This message is emitted as guidance by the compiler when a developer attempts to reassign a value to an immutable variable. Following the message will always currently work, but it may not always be the best course of action; following the 'consider ...' messaging pattern provides a hint to the developer that it could be wise to explore other alternatives.
This is step 2 towards fixing #77548.
In the codegen and codegen-units test suites, the `//` comment markers
were kept in order not to affect any source locations. This is because
these tests cannot be automatically `--bless`ed.
Identify unreachable subpatterns more reliably
In https://github.com/rust-lang/rust/pull/80104 I used `Span`s to identify unreachable sub-patterns in the presence of or-patterns during exhaustiveness checking. In https://github.com/rust-lang/rust/issues/80501 it was revealed that `Span`s are complicated and that this was not a good idea.
Instead, this PR identifies subpatterns logically: as a path in the tree of subpatterns of a given pattern. I made a struct that captures a set of such subpatterns. This is a bit complex, but thankfully self-contained; the rest of the code does not need to know anything about it.
Fixes https://github.com/rust-lang/rust/issues/80501. I think I managed to keep the perf neutral.
r? `@varkor`
For example, this code:
struct S(i32, f32);
let S(x) = S(0, 1.0);
will make the compiler suggest either:
let S(x, _) = S(0, 1.0);
or:
let S(x, ..) = S(0, 1.0);
Rust prints "type `&A` is non-empty" even is A is empty.
This is the intended behavior, but can be confusing.
This commit adds a note to non-exhaustive pattern errors if they are a
reference to something uninhabited.
I did not add tests to check that the note is not shown for
non-references or inhabited references, because this is already done
in other tests.
Maybe the added test is superfluous, because
`always-inhabited-union-ref` already checks for this case.
This does not handle &&Void or &&&void etc. I could add those as special
cases as well and ignore people who need quadruple
references.
Fixes#78123
Rename `overlapping_patterns` lint
As discussed in https://github.com/rust-lang/rust/issues/65477. I also tweaked a few things along the way.
r? `@varkor`
`@rustbot` modify labels: +A-exhaustiveness-checking
`PatKind::Ref(PatKind::Ident(BindingMode::ByValue(Mutability::Mut), ..), ..)`
is an AST representing `&(mut ident)`. It was errorneously printed as
`&mut ident` which reparsed into a syntactically different AST.
This affected help diagnostics in the parser.
or_patterns: implement :pat edition-specific behavior
cc #54883 `@joshtriplett`
This PR implements the edition-specific behavior of `:pat` wrt or-patterns, as determined by the crater runs and T-lang consensus in https://github.com/rust-lang/rust/issues/54883#issuecomment-745509090.
I believe this can unblock stabilization of or_patterns.
r? `@petrochenkov`
Handle empty matches cleanly in exhaustiveness checking
This removes the special-casing of empty matches that was done in `check_match`. This fixes most of https://github.com/rust-lang/rust/issues/55123.
Somewhat unrelatedly, I also made `_match.rs` more self-contained, because I think it's cleaner.
r? `@varkor`
`@rustbot` modify labels: +A-exhaustiveness-checking
