Add experimental x package to otlptracegrpc (#7401)

Part of #7007 

- Generate the base `x` package content
- Add a README.md describing the observability feature
- Add the observability feature

Author: MrAlias

exporters/otlp/otlptrace/otlptracegrpc/internal/gen.go

@@ -23,3 +23,6 @@ package internal // import "go.opentelemetry.io/otel/exporters/otlp/otlptrace/ot
 //go:generate gotmpl --body=../../../../../internal/shared/otlp/otlptrace/otlptracetest/collector.go.tmpl "--data={}" --out=otlptracetest/collector.go
 //go:generate gotmpl --body=../../../../../internal/shared/otlp/otlptrace/otlptracetest/data.go.tmpl "--data={}" --out=otlptracetest/data.go
 //go:generate gotmpl --body=../../../../../internal/shared/otlp/otlptrace/otlptracetest/otlptest.go.tmpl "--data={}" --out=otlptracetest/otlptest.go
+
+//go:generate gotmpl --body=../../../../../internal/shared/x/x.go.tmpl "--data={ \"pkg\": \"go.opentelemetry.io/otel/exporters/otlp/otlptrace/otlptracegrpc\" }" --out=x/x.go
+//go:generate gotmpl --body=../../../../../internal/shared/x/x_test.go.tmpl "--data={}" --out=x/x_test.go

exporters/otlp/otlptrace/otlptracegrpc/internal/x/README.md

@@ -0,0 +1,36 @@
+# Experimental Features
+
+The `otlptracegrpc` exporter contains features that have not yet stabilized in the OpenTelemetry specification.
+These features are added to the `otlptracegrpc` exporter prior to stabilization in the specification so that users can start experimenting with them and provide feedback.
+
+These feature may change in backwards incompatible ways as feedback is applied.
+See the [Compatibility and Stability](#compatibility-and-stability) section for more information.
+
+## Features
+
+- [Observability](#observability)
+
+### Observability
+
+The `otlptracegrpc` exporter provides a observability feature that allows you to monitor the SDK itself.
+
+To opt-in, set the environment variable `OTEL_GO_X_OBSERVABILITY` to `true`.
+
+When enabled, the SDK will create the following metrics using the global `MeterProvider`:
+
+- `otel.sdk.exporter.span.inflight`
+- `otel.sdk.exporter.span.exported`
+- `otel.sdk.exporter.operation.duration`
+
+Please see the [Semantic conventions for OpenTelemetry SDK metrics] documentation for more details on these metrics.
+
+[Semantic conventions for OpenTelemetry SDK metrics]: https://github.com/open-telemetry/semantic-conventions/blob/v1.37.0/docs/otel/sdk-metrics.md
+
+## Compatibility and Stability
+
+Experimental features do not fall within the scope of the OpenTelemetry Go versioning and stability [policy](../../../../../../VERSIONING.md).
+These features may be removed or modified in successive version releases, including patch versions.
+
+When an experimental feature is promoted to a stable feature, a migration path will be included in the changelog entry of the release.
+There is no guarantee that any environment variable feature flags that enabled the experimental feature will be supported by the stable version.
+If they are supported, they may be accompanied with a deprecation notice stating a timeline for the removal of that support.

exporters/otlp/otlptrace/otlptracegrpc/internal/x/observ.go

@@ -0,0 +1,22 @@
+// Copyright The OpenTelemetry Authors
+// SPDX-License-Identifier: Apache-2.0
+
+package x // import "go.opentelemetry.io/otel/exporters/otlp/otlptrace/otlptracegrpc/internal/x"
+
+import "strings"
+
+// Observability is an experimental feature flag that determines if exporter
+// observability metrics are enabled.
+//
+// To enable this feature set the OTEL_GO_X_OBSERVABILITY environment variable
+// to the case-insensitive string value of "true" (i.e. "True" and "TRUE"
+// will also enable this).
+var Observability = newFeature(
+	[]string{"OBSERVABILITY"},
+	func(v string) (string, bool) {
+		if strings.EqualFold(v, "true") {
+			return v, true
+		}
+		return "", false
+	},
+)

exporters/otlp/otlptrace/otlptracegrpc/internal/x/observ_test.go

@@ -0,0 +1,21 @@
+// Copyright The OpenTelemetry Authors
+// SPDX-License-Identifier: Apache-2.0
+
+package x
+
+import (
+	"testing"
+
+	"github.com/stretchr/testify/require"
+)
+
+func TestObservability(t *testing.T) {
+	const key = "OTEL_GO_X_OBSERVABILITY"
+	require.Contains(t, Observability.Keys(), key)
+
+	t.Run("100", run(setenv(key, "100"), assertDisabled(Observability)))
+	t.Run("true", run(setenv(key, "true"), assertEnabled(Observability, "true")))
+	t.Run("True", run(setenv(key, "True"), assertEnabled(Observability, "True")))
+	t.Run("false", run(setenv(key, "false"), assertDisabled(Observability)))
+	t.Run("empty", run(assertDisabled(Observability)))
+}