Auto merge of #86399 - JohnTitor:rollup-qlm2dvz, r=JohnTitor

Rollup of 7 pull requests

Successful merges:

 - #85663 (Document Arc::from)
 - #85802 (Rename IoSlice(Mut)::advance to advance_slice and add IoSlice(Mut)::advance)
 - #85970 (Remove methods under Implementors on trait pages)
 - #86340 (Use better error message for hard errors in CTFE)
 - #86343 (Do not emit invalid suggestions on multiple mutable borrow errors)
 - #86355 (Remove invalid suggestions for assoc consts on placeholder type error)
 - #86389 (Make `sum()` and `product()` documentation hyperlinks refer to `Iterator` methods.)

Failed merges:

r? `@ghost`
`@rustbot` modify labels: rollup

src/test/rustdoc-gui/hash-item-expansion.goml

@@ -2,9 +2,6 @@
 goto: file://|DOC_PATH|/test_docs/struct.Foo.html#method.borrow
 // In the blanket implementations list, "Borrow" is the second one, hence the ":nth(2)".
 assert: ("#blanket-implementations-list > details:nth-child(2)", "open", "")
-// Please note the "\" below is needed because otherwise ".borrow" would be interpreted as
-// a class selector.
-assert: ("#method\.borrow", {"display": "flex"})
 // We first check that the impl block is open by default.
 assert: ("#implementations + details", "open", "")
 // We collapse it.

src/test/rustdoc/ensure-src-link.rs

@@ -2,5 +2,5 @@
 
 // This test ensures that the [src] link is present on traits items.
 
-// @has foo/trait.Iterator.html '//div[@id="method.zip"]/a[@class="srclink"]' "[src]"
+// @has foo/trait.Iterator.html '//div[@id="method.zip"]//a[@class="srclink"]' "[src]"
 pub use std::iter::Iterator;

src/test/rustdoc/issue-19055.rs

@@ -1,20 +0,0 @@
-// @has issue_19055/trait.Any.html
-pub trait Any {}
-
-impl<'any> Any + 'any {
-    // @has - '//*[@id="method.is"]' 'fn is'
-    pub fn is<T: 'static>(&self) -> bool { loop {} }
-
-    // @has - '//*[@id="method.downcast_ref"]' 'fn downcast_ref'
-    pub fn downcast_ref<T: 'static>(&self) -> Option<&T> { loop {} }
-
-    // @has - '//*[@id="method.downcast_mut"]' 'fn downcast_mut'
-    pub fn downcast_mut<T: 'static>(&mut self) -> Option<&mut T> { loop {} }
-}
-
-pub trait Foo {
-    fn foo(&self) {}
-}
-
-// @has - '//*[@id="method.foo"]' 'fn foo'
-impl Foo for Any {}

src/test/rustdoc/src-links-auto-impls.rs

@@ -2,11 +2,11 @@
 
 // @has foo/struct.Unsized.html
 // @has - '//div[@id="impl-Sized"]/code' 'impl !Sized for Unsized'
-// @!has - '//div[@id="impl-Sized"]/a[@class="srclink"]' '[src]'
+// @!has - '//div[@id="impl-Sized"]//a[@class="srclink"]' '[src]'
 // @has - '//div[@id="impl-Sync"]/code' 'impl Sync for Unsized'
-// @!has - '//div[@id="impl-Sync"]/a[@class="srclink"]' '[src]'
+// @!has - '//div[@id="impl-Sync"]//a[@class="srclink"]' '[src]'
 // @has - '//div[@id="impl-Any"]/code' 'impl<T> Any for T'
-// @has - '//div[@id="impl-Any"]/a[@class="srclink"]' '[src]'
+// @has - '//div[@id="impl-Any"]//a[@class="srclink"]' '[src]'
 pub struct Unsized {
     data: [u8],
 }

src/test/rustdoc/trait-impl-items-links-and-anchors.rs

@@ -38,23 +38,15 @@ impl MyTrait for Vec<u8> {
 }
 
 impl MyTrait for MyStruct {
-    // @has trait_impl_items_links_and_anchors/trait.MyTrait.html '//div[@id="associatedtype.Assoc-3"]//a[@class="type"]/@href' #associatedtype.Assoc
-    // @has trait_impl_items_links_and_anchors/trait.MyTrait.html '//div[@id="associatedtype.Assoc-3"]//a[@class="anchor"]/@href' #associatedtype.Assoc-3
     // @has trait_impl_items_links_and_anchors/struct.MyStruct.html '//div[@id="associatedtype.Assoc"]//a[@class="type"]/@href' trait.MyTrait.html#associatedtype.Assoc
     // @has trait_impl_items_links_and_anchors/struct.MyStruct.html '//div[@id="associatedtype.Assoc"]//a[@class="anchor"]/@href' #associatedtype.Assoc
     type Assoc = bool;
-    // @has trait_impl_items_links_and_anchors/trait.MyTrait.html '//div[@id="associatedconstant.VALUE-3"]//a[@class="constant"]/@href' #associatedconstant.VALUE
-    // @has trait_impl_items_links_and_anchors/trait.MyTrait.html '//div[@id="associatedconstant.VALUE-3"]//a[@class="anchor"]/@href' #associatedconstant.VALUE-3
     // @has trait_impl_items_links_and_anchors/struct.MyStruct.html '//div[@id="associatedconstant.VALUE"]//a[@class="constant"]/@href' trait.MyTrait.html#associatedconstant.VALUE
     // @has trait_impl_items_links_and_anchors/struct.MyStruct.html '//div[@id="associatedconstant.VALUE"]//a[@class="anchor"]/@href' #associatedconstant.VALUE
     const VALUE: u32 = 20;
-    // @has trait_impl_items_links_and_anchors/trait.MyTrait.html '//div[@id="method.trait_function-2"]//a[@class="fnname"]/@href' #tymethod.trait_function
-    // @has trait_impl_items_links_and_anchors/trait.MyTrait.html '//div[@id="method.trait_function-2"]//a[@class="anchor"]/@href' #method.trait_function-2
     // @has trait_impl_items_links_and_anchors/struct.MyStruct.html '//div[@id="method.trait_function"]//a[@class="fnname"]/@href' trait.MyTrait.html#tymethod.trait_function
     // @has trait_impl_items_links_and_anchors/struct.MyStruct.html '//div[@id="method.trait_function"]//a[@class="anchor"]/@href' #method.trait_function
     fn trait_function(&self) {}
-    // @has trait_impl_items_links_and_anchors/trait.MyTrait.html '//div[@id="method.defaulted_override-3"]//a[@class="fnname"]/@href' #method.defaulted_override
-    // @has trait_impl_items_links_and_anchors/trait.MyTrait.html '//div[@id="method.defaulted_override-3"]//a[@class="anchor"]/@href' #method.defaulted_override-3
     // @has trait_impl_items_links_and_anchors/struct.MyStruct.html '//div[@id="method.defaulted_override"]//a[@class="fnname"]/@href' trait.MyTrait.html#method.defaulted_override
     // @has trait_impl_items_links_and_anchors/struct.MyStruct.html '//div[@id="method.defaulted_override"]//a[@class="anchor"]/@href' #method.defaulted_override
     fn defaulted_override(&self) {}

src/test/ui/borrowck/issue-85581.rs

@@ -0,0 +1,15 @@
+// Regression test of #85581.
+// Checks not to suggest to add `;` when the second mutable borrow
+// is in the first's scope.
+
+use std::collections::BinaryHeap;
+
+fn foo(heap: &mut BinaryHeap<i32>) {
+    match heap.peek_mut() {
+        Some(_) => { heap.pop(); },
+        //~^ ERROR: cannot borrow `*heap` as mutable more than once at a time
+        None => (),
+    }
+}
+
+fn main() {}

src/test/ui/borrowck/issue-85581.stderr

@@ -0,0 +1,17 @@
+error[E0499]: cannot borrow `*heap` as mutable more than once at a time
+  --> $DIR/issue-85581.rs:9:22
+   |
+LL |     match heap.peek_mut() {
+   |           ---------------
+   |           |
+   |           first mutable borrow occurs here
+   |           a temporary with access to the first borrow is created here ...
+LL |         Some(_) => { heap.pop(); },
+   |                      ^^^^ second mutable borrow occurs here
+...
+LL | }
+   | - ... and the first borrow might be used here, when that temporary is dropped and runs the destructor for type `Option<PeekMut<'_, i32>>`
+
+error: aborting due to previous error
+
+For more information about this error, try `rustc --explain E0499`.

src/test/ui/consts/const-eval/const_panic.rs

@@ -5,31 +5,31 @@
 const MSG: &str = "hello";
 
 const Z: () = std::panic!("cheese");
-//~^ ERROR any use of this value will cause an error
+//~^ ERROR evaluation of constant value failed
 
 const Z2: () = std::panic!();
-//~^ ERROR any use of this value will cause an error
+//~^ ERROR evaluation of constant value failed
 
 const Y: () = std::unreachable!();
-//~^ ERROR any use of this value will cause an error
+//~^ ERROR evaluation of constant value failed
 
 const X: () = std::unimplemented!();
-//~^ ERROR any use of this value will cause an error
+//~^ ERROR evaluation of constant value failed
 //
 const W: () = std::panic!(MSG);
-//~^ ERROR any use of this value will cause an error
+//~^ ERROR evaluation of constant value failed
 
 const Z_CORE: () = core::panic!("cheese");
-//~^ ERROR any use of this value will cause an error
+//~^ ERROR evaluation of constant value failed
 
 const Z2_CORE: () = core::panic!();
-//~^ ERROR any use of this value will cause an error
+//~^ ERROR evaluation of constant value failed
 
 const Y_CORE: () = core::unreachable!();
-//~^ ERROR any use of this value will cause an error
+//~^ ERROR evaluation of constant value failed
 
 const X_CORE: () = core::unimplemented!();
-//~^ ERROR any use of this value will cause an error
+//~^ ERROR evaluation of constant value failed
 
 const W_CORE: () = core::panic!(MSG);
-//~^ ERROR any use of this value will cause an error
+//~^ ERROR evaluation of constant value failed

src/test/ui/consts/const-eval/const_panic.stderr

@@ -1,100 +1,80 @@
-error[E0080]: any use of this value will cause an error
+error[E0080]: evaluation of constant value failed
   --> $DIR/const_panic.rs:7:15
    |
 LL | const Z: () = std::panic!("cheese");
-   | --------------^^^^^^^^^^^^^^^^^^^^^-
-   |               |
-   |               the evaluated program panicked at 'cheese', $DIR/const_panic.rs:7:15
+   |               ^^^^^^^^^^^^^^^^^^^^^ the evaluated program panicked at 'cheese', $DIR/const_panic.rs:7:15
    |
    = note: this error originates in the macro `$crate::panic::panic_2015` (in Nightly builds, run with -Z macro-backtrace for more info)
 
-error[E0080]: any use of this value will cause an error
+error[E0080]: evaluation of constant value failed
   --> $DIR/const_panic.rs:10:16
    |
 LL | const Z2: () = std::panic!();
-   | ---------------^^^^^^^^^^^^^-
-   |                |
-   |                the evaluated program panicked at 'explicit panic', $DIR/const_panic.rs:10:16
+   |                ^^^^^^^^^^^^^ the evaluated program panicked at 'explicit panic', $DIR/const_panic.rs:10:16
    |
    = note: this error originates in the macro `$crate::panic::panic_2015` (in Nightly builds, run with -Z macro-backtrace for more info)
 
-error[E0080]: any use of this value will cause an error
+error[E0080]: evaluation of constant value failed
   --> $DIR/const_panic.rs:13:15
    |
 LL | const Y: () = std::unreachable!();
-   | --------------^^^^^^^^^^^^^^^^^^^-
-   |               |
-   |               the evaluated program panicked at 'internal error: entered unreachable code', $DIR/const_panic.rs:13:15
+   |               ^^^^^^^^^^^^^^^^^^^ the evaluated program panicked at 'internal error: entered unreachable code', $DIR/const_panic.rs:13:15
    |
    = note: this error originates in the macro `$crate::panic::panic_2015` (in Nightly builds, run with -Z macro-backtrace for more info)
 
-error[E0080]: any use of this value will cause an error
+error[E0080]: evaluation of constant value failed
   --> $DIR/const_panic.rs:16:15
    |
 LL | const X: () = std::unimplemented!();
-   | --------------^^^^^^^^^^^^^^^^^^^^^-
-   |               |
-   |               the evaluated program panicked at 'not implemented', $DIR/const_panic.rs:16:15
+   |               ^^^^^^^^^^^^^^^^^^^^^ the evaluated program panicked at 'not implemented', $DIR/const_panic.rs:16:15
    |
    = note: this error originates in the macro `$crate::panic::panic_2015` (in Nightly builds, run with -Z macro-backtrace for more info)
 
-error[E0080]: any use of this value will cause an error
+error[E0080]: evaluation of constant value failed
   --> $DIR/const_panic.rs:19:15
    |
 LL | const W: () = std::panic!(MSG);
-   | --------------^^^^^^^^^^^^^^^^-
-   |               |
-   |               the evaluated program panicked at 'hello', $DIR/const_panic.rs:19:15
+   |               ^^^^^^^^^^^^^^^^ the evaluated program panicked at 'hello', $DIR/const_panic.rs:19:15
    |
    = note: this error originates in the macro `$crate::panic::panic_2015` (in Nightly builds, run with -Z macro-backtrace for more info)
 
-error[E0080]: any use of this value will cause an error
+error[E0080]: evaluation of constant value failed
   --> $DIR/const_panic.rs:22:20
    |
 LL | const Z_CORE: () = core::panic!("cheese");
-   | -------------------^^^^^^^^^^^^^^^^^^^^^^-
-   |                    |
-   |                    the evaluated program panicked at 'cheese', $DIR/const_panic.rs:22:20
+   |                    ^^^^^^^^^^^^^^^^^^^^^^ the evaluated program panicked at 'cheese', $DIR/const_panic.rs:22:20
    |
    = note: this error originates in the macro `$crate::panic::panic_2015` (in Nightly builds, run with -Z macro-backtrace for more info)
 
-error[E0080]: any use of this value will cause an error
+error[E0080]: evaluation of constant value failed
   --> $DIR/const_panic.rs:25:21
    |
 LL | const Z2_CORE: () = core::panic!();
-   | --------------------^^^^^^^^^^^^^^-
-   |                     |
-   |                     the evaluated program panicked at 'explicit panic', $DIR/const_panic.rs:25:21
+   |                     ^^^^^^^^^^^^^^ the evaluated program panicked at 'explicit panic', $DIR/const_panic.rs:25:21
    |
    = note: this error originates in the macro `$crate::panic::panic_2015` (in Nightly builds, run with -Z macro-backtrace for more info)
 
-error[E0080]: any use of this value will cause an error
+error[E0080]: evaluation of constant value failed
   --> $DIR/const_panic.rs:28:20
    |
 LL | const Y_CORE: () = core::unreachable!();
-   | -------------------^^^^^^^^^^^^^^^^^^^^-
-   |                    |
-   |                    the evaluated program panicked at 'internal error: entered unreachable code', $DIR/const_panic.rs:28:20
+   |                    ^^^^^^^^^^^^^^^^^^^^ the evaluated program panicked at 'internal error: entered unreachable code', $DIR/const_panic.rs:28:20
    |
    = note: this error originates in the macro `$crate::panic::panic_2015` (in Nightly builds, run with -Z macro-backtrace for more info)
 
-error[E0080]: any use of this value will cause an error
+error[E0080]: evaluation of constant value failed
   --> $DIR/const_panic.rs:31:20
    |
 LL | const X_CORE: () = core::unimplemented!();
-   | -------------------^^^^^^^^^^^^^^^^^^^^^^-
-   |                    |
-   |                    the evaluated program panicked at 'not implemented', $DIR/const_panic.rs:31:20
+   |                    ^^^^^^^^^^^^^^^^^^^^^^ the evaluated program panicked at 'not implemented', $DIR/const_panic.rs:31:20
    |
    = note: this error originates in the macro `$crate::panic::panic_2015` (in Nightly builds, run with -Z macro-backtrace for more info)
 
-error[E0080]: any use of this value will cause an error
+error[E0080]: evaluation of constant value failed
   --> $DIR/const_panic.rs:34:20
    |
 LL | const W_CORE: () = core::panic!(MSG);
-   | -------------------^^^^^^^^^^^^^^^^^-
-   |                    |
-   |                    the evaluated program panicked at 'hello', $DIR/const_panic.rs:34:20
+   |                    ^^^^^^^^^^^^^^^^^ the evaluated program panicked at 'hello', $DIR/const_panic.rs:34:20
    |
    = note: this error originates in the macro `$crate::panic::panic_2015` (in Nightly builds, run with -Z macro-backtrace for more info)
 

src/test/ui/consts/const-eval/const_panic_libcore_bin.rs

@@ -7,13 +7,13 @@
 use core::panic::PanicInfo;
 
 const Z: () = panic!("cheese");
-//~^ ERROR any use of this value will cause an error
+//~^ ERROR evaluation of constant value failed
 
 const Y: () = unreachable!();
-//~^ ERROR any use of this value will cause an error
+//~^ ERROR evaluation of constant value failed
 
 const X: () = unimplemented!();
-//~^ ERROR any use of this value will cause an error
+//~^ ERROR evaluation of constant value failed
 
 #[lang = "eh_personality"]
 fn eh() {}

src/test/ui/consts/const-eval/const_panic_libcore_bin.stderr

@@ -1,30 +1,24 @@
-error[E0080]: any use of this value will cause an error
+error[E0080]: evaluation of constant value failed
   --> $DIR/const_panic_libcore_bin.rs:9:15
    |
 LL | const Z: () = panic!("cheese");
-   | --------------^^^^^^^^^^^^^^^^-
-   |               |
-   |               the evaluated program panicked at 'cheese', $DIR/const_panic_libcore_bin.rs:9:15
+   |               ^^^^^^^^^^^^^^^^ the evaluated program panicked at 'cheese', $DIR/const_panic_libcore_bin.rs:9:15
    |
    = note: this error originates in the macro `$crate::panic::panic_2015` (in Nightly builds, run with -Z macro-backtrace for more info)
 
-error[E0080]: any use of this value will cause an error
+error[E0080]: evaluation of constant value failed
   --> $DIR/const_panic_libcore_bin.rs:12:15
    |
 LL | const Y: () = unreachable!();
-   | --------------^^^^^^^^^^^^^^-
-   |               |
-   |               the evaluated program panicked at 'internal error: entered unreachable code', $DIR/const_panic_libcore_bin.rs:12:15
+   |               ^^^^^^^^^^^^^^ the evaluated program panicked at 'internal error: entered unreachable code', $DIR/const_panic_libcore_bin.rs:12:15
    |
    = note: this error originates in the macro `$crate::panic::panic_2015` (in Nightly builds, run with -Z macro-backtrace for more info)
 
-error[E0080]: any use of this value will cause an error
+error[E0080]: evaluation of constant value failed
   --> $DIR/const_panic_libcore_bin.rs:15:15
    |
 LL | const X: () = unimplemented!();
-   | --------------^^^^^^^^^^^^^^^^-
-   |               |
-   |               the evaluated program panicked at 'not implemented', $DIR/const_panic_libcore_bin.rs:15:15
+   |               ^^^^^^^^^^^^^^^^ the evaluated program panicked at 'not implemented', $DIR/const_panic_libcore_bin.rs:15:15
    |
    = note: this error originates in the macro `$crate::panic::panic_2015` (in Nightly builds, run with -Z macro-backtrace for more info)
 

src/test/ui/consts/const-eval/panic-assoc-never-type.rs

@@ -9,7 +9,7 @@ struct PrintName;
 
 impl PrintName {
     const VOID: ! = panic!();
-    //~^ ERROR any use of this value will cause an error
+    //~^ ERROR evaluation of constant value failed
 }
 
 fn main() {

src/test/ui/consts/const-eval/panic-assoc-never-type.stderr

@@ -1,10 +1,8 @@
-error[E0080]: any use of this value will cause an error
+error[E0080]: evaluation of constant value failed
   --> $DIR/panic-assoc-never-type.rs:11:21
    |
 LL |     const VOID: ! = panic!();
-   |     ----------------^^^^^^^^-
-   |                     |
-   |                     the evaluated program panicked at 'explicit panic', $DIR/panic-assoc-never-type.rs:11:21
+   |                     ^^^^^^^^ the evaluated program panicked at 'explicit panic', $DIR/panic-assoc-never-type.rs:11:21
    |
    = note: this error originates in the macro `$crate::panic::panic_2015` (in Nightly builds, run with -Z macro-backtrace for more info)
 

src/test/ui/consts/const-eval/panic-never-type.rs

@@ -4,7 +4,7 @@
 #![feature(never_type)]
 
 const VOID: ! = panic!();
-//~^ ERROR any use of this value will cause an error
+//~^ ERROR evaluation of constant value failed
 
 fn main() {
     let _ = VOID;

src/test/ui/consts/const-eval/panic-never-type.stderr

@@ -1,10 +1,8 @@
-error[E0080]: any use of this value will cause an error
+error[E0080]: evaluation of constant value failed
   --> $DIR/panic-never-type.rs:6:17
    |
 LL | const VOID: ! = panic!();
-   | ----------------^^^^^^^^-
-   |                 |
-   |                 the evaluated program panicked at 'explicit panic', $DIR/panic-never-type.rs:6:17
+   |                 ^^^^^^^^ the evaluated program panicked at 'explicit panic', $DIR/panic-never-type.rs:6:17
    |
    = note: this error originates in the macro `$crate::panic::panic_2015` (in Nightly builds, run with -Z macro-backtrace for more info)
 

src/test/ui/consts/const-eval/unwind-abort.rs

@@ -2,7 +2,7 @@
 
 #[unwind(aborts)]
 const fn foo() {
-    panic!() //~ ERROR any use of this value will cause an error
+    panic!() //~ ERROR evaluation of constant value failed
 }
 
 const _: () = foo();

src/test/ui/consts/const-eval/unwind-abort.stderr

@@ -1,4 +1,4 @@
-error[E0080]: any use of this value will cause an error
+error[E0080]: evaluation of constant value failed
   --> $DIR/unwind-abort.rs:5:5
    |
 LL |     panic!()
@@ -6,10 +6,9 @@ LL |     panic!()
    |     |
    |     the evaluated program panicked at 'explicit panic', $DIR/unwind-abort.rs:5:5
    |     inside `foo` at $SRC_DIR/std/src/panic.rs:LL:COL
-   |     inside `_` at $DIR/unwind-abort.rs:8:15
 ...
 LL | const _: () = foo();
-   | --------------------
+   |               ----- inside `_` at $DIR/unwind-abort.rs:8:15
    |
    = note: this error originates in the macro `$crate::panic::panic_2015` (in Nightly builds, run with -Z macro-backtrace for more info)
 

src/test/ui/consts/const-unwrap.stderr

@@ -1,4 +1,4 @@
-error[E0080]: any use of this value will cause an error
+error[E0080]: evaluation of constant value failed
   --> $SRC_DIR/core/src/option.rs:LL:COL
    |
 LL |             None => panic!("called `Option::unwrap()` on a `None` value"),
@@ -6,12 +6,11 @@ LL |             None => panic!("called `Option::unwrap()` on a `None` value"),
    |                     |
    |                     the evaluated program panicked at 'called `Option::unwrap()` on a `None` value', $DIR/const-unwrap.rs:9:38
    |                     inside `Option::<i32>::unwrap` at $SRC_DIR/core/src/panic.rs:LL:COL
-   |                     inside `BAR` at $DIR/const-unwrap.rs:9:18
    | 
-  ::: $DIR/const-unwrap.rs:9:1
+  ::: $DIR/const-unwrap.rs:9:18
    |
 LL | const BAR: i32 = Option::<i32>::None.unwrap();
-   | ----------------------------------------------
+   |                  ---------------------------- inside `BAR` at $DIR/const-unwrap.rs:9:18
    |
    = note: this error originates in the macro `$crate::panic::panic_2015` (in Nightly builds, run with -Z macro-backtrace for more info)
 

src/test/ui/consts/control-flow/assert.const_panic.stderr

@@ -1,10 +1,8 @@
-error[E0080]: any use of this value will cause an error
+error[E0080]: evaluation of constant value failed
   --> $DIR/assert.rs:10:15
    |
 LL | const _: () = assert!(false);
-   | --------------^^^^^^^^^^^^^^-
-   |               |
-   |               the evaluated program panicked at 'assertion failed: false', $DIR/assert.rs:10:15
+   |               ^^^^^^^^^^^^^^ the evaluated program panicked at 'assertion failed: false', $DIR/assert.rs:10:15
    |
    = note: this error originates in the macro `assert` (in Nightly builds, run with -Z macro-backtrace for more info)
 

src/test/ui/consts/control-flow/assert.rs

@@ -9,6 +9,6 @@ const _: () = assert!(true);
 
 const _: () = assert!(false);
 //[stock]~^ ERROR panicking in constants is unstable
-//[const_panic]~^^ ERROR any use of this value will cause an error
+//[const_panic]~^^ ERROR evaluation of constant value failed
 
 fn main() {}

src/test/ui/typeck/type-placeholder-fn-in-const.rs

@@ -0,0 +1,14 @@
+struct MyStruct;
+
+trait Test {
+    const TEST: fn() -> _;
+    //~^ ERROR: the type placeholder `_` is not allowed within types on item signatures [E0121]
+    //~| ERROR: the type placeholder `_` is not allowed within types on item signatures [E0121]
+}
+
+impl Test for MyStruct {
+    const TEST: fn() -> _ = 42;
+    //~^ ERROR: the type placeholder `_` is not allowed within types on item signatures [E0121]
+}
+
+fn main() {}

src/test/ui/typeck/type-placeholder-fn-in-const.stderr

@@ -0,0 +1,21 @@
+error[E0121]: the type placeholder `_` is not allowed within types on item signatures
+  --> $DIR/type-placeholder-fn-in-const.rs:4:25
+   |
+LL |     const TEST: fn() -> _;
+   |                         ^ not allowed in type signatures
+
+error[E0121]: the type placeholder `_` is not allowed within types on item signatures
+  --> $DIR/type-placeholder-fn-in-const.rs:4:25
+   |
+LL |     const TEST: fn() -> _;
+   |                         ^ not allowed in type signatures
+
+error[E0121]: the type placeholder `_` is not allowed within types on item signatures
+  --> $DIR/type-placeholder-fn-in-const.rs:10:25
+   |
+LL |     const TEST: fn() -> _ = 42;
+   |                         ^ not allowed in type signatures
+
+error: aborting due to 3 previous errors
+
+For more information about this error, try `rustc --explain E0121`.