Use auto-instrumentation SDK in global tracing

When the auto-instrumentation attaches to a process using the global
TracerProvider, and there has not been a delegate set, create a span
from the go.opentelemetry.io/auto/sdk package so the OTel Go
auto-instrumentation can instrument the application by default.

Author: MrAlias

go.mod

@@ -1,18 +1,20 @@
 module go.opentelemetry.io/otel
 
-go 1.22
+go 1.22.0
 
 require (
 	github.com/go-logr/logr v1.4.2
 	github.com/go-logr/stdr v1.2.2
 	github.com/google/go-cmp v0.6.0
 	github.com/stretchr/testify v1.9.0
+	go.opentelemetry.io/auto/sdk v0.1.0-alpha
 	go.opentelemetry.io/otel/metric v1.31.0
 	go.opentelemetry.io/otel/trace v1.31.0
 )
 
 require (
 	github.com/davecgh/go-spew v1.1.1 // indirect
+	github.com/kr/text v0.2.0 // indirect
 	github.com/pmezard/go-difflib v1.0.0 // indirect
 	gopkg.in/yaml.v3 v3.0.1 // indirect
 )

go.sum

@@ -1,3 +1,4 @@
+github.com/creack/pty v1.1.9/go.mod h1:oKZEueFk5CKHvIhNR5MUki03XCEU+Q6VDXinZuGJ33E=
 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=
@@ -7,11 +8,20 @@ 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/kr/pretty v0.3.1 h1:flRD4NNwYAUpkphVc1HcthR4KEIFJ65n8Mw5qdRn3LE=
+github.com/kr/pretty v0.3.1/go.mod h1:hoEshYVHaxMs3cyo3Yncou5ZscifuDolrwPKZanG3xk=
+github.com/kr/text v0.2.0 h1:5Nx0Ya0ZqY2ygV366QzturHI13Jq95ApcVaJBhpS+AY=
+github.com/kr/text v0.2.0/go.mod h1:eLer722TekiGuMkidMxC/pM04lWEeraHUUmBw8l2grE=
 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/rogpeppe/go-internal v1.10.0 h1:TMyTOH3F/DB16zRVcYyreMH6GnZZrwQVAoYjRBZyWFQ=
+github.com/rogpeppe/go-internal v1.10.0/go.mod h1:UQnix2H7Ngw/k4C5ijL5+65zddjncjaFoBhdsK/akog=
 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=
-gopkg.in/check.v1 v0.0.0-20161208181325-20d25e280405 h1:yhCVgyC4o1eVCa2tZl7eS0r+SDo693bJlVdllGtEeKM=
+go.opentelemetry.io/auto/sdk v0.1.0-alpha h1:4Ys9FFRxjOu0QRtAf4OHUHklBdbQ7mxWWZNBxF8YLI4=
+go.opentelemetry.io/auto/sdk v0.1.0-alpha/go.mod h1:yPESko1QR5kd8fkS+cMrHdxVj08l+RWtnuuBgvT1H7Q=
 gopkg.in/check.v1 v0.0.0-20161208181325-20d25e280405/go.mod h1:Co6ibVJAznAaIkqp8huTwlJQCZ016jof/cbN4VW5Yz0=
+gopkg.in/check.v1 v1.0.0-20201130134442-10cb98267c6c h1:Hei/4ADfdWqJk1ZMxUNpqntNwaWcugrBjAiHlqqRiVk=
+gopkg.in/check.v1 v1.0.0-20201130134442-10cb98267c6c/go.mod h1:JHkPIbrfpd72SG/EVd6muEfDQjcINNoR0C8j2r3qZ4Q=
 gopkg.in/yaml.v3 v3.0.1 h1:fxVm/GzAzEWqLHuvctI91KS9hhNmmWOoWu0XTYJS7CA=
 gopkg.in/yaml.v3 v3.0.1/go.mod h1:K4uyk7z7BCEPqu6E+C64Yfv1cQ7kz7rIZviUmN+EgEM=

internal/global/trace.go

@@ -25,6 +25,7 @@ import (
 	"sync"
 	"sync/atomic"
 
+	"go.opentelemetry.io/auto/sdk"
 	"go.opentelemetry.io/otel/attribute"
 	"go.opentelemetry.io/otel/codes"
 	"go.opentelemetry.io/otel/trace"
@@ -139,6 +140,30 @@ func (t *tracer) Start(ctx context.Context, name string, opts ...trace.SpanStart
 		return delegate.(trace.Tracer).Start(ctx, name, opts...)
 	}
 
+	return t.newSpan(ctx, autoInstEnabled, name, opts)
+}
+
+// autoInstEnabled determines if the auto-instrumentation SDK span is returned
+// from the tracer when not backed by a delegate and auto-instrumentation has
+// attached to this process.
+//
+// The auto-instrumentation is expected to overwrite this value to true when it
+// attaches. By default, this will point to false and mean a tracer will return
+// a nonRecordingSpan by default.
+var autoInstEnabled *bool = new(bool)
+
+func (t *tracer) newSpan(ctx context.Context, autoSpan *bool, name string, opts []trace.SpanStartOption) (context.Context, trace.Span) {
+	// autoInstEnabled is passed to newSpan via the autoSpan parameter. This is
+	// so the auto-instrumentation can define a uprobe for (*t).newSpan and be
+	// provided with the address of the bool autoInstEnabled points to. It
+	// needs to be a parameter so that pointer can be reliably determined, it
+	// should not be read from the global.
+
+	if *autoSpan {
+		tracer := sdk.GetTracerProvider().Tracer(t.name, t.opts...)
+		return tracer.Start(ctx, name, opts...)
+	}
+
 	s := nonRecordingSpan{sc: trace.SpanContextFromContext(ctx), tracer: t}
 	ctx = trace.ContextWithSpan(ctx, s)
 	return ctx, s