sdk/trace: treat empty sampler env values as unset

CHANGELOG.md

@@ -8,6 +8,10 @@ This project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.htm
 
 ## [Unreleased]
 
+### Fixed
+
+- Treat empty `OTEL_TRACES_SAMPLER` and `OTEL_TRACES_SAMPLER_ARG` values as unset in `go.opentelemetry.io/otel/sdk/trace`.
+
 <!-- Released section -->
 <!-- Don't change this section unless doing release -->
 

sdk/trace/provider_test.go

@@ -464,6 +464,57 @@ func TestTracerProviderSamplerConfigFromEnv(t *testing.T) {
 	}
 }
 
+func TestTracerProviderSamplerConfigFromEnvEmptyValues(t *testing.T) {
+	tests := []struct {
+		name          string
+		sampler       string
+		samplerArg    string
+		setSamplerArg bool
+		description   string
+	}{
+		{
+			name:        "empty sampler",
+			sampler:     "",
+			description: ParentBased(AlwaysSample()).Description(),
+		},
+		{
+			name:          "empty traceidratio sampler arg",
+			sampler:       "traceidratio",
+			samplerArg:    "",
+			setSamplerArg: true,
+			description:   TraceIDRatioBased(1.0).Description(),
+		},
+		{
+			name:          "empty parentbased traceidratio sampler arg",
+			sampler:       "parentbased_traceidratio",
+			samplerArg:    "",
+			setSamplerArg: true,
+			description:   ParentBased(TraceIDRatioBased(1.0)).Description(),
+		},
+	}
+
+	for _, test := range tests {
+		t.Run(test.name, func(t *testing.T) {
+			handler.Reset()
+			t.Cleanup(handler.Reset)
+
+			t.Setenv(envTracesSampler, test.sampler)
+			if test.setSamplerArg {
+				t.Setenv(envTracesSamplerArg, test.samplerArg)
+			}
+
+			stp := NewTracerProvider(WithSyncer(NewTestExporter()))
+			t.Cleanup(func() {
+				//nolint:usetesting // required to avoid getting a canceled context at cleanup.
+				require.NoError(t, stp.Shutdown(context.Background()))
+			})
+
+			assert.Equal(t, test.description, stp.sampler.Description())
+			assert.Empty(t, handler.errs)
+		})
+	}
+}
+
 func testStoredError(t *testing.T, target any) {
 	t.Helper()
 

sdk/trace/sampler_env.go

@@ -46,14 +46,13 @@ func (e samplerArgParseError) Unwrap() error {
 }
 
 func samplerFromEnv() (Sampler, error) {
-	sampler, ok := os.LookupEnv(tracesSamplerKey)
-	if !ok {
+	sampler := strings.ToLower(strings.TrimSpace(os.Getenv(tracesSamplerKey)))
+	if sampler == "" {
 		return nil, nil
 	}
 
-	sampler = strings.ToLower(strings.TrimSpace(sampler))
-	samplerArg, hasSamplerArg := os.LookupEnv(tracesSamplerArgKey)
-	samplerArg = strings.TrimSpace(samplerArg)
+	samplerArg := strings.TrimSpace(os.Getenv(tracesSamplerArgKey))
+	hasSamplerArg := samplerArg != ""
 
 	switch sampler {
 	case samplerAlwaysOn: