tree 5cf635c2636961ce94f4bd560d1338119d6aca3e
parent 539bfc9870d26ab44c4912e65c08c0cc285f7d8b
author brandjon <brandjon@google.com> 1549576587 -0800
committer Copybara-Service <copybara-piper@google.com> 1549576695 -0800

Add `--incompatible_py3_is_default` to change `py_binary` and `py_test`'s default version

When this flag is enabled, `py_binary` and `py_test` targets that do not specify a version (by setting the `python_version` attribute, or its deprecated alias `default_python_version`) will default to `PY3` instead of `PY2`. In addition, the host configuration will use `PY3`, unless `--host_force_python=PY2` is set to override it.

The flag requires the new version semantics (`--incompatible_allow_python_version_transitions=true`), and will fail the build if it is not set.

The flag is implemented by eliminating PythonVersion#DEFAULT_TARGET_VALUE and replacing it with an accessor PythonOptions#getDefaultPythonVersion. For the case of rule transition factories in rule definitions, which previously relied on DEFAULT_TARGET_VALUE and which do not have access to a configuration, they are updated to instead pass a callback function that retrieves the default version from the configuration at the time of the transition.

Work toward #6647, #7359.

RELNOTES[INC]: Added --incompatible_py3_is_default to test switching the default Python version to PY3 for py_binary/py_test targets that do not specify a version. See #7359.

PiperOrigin-RevId: 232939284