Better tracebacks

[krlmlr]

When a complex expression inside mutate() or most other verbs fails, the traceback is not informative:

library(tidyverse)
f <- function(x) if (x < 3) 5 else g()
g <- function() stop("oops")
tibble(a = 1:10) %>% group_by(a) %>% mutate(b = f(a))
#> Error in mutate_impl(.data, dots): Evaluation error: oops.

Created on 2018-04-12 by the reprex package (v0.2.0).

It does contain the error message, but not the location. I wonder if the traceback can be made available.

If not, we could fix this by creating unrolled optimized R code in the C++ part, which then is passed to the R evaluator, and then transforming the results in C++ again:

mutate <- function(.data, ...) {
  code <- unroll_mutate(.data, !!!quos(...))
  res <- eval(code)
  apply_mutate(.data, res)
}

[romainfrancois]

Sounds like this could be an r-lib project in its own.

[krlmlr]

Maybe if we try {} catch {} at the C++ level? Is there a way to do Go-style evaluation in Rcpp, returning the result or an exception?

[romainfrancois]

For now, we will replace this by #3662

[lock]

This old issue has been automatically locked. If you believe you have found a related problem, please file a new issue (with reprex) and link to this issue. https://reprex.tidyverse.org/