[R] [External] Parser For Line Number Tracing

[IVO I WELCH]

There is a little catch-22 here.

I would be happy to fund a student to spend a summer cleaning up the error messages and making it more userfriendly, but the catch-22 problem is that I don’t have much confidence that this effort would be adopted into the basic R distribution — and the only way I think this will be worth it is if it rolls into the standard distribution.  (Well, with an option( verbose.errors ) enabling it.). with confidence of adoption, I think few are willing to exert the effort.

I would contribute a few thousand dollars to the cause if it funded the R core team hiring such a summer programming assistant for this purpose, too, if they don’t trust a random student I would hire.  But again…only if the expectation is that this will flow into the distribution.

If you think I am misreading the situation, please let me know who I should ask.

Regards,

/ivo


> On Jan 20, 2025, at 2:56 PM, Duncan Murdoch <murdoch.duncan using gmail.com> wrote:
> 
> I've posted a patch to bugs.r-project.org that fixes the traceback() issue.  It's not specific to findFun3; you get the same problem with errors from expressions like
> 
> 1 + "a"
> 
> In my testing, I occasionally saw cases where show.error.locations = TRUE didn't work.  I'll try to track down a reproducible case, and perhaps a patch to fix it.
> 
> Duncan Murdoch
> 
> 
> 
> On 2025-01-20 9:37 a.m., Duncan Murdoch wrote:
>> Sorry, I'm not seeing the first problem now:
>> options(show.error.locations = TRUE) works fine.  Not sure what I did
>> wrong before.
>> I'm still seeing `traceback()` failing to report the attempt to call
>> nofunction().  I suppose this is because a context is never set up for
>> the failed call.  Perhaps findFun3 could set up a fake context so that
>> traceback() adds one more entry?
>> Duncan Murdoch
>> On 2025-01-19 3:39 p.m., Duncan Murdoch wrote:
>>> Thanks for pointing out the options.  Using
>>> 
>>>      options(show.error.locations = TRUE)
>>> 
>>> works on Ivo's example, but it doesn't show a location if the error
>>> happens in a function that doesn't have srcrefs, because the known
>>> location isn't on the top of the stack.
>>> 
>>> Perhaps TRUE (and maybe "top"?) should look back through the stack until
>>> it finds a known location, and report that, or another option (e.g.
>>> "highest"?) could be added to do that.
>>> 
>>> And still I think traceback() should show the top call in Ivo's example.
>>> 
>>> Duncan
>>> 
>>> 
>>> On 2025-01-19 11:46 a.m., luke-tierney using uiowa.edu wrote:
>>>> On Sun, 19 Jan 2025, Ivo Welch wrote:
>>>> 
>>>>> Hi Duncan — Wonderful.  Thank you.  Bug or no bug, I think it would be
>>>>> a huge improvement for user-friendliness if R printed the last line by
>>>>> default *every time* a script dies.  Most computer languages do so.
>>>>> 
>>>>> Should I file it as a request for improvement to the R code
>>>>> development team?  Maybe R can be improved at a very low cost to the
>>>>> development team and a very high benefit to newbies.
>>>> 
>>>> No. There are already many ways to influence the way the default error
>>>> handler prints information about errors, mstly via options(). In
>>>> particular you may want to look at entries in ?options for
>>>> 
>>>> show.error.locations
>>>> showErrorCalls
>>>> showWarningCalls
>>>> 
>>>> and adjust your options settings accordingly.
>>>> 
>>>> Best,
>>>> 
>>>> luke
>>>> 
>>>>> 
>>>>> Regards,
>>>>> 
>>>>> /ivo
>>>>> 
>>>>> On Sun, Jan 19, 2025 at 2:39 AM Duncan Murdoch <murdoch.duncan using gmail.com> wrote:
>>>>>> 
>>>>>> On 2025-01-18 8:27 p.m., Ivo Welch wrote:
>>>>>>> I am afraid my errors are worse!  (so are my postings.  I should have
>>>>>>> given an example.)
>>>>>>> 
>>>>>>> ```
>>>>>>> x <- 1
>>>>>>> y <- 2
>>>>>>> nofunction("something stupid I am doing!")
>>>>>>> z <- 4
>>>>>>> ```
>>>>>>> 
>>>>>>> and
>>>>>>> 
>>>>>>> ```
>>>>>>>> source("where-is-my-water.R")
>>>>>>> Error in nofunction("something stupid I am doing!") :
>>>>>>>      could not find function "nofunction"
>>>>>>> ```
>>>>>>> 
>>>>>>> and no traceback is available.
>>>>>> 
>>>>>> Okay, I see.  In that case traceback() doesn't report the line, but it
>>>>>> still is known internally.  You can see it using the following function:
>>>>>> 
>>>>>> showKnownLocations <- function() {
>>>>>>      calls <- sys.calls()
>>>>>>      srcrefs <- sapply(calls, function(v) if (!is.null(srcref <- attr(v,
>>>>>> 
>>>>>> "srcref"))) {
>>>>>>        srcfile <- attr(srcref, "srcfile")
>>>>>>        paste0(basename(srcfile$filename), "#", srcref[1L])
>>>>>>      } else ".")
>>>>>>      cat("Current call stack locations:\n")
>>>>>>      cat(srcrefs, sep = " ")
>>>>>>      cat("\n")
>>>>>> }
>>>>>> 
>>>>>> I haven't done much testing on this, but I think it can be called
>>>>>> explicitly from any location if you want to know how you got there, or
>>>>>> you can set it as the error handler using
>>>>>> 
>>>>>>      options(error = showKnownLocations)
>>>>>> 
>>>>>> For example, try this script:
>>>>>> 
>>>>>>      options(error = showKnownLocations)
>>>>>>      f <- function() showKnownLocations()
>>>>>>      x <- 1
>>>>>>      f()
>>>>>>      y <- 2
>>>>>>      nofunction("something stupid I am doing!")
>>>>>>      z <- 4
>>>>>> 
>>>>>> I see this output from source("test.R"):
>>>>>> 
>>>>>>     > source("test.R")
>>>>>>      Current call stack locations:
>>>>>>      . . . . test.R#4 test.R#2
>>>>>>      Error in nofunction("something stupid I am doing!") :
>>>>>>        could not find function "nofunction"
>>>>>>      Current call stack locations:
>>>>>>      . . . . test.R#6
>>>>>> 
>>>>>> The first report is from the explicit call in f() on line 2 that was
>>>>>> invoked on line 4, and the second report happens during error handling.
>>>>>> 
>>>>>> I supppose the fact that traceback() isn't showing you the line 6
>>>>>> location could be considered a bug.
>>>>>> 
>>>>>> Duncan Murdoch
>>>>>> 
>>>>>> 
>>>>> 
>>>>> ______________________________________________
>>>>> R-help using r-project.org mailing list -- To UNSUBSCRIBE and more, see
>>>>> https://stat.ethz.ch/mailman/listinfo/r-help
>>>>> PLEASE do read the posting guide https://www.r-project.org/posting-guide.html
>>>>> and provide commented, minimal, self-contained, reproducible code.
>>>>> 
>>>> 
>>> 
>