binaryen has started to require CMAKE_OSX_DEPLOYMENT_TARGET of 10.14

[sbc100]

When we started using std::variant we inadvertently started requiring a 10.14 macOS deployment target.

This went unnoticed on the emscripten-releases builder because there we use out own version of libc++.

However for other users, such as those who want to build from source using emsdk, this is a new requirement and emsdk
currently pins CMAKE_OSX_DEPLOYMENT_TARGET to 10.11:

https://github.com/emscripten-core/emsdk/blob/2b3e0b91761ed8962a7c4eb84d8a288819e106d7/emsdk.py#L1061-L1063

I guess we either need to remove the requirements of binaryen or relax the requirements of emsdk.

[sbc100]

One option is to temporarily revert the use of std::variant in binaryen? @tlively would that be reasonable?

[dschuff]

However for other users, such as those who want to install using emsdk, this is a new requirement and emsdk
currently pins CMAKE_OSX_DEPLOYMENT_TARGET to 10.11:

I think this should be "those who want to build using emsdk". Those who just install are using the Chromium builds and are unaffected.

[sbc100]

However for other users, such as those who want to install using emsdk, this is a new requirement and emsdk
currently pins CMAKE_OSX_DEPLOYMENT_TARGET to 10.11:

I think this should be "those who want to build using emsdk". Those who just install are using the Chromium builds and are unaffected.

Thanks, clarified.

[kripken]

One option is to temporarily revert the use of std::variant in binaryen?

A variation (edit: no pun intended) on that could be to replace the current std::variant with a userspace replacement with similar syntax.

[dschuff]

We also might be able to work around it: https://stackoverflow.com/questions/52521388/stdvariantget-does-not-compile-with-apple-llvm-10-0

[sbc100]

Nice! That looks like it could work.

[tlively]

Yikes! It looks like std::visit is also affected: https://stackoverflow.com/questions/52310835/xcode-10-call-to-unavailable-function-stdvisit/53868971.

Using std::get_if exclusively should work ok technically, but do we have a way to automatically enforce that?

[sbc100]

This should enforce it: #4300

[sbc100]

This should enforce it: #4300

Once we set it to something lower..

[sbc100]

If we land #4300 then part of the fix for this issue will be to lower CMAKE_OSX_DEPLOYMENT_TARGET back to 10.11 (which is what emsdk currently needs/wants).