[gentoo-portage-dev] [PATCH] find_smallest_cycle: enhance search prioritization

[Zac Medico]

Enhance the find_smallest_cycle function to prioritize its
search so that it will minimize the use of installed packages
to break cycles. When installed packages must be used to
break cycles, it will now prefer to do this for runtime
dependencies over buildtime dependencies, since it's
preferable to build against latest versions of buildtime
dependencies whenever possible. This should solve some cases
of bug 199856 which have been triggered by unsafe reliance
on installed packages to break cycles.

Bug: https://bugs.gentoo.org/754903
Signed-off-by: Zac Medico <zmedico@g.o>
---
 lib/_emerge/DepPriorityNormalRange.py    |  2 +
 lib/_emerge/DepPrioritySatisfiedRange.py | 52 +++++++++++++-----------
 lib/_emerge/depgraph.py                  | 41 +++++++++++--------
 3 files changed, 54 insertions(+), 41 deletions(-)

diff --git a/lib/_emerge/DepPriorityNormalRange.py b/lib/_emerge/DepPriorityNormalRange.py
index 5f3f3da70..10f205a3b 100644
--- a/lib/_emerge/DepPriorityNormalRange.py
+++ b/lib/_emerge/DepPriorityNormalRange.py
@@ -14,6 +14,7 @@ class DepPriorityNormalRange:
 	"""
 	MEDIUM      = 3
 	MEDIUM_SOFT = 2
+	MEDIUM_POST = 2
 	SOFT        = 1
 	NONE        = 0
 
@@ -37,6 +38,7 @@ class DepPriorityNormalRange:
 
 	ignore_medium      = _ignore_runtime
 	ignore_medium_soft = _ignore_runtime_post
+	ignore_medium_post = _ignore_runtime_post
 	ignore_soft        = _ignore_optional
 
 DepPriorityNormalRange.ignore_priority = (
diff --git a/lib/_emerge/DepPrioritySatisfiedRange.py b/lib/_emerge/DepPrioritySatisfiedRange.py
index e056e676f..df2439f1f 100644
--- a/lib/_emerge/DepPrioritySatisfiedRange.py
+++ b/lib/_emerge/DepPrioritySatisfiedRange.py
@@ -8,17 +8,18 @@ class DepPrioritySatisfiedRange:
 
 	not satisfied and buildtime                    HARD
 	not satisfied and runtime              7       MEDIUM
-	not satisfied and runtime_post         6       MEDIUM_SOFT
-	satisfied and buildtime_slot_op        5       SOFT
-	satisfied and buildtime                4       SOFT
-	satisfied and runtime                  3       SOFT
-	satisfied and runtime_post             2       SOFT
+	satisfied and buildtime_slot_op        6       MEDIUM_SOFT
+	satisfied and buildtime                5       MEDIUM_SOFT
+	satisfied and runtime                  4       MEDIUM_SOFT
+	runtime_post                           3       MEDIUM_POST
+	satisfied and runtime_post             2       MEDIUM_POST
 	optional                               1       SOFT
 	(none of the above)                    0       NONE
 	"""
 	MEDIUM      = 7
 	MEDIUM_SOFT = 6
-	SOFT        = 5
+	MEDIUM_POST = 3
+	SOFT        = 1
 	NONE        = 0
 
 	@classmethod
@@ -37,15 +38,23 @@ class DepPrioritySatisfiedRange:
 			return False
 		return bool(priority.runtime_post)
 
+	@classmethod
+	def _ignore_runtime_post(cls, priority):
+		if priority.__class__ is not DepPriority:
+			return False
+		return bool(priority.optional or priority.runtime_post)
+
 	@classmethod
 	def _ignore_satisfied_runtime(cls, priority):
 		if priority.__class__ is not DepPriority:
 			return False
 		if priority.optional:
 			return True
-		if not priority.satisfied:
+		if priority.buildtime:
 			return False
-		return not priority.buildtime
+		if not priority.runtime:
+			return True
+		return bool(priority.satisfied)
 
 	@classmethod
 	def _ignore_satisfied_buildtime(cls, priority):
@@ -61,37 +70,32 @@ class DepPrioritySatisfiedRange:
 	def _ignore_satisfied_buildtime_slot_op(cls, priority):
 		if priority.__class__ is not DepPriority:
 			return False
-		return bool(priority.optional or \
-			priority.satisfied)
-
-	@classmethod
-	def _ignore_runtime_post(cls, priority):
-		if priority.__class__ is not DepPriority:
-			return False
-		return bool(priority.optional or \
-			priority.satisfied or \
-			priority.runtime_post)
+		if priority.optional:
+			return True
+		if priority.satisfied:
+			return True
+		return not priority.buildtime and not priority.runtime
 
 	@classmethod
 	def _ignore_runtime(cls, priority):
 		if priority.__class__ is not DepPriority:
 			return False
-		return bool(priority.satisfied or \
-			priority.optional or \
-			not priority.buildtime)
+		return bool(priority.optional or
+			priority.satisfied or priority.runtime)
 
 	ignore_medium      = _ignore_runtime
-	ignore_medium_soft = _ignore_runtime_post
-	ignore_soft        = _ignore_satisfied_buildtime
+	ignore_medium_soft = _ignore_satisfied_buildtime_slot_op
+	ignore_medium_post = _ignore_runtime_post
+	ignore_soft        = _ignore_optional
 
 
 DepPrioritySatisfiedRange.ignore_priority = (
 	None,
 	DepPrioritySatisfiedRange._ignore_optional,
 	DepPrioritySatisfiedRange._ignore_satisfied_runtime_post,
+	DepPrioritySatisfiedRange._ignore_runtime_post,
 	DepPrioritySatisfiedRange._ignore_satisfied_runtime,
 	DepPrioritySatisfiedRange._ignore_satisfied_buildtime,
 	DepPrioritySatisfiedRange._ignore_satisfied_buildtime_slot_op,
-	DepPrioritySatisfiedRange._ignore_runtime_post,
 	DepPrioritySatisfiedRange._ignore_runtime
 )
diff --git a/lib/_emerge/depgraph.py b/lib/_emerge/depgraph.py
index 6aaacfe44..b18d5d717 100644
--- a/lib/_emerge/depgraph.py
+++ b/lib/_emerge/depgraph.py
@@ -7905,7 +7905,7 @@ class depgraph:
 								if check_asap_parent:
 									for node in nodes:
 										parents = mygraph.parent_nodes(node,
-											ignore_priority=DepPrioritySatisfiedRange.ignore_soft)
+											ignore_priority=DepPrioritySatisfiedRange.ignore_medium_soft)
 										if any(x in asap_nodes for x in parents):
 											selected_nodes = [node]
 											break
@@ -7921,7 +7921,7 @@ class depgraph:
 
 			if not selected_nodes:
 
-				def find_smallest_cycle(mergeable_nodes, priority_ranges):
+				def find_smallest_cycle(mergeable_nodes, local_priority_range):
 					if prefer_asap and asap_nodes:
 						nodes = asap_nodes
 					else:
@@ -7938,18 +7938,25 @@ class depgraph:
 					# these smaller independent cycles.
 					smallest_cycle = None
 					ignore_priority = None
-					for node in nodes:
-						if not mygraph.parent_nodes(node):
-							continue
-						for local_priority_range in priority_ranges:
+
+					for priority in (local_priority_range.ignore_priority[i] for i in range(
+						local_priority_range.MEDIUM_POST,
+						local_priority_range.MEDIUM_SOFT + 1)):
+						for node in nodes:
+							if not mygraph.parent_nodes(node):
+								continue
 							selected_nodes = set()
-							if gather_deps(local_priority_range.ignore_medium_soft,
+							if gather_deps(priority,
 								mergeable_nodes, selected_nodes, node):
 								if smallest_cycle is None or \
 									len(selected_nodes) < len(smallest_cycle):
 									smallest_cycle = selected_nodes
-									ignore_priority = local_priority_range.ignore_medium_soft
-								break
+									ignore_priority = priority
+
+						# Exit this loop with the lowest possible priority, which
+						# minimizes the use of installed packages to break cycles.
+						if smallest_cycle is not None:
+							break
 
 					return smallest_cycle, ignore_priority
 
@@ -7963,7 +7970,7 @@ class depgraph:
 				for local_priority_range in priority_ranges:
 					mergeable_nodes = set(get_nodes(ignore_priority=local_priority_range.ignore_medium))
 					if mergeable_nodes:
-						selected_nodes, ignore_priority = find_smallest_cycle(mergeable_nodes, priority_ranges)
+						selected_nodes, ignore_priority = find_smallest_cycle(mergeable_nodes, local_priority_range)
 						if selected_nodes:
 							break
 
@@ -8001,19 +8008,19 @@ class depgraph:
 									(selected_nodes[0],), noiselevel=-1)
 
 			if selected_nodes and ignore_priority is not None:
-				# Try to merge ignored medium_soft deps as soon as possible
+				# Try to merge ignored medium_post deps as soon as possible
 				# if they're not satisfied by installed packages.
 				for node in selected_nodes:
 					children = set(mygraph.child_nodes(node))
 					soft = children.difference(
-						mygraph.child_nodes(node,
-						ignore_priority=DepPrioritySatisfiedRange.ignore_soft))
-					medium_soft = children.difference(
 						mygraph.child_nodes(node,
 							ignore_priority = \
-							DepPrioritySatisfiedRange.ignore_medium_soft))
-					medium_soft -= soft
-					for child in medium_soft:
+							DepPrioritySatisfiedRange.ignore_soft))
+					medium_post = children.difference(
+						mygraph.child_nodes(node,
+						ignore_priority=DepPrioritySatisfiedRange.ignore_medium_post))
+					medium_post -= soft
+					for child in medium_post:
 						if child in selected_nodes:
 							continue
 						if child in asap_nodes:
-- 
2.26.2