tests/test-arbitraryfilectx.t

context: skip path conflicts by default when clearing unknown file (issue5776)

Prior to adding path conflict checking in 989e884d1be9, the test-audit-path.t
tests failed as shown here (but it was globbed away).  989e884d1be9 made it fail
with a message about the destination manifest containing a conflict (though the
no-symlink case wasn't updated).  When the path conflict checking was gated
behind an experimental config in 2a774cae3a03^::2a774cae3a03, the update started
erroneously succeeding here.  It turns out that the child of 989e884d1be9 is the
origin of this change when path conflict checking is disabled, as shown by
grafting the experimental config range on top of it.

What's happening here is merge.batchget() is writing the symlink 'back' to wdir
(but as a regular file for the no-symlink case), and then tries to write
'back/test', but calls wctx['back/test'].clearunknown() first.  The code that's
gated here was removing the newly written 'back' file, allowing 'back/test' to
succeed.  I tried checking for the dir components of 'back/test' in dirstate,
and skipping removal if present.  But that didn't work because the dirstate
isn't updated after each file is written out.

This is the last persistent test failure on Windows, so the testbot should start
turning green now. \o/

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', [], b'hg eval CMD')
  > def eval_(ui, repo, *cmds, **opts):
  >     cmd = b" ".join(cmds)
  >     res = str(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('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.
#if symlink
  $ hg eval "not filecmp.cmp('real_A', 'sym_A')"
  True (no-eol)
#else
  $ hg eval "not filecmp.cmp('real_A', 'sym_A')"
  False (no-eol)
#endif