Trailing commas cause an unfriendly error message on R devel

[mikemahoney218]

Brief description of the problem

On R devel, trailing commas now cause an error:

glue::glue('{x}', x = 2,)
#> Error in eval(call("force", as.symbol(paste0("..", x)))): argument "..3" is missing, with no default

^{Created on 2024-02-01 with reprex v2.1.0}

Session info

sessioninfo::session_info()
#> ─ Session info ───────────────────────────────────────────────────────────────
#>  setting  value
#>  version  R Under development (unstable) (2024-01-31 r85845)
#>  os       Ubuntu 22.04.3 LTS
#>  system   x86_64, linux-gnu
#>  ui       X11
#>  language (EN)
#>  collate  en_US.UTF-8
#>  ctype    en_US.UTF-8
#>  tz       America/New_York
#>  date     2024-02-01
#>  pandoc   3.1.1 @ /usr/lib/rstudio/resources/app/bin/quarto/bin/tools/ (via rmarkdown)
#> 
#> ─ Packages ───────────────────────────────────────────────────────────────────
#>  package     * version date (UTC) lib source
#>  cli           3.6.2   2023-12-11 [1] CRAN (R 4.4.0)
#>  digest        0.6.34  2024-01-11 [1] CRAN (R 4.4.0)
#>  evaluate      0.23    2023-11-01 [1] CRAN (R 4.4.0)
#>  fastmap       1.1.1   2023-02-24 [1] CRAN (R 4.4.0)
#>  fs            1.6.3   2023-07-20 [1] CRAN (R 4.4.0)
#>  glue          1.7.0   2024-01-09 [1] CRAN (R 4.4.0)
#>  htmltools     0.5.7   2023-11-03 [1] CRAN (R 4.4.0)
#>  knitr         1.45    2023-10-30 [1] CRAN (R 4.4.0)
#>  lifecycle     1.0.4   2023-11-07 [1] CRAN (R 4.4.0)
#>  magrittr      2.0.3   2022-03-30 [1] CRAN (R 4.4.0)
#>  purrr         1.0.2   2023-08-10 [1] CRAN (R 4.4.0)
#>  R.cache       0.16.0  2022-07-21 [1] CRAN (R 4.4.0)
#>  R.methodsS3   1.8.2   2022-06-13 [1] CRAN (R 4.4.0)
#>  R.oo          1.26.0  2024-01-24 [1] CRAN (R 4.4.0)
#>  R.utils       2.12.3  2023-11-18 [1] CRAN (R 4.4.0)
#>  reprex        2.1.0   2024-01-11 [1] CRAN (R 4.4.0)
#>  rlang         1.1.3   2024-01-10 [1] CRAN (R 4.4.0)
#>  rmarkdown     2.25    2023-09-18 [1] CRAN (R 4.4.0)
#>  rstudioapi    0.15.0  2023-07-07 [1] CRAN (R 4.4.0)
#>  sessioninfo   1.2.2   2021-12-06 [1] CRAN (R 4.4.0)
#>  styler        1.10.2  2023-08-29 [1] CRAN (R 4.4.0)
#>  vctrs         0.6.5   2023-12-01 [1] CRAN (R 4.4.0)
#>  withr         3.0.0   2024-01-16 [1] CRAN (R 4.4.0)
#>  xfun          0.41    2023-11-01 [1] CRAN (R 4.4.0)
#>  yaml          2.3.8   2023-12-11 [1] CRAN (R 4.4.0)
#> 
#>  [1] /home/mikemahoney218/R/x86_64-pc-linux-gnu-library/4.4
#>  [2] /opt/R/devel/lib/R/library
#> 
#> ──────────────────────────────────────────────────────────────────────────────

This is new in R devel, and was not an error in previous versions:

glue::glue('{x}', x = 2,)
#> 2

^{Created on 2024-02-01 with reprex v2.0.2}

Session info

sessioninfo::session_info()
#> ─ Session info ───────────────────────────────────────────────────────────────
#>  setting  value
#>  version  R version 4.3.2 (2023-10-31)
#>  os       Ubuntu 22.04.3 LTS
#>  system   x86_64, linux-gnu
#>  ui       X11
#>  language (EN)
#>  collate  en_US.UTF-8
#>  ctype    en_US.UTF-8
#>  tz       America/New_York
#>  date     2024-02-01
#>  pandoc   2.9.2.1 @ /usr/bin/ (via rmarkdown)
#> 
#> ─ Packages ───────────────────────────────────────────────────────────────────
#>  package     * version date (UTC) lib source
#>  cli           3.6.2   2023-12-11 [1] CRAN (R 4.3.2)
#>  crayon        1.5.2   2022-09-29 [1] CRAN (R 4.3.2)
#>  digest        0.6.34  2024-01-11 [1] CRAN (R 4.3.2)
#>  evaluate      0.23    2023-11-01 [1] CRAN (R 4.3.2)
#>  fastmap       1.1.1   2023-02-24 [1] CRAN (R 4.3.2)
#>  fs            1.6.3   2023-07-20 [1] CRAN (R 4.3.2)
#>  glue          1.7.0   2024-01-09 [1] CRAN (R 4.3.2)
#>  htmltools     0.5.7   2023-11-03 [1] CRAN (R 4.3.2)
#>  knitr         1.45    2023-10-30 [1] CRAN (R 4.3.2)
#>  lifecycle     1.0.4   2023-11-07 [1] CRAN (R 4.3.2)
#>  magrittr      2.0.3   2022-03-30 [1] CRAN (R 4.3.2)
#>  purrr         1.0.2   2023-08-10 [1] CRAN (R 4.3.2)
#>  R.cache       0.16.0  2022-07-21 [1] CRAN (R 4.3.2)
#>  R.methodsS3   1.8.2   2022-06-13 [1] CRAN (R 4.3.2)
#>  R.oo          1.25.0  2022-06-12 [1] CRAN (R 4.3.2)
#>  R.utils       2.12.3  2023-11-18 [1] CRAN (R 4.3.2)
#>  reprex        2.0.2   2022-08-17 [1] CRAN (R 4.3.2)
#>  rlang         1.1.3   2024-01-10 [1] CRAN (R 4.3.2)
#>  rmarkdown     2.25    2023-09-18 [1] CRAN (R 4.3.2)
#>  sessioninfo   1.2.2   2021-12-06 [1] CRAN (R 4.3.2)
#>  styler        1.10.2  2023-08-29 [1] CRAN (R 4.3.2)
#>  vctrs         0.6.5   2023-12-01 [1] CRAN (R 4.3.2)
#>  withr         3.0.0   2024-01-16 [1] CRAN (R 4.3.2)
#>  xfun          0.41    2023-11-01 [1] CRAN (R 4.3.2)
#>  yaml          2.3.8   2023-12-11 [1] CRAN (R 4.3.2)
#> 
#>  [1] /home/mikemahoney218/R/x86_64-pc-linux-gnu-library/4.3
#>  [2] /usr/local/lib/R/site-library
#>  [3] /usr/lib/R/site-library
#>  [4] /usr/lib/R/library
#> 
#> ──────────────────────────────────────────────────────────────────────────────

I think it's perfectly fine for this to cause an error, but it took me a minute to find the root cause of a CRAN error based on the message and traceback that gets generated. Would it be possible to catch this and provide a friendlier error message?

[hadley]

We should be able to fix this so it's not an error.

[jennybc]

I'm inclined to think that maybe it's neutral to good that this is an error? In all the cases linked above, it revealed a trailing comma that seems to have been a mistake.

Is there a reason why we would want intentionally be silent about this?

[hadley]

It’s nice if you want one argument on each line, and an easy way to add new arguments. We support a trailing comma in dplyr and elsewhere for that reason.