Let a construction hold a designated initialiser in the graph

Coder.Graph/AstSchema.cs

@@ -25,12 +25,12 @@
 /// </remarks>
 public static class AstSchema
 {
 	private static readonly AstSlot ExpressionSlot = new("Expression", AstSlotCardinality.One, AstSlotKind.Expression);
 	private static readonly AstSlot LeftSlot = new("Left", AstSlotCardinality.One, AstSlotKind.Expression);
 	private static readonly AstSlot RightSlot = new("Right", AstSlotCardinality.One, AstSlotKind.Expression);
 	private static readonly AstSlot OperandSlot = new("Operand", AstSlotCardinality.One, AstSlotKind.Expression);
 	private static readonly AstSlot InitialValueSlot = new("InitialValue", AstSlotCardinality.One, AstSlotKind.Expression);
 	private static readonly AstSlot TargetSlot = new("Target", AstSlotCardinality.One, AstSlotKind.Expression);
 	private static readonly AstSlot ValueSlot = new("Value", AstSlotCardinality.One, AstSlotKind.Expression);
 	private static readonly AstSlot ParametersSlot = new("Parameters", AstSlotCardinality.Many, AstSlotKind.Parameter);
 	private static readonly AstSlot BodySlot = new("Body", AstSlotCardinality.Many, AstSlotKind.Statement);
@@ -63,6 +63,16 @@
 	private const string Unnamed = "<unnamed>";
 
 	private static readonly AstSlot ArgumentsSlot = new(ArgumentsSlotName, AstSlotCardinality.Many, AstSlotKind.Expression);
+
+	/// <summary>
+	/// A construction's arguments, which take a member initialiser where a call's do not.
+	/// </summary>
+	/// <remarks>
+	/// The same name as <see cref="ArgumentsSlot"/>, because the editor labels the pin the same way
+	/// and the attach cases switch on the name; a different kind, because what may stand in it
+	/// differs.
+	/// </remarks>
+	private static readonly AstSlot ElementsSlot = new(ArgumentsSlotName, AstSlotCardinality.Many, AstSlotKind.Element);
 	private static readonly AstSlot EnumMembersSlot = new("Members", AstSlotCardinality.Many, AstSlotKind.EnumMember);
 	private static readonly AstSlot ReceiverSlot = new(ReceiverSlotName, AstSlotCardinality.One, AstSlotKind.Expression);
 	private static readonly AstSlot ConditionSlot = new(ConditionSlotName, AstSlotCardinality.One, AstSlotKind.Expression);
@@ -83,7 +93,7 @@
 		FieldDeclaration => [InitialValueSlot],
 		PropertyDeclaration => [GetterSlot, SetterSlot],
 		MemberInitialiser => [ValueSlot],
-		ConstructionExpression => [ArgumentsSlot],
+		ConstructionExpression => [ElementsSlot],
 		CallExpression => [ReceiverSlot, ArgumentsSlot],
 		ConditionalExpression => [ConditionSlot, WhenTrueSlot, WhenFalseSlot],
 		ExpressionStatement => [ExpressionSlot],
@@ -625,6 +635,9 @@
 		{
 			AstSlotKind.Parameter => candidate is Parameter,
 			AstSlotKind.Expression => IsExpression(candidate),
+			// A member initialiser is an element and not an expression: it names the member a value
+			// is for rather than evaluating to one.
+			AstSlotKind.Element => IsExpression(candidate) || candidate is MemberInitialiser,
 			// A parameter is not a statement, and neither is an entry point: a program starts
 			// running at one, so it belongs to a class or to the document rather than inside a body.
 			AstSlotKind.Statement => candidate is not (Parameter or EntryPoint),

Coder.Graph/AstSlot.cs

@@ -36,6 +36,19 @@ public enum AstSlotKind
 	/// <summary>Anything that evaluates to a value, including the legacy leaf nodes.</summary>
 	Expression,
 
+	/// <summary>
+	/// One element of a braced list: an expression, or a
+	/// <see cref="ktsu.Coder.Ast.MemberInitialiser"/> naming the member it is for.
+	/// </summary>
+	/// <remarks>
+	/// Separate from <see cref="Expression"/> because a member initialiser does not evaluate to a
+	/// value — it says which member a value is for — and separate from a call's arguments because
+	/// only a construction has a spelling for one. Every generator reads a construction's arguments
+	/// for a member initialiser and none reads a call's, so the kinds part exactly where the
+	/// generators do.
+	/// </remarks>
+	Element,
+
 	/// <summary>Anything that can stand as a statement in a body.</summary>
 	Statement,
 

Coder.Test/Graph/AstGraphTests.cs

@@ -379,6 +379,32 @@ public void MoveTo_LeavesTheNodeInTheGraphWhenTheSlotRefusesIt()
 		Assert.IsNotNull(graph.Nodes.Values.SingleOrDefault(n => ReferenceEquals(n, returnStmt)));
 	}
 
+	/// <summary>
+	/// Tests that a designated initialiser can be wired into a construction from the editor.
+	/// </summary>
+	/// <remarks>
+	/// The whole chain, not just the schema's answer: the editor drags a link, the graph validates
+	/// it against the slot, and the AST ends up holding the node. Every generator writes one in this
+	/// position, and until the slot kind existed this was the one shape the graph could hold, the
+	/// serializer could persist and the editor could not build.
+	/// </remarks>
+	[TestMethod]
+	public void Connect_PutsAMemberInitialiserIntoAConstruction()
+	{
+		ConstructionExpression construction = new(new TypeReference("Point"));
+		AstGraph graph = new(construction);
+
+		MemberInitialiser initialiser = new("x") { Value = new LiteralExpression<int>(1) };
+		graph.AddDetached(initialiser, Vector2.Zero);
+
+		AstConnectResult result = Connect(graph, initialiser, construction, "Arguments", 0);
+
+		Assert.IsTrue(result.Success, result.Message);
+		Assert.HasCount(1, construction.Arguments);
+		Assert.AreSame(initialiser, construction.Arguments[0]);
+		Assert.IsEmpty(graph.Detached);
+	}
+
 	/// <summary>
 	/// Connects a node to a named slot of a parent, looking the pins up the way the editor does.
 	/// </summary>

Coder.Test/Graph/DeclarationSlotsTests.cs

@@ -135,6 +135,56 @@ public void MemberInitialiserValue_IsFilledAndEmptied()
 		Assert.IsNull(initialiser.Value);
 	}
 
+	/// <summary>
+	/// A construction takes a member initialiser among its arguments, which is what a designated
+	/// initialiser is.
+	/// </summary>
+	/// <remarks>
+	/// The AST, the serializer and all seven generators handle one in this position — it is a
+	/// designated initialiser in C++, an object initialiser in C#, a keyword argument in Python and
+	/// an object literal in JavaScript. The graph is the uniform view of the AST, so a shape every
+	/// other projection can express has to be one it can express too.
+	/// </remarks>
+	[TestMethod]
+	public void ConstructionArguments_TakeAMemberInitialiser()
+	{
+		ConstructionExpression construction = new(new TypeReference("holo::Kilograms"));
+		AstSlot arguments = AstSchema.SlotsOf(construction)[0];
+
+		Assert.IsTrue(AstSchema.Accepts(arguments, new MemberInitialiser("value_")));
+		Assert.IsTrue(AstSchema.TryAttach(
+			construction,
+			arguments,
+			new MemberInitialiser("value_") { Value = new LiteralExpression<double>(1.0) }));
+
+		Assert.HasCount(1, AstSchema.ChildrenOf(construction, arguments));
+		Assert.IsInstanceOfType<MemberInitialiser>(construction.Arguments[0]);
+
+		// And it comes out again, so one loaded from a document can be rewired rather than stranded.
+		Assert.IsTrue(AstSchema.TryDetachAt(construction, arguments, 0));
+		Assert.IsEmpty(construction.Arguments);
+	}
+
+	/// <summary>
+	/// A call does not take one, because no generator has a spelling for it there.
+	/// </summary>
+	/// <remarks>
+	/// The two share a slot name and a collection type, and the difference is the whole reason the
+	/// kinds are separate: every generator reads <c>construction.Arguments</c> for a member
+	/// initialiser and none reads a call's, so one attached to a call would be written as whatever
+	/// fell out rather than as a named argument.
+	/// </remarks>
+	[TestMethod]
+	public void CallArguments_DoNotTakeAMemberInitialiser()
+	{
+		CallExpression call = new("std::sqrt");
+		AstSlot arguments = AstSchema.SlotsOf(call).Single(slot => slot.Name == "Arguments");
+
+		Assert.IsFalse(AstSchema.Accepts(arguments, new MemberInitialiser("value_")));
+		Assert.IsFalse(AstSchema.TryAttach(call, arguments, new MemberInitialiser("value_")));
+		Assert.IsEmpty(call.Arguments);
+	}
+
 	/// <summary>
 	/// A construction's arguments are a sequence, so they are added, swapped and removed in order.
 	/// </summary>