Preserve root callables for managed callbacks

Author: fffonion

PdVm.Runtime/PdVmProgramBase.cs

@@ -713,12 +713,21 @@ private void EnterScriptCallable(
             throw new InvalidOperationException("callable parameter layout does not match its arity");
         }
 
+        // Managed callbacks start after the root frame has halted, so there is
+        // no active caller frame from which to inherit callable locals. The
+        // root locals remain the lexical environment for the program and may
+        // contain closure values referenced by the callback body (for example,
+        // an event wrapper calling another RSS function). Preserve those
+        // callable slots just as we do for a nested RSS call.
         var inheritedCallables = GetActiveFrameOrDefault() is { } caller
             ? _locals.Skip(caller.LocalBase).Take(caller.LocalCount)
                 .Select((value, slot) => (value, slot))
                 .Where(item => item.value.Kind == PdVmValueKind.Callable)
                 .ToArray()
-            : [];
+            : _locals.Take(_rootLocalCount)
+                .Select((value, slot) => (value, slot))
+                .Where(item => item.value.Kind == PdVmValueKind.Callable)
+                .ToArray();
         var localBase = _locals.Count;
         _locals.AddRange(Enumerable.Repeat(PdVmValue.Null(), prototype.FrameLocalCount));
         InitializeRootCallableBindings(localBase, prototype.FrameLocalCount);

PdVm.Tests/PdVmTypedDotNetInteropTests.cs

@@ -148,6 +148,33 @@ public async Task CallbackQueuePreservesFifoOrderAndBorrowedCaptureState()
         Assert.Throws<ObjectDisposedException>(() => callback.Post(PdVmValue.FromInt(4)));
     }
 
+    [Fact]
+    public async Task ManagedCallbackCanCallAClosureKeptInRootLocals()
+    {
+        using var fixture = new SourceFixture(
+            "let mut calls: int = 0;\n" +
+            "fn inner() -> int { calls = calls + 1; calls }\n" +
+            "pub fn wrapper() -> int { inner() }\n");
+        var output = PdVmDotNetSourceCompiler.CompileFile(fixture.SourcePath, fixture.OutputPath);
+        var program = Assert.IsAssignableFrom<IPdVmCallableProgram>(
+            PdVmAssemblyLoader.CreateProgram(Assembly.Load(File.ReadAllBytes(output))));
+        var host = PdVmDefaultHost.CreateConsoleHost();
+        _ = PdVmExecution.Run(program, host);
+        var adapter = PdVmCallbackAdapters.Create<PdVmUnit, PdVmValue>(
+            _ => Array.Empty<PdVmValue>(),
+            value => value,
+            Array.Empty<PdVmValueType>(),
+            PdVmValueType.Int);
+        using var callback = program.CreateCallback(
+            "wrapper",
+            adapter,
+            host);
+
+        var result = await callback.InvokeAsync(PdVmUnit.Value);
+
+        Assert.Equal(1, result.AsInt());
+    }
+
     [Fact]
     public async Task CallbackAdapterSchemaIsValidatedBeforeScriptExecution()
     {