Nikaia
Menu
v0.0.1343pre-alpha GitHub

agent: builder model: opus max_turns: 80 budget_usd: 16 —

Brief: #1078, filter_map over split_once loses the parts’ text kinds

Blocks: k3b-comptime-bundle.md

Score: compiler bug in the #901 family, a lowering rustc refuses (&str where String is meant) and a checker refusal (NK1245) of a plain iterator chain; it blocks the K3b move (runtime_dependencies’ record parse). Traced to a missing branch, fairly sure.

Facts: Where things live, Traps already met, Commands

Issue #1078 (summary)

After filter_map(fn(line) { line.split_once("=") }), a following map(fn((name, rlib)) { (name.clone(), ...) }) lowers name as a &str view and name.clone() stays &str, so collecting into Vec[(String, String)] fails in rustc. With map(fn(line) { line.split_once("=") ?? ("", "") }) in place of the filter_map, the chain works; a for (name, rlib) loop works too.

Probe (checked on 4520d400’s binary with nikaia run):

fn tag(text: String) -> String {
    f"<{text}>"
}

fn pairs(lines: Vec[String]) -> Vec[(String, String)] {
    lines.iter().skip(1).filter_map(fn(line) { line.split_once("=") }).map(fn((name, rlib)) { (name.clone(), tag(rlib)) }).collect()
}

fn main() {
    for (n, p) in pairs(["head", "a=x.rlib", "b=y.rlib"]) {
        println(f"{n} {p}")
    }
}

Row a (above): rustc Mismatched types, expected Vec<(String, String)>, found Vec<(&str, String)>. Expected output a <x.rlib>, b <y.rlib>. Row b: the same with .map(fn(pair) { (pair.0.clone(), tag(pair.1)) }): the checker refuses with NK1245 (can’t tell what type pair is). Expected the same output.

Suspected location (traced by reading)

To build

  1. Reproduce rows a and b on the unfixed binary; keep the result under Tests:.
  2. The text_tiers.nika fix for row a, with its lowered twin (lower-std, fixpoint).
  3. The checker fix for row b, with its lowered twin.
  4. Test tests/compiler/tests/filter_map_split_parts.nika + .stdout with rows a and b, failing on the unfixed binary. Commit tiers, check: filter_map hands on the parts of a split it keeps (Fixes #1078).

Done when

The new test fails on the unfixed compiler and passes through nikaia test --project tests/compiler --both-settings, with the tests whose names contain split, tier, lambda, map, view (by name); lower-std fixpoint clean; build, fmt, clippy, pre-push-check.sh; committed locally. Changelog: one line. Stop about 15 turns before max_turns: commit what is finished and report partial.

Stop and report if

An edit is needed outside text_tiers.nika, the checker file of row b, their lowered twins and the new test; an error in another agent’s file.

Not yours, never stage: every file git status shows modified or untracked at your start, and every docs/briefs/* file except your report.

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/bugs/b18-1078-filter-map-split-parts.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_01GFeMqxRbtUMiGVyDMxsvEq

This site is open source. Improve this page.