Apple build failed with json/single_include/nlohmann/json.hpp:4384:57: 'path' is unavailable

[tongyuze]

What is the issue you have?

I just updated the json.hpp from version 3.9.1 to 3.10.4. And the newest version failed the Mac/iOS build with the error:
"json/single_include/nlohmann/json.hpp:4384:57: 'path' is unavailable"
This happened during compilation.

Please describe the steps to reproduce the issue.

Can you provide a small but working code example?

What is the expected behavior?

Build should succeed.

And what is the actual behavior instead?

Build failed with the above error.

Which compiler and operating system are you using?

• Compiler: com.apple.compilers.llvm.clang.1_0.compiler
• Operating system: macOS 11.6

Which version of the library did you use?

• latest release version 3.10.4

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

[tongyuze]

I think that's because our deployment target is 10.11 which doesn't introduce "std::filesystem::path"

[nlohmann]

Seems to be related to #3090.

[jmelas]

I have the same problem. My macOS deployment target is 10.12 so std::filesystem is unavailable.
So we need something like this for filesystem on mac:
#if (MAC_OS_X_VERSION_MIN_REQUIRED >= MAC_OS_X_VERSION_10_15) && defined(JSON_HAS_CPP_17)
instead of simply
#ifdef JSON_HAS_CPP_17

[tongyuze]

I have the same problem. My macOS deployment target is 10.12 so std::filesystem is unavailable. So we need something like this for filesystem on mac: #if (MAC_OS_X_VERSION_MIN_REQUIRED >= MAC_OS_X_VERSION_10_15) && defined(JSON_HAS_CPP_17) instead of simply #ifdef JSON_HAS_CPP_17

And also the iOS version should be >= 13.0.

[nlohmann]

I have the same problem. My macOS deployment target is 10.12 so std::filesystem is unavailable. So we need something like this for filesystem on mac: #if (MAC_OS_X_VERSION_MIN_REQUIRED >= MAC_OS_X_VERSION_10_15) && defined(JSON_HAS_CPP_17) instead of simply #ifdef JSON_HAS_CPP_17

And also the iOS version should be >= 13.0.

Thanks for the input! I will see to add the preprocessor macros. What would be the macro to test the iOS version?

[tongyuze]

I have the same problem. My macOS deployment target is 10.12 so std::filesystem is unavailable. So we need something like this for filesystem on mac: #if (MAC_OS_X_VERSION_MIN_REQUIRED >= MAC_OS_X_VERSION_10_15) && defined(JSON_HAS_CPP_17) instead of simply #ifdef JSON_HAS_CPP_17

And also the iOS version should be >= 13.0.

Thanks for the input! I will see to add the preprocessor macros. What would be the macro to test the iOS version?

For ios, it should be #if __IPHONE_OS_VERSION_MIN_REQUIRED >= 130000
For mac, it should be if __MAC_OS_X_VERSION_MIN_REQUIRED >= 101500

[gregmarr]

It would be better to see if the feature test macros that are in PR now pick it up properly.
https://github.com/nlohmann/json/tree/issue3090

[nlohmann]

It would be better to see if the feature test macros that are in PR now pick it up properly.
https://github.com/nlohmann/json/tree/issue3090

If I understood the documentation correctly, then on macOS, the headers may be there, but the needed library is not present on earlier versions.

In any case, it would be great to add an example for such a macOS/iOS build to the CI. @tongyuze can you provide an example?

[gregmarr]

If I understood the documentation correctly, then on macOS, the headers may be there, but the needed library is not present on earlier versions.

Sigh.

[jmelas]

Another idea is to make std::filesystem support optional with something like
#define JSON_NO_STD_FILESYSTEM

[nlohmann]

PR #3101 does this: if you define JSON_HAS_FILESYSTEM or JSON_HAS_EXPERIMENTAL_FILESYSTEM, then you can override the auto-detection.

[nlohmann]

Fixed with #3090.