Harlan - 8 months ago 45
R Question

# get stack trace on tryCatch'ed error in R

This is related to some other questions, but I can't seem to figure out how to apply the answer, so I'm asking a new question.

I'm trying to figure out an uninformative error from a piece of code that looks like this:

tryCatch(MainLoop(),
error=function(e) { fatal(lgr, paste('caught fatal error:', as.character(e)));
exit.status <<- 1 })


The problem is that the error appears to be related to something buried in a library function:

Error in nrow(x): (subscript) logical subscript too long


That
nrow
is not in my code, as the C-level error above only applies to a type of indexing that never happens in any of my
nrow
calls.

So I'd really like to get a stack trace from within that
tryCatch
. Here's an analogous problem:

x <- function() { y(); }
y <- function() { z(); }
z <- function() { stop("asdf") }

> x()
Error in z() : asdf
> tryCatch(x(), error=function(e) { print(conditionCall(e)) } )
z()
> tryCatch(x(), error=function(e) { dump.frames() } )
> last.dump
$tryCatch(x(), error = function(e) { dump.frames() }) <environment: 0x1038e43b8>$tryCatchList(expr, classes, parentenv, handlers)
<environment: 0x1038e4c60>

$tryCatchOne(expr, names, parentenv, handlers[[1]]) <environment: 0x1038e4918>$value[[3]](cond)
<environment: 0x1038ea578>

attr(,"error.message")
[1] "asdf"
attr(,"class")
[1] "dump.frames"


How do I get the stack trace that includes the call to
y()
? Do I have to stop using
tryCatch
? What's a better way?

For interactive use one might trace(stop, quote(print(sys.calls()))) to print the call stack at the time stop() is invoked.

From ?tryCatch,

 The function 'tryCatch' evaluates its expression argument in a
context where the handlers provided in the '...'  argument are
available.


whereas

 Calling handlers are established by 'withCallingHandlers'...
the handler is called... in the context where the condition
was signaled...


so

>     withCallingHandlers(x(), error=function(e) print(sys.calls()))
[[1]]
withCallingHandlers(x(), error = function(e) print(sys.calls()))

[[2]]
x()

[[3]]
y()

[[4]]
z()

[[5]]
stop("asdf")

[[6]]
.handleSimpleError(function (e)
print(sys.calls()), "asdf", quote(z()))

[[7]]
h(simpleError(msg, call))

Error in z() : asdf


This is thwarted if there is an inner tryCatch

withCallingHandlers({
tryCatch(x(), error=function(e) stop("oops"))
}, error=function(e) print(sys.calls()))


as we only have access to the call stack after the tryCatch has 'handled' the error.