[Bug]: Incomplete type error with vector of unique_ptrs

[equeim]

Description

This code fails to compile with invalid application of 'sizeof' to an incomplete type 'Opaque' error using NDK r25b:

#include <memory>
#include <vector>

class Opaque;

class Foo {
public:
    Foo(); // defined in another translation unit
    ~Foo(); // defined in another translation unit
private:
    std::vector<std::unique_ptr<Opaque>> ptrs{};
};

void bar() {
    Foo foo{};
}

I believe that this code is legal. GCC and MSVC accept it, as well as Clang/libc++ starting with version 14 (which NDK r25b should based on).
It fails with Clang/libc++ 13, though.

Here is godbolt link: https://godbolt.org/z/YvnK5Wrod
If you change Clang version to 14.0.0 then error disappears.

Upstream bug

No response

Commit to cherry-pick

No response

Affected versions

r25

Canary version

No response

Host OS

Linux

Host OS version

Ubuntu 22.04

Affected ABIs

armeabi-v7a, arm64-v8a, x86, x86_64

[equeim]

It seems that godbolt's Clang 14 is built from commit llvm/llvm-project@282c83c which is somewhere between 14.0.0 and 14.0.1. While NDK r25b is on llvm/llvm-project@282c83c which is 14.0.0. Any plans to update to latest LLVM 14 release which already is 14.0.6?

[stephenhines]

NDK r25b is using clang-r450784d, which doesn't seem to reproduce this error for me. Can you confirm which Clang/NDK you are actually running? Also, Android's 14.0.0 designation is always based on a rolling git revision of upstream LLVM and not the official release version, so 14.0.0 usually refers to something before 14 has actually branched. Still, my version of clang-r450784d shows me:

$ /disk/android_trees/aosp/prebuilts/clang/host/linux-x86/clang-r450784d/bin/clang++ --version
Android (8490178, based on r450784d) clang version 14.0.6 (https://android.googlesource.com/toolchain/llvm-project 4c603efb0cca074e9238af8b4106c30add4418f6)
Target: x86_64-unknown-linux-gnu
Thread model: posix
InstalledDir: /disk/android_trees/aosp/prebuilts/clang/host/linux-x86/clang-r450784d/bin

The following command also works for your test file:

$ /disk/android_trees/aosp/prebuilts/clang/host/linux-x86/clang-r450784d/bin/clang++ -stdlib=libc++ -O2 -c t.cpp

[equeim]

alexey@localhost ~/projects $ ~/Android/Sdk/ndk/25.1.8937393/toolchains/llvm/prebuilt/linux-x86_64/bin/clang++ --version
Android (8490178, based on r450784d) clang version 14.0.6 (https://android.googlesource.com/toolchain/llvm-project 4c603efb0cca074e9238af8b4106c30add4418f6)
Target: x86_64-unknown-linux-gnu
Thread model: posix
InstalledDir: /home/alexey/Android/Sdk/ndk/25.1.8937393/toolchains/llvm/prebuilt/linux-x86_64/bin

Following command fails for me:

alexey@localhost ~/projects $ ~/Android/Sdk/ndk/25.1.8937393/toolchains/llvm/prebuilt/linux-x86_64/bin/aarch64-linux-android21-clang++ -std=c++17 -stdlib=libc++ -O2 -c test.cpp
In file included from test.cpp:1:
/home/alexey/Android/Sdk/ndk/25.1.8937393/toolchains/llvm/prebuilt/linux-x86_64/bin/../sysroot/usr/include/c++/v1/memory:2423:19: error: invalid application of 'sizeof' to an incomplete type 'Opaque'
    static_assert(sizeof(_Tp) > 0,
                  ^~~~~~~~~~~
/home/alexey/Android/Sdk/ndk/25.1.8937393/toolchains/llvm/prebuilt/linux-x86_64/bin/../sysroot/usr/include/c++/v1/memory:2682:7: note: in instantiation of member function 'std::default_delete<Opaque>::operator()' requested here
      __ptr_.second()(__tmp);
      ^
/home/alexey/Android/Sdk/ndk/25.1.8937393/toolchains/llvm/prebuilt/linux-x86_64/bin/../sysroot/usr/include/c++/v1/memory:2636:19: note: in instantiation of member function 'std::unique_ptr<Opaque>::reset' requested here
  ~unique_ptr() { reset(); }
                  ^
/home/alexey/Android/Sdk/ndk/25.1.8937393/toolchains/llvm/prebuilt/linux-x86_64/bin/../sysroot/usr/include/c++/v1/memory:1976:92: note: in instantiation of member function 'std::unique_ptr<Opaque>::~unique_ptr' requested here
    _LIBCPP_DEPRECATED_IN_CXX17 _LIBCPP_INLINE_VISIBILITY void destroy(pointer __p) {__p->~_Tp();}
                                                                                           ^
/home/alexey/Android/Sdk/ndk/25.1.8937393/toolchains/llvm/prebuilt/linux-x86_64/bin/../sysroot/usr/include/c++/v1/memory:1814:21: note: in instantiation of member function 'std::allocator<std::unique_ptr<Opaque>>::destroy' requested here
                __a.destroy(__p);
                    ^
/home/alexey/Android/Sdk/ndk/25.1.8937393/toolchains/llvm/prebuilt/linux-x86_64/bin/../sysroot/usr/include/c++/v1/memory:1640:14: note: in instantiation of function template specialization 'std::allocator_traits<std::allocator<std::unique_ptr<Opaque>>>::__destroy<std::unique_ptr<Opaque>>' requested here
            {__destroy(__has_destroy<allocator_type, _Tp*>(), __a, __p);}
             ^
/home/alexey/Android/Sdk/ndk/25.1.8937393/toolchains/llvm/prebuilt/linux-x86_64/bin/../sysroot/usr/include/c++/v1/vector:426:25: note: in instantiation of function template specialization 'std::allocator_traits<std::allocator<std::unique_ptr<Opaque>>>::destroy<std::unique_ptr<Opaque>>' requested here
        __alloc_traits::destroy(__alloc(), _VSTD::__to_address(--__soon_to_be_end));
                        ^
/home/alexey/Android/Sdk/ndk/25.1.8937393/toolchains/llvm/prebuilt/linux-x86_64/bin/../sysroot/usr/include/c++/v1/vector:369:29: note: in instantiation of member function 'std::__vector_base<std::unique_ptr<Opaque>, std::allocator<std::unique_ptr<Opaque>>>::__destruct_at_end' requested here
    void clear() _NOEXCEPT {__destruct_at_end(__begin_);}
                            ^
/home/alexey/Android/Sdk/ndk/25.1.8937393/toolchains/llvm/prebuilt/linux-x86_64/bin/../sysroot/usr/include/c++/v1/vector:463:9: note: in instantiation of member function 'std::__vector_base<std::unique_ptr<Opaque>, std::allocator<std::unique_ptr<Opaque>>>::clear' requested here
        clear();
        ^
/home/alexey/Android/Sdk/ndk/25.1.8937393/toolchains/llvm/prebuilt/linux-x86_64/bin/../sysroot/usr/include/c++/v1/vector:495:5: note: in instantiation of member function 'std::__vector_base<std::unique_ptr<Opaque>, std::allocator<std::unique_ptr<Opaque>>>::~__vector_base' requested here
    vector() _NOEXCEPT_(is_nothrow_default_constructible<allocator_type>::value)
    ^
test.cpp:11:46: note: in instantiation of member function 'std::vector<std::unique_ptr<Opaque>>::vector' requested here
    std::vector<std::unique_ptr<Opaque>> ptrs{};
                                             ^
test.cpp:4:7: note: forward declaration of 'Opaque'
class Opaque;
      ^
1 error generated.

If I use plain clang++ without specifying a --target option then it succeeds. It won't compile for necessary architectures this way of course.

[DanAlbert]

If I use plain clang++ without specifying a --target option then it succeeds.

If you omit --target but use --stdlib=libc++, does it work? If so this is just #1530

[rprichard]

The following command also works for your test file:

$ /disk/android_trees/aosp/prebuilts/clang/host/linux-x86/clang-r450784d/bin/clang++ -stdlib=libc++ -O2 -c t.cpp

I believe that command will use a newer libc++ than what the NDK is using.

I still see the reported problem with NDK r25b:

/x/android-ndk-r25b/toolchains/llvm/prebuilt/linux-x86_64/bin/aarch64-linux-android21-clang++ t.cpp -c

I assume this is #1530.

[equeim]

If I use plain clang++ without specifying a --target option then it succeeds.

If you omit --target but use --stdlib=libc++, does it work? If so this is just #1530

Yes (I have Clang 14.0.5 with libc++ installed on host machine (Fedora 36)).

[stephenhines]

Ah, I missed that I was using the wrong libc++ as part of my call. This indeed looks like #1530 again.

[DanAlbert]

Duplicate of #1530