feat: add //command_line_option:extra_toolchains pseudo-flag#3810
feat: add //command_line_option:extra_toolchains pseudo-flag#3810rickeylev wants to merge 4 commits into
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This pull request introduces support for the Bazel-builtin --extra_toolchains flag via a pseudo-flag //command_line_option:extra_toolchains. It includes parsing logic to convert a comma-separated string into a list of toolchains, updates transition labels, and adds documentation and tests. The feedback suggests using the newly defined labels.EXTRA_TOOLCHAINS constant in python/private/transition_labels.bzl instead of a hardcoded string literal to maintain consistency.
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Add support for transitioning on the //command_line_option:extra_toolchains built-in flag using py_binary.config_settings. Note that, unlike the normal Bazel built-in flag, it must be specified as a simple comma-separated string when set using config_settings, which is then parsed as a CSV string. This is implemented by: - Adding an alias extra_toolchains in command_line_option/BUILD.bazel. - Adding //command_line_option:extra_toolchains to TRANSITION_LABELS so that it is inherited by all transition-using rules (py_wheel, py_zipapp, etc). - Updating apply_config_settings_attr in python/private/attributes.bzl to parse the extra_toolchains CSV string into a list of strings when set via config_settings. - Adding a test case and updating documentation.
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Add support for transitioning on the //command_line_option:extra_toolchains built-in flag using py_binary.config_settings.
Note that, unlike the normal Bazel built-in flag, it must be specified as a simple comma-separated string when set using config_settings, which is then parsed as a CSV string.
This is to make it easier to, on a per-target basis, such as with a zipapp or wheels,
change the Python toolchains used.