1e0015d6b4
A plain union initialized with a struct literal (b : Overlay = .{ f = 3.14 })
silently miscompiled — it fell through the generic struct-literal path
(getStructFields returns empty for a union), building a malformed structInit
whose overlapping zero-fill clobbered the named member, so it read back 0.0
(and a type-pun read segfaulted).
lowerStructLiteral now detects a plain-union target and dispatches to a new
lowerUnionLiteral, which writes each named member into a union-sized slot via
the same lvalue resolver the u.member = v assignment path uses, then loads the
union value back. Validity: the named members must share one arm — a single
direct member, or several promoted members of the same anonymous-struct variant.
Overlapping members, members from different arms, and positional union literals
are rejected with a diagnostic (no silent last-wins); an empty .{} yields an
undefined union (matching the --- form).
specs.md updated. Regressions: examples/types/0194 (valid forms) +
examples/diagnostics/1191 (overlap rejection).
37 lines
1.6 KiB
Plaintext
37 lines
1.6 KiB
Plaintext
// Union struct-literal initialization — a union may be built with a struct
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// literal that sets a SINGLE arm: one direct member, or several promoted
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// members of the same anonymous-struct arm. Equivalent to the `--- `+per-field
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// form, and the two views stay consistent (type-punning still works).
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//
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// Regression (issue 0158): a union literal previously fell through the generic
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// struct-literal path (getStructFields returns empty for a union), building a
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// malformed structInit whose overlapping zero-fill clobbered the named member —
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// `b : Overlay = .{ f = 3.14 }` silently read back 0.0. Now it lowers like the
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// `--- `+member-write form: each named member is written into a union-sized slot.
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#import "modules/std.sx";
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Overlay :: union { f: f32; i: i32; }
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Vec2 :: union { data: [2]f32; struct { x, y: f32; }; }
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main :: () {
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// Single-member literal — the bug case. Reads back the value, and a
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// type-punning read of the other member sees the same bytes.
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b : Overlay = .{ f = 3.14 };
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print("b.f={} b.i={}\n", b.f, b.i);
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// Equivalence: the `--- `+member-write form produces identical bytes.
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a : Overlay = ---;
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a.f = 3.14;
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print("a.f={} a.i={}\n", a.f, a.i);
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// Promoted members of the anonymous-struct arm: both belong to the same
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// arm (offsets 0 and 4), so naming both is valid; the `data` view overlays.
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v : Vec2 = .{ x = 1.0, y = 2.0 };
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print("v.x={} v.y={} d0={} d1={}\n", v.x, v.y, v.data[0], v.data[1]);
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// Empty literal → undefined union (same as `---`); set a member after.
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e : Overlay = .{};
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e.i = 9;
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print("e.i={}\n", e.i);
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}
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