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addr_of! grants mutable access, maybe?

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The exact set of permissions granted when forming a raw reference is
currently undecided https://github.com/rust-lang/rust/issues/56604.

To avoid presupposing any particular outcome, adjust the const
qualification to be compatible with decision where raw reference
constructed from `addr_of!` grants mutable access.
This commit is contained in:
Tomasz Miąsko
2021-10-30 00:00:00 +00:00
parent b285e0c5d8
commit bc4931ed7e
4 changed files with 63 additions and 12 deletions
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11
compiler/rustc_const_eval/src/transform/check_consts/resolver.rs
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@@ -94,11 +94,10 @@ where
}
}
fn address_of_allows_mutation(&self, mt: mir::Mutability, place: mir::Place<'tcx>) -> bool {
match mt {
mir::Mutability::Mut => true,
mir::Mutability::Not => self.shared_borrow_allows_mutation(place),
}
fn address_of_allows_mutation(&self, _mt: mir::Mutability, _place: mir::Place<'tcx>) -> bool {
// Exact set of permissions granted by AddressOf is undecided. Conservatively assume that
// it might allow mutation until resolution of #56604.
true
}
fn ref_allows_mutation(&self, kind: mir::BorrowKind, place: mir::Place<'tcx>) -> bool {
@@ -110,7 +109,7 @@ where
}
}
/// `&` and `&raw` only allow mutation if the borrowed place is `!Freeze`.
/// `&` only allow mutation if the borrowed place is `!Freeze`.
///
/// This assumes that it is UB to take the address of a struct field whose type is
/// `Freeze`, then use pointer arithmetic to derive a pointer to a *different* field of