2637ae98a5
0164 if <optional> no-binding folds has_value to true (silent miscompile)
0165 parenthesized nested optional ?(?T) malformed double-wrap (crash)
0166 ?? .{ } struct-literal default unresolved type (crash)
0167 comptime regToValue array-in-aggregate gap + unclean recovery
54 lines
2.2 KiB
Markdown
54 lines
2.2 KiB
Markdown
# 0164 — `if <optional>` with no binding silently folds the has_value test to `true`
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## Symptom
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Branching on an optional **without a binding** (`if opt { ... }`) takes the
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present-branch unconditionally for any optional whose LLVM representation is a
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struct (`?i64`, `?T`, `?f64`, …). The has_value flag is never read — the IR
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emits `br i1 true`. SILENT MISCOMPILE (no diagnostic, wrong runtime result).
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Pointer-sentinel optionals (`?cstring`, `?*T`, `?Closure`) are unaffected — they
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lower to a bare `ptr` and hit the correct `icmp` path. The `if opt |x| { ... }`
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*binding* form is also correct (it emits `optional_has_value`).
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Observed vs expected: the repro prints `present` for a null optional; expected
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`absent`.
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## Reproduction
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```sx
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#import "modules/std.sx";
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check :: (n: ?i64) { if n { print("present\n"); } else { print("absent\n"); } }
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main :: () {
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a : ?i64 = null;
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b : ?i64 = 42;
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check(a); // prints "present" — WRONG, expected "absent"
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check(b); // prints "present" — correct
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}
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```
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Reproduces identically for function-return init, literal-`null` init,
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literal-value init, and param-passed optionals — universal, not init-path
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specific.
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## Investigation prompt
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Two sites collude:
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- `src/ir/lower/control_flow.zig` (`lowerIfExpr`, ~lines 69–72) emits
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`optional_has_value` **only when `ie.binding_name != null`**. For a bindingless
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`if opt`, it passes `cond = opt_val` (the raw `{T,i1}` aggregate) straight to
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`condBr`. Fix: emit `optional_has_value` whenever the condition's resolved type
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is an optional, binding or not.
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- `src/backend/llvm/ops.zig` (`emitCondBr`, ~lines 2378–2383) has a catch-all
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`else`/struct arm that does `cond = LLVMConstInt(i1, 1, 0)` with the comment
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"Struct values are always truthy". This is exactly the REJECTED
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silent-fallback pattern (see CLAUDE.md). After the lowering fix, make this arm
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a LOUD bail (a non-i1, non-pointer condition reaching condBr is a compiler
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bug) rather than a silent `true`.
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Verify: the repro prints `absent` / `present`; check the IR no longer contains
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`br i1 true` for the optional condition. Add an
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`examples/optionals/09xx-if-optional-no-binding.sx` regression covering null
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and present `?i64`/`?T` without a binding, both branches.
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