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/metricsdiff/metricsdiff.go

@@ -0,0 +1,197 @@
+// metricsdiff is a tool for generating a diff between two different files containing
+// prometheus metrics. metricsdiff outputs which metrics have been added, removed,
+// or have different sets of labels between the two files.
+package main
+
+import (
+	"flag"
+	"fmt"
+	"io"
+	"log"
+	"os"
+	"path/filepath"
+	"sort"
+	"strings"
+
+	dto "github.com/prometheus/client_model/go"
+	"github.com/prometheus/common/expfmt"
+)
+
+func init() {
+	flag.Usage = func() {
+		fmt.Fprintf(os.Stderr, `Usage: %[1]s <path1> <path2>
+
+Generate the diff between the two files of Prometheus metrics.
+The input should have the format output by a Prometheus HTTP endpoint.
+The tool indicates which metrics have been added, removed, or use different
+label sets from path1 to path2.
+
+`, filepath.Base(os.Args[0]))
+		flag.PrintDefaults()
+	}
+}
+
+// Diff contains the set of metrics that were modified between two files
+// containing prometheus metrics output.
+type Diff struct {
+	Adds    []string
+	Removes []string
+
+	Changes []LabelDiff
+}
+
+// LabelDiff describes the label changes between two versions of the same metric.
+type LabelDiff struct {
+	Metric  string
+	Adds    []string
+	Removes []string
+}
+
+type parsedMetric struct {
+	name   string
+	labels []string
+}
+
+type metricsList []parsedMetric
+
+func main() {
+	flag.Parse()
+	if flag.NArg() != 2 {
+		log.Fatalf("Usage is '%s <path1> <path2>', got %d arguments",
+			filepath.Base(os.Args[0]), flag.NArg())
+	}
+	fa, err := os.Open(flag.Arg(0))
+	if err != nil {
+		log.Fatalf("Open: %v", err)
+	}
+	defer fa.Close()
+	fb, err := os.Open(flag.Arg(1))
+	if err != nil {
+		log.Fatalf("Open: %v", err)
+	}
+	defer fb.Close()
+	md, err := DiffFromReaders(fa, fb)
+	if err != nil {
+		log.Fatalf("Generating diff: %v", err)
+	}
+	fmt.Print(md)
+}
+
+// DiffFromReaders parses the metrics present in the readers a and b and
+// determines which metrics were added and removed in b.
+func DiffFromReaders(a, b io.Reader) (Diff, error) {
+	var parser expfmt.TextParser
+	amf, err := parser.TextToMetricFamilies(a)
+	if err != nil {
+		return Diff{}, err
+	}
+	bmf, err := parser.TextToMetricFamilies(b)
+	if err != nil {
+		return Diff{}, err
+	}
+
+	md := Diff{}
+	aList := toList(amf)
+	bList := toList(bmf)
+
+	i, j := 0, 0
+	for i < len(aList) || j < len(bList) {
+		for j < len(bList) && (i >= len(aList) || bList[j].name < aList[i].name) {
+			md.Adds = append(md.Adds, bList[j].name)
+			j++
+		}
+		for i < len(aList) && j < len(bList) && aList[i].name == bList[j].name {
+			adds, removes := listDiff(aList[i].labels, bList[j].labels)
+			if len(adds) > 0 || len(removes) > 0 {
+				md.Changes = append(md.Changes, LabelDiff{
+					Metric:  aList[i].name,
+					Adds:    adds,
+					Removes: removes,
+				})
+			}
+			i++
+			j++
+		}
+		for i < len(aList) && (j >= len(bList) || aList[i].name < bList[j].name) {
+			md.Removes = append(md.Removes, aList[i].name)
+			i++
+		}
+	}
+	return md, nil
+}
+
+func toList(l map[string]*dto.MetricFamily) metricsList {
+	r := make([]parsedMetric, len(l))
+	var idx int
+	for name, family := range l {
+		r[idx] = parsedMetric{
+			name:   name,
+			labels: labelsToStringList(family.Metric[0].Label),
+		}
+		idx++
+	}
+	sort.Sort(metricsList(r))
+	return r
+}
+
+func labelsToStringList(ls []*dto.LabelPair) []string {
+	r := make([]string, len(ls))
+	for i, l := range ls {
+		r[i] = l.GetName()
+	}
+	return sort.StringSlice(r)
+}
+
+func listDiff(a, b []string) ([]string, []string) {
+	adds, removes := []string{}, []string{}
+	i, j := 0, 0
+	for i < len(a) || j < len(b) {
+		for j < len(b) && (i >= len(a) || b[j] < a[i]) {
+			adds = append(adds, b[j])
+			j++
+		}
+		for i < len(a) && j < len(b) && a[i] == b[j] {
+			i++
+			j++
+		}
+		for i < len(a) && (j >= len(b) || a[i] < b[j]) {
+			removes = append(removes, a[i])
+			i++
+		}
+	}
+	return adds, removes
+}
+
+func (m metricsList) Len() int           { return len(m) }
+func (m metricsList) Less(i, j int) bool { return m[i].name < m[j].name }
+func (m metricsList) Swap(i, j int)      { m[i], m[j] = m[j], m[i] }
+
+func (m Diff) String() string {
+	var s strings.Builder
+	if len(m.Adds) > 0 || len(m.Removes) > 0 {
+		fmt.Fprintln(&s, "Metric changes:")
+	}
+	if len(m.Adds) > 0 {
+		for _, add := range m.Adds {
+			fmt.Fprintf(&s, "+++ %s\n", add)
+		}
+	}
+	if len(m.Removes) > 0 {
+		for _, rem := range m.Removes {
+			fmt.Fprintf(&s, "--- %s\n", rem)
+		}
+	}
+	if len(m.Changes) > 0 {
+		fmt.Fprintln(&s, "Label changes:")
+		for _, ld := range m.Changes {
+			fmt.Fprintf(&s, "Metric: %s\n", ld.Metric)
+			for _, add := range ld.Adds {
+				fmt.Fprintf(&s, "+++ %s\n", add)
+			}
+			for _, rem := range ld.Removes {
+				fmt.Fprintf(&s, "--- %s\n", rem)
+			}
+		}
+	}
+	return s.String()
+}

scripts/metricsgen/metricsdiff/metricsdiff_test.go

@@ -0,0 +1,62 @@
+package main_test
+
+import (
+	"bytes"
+	"io"
+	"testing"
+
+	"github.com/stretchr/testify/require"
+	metricsdiff "github.com/tendermint/tendermint/scripts/metricsgen/metricsdiff"
+)
+
+func TestDiff(t *testing.T) {
+	for _, tc := range []struct {
+		name      string
+		aContents string
+		bContents string
+
+		want string
+	}{
+		{
+			name: "labels",
+			aContents: `
+			metric_one{label_one="content", label_two="content"} 0
+			`,
+			bContents: `
+			metric_one{label_three="content", label_four="content"} 0
+			`,
+			want: `Label changes:
+Metric: metric_one
++++ label_three
++++ label_four
+--- label_one
+--- label_two
+`,
+		},
+		{
+			name: "metrics",
+			aContents: `
+			metric_one{label_one="content"} 0
+			`,
+			bContents: `
+			metric_two{label_two="content"} 0
+			`,
+			want: `Metric changes:
++++ metric_two
+--- metric_one
+`,
+		},
+	} {
+		t.Run(tc.name, func(t *testing.T) {
+			bufA := bytes.NewBuffer([]byte{})
+			bufB := bytes.NewBuffer([]byte{})
+			_, err := io.WriteString(bufA, tc.aContents)
+			require.NoError(t, err)
+			_, err = io.WriteString(bufB, tc.bContents)
+			require.NoError(t, err)
+			md, err := metricsdiff.DiffFromReaders(bufA, bufB)
+			require.NoError(t, err)
+			require.Equal(t, tc.want, md.String())
+		})
+	}
+}

scripts/metricsgen/metricsgen.go

@@ -0,0 +1,347 @@
+// metricsgen is a code generation tool for creating constructors for Tendermint
+// metrics types.
+package main
+
+import (
+	"bytes"
+	"flag"
+	"fmt"
+	"go/ast"
+	"go/format"
+	"go/parser"
+	"go/token"
+	"go/types"
+	"io"
+	"io/fs"
+	"log"
+	"os"
+	"path"
+	"path/filepath"
+	"reflect"
+	"regexp"
+	"strconv"
+	"strings"
+	"text/template"
+)
+
+func init() {
+	flag.Usage = func() {
+		fmt.Fprintf(os.Stderr, `Usage: %[1]s  -struct <struct>
+
+Generate constructors for the metrics type specified by -struct contained in
+the current directory. The tool creates a new file in the current directory
+containing the generated code.
+
+Options:
+`, filepath.Base(os.Args[0]))
+		flag.PrintDefaults()
+	}
+}
+
+const metricsPackageName = "github.com/go-kit/kit/metrics"
+
+const (
+	metricNameTag = "metrics_name"
+	labelsTag     = "metrics_labels"
+	bucketTypeTag = "metrics_buckettype"
+	bucketSizeTag = "metrics_bucketsizes"
+)
+
+var (
+	dir   = flag.String("dir", ".", "Path to the directory containing the target package")
+	strct = flag.String("struct", "Metrics", "Struct to parse for metrics")
+)
+
+var bucketType = map[string]string{
+	"exprange": "stdprometheus.ExponentialBucketsRange",
+	"exp":      "stdprometheus.ExponentialBuckets",
+	"lin":      "stdprometheus.LinearBuckets",
+}
+
+var tmpl = template.Must(template.New("tmpl").Parse(`// Code generated by metricsgen. DO NOT EDIT.
+
+package {{ .Package }}
+
+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{
+		{{ range $metric := .ParsedMetrics }}
+		{{- $metric.FieldName }}: prometheus.New{{ $metric.TypeName }}From(stdprometheus.{{$metric.TypeName }}Opts{
+			Namespace: namespace,
+			Subsystem: MetricsSubsystem,
+			Name:      "{{$metric.MetricName }}",
+			Help:      "{{ $metric.Description }}",
+			{{ if ne $metric.HistogramOptions.BucketType "" }}
+			Buckets: {{ $metric.HistogramOptions.BucketType }}({{ $metric.HistogramOptions.BucketSizes }}),
+			{{ else if ne $metric.HistogramOptions.BucketSizes "" }}
+			Buckets: []float64{ {{ $metric.HistogramOptions.BucketSizes }} },
+			{{ end }}
+		{{- if eq (len $metric.Labels) 0 }}
+		}, labels).With(labelsAndValues...),
+		{{ else }}
+		}, append(labels, {{$metric.Labels}})).With(labelsAndValues...),
+		{{ end }}
+		{{- end }}
+	}
+}
+
+
+func NopMetrics() *Metrics {
+	return &Metrics{
+		{{- range $metric := .ParsedMetrics }}
+		{{ $metric.FieldName }}: discard.New{{ $metric.TypeName }}(),
+		{{- end }}
+	}
+}
+`))
+
+// ParsedMetricField is the data parsed for a single field of a metric struct.
+type ParsedMetricField struct {
+	TypeName    string
+	FieldName   string
+	MetricName  string
+	Description string
+	Labels      string
+
+	HistogramOptions HistogramOpts
+}
+
+type HistogramOpts struct {
+	BucketType  string
+	BucketSizes string
+}
+
+// TemplateData is all of the data required for rendering a metric file template.
+type TemplateData struct {
+	Package       string
+	ParsedMetrics []ParsedMetricField
+}
+
+func main() {
+	flag.Parse()
+	if *strct == "" {
+		log.Fatal("You must specify a non-empty -struct")
+	}
+	td, err := ParseMetricsDir(".", *strct)
+	if err != nil {
+		log.Fatalf("Parsing file: %v", err)
+	}
+	out := filepath.Join(*dir, "metrics.gen.go")
+	f, err := os.Create(out)
+	if err != nil {
+		log.Fatalf("Opening file: %v", err)
+	}
+	err = GenerateMetricsFile(f, td)
+	if err != nil {
+		log.Fatalf("Generating code: %v", err)
+	}
+}
+func ignoreTestFiles(f fs.FileInfo) bool {
+	return !strings.Contains(f.Name(), "_test.go")
+}
+
+// ParseMetricsDir parses the dir and scans for a struct matching structName,
+// ignoring all test files. ParseMetricsDir iterates the fields of the metrics
+// struct and builds a TemplateData using the data obtained from the abstract syntax tree.
+func ParseMetricsDir(dir string, structName string) (TemplateData, error) {
+	fs := token.NewFileSet()
+	d, err := parser.ParseDir(fs, dir, ignoreTestFiles, parser.ParseComments)
+	if err != nil {
+		return TemplateData{}, err
+	}
+	if len(d) > 1 {
+		return TemplateData{}, fmt.Errorf("multiple packages found in %s", dir)
+	}
+	if len(d) == 0 {
+		return TemplateData{}, fmt.Errorf("no go pacakges found in %s", dir)
+	}
+
+	// Grab the package name.
+	var pkgName string
+	var pkg *ast.Package
+	for pkgName, pkg = range d {
+	}
+	td := TemplateData{
+		Package: pkgName,
+	}
+	// Grab the metrics struct
+	m, mPkgName, err := findMetricsStruct(pkg.Files, structName)
+	if err != nil {
+		return TemplateData{}, err
+	}
+	for _, f := range m.Fields.List {
+		if !isMetric(f.Type, mPkgName) {
+			continue
+		}
+		pmf := parseMetricField(f)
+		td.ParsedMetrics = append(td.ParsedMetrics, pmf)
+	}
+
+	return td, err
+}
+
+// GenerateMetricsFile executes the metrics file template, writing the result
+// into the io.Writer.
+func GenerateMetricsFile(w io.Writer, td TemplateData) error {
+	b := []byte{}
+	buf := bytes.NewBuffer(b)
+	err := tmpl.Execute(buf, td)
+	if err != nil {
+		return err
+	}
+	b, err = format.Source(buf.Bytes())
+	if err != nil {
+		return err
+	}
+	_, err = io.Copy(w, bytes.NewBuffer(b))
+	if err != nil {
+		return err
+	}
+	return nil
+}
+
+func findMetricsStruct(files map[string]*ast.File, structName string) (*ast.StructType, string, error) {
+	var (
+		st *ast.StructType
+	)
+	for _, file := range files {
+		mPkgName, err := extractMetricsPackageName(file.Imports)
+		if err != nil {
+			return nil, "", fmt.Errorf("unable to determine metrics package name: %v", err)
+		}
+		if !ast.FilterFile(file, func(name string) bool {
+			return name == structName
+		}) {
+			continue
+		}
+		ast.Inspect(file, func(n ast.Node) bool {
+			switch f := n.(type) {
+			case *ast.TypeSpec:
+				if f.Name.Name == structName {
+					var ok bool
+					st, ok = f.Type.(*ast.StructType)
+					if !ok {
+						err = fmt.Errorf("found identifier for %q of wrong type", structName)
+					}
+				}
+				return false
+			default:
+				return true
+			}
+		})
+		if err != nil {
+			return nil, "", err
+		}
+		if st != nil {
+			return st, mPkgName, nil
+		}
+	}
+	return nil, "", fmt.Errorf("target struct %q not found in dir", structName)
+}
+
+func parseMetricField(f *ast.Field) ParsedMetricField {
+	pmf := ParsedMetricField{
+		Description: extractHelpMessage(f.Doc),
+		MetricName:  extractFieldName(f.Names[0].String(), f.Tag),
+		FieldName:   f.Names[0].String(),
+		TypeName:    extractTypeName(f.Type),
+		Labels:      extractLabels(f.Tag),
+	}
+	if pmf.TypeName == "Histogram" {
+		pmf.HistogramOptions = extractHistogramOptions(f.Tag)
+	}
+	return pmf
+}
+
+func extractTypeName(e ast.Expr) string {
+	return strings.TrimPrefix(path.Ext(types.ExprString(e)), ".")
+}
+
+func extractHelpMessage(cg *ast.CommentGroup) string {
+	if cg == nil {
+		return ""
+	}
+	var help []string //nolint: prealloc
+	for _, c := range cg.List {
+		mt := strings.TrimPrefix(c.Text, "//metrics:")
+		if mt != c.Text {
+			return strings.TrimSpace(mt)
+		}
+		help = append(help, strings.TrimSpace(strings.TrimPrefix(c.Text, "//")))
+	}
+	return strings.Join(help, " ")
+}
+
+func isMetric(e ast.Expr, mPkgName string) bool {
+	return strings.Contains(types.ExprString(e), fmt.Sprintf("%s.", mPkgName))
+}
+
+func extractLabels(bl *ast.BasicLit) string {
+	if bl != nil {
+		t := reflect.StructTag(strings.Trim(bl.Value, "`"))
+		if v := t.Get(labelsTag); v != "" {
+			var res []string
+			for _, s := range strings.Split(v, ",") {
+				res = append(res, strconv.Quote(strings.TrimSpace(s)))
+			}
+			return strings.Join(res, ",")
+		}
+	}
+	return ""
+}
+
+func extractFieldName(name string, tag *ast.BasicLit) string {
+	if tag != nil {
+		t := reflect.StructTag(strings.Trim(tag.Value, "`"))
+		if v := t.Get(metricNameTag); v != "" {
+			return v
+		}
+	}
+	return toSnakeCase(name)
+}
+
+func extractHistogramOptions(tag *ast.BasicLit) HistogramOpts {
+	h := HistogramOpts{}
+	if tag != nil {
+		t := reflect.StructTag(strings.Trim(tag.Value, "`"))
+		if v := t.Get(bucketTypeTag); v != "" {
+			h.BucketType = bucketType[v]
+		}
+		if v := t.Get(bucketSizeTag); v != "" {
+			h.BucketSizes = v
+		}
+	}
+	return h
+}
+
+func extractMetricsPackageName(imports []*ast.ImportSpec) (string, error) {
+	for _, i := range imports {
+		u, err := strconv.Unquote(i.Path.Value)
+		if err != nil {
+			return "", err
+		}
+		if u == metricsPackageName {
+			if i.Name != nil {
+				return i.Name.Name, nil
+			}
+			return path.Base(u), nil
+		}
+	}
+	return "", nil
+}
+
+var capitalChange = regexp.MustCompile("([a-z0-9])([A-Z])")
+
+func toSnakeCase(str string) string {
+	snake := capitalChange.ReplaceAllString(str, "${1}_${2}")
+	return strings.ToLower(snake)
+}

scripts/metricsgen/metricsgen_test.go

@@ -0,0 +1,259 @@
+package main_test
+
+import (
+	"bytes"
+	"fmt"
+	"go/parser"
+	"go/token"
+	"io"
+	"io/ioutil"
+	"os"
+	"path"
+	"path/filepath"
+	"testing"
+
+	"github.com/stretchr/testify/require"
+	metricsgen "github.com/tendermint/tendermint/scripts/metricsgen"
+)
+
+const testDataDir = "./testdata"
+
+func TestSimpleTemplate(t *testing.T) {
+	m := metricsgen.ParsedMetricField{
+		TypeName:    "Histogram",
+		FieldName:   "MyMetric",
+		MetricName:  "request_count",
+		Description: "how many requests were made since the start of the process",
+		Labels:      "first, second, third",
+	}
+	td := metricsgen.TemplateData{
+		Package:       "mypack",
+		ParsedMetrics: []metricsgen.ParsedMetricField{m},
+	}
+	b := bytes.NewBuffer([]byte{})
+	err := metricsgen.GenerateMetricsFile(b, td)
+	if err != nil {
+		t.Fatalf("unable to parse template %v", err)
+	}
+}
+
+func TestFromData(t *testing.T) {
+	infos, err := ioutil.ReadDir(testDataDir)
+	if err != nil {
+		t.Fatalf("unable to open file %v", err)
+	}
+	for _, dir := range infos {
+		t.Run(dir.Name(), func(t *testing.T) {
+			if !dir.IsDir() {
+				t.Fatalf("expected file %s to be directory", dir.Name())
+			}
+			dirName := path.Join(testDataDir, dir.Name())
+			pt, err := metricsgen.ParseMetricsDir(dirName, "Metrics")
+			if err != nil {
+				t.Fatalf("unable to parse from dir %q: %v", dir, err)
+			}
+			outFile := path.Join(dirName, "out.go")
+			if err != nil {
+				t.Fatalf("unable to open file %s: %v", outFile, err)
+			}
+			of, err := os.Create(outFile)
+			if err != nil {
+				t.Fatalf("unable to open file %s: %v", outFile, err)
+			}
+			defer os.Remove(outFile)
+			if err := metricsgen.GenerateMetricsFile(of, pt); err != nil {
+				t.Fatalf("unable to generate metrics file %s: %v", outFile, err)
+			}
+			if _, err := parser.ParseFile(token.NewFileSet(), outFile, nil, parser.AllErrors); err != nil {
+				t.Fatalf("unable to parse generated file %s: %v", outFile, err)
+			}
+			bNew, err := ioutil.ReadFile(outFile)
+			if err != nil {
+				t.Fatalf("unable to read generated file %s: %v", outFile, err)
+			}
+			goldenFile := path.Join(dirName, "metrics.gen.go")
+			bOld, err := ioutil.ReadFile(goldenFile)
+			if err != nil {
+				t.Fatalf("unable to read file %s: %v", goldenFile, err)
+			}
+			if !bytes.Equal(bNew, bOld) {
+				t.Fatalf("newly generated code in file %s does not match golden file %s\n"+
+					"if the output of the metricsgen tool is expected to change run the following make target: \n"+
+					"\tmake metrics", outFile, goldenFile)
+			}
+		})
+	}
+}
+
+func TestParseMetricsStruct(t *testing.T) {
+	const pkgName = "mypkg"
+	metricsTests := []struct {
+		name          string
+		shouldError   bool
+		metricsStruct string
+		expected      metricsgen.TemplateData
+	}{
+		{
+			name: "basic",
+			metricsStruct: `type Metrics struct {
+				myGauge metrics.Gauge
+			}`,
+			expected: metricsgen.TemplateData{
+				Package: pkgName,
+				ParsedMetrics: []metricsgen.ParsedMetricField{
+					{
+						TypeName:   "Gauge",
+						FieldName:  "myGauge",
+						MetricName: "my_gauge",
+					},
+				},
+			},
+		},
+		{
+			name: "histogram",
+			metricsStruct: "type Metrics struct {\n" +
+				"myHistogram metrics.Histogram `metrics_buckettype:\"exp\" metrics_bucketsizes:\"1, 100, .8\"`\n" +
+				"}",
+			expected: metricsgen.TemplateData{
+				Package: pkgName,
+				ParsedMetrics: []metricsgen.ParsedMetricField{
+					{
+						TypeName:   "Histogram",
+						FieldName:  "myHistogram",
+						MetricName: "my_histogram",
+
+						HistogramOptions: metricsgen.HistogramOpts{
+							BucketType:  "stdprometheus.ExponentialBuckets",
+							BucketSizes: "1, 100, .8",
+						},
+					},
+				},
+			},
+		},
+		{
+			name: "labeled name",
+			metricsStruct: "type Metrics struct {\n" +
+				"myCounter metrics.Counter `metrics_name:\"new_name\"`\n" +
+				"}",
+			expected: metricsgen.TemplateData{
+				Package: pkgName,
+				ParsedMetrics: []metricsgen.ParsedMetricField{
+					{
+						TypeName:   "Counter",
+						FieldName:  "myCounter",
+						MetricName: "new_name",
+					},
+				},
+			},
+		},
+		{
+			name: "metric labels",
+			metricsStruct: "type Metrics struct {\n" +
+				"myCounter metrics.Counter `metrics_labels:\"label1,label2\"`\n" +
+				"}",
+			expected: metricsgen.TemplateData{
+				Package: pkgName,
+				ParsedMetrics: []metricsgen.ParsedMetricField{
+					{
+						TypeName:   "Counter",
+						FieldName:  "myCounter",
+						MetricName: "my_counter",
+						Labels:     "\"label1\",\"label2\"",
+					},
+				},
+			},
+		},
+		{
+			name: "ignore non-metric field",
+			metricsStruct: `type Metrics struct {
+				myCounter metrics.Counter
+				nonMetric string
+				}`,
+			expected: metricsgen.TemplateData{
+				Package: pkgName,
+				ParsedMetrics: []metricsgen.ParsedMetricField{
+					{
+						TypeName:   "Counter",
+						FieldName:  "myCounter",
+						MetricName: "my_counter",
+					},
+				},
+			},
+		},
+	}
+	for _, testCase := range metricsTests {
+		t.Run(testCase.name, func(t *testing.T) {
+			dir, err := os.MkdirTemp(os.TempDir(), "metricsdir")
+			if err != nil {
+				t.Fatalf("unable to create directory: %v", err)
+			}
+			defer os.Remove(dir)
+			f, err := os.Create(filepath.Join(dir, "metrics.go"))
+			if err != nil {
+				t.Fatalf("unable to open file: %v", err)
+			}
+			pkgLine := fmt.Sprintf("package %s\n", pkgName)
+			importClause := `
+			import(
+				"github.com/go-kit/kit/metrics"
+			)
+			`
+
+			_, err = io.WriteString(f, pkgLine)
+			require.NoError(t, err)
+			_, err = io.WriteString(f, importClause)
+			require.NoError(t, err)
+			_, err = io.WriteString(f, testCase.metricsStruct)
+			require.NoError(t, err)
+
+			td, err := metricsgen.ParseMetricsDir(dir, "Metrics")
+			if testCase.shouldError {
+				require.Error(t, err)
+			} else {
+				require.NoError(t, err)
+				require.Equal(t, testCase.expected, td)
+			}
+		})
+	}
+}
+
+func TestParseAliasedMetric(t *testing.T) {
+	aliasedData := `
+			package mypkg
+
+			import(
+				mymetrics "github.com/go-kit/kit/metrics"
+			)
+			type Metrics struct {
+				m mymetrics.Gauge
+			}
+			`
+	dir, err := os.MkdirTemp(os.TempDir(), "metricsdir")
+	if err != nil {
+		t.Fatalf("unable to create directory: %v", err)
+	}
+	defer os.Remove(dir)
+	f, err := os.Create(filepath.Join(dir, "metrics.go"))
+	if err != nil {
+		t.Fatalf("unable to open file: %v", err)
+	}
+	_, err = io.WriteString(f, aliasedData)
+	if err != nil {
+		t.Fatalf("unable to write to file: %v", err)
+	}
+	td, err := metricsgen.ParseMetricsDir(dir, "Metrics")
+	require.NoError(t, err)
+
+	expected :=
+		metricsgen.TemplateData{
+			Package: "mypkg",
+			ParsedMetrics: []metricsgen.ParsedMetricField{
+				{
+					TypeName:   "Gauge",
+					FieldName:  "m",
+					MetricName: "m",
+				},
+			},
+		}
+	require.Equal(t, expected, td)
+}

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"`
+}