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Brief b945: a struct result points into the text parameter it is built from; a parameter only moved into a local struct is lent; a struct result viewing a local takes the caller’s keep (#945 step 1, #942 steps 2 and 5)

Score: bugs before moving (CLAUDE.md, docs/priorities.md); #945 blocks the yaml package (#928), and every shape here reaches rustc today (a message about a file nobody wrote, Part III C.1). Decided: ADR-353 D8, D10 (d84a15f); probe 1 needs no decision (ADR-353 D1, D5; ADR-283 D24).

Issue text (#945 and #942, copied; builders have no GitHub)

Common part of the probes (#945):

struct Event { text: String, line: i64 }
struct Parser { input: String, pos: i64 }

impl Parser {
    fn new(input: String) -> Parser { return Parser { input, pos: 0 } }

    fn next(ref mut self) -> Event? {
        let lines = self.input.lines().collect()
        if self.pos >= lines.len() { return null }
        let e = Event { text: lines[self.pos].trim(), line: self.pos + 1 }
        self.pos += 1
        return e
    }
}

Probe 1 (#945): main builds Parser { input: text.trim(), pos: 0 }, so the tiers make input a view: struct Parser<'a>, fn next(&mut self) -> Option<Event<'a>>, correct. But new lowers as fn new(input: &str) -> Parser<'a> { .. }; rustc: Explicit lifetime required in the type of input. Expected fn new(input: &'a str) -> Parser<'a>. Without new the program runs and prints both events.

Probe 2 (#945, now #942 step 2): a text parameter moved into a local struct, views handed back:

fn events(text: String) -> Vec[Event] {
    let mut p = Parser { input: text, pos: 0 }
    let mut events: Vec[Event] = []
    while true {
        let e = p.next() ?? break
        events.push(e)
    }
    return events
}

Lowered today: Parser { input: String, .. } (owned), fn next(&mut self) -> Option<Event<'_>>, fn events(text: String) -> Vec<Event<'static>>; rustc: Cannot borrow p as mutable more than once at a time. ADR-353 D8: a text parameter whose body only moves it into a local struct (tuple, list, variant) is not kept (Part I 6.5): it stays a view (&'a str), input is a view, events returns Vec<Event<'a>>.

F7 (#942 step 5, docs/decision-942-keep-moves.md §4):

use std::fs
struct View { head: String }
struct Cursor { input: String, pos: i64 }
fn parse(t: String) -> View { return View { head: t } }
fn make() -> Cursor throws {
    let text = fs::read_to_string("in.txt", fs::Root::Anywhere)
    let v = parse(text)
    let c = Cursor { input: v.head, pos: 0 }
    println(v.head)
    return c
}

Today NK2105 (“v.head was stored in Cursor.input”; help .clone()): the tiers make the returned field owned. ADR-353 D10: a struct (variant, tuple, list) result whose views point into what the body owns puts that buffer in the caller’s keep (ADR-283 D10, D23), as fn d() -> ref String already does; the field stays a view.

Locations (resolved 2026-10-29)

To build

  1. Constructor (#945 step 1): a function that builds a struct with a view field from a text parameter lowers the parameter with the struct’s lifetime, for a named one (Parser::new) and the anonymous constructor (pub fn(input: String) -> Parser, called Parser(text), Part I 4.2). Test: tests/compiler/tests/a_constructor_of_a_struct_of_views_points_into_its_parameter.nika + .stdout: probe 1 with Parser::new(text.trim()) and a second struct built by its anonymous constructor, both called from main, the events of both printed. Commit Fixes #945.
  2. Parameter lent (#942 step 2): probe 2 runs. Test: tests/compiler/tests/a_text_parameter_moved_into_a_local_struct_is_lent.nika + .stdout (main reads a text, calls events(text), prints each event’s text and line, then prints text itself, which is still there). Commit Part of #942.
  3. Struct result (#942 step 5): F7 runs, c.input read in main after make(). Test: tests/compiler/tests/a_struct_result_viewing_a_local_lives_in_the_callers_keep.nika + .stdout (in the test, the local text is text of its own made without a file, let text = f"a: {n}" with n a parameter or local; not .clone() on a literal, which is NK1301). Also a tuple result (View, i64) viewing the local, in the same test. Commit Part of #942.

Done when

The three new tests pass (target/fast/nikaia test --project tests/compiler filtered to each), each fails on the compiler before your change (say so under Tests:), the keep tests named above and it -- tether_keep result_source pass, the gate of builder.md (a change to tools/emit_*.nika runs 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 step needs a rule Part I/ADR-353 does not state (then Owner: names it), or a file another agent has uncommitted (git status first). Do not touch tools/view_changes.nika or tools/buffers.nika beyond what a step needs: the next brief (b942) changes them.

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/b945-struct-result-lifetimes.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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