Use interface for logging instead of log15 directly

logger.go

@@ -0,0 +1,26 @@
+package pgx
+
+// Logger is the interface used to get logging from pgx internals.
+// https://github.com/inconshreveable/log15 is the recommended logging package.
+// This logging interface was extracted from there. However, it should be simple
+// to adapt any logger to this interface.
+type Logger interface {
+	// New returns a new Logger that has this logger's context plus the given context
+	New(ctx ...interface{}) Logger
+
+	// Log a message at the given level with context key/value pairs
+	Debug(msg string, ctx ...interface{})
+	Info(msg string, ctx ...interface{})
+	Warn(msg string, ctx ...interface{})
+	Error(msg string, ctx ...interface{})
+	Crit(msg string, ctx ...interface{})
+}
+
+type DiscardLogger struct{}
+
+func (l *DiscardLogger) New(ctx ...interface{}) Logger        { return l }
+func (l *DiscardLogger) Debug(msg string, ctx ...interface{}) {}
+func (l *DiscardLogger) Info(msg string, ctx ...interface{})  {}
+func (l *DiscardLogger) Warn(msg string, ctx ...interface{})  {}
+func (l *DiscardLogger) Error(msg string, ctx ...interface{}) {}
+func (l *DiscardLogger) Crit(msg string, ctx ...interface{})  {}