fix(pypi): return yank reason from SimpleAPI HTML

[aignas]

This makes the logic in the parser a little bit more sophisticated, but
we also start handling the yank reason. With this the yank reason will
be present in the logs, which should be a usability improvement.

The yanked attribute will be None if the package is not yanked and a
string value if it is yanked. An empty string value should be treated
as "yanked with no reason provided".

This implementation assumes that we have HTML escaped sequences as tag
values. It also un-escapes them when returning the strings.

The possibilities that it gives us are, but out of scope for this PR:

• Use the data-requires-python to potentially discard any Python
  packages that are unsupported in the select_whl function.
• Also retrieve the provenance attributes if they are supported.

Work towards #260.
Work towards #2731.

[gemini-code-assist]

Summary of Changes

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This pull request significantly enhances the PyPI Simple API HTML parser to accurately process package metadata, particularly addressing the data-yanked attribute. By correctly extracting and unescaping the yank reason, it resolves a previous misinterpretation of yanked packages and provides a more robust foundation for package management. This also paves the way for leveraging other HTML attributes, such as data-requires-python, for advanced package selection.

Highlights

• Enhanced HTML Parsing: Implemented sophisticated parsing logic for PyPI Simple API HTML <a> tags to accurately extract attributes and their values.
• Corrected Yank Reason Handling: Correctly extracts and returns the data-yanked reason, resolving an issue where its mere presence was misinterpreted as a yanked package.
• New Utility Functions: Introduced _parse_attrs and _unescape_pypi_html helper functions for robust attribute extraction and HTML entity decoding.
• Data Structure Update: Modified the yanked field in the returned package struct to store the string reason instead of a boolean flag.
• Future Capabilities: Enabled future functionality to utilize data-requires-python for advanced package filtering.

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Changelog

• python/private/pypi/parse_simpleapi_html.bzl
  • Refactored HTML parsing logic to correctly extract attributes from <a> tags.
  • Introduced _parse_attrs function to parse HTML attributes.
  • Introduced _unescape_pypi_html function to decode HTML entities in attribute values.
  • Updated yanked field to store the yank reason string instead of a boolean.
• tests/pypi/parse_simpleapi_html/parse_simpleapi_html_tests.bzl
  • Updated test cases to reflect the change in yanked field from boolean to string.
  • Added new test cases for data-yanked with and without a reason, including HTML escaped characters.
  • Updated data-requires-python values to use HTML escaped characters in tests.

Activity

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[gemini-code-assist]

Code Review

This pull request refactors the Simple API HTML parser to correctly handle yanked packages and their reasons. However, a critical security vulnerability has been identified: the new custom HTML attribute parser fails to detect the data-yanked attribute when it is present without an explicit value. This flaw leads to a security regression, as yanked packages (often due to critical bugs or security vulnerabilities) are not recognized, potentially allowing Bazel to download and use compromised versions. Additionally, the _parse_attrs function has significant issues with its loop construct and general handling of valueless attributes, which could lead to incorrect behavior. The attribute parser must be updated to correctly handle boolean attributes and ensure data-yanked always signals a yanked status.