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).
14 lines
555 B
Plaintext
14 lines
555 B
Plaintext
// A union struct-literal may set only ONE arm — a single direct member, or
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// several promoted members of the same anonymous-struct arm. Naming two
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// members that overlay the same storage is a compile error (a later store
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// would otherwise silently clobber an earlier one). This guards that
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// diagnostic. (Companion: examples/types/0194 covers the valid forms.)
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#import "modules/std.sx";
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Overlay :: union { f: f32; i: i32; }
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main :: () {
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o : Overlay = .{ f = 3.14, i = 7 }; // ERROR: f and i overlay the same bytes
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print("{}\n", o.i);
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}
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