bug#54797: 27.1; "Old-style backquotes detected!" when there are no backquotes.

bug#54797: 27.1; "Old-style backquotes detected!" when there are no backquotes.

[Bruce Mardle via Bug reports for GNU Emacs, the Swiss army knife of text editors]

Short version:
Try to evaluate
'(, foo)
and you'll get (error "Old-style backquotes detected!"), which is
confusing considering that the expression doesn't contain a backquote!


Long version:
My code was evaluating happily yesterday (on what much have been an old
version of Emacs) but came up with that error on 27.1 today.  It turned
out I had "(, " in a few places. They should have been "(* ", (OCR
failure) so I suppose I should thank the error message for helping me find
those... but it's a confusing message when source doesn't contain any
backquotes!
(I spent a while Googling to find out what was happening but only found
cases of people getting the error message whose code *did* contain a
backquote.)






In GNU Emacs 27.1 (build 1, x86_64-pc-cygwin)
 of 2020-10-29 built on moufang2
Repository revision: 14432a33511ec750815c6f3b188f2c0d21b4cb22
Repository branch: master
Windowing system distributor 'Microsoft Corp.', version 6.1.7601
Recent messages:
Quit
Please type y or n, or C-v/M-v to scroll: y
View mode: type C-h for help, h for commands, q to quit.
Mark saved where search started
Mark set
Mark saved where search started
split-window: Attempt to split minibuffer window
command-execute: Command attempted to use minibuffer while in minibuffer
elisp--preceding-sexp: Old-style backquotes detected!
Making completion list...
Quit
Configured using:
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bug#54797: 27.1; "Old-style backquotes detected!" when there are no backquotes.

[Lars Ingebrigtsen]

Bruce Mardle <marblypup@yahoo.co.uk> writes:

> Short version:
> Try to evaluate
> '(, foo)
> and you'll get (error "Old-style backquotes detected!"), which is
> confusing considering that the expression doesn't contain a backquote!

I can reproduce this in Emacs 27.1, but not in Emacs 28.1 (it just
evaluates to ((\, foo))), so I guess this has been fixed now.

-- 
(domestic pets only, the antidote for overdose, milk.)
   bloggy blog: http://lars.ingebrigtsen.no

bug#54797: 27.1; "Old-style backquotes detected!" when there are no backquotes.

[Drew Adams]

> I can reproduce this in Emacs 27.1, but not in Emacs 28.1 (it just
> evaluates to ((\, foo))), so I guess this has been fixed now.

It's an Emacs 27 regression.  No such problem before Emacs 27.

bug#54797: 27.1; "Old-style backquotes detected!" when there are no backquotes.

[Lars Ingebrigtsen]

Bruce Mardle <marblypup@yahoo.co.uk> writes:

> I've only just read this properly [blush]. (I've just installed Emacs
> 28.1 under Cygwin under Windows 10.): Why DOES evaluating '(, foo)
> give ((\, foo), not (\, foo)? Evaluating '(bar foo) gives (bar foo),
> as expected.

I'm not sure -- it's not particularly valid syntax -- , is only valid
inside backquotes.

Perhaps somebody else knows.