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Description
I tried this code:
static __CALLSITE: tracing::callsite::DefaultCallsite = {
const META: tracing::Metadata<'static> = {
tracing::Metadata::new(
"my span",
"tracing_test::a",
tracing::Level::ERROR,
Some("src/a.rs"),
Some(35u32),
Some("tracing_test::a"),
tracing::field::FieldSet::new(
&["message"],
tracing::callsite::Identifier(&__CALLSITE),
),
tracing::metadata::Kind::SPAN,
)
};
tracing::callsite::DefaultCallsite::new(&META)
};I expected to see this happen: Either it fails to compile due to a type error or it compiles successfully.
Instead, this happened: "it is undefined behavior to use this value"
Here's a self-contained reproducer:
use std::sync::atomic::*;
static FOO: AtomicU32 = AtomicU32::new(0);
const C: &'static AtomicU32 = &FOO;yields
error[E0080]: it is undefined behavior to use this value
--> src/lib.rs:4:1
|
4 | const C: &'static AtomicU32 = &FOO;
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^ constructing invalid value: encountered reference to mutable memory in `const`
|
= note: The rules on what exactly is undefined behavior aren't clear, so this check might be overzealous. Please open an issue on the rustc repository if you believe it should not be considered undefined behavior.
= note: the raw bytes of the constant (size: 8, align: 8) {
╾───────alloc1────────╼ │ ╾──────╼
}
I lost context on "constants referencing statics" so I am not sure right now whether this is just a poorly worded error message, or whether there's some static check that should have caught this earlier but for some reason did not.
Cc @rust-lang/wg-const-eval
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Area: Constant evaluation, covers all const contexts (static, const fn, ...)Category: This is a bug.Items that are on lang's radar and will need eventual work or consideration.Relevant to the compiler team, which will review and decide on the PR/issue.Relevant to the language team, which will review and decide on the PR/issue.