bug#29597: 26.0.90; line-number-display-width returns incorrect width

[Paul Rankin]

I had a look in the source of display-line-numbers.el in the repo but cannot 
find the definition of line-number-display-width.

But this is irrelevant, the line number width is clearly 4 characters, lining 
up with File in the menu bar.

(string-width "File")
4

It clearly fails to count to four. Adding a docstring that 2 really equals 4 is 
absurd.

Please don’t close bugs until they’re actually closed.