bug#61514: 30.0.50; sadistically long xml line hangs emacs

[Gregory Heytings]

> What am I missing?

I don't know... but I observe that this alone:

(with-current-buffer (get-buffer-create "*bug*")
  (insert "<id name=\"")
  (insert (make-string 250000 ?n))
  (goto-char 5)
  (looking-at "[^<>\n]+?\\(\\(?:\\(xmlns\\)\\|[_[:alpha:]][-._[:alnum:]]*\\)\\(:[_[:alpha:]][-._[:alnum:]]*\\)?\\)[ \r\t\n]*=\\(?:[ 
\r\t\n]*\\('[^<'&\r\n\t]*\\([&\r\n\t][^<']*\\)?'\\|\"[^<\"&\r\n\t]*\\([&\r\n\t][^<\"]*\\)?\"\\)\\(?:\\([
 \r\t\n]*>\\)\\|\\(?:\\([ \r\t\n]*/\\)\\(>\\)?\\)\\|\\([ \r\t\n]+\\)\\)\\)?"))

doesn't fail, so I don't think it's this regexp which causes the overflow.