little KitchenandRichard Smith 8edd5eb9a1 fix: reject {} initialization for non-aggregate C++ classes (#6675) ...

## Summary

Fixes the toolchain incorrectly allowing `{}` initialization for
non-aggregate C++ classes.

## Problem

When importing an empty C++ class, the toolchain was treating it as a
Carbon empty struct, which allowed initialization from `{}`. This is
incorrect for non-aggregate classes (e.g., those with user-declared
constructors).

```carbon
import Cpp inline '''
struct X { X(); };  // non-aggregate (has user-declared constructor)
''';

fn Make() {
  var x: Cpp.X = {};  // incorrectly accepted, should be rejected
}
```

## Solution

Added a check for `clang_def->isAggregate()` in `ImportClassObjectRepr`
so that only aggregate classes get the empty struct representation.

**Before:**
```cpp
if (clang_def->isEmpty() && !clang_def->getNumBases()) {
```

**After:**
```cpp
if (clang_def->isEmpty() && !clang_def->getNumBases() &&
    clang_def->isAggregate()) {
```

## Testing

Added test file
`toolchain/check/testdata/interop/cpp/class/non_aggregate_init.carbon`
with:
- Non-aggregate class (`struct X { X(); }`) - should reject `{}`
initialization
- Aggregate class (`struct Y {}`) - should accept `{}` initialization

Note: I couldn't run tests locally due to clang version requirements
(needs >= 19, have 17). The CI should validate the changes.

Closes #6669

---------

Co-authored-by: Richard Smith <richard@metafoo.co.uk>

2026-02-24 18:19:50 +00:00

..

as.carbon

Skip C++ types when generating Destroy witnesses (#6732)

2026-02-14 00:43:11 +00:00

copy.carbon

Add an interface-with-self generic to each interface and same for constraints (#6667)

2026-02-19 16:24:07 +00:00

destroy.carbon

Implement unused pattern bindings, continued (#6518)

2026-02-19 23:33:36 +00:00

implicit_as.carbon

fix: reject {} initialization for non-aggregate C++ classes (#6675)

2026-02-24 18:19:50 +00:00