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Brief b942: a viewed text moved into a struct, variant, tuple or list is kept; NK2305 where the place must own (#944, #942 steps 1, 3, 4)

Score: bugs before moving (CLAUDE.md, docs/priorities.md); every shape here reaches rustc today (E0505, Part III C.1), and it is the yaml pull parser’s shape (#928). Decided by the owner, 2026-10-29: ADR-353 D8, D9 (d84a15f). Starts after b945 (docs/briefs/b945-struct-result-lifetimes.md) is pushed: check git log --oneline -- tests/compiler/tests/a_struct_result_viewing_a_local_lives_in_the_callers_keep.nika shows a commit; if not, report blocked.

Issue text (#942, #944, copied; builders have no GitHub)

#942 probe (nikaia run, in.txt holds a: 1):

use std::fs
struct View { head: String }
struct Cursor { input: String, pos: i64 }
fn parse(t: String) -> View { return View { head: t } }
fn main() throws {
    let text = fs::read_to_string("in.txt", fs::Root::Anywhere)
    let v = parse(text)                         // v views text
    let c = Cursor { input: text, pos: 0 }      // text moves into the Cursor
    println(f"{c.pos}")
    println(v.head)                             // v still used
    println(c.input)
}

Today: Cannot move out of text because it is borrowed (rustc E0505). The same with a tuple (text, 0), a list [text], a variant E::A(text), and inside a function returning c: E0505 each. let moved = text; Cursor { input: moved } is rustc E0308 (&String into String): __keep_frame.put(..) gives a &String. Already built (1b1d740): a text moved into a field, tuple or list is followed there, a change in place of it while v lives is NK2305.

Decision (ADR-353 D8, D9; Part I 6.6, Part III NK23xx row): the literal is a variable of the same function (D3). The move counts as a view flowing into the position (ADR-282 D13): the field/element/payload becomes a view of the kept buffer (EitherText where text of its own also flows in), program-wide; text stays in the frame or the keep as for let moved = text. Where the position must hold text of its own (changed in place, or handed to a callee that keeps it, in any function) while v is still used: NK2305 at the move, D6’s wording: headline names the value and the view; labels: the call that made v, the move (Cursor.input must hold text of its own), the place that forces it (c.input.push_str(..) in advance changes it in place), the later use; help: hand over a copy (Cursor { input: text.clone(), pos: 0 }) or build the value first and take the view from its field (let c = Cursor { input: text, pos: 0 } then parse(c.input)). NK1106 and NK2105 keep their cases where no view lives.

#944 (prerequisite: the help’s second way out is refused today):

    let mut c = Cursor { input: text, pos: 0 }
    let v = parse(c.input)          // v views c.input only
    c.pos = c.pos + 1               // a different field

gives NK2305 (c is changed here, but v may point into its data): a false refusal; v points into c.input, not c.pos (ADR-283 D13: a refusal stands only on a named buffer).

Locations (resolved 2026-10-29)

To build

In the tests, the text is text of its own made without a file (let text = f"a: {n}"), not fs::read_to_string and not .clone() on a literal (NK1301).

  1. #944: a view whose argument is a field path (c.input, c.a.b) records that path as its source, and a change is refused only where its path and the source path overlap (one a prefix of the other). Tests: tests/compiler/tests/a_view_of_one_field_lets_another_field_change.nika + .stdout (the #944 probe, completed as in #942’s probe); tests/compiler/tests/a_view_of_one_field_refuses_a_change_of_that_field.nika + .stderr (c.input.push_str("x") while v lives). Commit Fixes #944.
  2. Moved text kept (#942 step 1): the probe runs; so do a tuple, a list, a variant E::A(text) and let moved = text; Cursor { input: moved }. Test: tests/compiler/tests/a_viewed_text_moved_into_a_literal_is_kept.nika + .stdout, each printing v.head and the moved text. Also the moved form of the struct result (b945 built the view form): fn make() -> Cursor that reads a text, views it, moves it into the Cursor and returns it, v used before the return: tests/compiler/tests/a_struct_result_with_a_moved_text_lives_in_the_callers_keep.nika + .stdout. Commit Part of #942.
  3. Refusal (#942 step 3): the probe plus fn advance(mut c: Cursor) { c.input.push_str("!") } called on another Cursor elsewhere in the program: NK2305 at the move, with the labels and help above, no rustc message. Test: tests/compiler/tests/a_viewed_text_moved_into_a_field_that_owns_is_refused.nika + .stderr. The wording follows D6’s existing messages (:968, :992); no new NK code.
  4. Nothing else changes (#942 step 4): the step 3 program with v not used after the move runs (the field owned); F8 (let c = Cursor { input: v.head, pos: 0 } then c.input.push_str("!")) stays NK1106 (if no existing NK1106 test has this shape, add tests/compiler/tests/a_view_stored_in_a_field_changed_in_place_is_refused.nika + .stderr). Test: tests/compiler/tests/a_text_moved_into_a_field_that_owns_with_no_view_left_runs.nika + .stdout. Commit Fixes #942.

Done when

Every new test passes and fails on the compiler before your change (say so under Tests:), the existing NK2305, NK1106, keep and text_moved_into_a_field_* tests pass, the gate of builder.md (tools/check_*/tools/emit_* changed: nikaia test --both-settings --project tests/compiler), lower-std changes only the lowered files of the .nika you changed, clippy, cargo fmt, scripts/pre-push-check.sh. Changelog: one sentence per step.

Stop and report if

A case needs a rule ADR-353 D8/D9 or Part I 6.6 does not state (Owner: names it), the forcing place cannot be found from the check (then build the rest, and say what is missing under Needs:), or a file another agent has uncommitted (git status first).

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/b942-moved-text-tiers.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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