[inancgumus]

What?

Wires the feature-flag infra (#6055) and adds the first flag.

• Adds --features to k6 run and k6 cloud run.
• Adds k6 features and k6 features --json for discovery.
• Adds flags usage telemetry, metric tags, and propagates K6_FEATURES into archives.

Why?

Allows users to list and toggle flags.

How it works

Discover flags:

$ k6 features
FEATURE             LIFECYCLE      DESCRIPTION
native-histograms   Experimental   Use native histograms for trend metrics

$ k6 features --json
[
  {
    "feature": "native-histograms",
    "lifecycle": "Experimental",
    "description": "Use native histograms for trend metrics"
  }
]

Enable for a local run (CLI; comma-separated or repeated --features both work):

$ k6 run --features native-histograms script.js
INFO[0000] Experimental feature enabled  feature=native-histograms lifecycle=experimental

Same via env var or JSON config (K6_FEATURES, then config.json):

$ K6_FEATURES=native-histograms k6 run script.js
INFO[0000] Experimental feature enabled  feature=native-histograms lifecycle=experimental

// config.json
{ "features": ["native-histograms"] }

Cloud run — flags bake into the archive as K6_FEATURES and propagate to workers:

k6 cloud run --features native-histograms script.js

Active flags add a k6_feature_<name>="true" tag to every metric sample:

{
  "metric": "data_sent",
  "type": "Point",
  "data": {
    "value": 0,
    "tags": { "scenario": "s", "k6_feature_native_histograms": "true" }
  }
}

Legacy K6_PROMETHEUS_RW_TREND_AS_NATIVE_HISTOGRAM=true still work native-histograms, and warns:

WARN[0000] Legacy env var detected, use --features or K6_FEATURES iTREND_AS_NATIVE_HISTOGRAM feature=native-histogramssource=env_legacy_alias
INFO[0000] Experimental feature enabled  feature=native-histograms

Unknown names log an error and are skipped (run still proceeds, exit 0):

$ k6 run --features not-a-flag script.js
ERRO[0000] Unknown feature flag  feature=not-a-flag outcome=unknown source=cli

options.features in the script is unsupported and ignored with a

WARN[0000] Feature flags in script options are not supported; use --features, K6_FEATURES, or the JSON config  source=options

Precedence: --features > env (K6_FEATURES / legacy alias) > JSON.

Note

• Merge Feature flags (1/2): definition and resolution library #6055 first; this branch targets it.
• The CI failures are not caused by this PR.

Related

• Closes Feature flags #6057
• Feature flags (1/2): definition and resolution library #6055

[szkiba]

LGTM

The base branch was changed.

[szkiba]

LGTM

[oleiade]

🚀