depgraph: fix missed atom_not_selected initialization (bug 612846)

Fix the _slot_operator_update_probe method to ensure that the
atom_not_selected variable is always properly initialized. This
problem prevented the method from identifying slot operator rebuild
candidates, leading to dependency conflicts and/or missed updates.
For example, this may have triggered the missed llvm update reported
in bug 611742, since these dependencies from the mesa-17.0.1 ebuild
are capable of triggering the problem, when atom_not_selected is not
properly set to True for the second atom:

	|| (
		sys-devel/llvm:4[${MULTILIB_USEDEP}]
		>=sys-devel/llvm-3.6.0:0[${MULTILIB_USEDEP}]
	)

X-Gentoo-bug: 612846
X-Gentoo-bug-url: https://bugs.gentoo.org/show_bug.cgi?id=612846
Acked-by: Brian Dolbec <dolsen@gentoo.org>

1 files changed, 14 insertions, 3 deletions

diff --git a/pym/_emerge/depgraph.py b/pym/_emerge/depgraph.py
index ad94fb70f..f4145d05f 100644
--- a/pym/_emerge/depgraph.py
+++ b/pym/_emerge/depgraph.py
@@ -1895,7 +1895,9 @@ class depgraph(object):
 			all_candidate_pkgs = None
 
 			for atom in atoms:
-				atom_not_selected = False
+				# The _select_atoms_probe method is expensive, so initialization
+				# of this variable is only performed on demand.
+				atom_not_selected = None
 
 				if not atom.package:
 					unevaluated_atom = None
@@ -1977,8 +1979,8 @@ class depgraph(object):
 						if selected_atoms is None:
 							selected_atoms = self._select_atoms_probe(
 								dep.child.root, replacement_parent)
-						if unevaluated_atom not in selected_atoms:
-							atom_not_selected = True
+						atom_not_selected = unevaluated_atom not in selected_atoms
+						if atom_not_selected:
 							break
 
 					if not insignificant and \
@@ -1989,6 +1991,15 @@ class depgraph(object):
 							(pkg, unevaluated_atom or atom))
 						candidate_pkgs.append(pkg)
 
+				# When unevaluated_atom is None, it means that atom is
+				# an soname atom which is unconditionally selected, and
+				# _select_atoms_probe is not applicable.
+				if atom_not_selected is None and unevaluated_atom is not None:
+					if selected_atoms is None:
+						selected_atoms = self._select_atoms_probe(
+							dep.child.root, replacement_parent)
+					atom_not_selected = unevaluated_atom not in selected_atoms
+
 				if atom_not_selected:
 					continue
 				replacement_candidates.append(candidate_pkg_atoms)