Fix cross-module interface field/method vtable index mismatch

tslang/include/TypeScript/MLIRLogic/MLIRGenStore.h

@@ -539,6 +539,38 @@ struct InterfaceInfo
         return offset + methods.size() + fields.size();
     }
 
+    // vtable slot numbers must be a pure function of the interface's own declaration
+    // (extends, then own methods in order, then own fields in order) - NOT of whichever
+    // object happens to be cast to it first. getVirtualTable() re-derives the same
+    // methods-then-fields order per-cast (needed to mark per-object optional members
+    // missing), but a module that only reads an already-typed interface value - without
+    // ever casting an object to it itself (e.g. importing an already-boxed global from
+    // another compilation unit) - never runs getVirtualTable() at all. Without this
+    // eagerly-computed, cast-independent pass, such a module falls back on the
+    // interleaved declaration-order index assigned at member-registration time
+    // (mlirGenInterfaceAddFieldMember / addInterfaceMethod), which disagrees with the
+    // methods-first layout whenever a field is declared before a method in source order -
+    // reading through the wrong vtable slot (e.g. a method's function pointer
+    // reinterpreted as a field offset) and crashing.
+    void assignCanonicalVirtualIndexes()
+    {
+        auto offset = 0;
+        for (auto &extent : extends)
+        {
+            offset += std::get<1>(extent)->getVTableSize();
+        }
+
+        for (auto &method : methods)
+        {
+            method.virtualIndex = offset++;
+        }
+
+        for (auto &field : fields)
+        {
+            field.virtualIndex = offset++;
+        }
+    }
+
     void recalcOffsets()
     {
         auto offset = 0;

tslang/lib/TypeScript/MLIRGenInterfaces.cpp

@@ -581,6 +581,11 @@ namespace mlirgen
 
         } while (notResolved > 0);
 
+        // fix up vtable slot numbers to the canonical methods-then-fields order now that
+        // all members are known - see assignCanonicalVirtualIndexes() for why this can't
+        // be left to getVirtualTable()'s per-cast assignment alone.
+        newInterfacePtr->assignCanonicalVirtualIndexes();
+
         // add to export if any
         if (auto hasExport = getExportModifier(interfaceDeclarationAST))
         {

tslang/test/tester/tests/export_object_literal_with_interface.ts

@@ -14,4 +14,11 @@ namespace A {
 
     // invalid Point3d is not exported
     export var Origin3d: Point3d = { x: 0, y: 0, z: 0 };
+
+    export interface Counter {
+        count: number;
+        inc(): void;
+    }
+
+    export var counter: Counter = { count: 0, inc() { this.count = this.count + 1; } };
 }

tslang/test/tester/tests/import_object_literal_with_interface.ts

@@ -10,4 +10,6 @@ if (A.Origin3d.x == 0)
 	print("ok");
 }
 
+print(A.counter.count);
+
 print("done.");