tpl/debug: Add debug.Timer

Closes #11580

tpl/debug/debug.go

@@ -15,6 +15,11 @@
 package debug
 
 import (
+	"sort"
+	"sync"
+	"time"
+
+	"github.com/bep/logg"
 	"github.com/sanity-io/litter"
 	"github.com/spf13/cast"
 	"github.com/yuin/goldmark/util"
@@ -24,11 +29,58 @@ import (
 
 // New returns a new instance of the debug-namespaced template functions.
 func New(d *deps.Deps) *Namespace {
-	return &Namespace{}
+	var timers map[string][]*timer
+	if d.Log.Level() <= logg.LevelInfo {
+		timers = make(map[string][]*timer)
+	}
+	ns := &Namespace{
+		timers: timers,
+	}
+
+	if ns.timers == nil {
+		return ns
+	}
+
+	l := d.Log.InfoCommand("timer")
+
+	d.BuildEndListeners.Add(func() {
+		type nameCountDuration struct {
+			Name     string
+			Count    int
+			Duration time.Duration
+		}
+
+		var timersSorted []nameCountDuration
+
+		for k, v := range timers {
+			var total time.Duration
+			for _, t := range v {
+				// Stop any running timers.
+				t.Stop()
+				total += t.elapsed
+			}
+			timersSorted = append(timersSorted, nameCountDuration{k, len(v), total})
+		}
+
+		sort.Slice(timersSorted, func(i, j int) bool {
+			// Sort it so the slowest gets printed last.
+			return timersSorted[i].Duration < timersSorted[j].Duration
+		})
+
+		for _, t := range timersSorted {
+			l.WithField("name", t.Name).WithField("count", t.Count).WithField("duration", t.Duration).Logf("")
+		}
+
+		ns.timers = make(map[string][]*timer)
+	})
+
+	return ns
 }
 
 // Namespace provides template functions for the "debug" namespace.
 type Namespace struct {
+	timersMu sync.Mutex
+	timers   map[string][]*timer
 }
 
 // Dump returns a object dump of val as a string.
@@ -49,3 +101,44 @@ func (ns *Namespace) VisualizeSpaces(val any) string {
 	s := cast.ToString(val)
 	return string(util.VisualizeSpaces([]byte(s)))
 }
+
+func (ns *Namespace) Timer(name string) Timer {
+	if ns.timers == nil {
+		return nopTimer
+	}
+	ns.timersMu.Lock()
+	defer ns.timersMu.Unlock()
+	t := &timer{start: time.Now()}
+	ns.timers[name] = append(ns.timers[name], t)
+	return t
+}
+
+var nopTimer = nopTimerImpl{}
+
+type nopTimerImpl struct{}
+
+func (nopTimerImpl) Stop() string {
+	return ""
+}
+
+// Timer is a timer that can be stopped.
+type Timer interface {
+	// Stop stops the timer and returns an empty string.
+	// Stop can be called multiple times, but only the first call will stop the timer.
+	// If Stop is not called, the timer will be stopped when the build ends.
+	Stop() string
+}
+
+type timer struct {
+	start    time.Time
+	elapsed  time.Duration
+	stopOnce sync.Once
+}
+
+func (t *timer) Stop() string {
+	t.stopOnce.Do(func() {
+		t.elapsed = time.Since(t.start)
+	})
+	// This is used in templates, we need to return something.
+	return ""
+}