Stubbing method returning the vector of unique_ptr's generates the compile error.

[wojweb]

Hi Everyone,
I have discovered the following issue.

I have simple interface, which returns the vector of unique_ptr, but when I try to fake the return value, I got the compilation error.

usr/include/fakeit/catch/fakeit.hpp:7519:92: required from 'typename std::enable_if<(! std::is_reference::value), fakeit::MethodStubbingProgress<R, arglist>&>::type fakeit::MethodStubbingProgress<R, arglist>::Return(const R&) [with U = std::vector<std::unique_ptrtest::A >; R = std::vector<std::unique_ptrtest::A >; arglist = {}; typename std::enable_if<(! std::is_reference::value), fakeit::MethodStubbingProgress<R, arglist>&>::type = fakeit::MethodStubbingProgress<std::vector<std::unique_ptrtest::A > >&]'

Projects/update-controller/test/deviceManagerTest.cpp:273:59: required from here
usr/include/c++/9.3.0/bits/stl_uninitialized.h:127:72: error: static assertion failed: result type must be constructible from value type of input range
127 | static_assert(is_constructible<_ValueType2, decltype(*__first)>::value,

"error: static assertion failed: result type must be constructible from value type of input range".

The simplest example looks like the following:

`class A {};

class Interface {
public:
virtual std::vector<std::unique_ptr> getVectorOfA();
};

SCENARIO("Vector of A cannot be returned") {
fakeit::Mock mock;
std::vector<std::unique_ptr> vector;
vector.push_back(std::make_unique());
fakeit::When(Method(mock, getVectorOfA)).Return(std::move(vector));
}`

I think that the problem is that the moving return call() in fakeit.h:7530 is enabled if type is not copy_constructible, but vector of pointers is marked as copy_constructible despite that it cannot be copied, as described here: https://devblogs.microsoft.com/oldnewthing/20190926-00/?p=102924.

The workaround is not to use the Return faking, and replace it by the Do, but I wanted to point out these issue.

[FranckRJ]

We already have a smart_is_copy_constructible that handles vector properly, we just need to use it more often, it should be easy to fix, thanks for notifying.

[malcolmdavey]

From memory I think I tried to handle unique_ptr, but maybe didn't handle things like vector<unique_ptr>, so the conditions might not be right ... for Return(), it should be default move or better(elide), in preference to copy.
AlwaysReturn can't move though

[FranckRJ]

Should be fixed #330 which will be available in the next version.