[ASDAlexander77]

Phase 2 of -mm=own (spec §2.2 verdict 2). The plan is tslang/docs/superpowers/plans/2026-09-29-own-phase-2.md and the results are in spec §13. Only OwnershipInferencePass.cpp changed, and gc, rc and none are unaffected.

What changes

The verdicts now run in the spec's order: move, then borrow, then error.

• Borrowing. When a value can't be moved, a let declared from it borrows it: an owning let that took its own reference, not captured. The borrower's retain and all its releases are erased, and the owner keeps its own.
• When a borrow is sound. No use of the borrower may be reachable from any release or assignment of the owner. "Use" covers anything derived from reading it that can still point into the block: field references, values loaded through them, bound methods, and catch/finally locals.
• Escapes. The borrower must never escape: stored, pushed, returned, retained, boxed, chained into another let, or assigned.
• Several receivers. When one owner has several receivers, all of them must borrow, because a borrow pins its owner. A field store next to a borrowing let is 'a' is moved here while 'b' borrows it.
• Errors now accepted. These phase-1 errors are now legal programs:
  • an inner let of a value used again;
  • let b = a; let c = a;;
  • a let in a loop body of a value made outside the loop;
  • a let on one branch only.
• Errors. They follow §5 and name both variables under --di:
  • 'b' borrows 'a' but is used here after 'a' is released or overwritten;
  • ... cannot be stored, returned or captured;
  • ... cannot be assigned.

Tests

• New positives: own_borrow_inner_let, own_borrow_loop, own_borrow_branch, own_borrow_two_lets, own_borrow_nullable. Each runs under JIT and AOT with a churn() read, plus the no-counting check.
• New negatives: own_err_borrow_escape, own_err_borrow_and_move, own_err_move_some_paths_field, and four from the review: own_err_borrow_bound_method, _catch_local, _finally_local, _derived_ref.
• Removed negatives: six phase-1 negatives that phase 2 accepts, replaced by the positives above.
• Teeth: with the borrower's releases kept, 10/10 borrow checks fail.

Verification

• Release suite (Windows): 3146/3146.
• Debug own tests: 240/240. owned-async and ownership-verifier-4 were excluded; they fail on main too.
• 1M iterations: own is 4.7–4.8 MB, the same as rc, while none reaches 113 MB–1.1 GB. Measured at both -O3 and -O1.
• A fresh-context review found one Critical and one Important, both fixed in the last commit, each with a test that failed first:
  • Critical: derived values weren't tracked. const f = b.m, a for…of over b.v, and a catch local of b compiled to reads of freed memory.
  • Important: if (b) on a nullable borrower was a false escape.
• Linux not run.

Still rejected (spec §13.5, input to phase 3)

• borrows out of containers (arr[i], h.c), bounded by pop/splice/overwrite;
• borrow chains, and borrowers that get assigned;
• borrows of parameters and of this (phase 4);
• a move after every borrower's last use.

An alias of the owner itself held across an assignment of it compiles to a use-after-free under rc as well (§12.5).

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