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Skip only truly recursive fields when dropping an enum #342

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Skip only truly recursive fields when dropping an enum #342

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2 changes: 1 addition & 1 deletion src/refine/env.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -1160,7 +1160,7 @@ where
pred_args.push(field_term.clone());

if let Some(p) = field_type.as_pointer() {
if matches!(&p.elem.ty, rty::Type::Enum(e) if e.symbol == ety.symbol) {
if p.elem.ty.to_sort() == ty.to_sort() {

@chatgpt-codex-connector chatgpt-codex-connector Bot Oct 16, 2026

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P1 Badge Detect recursive cycles across generic instantiations

When a recursive enum permutes its type arguments, exact sort equality never identifies the recursive field. For example, enum E<T, U> { Value(T, U), Next(Box<E<U, T>>) } is valid Rust, but dropping E<i32, bool> recursively alternates between E<i32, bool> and E<bool, i32> here until Thrust overflows its stack. The previous symbol comparison stopped this recursion, so the recursion guard needs to track datatype cycles rather than only an identical instantiated sort.

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// TODO: we need recursively defined drop_pred for the recursive ADTs!
tracing::warn!("skipping recursive variant");
continue;
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14 changes: 14 additions & 0 deletions tests/ui/fail/enum_nested_same_enum_mut_drop.rs
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@@ -0,0 +1,14 @@
//@error-in-other-file: Unsat
//@compile-flags: -C debug-assertions=off

fn main() {
let mut slot: Option<i64> = None;
let o: Option<&mut Option<i64>> = Some(&mut slot);
if let Some(s) = o {
*s = Some(3);
}
match slot {
Some(y) => assert!(y == 4),
None => assert!(false),
}
}
14 changes: 14 additions & 0 deletions tests/ui/pass/enum_nested_same_enum_mut_drop.rs
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Original file line number Diff line number Diff line change
@@ -0,0 +1,14 @@
//@check-pass
//@compile-flags: -C debug-assertions=off

fn main() {
let mut slot: Option<i64> = None;
let o: Option<&mut Option<i64>> = Some(&mut slot);
if let Some(s) = o {
*s = Some(3);
}
match slot {
Some(y) => assert!(y == 3),
None => assert!(false),
}
}
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