tree f8a60c0d3400154686f501689f3ad83e1d015919
parent d791344a7743ac9955139a92eb44b72659cee3bd
author brandjon <brandjon@google.com> 1548192537 -0800
committer Copybara-Service <copybara-piper@google.com> 1548192685 -0800

Make --experimental_remove_old_python_version_api not breaking existing_rules()

The current way of gating access to the deprecated attribute `default_python_version` is to have the rule check whether or not the attribute was set explicitly (AttributeMap#isAttributeValueExplicitlySpecified), and match that against whether or not the attribute is allowed. However, this breaks the use case of copying a rule definition programmatically via `native.existing_rules()`, because when the definition is copied all the attributes of the new target appear to be explicitly specified.

The solution is to use a sentinel value as the physical default value in the attribute definition. Then the rule just checks for equality with that sentinel. If the configuration permits use of that attribute, then the sentinel is interpreted the same as what the logical default would be.

This requires adding an item to the PythonVersion enum. Ugly, but necessary. We can remove it once the incompatible flag is flipped to remove the old API.

Work toward #6583. Fixes #7071.

RELNOTES: None
PiperOrigin-RevId: 230399577