Setup:

  $ cat > eval.py <<EOF

  > from __future__ import absolute_import

  > import filecmp

  > from mercurial import commands, context, registrar

  > cmdtable = {}

  > command = registrar.command(cmdtable)

  > @command(b'eval', [], 'hg eval CMD')

  > def eval_(ui, repo, *cmds, **opts):

  >     cmd = " ".join(cmds)

  >     res = str(eval(cmd, globals(), locals()))

  >     ui.warn("%s" % res)

  > EOF

  $ echo "[extensions]" >> $HGRCPATH

  $ echo "eval=`pwd`/eval.py" >> $HGRCPATH

Arbitraryfilectx.cmp does not follow symlinks:

  $ mkdir case1

  $ cd case1

  $ hg init

  $ printf "A" > real_A

  $ printf "foo" > A

  $ printf "foo" > B

  $ ln -s A sym_A

  $ hg add .

  adding A

  adding B

  adding real_A

  adding sym_A

  $ hg commit -m "base"

These files are different and should return True (different):

(Note that filecmp.cmp's return semantics are inverted from ours, so we invert

for simplicity):

  $ hg eval "context.arbitraryfilectx('A', repo).cmp(repo[None]['real_A'])"

  True (no-eol)

  $ hg eval "not filecmp.cmp('A', 'real_A')"

  True (no-eol)

These files are identical and should return False (same):

  $ hg eval "context.arbitraryfilectx('A', repo).cmp(repo[None]['A'])"

  False (no-eol)

  $ hg eval "context.arbitraryfilectx('A', repo).cmp(repo[None]['B'])"

  False (no-eol)

  $ hg eval "not filecmp.cmp('A', 'B')"

  False (no-eol)

This comparison should also return False, since A and sym_A are substantially

the same in the eyes of ``filectx.cmp``, which looks at data only.

  $ hg eval "context.arbitraryfilectx('real_A', repo).cmp(repo[None]['sym_A'])"

  False (no-eol)

A naive use of filecmp on those two would wrongly return True, since it follows

the symlink to "A", which has different contents.

  $ hg eval "not filecmp.cmp('real_A', 'sym_A')"

  True (no-eol)