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agent: builder model: opus max_turns: 100 budget_usd: 20 —

Brief #933: a String returned by a method call, then viewed, lowers as a view of the parameters (rustc: cannot return value referencing local)

Score: bugs before moving (CLAUDE.md, docs/priorities.md); a wrong lowering that reaches rustc, and it blocks the rest of P5a (root_tag, program_name, own_copy in project.rs, plan row P5a of docs/selfhosting-plan.md). Lowering lane only (views.nika / text_tiers.nika); the second brief of this batch is in the checker (check_*).

Issue text (#933, copied; builders have no GitHub; probe corrected 2026-10-29)

Found by P5a (2e13458). A function -> String that returns a view (trim()) of a local String it got from a method call lowers its result as a view of its parameters. Probe (re-run on 6ccf6c8, both functions fail in rustc with Cannot return value referencing local variable hex):

trait Hasher { fn hex(ref self, seed: ref String) -> String }
struct Plain {}
impl Hasher for Plain { fn hex(ref self, seed: ref String) -> String { return f"  {seed}  " } }
fn tag[H: Hasher](seed: String, host: ref H) -> String {
    let hex = host.hex(seed)
    return hex.trim()
}
fn tag2(seed: String, host: ref Plain) -> String {
    let hex = host.hex(seed)
    return hex.trim()
}
fn main() {
    let p = Plain {}
    println(tag("ab", p))
    println(tag2("cd", p))
}

Expected output ab and cd. The issue saw fn tag<'r, H>(seed: &'r str, host: &'r H) -> &'r str for the generic host and -> &'static str for the concrete one. The result is a view of a local owned String, not of a parameter: the function must lower -> String (owned), which is the checker’s own reading of -> String. (The issue’s first probe had fn hex(self, seed: String); the checker refuses that with NK1102 for an unrelated, correct reason, so the probe above uses ref self and ref String.)

Locations (resolved 2026-10-29)

To build

  1. Test tests/compiler/tests/a_text_from_a_method_call_viewed_and_returned_is_owned.nika with the probe and its .stdout (ab\ncd\n; println ends each line). Run it once on the unfixed compiler and see it fail in rustc; say so under Tests:.
  2. Fix in the lowering so the result reaches no parameter through a method call whose result is an owned String; both functions lower -> String. Then target/fast/nikaia lower-std twice: the second run changes nothing (fixpoint), and only the lowered files of the .nika you changed differ. Commit Fixes #933.

Done when

The new test passes run through target/fast/nikaia test --project tests/compiler filtered to its name (not only with nikaia run: the test’s .stdout is compared byte for byte, 7c1643d went red on a newline), cargo test -p nikaia --test it -- views text_tiers lent, the gate of .claude/agents/builder.md (a change to the lowering runs nikaia test --both-settings --project tests/compiler), clippy, cargo fmt, scripts/pre-push-check.sh. Changelog: one sentence.

Stop and report if

The fix would make a result that really is a view of a parameter (fn first(s: String) -> String { return s.trim() }) owned; or it needs a file another agent has uncommitted (git status first: crates/rs2nika/convert/nikaia.* and docs/briefs/k1-comptime-tree.* were another session’s at the time of writing).

Rules (CLAUDE.md; this block is pasted into every brief, also a fix-forward)

Report (at most 15 lines, to exactly /home/user/Nikaia/docs/briefs/b933-method-result-owned.md.report.md)

Fields of docs/architect.md, Briefs and reports: Result: done|noop|partial|blocked (the bare word alone on that line: Result: done, never a summary after it, which cuts the batch, b869a 2026-10-27; Owner: is a question for the owner or none, never a role), Files, Commit, Body (optional, one paragraph for the commit message), Fixes, Pushed, Tests, Gate (green|red), Deviation, Found, Needs, Changelog, Owner, Disk freed, and for a move Rs2nika: (the kept N of M lines of rs2nika --score, then the three costliest hand edits; none for a task that moves no Rust, none (redesign) for a brief with Shape: redesign and no Convert: line). none where nothing, and then the bare word: Deviation: none (a note) cuts the batch (batch.nika compares exactly); a note goes into the commit message. Found: is only for a defect outside your change (it cuts the batch); a process event such as another session resetting or rewriting your files is no Found:, it goes under Needs: (m3a 2026-10-28); a converter draft that came out wrong is no Found:, it is one of the costliest edits under Rs2nika:, which the converter lane reads (e12-4b 2026-10-27); how you solved your own step goes into the commit message. Deviation: is only a step of the brief built otherwise than written or not built (a choice the brief left to you, such as keep what X needs and say so, is no deviation: it goes into the commit message; nor is building two steps in one commit when every step is built, e12-3a 2026-10-27, nor a step another commit on develop already built, shown by your test failing with that commit’s change reverted, b889 2026-10-27: name the commit in Body:, nor re-keying an allow-list entry (KNOWN) whose hash changed for the same program and the same reason, b-fixforward-sweep2 2026-10-28: say so in Body:); how you verified (e.g. a test not run against the unfixed compiler) goes under Tests:. A noop says why under Tests: (what was probed), not under Deviation:. Final answer, one line: done <sha>, report <path> (or BLOCKED: ... / PUSH REJECTED ...).

Attribution: Co-Authored-By: Claude Opus 5.5 noreply@anthropic.com Claude-Session: https://claude.ai/code/session_01GFeMqxRbtUMiGVyDMxsvEq

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