Fix panic on format nil *fmt.Stringer type value (#1200)

Author: zaneli

bind.go

@@ -306,6 +306,11 @@ func format(tz *time.Location, scale TimeUnit, v any) (string, error) {
 		}
 		return fmt.Sprintf("[%s]", val), nil
 	case fmt.Stringer:
+		if v := reflect.ValueOf(v); v.Kind() == reflect.Pointer &&
+			v.IsNil() &&
+			v.Type().Elem().Implements(reflect.TypeOf((*fmt.Stringer)(nil)).Elem()) {
+			return "NULL", nil
+		}
 		return quote(v.String()), nil
 	case column.OrderedMap:
 		values := make([]string, 0)

tests/issues/1200_pr_test.go

@@ -0,0 +1,84 @@
+package issues
+
+import (
+	"context"
+	"fmt"
+	"testing"
+
+	"github.com/ClickHouse/clickhouse-go/v2"
+	clickhouse_tests "github.com/ClickHouse/clickhouse-go/v2/tests"
+	"github.com/stretchr/testify/require"
+)
+
+func Test1200(t *testing.T) {
+	var (
+		conn, err = clickhouse_tests.GetConnection("issues", clickhouse.Settings{
+			"max_execution_time":             60,
+			"allow_experimental_object_type": true,
+		}, nil, &clickhouse.Compression{
+			Method: clickhouse.CompressionLZ4,
+		})
+	)
+	ctx := context.Background()
+	require.NoError(t, err)
+	const ddl = "CREATE TABLE test_1200 (id UInt32, null_str Nullable(FixedString(5))) Engine MergeTree() ORDER BY tuple()"
+	require.NoError(t, conn.Exec(ctx, ddl))
+	defer func() {
+		conn.Exec(ctx, "DROP TABLE IF EXISTS test_1200")
+	}()
+
+	v := "value"
+
+	tests := []struct {
+		name  string
+		value fmt.Stringer
+		want  *string
+	}{
+		{
+			name:  "fmt.Stringer implemented struct value",
+			value: Test1200NullStr{underlying: v},
+			want:  &v,
+		},
+		{
+			name:  "nil value",
+			value: nil,
+			want:  nil,
+		},
+		{
+			name:  "fmt.Stringer implemented struct pointer value",
+			value: &Test1200NullStr{underlying: v},
+			want:  &v,
+		},
+		{
+			name:  "fmt.Stringer implemented struct typed-nil value",
+			value: (*Test1200NullStr)(nil),
+			want:  nil,
+		},
+	}
+	for i, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			id := i + 1
+			err = conn.Exec(ctx, "INSERT INTO test_1200 (id, null_str) VALUES (?, ?)", id, tt.value)
+			require.NoError(t, err)
+
+			var got *string
+			err = conn.QueryRow(ctx, "SELECT null_str FROM test_1200 WHERE id = ?", id).Scan(&got)
+			require.NoError(t, err)
+
+			if tt.want == nil {
+				require.Nil(t, got)
+			} else {
+				require.NotNil(t, got)
+				require.Equal(t, *tt.want, *got)
+			}
+		})
+	}
+}
+
+type Test1200NullStr struct {
+	underlying string
+}
+
+func (nc Test1200NullStr) String() string {
+	return nc.underlying
+}