce()` closure, found `()`
     Thunk::new(|cont| cont)
     //~^ ERROR: mismatched types
-    //~| ERROR: expected a `FnOnce()` closure, found `()`
+    //~| ERROR: expected an `FnOnce()` closure, found `()`
 }
 
 struct Thunk<F>(F);
diff --git a/tests/ui/type-alias-impl-trait/lazy_subtyping_of_opaques.stderr b/tests/ui/type-alias-impl-trait/lazy_subtyping_of_opaques.stderr
index 0bee0dfa9c7a3..22d16e39fc404 100644
--- a/tests/ui/type-alias-impl-trait/lazy_subtyping_of_opaques.stderr
+++ b/tests/ui/type-alias-impl-trait/lazy_subtyping_of_opaques.stderr
@@ -10,7 +10,7 @@ LL |     Thunk::new(|cont| cont)
    = note: expected struct `Thunk<_>`
            found unit type `()`
 
-error[E0277]: expected a `FnOnce()` closure, found `()`
+error[E0277]: expected an `FnOnce()` closure, found `()`
   --> $DIR/lazy_subtyping_of_opaques.rs:12:23
    |
 LL |     Thunk::new(|cont| cont)
@@ -19,7 +19,7 @@ LL |     Thunk::new(|cont| cont)
    = 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 an `FnOnce()` closure, found `()`
   --> $DIR/lazy_subtyping_of_opaques.rs:10:23
    |
 LL | fn reify_as_tait() -> Thunk<Tait> {
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 0dd6dcfe6a3f2..d579b5bd75002 100644
--- a/tests/ui/unboxed-closures/unboxed-closures-fnmut-as-fn.stderr
+++ b/tests/ui/unboxed-closures/unboxed-closures-fnmut-as-fn.stderr
@@ -1,4 +1,4 @@
-error[E0277]: expected a `Fn(isize)` closure, found `S`
+error[E0277]: expected an `Fn(isize)` closure, found `S`
   --> $DIR/unboxed-closures-fnmut-as-fn.rs:27:21
    |
 LL |     let x = call_it(&S, 22);
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 dfdb3ea19c3f2..a637b180e31e7 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 an `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 an `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 an `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 b4521cc6890d8..25cf793ca00e8 100644
--- a/tests/ui/unboxed-closures/unboxed-closures-wrong-abi.stderr
+++ b/tests/ui/unboxed-closures/unboxed-closures-wrong-abi.stderr
@@ -1,4 +1,4 @@
-error[E0277]: expected a `Fn(&isize)` closure, found `for<'a> extern "C" fn(&'a isize) -> isize {square}`
+error[E0277]: expected an `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);
@@ -13,7 +13,7 @@ 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> extern "C" fn(&'a isize) -> isize {square}`
+error[E0277]: expected an `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);
@@ -28,7 +28,7 @@ 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> extern "C" fn(&'a isize) -> isize {square}`
+error[E0277]: expected an `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);
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 5519bb33ebc27..e09eda3b99d29 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 an `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 an `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 an `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);