feat: command_line_option transition support, default windows to enable_runfiles=true

[rickeylev]

In order to run a py_binary on Windows, runfiles need to be created. However, Bazel
defaults to --enable_runfiles=false for Windows.

To fix, make py_binary set enable_runfiles=true for Windows by default. This
is chosen because supporting a runfiles-less mode is quite invasive (many changes
to bootstraps, plus improving the existing "recreate venv at runtime" logic to
recreate the entire venv).

A complication is that the //command_line_option:... targets don't actually
exist, so they can't be passed as targets to the config_settings attribute
(Bazel special cases them in other contexts). To fix, fake alias targets are created,
and the py_binary transition logic is updated to treat those fakes as aliases
for the real ones.

To allow arbitrary //command_line_option flags to be transitioned on (using the
add_transition_label() apis), the parsing logic treats any label whose package
is command_line_option as such a special aliases.

[gemini-code-assist]

Summary of Changes

Hello @rickeylev, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request introduces significant enhancements to how py_binary and py_test rules interact with Bazel's configuration system, specifically by enabling them to transition on //command_line_option settings. This change provides greater flexibility in defining target configurations and improves cross-platform compatibility, particularly for Windows environments. The modifications involve new Bazel BUILD files for command_line_option aliases, updates to configuration processing logic, and refactoring of rule macros for cleaner code.

Highlights

• Command Line Option Transition Support: Introduced a new command_line_option package to provide aliases for Bazel's built-in //command_line_option pseudo-targets, enabling py_binary and py_test rules to transition on these settings.
• Configuration Setting Handling: Modified the apply_config_settings_attr function to specially handle command_line_option labels, ensuring they are correctly mapped to Bazel's internal configuration settings.
• Windows Compatibility Improvements: Enhanced the build_data_writer.ps1 script for robust file writing on Windows by using .NET methods, addressing encoding and file locking issues. Also, improved stage2_bootstrap_template.py to handle Windows path conversions and error reporting for BUILD_DATA_FILE.
• Macro Refactoring: Refactored py_binary_macro and py_test_macro to utilize a common setup function, common_executable_macro_kwargs_setup, which now also applies default configuration settings.
• New Labels and Debugging: Added new labels like BUILD_RUNFILE_LINKS, ENABLE_RUNFILES, and PLATFORMS_OS_WINDOWS to common_labels.bzl, and included additional verbose print statements in python_bootstrap_template.txt for debugging runtime environment variables.

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Changelog

• BUILD.bazel
  • Added //command_line_option:distribution to the filegroup for internal development dependencies.
• command_line_option/BUILD.bazel
  • Added a new BUILD file defining alias targets for build_runfile_links and enable_runfiles under the command_line_option package, along with a filegroup for distribution.
• docs/api/rules_python/command_line_option/index.md
  • Added new documentation for the //command_line_option package.
• python/private/attributes.bzl
  • Added an important note explaining the special handling of command_line_option labels in config_settings.
  • Modified apply_config_settings_attr to convert command_line_option labels to their Bazel-builtin pseudo-target format.
• python/private/build_data_writer.ps1
  • Refactored the PowerShell script to collect all output lines into an array and write them using .NET's WriteAllLines with UTF8 without BOM, improving encoding and avoiding locking issues.
  • Added logic to set file permissions to allow everyone read access to the output file.
• python/private/common_labels.bzl
  • Added BUILD_RUNFILE_LINKS and ENABLE_RUNFILES labels, referencing the new command_line_option aliases.
  • Added PLATFORMS_OS_WINDOWS label for platform-specific selections.
• python/private/py_binary_macro.bzl
  • Replaced the direct call to convert_legacy_create_init_to_int with common_executable_macro_kwargs_setup.
• python/private/py_executable.bzl
  • Updated _create_stage1_bootstrap to use runfiles_root_path for stage2_bootstrap.
  • Added add_config_setting_defaults function to apply default config_settings based on platform.
  • Introduced common_executable_macro_kwargs_setup to encapsulate common macro setup logic, including convert_legacy_create_init_to_int and add_config_setting_defaults.
  • Expanded the inputs and outputs for the transition to include //command_line_option:build_runfile_links and //command_line_option:enable_runfiles.
• python/private/py_test_macro.bzl
  • Replaced the direct call to convert_legacy_create_init_to_int with common_executable_macro_kwargs_setup.
• python/private/python_bootstrap_template.txt
  • Added verbose print statements for various environment variables and paths to aid debugging.
  • Improved the error message when the Python binary cannot be found, including both PYTHON_BINARY and PYTHON_BINARY_ACTUAL.
• python/private/stage2_bootstrap_template.py
  • Added a comment noting that BUILD_DATA_FILE uses forward slashes and needs conversion for Windows.
  • Modified get_build_data to handle Windows paths by replacing forward slashes with backslashes and normalizing the path.
  • Updated get_build_data to open files with utf-8-sig encoding to handle Windows BOM and added detailed error notes for debugging file access issues.
  • Added a comment to find_runfiles_root indicating that --enable_runfiles=false is likely set when runfiles cannot be found.
• tests/bootstrap_impls/BUILD.bazel
  • Loaded py_binary and py_test rules.
  • Added a new py_test target named system_python_nodeps_test.
• tests/bootstrap_impls/system_python_nodeps_test.py
  • Added a simple Python script for testing.
• tests/pypi/whl_installer/wheel_installer_test.py
  • Modified the tearDown method to ignore errors when removing the wheel directory on Windows, addressing file locking issues.
• tests/support/py_reconfig.bzl
  • Removed the direct processing of attr.config_settings from _perform_transition_impl.
  • Added //command_line_option:build_runfile_links and //command_line_option:stamp to _RECONFIG_INPUTS.

Activity

• The pull request is currently marked as 'DO NOT MERGE' and is awaiting changes from pull request test: add system_python_nodeps_test #3609.

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[gemini-code-assist]

Code Review

This pull request introduces support for //command_line_option transitions in py_binary and py_test rules, providing more flexible configurations. However, a critical security issue was identified in the PowerShell script (build_data_writer.ps1) used to write build data on Windows, as it explicitly grants global read access to the output file. This violates the principle of least privilege and requires remediation. Additionally, consider adding documentation for the new feature and a minor refactoring for improved code conciseness.