🚀 go-pugleaf

In GNU Emacs 19.25.1 of Fri Jun  3 1994 on kleph (hppa1.1-hp-hpux9)

'C-M-U' (backward-up-list) within the following string incorrectly
moves to the start of the defun. The same bug occurs in 18.57 and
lemacs 19.6. The bug happens no matter what the value of
parse-sexp-ignore-comments.

(defun foo () ; "
   )
(progn "Bug: a C-M-U within this string goes to start of foo's def")

If you delete the commented-out double-quote, or back-slashify it then
you instead get an "Unbalanced parenthesis" error. Shouldn't it move
to the start of the progn in this case?

Note that the lemacs (but not emacs) Info node on "Lists" says:

 "In Lisp and other languages where comments run until the end of a
 line, it is very difficult to ignore comments when parsing backwards;
 therefore, in such languages the sexp commands treat the text of
 comments as if it were code."

Is this comment also supposed to apply to 'list' commands in addition
to 'sexp' commands? I guess that would explain the above behavior if so.

Its rather ironic that Emacs now has all these fancy tools for doing 
syntax highlighting yet it still cannot even parse backwards correctly.
Perhaps extents and or text-properties could be used to fix this.

Note: the above example is not artificially contrived: it was
narrowed-down from an actual piece of code.