fix(datadog metrics sink): fix metric type comparison using wrong operand in sort

[gwenaskell]

Summary

In sort_and_collapse_counters_by_series_and_timestamp, the second tuple of the .cmp() call was incorrectly using a.value().as_name() instead of b.value().as_name(). This caused the metric type name (counter/gauge/histogram) to always compare equal to itself, making it a no-op as a sort key. The sort was effectively only ordering by series() and timestamp(), not by metric type name as intended.

Vector configuration

No configuration change — this is an internal sink implementation fix.

How did you test this PR?

Added a unit test.

Change Type

• Bug fix
• New feature
• Dependencies
• Non-functional (chore, refactoring, docs)
• Performance

Is this a breaking change?

• Yes
• No

Does this PR include user facing changes?

• Yes. Please add a changelog fragment based on our guidelines.
• No. A maintainer will apply the no-changelog label to this PR.

References

Made with Cursor

[pront]

Good catch! Please add a changelog entry.

[bruceg]

Existing unit tests in sort_and_collapse_counters_by_series_and_timestamp cover this code path.

@gwenaskell Please clarify. If the unit tests did cover this typo, it should have been failing to start with, so it would seem this code path is not actually covered.

[bruceg]

The fix looks correct but it needs a coverage test and changelog entry.

[gwenaskell]

@bruceg @pront This fix should have a very limited functional impact that will probably go unnoticed, because the current logic already sorts by metric name and tags which is the most important thing for optimizing compression. the only difference this will make is that a set of metrics (type, name) previously sorted as (gauge, aaaa), (counter, aaab), (counter, bbbb), (gauge, bbbc) will now be sorted (counter, aaab), (counter, bbbb), (gauge, aaaa), (gauge, bbbc).

Added a unit test and a changelog.