Issue #1215: Borrow checker: three wrong diagnostics found while writing the ownership guide

ready · opened 2026-11-03 · updated 2026-11-03 · 0 comments

Found by the builder of the guide chapter guide/ownership.md (docs lane, d1). Each one is a defect: the specification (Part I 6.6) says otherwise.

Probes

A struct built from an owned String and an int is refused, although nothing is lent:
```
struct Badge { owner: String, number: int }
fn badge_for(name: String, n: int) -> Badge { return Badge { owner: name, number: n } }
// called with "grace".to_uppercase()
```
The compiler refuses it with NK2302, “hands back a view of n”, even though n is an int. Without the int field the program runs.
A change after a kept view gives the wrong code:
```
let mut y = "short"; let r = longest(x, y); y.push_str("er"); println(r)
```
The compiler gives NK2105, “longest keeps it”. The right code is NK2305, which is what it gives with "short".to_uppercase().
fn add_guest(names: Vec[String]) { names.push(..) } gets NK1138, which is correct. A second error, NK2105, then appears at the caller and names Vec[ref String]. That second error should not be there.

To build

Fix each of the three in the checker, in Nikaia where the code is in tools/*.nika.
Add one test per probe under tests/compiler/, with its .stdout / .stderr.
Check against ADR-views-3 (#1213): where a rule of views-3 changes the case, test it under the views-3 rule.

Also found, for the specification lane (#1213, v1)

Part I 6.8’s example shows NK2301. The compiler emits NK2305, as Part III C.3 says, and emits NK2301 nowhere.
Part I 6.6’s examples write "short".clone(), which the compiler refuses today with NK1301.