Allow asking if a node name is a node group. Return an single item wh…

…en querying for salient options given a non-group node name.

YarnSpinner.Compiler/NodeGroupCompiler.cs

@@ -193,6 +193,14 @@ internal IEnumerable<NodeCompilationResult> CompileNodeGroup()
                 Name = NodeGroupName,
             };
 
+            // Mark that this node is a hub node, so that it can be queried for
+            // later
+            hubNode.Headers.Add(new Header
+            {
+                Key = Node.NodeIsHubNodeHeader,
+                Value = "1"
+            });
+
             var hubNodeDebugInfo = new NodeDebugInfo("<generated>", NodeGroupName);
             this.CurrentNode = hubNode;
             this.CurrentNodeDebugInfo = hubNodeDebugInfo;

YarnSpinner.Tests/SaliencyTests.cs

@@ -278,5 +278,48 @@ This content is only seen once.
             var availableContentAfterRun = this.dialogue.GetSaliencyOptionsForNodeGroup("Start");
             availableContentAfterRun.Where(c => c.FailingConditionValueCount == 0).Should().HaveCount(0);
         }
+
+        [Fact]
+        public void TestDialogueCanBeQueriedForNodeGroups()
+        {
+            // Given
+
+            string source = @"
+title: Start
+when: once
+---
+This content is only seen once.
+===
+title: Start
+when: $a == 2
+---
+This content is only seen when a is 2.
+===
+title: NotAGroup
+---
+This node is not part of a node group.
+===
+";
+
+            CompileAndPrepareDialogue(source);
+
+            this.dialogue.NodeExists("DoesntExist").Should().BeFalse();
+
+            this.dialogue.NodeExists("Start").Should().BeTrue();
+            this.dialogue.IsNodeGroup("Start").Should().BeTrue();
+
+            this.dialogue.NodeExists("NotAGroup").Should().BeTrue();
+            this.dialogue.IsNodeGroup("NotAGroup").Should().BeFalse();
+
+            // We can always ask for saliency options given a valid node name,
+            // even if it's not a node group
+
+            var queryInvalidNodeName = () => { this.dialogue.GetSaliencyOptionsForNodeGroup("DoesntExist"); };
+            queryInvalidNodeName.Should().ThrowExactly<ArgumentException>().WithMessage("*not a valid node name*");
+
+            this.dialogue.GetSaliencyOptionsForNodeGroup("Start").Should().HaveCount(2);
+            this.dialogue.GetSaliencyOptionsForNodeGroup("NotAGroup").Should().HaveCount(1);
+
+        }
     }
 }

YarnSpinner/Dialogue.cs

@@ -1076,11 +1076,62 @@ public bool TryGetSmartVariable<T>(string name, out T result)
         /// cref="Saliency.ContentSaliencyOption"/> objects that may appear if
         /// and when the node group <paramref name="nodeGroup"/> is run.
         /// </returns>
+        /// <exception cref="ArgumentException">Thrown when <paramref
+        /// name="nodeGroup"/> is not a valid node name.</exception>
         public IEnumerable<Saliency.ContentSaliencyOption> GetSaliencyOptionsForNodeGroup(string nodeGroup)
         {
+            if (NodeExists(nodeGroup) == false)
+            {
+                // This node doesn't exist - it can't be a node OR a node group,
+                // and we've been asked for an invalid value.
+                throw new ArgumentException($"{nodeGroup} is not a valid node name");
+            }
+
+            if (IsNodeGroup(nodeGroup) == false)
+            {
+                // This is not a node group, it's a plain node. Return a single
+                // content saliency "option" that represents this node.
+                return new[] {
+                    new Saliency.ContentSaliencyOption(nodeGroup) {
+                        ComplexityScore = 0,
+                        ContentType = Saliency.ContentSaliencyContentType.Node,
+                        PassingConditionValueCount = 1,
+                        FailingConditionValueCount = 0,
+                    }
+                };
+            }
+
+            // This is a valid node group name. Ask the saliency system to
+            // produce the collection of options that could run.
             return SmartVariableEvaluationVirtualMachine.GetSaliencyOptionsForNodeGroup(nodeGroup, this.VariableStorage, this.Library);
         }
 
+        /// <summary>
+        /// Gets a value indicating whether <paramref name="nodeName"/> is the
+        /// name of a valid node group in the program.
+        /// </summary>
+        /// <param name="nodeName">The name of the node group to check.</param>
+        /// <returns><see langword="true"/> if <paramref name="nodeName"/> is
+        /// the name of a node group; <see langword="false"/>
+        /// otherwise.</returns>
+        /// <exception cref="InvalidOperationException">Thrown when <see
+        /// cref="Program"/> is null.</exception>
+        public bool IsNodeGroup(string nodeName)
+        {
+            if (this.Program == null)
+            {
+                throw new InvalidOperationException($"Can't determine if {nodeName} is a hub node, because no program has been set.");
+            }
+
+            if (this.Program.Nodes.TryGetValue(nodeName, out var node) == false)
+            {
+                // Not a valid node, so not a valid node group.
+                return false;
+            }
+
+            return node.IsNodeGroupHub;
+        }
+
         // The standard, built-in library of functions and operators.
         internal class StandardLibrary : Library
         {

YarnSpinner/Program.cs

@@ -570,6 +570,7 @@ public IEnumerable<string> Tags
         internal const string TrackingVariableNameHeader = "$Yarn.Internal.TrackingVariable";
         internal const string ContentSaliencyConditionVariablesHeader = "$Yarn.Internal.ContentSaliencyVariables";
         internal const string ContentSaliencyConditionComplexityScoreHeader = "$Yarn.Internal.ContentSaliencyComplexity";
+        internal const string NodeIsHubNodeHeader = "$Yarn.Internal.NodeGroupHub";
 
         /// <summary>
         /// The name of the header that indicates a node's title.
@@ -612,6 +613,18 @@ public string? TrackingVariableName
             }
         }
 
+        /// <summary>
+        /// Gets a value indicating whether this node is the 'hub' node for a
+        /// node group.
+        /// </summary>
+        public bool IsNodeGroupHub
+        {
+            get
+            {
+                return GetHeaderValue(NodeIsHubNodeHeader) != null;
+            }
+        }
+
         /// <summary>
         /// Gets an enumerable containing the names of variables that must be
         /// evaluated in order to determine whether this node can be selected as