`#` instead of `\\` for comment is fatal in RStan 2.26

[ChrisHIV]

Summary:

Using # instead of \\ to begin a comment in RStan 2.26 resulted in fatal mysterious parser failed badly error.

Description:

I encountered this error in RStan 2.26. I tried to update to see if it persists in a more recent version by removing RStan and reinstalling with remotes::install_github("stan-dev/rstan", subdir = "rstan/rstan"); unfortunately this fails to install (with nothing more informative than clang: error: linker command failed with exit code 1, which I don't know how to solve). So I'm now back on RStan 2.21.0 from CRAN, for which the problem is not fatal and gives the desired Info: Comments beginning with # are deprecated. Please use // in place of # for line comments.

Reproducible Steps:

Before I downgraded from RStan 2.26, this Stan program gave the error

data {
  int<lower = 1> N;
  vector[N] y;
}

parameters {
  real mu;
  real<lower = 0> sigma;
}

# test comment
model {
  y ~ normal(mu, sigma);
}

Expected Output:

I would expect Info: Comments beginning with # are deprecated. Please use // in place of # for line comments on any version of RStan (or at least an explanation of the problem even if it's fatal).

RStan Version:

2.26 (point-something-else which I can no longer remember)

R Version:

4.2.1

Operating System:

macOS Ventura Version 13.3.1 (a)

[ChrisHIV]

Update: I managed to update back up to rstan version 2.26.22 (Stan version 2.26.1) using the officially recommended install.packages("rstan", repos = c("https://mc-stan.org/r-packages/", getOption("repos"))) (instead of that previous StackOverflow-recommended installation command), and can confirm I have the problem there.

 > sessionInfo()
R version 4.2.1 (2022-06-23)
Platform: x86_64-apple-darwin17.0 (64-bit)
Running under: macOS Ventura 13.3.1

Matrix products: default
LAPACK: /Library/Frameworks/R.framework/Versions/4.2/Resources/lib/libRlapack.dylib

locale:
[1] en_US.UTF-8/en_US.UTF-8/en_US.UTF-8/C/en_US.UTF-8/en_US.UTF-8

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

other attached packages:
 [1] forcats_0.5.2       stringr_1.4.1       dplyr_1.0.10        purrr_0.3.5         readr_2.1.3        
 [6] tidyr_1.2.1         tibble_3.2.1        ggplot2_3.4.2       tidyverse_1.3.2     rstan_2.26.22      
[11] StanHeaders_2.26.22

loaded via a namespace (and not attached):
 [1] Rcpp_1.0.10         lubridate_1.8.0     prettyunits_1.1.1   ps_1.7.5            assertthat_0.2.1   
 [6] utf8_1.2.3          V8_4.3.0            R6_2.5.1            cellranger_1.1.0    backports_1.4.1    
[11] reprex_2.0.2        stats4_4.2.1        httr_1.4.4          pillar_1.9.0        rlang_1.1.1        
[16] googlesheets4_1.0.1 curl_5.0.0          readxl_1.4.1        rstudioapi_0.14     callr_3.7.3        
[21] googledrive_2.0.0   loo_2.6.0           munsell_0.5.0       broom_1.0.1         compiler_4.2.1     
[26] modelr_0.1.9        pkgconfig_2.0.3     pkgbuild_1.4.0      tidyselect_1.2.0    gridExtra_2.3      
[31] codetools_0.2-18    matrixStats_0.63.0  fansi_1.0.4         crayon_1.5.2        tzdb_0.3.0         
[36] dbplyr_2.2.1        withr_2.5.0         grid_4.2.1          jsonlite_1.8.4      gtable_0.3.3       
[41] lifecycle_1.0.3     DBI_1.1.3           magrittr_2.0.3      scales_1.2.1        RcppParallel_5.1.7 
[46] stringi_1.7.8       cli_3.6.1           fs_1.5.2            xml2_1.3.3          ellipsis_0.3.2     
[51] generics_0.1.3      vctrs_0.6.2         tools_4.2.1         glue_1.6.2          hms_1.1.2          
[56] processx_3.8.1      parallel_4.2.1      inline_0.3.19       colorspace_2.1-0    gargle_1.2.1       
[61] rvest_1.0.3         haven_2.5.1