schools.stan example crashing R GUI on macOS Catalina

Summary:

Attempting to run schools example in the R GUI cashes the GUI

Description:

Running the standard schools.stan example from the rstan vignette. Running it in RStudio works (though now producing the message)

sh: clang++ -mmacosx-version-min=10.13: command not found
The NEXT version of Stan will not be able to pre-process your Stan program.

referenced in https://github.com/stan-dev/rstan/issues/774

In trying to figure out what was up with that, I tried running the same example through the R GUI. After navigating to the correct directory and ensuring the code works in RStudio, running the below in R GUI results in the R GUI getting stuck indefinitely. The same thing happens if I try and run rstanarm with more than one core in the R GUI (GUI hangs indefinitely).

Actually, even if you force quite the R GUI, after this happens R keeps running in the background after the force quit, which I discovered from a very noisy fan.

schools <- "
data {
  int<lower=0> J;         // number of schools 
  real y[J];              // estimated treatment effects
  real<lower=0> sigma[J]; // standard error of effect estimates 
}
parameters {
  real mu;                // population treatment effect
  real<lower=0> tau;      // standard deviation in treatment effects
  vector[J] eta;          // unscaled deviation from mu by school
}
transformed parameters {
  vector[J] theta = mu + tau * eta;        // school treatment effects
}
model {
  target += normal_lpdf(eta | 0, 1);       // prior log-density
  target += normal_lpdf(y | theta, sigma); // log-likelihood
}

"

library(rstan)

schools_data <- list(
  J = 8,
  y = c(28,  8, -3,  7, -1,  1, 18, 12),
  sigma = c(15, 10, 16, 11,  9, 11, 10, 18)
)

library(rstan)
fit1 <- stan(
  model_code = schools,
  model_name = "schools",# Stan program
  data = schools_data,    # named list of data
  chains = 4,             # number of Markov chains
  warmup = 1000,          # number of warmup iterations per chain
  iter = 2000,            # total number of iterations per chain
  cores = 1,              # number of cores (could use one per chain)
  refresh = 100             
)

RStan Version:

2.21.1

R Version:

"R version 4.0.2 (2020-06-22)"

Operating System:

macOS 10.15.5

Start by reproducing the supplied schools example through the R GUI on macOS, comparing it with RStudio and with cores set to 1. Investigate the R GUI behavior around the stan(...) call and confirm that the GUI and R process finish normally without hanging after the run.