FA-43578 / Borrow checking / Member archive

Removing a binder leaves outer lifetime indices off by one · case 03

Removing a binder leaves outer lifetime indices off by one.

Member previewVariant 3 · 3 implementations · 21 checks per implementation

Case contract

Check higher-ranked borrow instantiation using de Bruijn binder depths and universes. Bound occurrence index less than binder arity; substitutions shift free lifetimes when crossing binders; fresh universes strictly exceed caller universe; existential solutions cannot mention newer universes; universally quantified input must be checked for every listed placeholder; alpha renaming preserves equal occurrences; distinct bound parameters remain distinct; dropping a binder decrements outside indices; bound lifetimes cannot be selected as static; placeholder obligations cannot be discharged by one concrete lifetime. Input is a fully explicit descriptor of the stated toy IR. Return rule identifiers in declaration order; absent optional obligations use the provided neutral defaults. No rule is an assertion about a production language.

Why this case matters

A finite offline static-analysis model of ownership and borrowing; it does not execute the analyzed program.

One recorded failure

Sample boundary fixture

This sample comes from the broken implementation of a controlled reproducer.

Boundary fixture	Actual	Expected	Outcome
binder-pop regression 0	`[]`	`["binder-pop"]`	Failed

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