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Compound assignment evaluates a borrowing destination expression twice · case 04

Compound assignment evaluates a borrowing destination expression twice.

Member previewVariant 4 · 3 implementations · 21 checks per implementation

Case contract

Validate borrow-sensitive desugaring proof facts. For-loop iterator temporary covers loop; question-mark error exit drops body loans; short-circuit right operand is conditionally evaluated; method autoref targets receiver after autoderef; compound assignment evaluates destination once; indexing evaluates base before index; await suspension preserves the borrowed future owner; let-else failure cannot access successful bindings; destructuring assignment stages RHS borrows before writing destinations; return expression lifetime is checked before local cleanup. 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
compound-destination-once regression 0	`[]`	`["compound-destination-once"]`	Failed

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