Document that assert! format arguments are evaluated lazily
#82169
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@bors r+ rollup |
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📌 Commit 21293582fe02785cb2978d080915d7886e15acf4 has been approved by |
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@bors r- CI is failing. |
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It can be useful to do some computation in `assert!` format arguments, in order to get better error messages. For example:
```rust
assert!(
some_condition,
"The state is invalid. Details: {}",
expensive_call_to_get_debugging_info(),
);
```
It seems like `assert!` only evaluates the format arguments if the assertion fails, which is useful but doesn't appear to be documented anywhere. This PR documents the behavior and adds some tests.
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CI is hopefully fixed now. @rustbot label -S-waiting-on-author +S-waiting-on-review |
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| #[allow(unreachable_code)] | ||
| fn main() { | ||
| assert!(true, "Failed: {:?}", panic!("assert! evaluated format expressions")); | ||
| debug_assert!(true, "Failed: {:?}", panic!("debug_assert! evaluated format expressions")); |
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Are debug assertions disabled for tests? If so, this doesn't test what is intended.
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I believe it does right?
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From trying it out, it looks like the debug assertions were indeed disabled for this test, so I updated it to ensure they're enabled. (I verified that the test now fails when debug_assert!(true, ...) is changed to debug_assert!(false, ...).
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@bors r+ rollup |
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📌 Commit 15197cb has been approved by |
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…laumeGomez Rollup of 11 pull requests Successful merges: - rust-lang#79981 (Add 'consider using' message to overflowing_literals) - rust-lang#82094 (To digit simplification) - rust-lang#82105 (Don't fail to remove files if they are missing) - rust-lang#82136 (Fix ICE: Use delay_span_bug for mismatched subst/hir arg) - rust-lang#82169 (Document that `assert!` format arguments are evaluated lazily) - rust-lang#82174 (Replace File::create and write_all with fs::write) - rust-lang#82196 (Add caveat to Path::display() about lossiness) - rust-lang#82198 (Use internal iteration in Iterator::is_sorted_by) - rust-lang#82204 (Update books) - rust-lang#82207 (rustdoc: treat edition 2021 as unstable) - rust-lang#82231 (Add long explanation for E0543) Failed merges: r? `@ghost` `@rustbot` modify labels: rollup
It can be useful to do some computation in
assert!format arguments, in order to get better error messages. For example:It seems like
assert!only evaluates the format arguments if the assertion fails, which is useful but doesn't appear to be documented anywhere. This PR documents the behavior and adds some tests.