Remove global logger

By default, if the logger in the cluster config is not set,
the NewSession() method sets a default logger instance
which is a deprecated global variable.

patch by Oleksandr Luzhniy; reviewed by João Reis, Stanislav Bychkov, for CASSGO-24

CHANGELOG.md

@@ -14,6 +14,8 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 - Remove global NewBatch function (CASSGO-15)
 
+- Remove deprecated global logger (CASSGO-24)
+
 ### Fixed
 
 - Retry policy now takes into account query idempotency (CASSGO-27)

cluster.go

@@ -254,7 +254,7 @@ type ClusterConfig struct {
 	HostDialer HostDialer
 
 	// Logger for this ClusterConfig.
-	// If not specified, defaults to the global gocql.Logger.
+	// If not specified, defaults to the gocql.defaultLogger.
 	Logger StdLogger
 
 	// internal config for testing
@@ -298,7 +298,7 @@ func NewCluster(hosts ...string) *ClusterConfig {
 
 func (cfg *ClusterConfig) logger() StdLogger {
 	if cfg.Logger == nil {
-		return Logger
+		return &defaultLogger{}
 	}
 	return cfg.Logger
 }

conn.go

@@ -151,7 +151,7 @@ type ConnConfig struct {
 
 func (c *ConnConfig) logger() StdLogger {
 	if c.Logger == nil {
-		return Logger
+		return &defaultLogger{}
 	}
 	return c.Logger
 }

logger.go

@@ -58,7 +58,3 @@ type defaultLogger struct{}
 func (l *defaultLogger) Print(v ...interface{})                 { log.Print(v...) }
 func (l *defaultLogger) Printf(format string, v ...interface{}) { log.Printf(format, v...) }
 func (l *defaultLogger) Println(v ...interface{})               { log.Println(v...) }
-
-// Logger for logging messages.
-// Deprecated: Use ClusterConfig.Logger instead.
-var Logger StdLogger = &defaultLogger{}