Improve error message could not find input line in code block by indicating location of that code block

[fingolfin]

I just did execute makedocs with doctest = :fix in a package to adjust docstrings to some printing tweaks I made, and got this very frustrating message:

julia> include("docs/make.jl")
[ Info: SetupBuildDirectory: setting up build directory.
[ Info: Doctest: running doctests.
┌ Warning: could not find input line in code block
└ @ Documenter ~/.julia/packages/Documenter/C1XEF/src/doctests.jl:507

I call it frustrating because all I know now is that "some docstring somewhere in your package has a problem, maybe". That's not a lot to go on.

If I knew which docstring it was, at least I'd have a chance.

If there is any way to improve this message to tell me more, that'd be awesome. Ideally of course the file and starting line of the code block, but even just the file would be a great start. Or a snippet of the content. Anything?