| // Copyright (c) 2019, the Dart project authors. Please see the AUTHORS file |
| // for details. All rights reserved. Use of this source code is governed by a |
| // BSD-style license that can be found in the LICENSE file. |
| |
| import 'package:analysis_server/src/nullability/nullability_node.dart'; |
| import 'package:meta/meta.dart'; |
| |
| /// Data structure to keep track of the relationship between [NullabilityNode] |
| /// objects. |
| class NullabilityGraph { |
| /// Map from a nullability node to a list of [_NullabilityEdge] objects |
| /// describing the node's relationship to other nodes that are "downstream" |
| /// from it (meaning that if a key node is nullable, then all the nodes in the |
| /// corresponding value will either have to be nullable, or null checks will |
| /// have to be added). |
| final _downstream = Map<NullabilityNode, List<_NullabilityEdge>>.identity(); |
| |
| /// Map from a nullability node to those nodes that are "upstream" from it |
| /// via unconditional control flow (meaning that if a node in the value is |
| /// nullable, then there exists code that is unguarded by an "if" statement |
| /// that indicates that the corresponding key node will have to be nullable, |
| /// or null checks will have to be added). |
| final _unconditionalUpstream = |
| Map<NullabilityNode, List<NullabilityNode>>.identity(); |
| |
| final _nonNullIntentNodes = Set<NullabilityNode>.identity(); |
| |
| /// Records that [sourceNode] is immediately upstream from [destinationNode]. |
| void connect(NullabilityNode sourceNode, NullabilityNode destinationNode, |
| {bool unconditional: false, List<NullabilityNode> guards: const []}) { |
| var sources = [sourceNode]..addAll(guards); |
| var edge = _NullabilityEdge(destinationNode, sources); |
| for (var source in sources) { |
| (_downstream[source] ??= []).add(edge); |
| } |
| if (unconditional) { |
| (_unconditionalUpstream[destinationNode] ??= []).add(sourceNode); |
| } |
| } |
| |
| void debugDump() { |
| for (var entry in _downstream.entries) { |
| var destinations = entry.value |
| .where((edge) => edge.primarySource == entry.key) |
| .map((edge) { |
| var suffixes = <Object>[]; |
| if (getUnconditionalUpstreamNodes(edge.destinationNode) |
| .contains(entry.key)) { |
| suffixes.add('unconditional'); |
| } |
| suffixes.addAll(edge.guards); |
| var suffix = suffixes.isNotEmpty ? ' (${suffixes.join(', ')})' : ''; |
| return '${edge.destinationNode}$suffix'; |
| }); |
| var suffixes = <String>[]; |
| if (entry.key.isNullable) { |
| suffixes.add('nullable'); |
| } |
| if (_nonNullIntentNodes.contains(entry.key)) { |
| suffixes.add('non-null intent'); |
| } |
| var suffix = suffixes.isNotEmpty ? ' (${suffixes.join(', ')})' : ''; |
| print('${entry.key}$suffix -> ${destinations.join(', ')}'); |
| } |
| } |
| |
| /// Iterates through all nodes that are "downstream" of [node] (i.e. if |
| /// [node] is nullable, then all the iterated nodes will either have to be |
| /// nullable, or null checks will have to be added). |
| /// |
| /// There is no guarantee of uniqueness of the iterated nodes. |
| Iterable<NullabilityNode> getDownstreamNodes(NullabilityNode node) => |
| (_downstream[node] ?? const []) |
| .where((edge) => edge.primarySource == node) |
| .map((edge) => edge.destinationNode); |
| |
| /// Iterates through all nodes that are "upstream" of [node] due to |
| /// unconditional control flow. |
| /// |
| /// There is no guarantee of uniqueness of the iterated nodes. |
| Iterable<NullabilityNode> getUnconditionalUpstreamNodes( |
| NullabilityNode node) => |
| _unconditionalUpstream[node] ?? const []; |
| |
| /// Iterates through all nodes that are "upstream" of [node] (i.e. if |
| /// any of the iterated nodes are nullable, then [node] will either have to be |
| /// nullable, or null checks will have to be added). |
| /// |
| /// There is no guarantee of uniqueness of the iterated nodes. |
| /// |
| /// This method is inefficent since it has to search the entire graph, so it |
| /// is for testing only. |
| @visibleForTesting |
| Iterable<NullabilityNode> getUpstreamNodesForTesting( |
| NullabilityNode node) sync* { |
| for (var entry in _downstream.entries) { |
| for (var edge in entry.value) { |
| if (edge.destinationNode == node) { |
| yield entry.key; |
| } |
| } |
| } |
| } |
| |
| /// Determines the nullability of each node in the graph by propagating |
| /// nullability information from one node to another. |
| void propagate() { |
| _propagateUpstream(); |
| _propagateDownstream(); |
| } |
| |
| /// Propagates nullability downstream. |
| void _propagateDownstream() { |
| var pendingEdges = <_NullabilityEdge>[] |
| ..addAll(_downstream[NullabilityNode.always] ?? const []); |
| var pendingSubstitutions = <NullabilityNodeForSubstitution>[]; |
| while (true) { |
| nextEdge: |
| while (pendingEdges.isNotEmpty) { |
| var edge = pendingEdges.removeLast(); |
| var node = edge.destinationNode; |
| if (_nonNullIntentNodes.contains(node)) { |
| // Non-null intent nodes are never made nullable; a null check will need |
| // to be added instead. |
| continue; |
| } |
| for (var source in edge.sources) { |
| if (!source.isNullable) { |
| // Note all sources are nullable, so this edge doesn't apply yet. |
| continue nextEdge; |
| } |
| } |
| if (node is NullabilityNodeMutable && node.becomeNullable()) { |
| // Was not previously nullable, so we need to propagate. |
| pendingEdges.addAll(_downstream[node] ?? const []); |
| if (node is NullabilityNodeForSubstitution) { |
| pendingSubstitutions.add(node); |
| } |
| } |
| } |
| if (pendingSubstitutions.isEmpty) break; |
| var node = pendingSubstitutions.removeLast(); |
| if (node.innerNode.isNullable || node.outerNode.isNullable) { |
| // No further propagation is needed, since some other connection already |
| // propagated nullability to either the inner or outer node. |
| continue; |
| } |
| // Heuristically choose to propagate to the inner node since this seems |
| // to lead to better quality migrations. |
| pendingEdges.add(_NullabilityEdge(node.innerNode, const [])); |
| } |
| } |
| |
| /// Propagates non-null intent upstream along unconditional control flow |
| /// lines. |
| void _propagateUpstream() { |
| var pendingNodes = [NullabilityNode.never]; |
| while (pendingNodes.isNotEmpty) { |
| var node = pendingNodes.removeLast(); |
| if (node == NullabilityNode.always) { |
| // The "always" node cannot have non-null intent. |
| continue; |
| } |
| if (_nonNullIntentNodes.add(node)) { |
| // Was not previously in the set of non-null intent nodes, so we need to |
| // propagate. |
| pendingNodes.addAll(getUnconditionalUpstreamNodes(node)); |
| } |
| } |
| } |
| } |
| |
| /// Data structure to keep track of the relationship from one [NullabilityNode] |
| /// object to another [NullabilityNode] that is "downstream" from it (meaning |
| /// that if the former node is nullable, then the latter node will either have |
| /// to be nullable, or null checks will have to be added). |
| class _NullabilityEdge { |
| /// The node that is downstream. |
| final NullabilityNode destinationNode; |
| |
| /// A set of source nodes. By convention, the first node is the primary |
| /// source and the other nodes are "guards". The destination node will only |
| /// need to be made nullable if all the source nodes are nullable. |
| final List<NullabilityNode> sources; |
| |
| _NullabilityEdge(this.destinationNode, this.sources); |
| |
| Iterable<NullabilityNode> get guards => sources.skip(1); |
| |
| NullabilityNode get primarySource => sources.first; |
| } |