Fix source-created codegen variable reuse

src/CodegenTests/MethodFrameArrangerTests.cs

@@ -0,0 +1,160 @@
+using JasperFx.CodeGeneration;
+using JasperFx.CodeGeneration.Frames;
+using JasperFx.CodeGeneration.Model;
+using Shouldly;
+
+namespace CodegenTests;
+
+public class MethodFrameArrangerTests
+{
+    [Fact]
+    public void reuses_source_created_variable_from_a_different_requested_type()
+    {
+        var assembly = GeneratedAssembly.Empty();
+        var type = assembly.AddType("GeneratedHandler", typeof(IHttpHandlerShape));
+        var method = type.MethodFor(nameof(IHttpHandlerShape.Handle));
+        method.Sources.Add(new MessageContextVariableSource());
+
+        method.Frames.Add(new DetectTenantFrame());
+        method.Frames.Add(new UsesMessageBusFrame());
+        method.Frames.Add(new OpenOutboxedSessionFrame());
+
+        var code = assembly.GenerateCode();
+
+        CountOccurrences(code, "var messageContext = new CodegenTests.TestMessageContext()").ShouldBe(1);
+        code.ShouldContain("OpenSession(messageContext, tenantId)");
+    }
+
+    private static int CountOccurrences(string haystack, string needle)
+    {
+        return haystack.Split(needle).Length - 1;
+    }
+}
+
+public interface IHttpHandlerShape
+{
+    void Handle();
+}
+
+public interface ITestMessageBus
+{
+}
+
+public interface ITestMessageContext
+{
+}
+
+public class TestMessageContext : ITestMessageBus, ITestMessageContext
+{
+}
+
+public class TestOutboxedSessionFactory
+{
+    public void OpenSession(TestMessageContext context, string tenantId)
+    {
+    }
+}
+
+public class MessageContextVariableSource : IVariableSource
+{
+    public bool Matches(Type type)
+    {
+        return type == typeof(ITestMessageBus) || type == typeof(ITestMessageContext) ||
+               type == typeof(TestMessageContext);
+    }
+
+    public Variable Create(Type type)
+    {
+        return new TestMessageContextFrame().Variable;
+    }
+}
+
+public class TestMessageContextFrame : SyncFrame
+{
+    private Variable? _tenantId;
+
+    public TestMessageContextFrame()
+    {
+        Variable = new Variable(typeof(TestMessageContext), "messageContext", this);
+        creates.Add(new CastVariable(Variable, typeof(ITestMessageBus)));
+        creates.Add(new CastVariable(Variable, typeof(ITestMessageContext)));
+    }
+
+    public Variable Variable { get; }
+
+    public override IEnumerable<Variable> FindVariables(IMethodVariables chain)
+    {
+        if (chain.TryFindVariableByName(typeof(string), "tenantId", out _tenantId))
+        {
+            yield return _tenantId;
+        }
+    }
+
+    public override void GenerateCode(GeneratedMethod method, ISourceWriter writer)
+    {
+        writer.WriteLine($"var {Variable.Usage} = new {typeof(TestMessageContext).FullName}();");
+        if (_tenantId != null)
+        {
+            writer.WriteLine($"{Variable.Usage}.ToString();");
+        }
+
+        Next?.GenerateCode(method, writer);
+    }
+}
+
+public class DetectTenantFrame : SyncFrame
+{
+    public DetectTenantFrame()
+    {
+        TenantId = new Variable(typeof(string), "tenantId", this);
+    }
+
+    public Variable TenantId { get; }
+
+    public override void GenerateCode(GeneratedMethod method, ISourceWriter writer)
+    {
+        writer.WriteLine($"var {TenantId.Usage} = \"tenant1\";");
+        Next?.GenerateCode(method, writer);
+    }
+}
+
+public class UsesMessageBusFrame : SyncFrame
+{
+    private Variable _bus = null!;
+
+    public override IEnumerable<Variable> FindVariables(IMethodVariables chain)
+    {
+        _bus = chain.FindVariable(typeof(ITestMessageBus));
+        yield return _bus;
+    }
+
+    public override void GenerateCode(GeneratedMethod method, ISourceWriter writer)
+    {
+        writer.WriteLine($"{_bus.Usage}.ToString();");
+        Next?.GenerateCode(method, writer);
+    }
+}
+
+public class OpenOutboxedSessionFrame : SyncFrame
+{
+    private Variable _context = null!;
+    private Variable _tenantId = null!;
+    private readonly Variable _factory = new InjectedField(typeof(TestOutboxedSessionFactory), "factory");
+
+    public override IEnumerable<Variable> FindVariables(IMethodVariables chain)
+    {
+        _tenantId = chain.FindVariableByName(typeof(string), "tenantId");
+        yield return _tenantId;
+
+        _context = chain.FindVariable(typeof(TestMessageContext));
+        yield return _context;
+
+        yield return _factory;
+    }
+
+    public override void GenerateCode(GeneratedMethod method, ISourceWriter writer)
+    {
+        writer.WriteLine($"{_factory.Usage}.OpenSession({_context.Usage}, {_tenantId.Usage});");
+        Next?.GenerateCode(method, writer);
+    }
+}

src/JasperFx/CodeGeneration/Model/MethodFrameArranger.cs

@@ -227,7 +227,7 @@ private IEnumerable<IVariableSource> allVariableSources(VariableSource variableS
             return argument;
         }
 
-        var created = _method.Frames.SelectMany(x => x.Creates).FirstOrDefault(x => x.VariableType == type);
+        var created = knownCreatedVariables().FirstOrDefault(x => x.VariableType == type);
         if (created != null)
         {
             return created;
@@ -236,4 +236,32 @@ private IEnumerable<IVariableSource> allVariableSources(VariableSource variableS
         var source = allVariableSources(variableSource).FirstOrDefault(x => x.Matches(type));
         return source?.Create(type);
     }
-}
+
+    private IEnumerable<Variable> knownCreatedVariables()
+    {
+        // Variable sources can return a concrete variable for an interface request. Reuse that
+        // creator and its cast siblings before asking the source to build another frame.
+        foreach (var variable in _variables.Values)
+        {
+            yield return variable;
+
+            if (variable.Creator == null)
+            {
+                continue;
+            }
+
+            foreach (var sibling in variable.Creator.Creates)
+            {
+                yield return sibling;
+            }
+        }
+
+        foreach (var frame in _method.Frames)
+        {
+            foreach (var variable in frame.Creates)
+            {
+                yield return variable;
+            }
+        }
+    }
+}