[pkg/translator/prometheusremotewrite] preserve multiple underscores when permissive sanitization is enabled

[s3onghyun]

Description

newPrometheusConverter builds its LabelNamer with only UnderscoreLabelSanitization set:

labelNamer: otlptranslator.LabelNamer{UnderscoreLabelSanitization: !prometheus.DropSanitizationGate.IsEnabled(), UTF8Allowed: utf8Allowed},

Because PreserveMultipleUnderscores is never set, label names with consecutive underscores (e.g. a__b) are collapsed to a single underscore (a_b) even when the pkg.translator.prometheus.PermissiveLabelSanitization feature gate is enabled — so enabling the gate does not fully drop sanitization as documented.

This sets PreserveMultipleUnderscores from the same feature gate, so when the gate is on, consecutive underscores are preserved. otlptranslator.LabelNamer already exposes this field (v1.0.0), and reserved __-prefixed labels remain untouched.

Link to tracking issue

Fixes #48991

Testing

Added TestNewPrometheusConverterLabelNamerMultipleUnderscores covering:

• gate enabled: a__b is preserved
• gate disabled: a__b is collapsed to a_b (unchanged behavior)
• reserved __name__ is preserved regardless of the gate

The gate-enabled case fails before this change and passes after; the full package test suite still passes.

Documentation

No user-facing docs change; the feature gate behavior now matches its documented intent.

[Copilot]

Pull request overview

This PR aligns pkg/translator/prometheusremotewrite label-name handling with the intended behavior of the pkg.translator.prometheus.PermissiveLabelSanitization (DropSanitizationGate) feature gate by preserving consecutive underscores (e.g., a__b) when permissive sanitization is enabled.

Changes:

• Configure otlptranslator.LabelNamer to set PreserveMultipleUnderscores when DropSanitizationGate is enabled.
• Add a unit test covering multiple-underscore behavior for gate enabled/disabled and reserved labels.
• Add module dependency needed for the new test helper and include a changelog entry.

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated 3 comments.

File	Description
pkg/translator/prometheusremotewrite/metrics_to_prw.go	Updates the converter’s LabelNamer configuration to preserve consecutive underscores when the feature gate is enabled.
pkg/translator/prometheusremotewrite/labelnamer_underscore_test.go	Adds test coverage for multiple-underscore label behavior under the feature gate.
pkg/translator/prometheusremotewrite/go.mod	Adds the internal/common module dependency used by the new test helper.
.chloggen/prw-preserve-multiple-underscores.yaml	Adds a changelog entry for the bug fix in label sanitization behavior.

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Pull request dashboard status

Merged · refreshed 2026-08-05 08:32 UTC

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[singhvibhanshu]

@s3onghyun,
Please fix the merge conflicts and we will get this in.

[s3onghyun]

Thanks @singhvibhanshu — rebased on latest main, conflicts resolved (f9bf8ec). The only conflict was pkg/translator/prometheusremotewrite/go.mod (version bump to v0.158.0); kept the internal/common dependency since the test uses internal/common/testutil. go build ./... and the underscore tests (v1 + v2) pass locally. Should be good to merge now.

[otelbot]

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