Add support for opentelemetry tracing.

Trace our render and record some useful events during the rendering.

go.mod

@@ -1,3 +1,14 @@
 module impractical.co/temple
 
 go 1.21
+
+require (
+	go.opentelemetry.io/otel v1.26.0
+	go.opentelemetry.io/otel/trace v1.26.0
+)
+
+require (
+	github.com/go-logr/logr v1.4.1 // indirect
+	github.com/go-logr/stdr v1.2.2 // indirect
+	go.opentelemetry.io/otel/metric v1.26.0 // indirect
+)

go.sum

@@ -0,0 +1,21 @@
+github.com/davecgh/go-spew v1.1.1 h1:vj9j/u1bqnvCEfJOwUhtlOARqs3+rkHYY13jYWTU97c=
+github.com/davecgh/go-spew v1.1.1/go.mod h1:J7Y8YcW2NihsgmVo/mv3lAwl/skON4iLHjSsI+c5H38=
+github.com/go-logr/logr v1.2.2/go.mod h1:jdQByPbusPIv2/zmleS9BjJVeZ6kBagPoEUsqbVz/1A=
+github.com/go-logr/logr v1.4.1 h1:pKouT5E8xu9zeFC39JXRDukb6JFQPXM5p5I91188VAQ=
+github.com/go-logr/logr v1.4.1/go.mod h1:9T104GzyrTigFIr8wt5mBrctHMim0Nb2HLGrmQ40KvY=
+github.com/go-logr/stdr v1.2.2 h1:hSWxHoqTgW2S2qGc0LTAI563KZ5YKYRhT3MFKZMbjag=
+github.com/go-logr/stdr v1.2.2/go.mod h1:mMo/vtBO5dYbehREoey6XUKy/eSumjCCveDpRre4VKE=
+github.com/google/go-cmp v0.6.0 h1:ofyhxvXcZhMsU5ulbFiLKl/XBFqE1GSq7atu8tAmTRI=
+github.com/google/go-cmp v0.6.0/go.mod h1:17dUlkBOakJ0+DkrSSNjCkIjxS6bF9zb3elmeNGIjoY=
+github.com/pmezard/go-difflib v1.0.0 h1:4DBwDE0NGyQoBHbLQYPwSUPoCMWR5BEzIk/f1lZbAQM=
+github.com/pmezard/go-difflib v1.0.0/go.mod h1:iKH77koFhYxTK1pcRnkKkqfTogsbg7gZNVY4sRDYZ/4=
+github.com/stretchr/testify v1.9.0 h1:HtqpIVDClZ4nwg75+f6Lvsy/wHu+3BoSGCbBAcpTsTg=
+github.com/stretchr/testify v1.9.0/go.mod h1:r2ic/lqez/lEtzL7wO/rwa5dbSLXVDPFyf8C91i36aY=
+go.opentelemetry.io/otel v1.26.0 h1:LQwgL5s/1W7YiiRwxf03QGnWLb2HW4pLiAhaA5cZXBs=
+go.opentelemetry.io/otel v1.26.0/go.mod h1:UmLkJHUAidDval2EICqBMbnAd0/m2vmpf/dAM+fvFs4=
+go.opentelemetry.io/otel/metric v1.26.0 h1:7S39CLuY5Jgg9CrnA9HHiEjGMF/X2VHvoXGgSllRz30=
+go.opentelemetry.io/otel/metric v1.26.0/go.mod h1:SY+rHOI4cEawI9a7N1A4nIg/nTQXe1ccCNWYOJUrpX4=
+go.opentelemetry.io/otel/trace v1.26.0 h1:1ieeAUb4y0TE26jUFrCIXKpTuVK7uJGN9/Z/2LP5sQA=
+go.opentelemetry.io/otel/trace v1.26.0/go.mod h1:4iDxvGDQuUkHve82hJJ8UqrwswHYsZuWCBllGV2U2y0=
+gopkg.in/yaml.v3 v3.0.1 h1:fxVm/GzAzEWqLHuvctI91KS9hhNmmWOoWu0XTYJS7CA=
+gopkg.in/yaml.v3 v3.0.1/go.mod h1:K4uyk7z7BCEPqu6E+C64Yfv1cQ7kz7rIZviUmN+EgEM=

render.go

@@ -7,6 +7,10 @@ import (
 	"html/template"
 	"io"
 	"io/fs"
+
+	"go.opentelemetry.io/otel"
+	"go.opentelemetry.io/otel/attribute"
+	"go.opentelemetry.io/otel/trace"
 )
 
 var (
@@ -111,6 +115,10 @@ func Render[SiteType Site, PageType Renderable](ctx context.Context, out io.Writ
 		}
 	}()
 
+	tracer := otel.GetTracerProvider().Tracer("impractical.co/temple")
+	var span trace.Span
+	ctx, span = tracer.Start(ctx, "render")
+	defer span.End()
 	// try to render the page
 	err := basicRender(ctx, out, site, page)
 
@@ -126,6 +134,11 @@ func Render[SiteType Site, PageType Renderable](ctx context.Context, out io.Writ
 	logger(ctx).
 		ErrorContext(ctx, "error rendering page", "error", err)
 
+	span.AddEvent("error rendering span",
+		trace.WithStackTrace(true),
+		trace.WithAttributes(attribute.String("error", err.Error())),
+	)
+
 	// now let's render the server error page
 	if pager, ok := Site(site).(ServerErrorPager); ok {
 		err = basicRender(ctx, out, site, pager.ServerErrorPage(ctx))
@@ -170,10 +183,14 @@ func basicRender[SiteType Site, PageType Renderable](ctx context.Context, output
 }
 
 func getTemplate(ctx context.Context, site Site, page Renderable) (*template.Template, error) {
+	span := trace.SpanFromContext(ctx)
 	key := page.Key(ctx)
 	if cache, ok := site.(TemplateCacher); ok {
 		cached := cache.GetCachedTemplate(ctx, key)
 		if cached != nil {
+			span.AddEvent("got cached template",
+				trace.WithAttributes(attribute.String("key", key)),
+			)
 			return cached, nil
 		}
 	}
@@ -189,6 +206,10 @@ func getTemplate(ctx context.Context, site Site, page Renderable) (*template.Tem
 	if cache, ok := site.(TemplateCacher); ok {
 		cache.SetCachedTemplate(ctx, key, parsed)
 	}
+	span.AddEvent("parsed templates",
+		trace.WithAttributes(attribute.String("key", key)),
+		trace.WithAttributes(attribute.StringSlice("templates", tmplPaths)),
+	)
 	return parsed, nil
 }