Debugging package::function() although lazy evaluation is used

Question

How can I debug efficiently in R if packages are unknown due to lazy evaluation. I would like to keep the basic browser() functionality as it works great - even with the testthat package. As explained in the following post, --with-keep.source is set for my project in "project options => Build Tools".

To reproduce the behavior, create a package TestDebug containing

myfun <- function(a,b) {return(a+b)}

and a script example.R

{
browser()
TestDebug::myfun(1,2)
}

Edit: The situation where TestDebug::myfun(1,2) calls otherpackage::myfun2(1,2) should be also covered. I think the situation should occur in every "real" package?

Answer 1

The following works for me.

I have my package TestDebug with my function

myfun <- function(a,b) {return(a+b)}

If I run the script

debug(TestDebug::myfun)
TestDebug::myfun(1,2)

The debugger steps right into the source of TestDebug::myfun() not into the :: function as it does when you place a browser() before the call to TestDebug::myfun(1,2).

As you mention in your question: in real-life situations TestDebug::myfun(1,2) often calls otherpackage::myfun2(1,2). If you try to step into otherpackage::myfun2(1,2) you will end up inside the :: function again.

To prevent this I add this functions called inside other functions to the debug index on the fly:

As soon as you are on the line inside TestDebug::myfun() where otherpackage::myfun2(1,2) is called I run debug(otherpackage::myfun2(1,2)) in the console. After that I can step into otherpackage::myfun2(1,2) without problems and end up in the source code of otherpackage::myfun2(1,2). (..and not in the source code of ::)

Don't forget to call undebug(otherpackage::myfun2(1,2)) after you're sure that your problem is not inside otherpackage::myfun2(1,2) to prevent the debugger to jump into otherpackage::myfun2(1,2) the next time it is called.

If you prefer you can also use debugonce(otherpackage::myfun(1,2)) (instead of debug(..)) to only debug a function once.