metricsgen: port metrics code generation tool (#9156)

This is a port of #8470 and #8501 from the former mainline branch, in
support of #2600 and #9076. 

No additional changes other than checking out the code have been
implemented in this PR. A subsequent PR will incorporate this code.

scripts/metricsgen/testdata/basic/metrics.gen.go

@@ -0,0 +1,30 @@
+// Code generated by metricsgen. DO NOT EDIT.
+
+package basic
+
+import (
+	"github.com/go-kit/kit/metrics/discard"
+	prometheus "github.com/go-kit/kit/metrics/prometheus"
+	stdprometheus "github.com/prometheus/client_golang/prometheus"
+)
+
+func PrometheusMetrics(namespace string, labelsAndValues ...string) *Metrics {
+	labels := []string{}
+	for i := 0; i < len(labelsAndValues); i += 2 {
+		labels = append(labels, labelsAndValues[i])
+	}
+	return &Metrics{
+		Height: prometheus.NewGaugeFrom(stdprometheus.GaugeOpts{
+			Namespace: namespace,
+			Subsystem: MetricsSubsystem,
+			Name:      "height",
+			Help:      "simple metric that tracks the height of the chain.",
+		}, labels).With(labelsAndValues...),
+	}
+}
+
+func NopMetrics() *Metrics {
+	return &Metrics{
+		Height: discard.NewGauge(),
+	}
+}

scripts/metricsgen/testdata/basic/metrics.go

@@ -0,0 +1,11 @@
+package basic
+
+import "github.com/go-kit/kit/metrics"
+
+//go:generate go run ../../../../scripts/metricsgen -struct=Metrics
+
+// Metrics contains metrics exposed by this package.
+type Metrics struct {
+	// simple metric that tracks the height of the chain.
+	Height metrics.Gauge
+}

scripts/metricsgen/testdata/commented/metrics.gen.go

@@ -0,0 +1,30 @@
+// Code generated by metricsgen. DO NOT EDIT.
+
+package commented
+
+import (
+	"github.com/go-kit/kit/metrics/discard"
+	prometheus "github.com/go-kit/kit/metrics/prometheus"
+	stdprometheus "github.com/prometheus/client_golang/prometheus"
+)
+
+func PrometheusMetrics(namespace string, labelsAndValues ...string) *Metrics {
+	labels := []string{}
+	for i := 0; i < len(labelsAndValues); i += 2 {
+		labels = append(labels, labelsAndValues[i])
+	}
+	return &Metrics{
+		Field: prometheus.NewGaugeFrom(stdprometheus.GaugeOpts{
+			Namespace: namespace,
+			Subsystem: MetricsSubsystem,
+			Name:      "field",
+			Help:      "Height of the chain. We expect multi-line comments to parse correctly.",
+		}, labels).With(labelsAndValues...),
+	}
+}
+
+func NopMetrics() *Metrics {
+	return &Metrics{
+		Field: discard.NewGauge(),
+	}
+}

scripts/metricsgen/testdata/commented/metrics.go

@@ -0,0 +1,11 @@
+package commented
+
+import "github.com/go-kit/kit/metrics"
+
+//go:generate go run ../../../../scripts/metricsgen -struct=Metrics
+
+type Metrics struct {
+	// Height of the chain.
+	// We expect multi-line comments to parse correctly.
+	Field metrics.Gauge
+}

scripts/metricsgen/testdata/tags/metrics.gen.go

@@ -0,0 +1,55 @@
+// Code generated by metricsgen. DO NOT EDIT.
+
+package tags
+
+import (
+	"github.com/go-kit/kit/metrics/discard"
+	prometheus "github.com/go-kit/kit/metrics/prometheus"
+	stdprometheus "github.com/prometheus/client_golang/prometheus"
+)
+
+func PrometheusMetrics(namespace string, labelsAndValues ...string) *Metrics {
+	labels := []string{}
+	for i := 0; i < len(labelsAndValues); i += 2 {
+		labels = append(labels, labelsAndValues[i])
+	}
+	return &Metrics{
+		WithLabels: prometheus.NewCounterFrom(stdprometheus.CounterOpts{
+			Namespace: namespace,
+			Subsystem: MetricsSubsystem,
+			Name:      "with_labels",
+			Help:      "",
+		}, append(labels, "step", "time")).With(labelsAndValues...),
+		WithExpBuckets: prometheus.NewHistogramFrom(stdprometheus.HistogramOpts{
+			Namespace: namespace,
+			Subsystem: MetricsSubsystem,
+			Name:      "with_exp_buckets",
+			Help:      "",
+
+			Buckets: stdprometheus.ExponentialBuckets(.1, 100, 8),
+		}, labels).With(labelsAndValues...),
+		WithBuckets: prometheus.NewHistogramFrom(stdprometheus.HistogramOpts{
+			Namespace: namespace,
+			Subsystem: MetricsSubsystem,
+			Name:      "with_buckets",
+			Help:      "",
+
+			Buckets: []float64{1, 2, 3, 4, 5},
+		}, labels).With(labelsAndValues...),
+		Named: prometheus.NewCounterFrom(stdprometheus.CounterOpts{
+			Namespace: namespace,
+			Subsystem: MetricsSubsystem,
+			Name:      "metric_with_name",
+			Help:      "",
+		}, labels).With(labelsAndValues...),
+	}
+}
+
+func NopMetrics() *Metrics {
+	return &Metrics{
+		WithLabels:     discard.NewCounter(),
+		WithExpBuckets: discard.NewHistogram(),
+		WithBuckets:    discard.NewHistogram(),
+		Named:          discard.NewCounter(),
+	}
+}

scripts/metricsgen/testdata/tags/metrics.go

@@ -0,0 +1,12 @@
+package tags
+
+import "github.com/go-kit/kit/metrics"
+
+//go:generate go run ../../../../scripts/metricsgen -struct=Metrics
+
+type Metrics struct {
+	WithLabels     metrics.Counter   `metrics_labels:"step,time"`
+	WithExpBuckets metrics.Histogram `metrics_buckettype:"exp" metrics_bucketsizes:".1,100,8"`
+	WithBuckets    metrics.Histogram `metrics_bucketsizes:"1, 2, 3, 4, 5"`
+	Named          metrics.Counter   `metrics_name:"metric_with_name"`
+}