* lisp/progmodes/etags-regen.el (etags-regen-file-extensions):
Add .pm.
;; when it cannot determine the type of the file.
;; http://lists.gnu.org/archive/html/emacs-devel/2018-01/msg00323.html
(defcustom etags-regen-file-extensions
- '("rb" "js" "py" "pl" "el" "c" "cpp" "cc" "h" "hh" "hpp"
+ '("rb" "js" "py" "pl" "pm" "el" "c" "cpp" "cc" "h" "hh" "hpp"
"java" "go" "cl" "lisp" "prolog" "php" "erl" "hrl"
"F" "f" "f90" "for" "cs" "a" "asm" "ads" "adb" "ada")
"Code file extensions for `etags-regen-mode'.