Releases 3.6.0 and 3.6.1 don't build on conda / windows

[SylvainCorlay]

• What is the issue you have?

I am the maintainer of the nlohman_json package on conda-forge. The package for the latest releases don't build on windows (VS 2015)

• Please describe the steps to reproduce the issue. Can you provide a small but working code example?

  The logs for the failing builds are available

  • here: (version 3.6.1) nlohmann_json v3.6.1 conda-forge/nlohmann_json-feedstock#7
  • here: (version 3.6.0) nlohmann_json v3.6.0 conda-forge/nlohmann_json-feedstock#6

• Which compiler and operating system are you using? Is it a supported compiler?

MSVC / Windows / (VS 2015)

• Did you use a released version of the library or the version from the develop branch?

Released version.

• If you experience a compilation error: can you compile and run the unit tests?

The compilation error occurs while building the tests, as per the logs above.

[nlohmann]

That is odd, because the MSVC 2015 build runs successfully at our AppVeyor, see https://ci.appveyor.com/project/nlohmann/json/builds/23234117.

[SylvainCorlay]

Note that this only occurs with 3.6.x. Previous versions of nlohmann_json up until 3.5.x have been packaged succesfully on conda-forge.

[nlohmann]

The compilation error is in file unit-allocator.cpp. The changes there toward 3.6.0 came with #1492. I'm no expert in MSVC. Maybe @stac47 or @theodelrieu have an idea on this, as they also proposed the fixes for GCC 9.

[theodelrieu]

It would be great to look at the xmemory file to see what the call is. But my guess is that my_allocator only defines some requirements of Allocator, it seems to miss constructors at least.

Maybe using std::allocator<T>::allocator will be enough. If not, adding the constructors should do the trick.

I would suggest removing the inheritance from std::allocator and rewrite it from scratch though.

[nlohmann]

@theodelrieu Good point, I'll try the using std::allocator<T>::allocator.

[nlohmann]

@SylvainCorlay Could you try whether baaa2a4 builds?

[mistersandman]

The issue appears only when building test-allocator with MSVC in Debug mode, where the STL is augmented with debugging constructs. Adding the following constructors to my_allocator in unit-allocator.cpp seems to also fix the issue:

my_allocator() = default;

template <class U>
my_allocator(const my_allocator<U>&) {}

[nlohmann]

@mistersandman Thanks for the info! As you seem to have access to MSVC (I don't...), could you please check whether baaa2a4 also works?

[mistersandman]

I just checked and it works! Your fix is cleaner than mine 😃

[mistersandman]

The question for @SylvainCorlay remains, whether it is even necessary for his case to build the test suite. If the goal is only to install the library, there's no need for it. Building the test suite can be turned off by adding -DBUILD_TESTING=OFF to the command line when invoking CMake.

[SylvainCorlay]

Hey, thanks for the responses, I am busy for the next couple of hours but will respond after.

[nlohmann]

@SylvainCorlay Does baaa2a4 fix the issue?

[SylvainCorlay]

Trying it out now.

[SylvainCorlay]

Including your patch in the recipe appears to be fixing the compilation issue!

[SylvainCorlay]

3.6.0 and 3.6.1 are now on conda-forge!

[nlohmann]

Thanks a lot for your efforts!

[nlohmann]

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Type

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• 🐛 Bug Fix
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Description

• The test suite could not be compiled on MSVC in debug mode. Releases 3.6.0 and 3.6.1 don't build on conda / windows #1536

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