3e8d003e3d
lowerIfExpr emitted optional_has_value only for the binding form; a bare
'if opt' passed the raw {T,i1} aggregate to condBr, where emitCondBr's
catch-all struct arm silently folded it to 'i1 true' (structs always
truthy) — a silent miscompile that took the present-branch for null
optionals. while / and / or shared the same defect.
Reduce bindingless optional conditions to optional_has_value in
lowerIfExpr/lowerWhile and via a new lowerBoolCondition helper for and/or
operands. Replace the silent-true emitCondBr arm with a lowering-time
diagnostic (checkConditionType/isValidConditionType) rejecting conditions
whose type isn't bool/integer/pointer/optional; the backend @panic is now
an unreachable tripwire.
Regressions: examples/optionals/0908..0910 + diagnostics/1194 (negative).
Verified by 3+3 adversarial reviews.
Filed adjacent bugs found during review: 0168 (array-of-optionals element
load), 0169 (optional->bool coercion), 0170 (closure-optional layout).
46 lines
2.0 KiB
Markdown
46 lines
2.0 KiB
Markdown
# 0168 — indexing an array of optionals `[N]?T` produces a wrong/garbage element (segfault or wrong value)
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## Symptom
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Reading an element of an array whose element type is an optional (`[N]?T`) is
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broken: depending on how the result is used it either SEGFAULTS or yields the
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WRONG value (reads a present element as absent). Independent of issue 0164 (the
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`if`-on-optional fix) — reproduces with a plain `??` and with a copy-to-local.
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## Reproduction
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```sx
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#import "modules/std.sx";
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main :: () {
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arr : [2]?i64 = .{ null, 7 };
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// (1) index result used directly → SEGFAULT (exit 134)
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x := arr[1];
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print("{}\n", x ?? -1); // expected: 7
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// (2) copy element to a local then test → WRONG VALUE
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e := arr[1]; // element 1 is present (7)
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if e { print("present\n"); } else { print("absent\n"); } // prints "absent" — WRONG
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}
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```
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Expected: element 1 is the present optional `7`. Observed: segfault in case
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(1); `absent` (a wrong/absent optional) in case (2). The original surfacing form
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`if arr[0] { ... }` also segfaults.
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## Investigation prompt
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The element load / addressing for an array of optionals appears to compute the
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wrong element stride or mis-materialize the loaded `{T,i1}` optional aggregate.
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Suspect the index/element-load lowering (`src/ir/lower/expr.zig` index-get path,
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and `src/backend/llvm/ops.zig` `emitIndexGet`) when the element type is an
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optional aggregate `{T,i1}` — check that the element size/alignment used for the
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GEP matches the optional's real size (cf. the `size_of` vs `typeSizeBytes`
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nuance for optionals), and that the loaded value is the full aggregate, not a
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truncated/garbage read. Compare against a working `[N]T` (non-optional) array
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load to isolate whether it's stride math or aggregate materialization.
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Verify: case (1) prints `7`, case (2) prints `present`; also test `[N]?T` with a
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struct payload (`[2]?Pt`) and writing elements then reading them back. Add an
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`examples/optionals/09xx-array-of-optionals.sx` regression.
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