Wrong result dumping Float4 on ppc64le architecture

[dvarrazzo]

Looking at the packages build job to attempt the release of 3.0.14: https://github.com/psycopg/psycopg/runs/6441951787?check_suite_focus=true

ppc64le fails tests dumping arrays of Float4-wrapped numbers, only on musllinux. Pretty weird.

[dvarrazzo]

This build shows that there is something broken in the struct module. Maybe a musl libc problem?

On manylinux: struct.Struct('!f').pack(1.0).hex()='3f800000'
On musllinux: struct.Struct('!f').pack(1.0).hex()='00000000'

[dvarrazzo]

Reported upstream to Alpine: https://gitlab.alpinelinux.org/alpine/aports/-/issues/13811

[dvarrazzo]

Reported upstream to Python: python/cpython#92826

[dvarrazzo]

Working the issue around by adding a C Float4 dumper which is not affected by the issue. The issue remains in the Python implementation, but now we raise an exception if we detect an attempt to dump using a broken struct package.

[dvarrazzo]

Workaround released in psycopg 3.0.14.