fixup! enhancement: add feature gate checks

Signed-off-by: Pranshu Srivastava <[email protected]>

.circleci/config.yml

@@ -14,6 +14,11 @@ executors:
     resource_class: arm.medium
 
 jobs:
+  feature-gates:
+    executor: golang
+    steps:
+      - checkout
+      - run: make feature-gates-verify
   test:
     executor: golang
     steps:

Makefile

@@ -28,6 +28,8 @@ MACH                    ?= $(shell uname -m)
 
 STATICCHECK_IGNORE =
 
+FEATURE_GATES_MANIFEST = featuregate/feature-gates.md
+
 ifeq ($(GOHOSTOS), linux)
 	test-e2e := test-e2e
 else
@@ -145,3 +147,15 @@ promtool: $(PROMTOOL)
 $(PROMTOOL):
 	mkdir -p $(FIRST_GOPATH)/bin
 	curl -fsS -L $(PROMTOOL_URL) | tar -xvzf - -C $(FIRST_GOPATH)/bin --strip 1 "prometheus-$(PROMTOOL_VERSION).$(GO_BUILD_PLATFORM)/promtool"
+
+.PHONY: feature-gates
+feature-gates:
+	@echo ">> checking feature gates"
+	./feature-gates.sh
+
+.PHONY: feature-gates-verify
+feature-gates-verify: feature-gates
+	@if [ $$(git diff --exit-code -- $(FEATURE_GATES_MANIFEST)  &>/dev/null; echo $$?) -ne 0 ]; then \
+		echo ">> feature gates have changed, needs staging"; \
+		exit 1; \
+	fi

README.md

@@ -349,8 +349,7 @@ This can be useful for having different Prometheus servers collect specific metr
 
 ### Feature Flags
 
-Feature flags are used to enable or disable specific features. They can be set using the `--feature.gates` flag (`key1=true,key2=false,...`). The following feature flags are available:
-* `ConsistentZFSLinuxMetricNames` (default: `false`): Use consistent metric names for ZFS metrics on Linux (same as BSD).
+The `node_exporter` supports feature flags to enable or disable experimental features. These can be found in [./featuregate/feature-gates.md](./featuregate/feature-gates.md).
 
 ## Development building and running
 

feature-gates.sh

@@ -0,0 +1,46 @@
+#!/usr/bin/env bash
+set -euo pipefail
+
+# Fetch the feature-gates manifest from remote. This is the source of truth.
+FEATURE_GATES_MANIFEST_PATH="featuregate/feature-gates.md"
+FEATURE_GATES_REMOTE_MANIFEST_RAW_URL="https://raw.githubusercontent.com/rexagod/node_exporter/feature-gated/$FEATURE_GATES_MANIFEST_PATH" # TODO: Point to prometheus remote.
+FEATURE_GATES_REMOTE_MANIFEST_RAW_STATUS_CODE=$(curl -s -o /dev/null -w "%{http_code}\n" "$FEATURE_GATES_REMOTE_MANIFEST_RAW_URL")
+if [ "$FEATURE_GATES_REMOTE_MANIFEST_RAW_STATUS_CODE" -ne 200 ]; then
+  echo "Failed to fetch feature-gates data from remote, got $FEATURE_GATES_REMOTE_MANIFEST_RAW_STATUS_CODE."
+  exit 1
+fi
+mkdir -p /tmp/featuregate
+curl -s "$FEATURE_GATES_REMOTE_MANIFEST_RAW_URL" > "/tmp/$FEATURE_GATES_MANIFEST_PATH"
+
+# Generate the updated feature-gates manifest locally. This is the working copy.
+echo -e "<!-- This file is auto-generated. DO NOT EDIT MANUALLY. -->
+# Feature gates
+Below is the set of feature-gates currently present in the repository, along with the versions they were added and retired in.
+| Name | Description | Adding Version | Retiring Version |
+|------|-------------|----------------|------------------|" > "./$FEATURE_GATES_MANIFEST_PATH"
+# For all non-test collector files, extract the feature-gates and their metadata.
+find ./collector -type f ! -name "*_test.go" -exec cat {} \; | \
+# * -0777: Slurp the entire file into a single string.
+# * -n: Process the input line by line.
+# * -e: Provide the script as an argument instead of reading it from a file.
+# * $args =~ s/\n/ /g: Replace all newlines in the arguments with spaces (for multi-line arguments).
+perl -0777 -ne '
+    while (m/featuregate\.NewFeatureGate\(\s*([^)]*?)\s*\)/sg) {
+        $args = $1;
+        $args =~ s/\n/ /g;
+        print "$args\n";
+    }
+' | \
+# Squeeze multiple spaces into a single space.
+tr -s ' ' | \
+# Replace commas with pipes.
+tr ',' '|' | \
+# Remove double quotes.
+sed 's/\"//g' >> "./$FEATURE_GATES_MANIFEST_PATH"
+
+# Check for changes to existing feature-gates (instead of adding new ones) by comparing the local and remote feature-gates manifests.
+if grep -Fxf "/tmp/$FEATURE_GATES_MANIFEST_PATH" "./$FEATURE_GATES_MANIFEST_PATH" > /dev/null; then
+  exit 0
+else
+  echo "Manifest modifications are not consistent with the remote. Ensure that no existing feature-gate version commitments were changed."
+fi

featuregate/feature-gates.md

@@ -0,0 +1,5 @@
+<!-- This file is auto-generated. DO NOT EDIT MANUALLY. -->
+# Feature gates
+Below is the set of feature-gates currently present in the repository, along with the versions they were added and retired in.
+| Name | Description | Adding Version | Retiring Version |
+|------|-------------|----------------|------------------|