diff --git a/src/libstd/future.rs b/src/libstd/future.rs
index f74c84e6dfd48..7b1beb1ecda80 100644
--- a/src/libstd/future.rs
+++ b/src/libstd/future.rs
@@ -16,9 +16,10 @@ pub use core::future::*;
 ///
 /// This function returns a `GenFuture` underneath, but hides it in `impl Trait` to give
 /// better error messages (`impl Future` rather than `GenFuture<[closure.....]>`).
+// This is `const` to avoid extra errors after we recover from `const async fn`
 #[doc(hidden)]
 #[unstable(feature = "gen_future", issue = "50547")]
-pub fn from_generator<T: Generator<Yield = ()>>(x: T) -> impl Future<Output = T::Return> {
+pub const fn from_generator<T: Generator<Yield = ()>>(x: T) -> impl Future<Output = T::Return> {
     GenFuture(x)
 }
 
diff --git a/src/test/ui/async-await/no-const-async.rs b/src/test/ui/async-await/no-const-async.rs
index b3c59734e036f..57a9f175ca318 100644
--- a/src/test/ui/async-await/no-const-async.rs
+++ b/src/test/ui/async-await/no-const-async.rs
@@ -3,3 +3,4 @@
 
 pub const async fn x() {}
 //~^ ERROR functions cannot be both `const` and `async`
+//~| ERROR `impl Trait` in const fn is unstable
diff --git a/src/test/ui/async-await/no-const-async.stderr b/src/test/ui/async-await/no-const-async.stderr
index f6ae0f1447ced..07559cd240bb6 100644
--- a/src/test/ui/async-await/no-const-async.stderr
+++ b/src/test/ui/async-await/no-const-async.stderr
@@ -7,5 +7,15 @@ LL | pub const async fn x() {}
    |     |     `async` because of this
    |     `const` because of this
 
-error: aborting due to previous error
+error[E0723]: `impl Trait` in const fn is unstable
+  --> $DIR/no-const-async.rs:4:24
+   |
+LL | pub const async fn x() {}
+   |                        ^
+   |
+   = note: see issue #57563 <https://github.com/rust-lang/rust/issues/57563> for more information
+   = help: add `#![feature(const_fn)]` to the crate attributes to enable
+
+error: aborting due to 2 previous errors
 
+For more information about this error, try `rustc --explain E0723`.
diff --git a/src/test/ui/borrowck/borrow-immutable-upvar-mutation-impl-trait.rs b/src/test/ui/borrowck/borrow-immutable-upvar-mutation-impl-trait.rs
new file mode 100644
index 0000000000000..57198cb95e770
--- /dev/null
+++ b/src/test/ui/borrowck/borrow-immutable-upvar-mutation-impl-trait.rs
@@ -0,0 +1,14 @@
+#![feature(unboxed_closures)]
+
+// Tests that we can't assign to or mutably borrow upvars from `Fn`
+// closures (issue #17780)
+
+fn main() {}
+
+fn bar() -> impl Fn() -> usize {
+    let mut x = 0;
+    move || {
+        x += 1; //~ ERROR cannot assign
+        x
+    }
+}
diff --git a/src/test/ui/borrowck/borrow-immutable-upvar-mutation-impl-trait.stderr b/src/test/ui/borrowck/borrow-immutable-upvar-mutation-impl-trait.stderr
new file mode 100644
index 0000000000000..003c40d27736d
--- /dev/null
+++ b/src/test/ui/borrowck/borrow-immutable-upvar-mutation-impl-trait.stderr
@@ -0,0 +1,16 @@
+error[E0594]: cannot assign to `x`, as it is a captured variable in a `Fn` closure
+  --> $DIR/borrow-immutable-upvar-mutation-impl-trait.rs:11:9
+   |
+LL |   fn bar() -> impl Fn() -> usize {
+   |      ---      ------------------ change this to return `FnMut` instead of `Fn`
+LL |       let mut x = 0;
+LL | /     move || {
+LL | |         x += 1;
+   | |         ^^^^^^ cannot assign
+LL | |         x
+LL | |     }
+   | |_____- in this closure
+
+error: aborting due to previous error
+
+For more information about this error, try `rustc --explain E0594`.
diff --git a/src/test/ui/borrowck/borrow-immutable-upvar-mutation.rs b/src/test/ui/borrowck/borrow-immutable-upvar-mutation.rs
index 62e27bcf1643f..e2f016614bf86 100644
--- a/src/test/ui/borrowck/borrow-immutable-upvar-mutation.rs
+++ b/src/test/ui/borrowck/borrow-immutable-upvar-mutation.rs
@@ -3,10 +3,16 @@
 // Tests that we can't assign to or mutably borrow upvars from `Fn`
 // closures (issue #17780)
 
-fn set(x: &mut usize) { *x = 5; }
+fn set(x: &mut usize) {
+    *x = 5;
+}
 
-fn to_fn<A,F:Fn<A>>(f: F) -> F { f }
-fn to_fn_mut<A,F:FnMut<A>>(f: F) -> F { f }
+fn to_fn<A, F: Fn<A>>(f: F) -> F {
+    f
+}
+fn to_fn_mut<A, F: FnMut<A>>(f: F) -> F {
+    f
+}
 
 fn main() {
     // By-ref captures
@@ -33,7 +39,11 @@ fn main() {
         let _g = to_fn(move || set(&mut y)); //~ ERROR cannot borrow
 
         let mut z = 0;
-        let _h = to_fn_mut(move || { set(&mut z); to_fn(move || z = 42); }); //~ ERROR cannot assign
+        let _h = to_fn_mut(move || {
+            set(&mut z);
+            to_fn(move || z = 42);
+            //~^ ERROR cannot assign
+        });
     }
 }
 
@@ -44,11 +54,3 @@ fn foo() -> Box<dyn Fn() -> usize> {
         x
     })
 }
-
-fn bar() -> impl Fn() -> usize {
-    let mut x = 0;
-    move || {
-        x += 1; //~ ERROR cannot assign
-        x
-    }
-}
diff --git a/src/test/ui/borrowck/borrow-immutable-upvar-mutation.stderr b/src/test/ui/borrowck/borrow-immutable-upvar-mutation.stderr
index 3046b047d00f6..a28cb7431e6a9 100644
--- a/src/test/ui/borrowck/borrow-immutable-upvar-mutation.stderr
+++ b/src/test/ui/borrowck/borrow-immutable-upvar-mutation.stderr
@@ -1,8 +1,8 @@
 error[E0594]: cannot assign to `x`, as it is a captured variable in a `Fn` closure
-  --> $DIR/borrow-immutable-upvar-mutation.rs:15:27
+  --> $DIR/borrow-immutable-upvar-mutation.rs:21:27
    |
-LL | fn to_fn<A,F:Fn<A>>(f: F) -> F { f }
-   |                        - change this to accept `FnMut` instead of `Fn`
+LL | fn to_fn<A, F: Fn<A>>(f: F) -> F {
+   |                          - change this to accept `FnMut` instead of `Fn`
 ...
 LL |         let _f = to_fn(|| x = 42);
    |                  -----    ^^^^^^ cannot assign
@@ -10,10 +10,10 @@ LL |         let _f = to_fn(|| x = 42);
    |                  expects `Fn` instead of `FnMut`
 
 error[E0596]: cannot borrow `y` as mutable, as it is a captured variable in a `Fn` closure
-  --> $DIR/borrow-immutable-upvar-mutation.rs:18:31
+  --> $DIR/borrow-immutable-upvar-mutation.rs:24:31
    |
-LL | fn to_fn<A,F:Fn<A>>(f: F) -> F { f }
-   |                        - change this to accept `FnMut` instead of `Fn`
+LL | fn to_fn<A, F: Fn<A>>(f: F) -> F {
+   |                          - change this to accept `FnMut` instead of `Fn`
 ...
 LL |         let _g = to_fn(|| set(&mut y));
    |                  -----        ^^^^^^ cannot borrow as mutable
@@ -21,10 +21,10 @@ LL |         let _g = to_fn(|| set(&mut y));
    |                  expects `Fn` instead of `FnMut`
 
 error[E0594]: cannot assign to `z`, as it is a captured variable in a `Fn` closure
-  --> $DIR/borrow-immutable-upvar-mutation.rs:23:22
+  --> $DIR/borrow-immutable-upvar-mutation.rs:29:22
    |
-LL | fn to_fn<A,F:Fn<A>>(f: F) -> F { f }
-   |                        - change this to accept `FnMut` instead of `Fn`
+LL | fn to_fn<A, F: Fn<A>>(f: F) -> F {
+   |                          - change this to accept `FnMut` instead of `Fn`
 ...
 LL |             to_fn(|| z = 42);
    |             -----    ^^^^^^ cannot assign
@@ -32,10 +32,10 @@ LL |             to_fn(|| z = 42);
    |             expects `Fn` instead of `FnMut`
 
 error[E0594]: cannot assign to `x`, as it is a captured variable in a `Fn` closure
-  --> $DIR/borrow-immutable-upvar-mutation.rs:30:32
+  --> $DIR/borrow-immutable-upvar-mutation.rs:36:32
    |
-LL | fn to_fn<A,F:Fn<A>>(f: F) -> F { f }
-   |                        - change this to accept `FnMut` instead of `Fn`
+LL | fn to_fn<A, F: Fn<A>>(f: F) -> F {
+   |                          - change this to accept `FnMut` instead of `Fn`
 ...
 LL |         let _f = to_fn(move || x = 42);
    |                  -----         ^^^^^^ cannot assign
@@ -43,10 +43,10 @@ LL |         let _f = to_fn(move || x = 42);
    |                  expects `Fn` instead of `FnMut`
 
 error[E0596]: cannot borrow `y` as mutable, as it is a captured variable in a `Fn` closure
-  --> $DIR/borrow-immutable-upvar-mutation.rs:33:36
+  --> $DIR/borrow-immutable-upvar-mutation.rs:39:36
    |
-LL | fn to_fn<A,F:Fn<A>>(f: F) -> F { f }
-   |                        - change this to accept `FnMut` instead of `Fn`
+LL | fn to_fn<A, F: Fn<A>>(f: F) -> F {
+   |                          - change this to accept `FnMut` instead of `Fn`
 ...
 LL |         let _g = to_fn(move || set(&mut y));
    |                  -----             ^^^^^^ cannot borrow as mutable
@@ -54,18 +54,18 @@ LL |         let _g = to_fn(move || set(&mut y));
    |                  expects `Fn` instead of `FnMut`
 
 error[E0594]: cannot assign to `z`, as it is a captured variable in a `Fn` closure
-  --> $DIR/borrow-immutable-upvar-mutation.rs:36:65
+  --> $DIR/borrow-immutable-upvar-mutation.rs:44:27
    |
-LL | fn to_fn<A,F:Fn<A>>(f: F) -> F { f }
-   |                        - change this to accept `FnMut` instead of `Fn`
+LL | fn to_fn<A, F: Fn<A>>(f: F) -> F {
+   |                          - change this to accept `FnMut` instead of `Fn`
 ...
-LL |         let _h = to_fn_mut(move || { set(&mut z); to_fn(move || z = 42); });
-   |                                                   -----         ^^^^^^ cannot assign
-   |                                                   |
-   |                                                   expects `Fn` instead of `FnMut`
+LL |             to_fn(move || z = 42);
+   |             -----         ^^^^^^ cannot assign
+   |             |
+   |             expects `Fn` instead of `FnMut`
 
 error[E0594]: cannot assign to `x`, as it is a captured variable in a `Fn` closure
-  --> $DIR/borrow-immutable-upvar-mutation.rs:43:9
+  --> $DIR/borrow-immutable-upvar-mutation.rs:53:9
    |
 LL |   fn foo() -> Box<dyn Fn() -> usize> {
    |      ---      ---------------------- change this to return `FnMut` instead of `Fn`
@@ -78,20 +78,7 @@ LL | |         x
 LL | |     })
    | |_____- in this closure
 
-error[E0594]: cannot assign to `x`, as it is a captured variable in a `Fn` closure
-  --> $DIR/borrow-immutable-upvar-mutation.rs:51:9
-   |
-LL |   fn bar() -> impl Fn() -> usize {
-   |      ---      ------------------ change this to return `FnMut` instead of `Fn`
-LL |       let mut x = 0;
-LL | /     move || {
-LL | |         x += 1;
-   | |         ^^^^^^ cannot assign
-LL | |         x
-LL | |     }
-   | |_____- in this closure
-
-error: aborting due to 8 previous errors
+error: aborting due to 7 previous errors
 
 Some errors have detailed explanations: E0594, E0596.
 For more information about an error, try `rustc --explain E0594`.