chore: better build data error handling

[rickeylev]

This add some additional error handling, debugging, and normalization logic to
retrieving build data.

This came in handy when diagnosing errors on Windows.

[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 focuses on improving the robustness and cross-platform compatibility of build data handling, particularly for Windows environments. It refactors the PowerShell script responsible for writing build data to use more reliable .NET file operations and sets appropriate file permissions. Additionally, it updates the Python bootstrap logic to correctly resolve build data file paths on Windows and significantly enhances error reporting when these files cannot be read, providing critical debugging information.

Highlights

• Improved Build Data Writing: Refactored the PowerShell script for writing build data to use .NET APIs, ensuring consistent UTF8 encoding without Byte Order Marks (BOM) and setting appropriate file permissions for broader access.
• Enhanced Cross-Platform Path Handling: Implemented Windows-specific path normalization for build data files within the Python bootstrap, converting forward slashes to backslashes and using os.path.normpath.
• Strengthened Error Reporting: Significantly improved error handling when reading build data files, adding detailed diagnostic notes to exceptions, including the lookup path, file existence, and readability status.

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Changelog

• python/private/build_data_writer.ps1
  • Refactored file writing to use System.IO.File::WriteAllLines with UTF8 No BOM encoding.
  • Added Test-Path checks for VERSION_FILE and INFO_FILE before attempting to read their content.
  • Applied read permissions for "Everyone" to the output build data file.
• python/private/py_executable.bzl
  • Updated stage2_bootstrap path construction to use runfiles_root_path for consistent path resolution.
• python/private/stage2_bootstrap_template.py
  • Added Windows-specific path normalization for BUILD_DATA_FILE by replacing forward slashes with backslashes and using os.path.normpath.
  • Modified file opening to use utf-8-sig encoding to correctly handle Byte Order Marks (BOM) on Windows.
  • Implemented detailed exception handling for get_build_data, adding notes about the lookup path, file existence, and readability status.

Activity

• The pull request is currently on hold, awaiting the merge of fix: use runfiles_root_path in stage2 bootstrap #3605, as indicated by the "DO NOT MERGE" note in the description.

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[gemini-code-assist]

Code Review

This pull request improves error handling for build data generation. The PowerShell script build_data_writer.ps1 is made more robust by collecting lines in memory before writing and checking for file existence. The Bazel file py_executable.bzl is refactored to use a helper function for path construction, which is a good cleanup. The Python template stage2_bootstrap_template.py adds more detailed error reporting when reading build data. However, I found a potential TypeError in the new error handling logic if the runfile path is not found, which could mask the original error. Please see my detailed comment.