Add the Enabled method to the Logger (#5071)

* Add the Enabled method to the Logger

* Add a changelog entry

* Rename enabled.go to min_sev.go

* Remove MinSeverityProcessor

* Document lack of interaction between OnEmit and Enabled

* Update sdk/log/processor.go

---------

Co-authored-by: Robert Pająk <pellared@hotmail.com>

CHANGELOG.md

@@ -12,6 +12,8 @@ This project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.htm
 
 - Add `WithProxy` option in `go.opentelemetry.io/otel/exporters/otlp/otlpmetric/otlpmetrichttp`. (#4906)
 - Add `WithProxy` option in `go.opentelemetry.io/otel/exporters/otlp/otlpmetric/otlptracehttp`. (#4906)
+- The `Enabled` method is added to the `Logger` interface in `go.opentelemetry.io/otel/log`.
+  This method is used to notify users if a log record will be emitted or not. (#5071)
 - Add `SeverityUndefined` `const` to `go.opentelemetry.io/otel/log`.
   This value represents an unset severity level. (#5072)
 - Add `Empty` function in `go.opentelemetry.io/otel/log` to return a `KeyValue` for an empty value. (#5076)

log/logger.go

@@ -29,6 +29,28 @@ type Logger interface {
 	// Implementations of this method need to be safe for a user to call
 	// concurrently.
 	Emit(ctx context.Context, record Record)
+
+	// Enabled returns whether the Logger emits for the given context and
+	// record.
+	//
+	// The passed record is likely to be a partial record with only the
+	// bridge-relevant information being provided (e.g a record with only the
+	// Severity set). If a Logger needs more information than is provided, it
+	// is said to be in an indeterminate state (see below).
+	//
+	// The returned value will be true when the Logger will emit for the
+	// provided context and record, and will be false if the Logger will not
+	// emit. The returned value may be true or false in an indeterminate state.
+	// An implementation should default to returning true for an indeterminate
+	// state, but may return false if valid reasons in particular circumstances
+	// exist (e.g. performance, correctness).
+	//
+	// The record should not be held by the implementation. A copy should be
+	// made if the record needs to be held after the call returns.
+	//
+	// Implementations of this method need to be safe for a user to call
+	// concurrently.
+	Enabled(ctx context.Context, record Record) bool
 }
 
 // LoggerOption applies configuration options to a [Logger].

log/noop/noop.go

@@ -45,3 +45,6 @@ type Logger struct{ embedded.Logger }
 
 // Emit does nothing.
 func (Logger) Emit(context.Context, log.Record) {}
+
+// Enabled returns false. No log records are ever emitted.
+func (Logger) Enabled(context.Context, log.Record) bool { return false }

sdk/log/batch.go

@@ -33,6 +33,11 @@ func (b *BatchingProcessor) OnEmit(ctx context.Context, r Record) error {
 	return nil
 }
 
+// Enabled returns true.
+func (b *BatchingProcessor) Enabled(context.Context, Record) bool {
+	return true
+}
+
 // Shutdown flushes queued log records and shuts down the decorated expoter.
 func (b *BatchingProcessor) Shutdown(ctx context.Context) error {
 	// TODO (#5063): Implement.

sdk/log/logger.go

@@ -20,3 +20,8 @@ type logger struct {
 func (l *logger) Emit(ctx context.Context, r log.Record) {
 	// TODO (#5061): Implement.
 }
+
+func (l *logger) Enabled(ctx context.Context, r log.Record) bool {
+	// TODO (#5061): Implement.
+	return true
+}

sdk/log/processor.go

@@ -15,6 +15,9 @@ import (
 type Processor interface {
 	// OnEmit is called when a Record is emitted.
 	//
+	// OnEmit will be called independent of Enabled. Implementations need to
+	// validate the arguments themselves before processing.
+	//
 	// Implementation should not interrupt the record processing
 	// if the context is canceled.
 	//
@@ -26,6 +29,24 @@ type Processor interface {
 	// Before modifying a Record, the implementation must use Record.Clone
 	// to create a copy that shares no state with the original.
 	OnEmit(ctx context.Context, record Record) error
+	// Enabled returns whether the Processor will process for the given context
+	// and record.
+	//
+	// The passed record is likely to be a partial record with only the
+	// bridge-relevant information being provided (e.g a record with only the
+	// Severity set). If a Logger needs more information than is provided, it
+	// is said to be in an indeterminate state (see below).
+	//
+	// The returned value will be true when the Processor will process for the
+	// provided context and record, and will be false if the Processor will not
+	// process. The returned value may be true or false in an indeterminate
+	// state. An implementation should default to returning true for an
+	// indeterminate state, but may return false if valid reasons in particular
+	// circumstances exist (e.g. performance, correctness).
+	//
+	// Before modifying a Record, the implementation must use Record.Clone
+	// to create a copy that shares no state with the original.
+	Enabled(ctx context.Context, record Record) bool
 	// Shutdown is called when the SDK shuts down. Any cleanup or release of
 	// resources held by the exporter should be done in this call.
 	//

sdk/log/simple.go

@@ -35,6 +35,11 @@ func (s *SimpleProcessor) OnEmit(ctx context.Context, r Record) error {
 	return nil
 }
 
+// Enabled returns true.
+func (s *SimpleProcessor) Enabled(context.Context, Record) bool {
+	return true
+}
+
 // Shutdown shuts down the expoter.
 func (s *SimpleProcessor) Shutdown(ctx context.Context) error {
 	// TODO (#5062): Implement.