Adds generic support to record unions.

src/Dunet/GenerateUnionRecord/StringBuilderExtensions.cs

@@ -0,0 +1,23 @@
+using System.Text;
+
+namespace Dunet.GenerateUnionRecord;
+
+internal static class StringBuilderExtensions
+{
+    public static void AppendTypeParams(
+        this StringBuilder builder,
+        IReadOnlyList<TypeParameter> typeParams
+    )
+    {
+        if (typeParams.Count <= 0)
+        {
+            return;
+        }
+
+        var typeParamList = string.Join(", ", typeParams.Select(typeParam => typeParam.Name));
+
+        builder.Append("<");
+        builder.Append(typeParamList);
+        builder.Append(">");
+    }
+}

src/Dunet/GenerateUnionRecord/UnionRecord.cs

@@ -19,4 +19,7 @@ internal record TypeParameter(string Name)
     public sealed override string ToString() => Name;
 }
 
-internal record RecordProperty(string Type, string Name);
+internal record RecordProperty(string Type, string Name)
+{
+    public sealed override string ToString() => $"{Type} {Name}";
+}

src/Dunet/GenerateUnionRecord/UnionRecordSource.cs

@@ -18,14 +18,19 @@ public static string GenerateRecord(UnionRecord record)
             builder.AppendLine($"namespace {record.Namespace};");
         }
 
-        builder.AppendLine($"abstract partial record {record.Name}");
+        builder.Append($"abstract partial record {record.Name}");
+        builder.AppendTypeParams(record.TypeParameters);
+        builder.AppendLine();
         builder.AppendLine("{");
         builder.AppendLine($"    private {record.Name}() {{}}");
 
         foreach (var member in record.Members)
         {
-            builder.AppendLine($"    public sealed partial record {member.Name} : {record.Name};");
-            builder.AppendLine();
+            builder.Append($"    public sealed partial record {member.Name}");
+            builder.AppendTypeParams(member.TypeParameters);
+            builder.Append($" : {record.Name}");
+            builder.AppendTypeParams(record.TypeParameters);
+            builder.AppendLine(" {}");
         }
 
         builder.AppendLine("}");

test/Dunet.Test/GenerateUnionRecord/GenericGenerationTests.cs

@@ -0,0 +1,104 @@
+using Dunet.Test.Runtime;
+
+namespace Dunet.Test.GenerateUnionRecord;
+
+public class GenericGenerationTests : UnionRecordTests
+{
+    [Fact]
+    public void UnionTypeMayHaveGenericParameter()
+    {
+        var programCs =
+            @"
+using Dunet;
+
+Option<int> some = new Option<int>.Some(1);
+Option<int> none = new Option<int>.None();
+
+[Union]
+partial record Option<T>
+{
+    partial record Some(T Value);
+    partial record None();
+}";
+        // Act.
+        var result = Compile.ToAssembly(programCs);
+
+        // Assert.
+        result.CompilationErrors.Should().BeEmpty();
+        result.GenerationDiagnostics.Should().BeEmpty();
+    }
+
+    [Fact]
+    public void UnionMemberMayHaveGenericParameter()
+    {
+        var programCs =
+            @"
+using Dunet;
+
+Option some = new Option.Some<int>(1);
+Option none = new Option.None();
+
+[Union]
+partial record Option
+{
+    partial record Some<T>(T Value);
+    partial record None();
+}";
+        // Act.
+        var result = Compile.ToAssembly(programCs);
+
+        // Assert.
+        result.CompilationErrors.Should().BeEmpty();
+        result.GenerationDiagnostics.Should().BeEmpty();
+    }
+
+    [Theory]
+    [InlineData(1, 2, "0.5")]
+    [InlineData(1, 0, "Error: division by zero.")]
+    public void CanReturnImplementationsOfGenericUnion(
+        int dividend,
+        int divisor,
+        string expectedOutput
+    )
+    {
+        var programCs =
+            @$"
+using Dunet;
+
+static string GetActualArea() => Divide() switch
+{{
+    Option.Some<double> some => some.Value.ToString(),
+    Option.None none => ""Error: division by zero."",
+    _ => throw new System.InvalidOperationException(),
+}};
+
+static Option Divide()
+{{
+    var dividend = {dividend};
+    var divisor = {divisor};
+
+    if (divisor is 0)
+    {{
+        return new Option.None();
+    }}
+
+    return new Option.Some<double>((double)dividend / divisor);
+}}
+
+[Union]
+partial record Option
+{{
+    partial record Some<T>(T Value);
+    partial record None();
+}}";
+
+        // Act.
+        var result = Compile.ToAssembly(programCs);
+        var actualArea = result.Assembly.ExecuteStaticMethod<string>("GetActualArea");
+
+        // Assert.
+        result.CompilationErrors.Should().BeEmpty();
+        result.GenerationErrors.Should().BeEmpty();
+        actualArea.Should().Be(expectedOutput);
+    }
+}

test/Dunet.Test/GenerateUnionRecord/SwitchExpressionTests.cs

@@ -48,7 +48,7 @@ public void SwitchExpressionMatchesCorrectCase(string shapeDeclaration, double e
             @$"
 using Dunet;
 
-static double GetArea()
+static double GetActualArea()
 {{
     {shapeDeclaration}
     return shape switch
@@ -69,7 +69,7 @@ partial record Triangle(double Base, double Height);
 }}";
         // Act.
         var result = Compile.ToAssembly(source);
-        var actualArea = result.Assembly.ExecuteStaticMethod<double>("GetArea");
+        var actualArea = result.Assembly.ExecuteStaticMethod<double>("GetActualArea");
 
         // Assert.
         result.CompilationErrors.Should().BeEmpty();