Emit feature gate suggestion

src/test/ui/consts/min_const_fn/min_const_fn_unsafe.rs

@@ -18,13 +18,13 @@ const fn no_unsafe() { unsafe {} }
 
 // not ok
 const fn foo8() -> i32 {
-    unsafe { foo4() } //~ ERROR unsafe operations are not allowed in const fn
+    unsafe { foo4() } //~ ERROR calls to `const unsafe fn` in const fns are unstable
 }
 const fn foo9() -> *const String {
-    unsafe { foo5::<String>() } //~ ERROR unsafe operations are not allowed in const fn
+    unsafe { foo5::<String>() } //~ ERROR calls to `const unsafe fn` in const fns are unstable
 }
 const fn foo10() -> *const Vec<std::cell::Cell<u32>> {
-    unsafe { foo6::<Vec<std::cell::Cell<u32>>>() } //~ ERROR not allowed in const fn
+    unsafe { foo6::<Vec<std::cell::Cell<u32>>>() } //~ ERROR calls to `const unsafe fn` in const fns
 }
 const unsafe fn foo30_3(x: *mut usize) -> usize { *x } //~ ERROR not allowed in const fn
 //~^ dereferencing raw pointers in constant functions

src/test/ui/consts/min_const_fn/min_const_fn_unsafe.stderr

@@ -14,29 +14,29 @@ LL |     Foo { x: () }.y //~ ERROR not allowed in const fn
    |
    = help: add #![feature(const_fn_union)] to the crate attributes to enable
 
-error: call to unsafe function is unsafe and unsafe operations are not allowed in const fn
+error[E0658]: calls to `const unsafe fn` in const fns are unstable (see issue #55607)
   --> $DIR/min_const_fn_unsafe.rs:21:14
    |
-LL |     unsafe { foo4() } //~ ERROR unsafe operations are not allowed in const fn
-   |              ^^^^^^ call to unsafe function
+LL |     unsafe { foo4() } //~ ERROR calls to `const unsafe fn` in const fns are unstable
+   |              ^^^^^^
    |
-   = note: consult the function's documentation for information on how to avoid undefined behavior
+   = help: add #![feature(min_const_unsafe_fn)] to the crate attributes to enable
 
-error: call to unsafe function is unsafe and unsafe operations are not allowed in const fn
+error[E0658]: calls to `const unsafe fn` in const fns are unstable (see issue #55607)
   --> $DIR/min_const_fn_unsafe.rs:24:14
    |
-LL |     unsafe { foo5::<String>() } //~ ERROR unsafe operations are not allowed in const fn
-   |              ^^^^^^^^^^^^^^^^ call to unsafe function
+LL |     unsafe { foo5::<String>() } //~ ERROR calls to `const unsafe fn` in const fns are unstable
+   |              ^^^^^^^^^^^^^^^^
    |
-   = note: consult the function's documentation for information on how to avoid undefined behavior
+   = help: add #![feature(min_const_unsafe_fn)] to the crate attributes to enable
 
-error: call to unsafe function is unsafe and unsafe operations are not allowed in const fn
+error[E0658]: calls to `const unsafe fn` in const fns are unstable (see issue #55607)
   --> $DIR/min_const_fn_unsafe.rs:27:14
    |
-LL |     unsafe { foo6::<Vec<std::cell::Cell<u32>>>() } //~ ERROR not allowed in const fn
-   |              ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ call to unsafe function
+LL |     unsafe { foo6::<Vec<std::cell::Cell<u32>>>() } //~ ERROR calls to `const unsafe fn` in const fns
+   |              ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
    |
-   = note: consult the function's documentation for information on how to avoid undefined behavior
+   = help: add #![feature(min_const_unsafe_fn)] to the crate attributes to enable
 
 error: dereference of raw pointer is unsafe and unsafe operations are not allowed in const fn
   --> $DIR/min_const_fn_unsafe.rs:29:51