Do you mean the line number *in the library function* ??
In general, I think that's an impossible problem. Consider a somewhat
convoluted example of a library function:
func Bar(...) {
...
if xyz() {
blah = true
}
if abc() {
baz = false
}
...
if blah && flurble() && !baz {
err = SomeError // A
}
...
...
if err {
return 0, err // B
}
...
}
At what point was it "decided" that SomeError should be returned? A number
of conditions had to be met before line A was executed. If you modified
the code there, it could record as part of the error value the line number
at which the err variable was set. However without modifying the code (or
changing the language, so that every variable value remembers the line
number where it was last set), I think the best you could get is the line
number of B. And that's not very useful.
Your own code presumably looks something like this:
foo, err := library.Bar(baz)
if err {
...
}
This means you already know exactly which function you're calling; the
error must have "come from" somewhere in that function. (Of course, that
function may have used the results from other functions before deciding to
return an error)
There are only a fixed number of return points from library.Bar - quite
possible only one. Would it really help much to know which "return"
statement was used?
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