Add the log/noop package (#4943)

* Add the `log/noop` package

* Add implementation tests

---------

Co-authored-by: Robert Pająk <[email protected]>

log/noop/noop.go

@@ -0,0 +1,56 @@
+// Copyright The OpenTelemetry Authors
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+// Package noop provides an implementation of the OpenTelemetry Logs Bridge API
+// that produces no telemetry and minimizes used computation resources.
+//
+// Using this package to implement the OpenTelemetry Logs Bridge API will
+// effectively disable OpenTelemetry.
+//
+// This implementation can be embedded in other implementations of the
+// OpenTelemetry Logs Bridge API. Doing so will mean the implementation
+// defaults to no operation for methods it does not implement.
+package noop // import "go.opentelemetry.io/otel/log/noop"
+
+import (
+	"context"
+
+	"go.opentelemetry.io/otel/log"
+	"go.opentelemetry.io/otel/log/embedded"
+)
+
+var (
+	// Compile-time check this implements the OpenTelemetry API.
+	_ log.LoggerProvider = LoggerProvider{}
+	_ log.Logger         = Logger{}
+)
+
+// LoggerProvider is an OpenTelemetry No-Op LoggerProvider.
+type LoggerProvider struct{ embedded.LoggerProvider }
+
+// NewLoggerProvider returns a LoggerProvider that does not record any telemetry.
+func NewLoggerProvider() LoggerProvider {
+	return LoggerProvider{}
+}
+
+// Logger returns an OpenTelemetry Logger that does not record any telemetry.
+func (LoggerProvider) Logger(string, ...log.LoggerOption) log.Logger {
+	return Logger{}
+}
+
+// Logger is an OpenTelemetry No-Op Logger.
+type Logger struct{ embedded.Logger }
+
+// Emit does nothing.
+func (Logger) Emit(context.Context, log.Record) {}

log/noop/noop_test.go

@@ -0,0 +1,81 @@
+// Copyright The OpenTelemetry Authors
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package noop // import "go.opentelemetry.io/otel/log/noop"
+
+import (
+	"context"
+	"reflect"
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+
+	"go.opentelemetry.io/otel/log"
+)
+
+func TestImplementationNoPanics(t *testing.T) {
+	// Check that if type has an embedded interface and that interface has
+	// methods added to it than the No-Op implementation implements them.
+	t.Run("LoggerProvider", assertAllExportedMethodNoPanic(
+		reflect.ValueOf(LoggerProvider{}),
+		reflect.TypeOf((*log.LoggerProvider)(nil)).Elem(),
+	))
+	t.Run("Logger", assertAllExportedMethodNoPanic(
+		reflect.ValueOf(Logger{}),
+		reflect.TypeOf((*log.Logger)(nil)).Elem(),
+	))
+}
+
+func assertAllExportedMethodNoPanic(rVal reflect.Value, rType reflect.Type) func(*testing.T) {
+	return func(t *testing.T) {
+		for n := 0; n < rType.NumMethod(); n++ {
+			mType := rType.Method(n)
+			if !mType.IsExported() {
+				t.Logf("ignoring unexported %s", mType.Name)
+				continue
+			}
+			m := rVal.MethodByName(mType.Name)
+			if !m.IsValid() {
+				t.Errorf("unknown method for %s: %s", rVal.Type().Name(), mType.Name)
+			}
+
+			numIn := mType.Type.NumIn()
+			if mType.Type.IsVariadic() {
+				numIn--
+			}
+			args := make([]reflect.Value, numIn)
+			ctx := context.Background()
+			for i := range args {
+				aType := mType.Type.In(i)
+				if aType.Name() == "Context" {
+					// Do not panic on a nil context.
+					args[i] = reflect.ValueOf(ctx)
+				} else {
+					args[i] = reflect.New(aType).Elem()
+				}
+			}
+
+			assert.NotPanicsf(t, func() {
+				_ = m.Call(args)
+			}, "%s.%s", rVal.Type().Name(), mType.Name)
+		}
+	}
+}
+
+func TestNewTracerProvider(t *testing.T) {
+	provider := NewLoggerProvider()
+	assert.Equal(t, provider, LoggerProvider{})
+	logger := provider.Logger("")
+	assert.Equal(t, logger, Logger{})
+}