Fix casting object literal that omits an extends-inherited optional field

tslang/include/TypeScript/MLIRLogic/MLIRGenStore.h

@@ -348,7 +348,7 @@ struct InterfaceInfo
 
         for (auto &field : fields)
         {
-            tupleFields.push_back({field.id, field.type, false, mlir_ts::AccessLevel::Public});
+            tupleFields.push_back({field.id, field.type, field.isConditional, mlir_ts::AccessLevel::Public});
         }
 
         return mlir::success();

tslang/lib/TypeScript/MLIRGenCast.cpp

@@ -40,6 +40,22 @@ namespace mlirgen
             if (std::find_if(fields.begin(), fields.end(),
                              [&](auto &item) { return item.id == interfaceField.id; }) == fields.end())
             {
+                // the source has no field of this name at all - only reachable for a
+                // conditional (`?`) interface member (getVirtualTable's resolveField
+                // already rejects a missing non-conditional one, failing
+                // canCastTupleToInterface before this clone path even runs). Match the
+                // convention InterfaceSymbolRefOp's `optional` slot-count check already
+                // relies on for the non-clone path (see 00interface_optional_cast_order.ts):
+                // the field is simply ABSENT from the storage tuple, not present with a
+                // placeholder value - so skip it here rather than appending it. Appending it
+                // with any value/type would desync the clone's field COUNT from what
+                // interfaceVTableNameForObject's slot-index math and the interface's runtime
+                // "is this slot within the actual object's tuple size" check expect.
+                if (interfaceField.isConditional)
+                {
+                    continue;
+                }
+
                 fields.push_back(interfaceField);
             }
         }

tslang/test/tester/CMakeLists.txt

@@ -292,6 +292,7 @@ add_test(NAME test-compile-00-object-annotated-method-params COMMAND test-runner
 add_test(NAME test-compile-00-object-annotated-method-interleaved COMMAND test-runner "${PROJECT_SOURCE_DIR}/test/tester/tests/00object_annotated_method_interleaved.ts")
 add_test(NAME test-compile-00-object-annotated-method-extends-interface COMMAND test-runner "${PROJECT_SOURCE_DIR}/test/tester/tests/00object_annotated_method_extends_interface.ts")
 add_test(NAME test-compile-00-object-annotated-method-extends-interface-multilevel COMMAND test-runner "${PROJECT_SOURCE_DIR}/test/tester/tests/00object_annotated_method_extends_interface_multilevel.ts")
+add_test(NAME test-compile-00-interface-optional-extends COMMAND test-runner "${PROJECT_SOURCE_DIR}/test/tester/tests/00interface_optional_extends.ts")
 add_test(NAME test-compile-00-interface-object-array COMMAND test-runner "${PROJECT_SOURCE_DIR}/test/tester/tests/00interface_object_array.ts")
 add_test(NAME test-compile-00-interface-generic COMMAND test-runner "${PROJECT_SOURCE_DIR}/test/tester/tests/00interface_generic.ts")
 add_test(NAME test-compile-00-interface-new COMMAND test-runner "${PROJECT_SOURCE_DIR}/test/tester/tests/00interface_new.ts")
@@ -651,6 +652,7 @@ add_test(NAME test-jit-00-object-annotated-method-params COMMAND test-runner -ji
 add_test(NAME test-jit-00-object-annotated-method-interleaved COMMAND test-runner -jit "${PROJECT_SOURCE_DIR}/test/tester/tests/00object_annotated_method_interleaved.ts")
 add_test(NAME test-jit-00-object-annotated-method-extends-interface COMMAND test-runner -jit "${PROJECT_SOURCE_DIR}/test/tester/tests/00object_annotated_method_extends_interface.ts")
 add_test(NAME test-jit-00-object-annotated-method-extends-interface-multilevel COMMAND test-runner -jit "${PROJECT_SOURCE_DIR}/test/tester/tests/00object_annotated_method_extends_interface_multilevel.ts")
+add_test(NAME test-jit-00-interface-optional-extends COMMAND test-runner -jit "${PROJECT_SOURCE_DIR}/test/tester/tests/00interface_optional_extends.ts")
 add_test(NAME test-jit-00-interface-object-array COMMAND test-runner -jit "${PROJECT_SOURCE_DIR}/test/tester/tests/00interface_object_array.ts")
 add_test(NAME test-jit-00-interface-generic COMMAND test-runner -jit "${PROJECT_SOURCE_DIR}/test/tester/tests/00interface_generic.ts")
 add_test(NAME test-jit-00-interface-new COMMAND test-runner -jit "${PROJECT_SOURCE_DIR}/test/tester/tests/00interface_new.ts")

tslang/test/tester/tests/00interface_optional_extends.ts

@@ -0,0 +1,38 @@
+// Combines two previously-separate axes of interface coverage that had never
+// been tested together: an optional member (00interface_optional_cast_order.ts
+// - optional member's virtualIndex can get clobbered to -1 on the SHARED
+// InterfaceInfo by whichever cast ran most recently) and `extends`
+// (00object_annotated_method_extends_interface*.ts - inherited members need
+// vtableOffset added to their own-interface-relative virtualIndex). The
+// optional member here is declared on the BASE interface, so resolving it
+// through the DERIVED interface's combined vtable exercises both the
+// extends-offset math and the optional-member vtable-patch path at once.
+
+function main() {
+    interface Base {
+        base: number;
+        opt?: number;
+    }
+
+    interface Derived extends Base {
+        derived: number;
+    }
+
+    let present: Derived = <Derived>{ base: 1, opt: 5, derived: 10 };
+    let missing: Derived = <Derived>{ base: 2, derived: 20 };
+
+    assert(present.base == 1);
+    assert(present.opt == 5);
+    assert(present.derived == 10);
+
+    assert(missing.base == 2);
+    assert(missing.opt == undefined);
+    assert(missing.derived == 20);
+
+    // re-read the providing object after the non-providing one was cast, to
+    // catch the shared-virtualIndex-clobber bug class if it resurfaces here
+    print(present.opt);
+    assert(present.opt == 5);
+
+    print("done.");
+}