out of curiosity: why not use pkg-config for flags?

@deronnax it seemed like pkg-config wasn't working for me, I kept getting the osx system libxml2 instead of the one from brew. Happy to try again though, pkg-config seems like a better solution here. Any suggestions of things to try?

@deronnax hmm so this seems to be working for me now, just setting PKG_CONFIG_PATH. Not sure what was going on before. Thanks for the suggestion, I pushed a commit to drop the CFLAGS and LDFLAGS.

@deronnax a small follow up to this. For me locally on my mac, its not enough to just setting PKG_CONFIG_PATH, I still end up with segfaults because of mismatching libxml2 versions. I actually have to set CFLAGS and LDFLAGS. Thats why I initially had them set in this PR.

This must be something about my local setup though, since it seems in CI its enough to set PKG_CONFIG_PATH.

@nosnilmot thank you for the great suggestions. I have accepted them into the PR.

I had to make a slight change to #296 (comment) as it resulted in the build failing because GH actions does not do shell expansion on the env vars defined in the env key. So I moved your suggested change to the PKG_CONFIG_PATH into the run block, so it gets properly expanded.

@jonathangreen thank you for this precious insights. You made me discover that on my mac, I am probably actually linking against the system libxml2 and not homebrew's one, which I thought I did. Do you have tips to check that?

Btw, I see you are not using --no-binary lxml with pip, so you must be getting the lxml wheel and using the libxml2 provided by lxml, no?

Btw, I see you are not using --no-binary lxml with pip, so you must be getting the lxml wheel and using the libxml2 provided by lxml, no?

Yes. In this PR I'm using the lxml wheel, and relying on the fact that the version of libxml2 being installed by brew is the same as the version being used in the most recent lxml builds. So as long as the xmlsec build uses the libxml2 from brew instead of the old version provided by osx everything works as intended.

You made me discover that on my mac, I am probably actually linking against the system libxml2 and not homebrew's one, which I thought I did. Do you have tips to check that?

Now that #299 is merged in, if you build the latest it should give you a useful exception if that is the case. A couple things to try if you are having issues getting this module to build and link against the correct version of libxml2:

• Make sure pip isn't installing a cached previously built wheel
• If just setting PKG_CONFIG_PATH isn't working, try also setting CFLAGS and LDFLAGS. For some reason this was necessary for me when building locally on my M1 mac.

@jonathangreen The reason cp35 is failing is because of type hints. Type hints like Dict and List are supported from >=3.6. I removed them in a separate PR (#303) so yours should pass too after the merge.