size_of_val is allowed on an uninitialized static

I don't know if this is a bug or working as intended. So I'm filing an issue just in case.

trait Trait {}
impl Trait for usize {}

static X: usize = std::mem::size_of_val(&X as &dyn Trait);

fn main() {
    println!("{X}");
}

This code compiles and prints 8. I'm not sure if this code is supposed to compile.

See also https://github.com/rust-lang/rust/issues/142532 and https://github.com/rust-lang/rust/issues/142404 for shenanigans with uninitialized statics.

Meta

rustc --version --verbose:

rustc 1.89.0-nightly (be19eda0d 2025-06-22)
binary: rustc
commit-hash: be19eda0dc4c22c5cf5f1b48fd163acf9bd4b0a6
commit-date: 2025-06-22
host: aarch64-apple-darwin
release: 1.89.0-nightly
LLVM version: 20.1.7

@rustbot labels +A-const-eval

Start by compiling the supplied Rust reproduction with the reported nightly version and compare its behavior with issues #142532 and #142404. The issue names no source file or test; progress would require establishing whether this const-evaluation behavior is valid and documenting a clear expected outcome.