032 reject borrow return of param

✓ Passing Passing: the compiler rejects this program as expected.

Code

// TEST: KORU095 — a `-> string` bare return may not hand back a borrow of its
// parameter ("borrows flow down, never up").
//
// Found 2026-09-06: the rule landed 2026-09-05 (610_007) and the next day
// orisha's `pump:raw` (`raw -> x.raw`) tripped it — blocking every Orisha
// build, native and the korulang.org wasm reactor alike, until `raw` became
// an owned arena copy. This pins the refusal on the minimal shape: returning
// `s.data` claims an owned string while handing back the caller's memory,
// which the owner could invalidate by discharge or mutation.

~tor sink { s: string }
~proc sink|zig {}

~tor borrow-back { s: string } -> string
~borrow-back -> s.data

~borrow-back(s: "hello"): r |> sink(s: r)

input.kz

Actual compiler output

error[KORU095]: tor 'borrow-back' returns a borrow of its parameter 's' (`s.data`) — borrows flow down, never up; a `-> string` return must own what it carries
  --> tests/regression/200_COMPILER_FEATURES/220_FLOW_CHECKER/220_032_reject_borrow_return_of_param/input.kz:16:0
    |
 16 | 
    | ^
  hint: copy it into an owned String and return the handle (*String<view!>), or take the handle at the consumer instead of reading (610_007)

Frontend must reject with:

CONTAINS error[KORU095
CONTAINS borrows flow down, never up

Flows

flow ~borrow-back click a branch to expand · @labels scroll to their anchor

borrow-back (s: "hello")

Test Configuration

MUST_ERROR

← 029 nested chain base handler is not a claim 033 void rereturn inline transform →