Fix scanning json column into **string

refs https://github.com/jackc/pgx/issues/1470

pgtype/json.go

@@ -95,11 +95,22 @@ func (JSONCodec) PlanScan(m *Map, oid uint32, format int16, target any) ScanPlan
 	// https://github.com/jackc/pgx/issues/1418
 	case sql.Scanner:
 		return &scanPlanSQLScanner{formatCode: format}
-
-	default:
-		return scanPlanJSONToJSONUnmarshal{}
 	}
 
+	// This is to fix **string scanning. It seems wrong to special case sql.Scanner and pointer to pointer, but it's not
+	// clear what a better solution would be.
+	//
+	// https://github.com/jackc/pgx/issues/1470
+	if wrapperPlan, nextDst, ok := TryPointerPointerScanPlan(target); ok {
+		if nextPlan := m.planScan(oid, format, nextDst); nextPlan != nil {
+			if _, failed := nextPlan.(*scanPlanFail); !failed {
+				wrapperPlan.SetNext(nextPlan)
+				return wrapperPlan
+			}
+		}
+	}
+
+	return scanPlanJSONToJSONUnmarshal{}
 }
 
 type scanPlanAnyToString struct{}

pgtype/json_test.go

@@ -101,6 +101,21 @@ func TestJSONCodecUnmarshalSQLNull(t *testing.T) {
 	})
 }
 
+// https://github.com/jackc/pgx/issues/1470
+func TestJSONCodecPointerToPointerToString(t *testing.T) {
+	defaultConnTestRunner.RunTest(context.Background(), t, func(ctx context.Context, t testing.TB, conn *pgx.Conn) {
+		var s *string
+		err := conn.QueryRow(ctx, "select '{}'::json").Scan(&s)
+		require.NoError(t, err)
+		require.NotNil(t, s)
+		require.Equal(t, "{}", *s)
+
+		err = conn.QueryRow(ctx, "select null::json").Scan(&s)
+		require.NoError(t, err)
+		require.Nil(t, s)
+	})
+}
+
 func TestJSONCodecClearExistingValueBeforeUnmarshal(t *testing.T) {
 	defaultConnTestRunner.RunTest(context.Background(), t, func(ctx context.Context, t testing.TB, conn *pgx.Conn) {
 		m := map[string]any{}