Rollup merge of #50788 - varkor:missing-const-cast, r=cramertj

Fix an ICE when casting a nonexistent const

Fixes https://github.com/rust-lang/rust/issues/50599.

src/test/ui/issue-50599.rs

@@ -0,0 +1,15 @@
+// Copyright 2018 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+fn main() {
+    const N: u32 = 1_000;
+    const M: usize = (f64::from(N) * std::f64::LOG10_2) as usize; //~ ERROR cannot find value
+    let mut digits = [0u32; M];
+}

src/test/ui/issue-50599.stderr

@@ -0,0 +1,15 @@
+error[E0425]: cannot find value `LOG10_2` in module `std::f64`
+  --> $DIR/issue-50599.rs:13:48
+   |
+LL |     const M: usize = (f64::from(N) * std::f64::LOG10_2) as usize; //~ ERROR cannot find value
+   |                                                ^^^^^^^ not found in `std::f64`
+help: possible candidates are found in other modules, you can import them into scope
+   |
+LL | use std::f32::consts::LOG10_2;
+   |
+LL | use std::f64::consts::LOG10_2;
+   |
+
+error: aborting due to previous error
+
+For more information about this error, try `rustc --explain E0425`.