FA-43879 / Borrow checking / Member archive

A nonexhaustive guarded match omits the no-arm-taken ownership state · case 04

A nonexhaustive guarded match omits the no-arm-taken ownership state.

Member previewVariant 4 · 3 implementations · 21 checks per implementation

Case contract

Check borrow state across guarded matches. Guard failure restores prearm ownership; guard evaluation cannot move a noncopy scrutinee; arm-local loans end before another arm; guard mutation cannot change a discriminant supporting a projected borrow; arm move commits only after guard success; pattern tests are shared observations; exhaustive join includes every reachable arm; nonexhaustive matches retain fallback state; guard temporaries die on failed guard; a borrowed binding used by guard remains valid through guard expression. 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
fallback-state regression 0	`[]`	`["fallback-state"]`	Failed

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