Subject: Incorrect path canonicalisation
From: Mattias Andrée <[email-masked]>
To: [email-masked]
Date: Sat, 1 Dec 2018 21:04:50 +0100
List-Id: <debbugs-submit.debbugs.gnu.org>

Emacs 26.1 removes ..'s incorrectly from file names.
Emacs removes the directory in front the .. rather than
getting its parent directory.

Example:

	cd
	mkdir -p 1/2
	cd 1/2
	echo 3 > ../../3
	ln -s ~ 4
	echo 5 > 5
	emacs 4/../5 # works, but shouldn't
	emacs 4/../$USER/3 # does not works, should

On Linux, the proper way to get the canonical path
for a file with the file descriptor $fd:

	stat(3) /dev/fd/$fd
	p := readlink(3) /dev/fd/$fd
	if (st_nlinks != 0) {
		stat(3) /dev/fd/$fd
		if (st_nlinks == 0) {
			p := readlink(3) /dev/fd/$fd
			remove " (deleted)" from the end of p
		}
	} else {
		remove " (deleted)" from the end of p
	}
	canonical path is p