2ea25e84ec
The RHS of a null-coalesce was lowered with no target type, so a bare
struct literal default (x ?? .{ ... }) produced a struct_init with
.ty == .unresolved that panicked in emitStructInit. lowerNullCoalesce
now saves self.target_type, sets it to the optional's resolved child
before lowering nc.rhs, and restores it (leak-free). Verified across
struct/slice/enum/tuple/protocol/nested-optional/generic child types by
3 adversarial reviews.
Regression: examples/optionals/0912-null-coalesce-struct-literal.sx.
Filed adjacent pre-existing bug 0172 (?? on a non-optional lhs panics).
54 lines
2.4 KiB
Markdown
54 lines
2.4 KiB
Markdown
# 0166 — `?? .{ ... }` struct-literal default panics with "unresolved type reached LLVM emission"
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> **RESOLVED.** The `??` RHS struct literal was lowered with no target type, so
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> its `struct_init.ty` stayed `.unresolved` and reached `emitStructInit`. Fix:
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> in `src/ir/lower/expr.zig` `lowerNullCoalesce`, save `self.target_type`, set it
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> to `inner_ty` (the optional's resolved child) before lowering `nc.rhs`, and
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> restore afterward (unconditional, leak-free — `lowerExpr` returns a plain
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> `Ref`). Verified across struct/slice/enum/tuple/protocol/nested-optional/
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> generic child types and present/absent branches by 3 adversarial reviews.
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> Regression: `examples/optionals/0912-null-coalesce-struct-literal.sx`.
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> (Adjacent pre-existing bug found + filed: 0172 — `??` on a NON-optional lhs
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> panics; `lowerNullCoalesce` must diagnose it.)
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## Symptom
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Using a struct literal as the default of a `??` (null-coalesce) operator panics:
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```
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panic: unresolved type reached LLVM emission
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```
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in `emitStructInit` (exit 134 / SIGABRT). The coalesce result type is inferred
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correctly (the optional's child `T`), but that target type is NOT threaded into
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the RHS struct-literal lowering, so the `struct_init` instruction's `.ty` stays
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`.unresolved` and reaches codegen.
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## Reproduction
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```sx
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#import "modules/std.sx";
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T :: struct { a: i64 = 0; }
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mk :: () -> ?T { return null; }
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main :: () { t := mk() ?? .{ a = 9 }; print("{}\n", t.a); }
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```
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Expected: `9` (null lhs → take the struct-literal default, typed as `T`).
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Observed: `panic: unresolved type reached LLVM emission`, exit 134.
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## Investigation prompt
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The result type IS inferred correctly — `src/ir/expr_typer.zig` (~lines 413–425)
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returns the optional's child `T` for the coalesce expression. The gap is in
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lowering: the `??` RHS struct literal is lowered without a target type. Suspected
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area: `src/ir/lower/expr.zig` `lowerNullCoalesce` (dispatched ~expr.zig:2417)
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must set the lowering target type to the lhs optional's child (`T`) before
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lowering `nc.rhs`, so an untyped `.{ ... }` literal on the RHS resolves to `T`
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the same way an assignment/return target would. Mirror however other contexts
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push an expected type into an untyped struct-literal lowering.
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Verify: the repro prints `9`; also test a present lhs (`mk` returns a value →
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prints the value's field, default not taken) and a nested-field struct literal
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default. Add an `examples/optionals/09xx-null-coalesce-struct-literal.sx`
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regression.
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