const functions can assert! but cannot assert_eq!
Open
Nobody has claimed this yet.
A-const-eval
A-trait-system
C-feature-request
T-libs
- Dominant language
- Rust
- Stars
- 119k
- Forks
- 16.1k
- PR merge metrics
- PR metrics pending
Description
This is probably a well-known limitation, but I couldn't find any other issues for it with a quick search. Apologies if it's a duplicate.
// compiles
pub const fn foo() {
assert!(1 == 1);
}
// does not compile
pub const fn bar() {
assert_eq!(1, 1);
}
error[E0015]: cannot call non-const fn `core::panicking::assert_failed::<i32, i32>` in constant functions
--> src/lib.rs:6:5
|
6 | assert_eq!(1, 1);
| ^^^^^^^^^^^^^^^^
|
Can core::panicking::assert_failed be made const?
Contributor guide
First steps
- Read the whole issue, then the project's contributing guide.
- Comment on the issue to say you are picking it up — it saves two people doing the same work.
- Fork the repository and make your change on a branch.
- Open a pull request that references the issue number.
Research direction
Start with the const-function reproduction in src/lib.rs and the reported error for core::panicking::assert_failed. Trace how assert! and assert_eq! expand, then determine whether assert_failed can be const; done means the shown assert_eq! example compiles in a const fn without the reported E0015 error.
Written by the indexing model from the issue text.
Assessment
- Tech stack
- rust
- Domain
- compilers
- Issue type
- Feature
- Difficulty
- 4/5
- Estimated time
- 3-5 days
- Activity status
- Stale
- Clarity
- Mostly clear
- Newbie friendliness
- 35/100