🚀 feature request

Relevant Rules

rules_python

Description

When using --no_legacy_external_runfiles, env vars set via $(PYTHON3) are not found at runtime due to the missing location in external/....

Describe the solution you'd like

Something that looks like bazelbuild/rules_java#272 whereby $(PYTHON3) or a new make var, correctly stubs out runfile locations, so that the code is compatible with --no_legacy_external_runfiles.

Describe alternatives you've considered

Using sys.executable inside binary/test code to set the env var manually.

Using non hermetic Python.