Why adding threads to brms causes the array error

I have run two same models in brms except the latter added “threads = threading(2)”. This change brought the errors.

> t_long_CNSubset20red1_sub3_ord = read.csv("https://discourse.mc-stan.org/uploads/short-url/byihhT2MGE2yXgTZB1pg93wPxio.csv")
> 
> t = brm(bf(y ~ mo(g_size) * mo(g_noise) * g_shape * g_interps),
+         data = t_long_CNSubset20red1_sub3_ord, chains = 2,
+         threads = threading(2), backend = "cmdstanr")
Compiling Stan program...
Error in '/var/folders/sj/jdgnsm9n14vgsjctfrk5x2_80000gn/T/Rtmpvz9N5l/model-2a69573d776.stan', line 258, column 2: Declaration
    of arrays by placing brackets after a variable name was removed in Stan
    2.33.0. Instead use the array keyword before the type. This can be
    changed automatically using the auto-format flag to stanc

make: *** [/var/folders/sj/jdgnsm9n14vgsjctfrk5x2_80000gn/T/Rtmpvz9N5l/model-2a69573d776.hpp] Error 65

Error: An error occured during compilation! See the message above for more information. 
To fix deprecated or removed syntax please see ?cmdstanr::format for an example.
> t_long_CNSubset20red1_sub3_ord = read.csv("https://discourse.mc-stan.org/uploads/short-url/byihhT2MGE2yXgTZB1pg93wPxio.csv")
> 
> t = brm(bf(y ~ mo(g_size) * mo(g_noise) * g_shape * g_interps),
+         data = t_long_CNSubset20red1_sub3_ord, chains = 2,
+         backend = "cmdstanr")
Compiling Stan program...
ld: warning: duplicate -rpath '/Users/zhang/.cmdstan/cmdstan-2.33.1/stan/lib/stan_math/lib/tbb' ignored

ld: warning: duplicate -rpath '/Users/zhang/.cmdstan/cmdstan-2.33.1/stan/lib/stan_math/lib/tbb' ignored

Start sampling
Running MCMC with 2 sequential chains...

Chain 1 Iteration:    1 / 2000 [  0%]  (Warmup) 
Chain 1 Iteration:  100 / 2000 [  5%]  (Warmup) 

If possible, add also code to simulate data or attach a (subset of) the dataset you work with.

Please provide this additional information in addition to your question:

  • Operating System: macos sonoma
  • CmdStan Version: 0.6.1.9
  • Compiler/Toolkit: llvm clang

This is the same bug that forced me to downgrade to brms 2.19.0 after updating CmdStanR.