diff --git a/compiler/rustc_mir_build/src/check_unsafety.rs b/compiler/rustc_mir_build/src/check_unsafety.rs index 57390dd58f4..4fe984b961e 100644 --- a/compiler/rustc_mir_build/src/check_unsafety.rs +++ b/compiler/rustc_mir_build/src/check_unsafety.rs @@ -322,14 +322,15 @@ impl<'a, 'tcx> Visitor<'a, 'tcx> for UnsafetyVisitor<'a, 'tcx> { | PatKind::DerefPattern { .. } | PatKind::Range { .. } | PatKind::Slice { .. } - | PatKind::Array { .. } => { + | PatKind::Array { .. } + // Never constitutes a witness of uninhabitedness. + | PatKind::Never => { self.requires_unsafe(pat.span, AccessToUnionField); return; // we can return here since this already requires unsafe } - // wildcard/never don't take anything + // wildcard doesn't read anything. PatKind::Wild | - PatKind::Never | - // these just wrap other patterns + // these just wrap other patterns, which we recurse on below. PatKind::Or { .. } | PatKind::InlineConstant { .. } | PatKind::AscribeUserType { .. } | diff --git a/tests/ui/rfcs/rfc-0000-never_patterns/never-pattern-is-a-read.rs b/tests/ui/rfcs/rfc-0000-never_patterns/never-pattern-is-a-read.rs new file mode 100644 index 00000000000..a66c4464417 --- /dev/null +++ b/tests/ui/rfcs/rfc-0000-never_patterns/never-pattern-is-a-read.rs @@ -0,0 +1,16 @@ +// Make sure we consider `!` to be a union read. + +#![feature(never_type, never_patterns)] +//~^ WARN the feature `never_patterns` is incomplete + +union U { + a: !, + b: usize, +} + +fn foo(u: U) -> ! { + let U { a: ! } = u; + //~^ ERROR access to union field is unsafe +} + +fn main() {} diff --git a/tests/ui/rfcs/rfc-0000-never_patterns/never-pattern-is-a-read.stderr b/tests/ui/rfcs/rfc-0000-never_patterns/never-pattern-is-a-read.stderr new file mode 100644 index 00000000000..d7dc7a47e72 --- /dev/null +++ b/tests/ui/rfcs/rfc-0000-never_patterns/never-pattern-is-a-read.stderr @@ -0,0 +1,20 @@ +warning: the feature `never_patterns` is incomplete and may not be safe to use and/or cause compiler crashes + --> $DIR/never-pattern-is-a-read.rs:3:24 + | +LL | #![feature(never_type, never_patterns)] + | ^^^^^^^^^^^^^^ + | + = note: see issue #118155 for more information + = note: `#[warn(incomplete_features)]` on by default + +error[E0133]: access to union field is unsafe and requires unsafe function or block + --> $DIR/never-pattern-is-a-read.rs:12:16 + | +LL | let U { a: ! } = u; + | ^ access to union field + | + = note: the field may not be properly initialized: using uninitialized data will cause undefined behavior + +error: aborting due to 1 previous error; 1 warning emitted + +For more information about this error, try `rustc --explain E0133`.