agent: builder model: opus max_turns: 90 budget_usd: 18 —
m.get(k) ?? <jump> or match m.get(k) { null => <jump> x => x } is lent; a match on its field borrows (#1089)Score: blocks #928 step 4’s second half (yaml’s load, ADR-yaml-1 D6, D8; y27-load run 1 blocked on it, draft on local branch wip/y27-load at eef3a2e7). A compiler defect found by the yaml lane, fixed in this lane because only yaml needs it now. It changes crates/: name in the report what it decided (the supervisor raises the version), Changelog: one sentence. The commit says Fixes #1089.
Facts: Where things live, Traps already met
Problem. A local bound to an element through a read whose miss jumps - let a = m.get(k) ?? throw .. / ?? return .., or let a = match m.get(k) { null => throw .. x => x } - is not taken as lent. A match or ?? on one of its non-copy optional fields then lowers without & (match a.node { Some(x) => x }), and rustc refuses it: Cannot move out of a.node as enum variant Some which is behind a shared reference. The same match on a ref A parameter, or on let a = m[k], lowers match &a.node and runs. Found by the yaml lane (y27-load, load’s alias resolution reads an anchor table this way); probed by the architect on target/fast/nikaia at 6eab43c4.
Probe (nikaia run p.nika; wanted 2):
use std::collections
struct E { msg: String }
impl Error for E { fn message(ref self) -> String { return self.msg.clone() } }
struct N { v: Vec[i64] }
struct A { node: N? }
fn get(m: ref collections::HashMap[String, A], k: String) -> N sync throws {
let a = match m.get(k) { null => throw E { msg: "no key" } x => x }
let node = match a.node { null => throw E { msg: "no node" } x => x }
return node.clone()
}
fn main() throws {
let mut m: collections::HashMap[String, A] = collections::HashMap()
m.insert("a", A { node: N { v: [1, 2] } })
let n = get(m, "a")
print(f"{n.v.len()}")
}Rows (all checked; the body of get changed):
match .. null => throw) - rustc E0507.let a = m.get(k) ?? throw E{..} - rustc E0507.let a = m.get(k) ?? return N { v: [] } - rustc E0507.m: ref Vec[A], let a = m.get(k) ?? throw E{..} and the match form - rustc E0507.let node = a.node ?? throw E{..} (a ?? on the field, not a match) - rustc E0507, lowered match a.node { Some(__nikaia_value) => .. }.let a = m[k] over ref Vec[A], with the field match or ?? - prints 2 (lowered match &a.node).a: ref A - prints 2.x => x.clone() - prints 2.Suspected location (medium confidence). crates/nikaia-std/src/tools/check_core_flow.nika, check_core_flow_through_a_view (:482) decides lent_scrutinees (the & the emitter writes, emit_core_match.nika:1096) from local.lent || local.ty.is_a_view() || state.a_lent_let(world, root). For rows a-e none holds: the let in crates/nikaia-std/src/tools/check_core_stmt.nika (the let walk around :700-750) marks check_core_stmt_lent_let for a place (m[k], row f), a seen-through value and check_core_stmt_a_lent_list_read (:87, a Coalesce whose read is in flow.lent_list_reads and whose fallback jumps) - which misses the map get, the ref Vec parameter’s get (row d) and the match .. { null => <jump> x => x } form entirely. The ?? on the field (row e) goes through the coalesce lowering, which reads the same facts or its own: find which.
tools/*.nika change, lower-std regenerates its lowered/*.rs; commit both)& (or any lowering rustc accepts) and print 2; rows f-h unchanged. A local so bound is a view of the collection for the rest of the checker too (it may not be handed away or kept past the collection). #1057 is the neighbouring refusal of return a.field (bug lane, b13): do not build it, do not change its rows. Test tests/compiler/tests/match_on_a_field_of_a_get_bound_local.nika + .stdout (rows a-e and f-h in one program, each printing), refused by the unfixed binary (say so in Tests:).tests/compiler --both-settings green; the view tests of the gate (it text_views stored_views tethers views_kept) green.git show eef3a2e7:packages/yaml/src/main.nika > <your scratchpad>/y.nika; target/fast/nikaia check on it is clean, and nikaia run of a scratch copy calling load once (defaults written out) builds (y27’s Loader::expansion has let node = match a.node { .. }). Say in Tests: that it builds. Commit nothing under packages/yaml/: y27 run 2 takes the draft.Files you may change: the tools/*.nika under the suspected location (and the coalesce lowering’s file if row e needs it) with their lowered/*.rs, the new test, and an existing test’s expected output your change rightly changes (name it in Body:). If the fix needs a language decision, stop: Result: blocked, Needs: architect decision. A builder that has found no cause after about 40 turns stops and reports partial with what it ruled out.
docs/builder-facts.md first. develop in the main checkout; git status at start: other agents’ uncommitted files are not yours, never touch or stage them.git add <files> only; commit after each step. Do not push: the driver runs the suite on your commit and pushes it (CLAUDE.md, Builders commit, the driver tests and pushes).cargo fmt, cargo clippy --all-targets -- -D warnings, scripts/pre-push-check.sh, and the gate of .claude/agents/builder.md (#852).CHANGELOG.md, badges; no new NK code. New tests in Nikaia only; never the full suite. No foreground sleep, no polling; scripts in files.std or the toolchain lacks stops the work: no code around it unless an ADR or Part I-III refuses it (name it). Else Result: blocked, Found: gap + probe, Needs: architect decision (CLAUDE.md, A missing form stops the work).NIKAIA_CACHE_LIMIT=2G; at most two clones with target/ in the machine; delete your own clone’s target/ and target/release/nikaia-scratch at the end; report GB freed.Pushed: line is local <sha> of your last commit. A report without a Pushed: line, or with a placeholder left in (TC, DISK), is not done and cuts the batch (k3a1 2026-10-29: Result: done, nothing committed).NIKAIA_CACHE_LIMIT=2G target/fast/nikaia test --project packages/yaml green, and cargo test --profile fast -p nikaia --test it -- fmt::every_nika_file (it formats every .nika under packages/). For a change only under packages/yaml/ this is the gate the line above asks for; a change under crates/ runs the gate of .claude/agents/builder.md (#852) as well. target/fast/nikaia is built by the session hook; if it is missing, cargo build --profile fast -p nikaia once.Changelog: none, unless the brief changes crates/.Files not to touch: anything outside packages/yaml/ and the brief’s own report, unless the brief names it; never docs/briefs/batch.txt or a brief of another lane.
max_turns: commit every finished step, then report Result: partial with what is left under Needs:. Uncommitted work at the end is lost work (y4 ran out at 110)./home/user/Nikaia/docs/briefs/yaml/y29-1089-match-on-a-get-bound-local.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 a test’s expected .stdout/.stderr taken from what the program really prints where the brief’s sketch of it was short or wrong, b934 2026-10-29: say so in Body:, nor a lowering that follows the ADR governing it where the brief’s expected lowering contradicts that ADR, b933 2026-10-29: name the ADR in Body:, nor a lowering other than the brief’s where rustc cannot take the brief’s, b1029 2026-10-31: say why 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:, nor an existing test’s expected .stdout/.stderr updated because your change rightly changes the message it prints, b1012b 2026-10-31: name the test 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_01UVxJDveRM5qKZKyCqq6Y24