A compile-time const variable is referring to a thread-local static variable.

Erroneous code example:

#![feature(thread_local)]

#[thread_local]
static X: usize = 12;

const Y: usize = 2 * X;

Static and const variables can refer to other const variables but a const variable cannot refer to a thread-local static variable. In this example, Y cannot refer to X. To fix this, the value can be extracted as a const and then used:

#![feature(thread_local)]

const C: usize = 12;

#[thread_local]
static X: usize = C;

const Y: usize = 2 * C;