`rstan` fails to read `cmdstanr` output .csv files

Summary:

rstan::read_stan_csv() no longer works for for .csv files produced by cmdstanr

Description:

It seems that rstan expects the save_warmup field to be an integer value, but cmdstanr instead writes this as a logical value (e.g., false) to the conversion to integer fails in rstan:::parse_stancsv_comments() resulting in an NA value for save_warmup. This used to work with earlier versions of cmdstanr/CmdStan.

Reproducible Steps:

library("cmdstanr")
#> This is cmdstanr version 0.8.1
#> - CmdStanR documentation and vignettes: mc-stan.org/cmdstanr
#> - CmdStan path: C:/Users/Santtu/.cmdstan/cmdstan-2.35.0
#> - CmdStan version: 2.35.0
file <- file.path(cmdstan_path(), "examples", "bernoulli", "bernoulli.stan")
mod <- cmdstan_model(file)
data_list <- list(N = 10, y = c(0, 1, 0, 0, 0, 0, 0, 0, 0, 1))
samples <- mod$sample(
  data = data_list,
  refresh = 0,
  chains = 1,
  iter_sampling = 10,
  iter_warmup = 10
)
#> Running MCMC with 1 chain...
#> 
#> Chain 1 WARNING: No variance estimation is 
#> Chain 1          performed for num_warmup < 20 
#> Chain 1 finished in 0.0 seconds.
rstan::read_stan_csv(samples$output_files())
#> Warning in parse_stancsv_comments(comments): NAs introduced by coercion
#> Error in if (max(save_warmup) == 0L) {: missing value where TRUE/FALSE needed

^{Created on 2024-07-10 with reprex v2.1.1}

RStan Version:

2.32.6

R Version:

R version 4.4.0 (2024-04-24 ucrt)

Operating System:

Windows 11 Pro 23H2

Start with rstan::read_stan_csv() and rstan:::parse_stancsv_comments() using the provided cmdstanr reproduction. Trace how the save_warmup field is parsed and verify that the resulting CSV can be read without the coercion warning or missing-value error.