Implement native exit request control flow

engine/Age.Engine.Tests/ExitRequestTests.cs

@@ -0,0 +1,53 @@
+using Age.Engine.Model;
+using Age.Engine.Sys4;
+using Age.Engine.Vm;
+using Xunit;
+
+public class ExitRequestTests
+{
+    private static Operand I(long value) => new(0, value);
+    private static Operand G(long address) => new(3, address);
+
+    [Fact]
+    public void ThrowExitRequestDoesNotFallThroughToFollowingBytecode()
+    {
+        var table = OpcodeTableJson.Load(Paths.OpcodesJson);
+        var script = ScriptAssembler.Assemble(table, "TITLE.BIN", new List<(int, Operand[])>
+        {
+            (0x1, Array.Empty<Operand>()),
+            (0x55, new[] { G(0x7000), I(1) }),
+        }, Array.Empty<string>());
+        var vm = new VirtualMachine(script, table, new RecordingHost());
+
+        vm.Run();
+
+        Assert.Equal("exit-request", vm.HaltReason);
+        Assert.False(vm.Globals.ContainsKey(0x7000));
+    }
+
+    [Fact]
+    public void ThrowExitRequestEscapesNestedScriptFrames()
+    {
+        var table = OpcodeTableJson.Load(Paths.OpcodesJson);
+        var root = ScriptAssembler.Assemble(table, "SYSTEM4.BIN", new List<(int, Operand[])>
+        {
+            (0x3, new[] { I(1) }),
+            (0x55, new[] { G(0x7001), I(1) }),
+        }, Array.Empty<string>());
+        var child = ScriptAssembler.Assemble(table, "TITLE.BIN", new List<(int, Operand[])>
+        {
+            (0x1, Array.Empty<Operand>()),
+            (0x55, new[] { G(0x7002), I(1) }),
+        }, Array.Empty<string>());
+        var vm = new VirtualMachine(root, table, new RecordingHost(), provider: new MapProvider(new()
+        {
+            [1] = child,
+        }));
+
+        vm.Run();
+
+        Assert.Equal("exit-request", vm.HaltReason);
+        Assert.False(vm.Globals.ContainsKey(0x7001));
+        Assert.False(vm.Globals.ContainsKey(0x7002));
+    }
+}