Nikaia
Menu
v0.0.1343pre-alpha GitHub

agent: builder model: opus max_turns: 80 budget_usd: 15 —

Brief: #1017, a lambda typed -> T? whose tail arms are all non-null is not wrapped in Some

Score: compiler bug (false acceptance: the checker passes, rustc refuses), bugs-first default of docs/priorities.md; small, one checker site.

Problem (issue #1017, probed by the architect at ed30efd5)

fn main() {
    let f: fn(i64) -> i64? = fn(x) { if x > 0 { x } else { 0 } }
    println(f(3) ?? 9)
}

Today: rustc Expected ... a future that resolves to Option<i64>, but it resolves to i64 at line 2. Expected 3. The control row let g: fn(i64) -> i64? = fn(x) { if x > 0 { x } else { null } } / println(g(-1) ?? 9) already prints 9 (checked).

Locations

To build

  1. The lambda’s tail is wrapped as a named function’s is: a branching tail (if/match) under a nullable expected result gets some_at_the_tails; a single non-null tail value the same wrapped fact as a function’s. Test tests/compiler/tests/a_lambda_typed_optional_widens_its_arms.nika + .stdout: the probe (3), the control row (9), and a one-expression lambda let h: fn(i64) -> i64? = fn(x) { x + 1 } / println(h(1) ?? 9) (2; unverified by the architect: if it fails for another cause, report it under Found:). Commit check: a lambda typed -> T? wraps its non-null arms in Some (#1017), Fixes #1017.

Done when

The test passes through nikaia test; lower-std fixpoint clean; cargo build --profile fast -p nikaia; the guard set of .claude/agents/builder.md green; pushed. Changelog: one line (a lambda whose declared result is optional widens a non-optional tail, as a function does).

Stop and report if

An edit is needed outside crates/nikaia-std/src/tools/check_*.nika, emit_core_flow.nika, their lowered files 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/b1017-lambda-optional-tail.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 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.