bug#71042: 29.3; csv-mode: csv-guess-set-separator chokes on comment lines

[Marco Emilio Poleggi]

Comment lines seem well supported by csv-mode. However, function 
`csv-guess-set-separator` has troubles with them.

Visit this input file:

-------------------------8<-----------------------
$ cat >csv-test.csv <<EOF
###
###
Foo;Bar;Quux
123;456;blah, blah
EOF
------------------------->8-----------------------

With no special settings, the default comma (',') separator is
detected.

Now, issue `M-x csv-guess-set-separator`: I'd expect that the effective
semicolon (';') separator is detected. But it's not and instead the hash
('#') is detected, as confirmed by `C-h v csv-separators`.

It looks like csv-guess-set-separator is fooled by the first two lines
with an even number of hash characters. Indeed, breaking that symmetry
makes the ';' detectable.

But, hey, csv-mode says:

;; CSV mode commands ignore blank lines and comment lines beginning
;; with the value of the buffer local variable `csv-comment-start',
;; which by default is #. ...

So there's probably a bug in `csv-guess-set-separator`.

Cheers,

  Marco



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