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Make visit_clobber's impl safe #127560

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Merged
merged 1 commit into from
Jul 11, 2024
Merged

Make visit_clobber's impl safe #127560

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17 changes: 3 additions & 14 deletions compiler/rustc_ast/src/mut_visit.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -20,7 +20,7 @@ use rustc_span::symbol::Ident;
use rustc_span::Span;
use smallvec::{smallvec, Array, SmallVec};
use std::ops::DerefMut;
use std::{panic, ptr};
use std::panic;
use thin_vec::ThinVec;

pub trait ExpectOne<A: Array> {
Expand Down Expand Up @@ -318,19 +318,8 @@ pub trait MutVisitor: Sized {
//
// No `noop_` prefix because there isn't a corresponding method in `MutVisitor`.
pub fn visit_clobber<T: DummyAstNode>(t: &mut T, f: impl FnOnce(T) -> T) {
unsafe {
// Safe because `t` is used in a read-only fashion by `read()` before
// being overwritten by `write()`.
let old_t = ptr::read(t);
let new_t =
panic::catch_unwind(panic::AssertUnwindSafe(|| f(old_t))).unwrap_or_else(|err| {
// Set `t` to some valid but possible meaningless value,
// and pass the fatal error further.
ptr::write(t, T::dummy());
panic::resume_unwind(err);
});
ptr::write(t, new_t);
}
let old_t = std::mem::replace(t, T::dummy());
*t = f(old_t);
}

// No `noop_` prefix because there isn't a corresponding method in `MutVisitor`.
Expand Down
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