Store original config in Conn before updating it.

conn.go

@@ -174,6 +174,7 @@ func connect(ctx context.Context, config *ConnConfig) (c *Conn, err error) {
 	if !config.createdByParseConfig {
 		panic("config must be created by ParseConfig")
 	}
+	originalConfig := config
 
 	// This isn't really a deep copy. But it is enough to avoid the config.Config.OnNotification mutation from affecting
 	// other connections with the same config. See https://github.com/jackc/pgx/issues/618.
@@ -183,7 +184,7 @@ func connect(ctx context.Context, config *ConnConfig) (c *Conn, err error) {
 	}
 
 	c = &Conn{
-		config:   config,
+		config:   originalConfig,
 		connInfo: pgtype.NewConnInfo(),
 		logLevel: config.LogLevel,
 		logger:   config.Logger,

conn_test.go

@@ -51,7 +51,7 @@ func TestConnect(t *testing.T) {
 		t.Fatalf("Unable to establish connection: %v", err)
 	}
 
-	assert.Equal(t, connString, conn.Config().ConnString())
+	assert.Equal(t, config, conn.Config())
 
 	var currentDB string
 	err = conn.QueryRow(context.Background(), "select current_database()").Scan(&currentDB)

go.mod

@@ -14,7 +14,6 @@ require (
 	github.com/shopspring/decimal v0.0.0-20200227202807-02e2044944cc
 	github.com/sirupsen/logrus v1.4.2
 	github.com/stretchr/testify v1.5.1
-	go.uber.org/multierr v1.5.0 // indirect
 	go.uber.org/zap v1.10.0
 	golang.org/x/xerrors v0.0.0-20191204190536-9bdfabe68543
 	gopkg.in/inconshreveable/log15.v2 v2.0.0-20180818164646-67afb5ed74ec