WISH: browser() support redirecting stdout to stderr

[HenrikBengtsson]

Issue

base::browser() outputs to standard output (stdout). This causes problem whenever stdout is captured, e.g. by utils::capture.output() or future::future(). For example,

$ R --quiet --vanilla
> foo <- function() browser(); utils::capture.output(foo())
Browse[1]> 1+2
Browse[1]> str(3)
Browse[1]> cat("42\n", file = stderr())
42
Browse[1]> 

Suggestion

Add support for outputting to standard error (stderr), e.g.

browser(file = stderr())

Relevant source code

To the best of my understanding, the browser-related code is in src/main/eval.c. There is not one single location where the output is produced, so adding support for stderr requires changes in multiple locations.