OSS-Fuzz build fails when setup.py imports unavailable pkg_resources #604

The html5lib-python OSS-Fuzz build fails while pip is preparing the package metadata.

The failure occurs during:

Getting requirements to build wheel

The relevant error is:

ModuleNotFoundError: No module named 'pkg_resources'
ERROR: Failed to build 'file:///src/html5lib-python' when getting requirements to build wheel

At the affected source revision, setup.py imports pkg_resources during build-time setup processing:

from pkg_resources import parse_version
import pkg_resources

Because pkg_resources is unavailable in the build environment, setup.py cannot complete the wheel metadata preparation step, and the fuzz targets are not compiled.

The fix makes pkg_resources optional:

try:
    import pkg_resources
except ImportError:
    pkg_resources = None

The existing setuptools compatibility logic is executed only when pkg_resources is available, and version parsing is performed through pkg_resources.parse_version() within that guarded branch.

This removes the unconditional import that caused the metadata-generation failure while preserving the existing compatibility behavior when the module is present.

The patch was successfully verified with the OSS-Fuzz fuzzing build and check_build.