Migrate lowerAssignment's `.field_access` target onto the shared
`fieldLvaluePtr` resolver, deleting its duplicated union / promoted /
tuple / vector / struct walk. All three lvalue field-store sites —
single-assign, address-of (lowerExprAsPtr), and multi-assign
(lowerMultiAssign) — now resolve through the one resolver, removing the
issue-0083 two-resolver divergence.
Fold vector-lane resolution into `fieldLvaluePtr` (reusing
vectorLaneIndex) so the single resolver covers struct fields, union
direct fields, promoted anonymous-struct union members, tuple elements,
and vector lanes — null only on a genuine miss, which every caller turns
into the read path's `emitFieldError` diagnostic.
`fieldLvaluePtr` now types every field GEP `*field_ty` (the convention
the single-assign path always used), not the bare field value type:
emitStore unwraps one pointer level to find the stored value's type.
The earlier lowerExprAsPtr / lowerMultiAssign walks typed the GEP with
the bare field type, so a field whose own type is a pointer-to-aggregate
(`*Pair`, a two-pointer struct) made emitStore unwrap to the aggregate
and coerceArg's closure auto-promotion store a 16-byte `{ptr,null}`
struct over the 8-byte slot, clobbering the neighbouring field.
Consolidating onto the one `*field_ty` resolver preserves single-assign
and fixes that pre-existing multi-assign / address-of clobber.
The types.zig `.unresolved` tripwire is untouched; no `.s64` / `.void` /
`.unresolved` default remains.
Regression: examples/0167-types-ptr-to-aggregate-field-store.sx (a
`*Pair` field stored via all three lvalue sites leaves the neighbour
intact) + a lowering unit test asserting the `*field_ty` GEP convention.
Completes the issue-0094 fix. attempt-1 made single-assign and address-of
diagnose a missing struct field; the stress-review found two remaining defects
in that change:
1. lowerMultiAssign's `.field_access` target kept the pre-fix shape — a
struct-only loop that defaulted `field_idx 0` / `field_ty .unresolved` on a
miss, then built the GEP and stored unconditionally. A missing field
(`p.q, y = 2, 3`) silently wrote field 0 (printed `x=2 y=3`, no diagnostic),
and a valid promoted-union / tuple member at a non-zero offset corrupted
field 0 instead of its own slot.
2. attempt-1's new union branch in lowerExprAsPtr resolved only DIRECT union
field names, so `@v.x` on a promoted anonymous-struct member reported
"field 'x' not found on type 'Vec2'" even though `v.x = 41` worked.
Both lvalue-pointer sites and the multi-assign store now route through one
shared resolver, `fieldLvaluePtr`, that handles struct fields, union direct
fields, promoted anonymous-struct union members, and tuple elements, and
returns null (no field-0 / `.unresolved` default) on a genuine miss. Each
caller emits the read path's `emitFieldError` on null. This collapses the
three previously-divergent field-lvalue walks into one, fixing the
multi-assign missing-field corruption, the promoted-member over-rejection,
and (as a side effect of correct resolution) non-zero-offset promoted-union
and tuple multi-assign stores. The types.zig tripwire is untouched.
Regression tests:
- examples/1145 extended: multi-assign missing field (`p.r, y`) errors, exit 1.
- examples/0166 (new): promoted union member written and address-of'd,
including a non-zero-offset member (`@v.y`), compiles and runs.
- src/ir/lower.test.zig: multi-assign missing-field field-not-found unit test.
Assigning to a nonexistent struct field (`p.q = 2` where Point has no `q`)
aborted the compiler with the `.unresolved` LLVM tripwire instead of a source
diagnostic (issue 0094). The lvalue field lookup never diagnosed a miss:
- `lowerAssignment`'s `.field_access` target left `field_ty = .unresolved` when
no struct field matched, then built `ptrTo(field_ty)` and stored — so a
pointer-to-`.unresolved` reached LLVM emission and tripped the panic.
- `lowerExprAsPtr`'s `.field_access` fallback returned
`structGepTyped(obj_ptr, 0, .s64, obj_ty)` on a miss — a silent field-0/`.s64`
default that mislowered the lvalue.
Both sites now reuse the read path's `emitFieldError` (the exact facility
`lowerFieldAccessOnType` uses), so read and write reject identically with
`field 'q' not found on type 'Point'`. `lowerExprAsPtr` also resolves
union/tagged-union fields via `union_gep` (the old `.s64` fallback was silently
standing in for union field access — e.g. `u.a[0] = v`), so that path is fixed,
not just made loud. The `types.zig` tripwire is untouched: the fix is to never
produce `.unresolved` for a missing-field store.
Regression tests:
- examples/1145-diagnostics-missing-struct-field-assign.sx — negative, both
sites error, exit 1.
- examples/0165-types-nested-struct-field-assign.sx — positive, nested struct
field write + address-of a matched field still work.
- src/ir/lower.test.zig — lowering unit test asserting the field-not-found
diagnostic for a missing-field assignment.
