json_fwd.hpp not installed

[zerodefect]

Bug Report

• What is the issue you have?

Not sure if this is by design or not, but I notice that when I perform 'cmake install', the json_fwd.hpp is not installed.

• What is the expected behavior?

Well, if I want to perform an in-source build (ExternalProject_Add()), as an example, it makes things difficult if their is no install procedure for the fwd declaration.

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

Ubuntu 17.10 and GCC v7.2

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

Released

[theodelrieu]

The default install method only installs the amalgamated json.hpp, you have to set the CMake option -DJSON_MultipleHeaders=ON.

[gregmarr]

I think installing the fwd header in the default install would make sense. Lots of people want forward declarations but don't need the rest of the individual headers.

[zerodefect]

@gregmarr I agree actually. Nonetheless, I feel that is a separate issue (imho).

[theodelrieu]

I personally want to include only adl_serializer.hpp in my code, for this I need every header installed.

That's why I think adding another target to install the amalgamated version + json_fwd is superfluous.

Users can still only include json.hpp as before, I'm not sure having every header or not is a big issue.