Can't find start of slur

[Maurizio Tomasi]

Hello to everybody!

I have a feature request for Lilypond 1.5.61.  Consider this file,
where there is a multimeasure rest, followed by a slur that has not
been properly opened:

----------------------------------------------------------------------
\score {
    \context Staff {
        \notes \relative g'' {
            R1*5
            | a4 b c )d
        }
    }
}
----------------------------------------------------------------------

If I compile it, Lilypond correctly warns me there is something wrong.
I can understand this error is before the seventh bar before Lily
prints the message before a `[7]':

----------------------------------------------------------------------
GNU LilyPond 1.5.61
Now processing: `/home/ziotom/music/test.ly'
Parsing...
Interpreting music...
warning: can't find start of slur
[7]
Preprocessing elements...
Calculating column positions... [3][6][7]
paper output to `test.tex'...
----------------------------------------------------------------------

Now, suppose I modify the example slightly:

----------------------------------------------------------------------
\score {
    \context Staff {
        \property Score.skipBars = ##t

        \notes \relative g'' {
            R1*5
            | a4 b c )d
        }
    }
}
----------------------------------------------------------------------

Then Lilypond prints:

----------------------------------------------------------------------
GNU LilyPond 1.5.61
Now processing: `/home/ziotom/music/test.ly'
Parsing...
Interpreting music...
warning: can't find start of slur
[3]
Preprocessing elements...
Calculating column positions...
paper output to `test.tex'...
----------------------------------------------------------------------

I cannot understand where the slur is, since lily prints "[3]", which
is not a `real' bar number.  This is quite tedious, since it is
difficult to find wrong slurs, especially in a long score.  Would it
be easy to modify Lilypond so that it prints where it found the wrong
slur in the .ly file?  I mean something like this:

----------------------------------------------------------------------
test.ly:7: warning: can't find start of slur:
            | a4 b c )d
----------------------------------------------------------------------

Thanks
Maurizio