[mdatagen] Fix panic in TestValue() and TestValueTwo() for single-element or empty enum attributes

[bhuvan-somisetty]

Description

Fix index-out-of-range panic in cmd/mdatagen when handling single-element enum attributes or empty enum slices. Also add validation in validateAttributes() and validateResourceAttributes() to reject empty enum attributes.

Link to tracking issue

Fixes #15644

Testing

Added unit tests in cmd/mdatagen/internal/metadata_test.go covering single-element, multi-element, empty enum, and non-enum attributes, as well as metadata validation tests. Verified all tests pass in cmd/mdatagen.

Documentation

None

Authorship

• I, a human, wrote this pull request description myself.

[bhuvan-somisetty]

Hi @dmitryax , @mx-psi whenever you have a moment, could you please approve the CI workflow run for this PR? Thank you!

[osullivandonal]

This is very much an edge case, I would argue an enum with less than 2 enumerations is not an enum. Given that if an enum is presented with less than 2 I would expect it to error, something like:

  if len(attr.Enum) == 1 {
      errs = errors.Join(errs, fmt.Errorf("enum for attribute %v must have at least two values", attrName))
  }

If you want to use an enum with one value I would agrue that it should be a constant.

[codecov]

Codecov Report

❌ Patch coverage is 57.14286% with 3 lines in your changes missing coverage. Please review.
✅ Project coverage is 91.04%. Comparing base (c823638) to head (2d31d94).
⚠️ Report is 8 commits behind head on main.

Files with missing lines	Patch %	Lines
cmd/mdatagen/internal/metadata.go	57.14%	2 Missing and 1 partial ⚠️

❌ Your patch check has failed because the patch coverage (57.14%) is below the target coverage (95.00%). You can increase the patch coverage or adjust the target coverage.

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #15646      +/-   ##
==========================================
- Coverage   91.04%   91.04%   -0.01%     
==========================================
  Files         728      729       +1     
  Lines       48467    48497      +30     
==========================================
+ Hits        44129    44154      +25     
- Misses       3011     3018       +7     
+ Partials     1327     1325       -2     

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[bhuvan-somisetty]

Thanks for the feedback @osullivandonal! That makes complete sense — an enum with fewer than 2 values should be rejected as invalid metadata.

I've updated validateAttributes() and validateResourceAttributes() to enforce that enum attributes must have at least two values, and added corresponding unit tests.