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Use doc comment for explanation of shared_borrow_allows_mutation

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This commit is contained in:
Dylan MacKenzie 2020-02-17 13:39:50 -08:00
parent 668d2fe807
commit 9d423950cc
1 changed files with 9 additions and 9 deletions
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18
src/librustc_mir/dataflow/impls/borrowed_locals.rs
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@ -221,15 +221,15 @@ pub struct MutBorrow<'mir, 'tcx> {
}
impl MutBorrow<'mir, 'tcx> {
// `&` and `&raw` 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
// that same struct whose type is `!Freeze`. If we decide that this is not UB, we will
// have to check the type of the borrowed **local** instead of the borrowed **place**
// below. See [rust-lang/unsafe-code-guidelines#134].
//
// [rust-lang/unsafe-code-guidelines#134]: https://github.com/rust-lang/unsafe-code-guidelines/issues/134
/// `&` and `&raw` 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
/// that same struct whose type is `!Freeze`. If we decide that this is not UB, we will
/// have to check the type of the borrowed **local** instead of the borrowed **place**
/// below. See [rust-lang/unsafe-code-guidelines#134].
///
/// [rust-lang/unsafe-code-guidelines#134]: https://github.com/rust-lang/unsafe-code-guidelines/issues/134
fn shared_borrow_allows_mutation(&self, place: &Place<'tcx>) -> bool {
!place.ty(self.body, self.tcx).ty.is_freeze(self.tcx, self.param_env, DUMMY_SP)
}