[Bug 12616] New: realpath/readlink is incompatible with coreutils implementation

[bugzilla at busybox.net]

https://bugs.busybox.net/show_bug.cgi?id=12616

            Bug ID: 12616
           Summary: realpath/readlink is incompatible with coreutils
                    implementation
           Product: Busybox
           Version: 1.31.x
          Hardware: All
                OS: Linux
            Status: NEW
          Severity: minor
          Priority: P5
         Component: Standard Compliance
          Assignee: unassigned at busybox.net
          Reporter: koichi at nksm.name
                CC: busybox-cvs at busybox.net
  Target Milestone: ---

Version:
https://git.busybox.net/busybox/commit/?id=9aa751b08ab03d6396f86c3df77937a19687981b

----------------
Repro 1:
$ cd /tmp
$ ln -s no-such-a-file symlink

Coreutils (expected):
$ readlink -f /tmp/symlink
/tmp/no-such-a-file
$ realpath /tmp/symlink
/tmp/no-such-a-file

Busybox (incorrect):
$ readlink -f symlink
/tmp/symlink
$ realpath symlink
/tmp/symlink

----------------
Repro 2:
$ cd /usr/bin

Coreutils (expected):
$ readlink -f ../.../
/usr/...
$ realpath ../.../
/usr/...

Busybox (incorrect):
$ readlink -f ../.../
(none, exit status: 1) 
$ realpath ../.../
realpath: ../...: No such file or directory

----------------
Repro 3:

Coreutils (expected):
$ readlink -f /no-such-a-file
/no-such-a-file
$ realpath /no-such-a-file
/no-such-a-file

Busybox (incorrect):
$ readlink -f /no-such-a-file
(none, exit status: 1) 
$ realpath /no-such-a-file
realpath: : No such file or directory

----------------
Repro 4:
$ cd /

Coreutils (expected):
$ readlink -f /./no-such-a-file
/no-such-a-file
$ realpath /./no-such-a-file
/no-such-a-file

Busybox (incorrect):
$ readlink -f /./no-such-a-file
//no-such-a-file
$ realpath /./no-such-a-file
//no-such-a-file

----------------
Repro 5:
$ cd /
$ ln -s ./no-such-a-file2 /symlink2

Coreutils (expected):
$ readlink -f symlink2
/no-such-a-file2
$ realpath symlink2
/no-such-a-file2

Busybox (incorrect):
$ readlink -f /symlink2
/./no-such-a-file2
$ realpath symlink2
/./no-such-a-file2

----------------
This is a different bug from
- https://bugs.busybox.net/show_bug.cgi?id=11021
- https://bugs.busybox.net/show_bug.cgi?id=11956

This bug was found during the development of
https://github.com/ko1nksm/readlinkf. It may be your help.

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