Prevent inspector float edits from collapsing/rounding literal values

Coder.Graph/AstGraphEditor.cs

@@ -50,7 +50,7 @@
 	/// sits beside the graph, and the names it draws — <c>Visibility</c>, <c>Parameters</c> — are
 	/// longer than most of the values beside them. It stays the user's to drag either way.
 	/// <para>
-	/// Fractions are spelled to fifteen significant digits rather than the widget's six decimal
+	/// Fractions are spelled to seventeen significant digits rather than the widget's six decimal
 	/// places. A literal is a value the generated source will carry, so the row has to show what the
 	/// document holds: 3.14 has to read as 3.14 rather than as 3.140000, and a value with more digits
 	/// than that has to keep them when the user opens the box to change something else about it.
@@ -59,7 +59,7 @@
 	private static readonly ImGuiWidgets.PropertyGridOptions InspectorGridOptions = new()
 	{
 		LabelColumnWeight = 0.95f,
-		DoubleFormat = "%.15g",
+		DoubleFormat = "%.17g",
 	};
 
 	private string statusMessage = string.Empty;
@@ -983,7 +983,7 @@
 			{
 				// Undone in the order the replacement was made: the original goes back into its place,
 				// then each child that moved goes back into the slot it came from.
 				Graph.Replace(replacement, existing);
 				Graph.MoveTo(existing, from);
 				foreach ((AstNode child, AstLocation origin) in moved)
 				{
@@ -1245,7 +1245,7 @@
 
 			// A category's operator entries are one submenu deep, so eighteen binary operators do not
 			// bury the four literals.
 			foreach (string group in AstNodeCatalog.GroupsIn(category))
 			{
 				if (ImGui.BeginMenu(group))
 				{

Coder.Test/Graph/AstGraphEditorInspectorPanelTests.cs

@@ -2,6 +2,8 @@
 
 namespace ktsu.Coder.Test.Graph;
 
+using System.Globalization;
+using System.Reflection;
 using System.Numerics;
 
 using Hexa.NET.ImGui;
@@ -42,6 +44,14 @@ private static FunctionDeclaration SampleFunction()
 		return function;
 	}
 
+	private static (FunctionDeclaration Function, LiteralExpression<double> Literal) SampleFunctionWithSmallFractionLiteral()
+	{
+		LiteralExpression<double> literal = Literal.DecimalValue(1e-9);
+		FunctionDeclaration function = new("tiny") { ReturnType = "double" };
+		function.Body.Add(new ReturnStatement(literal));
+		return (function, literal);
+	}
+
 	/// <summary>
 	/// Draws the whole editor, because selecting a node is ImNodes' business and it faults inside
 	/// native code when its context is missing rather than throwing.
@@ -207,4 +217,40 @@ public void Inspector_AddsAndRemovesChildrenFromASlotRow()
 
 		Assert.HasCount(1, function.Parameters);
 	}
+
+	/// <summary>
+	/// Tests that a tiny floating-point literal keeps its value through inspector draws and edit
+	/// commits, rather than being collapsed to zero by the row's display format.
+	/// </summary>
+	[TestMethod]
+	public void Inspector_PreservesASmallFractionLiteralAcrossDrawAndEdit()
+	{
+		FieldInfo optionsField = typeof(AstGraphEditor).GetField("InspectorGridOptions", BindingFlags.NonPublic | BindingFlags.Static)
+			?? throw new AssertFailedException("Inspector grid options should exist.");
+
+		ktsu.ImGui.Widgets.ImGuiWidgets.PropertyGridOptions options =
+			(ktsu.ImGui.Widgets.ImGuiWidgets.PropertyGridOptions)optionsField.GetValue(null)!;
+		Assert.AreEqual("%.17g", options.DoubleFormat);
+
+		(FunctionDeclaration function, LiteralExpression<double> literal) = SampleFunctionWithSmallFractionLiteral();
+		AstGraphEditor editor = new(function);
+		double expected = literal.Value;
+
+		using ImGuiAppHarness harness = Inspecting(editor, literal);
+
+		// Rendering and selecting the node must leave the document value untouched.
+		Assert.AreEqual(expected, literal.Value);
+
+		harness.Click("Value");
+		harness.Step(2);
+
+		harness.Keyboard.Press(ImGuiKey.A, ctrl: true);
+		harness.Keyboard.Type(expected.ToString("G17", CultureInfo.InvariantCulture));
+		harness.Step(2);
+
+		harness.Keyboard.Press(ImGuiKey.Enter);
+		harness.Step(2);
+
+		Assert.AreEqual(expected, literal.Value);
+	}
 }