FA-43249 / Borrow checking / Member archive

Later pattern alternatives introduce a different binding set · case 04

Later pattern alternatives introduce a different binding set.

Member previewVariant 4 · 3 implementations · 21 checks per implementation

Case contract

Check a toy destructuring pattern after type resolution. Binding names unique; alternatives bind identical name sets and modes; mutable reference binding needs mutable access; an explicit dereference pattern cannot move a noncopy referent; rest binding cannot overlap explicitly bound array positions; union fields require an explicit unsafe pattern; bindings introduced in a guard cannot escape guard region; simultaneous move and borrow of overlapping prefix places forbidden; a reference default binding mode cannot be reset implicitly by a plain identifier. 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
alternative-name-agreement regression 0	`[]`	`["alternative-name-agreement"]`	Failed

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