Reproduce the underlying issue

nll (and thus the algorithm for actual promotion) don't know about some casts anymore

Author: oli-obk

src/test/ui/consts/dangling-alloc-id-ice-2.nll.stderr

@@ -0,0 +1,30 @@
+warning[E0716]: temporary value dropped while borrowed
+  --> $DIR/dangling-alloc-id-ice-2.rs:5:28
+   |
+LL |    static MAP: Slice = Slice(&[
+   |   ___________________________-^
+   |  |___________________________|
+   | ||
+LL | ||     b"CloseEvent" as &'static [u8],
+LL | || ]);
+   | || -- temporary value is freed at the end of this statement
+   | ||_|
+   | |__creates a temporary which is freed while still in use
+   |    cast requires that borrow lasts for `'static`
+   |
+   = warning: This error has been downgraded to a warning for backwards compatibility with previous releases.
+           It represents potential unsoundness in your code.
+           This warning will become a hard error in the future.
+
+error[E0080]: could not evaluate static initializer
+  --> $DIR/dangling-alloc-id-ice-2.rs:5:1
+   |
+LL | / static MAP: Slice = Slice(&[
+LL | |     b"CloseEvent" as &'static [u8],
+LL | | ]);
+   | |___^ type validation failed: encountered dangling pointer in final constant
+
+error: aborting due to previous error
+
+Some errors occurred: E0080, E0716.
+For more information about an error, try `rustc --explain E0080`.

src/test/ui/consts/dangling-alloc-id-ice-2.rs

@@ -0,0 +1,10 @@
+// https://github.com/rust-lang/rust/issues/55223
+
+struct Slice(&'static [&'static [u8]]);
+
+static MAP: Slice = Slice(&[
+    b"CloseEvent" as &'static [u8],
+]);
+
+
+fn main() {}

src/test/ui/consts/dangling-alloc-id-ice-2.stderr

@@ -0,0 +1,11 @@
+error[E0080]: could not evaluate static initializer
+  --> $DIR/dangling-alloc-id-ice-2.rs:5:1
+   |
+LL | / static MAP: Slice = Slice(&[
+LL | |     b"CloseEvent" as &'static [u8],
+LL | | ]);
+   | |___^ type validation failed: encountered dangling pointer in final constant
+
+error: aborting due to previous error
+
+For more information about this error, try `rustc --explain E0080`.