Merge colliding Prometheus label values

[ADITYA-CODE-SOURCE]

Summary

• merge colliding normalized attribute labels by joining values with ';' in original-key order
• preserve existing precedence between metric, resource, and synthetic labels while fixing collision handling
• add regression tests for both metric attribute and allowed resource attribute normalization conflicts

Fixes #8236

[codecov]

Codecov Report

❌ Patch coverage is 84.05797% with 11 lines in your changes missing coverage. Please review.
✅ Project coverage is 91.61%. Comparing base (78d0177) to head (98f2820).
⚠️ Report is 6 commits behind head on main.

Files with missing lines	Patch %	Lines
.../exporter/prometheus/Otel2PrometheusConverter.java	84.05%	8 Missing and 3 partials ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##               main    #8364      +/-   ##
============================================
- Coverage     91.61%   91.61%   -0.01%     
- Complexity    10320    10343      +23     
============================================
  Files          1013     1013              
  Lines         27287    27352      +65     
  Branches       3203     3215      +12     
============================================
+ Hits          25000    25059      +59     
- Misses         1559     1566       +7     
+ Partials        728      727       -1     

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[ADITYA-CODE-SOURCE]

@psx95 Thanks for the thoughtful review
I’ve addressed the suggestions in the latest commits, including broader collision coverage, stronger assertions, a cross-source collision case, and helper naming/documentation cleanup. I also fixed a follow-up test expectation in the new ordering case.
Appreciate the detailed feedback.

[zeitlinger]

There's significant conceptual overlap with #8346 - so I'd park this PR for now.

[ADITYA-CODE-SOURCE]

There's significant conceptual overlap with #8346 - so I'd park this PR for now.

Understood, thanks for the context. There's definitely conceptual overlap with #8346 in the Otel2PrometheusConverter label translation logic. I'll park this PR for now and revisit once #8346 settles, so the collision-handling fix can be cleanly applied on top of the final translation model.
Let me know if there's anything else I should do in the meantime.

[ADITYA-CODE-SOURCE]

@jack-berg Thanks for the review. Those are good points — I’ll make sure to optimize the allocation with a fast path for the no-collision case, extend the collision check to resource/scope/additionalAttributes sources, and add the comment explaining the sorting logic.\n\nThis PR is currently parked per @zeitlinger’s request pending #8346. Once that settles, I’ll rebase, apply these changes, and re-request review.

[zeitlinger]

PR is currently parked per @zeitlinger’s request pending #8346.

@ADITYA-CODE-SOURCE this is unblocked now

[ADITYA-CODE-SOURCE]

Rebased this parked PR onto current main now that #8346 has landed.

Latest update:

• rebuilt the collision handling on top of the current translation-strategy-aware converter instead of replaying the old patch mechanically
• added a fast path that keeps the existing cheap insertion behavior unless a normalized label collision is actually detected
• kept collision merging source-local so existing precedence still holds: metric attributes first, synthetic/scope labels unchanged, filtered resource attributes last via putIfAbsent
• preserved current label rendering by using toLabelValue(...) in the merged resource path as well
• expanded regression coverage for metric collisions, resource collisions, metric-vs-resource precedence, array-valued resource collisions, and non-escaping strategy behavior
• added a short comment explaining the custom MapAttributes helper used by the ordering-sensitive tests

Local verification completed with:

• ./gradlew :exporters:prometheus:test --tests "*Otel2PrometheusConverterTest"
• ./gradlew :exporters:prometheus:spotlessCheck
• ./gradlew :exporters:prometheus:check

The branch was force-pushed after rebase.

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[ADITYA-CODE-SOURCE]

Pushed a follow-up for the failing CI. The Linux/macOS Build jobs were not failing in the build/test steps themselves; they were failing in the post-build diff check because ./gradlew build regenerated tracked docs/apidiffs/current_vs_latest/*.txt files after the rebase onto current main.

I regenerated the apidiffs with ./gradlew jApiCmp, committed the updated files, and pushed them in f11595db6.

Local verification:

• ./gradlew :exporters:prometheus:test --tests "*Otel2PrometheusConverterTest"
• ./gradlew :exporters:prometheus:spotlessCheck
• ./gradlew :exporters:prometheus:check
• ./gradlew jApiCmp

At this point the code-side maintainer feedback is addressed and CI should rerun cleanly on the updated branch. The remaining merge blocker after CI is the stale review state from the earlier requested-changes review, which will still need maintainer re-review or dismissal.

[ADITYA-CODE-SOURCE]

@psx95 @jack-berg CI is green now, and I’ve addressed the earlier review feedback in the rebased branch.

The main implementation update is in 6e3a97f, and the follow-up f11595d only refreshes the tracked docs/apidiffs/current_vs_latest/ files after rebasing onto current main.

Could you please take another look

[ADITYA-CODE-SOURCE]

@psx95 @jack-berg All checks are green now, and the branch has been rebased onto current main with the latest follow-ups incorporated.

At this point the remaining merge blocker appears to be the old CHANGES_REQUESTED review state from the earlier version of the PR. Could you please take another look

[jack-berg]

Hey @ADITYA-CODE-SOURCE - thanks for the update. I was it challenging to grok what was actually happening with all the helper methods doing similar but slightly different things. Also, the fast path was still allocating an inner LinkedHashMap inside normalizeAndMergeAttributeLabels, so we were still missing the mark on avoiding allocations for the common case of no collisions.

I took a crack at trying to simplify and avoid the allocations, and opened a PR against your branch on your fork for you to consider: ADITYA-CODE-SOURCE#1

If you approve, go ahead and merge, or go ahead and tweak whatever you see fit and we'll go from there.

[ADITYA-CODE-SOURCE]

Applied the simplification suggested in ADITYA-CODE-SOURCE#1 in 98f2820.\n\nThis keeps the current behavior unchanged:\n- metric and resource collisions still merge within their own source\n- values are still joined in original-key sort order\n- existing cross-source precedence remains unchanged\n- non-escaping strategies are unchanged\n\nThe main change is implementation shape: the common no-collision path now avoids the extra helper/map allocation that was still present before.\n\nLocal verification:\n- ./gradlew :exporters:prometheus:test --tests "*Otel2PrometheusConverterTest"\n- ./gradlew :exporters:prometheus:spotlessCheck\n- ./gradlew :exporters:prometheus:check\n\nCould you please take another look?

[jack-berg]

Thanks for working through this!

Stale

[jack-berg]

@psx95 I've dismissed your change request as stale. Any remaining issues with this? Will wait until tomorrow and then merge

[psx95]

@psx95 I've dismissed your change request as stale. Any remaining issues with this? Will wait until tomorrow and then merge

Hi @jack-berg , thanks!
Yeah I will make sure to take another look today - but I think most of my comments were addressed.

[psx95]

Thanks for working through this!

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