When there is a folder with the cmdstan model name cmdstanr produces strange errors

[bbbales2]

This is from @MerlinHeidemanns

Make a model called 'test4.stan' in your working directory.

Something like this is fine:

parameters {
  real x;
}

model {
  x ~ normal(0, 1);
}

Now create a directory 'test4'. cmdstan_model will think the model is built and up to date and produce an error when running.

> dir.create('test4')
> mod = cmdstan_model('test4.stan')
Model executable is up to date!
> mod$sample()
Running MCMC with 4 sequential chains...

 Error in rethrow_call(c_processx_exec, command, c(command, args), stdin,  : 
  cannot start processx process './test4' (system error 13, Permission denied) @unix/processx.c:592 (processx_exec)
Type .Last.error.trace to see where the error occured 

If you update the model, it builds and then gets put in that folder:

> mod = cmdstan_model('test4.stan')
Compiling Stan program...
 
> mod$sample()
Running MCMC with 4 sequential chains...

 Error in rethrow_call(c_processx_exec, command, c(command, args), stdin,  : 
  cannot start processx process './test4' (system error 13, Permission denied) @unix/processx.c:592 (processx_exec)
Type .Last.error.trace to see where the error occured 
> list.files("test4/")
[1] "model-13792589c4fe"

[rok-cesnovar]

Nice find. And once for a change this is unlikely to cause problem for windows. I think the best fix here is to check if a file is a directory and if so just stop and throw an error to the user to rename either the stan model name or the folder.

[bbbales2]

I think the best fix here is to check if a file is a directory

That makes sense to me.