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Confusing error messages when a pattern match contains .foo() expressions #107523
Description
Code
#[derive(Debug, PartialEq)]
enum Pet {
Dog(String),
}
fn main() {
let d = Pet::Dog("fido".to_string());
// Intended.
assert_eq!(d, Pet::Dog("fido".to_string()));
// What I wrote by accident.
assert!(matches!(d, Pet::Dog("fido".to_string())));
}Current output
error: expected one of `)`, `,`, `...`, `..=`, `..`, or `|`, found `.`
--> src/main.rs:14:40
|
14 | assert!(matches!(d, Pet::Dog("fido".to_string())));
| ^
| |
| expected one of `)`, `,`, `...`, `..=`, `..`, or `|`
| help: missing `,`
error[E0531]: cannot find tuple struct or tuple variant `to_string` in this scope
--> src/main.rs:14:41
|
14 | assert!(matches!(d, Pet::Dog("fido".to_string())));
| ^^^^^^^^^ not found in this scope
error[E0023]: this pattern has 2 fields, but the corresponding tuple variant has 1 field
--> src/main.rs:14:34
|
3 | Dog(String),
| ------ tuple variant has 1 field
...
14 | assert!(matches!(d, Pet::Dog("fido".to_string())));
| ^^^^^^ ^^^^^^^^^^^ expected 1 field, found 2Desired output
No response
Rationale and extra context
The third message is really confusing: I think rustc has assumed I intended "fido", to_string()? It's surprising to see an error talk about a field with two patterns.
Other cases
No response
Anything else?
No response
Activity
mejrs commentedon Jan 31, 2023
It seems that
expands to
fmease commentedon Feb 29, 2024
For the manually expanded
matchform we now provide a better error message since #118625:For the
matches!form, nothing has changed because we generally no longer try to recover anything inside of a macro context to prevent issues of the form #103534 (we haven't updated the entirety of the parser yet though that's why the issue is still open). Ideally, we would actually do that but due to the way macro matching is implemented, recovery is oftentimes observable by macros and may lead to breakage.