Description
Proposal
Add a new lint that checks for missing patterns in matches and destructuring assignment of non_exhaustive enums and structs.
This was suggested in the original non_exhaustive PR rust-lang/rust#45394 and there is an open issue rust-lang/rust#84332 for this lint as well as a very early PR rust-lang/rust#86809.
If the attribute is put on the wildcard pattern there is this issue with .. rust-lang/rust#81282.
Example
// crate x
#[non_exhaustive]
pub struct Foo {
a: u8,
b: usize,
c: String,
}
#[non_exhaustive]
pub enum Bar {
A,
B,
C,
}
// crate y
match Bar::A {
Bar::A => {},
Bar::B => {},
#[deny(reachable)] // attribute goes here or on the expresion
_ => {} // triggers lint "missing Bar::C..."
}
let Foo {
a
b,
#[warn(reachable)]
.. // triggers lint "missing field `c`..."
} = structure;Summary and problem statement
Since the non_exhaustive attribute was introduced it allows crate authors to make normally breaking API changes in a non-breaking way. This lint will warn users of non_exhaustive types when the type changes and they are no longer handling all cases, using the _/.. for more than the NonExhaustive variant/field.
Motivation, use-cases, and solution sketches
Implement this as a lint inside of rustc_lint or implement the lint as part of the usefulness checker here
Links and related work
WIP PR: rust-lang/rust#86809
lint in usefulness checker commit: DevinR528/rust@df377ca
compiler-team MCP: rust-lang/compiler-team#445
zulip compiler/major changes: https://rust-lang.zulipchat.com/#narrow/stream/233931-t-compiler.2Fmajor-changes/topic/Non.20exhaustive.20reachable.20patterns.20lint.20compiler-team.23445
Initial people involved
I have started a WIP PR and plan to finish this as part of my GSoC project.
- Owner, if known: ?
- Liaison
What happens now?
This issue is part of the lang-team initiative process. Once this issue is filed, a Zulip topic will be opened for discussion, and the lang-team will review open proposals in its weekly triage meetings. You should receive feedback within a week or two.
This issue is not meant to be used for technical discussion. There is a Zulip stream for that. Use this issue to leave procedural comments, such as volunteering to review, indicating that you second the proposal (or third, etc), or raising a concern that you would like to be addressed.