Build process notes
This section contains notes on complexities in the GitHub Actions build-deploy workflow.
macOS crypto provider
Users reported trouble with open legacy encrypted files on macOS specifically, e.g. https://github.com/pikepdf/pikepdf/issues/520
It appears this is because we were using Homebrew’s qpdf which is currently linked against Homebrew’s openssl. The error came from qpdf specifically not finding openssl’s legacy crypto provider. How exactly that comes about is unclear - it may be that delocate-wheel is inconsistent, it may be Homebrew has disabled the legacy provider, etc. Since we use gnutls for crypto and build libqpdf on the fly for Linux wheels, might as well do the same for macOS to address this.
So now we build and link against our own libqpdf, which in turn is linked against gnutls, which does not seem to have the same issues. All of our Linux and macOS builds are doing the same thing now, rather than being split on crypto provider.
Some ugly complications emerged:
1. QPDF now uses some C++17 features like std::get that are not available on macOS 10.9, the default, which seems to support only a subset of C++17. Because of that we need to explicitly set MACOSX_DEPLOYMENT_TARGET=”11.0” when building QPDF.
2. x86_64. For reasons unclear, when MACOSX_DEPLOYMENT_TARGET=”11.0” is set and pikepdf builds, the generated wheel is built without issue, but installing on a macos-12-x86_64 runner gives this error:
ERROR: pikepdf-8.11.0-cp38-cp38-macosx_11_0_x86_64.whl is not a supported wheel on this platform.
(Same for MACOSX_DEPLOYMENT_TARGET=”12.0”).
Thus, we have to pick a different value for this environment variable for the pikepdf. Clearly something is wrong here, but this unintuitive configuration is what works. When MACOSX_DEPLOYMENT_TARGET is not set pybind11’s Pybind11Extension class examines other settings and should set -mmacosx-version-min=10.14 for when cxx_std=17.
Adding to confusion, the build logs from setuptools show that are targeting 10.9, and the wheels are generated for 10.9.
There may be dragons here, still.
3. arm64. MACOSX_DEPLOYMENT_TARGET=”11.0” is the minimum version for arm64. We set this to ensure that pikepdf builds for this target, and then because of the aforementioned Pybind11Extension check, pikepdf’s deployment target would be set to 10.14. To override this, we set MACOSX_DEPLOYMENT_TARGET=”11.0” for each builder, as well as when building libqpdf.
4. Environment differences between GitHub runners and Cirrus CI runners mean we need to use sudo for Cirrus CI, hence maybe_sudo.
Taking a quick peek at numpy, it may be easier to build universal2 wheels and use QEMU or Cirrus CI to confirm that they work. That would be another big build overhaul, so let’s wait for GitHub Actions to release arm64 runners instead.