std::vector<std::string> fails to conform to CxxRandomAccessCollection

[hyp]

As reported here: https://forums.swift.org/t/c-interop-for-in-loop-requires-std-1-vector-element-to-conform-to-sequence/66232

Reproducer:
https://github.com/Sajjon/CxxRandomAccessCollectionNotWorking

[hyp]

over to @egorzhdan

[Sajjon]

Btw it works to call a method returning std::string so using string alone is not an issue, and std::vector<int> is not an issue, just the combination of vector<string> fails to compile.

[moretromain]

I'm facing the same issue, not only with std::string, but even with builtin char/int types:

On the C++ side, I do a few aliases:

using CharArray     = std::vector<char>;
using UCharArray    = std::vector<unsigned char>;
using I8Array       = std::vector<int8_t>;
using U8Array       = std::vector<uint8_t>;
using I16Array      = std::vector<int16_t>;
using U16Array      = std::vector<uint16_t>;
using I32Array      = std::vector<int32_t>;
using U32Array      = std::vector<uint32_t>;
using I64Array      = std::vector<int64_t>;
using U64Array      = std::vector<uint64_t>;

On the Swift side, for each of those, a simple function:

    public static func i8ArrayTest(_ data: I8Array) -> [Int8] {
        let ret = Array<Int8>(data)
        return ret
    }

The results are interesting:

• int, int32_t and uint32_t are working as expected
• all other types are not working (error: doesn't conform to Sequence or CxxConvertibleToCollection in the Array initialization)

Furthermore, if I keep only the two that work (int32_t and uint32_t), I get a link error a bit later, with multiply defined symbols:

<unknown>:0: error: multiple definitions of symbol '$sSo1soiySiSo3stdO3__1O0020___wrap_iter__udAAdDaV_AGtFTO'
<unknown>:0: error: multiple definitions of symbol '$sSo2eeoiySbSo3stdO3__1O0020___wrap_iter__udAAdDaV_AGtFTO'
<unknown>:0: error: multiple definitions of symbol '$sSo3stdO3__1O0020___wrap_iter__udAAdDaV9successorAFyF'
<unknown>:0: error: multiple definitions of symbol '$sSo3stdO3__1O0020___wrap_iter__udAAdDaV2peoiyyAFz_SitFZ'

I also tried this:

#pragma pack(push, 4)
struct FourBytes
{
    char x[4];
};
#pragma pack(pop)
using B4Array  = std::vector<FourBytes>;

Just to see if the issue was with a vector of element of sizeof(Element) != 4 (the multiply defined symbols could indicate that the generated code only cares about the size of an element, not its type), but I'm getting the same "doesn't conform" error on the Swift side, so the issue is really int/int32_t/uint32_t vs. anything else.

Swift 5.9 / Xcode 15 Beta 4, same issue when compiling from Xcode, or by invoking swiftc directly