Allow module extension tags to be compared

[fmeum]

RELNOTES: By comparing tag objects, module extensions can check which one preceded the other within a module file and/or in BFS module order, even across tag classes. This allows them to determine precedence based on order when tags from multiple tag classes interact.

Context: https://github.com/bazel-contrib/rules_go/pull/4526/files#r2586719526

[fmeum]

@bazel-io fork 9.0.0

[gemini-code-assist]

Summary of Changes

Hello @fmeum, 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 a significant enhancement to module extensions by enabling the comparison of tag objects. This functionality allows module extensions to programmatically understand the relative ordering of tags, which is crucial for implementing logic that depends on the sequence in which tags are defined. The change provides module extension authors with greater control and flexibility in how they process and interpret tag configurations.

Highlights

• Module Extension Tag Comparison: Module extension tags can now be compared, allowing module extensions to determine the relative order of tags, even across different tag classes.
• Precedence Based on Order: This new comparison capability enables module extensions to establish precedence among tags based on their definition order within a module file and across modules in BFS order.
• Internal Implementation Changes: The TypeCheckedTag class now implements Comparable and includes a compareKey derived from the module and tag indices to facilitate ordered comparison.

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[gemini-code-assist]

Code Review

This pull request introduces the ability to compare module extension tags, which is a great feature for determining precedence. The implementation is solid: TypeCheckedTag now implements Comparable, using a cleverly constructed compareKey from module and tag indices to ensure a correct and efficient sort order. The new tests are thorough, covering both unit-level comparisons and an end-to-end scenario with multiple modules and tag classes. The switch to LinkedHashMap for storing tags is also a nice touch for improving determinism.

I've found one area for improvement regarding the Comparable contract, which I've detailed in a specific comment.

[fmeum]

@bazel-io fork 8.5.0