`qnorm()` AD overload not detected after call to `optim()`

[andrjohns]

I've run into what feels like a very narrow edge-case, where calling the optim function before MakeADFun results in the AD overload for qnorm failing to be found. But if the function is re-declared after the call to optim, then all works as expected:

y <- matrix(rep(0.8, 4), ncol = 2)

library(RTMB)

ll_function <- function(v) {
  # Works if uncommented
  # y <- matrix(rep(0.8, 4), ncol = 2)
  
  lambda <- v[1]
  
  u <- y
  u[,1] <- pexp(y[,1], rate = v[1])
  u[,2] <- pexp(y[,2], rate = v[1])
  
  # Works if uncommented
  #u <- pexp(y, rate = v[1])
  
  sum(qnorm(u))
}

result <- optim(
  par = 0.1,
  fn = \(x) -ll_function(x)
)
#> Warning in optim(par = 0.1, fn = function(x) -ll_function(x)): one-dimensional optimization by Nelder-Mead is unreliable:
#> use "Brent" or optimize() directly


obj <- MakeADFun(
  func = \(v) ll_function(v$v),
  parameters = list(v=0.1),
  silent = TRUE
)
#> Error in stats::qnorm(p = p, mean = mean, sd = sd): Non-numeric argument to mathematical function

# Re-evaluate function declaration
ll_function2 <- eval(parse(text = deparse(ll_function)))

obj <- MakeADFun(
  func = \(v) ll_function2(v$v),
  parameters = list(v=0.1),
  silent = TRUE
)

str(obj)
#> List of 11
#>  $ par         : Named num 0.1
#>   ..- attr(*, "names")= chr "v"
#>  $ fn          :function (x = last.par[lfixed()], ...)  
#>  $ gr          :function (x = last.par[lfixed()], ...)  
#>  $ he          :function (x = last.par[lfixed()], atomic = usingAtomics())  
#>  $ hessian     : logi FALSE
#>  $ method      : chr "BFGS"
#>  $ retape      :function (set.defaults = TRUE)  
#>  $ env         :<environment: 0x1137d0210> 
#>  $ report      :function (par = obj$env$last.par, ...)  
#>  $ simulate    :function (par = obj$env$last.par, ...)  
#>  $ force.update:function ()

^{Created on 2025-10-18 with reprex v2.1.1}

Very odd!

[kaskr]

This is a side effect of R's byte compiler. Putting this line at the beginning of your script fixes it:

compiler::enableJIT(0) ## disable!