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

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

[Marco Emilio Poleggi via Bug reports for GNU Emacs, the Swiss army knife of text editors]

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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



--------------------------------------------------------------------------------

In GNU Emacs 29.3 (build 1, x86_64-pc-linux-gnu, GTK+ Version 3.24.41,
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Windowing system distributor 'The X.Org Foundation', version 11.0.12101013
System Description: Gentoo Linux

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