[ASDAlexander77]

What

Under -mm=own, let [a, b] = pair now borrows each element, as let a = pair[0] already does. String elements are copied, as any string read out of an element is (spec 22).

Why

A destructuring declaration reads each element behind a test of the array's length whose other branch yields the default. The local's value therefore arrives through a merge (a block argument), and own refused it: "is merged from several branches". This cost the corpus file 00owned_locals (follow-up 14 from own-raytrace).

soleBlockMergedInto (OwnershipFacts.h) finds the one value a merge can bring a block in by, when every other way in passes ts.Default / ts.Null / ts.Undef or something that holds no block. placeReadOf uses it, so the local becomes that element read. checkPlaceRead's walk from the read already follows the branch to the local, so the borrow's end is still checked.

These are still errors (probed, and two of them pinned): reassigning the array, storing into an element, shift, returning the local, storing it into a field, and capturing it.

Tests

• own_destructure_elements covers class elements, built strings that outlive their array, and destructuring in a loop. It runs under own (including the no-counting check) and under rc, gc and none.
• 00owned_locals now runs under own.
• New negatives with pinned messages: own_err_destructure_element_reassigned and own_err_destructure_element_returned.
• Own corpus on Linux: 533 → 534 files accepted. Nothing is lost; the one gained file gives the same output as gc under MALLOC_PERTURB_.
• Full suite: Windows 5469/5469, Linux 5448/5448.

🤖 Generated with Claude Code