Fix infloop in uncomment-region-default (Bug#27112)

When `comment-continue' has only blanks, `comment-padright' produces a
regexp that matches the empty string, so `uncomment-region-default'
will loop infinitely.
* lisp/newcomment.el (comment-padright): Only return a regexp if STR
has nonblank characters.

diff --git a/lisp/newcomment.el b/lisp/newcomment.el
index 4b261c34c65f8fee7ce100f6a20a4c9d8e4e5663..118549f421ce24324eec9ad992f34f0e704e4199 100644 (file)
--- a/lisp/newcomment.el
+++ b/lisp/newcomment.el
@@ -815,7 +815,7 @@ N defaults to 0.
 If N is `re', a regexp is returned instead, that would match
 the string for any N."
   (setq n (or n 0))
-  (when (and (stringp str) (not (string= "" str)))
+  (when (and (stringp str) (string-match "\\S-" str))
     ;; Separate the actual string from any leading/trailing padding
     (string-match "\\`\\s-*\\(.*?\\)\\s-*\\'" str)
     (let ((s (match-string 1 str))     ;actual string