# 0085 — nested slice literal elements are stored as raw arrays

> **RESOLVED.** Root cause: `Lowering.lowerArrayLiteral` lowered each element with
> the element type as `target_type` but appended the returned value directly. For
> a nested `.[...]` element whose expected element type is a slice (`[]T`), the
> inner literal still lowers to an aggregate ARRAY `[N]T` — so the outer aggregate
> (typed array-of-`[]T`) held raw arrays where slice {ptr,len} headers were
> expected; indexing the inner slice read a garbage pointer and segfaulted. Fix:
> after lowering each element, when the element type is a slice and the lowered
> value is a same-element array, coerce it via the existing `array_to_slice` op
> (materialize backing storage + build the header) — identical to the whole-
> literal coercion the var-decl / call-arg paths already run. The coercion
> recurses with the nesting, so `[][]T` and deeper materialize at every level.
> Files: `src/ir/lower.zig` (`lowerArrayLiteral`). Regression:
> `examples/0142-types-nested-slice-literal-elements.sx` (`[][]i64` + `[][]string`,
> local-bound AND direct-call-argument forms).

## Symptom
Nested array/slice literals such as `.[.[1, 2], .[3, 4]]` miscompile when the
expected element type is a slice (`[][]i64`). Observed: both the local-bound and
direct-call forms segfault while indexing the inner slice. Expected: both forms
materialize each inner `[N]T` literal as a `[]T` slice and print the same value.

## Reproduction
```sx
#import "modules/std.sx";

sum_nested :: (xss: [][]i64) -> i64 {
    return xss[0][1] + xss[1][0];
}

main :: () {
    local : [][]i64 = .[.[1, 2], .[3, 4]];
    print("local={}\n", sum_nested(local));
    print("direct={}\n", sum_nested(.[.[1, 2], .[3, 4]]));
}
```
Observed on `flow/sx-foundation/F0.4`: segfault at address `0x9` before either
line prints. Expected output:
```text
local=5
direct=5
```

## Investigation prompt
Fix nested slice literal materialization. The likely area is
`src/ir/lower.zig` in `Lowering.lowerArrayLiteral`: the outer literal can know
its expected element type is `[]T`, and the loop sets `self.target_type =
elem_ty` while lowering each inner literal, but it appends the returned value
directly. For an inner `.[...]`, that returned value is still an array aggregate
`[N]T`, not the target `[]T` slice. Add per-element coercion/materialization
after lowering each element, using the element source type and expected
`elem_ty` (the existing `array_to_slice` coercion should be reused). Verify the
repro prints `local=5` and `direct=5`, then run `zig build && zig build test &&
bash tests/run_examples.sh`.
