Add global log package (#5085)

* Add the log/global package

* Implement the stubbed features

* Add ConcurrentSafe tests

* Restructure with internal implementation

* Add internal global state

* Use internal state in log/global

* Add TestDelegation

* Fix lint

* Clean log_test.go

* Clean up

* Add changelog entry

* Simplify TestMultipleGlobalLoggerProvider

* Shorten log.go

* Fix comment text wrapping

* Shorten state_test.go

* Don't pollute output in TestSetLoggerProvider

log/global/log.go

@@ -0,0 +1,49 @@
+// Copyright The OpenTelemetry Authors
+// SPDX-License-Identifier: Apache-2.0
+
+/*
+Package global provides access to a global implementation of the OpenTelemetry
+Logs Bridge API.
+
+This package is experimental. It will be deprecated and removed when the [log]
+package becomes stable. Its functionality will be migrated to
+go.opentelemetry.io/otel.
+*/
+package global // import "go.opentelemetry.io/otel/log/global"
+
+import (
+	"go.opentelemetry.io/otel/log"
+	"go.opentelemetry.io/otel/log/internal/global"
+)
+
+// Logger returns a [log.Logger] configured with the provided name and options
+// from the globally configured [log.LoggerProvider].
+//
+// If this is called before a global LoggerProvider is configured, the returned
+// Logger will be a No-Op implementation of a Logger. When a global
+// LoggerProvider is registered for the first time, the returned Logger is
+// updated in-place to report to this new LoggerProvider. There is no need to
+// call this function again for an updated instance.
+//
+// This is a convenience function. It is equivalent to:
+//
+//	GetLoggerProvider().Logger(name, options...)
+func Logger(name string, options ...log.LoggerOption) log.Logger {
+	return GetLoggerProvider().Logger(name, options...)
+}
+
+// GetLoggerProvider returns the globally configured [log.LoggerProvider].
+//
+// If a global LoggerProvider has not been configured with [SetLoggerProvider],
+// the returned Logger will be a No-Op implementation of a LoggerProvider. When
+// a global LoggerProvider is registered for the first time, the returned
+// LoggerProvider and all of its created Loggers are updated in-place. There is
+// no need to call this function again for an updated instance.
+func GetLoggerProvider() log.LoggerProvider {
+	return global.GetLoggerProvider()
+}
+
+// SetLoggerProvider configures provider as the global [log.LoggerProvider].
+func SetLoggerProvider(provider log.LoggerProvider) {
+	global.SetLoggerProvider(provider)
+}

log/global/log_test.go

@@ -0,0 +1,24 @@
+// Copyright The OpenTelemetry Authors
+// SPDX-License-Identifier: Apache-2.0
+
+package global // import "go.opentelemetry.io/otel/log/global"
+
+import (
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+
+	"go.opentelemetry.io/otel/log"
+	"go.opentelemetry.io/otel/log/noop"
+)
+
+func TestMultipleGlobalLoggerProvider(t *testing.T) {
+	type provider struct{ log.LoggerProvider }
+
+	p1, p2 := provider{}, noop.NewLoggerProvider()
+
+	SetLoggerProvider(&p1)
+	SetLoggerProvider(p2)
+
+	assert.Equal(t, p2, GetLoggerProvider())
+}