write.xlsx() does not work properly with S3 class vctrs_list_of

[MChiabudini]

Describe the bug
When passing a list of dataframes with S3 class vctrs_list_of (e.g., as returned by dplyr::group_split()) to write.xlsx, the resulting Excel file has an unexpected structure. Instead of containing one sheet per list element, each list element ends up in a single cell with all columns concatenated. Only after calling as.list() on the list of class vctrs_list_of, the expected behavior is restored.

To Reproduce

library(dplyr)
library(openxlsx)

data(iris)

iris_list <- iris %>% 
  group_split(Species)

tmp_file <- temp_xlsx()

# Unexpected
write.xlsx(iris_list, tmp_file)

# Can be fixed by calling as.list() on vctrs_list_of
iris_list2 <- iris %>% 
  group_split(Species) %>% 
  as.list()

tmp_file2 <- temp_xlsx()

# Expected
write.xlsx(iris_list2, tmp_file2)

Expected behavior
Excel file is expected to contain one sheet per list element with the columns as the dataframes in the list.

Example files
unexpected.xlsx
expected.xlsx

Additional context

sessionInfo()
R version 4.2.2 (2022-10-31 ucrt)
Platform: x86_64-w64-mingw32/x64 (64-bit)
Running under: Windows 10 x64 (build 19045)

Matrix products: default

locale:
[1] LC_COLLATE=English_United States.utf8  LC_CTYPE=English_United States.utf8    LC_MONETARY=English_United States.utf8 LC_NUMERIC=C                           LC_TIME=English_United States.utf8    

attached base packages:
[1] stats     graphics  grDevices utils     datasets  methods   base     

other attached packages:
[1] openxlsx_4.2.5.1 dplyr_1.1.4     

loaded via a namespace (and not attached):
  [1] fs_1.6.0          lubridate_1.9.1   insight_0.19.0    webshot_0.5.4     httr_1.4.7        R.cache_0.16.0    tools_4.2.2       backports_1.4.1   utf8_1.2.2        R6_2.5.1          sjlabelled_1.2.0 
 [12] lazyeval_0.2.2    colorspace_2.1-0  withr_2.5.2       tidyselect_1.2.0  gridExtra_2.3     processx_3.8.4    compiler_4.2.2    cli_3.6.0         binom_1.1-1.1     plotly_4.10.3     macRtools_1.1.2  
 [23] scales_1.3.0      survMisc_0.5.6    readr_2.1.3       callr_3.7.3       stringr_1.5.1     digest_0.6.35     R.utils_2.12.3    rmarkdown_2.25    pkgconfig_2.0.3   htmltools_0.5.7   styler_1.10.3    
 [34] labelled_2.10.0   fastmap_1.1.1     import_1.3.0      htmlwidgets_1.6.3 rlang_1.1.1       rstudioapi_0.14   generics_0.1.3    zoo_1.8-11        jsonlite_1.8.7    R.oo_1.26.0       zip_2.2.2        
 [45] car_3.1-1         magrittr_2.0.3    huxtable_5.5.2    Matrix_1.5-1      Rcpp_1.0.10       munsell_0.5.0     fansi_1.0.4       abind_1.4-5       clipr_0.8.0       viridis_0.6.2     R.methodsS3_1.8.2
 [56] lifecycle_1.0.4   stringi_1.7.12    yaml_2.3.7        carData_3.0-5     grid_4.2.2        promises_1.2.0.1  forcats_1.0.0     crayon_1.5.2      survminer_0.4.9   lattice_0.20-45   haven_2.5.1      
 [67] splines_4.2.2     chromote_0.1.1    hms_1.1.2         knitr_1.46        ps_1.7.6          pillar_1.9.0      ggpubr_0.5.0      ggsignif_0.6.4    codetools_0.2-18  reprex_2.0.2      googleVis_0.7.0  
 [78] glue_1.6.2        evaluate_0.23     data.table_1.14.8 vctrs_0.6.4       tzdb_0.3.0        gtable_0.3.4      purrr_1.0.1       tidyr_1.3.0       km.ci_0.5-6       assertthat_0.2.1  ggplot2_3.5.1    
 [89] xfun_0.43         xtable_1.8-4      broom_1.0.3       rstatix_0.7.2     later_1.3.0       admiraldev_1.0.0  survival_3.4-0    viridisLite_0.4.2 tibble_3.2.1      websocket_1.4.1   KMsurv_0.1-5     
[100] timechange_0.2.0  ellipsis_0.3.2   

packageVersion("openxlsx")
[1] ‘4.2.5.1’