pub static NON_EXHAUSTIVE_OMITTED_PATTERNS: &'static Lint
Expand description
The non_exhaustive_omitted_patterns
lint detects when a wildcard (_
or ..
) in a
pattern for a #[non_exhaustive]
struct or enum is reachable.
Example
ⓘ
// crate A
#[non_exhaustive]
pub enum Bar {
A,
B, // added variant in non breaking change
}
// in crate B
#![feature(non_exhaustive_omitted_patterns_lint)]
match Bar::A {
Bar::A => {},
#[warn(non_exhaustive_omitted_patterns)]
_ => {},
}
This will produce:
warning: reachable patterns not covered of non exhaustive enum
--> $DIR/reachable-patterns.rs:70:9
|
LL | _ => {}
| ^ pattern `B` not covered
|
note: the lint level is defined here
--> $DIR/reachable-patterns.rs:69:16
|
LL | #[warn(non_exhaustive_omitted_patterns)]
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
= help: ensure that all possible cases are being handled by adding the suggested match arms
= note: the matched value is of type `Bar` and the `non_exhaustive_omitted_patterns` attribute was found
Explanation
Structs and enums tagged with #[non_exhaustive]
force the user to add a
(potentially redundant) wildcard when pattern-matching, to allow for future
addition of fields or variants. The non_exhaustive_omitted_patterns
lint
detects when such a wildcard happens to actually catch some fields/variants.
In other words, when the match without the wildcard would not be exhaustive.
This lets the user be informed if new fields/variants were added.