Fix nominal type layout for enum-like tag unions in tuples #9026
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When a nominal type wraps an enum-like tag union (one with no payloads), the layout computation would incorrectly skip the nominal update because it checked for `.tag_union` structure type but didn't verify whether a pending container actually existed. Enum-like tag unions resolve directly to scalar layouts (the discriminant) without creating a pending container. The existing code assumed all tag unions would have pending containers, causing the nominal's placeholder layout (Box(opaque_ptr)) to never be updated to the actual scalar layout. This resulted in tuple elements getting Box layouts when they should have had scalar layouts, causing crashes when the interpreter tried to incref a discriminant value as if it were a pointer. The fix checks if there's actually a pending container for the current var before skipping the nominal update. If no pending container exists (as is the case for enum-like tag unions), the update proceeds normally. Fixes #9011 Co-Authored-By: Claude Opus 4.5 <[email protected]>
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Summary
When a nominal type wraps an enum-like tag union (one with no payloads), the layout computation would incorrectly skip the nominal update, causing crashes with "cast causes pointer to be null" or "integer overflow" errors.
Fixes #9011
Co-authored by Claude Opus 4.5