slot_conflict_handler: report packages that can't be rebuilt (bug 602964)

Report packages that need to be rebuilt in order to solve slot
conflicts, but cannot be rebuilt for some reason. The following
reasons will be detected:

* matched by --exclude argument
* matched by --useoldpkg-atoms argument
* ebuild is masked or unavailable

Example output:

!!! The slot conflict(s) shown above involve package(s) which may need to
!!! be rebuilt in order to solve the conflict(s). However, the following
!!! package(s) cannot be rebuilt for the reasons shown:

  (sys-apps/less-480:0/0::gentoo, installed): ebuild is masked or unavailable

X-Gentoo-bug: 602964
X-Gentoo-bug-url: https://bugs.gentoo.org/602964
Acked-by: Brian Dolbec <dolsen@gentoo.org>

1 files changed, 35 insertions, 2 deletions

diff --git a/pym/_emerge/resolver/slot_collision.py b/pym/_emerge/resolver/slot_collision.py
index cfb588596..f676b38c8 100644
--- a/pym/_emerge/resolver/slot_collision.py
+++ b/pym/_emerge/resolver/slot_collision.py
@@ -241,6 +241,8 @@ class slot_conflict_handler(object):
 		Print all slot conflicts in a human readable way.
 		"""
 		_pkg_use_enabled = self.depgraph._pkg_use_enabled
+		usepkgonly = "--usepkgonly" in self.myopts
+		need_rebuild = {}
 		verboseconflicts = "--verbose-conflicts" in self.myopts
 		any_omitted_parents = False
 		msg = self.conflict_msg
@@ -394,6 +396,29 @@ class slot_conflict_handler(object):
 								selected_for_display.update(
 										best_matches.values())
 						elif type in ("soname", "slot"):
+							# Check for packages that might need to
+							# be rebuilt, but cannot be rebuilt for
+							# some reason.
+							for ppkg, atom, other_pkg in parents:
+								if not (isinstance(ppkg, Package) and ppkg.installed):
+									continue
+								if not (atom.soname or atom.slot_operator_built):
+									continue
+								if self.depgraph._frozen_config.excluded_pkgs.findAtomForPackage(ppkg,
+									modified_use=self.depgraph._pkg_use_enabled(ppkg)):
+									selected_for_display.add((ppkg, atom))
+									need_rebuild[ppkg] = 'matched by --exclude argument'
+								elif self.depgraph._frozen_config.useoldpkg_atoms.findAtomForPackage(ppkg,
+									modified_use=self.depgraph._pkg_use_enabled(ppkg)):
+									selected_for_display.add((ppkg, atom))
+									need_rebuild[ppkg] = 'matched by --useoldpkg-atoms argument'
+								elif usepkgonly:
+									# This case is tricky, so keep quiet in order to avoid false-positives.
+									pass
+								elif not self.depgraph._equiv_ebuild_visible(ppkg):
+									selected_for_display.add((ppkg, atom))
+									need_rebuild[ppkg] = 'ebuild is masked or unavailable'
+
 							for ppkg, atom, other_pkg in parents:
 								selected_for_display.add((ppkg, atom))
 								if not verboseconflicts:
@@ -611,10 +636,18 @@ class slot_conflict_handler(object):
 			msg.append(colorize("INFORM",
 				"NOTE: Use the '--verbose-conflicts'"
 				" option to display parents omitted above"))
-			msg.append("\n\n")
-		else:
 			msg.append("\n")
 
+		if need_rebuild:
+			msg.append("\n!!! The slot conflict(s) shown above involve package(s) which may need to\n")
+			msg.append("!!! be rebuilt in order to solve the conflict(s). However, the following\n")
+			msg.append("!!! package(s) cannot be rebuilt for the reason(s) shown:\n\n")
+			for ppkg, reason in need_rebuild.items():
+				msg.append("%s%s: %s\n" % (indent, ppkg, reason))
+			msg.append("\n")
+
+		msg.append("\n")
+
 	def get_explanation(self):
 		msg = ""