bug#35286: 26.2; indent-sexp broken

[Leo Liu <sdl.web@gmail.com>]

I am only using the following ruby code to demonstrate the issue. I
noticed this issue while editing other programming text.

  def sum_eq_n?(arr, n)
    return true if arr.empty? && n == 0
    arr.product(arr).reject { |a,b| a == b }.any? !{ |a,b| a + b == n } #
  
  def sum_eq_n?(arr, n)
    return true if arr.empty? && n == 0
    arr.product(arr).reject { |a,b| a == b }.any? { |a,b| a + b == n }
  end

Put the above ruby code in a ruby-mode buffer. ! is used to indicate
where point is and is not part of the code.

M-x indent-sexp and see indentation of every line after the point
changed.


The bug is caused by the following unsafe part of indent-sexp introduced
in 26.2:

  (save-excursion
    (let ((eol (line-end-position)))
      (forward-sexp 1)
      (condition-case ()
          (while (and (< (point) eol) (not (eobp)))
            (forward-sexp 1))
        (scan-error nil)))
    (point))

which can easily include two or more sexps after point. This looks like
a major breakage.