Promote mixed int and float operands to the wider type [patch]

Coder.Test/Languages/GoGeneratedSourceCompilesTests.cs

@@ -1,4 +1,4 @@
-// Copyright (c) 2023-2026 ktsu-dev contributors
+// Copyright (c) 2023-2026 ktsu-dev contributors
 
 namespace ktsu.Coder.Test.Languages;
 
@@ -229,6 +229,59 @@ public void ConditionalExpressions_InferParameterTypesAndLowerNestedReturns()
 		});
 	}
 
+	/// <summary>
+	/// Tests that mixing an integer and a floating operand types the whole as the floating one, so
+	/// the function literal a conditional argument becomes returns <c>float64</c>, and a local
+	/// inferred from <c>1 + 0.5</c> is known to be one where a later conditional uses it (issue #152).
+	/// </summary>
+	[TestMethod]
+	public void MixedIntegerAndFloatingOperands_PromoteToFloating()
+	{
+		if (ToolchainHarness.FindOnPath("version", "go") is null)
+		{
+			Assert.Inconclusive("No Go toolchain on the path, so nothing was compiled.");
+			return;
+		}
+
+		SourceFile file = new("promotion");
+
+		FunctionDeclaration half = new("half") { ReturnType = new TypeReference("double") };
+		half.Parameters.Add(new Parameter("v", "double"));
+		half.Body.Add(new ReturnStatement(new BinaryExpression(new VariableReference("v"), BinaryOperator.Divide, Literal.DecimalValue(2.0))));
+		file.Members.Add(half);
+
+		FunctionDeclaration argument = new("argument") { ReturnType = new TypeReference("double") };
+		argument.Parameters.Add(new Parameter("ready", "bool"));
+		CallExpression halfOfChoice = new("half");
+		halfOfChoice.Arguments.Add(new ConditionalExpression(new VariableReference("ready"), Literal.Number(1), Literal.DecimalValue(2.5)));
+		argument.Body.Add(new ReturnStatement(halfOfChoice));
+		file.Members.Add(argument);
+
+		FunctionDeclaration inferred = new("inferred") { ReturnType = new TypeReference("double") };
+		inferred.Parameters.Add(new Parameter("ready", "bool"));
+		inferred.Body.Add(new VariableDeclaration("x", initialValue: new BinaryExpression(Literal.Number(1), BinaryOperator.Add, Literal.DecimalValue(0.5))));
+		CallExpression halfOfLocal = new("half");
+		halfOfLocal.Arguments.Add(new ConditionalExpression(new VariableReference("ready"), new VariableReference("x"), Literal.Number(1)));
+		inferred.Body.Add(new ReturnStatement(halfOfLocal));
+		file.Members.Add(inferred);
+
+		string source = new GoGenerator().Generate(file);
+		Assert.Contains("func() float64 {", source, StringComparison.Ordinal);
+		Assert.DoesNotContain("func() int {", source, StringComparison.Ordinal);
+
+		ToolchainHarness.InTemporaryDirectory(directory =>
+		{
+			File.WriteAllText(Path.Combine(directory, "go.mod"), Module);
+			File.WriteAllText(Path.Combine(directory, "promotion.go"), source);
+			(int exitCode, string output) = ToolchainHarness.Run("go", "build ./...", directory);
+			Assert.AreEqual(0, exitCode, $"Go rejected the generated source:{Environment.NewLine}{output}{Environment.NewLine}{source}");
+
+			(int formatted, string differs) = ToolchainHarness.Run("gofmt", "-l promotion.go", directory);
+			Assert.AreEqual(0, formatted, $"gofmt did not run:{Environment.NewLine}{differs}");
+			Assert.AreEqual(string.Empty, differs.Trim(), "gofmt would rewrite the generated source.");
+		});
+	}
+
 	/// <summary>
 	/// Tests that a condition comparing against a struct literal compiles in every position a
 	/// conditional is lowered to an <c>if</c>, and is still what <c>gofmt</c> writes.

Coder/Languages/GoGenerator.cs

@@ -1,4 +1,4 @@
-// Copyright (c) 2023-2026 ktsu-dev contributors
+// Copyright (c) 2023-2026 ktsu-dev contributors
 
 namespace ktsu.Coder.Languages;
 
@@ -269,7 +269,7 @@
 	/// holds one.
 	/// </remarks>
 	protected override string SpellNonFiniteDouble(double value) =>
 		double.IsNaN(value) ? "math.NaN()" : value > 0 ? "math.Inf(1)" : "math.Inf(-1)";
 
 	/// <inheritdoc/>
 	/// <remarks>
@@ -1763,15 +1763,17 @@
 	/// Where the statement around it could not take the lowering — nested inside another expression,
 	/// or passed as an argument — what is left is a function literal called where it stands, which is
 	/// the only expression Go has that can choose. It has to name what it answers with and the AST
-	/// does not say, so the type is read off whichever branch says what it is, and is <c>any</c> when
-	/// neither does — which is what this generator writes wherever a type was never given.
+	/// may not say, so the type is the conditional's own expected type if it has one, and otherwise is
+	/// read off its branches — the wider of the two when both are numbers, since <c>1</c> fits a
+	/// <c>float64</c> and <c>2.5</c> does not fit an <c>int</c> — and is <c>any</c> when neither says,
+	/// which is what this generator writes wherever a type was never given.
 	/// </remarks>
 	protected override void GenerateConditionalExpression(ConditionalExpression conditional, CodeBlocker code)
 	{
 		Ensure.NotNull(conditional);
 		Ensure.NotNull(code);
 
-		TypeReference? branchType = StaticType(conditional.WhenTrue) ?? StaticType(conditional.WhenFalse);
+		TypeReference? branchType = StaticType(conditional);
 		code.WriteLine($"func() {(branchType is null ? TypeMappings[UnknownTypeName] : SpellType(branchType))} {{");
 		code.Indent();
 		if (branchType is null)

Coder/Languages/StandardLanguageGenerator.cs

@@ -183,7 +183,7 @@ protected void RegisterStaticType(VariableDeclaration declaration)
 			case ConstructionExpression { Type: not null } construction:
 				return construction.Type;
 			case ConditionalExpression conditional:
-				return StaticType(conditional.WhenTrue) ?? StaticType(conditional.WhenFalse);
+				return Promoted(StaticType(conditional.WhenTrue), StaticType(conditional.WhenFalse));
 			case BinaryExpression binary when binary.Operator is BinaryOperator.Equal
 				or BinaryOperator.NotEqual
 				or BinaryOperator.LessThan
@@ -194,7 +194,7 @@ or BinaryOperator.LogicalAnd
 				or BinaryOperator.LogicalOr:
 				return new TypeReference("bool");
 			case BinaryExpression binary:
-				return StaticType(binary.Left) ?? StaticType(binary.Right);
+				return Promoted(StaticType(binary.Left), StaticType(binary.Right));
 			case VariableReference reference:
 				foreach (StaticTypeScope scope in staticTypeScopes)
 				{
@@ -221,6 +221,36 @@ or BinaryOperator.LogicalAnd
 		return staticTypeScopes.TryPeek(out StaticTypeScope? scope) ? scope.ReturnType : null;
 	}
 
+	/// <summary>
+	/// The numeric types in the order a mixed operation widens to, narrowest first.
+	/// </summary>
+	private static readonly string[] NumericPromotionOrder = ["int", "long", "float", "double"];
+
+	/// <summary>
+	/// Combines the types of two operands, or of a conditional's two branches, into the type of the
+	/// whole.
+	/// </summary>
+	/// <param name="first">The first operand's type, if known.</param>
+	/// <param name="second">The second operand's type, if known.</param>
+	/// <returns>
+	/// The wider of two numeric types, so <c>1 + 0.5</c> and <c>ready ? 1 : 2.5</c> are a
+	/// <c>double</c> as they are in every C-family language; otherwise the first known type.
+	/// </returns>
+	protected static TypeReference? Promoted(TypeReference? first, TypeReference? second)
+	{
+		int firstRank = NumericRank(first);
+		int secondRank = NumericRank(second);
+		return firstRank >= 0 && secondRank > firstRank ? second : first ?? second;
+	}
+
+	/// <summary>
+	/// Reports where a type stands in <see cref="NumericPromotionOrder"/>.
+	/// </summary>
+	/// <param name="type">The type to place.</param>
+	/// <returns>Its position, or -1 when it is not a plain numeric type.</returns>
+	private static int NumericRank(TypeReference? type) =>
+		type is null ? -1 : Array.IndexOf(NumericPromotionOrder, type.ToString());
+
 	private sealed record StaticTypeScope(Dictionary<string, TypeReference> Types, TypeReference? ReturnType);
 
 	private sealed class StaticTypeScopeGuard(StandardLanguageGenerator generator) : IDisposable