GPL License for dependencies

[sirzooro]

I have checked license details for dependencies listed on https://github.com/open-telemetry/opentelemetry-cpp/blob/main/docs/dependencies.md and to my surprise I found that some of them uses GNU GPL License. This means that anyone who would use this library in his proprietary closed-source app would have to release its source code.

After closer look I realized that information on that page are not fully correct. GNU Standard C++ library is licensed on GNU GPL with special exception for compiled code, so OTLP libs compiled with WITH_STL cmake option would be fine for proprietary apps: https://gcc.gnu.org/onlinedocs/libstdc++/faq.html#faq.license.what

I am worried about nostd::span, which you copied from libstdc++. Linked page also mentions GNU GPL, but in source code you have Apache 2.0. That page also mentions possible fallback to gsl::span, but as a fallback when WITH_STL is used and compiler with C++ below C++20 is used.

Please clarify these licensing issues. For now it seems that the safest way for proprietary apps is to compile OTLP libs with WITH_STL enabled and GSL libs in order to avoid possible problems with nostd::span.

[lalitb]

Thanks for raising this issue. It is important for licensing information to be correct.

After closer look I realized that information on that page are not fully correct. GNU Standard C++ library is licensed on GNU GPL with special exception for compiled code

Can you suggest the wordings here to clarify - We can explicitly mention GPL v3 for nostd::span if that helps?

I am worried about nostd::span, which you copied from libstdc++. Linked page also mentions GNU GPL, but in source code you have Apache 2.0.

Correct. The nostd::span header got included by mistake in the automated script used to add Apache 2.0 license, and need to be fixed.

That page also mentions possible fallback to gsl::span, but as a fallback when WITH_STL is used and compiler with C++ below C++20 is used.

This has been fixed in #1167. The gsl::span would be used only if the WITH_GSL build option is provided. The dependency document needs an update.

[sirzooro]

Thanks for raising this issue. It is important for licensing information to be correct.

After closer look I realized that information on that page are not fully correct. GNU Standard C++ library is licensed on GNU GPL with special exception for compiled code

Can you suggest the wordings here to clarify - We can explicitly mention GPL v3 for nostd::span if that helps?

My intention here was to point that things in std namespace used by #include-ing appropriate headers from standard C++ library are on GNU GPL with special exception. This applies to 1st bullet in API&SDK section.

nostd::span code is copied with some changes (like namespace name change), so this is different thing and I am not sure about exact license details for it, as IANAL.

[sirzooro]

I wonder if you could replace code of nostd::span with copy of gsl::span, which uses MIT License. My main concern here is that this may break ABI compatibility, so it may not be so easy to perform.

[lalitb]

IANAL too, does anyone see an issue with adding GPLv3 license along with the Section 7 exception in the nostd::span file header keeping the OpenTelemetry copyright intact? Same for std::variant.

Or else keep the license and copyright intact as currently, add extra information that some portion of code is backported from GPLv3 licensed code.

[lalitb]

I wonder if you could replace code of nostd::span with copy of gsl::span

As you rightly mentioned it won't be a good idea to do it now with the stable release of traces, as this may break ABI compatibility.