Setup:

  $ cat > eval.py <<EOF

  > from __future__ import absolute_import

  > import filecmp

  > from mercurial import commands, context, pycompat, registrar

  > cmdtable = {}

  > command = registrar.command(cmdtable)

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

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

  >     cmd = b" ".join(cmds)

  >     res = pycompat.bytestr(eval(cmd, globals(), locals()))

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

  > EOF

  $ echo "[extensions]" >> $HGRCPATH

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

Arbitraryfilectx.cmp does not follow symlinks:

  $ mkdir case1

  $ cd case1

  $ hg init

#if symlink

  $ 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"

#else

  $ hg import -q --bypass - <<EOF

  > # HG changeset patch

  > # User test

  > # Date 0 0

  > base

  > 

  > diff --git a/A b/A

  > new file mode 100644

  > --- /dev/null

  > +++ b/A

  > @@ -0,0 +1,1 @@

  > +foo

  > \ No newline at end of file

  > diff --git a/B b/B

  > new file mode 100644

  > --- /dev/null

  > +++ b/B

  > @@ -0,0 +1,1 @@

  > +foo

  > \ No newline at end of file

  > diff --git a/real_A b/real_A

  > new file mode 100644

  > --- /dev/null

  > +++ b/real_A

  > @@ -0,0 +1,1 @@

  > +A

  > \ No newline at end of file

  > diff --git a/sym_A b/sym_A

  > new file mode 120000

  > --- /dev/null

  > +++ b/sym_A

  > @@ -0,0 +1,1 @@

  > +A

  > \ No newline at end of file

  > EOF

  $ hg up -q

#endif

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(b'A', repo).cmp(repo[None][b'real_A'])"

  True (no-eol)

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

  True (no-eol)

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

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

  False (no-eol)

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

  False (no-eol)

  $ hg eval "not filecmp.cmp(b'A', b'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(b'real_A', repo).cmp(repo[None][b'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.

#if symlink

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

  True (no-eol)

#else

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

  False (no-eol)

#endif