resume_depgraph: check for alternative installed

When pruning packages from the merge list, only prune them if the
relevant dependency is not satisfied by an alternative package which
is already installed. This should fix bug #448176, and now there's also
reasons logged for why a particular package is dropped.

3 files changed, 33 insertions, 15 deletions

diff --git a/pym/_emerge/Scheduler.py b/pym/_emerge/Scheduler.py
index 6a494970e..a42327473 100644
--- a/pym/_emerge/Scheduler.py
+++ b/pym/_emerge/Scheduler.py
@@ -1791,7 +1791,7 @@ class Scheduler(PollScheduler):
 			#              scope
 			e = exc
 			mydepgraph = e.depgraph
-			dropped_tasks = set()
+			dropped_tasks = {}
 
 		if e is not None:
 			def unsatisfied_resume_dep_msg():
@@ -1841,7 +1841,7 @@ class Scheduler(PollScheduler):
 		self._init_graph(mydepgraph.schedulerGraph())
 
 		msg_width = 75
-		for task in dropped_tasks:
+		for task, atoms in dropped_tasks.items():
 			if not (isinstance(task, Package) and task.operation == "merge"):
 				continue
 			pkg = task
@@ -1849,7 +1849,10 @@ class Scheduler(PollScheduler):
 				" %s" % (pkg.cpv,)
 			if pkg.root_config.settings["ROOT"] != "/":
 				msg += " for %s" % (pkg.root,)
-			msg += " dropped due to unsatisfied dependency."
+			if not atoms:
+				msg += " dropped because it is masked or unavailable"
+			else:
+				msg += " dropped because it requires %s" % ", ".join(atoms)
 			for line in textwrap.wrap(msg, msg_width):
 				eerror(line, phase="other", key=pkg.cpv)
 			settings = self.pkgsettings[pkg.root]
diff --git a/pym/_emerge/actions.py b/pym/_emerge/actions.py
index 6a3815a9c..19265d03e 100644
--- a/pym/_emerge/actions.py
+++ b/pym/_emerge/actions.py
@@ -286,8 +286,14 @@ def action_build(settings, trees, mtimedb,
 					"dropped due to\n" + \
 					"!!! masking or unsatisfied dependencies:\n\n",
 					noiselevel=-1)
-				for task in dropped_tasks:
-					portage.writemsg("  " + str(task) + "\n", noiselevel=-1)
+				for task, atoms in dropped_tasks.items():
+					if not atoms:
+						writemsg("  %s is masked or unavailable\n" %
+							(task,), noiselevel=-1)
+					else:
+						writemsg("  %s requires %s\n" %
+							(task, ", ".join(atoms)), noiselevel=-1)
+
 				portage.writemsg("\n", noiselevel=-1)
 			del dropped_tasks
 		else:
diff --git a/pym/_emerge/depgraph.py b/pym/_emerge/depgraph.py
index 47f1b6002..f02ccb6e9 100644
--- a/pym/_emerge/depgraph.py
+++ b/pym/_emerge/depgraph.py
@@ -7477,7 +7477,7 @@ def _resume_depgraph(settings, trees, mtimedb, myopts, myparams, spinner):
 	skip_masked = True
 	skip_unsatisfied = True
 	mergelist = mtimedb["resume"]["mergelist"]
-	dropped_tasks = set()
+	dropped_tasks = {}
 	frozen_config = _frozen_depgraph_config(settings, trees,
 		myopts, spinner)
 	while True:
@@ -7491,12 +7491,21 @@ def _resume_depgraph(settings, trees, mtimedb, myopts, myparams, spinner):
 				raise
 
 			graph = mydepgraph._dynamic_config.digraph
-			unsatisfied_parents = dict((dep.parent, dep.parent) \
-				for dep in e.value)
+			unsatisfied_parents = {}
 			traversed_nodes = set()
-			unsatisfied_stack = list(unsatisfied_parents)
+			unsatisfied_stack = [(dep.parent, dep.atom) for dep in e.value]
 			while unsatisfied_stack:
-				pkg = unsatisfied_stack.pop()
+				pkg, atom = unsatisfied_stack.pop()
+				if atom is not None and \
+					mydepgraph._select_pkg_from_installed(
+					pkg.root, atom)[0] is not None:
+					continue
+				atoms = unsatisfied_parents.get(pkg)
+				if atoms is None:
+					atoms = []
+					unsatisfied_parents[pkg] = atoms
+				if atom is not None:
+					atoms.append(atom)
 				if pkg in traversed_nodes:
 					continue
 				traversed_nodes.add(pkg)
@@ -7505,7 +7514,8 @@ def _resume_depgraph(settings, trees, mtimedb, myopts, myparams, spinner):
 				# package scheduled for merge, removing this
 				# package may cause the the parent package's
 				# dependency to become unsatisfied.
-				for parent_node in graph.parent_nodes(pkg):
+				for parent_node, atom in \
+					mydepgraph._dynamic_config._parent_atoms.get(pkg, []):
 					if not isinstance(parent_node, Package) \
 						or parent_node.operation not in ("merge", "nomerge"):
 						continue
@@ -7513,8 +7523,7 @@ def _resume_depgraph(settings, trees, mtimedb, myopts, myparams, spinner):
 					# ensure that a package with an unsatisfied depenedency
 					# won't get pulled in, even indirectly via a soft
 					# dependency.
-					unsatisfied_parents[parent_node] = parent_node
-					unsatisfied_stack.append(parent_node)
+					unsatisfied_stack.append((parent_node, atom))
 
 			unsatisfied_tuples = frozenset(tuple(parent_node)
 				for parent_node in unsatisfied_parents
@@ -7535,8 +7544,8 @@ def _resume_depgraph(settings, trees, mtimedb, myopts, myparams, spinner):
 			# Exclude installed packages that have been removed from the graph due
 			# to failure to build/install runtime dependencies after the dependent
 			# package has already been installed.
-			dropped_tasks.update(pkg for pkg in \
-				unsatisfied_parents if pkg.operation != "nomerge")
+			dropped_tasks.update((pkg, atoms) for pkg, atoms in \
+				unsatisfied_parents.items() if pkg.operation != "nomerge")
 
 			del e, graph, traversed_nodes, \
 				unsatisfied_parents, unsatisfied_stack