e5b682e622
The Optional->Concrete unwrap classify rule treated ?i64 -> bool as unwrap+narrow (both builtin), silently yielding false for every optional (present or null). specs.md defines no implicit optional->bool conversion. Reject it: conversions.zig adds an optional_to_bool_reject plan (dst == bool, child != bool); coerce.zig emits a located diagnostic suggesting '!= null'. Covers arg/field-init/return via the shared coerceMode. The if-opt presence test (issue 0164) is a separate path, untouched. Regression: examples/diagnostics/1199-diagnostics-optional-to-bool.sx + conversions.test.zig unit test. Verified by 3 adversarial reviews, suite 789/0. Filed adjacent issue 0179 (whole implicit ?T->concrete unwrap family silently miscompiles a null optional; design-touching).
66 lines
3.1 KiB
Markdown
66 lines
3.1 KiB
Markdown
# 0169 — optional passed where `bool` is expected silently coerces to `false` (always)
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> **RESOLVED** (scoped to `?T → bool`, `T ≠ bool`). The "Optional → Concrete
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> unwrap" classify rule treated `?i64 → bool` as unwrap+narrow (both i64 and bool
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> are builtin), silently yielding `false`. specs.md defines no implicit
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> optional→bool conversion, so the fix REJECTS it: `src/ir/conversions.zig` adds
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> an `optional_to_bool_reject` plan (when `dst == bool` and `child ≠ bool`);
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> `src/ir/lower/coerce.zig` emits a located diagnostic ("…use '!= null'…")
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> instead of a constant false. Covers arg / field-init / return (all share
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> `coerceMode`). `if opt` presence-test (issue 0164) is a separate path,
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> untouched. Verified by 3 adversarial reviews; suite 789/0. Regression:
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> `examples/diagnostics/1199-diagnostics-optional-to-bool.sx` + a
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> `conversions.test.zig` unit test. NOTE: review surfaced a larger sibling
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> surface — the whole implicit `?T → concrete` unwrap family (incl. the
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> `?bool → bool` cell still allowed here) silently miscompiles a NULL optional to
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> garbage — filed as **0179** (design-touching: needs the flow-narrowing
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> decision).
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## Symptom
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Passing an optional (`?T`) to a `bool` parameter (or any bool-typed position:
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bool field initializer, `-> bool` return) compiles WITHOUT a diagnostic and
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silently yields `false` for EVERY optional — present or null alike. Silent
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miscompile.
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This is inconsistent with `if opt` / `while opt`, which (after issue 0164)
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correctly test the has_value flag. The argument/field-coercion path does not.
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## Reproduction
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```sx
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#import "modules/std.sx";
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takes_bool :: (b: bool) { if b { print("true\n"); } else { print("false\n"); } }
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main :: () {
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a : ?i64 = 42;
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n : ?i64 = null;
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takes_bool(a); // prints "false" — should be a type error, or "true" (present)
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takes_bool(n); // prints "false" — (correct only by accident)
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}
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```
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Expected: EITHER a compile-time type error (no implicit optional→bool
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coercion), OR — if implicit coercion is intended — `true` for the present
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optional and `false` for null, matching `if opt` semantics. Observed: always
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`false`, no diagnostic.
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## Investigation prompt
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Decide the intended semantics first (check `specs.md` for whether optional→bool
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is a legal implicit coercion):
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- If NOT legal: the call-argument / assignment type-checker
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(`src/ir/expr_typer.zig` / the coercion/check path) must REJECT an optional in
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a bool-typed position with a located diagnostic — not silently produce a
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zero/false. Find where the bool target type accepts the optional operand and
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emit `self.diagnostics.addFmt(.err, span, ...)`.
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- If legal (consistent with `if opt`): the coercion must lower to the
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optional's has_value test (reuse `optional_has_value`), not a constant/garbage
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`false`. The silent always-`false` is the rejected silent-fallback pattern.
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Whichever is correct, the current always-`false` is wrong. Verify with the repro
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(present → `true` or a type error; null → `false` or a type error). Add a
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regression: an `examples/optionals/09xx-...` if coercion is legal, or a
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`examples/diagnostics/11xx-...` negative test if it's rejected.
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