`pup metrics list --filter` always returns empty results (uses tag_filter instead of metric name filter)

[dasch]

Summary

pup metrics list --filter always returns empty results regardless of the filter value. The --filter flag is documented as filtering by metric name pattern, but the implementation passes the value to the Datadog API's tag_filter parameter, which filters by Datadog tags (e.g., env:prod) — not metric names.

Steps to Reproduce

# List all metrics — works, returns 221k+ metrics
pup metrics list | python3 -c "import sys,json; d=json.load(sys.stdin); print(len(d['metrics']))"
# Output: 221561

# Filter by metric name — returns empty
pup metrics list --filter="system.cpu"
# Output: {"from": "...", "metrics": []}

# Even an exact metric name returns empty
pup metrics list --filter="system.cpu.user"
# Output: {"from": "...", "metrics": []}

# But these metrics exist in the unfiltered list
pup metrics list | python3 -c "
import sys, json
d = json.load(sys.stdin)
matches = [m for m in d['metrics'] if 'system.cpu' in m]
print(f'system.cpu matches: {len(matches)}')
"
# Output: system.cpu matches: 241

Every filter value produces empty results: kafka_index, system.*, *cpu*, bare strings, wildcards — all return {"metrics": []}.

Root Cause

In cmd/metrics.go, the runMetricsList function passes the --filter value as WithTagFilter():

opts := datadogV1.NewListActiveMetricsOptionalParameters()
if filterPattern != "" {
    opts = opts.WithTagFilter(filterPattern)
}

The Datadog v1 ListActiveMetrics API's tag_filter parameter filters by Datadog tags (comma-separated, e.g., env:prod,service:api) — not by metric name patterns. Since kafka_index, system.cpu, etc. are not valid tags, the API returns no matching metrics.

Expected Behavior

pup metrics list --filter="kafka_index" should return metrics whose names contain or match kafka_index, consistent with the help text:

FILTERING:
  Use the --filter flag to search for metrics matching a pattern:
  • system.* - All system metrics
  • *.cpu.* - All CPU-related metrics
  • custom.* - All custom metrics

Suggested Fix

The v1 ListActiveMetrics API doesn't support metric name filtering server-side. Options:

1. Client-side name filtering: Fetch all metrics and filter names locally (simplest, matches documented behavior)
2. Add --tag-filter flag: Expose the actual tag_filter API parameter under its correct name, and use --filter for client-side name matching
3. Use v2 API: The v2 ListMetricAssets or metric search APIs may support name-based filtering

Environment

• pup version: dev (unknown)
• Installed via: go install github.com/DataDog/pup@latest
• OS: macOS (Darwin 24.6.0)

[platinummonkey]

thanks for reporting!