Fix cross-module abstract-class vtable slot shift (printer dropped abstract) (#290)

DeclarationPrinter never printed the `abstract` modifier (class- or
method-level) when embedding a class declaration into a compiled binary's
__decls. The reimporting module re-parsed the declaration as a CONCRETE
class, so mlirGenClassNew - which skips `.new` synthesis for abstract
classes - generated a `.new` vtable slot the exporting module never had.
Every base-class slot after `.instanceOf` shifted by one, and the exporting
module's compiled method bodies (with slot indexes baked in) dispatched
`this.<abstractMethod>()` into the wrong slot: a pointer-returning `.new`
called through a double-returning signature, "returning" stale XMM0.

That stale-register garbage is why this hid so well: a directly preceding
`assert(s.area() == 9)` left 9.0 in XMM0, so direct and base-class-cast
calls passed by luck while an interface-path call got 0 - which is why the
disabled test's comment misattributed this to an interface `this`-binding
gap, and why import_class_abstract (2-level chain) appeared to pass.

Fix: print `abstract ` before `class` (layout-relevant: controls `.new`
synthesis) and before abstract method signatures (semantic: the importer
must not treat the exporter's abstract methods as linkable symbols).

Also: re-enable both disabled *-class-implements-interface-abstract tests,
add a deterministic single-level regression pair
(*_class_abstract_virtual_dispatch.ts - describe() twice before any area()
call so register luck can't mask a regression), and add an opt-in
TSLANG_TEST_KEEP_TEMP env var to test-runner so failing tests' artifacts
survive for inspection.

816/816 tests green.

Co-authored-by: Claude Fable 5 <noreply@anthropic.com>

Author: ASDAlexander77

tslang/lib/TypeScript/DeclarationPrinter.cpp

@@ -401,6 +401,17 @@ namespace typescript
         printNamespaceBegin(classType->elementNamespace);
 
         printBeforeDeclaration();
+        // `abstract` is layout-relevant, not just semantic: mlirGenClassNew skips
+        // synthesizing the `.new` method for abstract classes, so dropping the
+        // modifier makes the reimporting module insert a `.new` vtable slot the
+        // exporting module never had, shifting every subsequent virtual index and
+        // corrupting cross-module virtual dispatch (base-module code calling
+        // this.method() lands on the wrong slot).
+        if (classType->isAbstract)
+        {
+            os << "abstract ";
+        }
+
         os << "class " << classType->name;
 
         if (classType->baseClasses.size() > 0)
@@ -554,6 +565,11 @@ namespace typescript
                 os << "private ";
             }
 
+            if (method.isAbstract)
+            {
+                os << "abstract ";
+            }
+
             printMethod(
                 method.isStatic,
                 method.name,

tslang/test/tester/CMakeLists.txt

@@ -946,20 +946,22 @@ add_test(NAME test-compile-shared-export-import-class-static COMMAND test-runner
 add_test(NAME test-compile-shared-export-import-class-implements-interface-multilevel COMMAND test-runner -shared "${PROJECT_SOURCE_DIR}/test/tester/tests/import_class_implements_interface_multilevel.ts" "${PROJECT_SOURCE_DIR}/test/tester/tests/export_class_implements_interface_multilevel.ts")
 add_test(NAME test-compile-shared-export-import-class-implements-interface-optional COMMAND test-runner -shared "${PROJECT_SOURCE_DIR}/test/tester/tests/import_class_implements_interface_optional.ts" "${PROJECT_SOURCE_DIR}/test/tester/tests/export_class_implements_interface_optional.ts")
 add_test(NAME test-compile-shared-export-import-class-structural-interface COMMAND test-runner -shared "${PROJECT_SOURCE_DIR}/test/tester/tests/import_class_structural_interface.ts" "${PROJECT_SOURCE_DIR}/test/tester/tests/export_class_structural_interface.ts")
-# DISABLED: a separate, NOT fixed bug found 2026-07-22 while verifying the fix above. Unlike the
-# multilevel/optional/structural variants (all pass now), this one calls describe() - a CONCRETE
-# method inherited from the abstract dynamic-import base M.Shape, whose body internally calls the
-# still-virtual this.area() - through an interface reference
-# (`const asDescribable: M.Describable = s; asDescribable.describe()`). Confirmed via the real
-# harness (instrumented with print instead of assert, see the session transcript): the DIRECT call
-# `s.describe()` and the base-class-cast call `asShape.describe()` both return the correct
-# "red area=9", but the SAME describe() reached through the interface returns "red area=0" -
-# this.area() silently resolves to 0 instead of dispatching to Square's override, specifically
-# when invoked via the interface's function-pointer slot. Root cause not yet isolated (likely a
-# `this`-identity/binding gap specific to calling an inherited concrete method through an
-# interface vtable slot, distinct from the link-time issue fixed above) - left for a dedicated
-# follow-up.
-# add_test(NAME test-compile-shared-export-import-class-implements-interface-abstract COMMAND test-runner -shared "${PROJECT_SOURCE_DIR}/test/tester/tests/import_class_implements_interface_abstract.ts" "${PROJECT_SOURCE_DIR}/test/tester/tests/export_class_implements_interface_abstract.ts")
+# FIXED 2026-07-23 (was disabled): the "this.area()-returns-0-via-interface" symptom had nothing
+# to do with interfaces or `this` binding. DeclarationPrinter dropped the `abstract` modifier when
+# embedding the class declaration into the compiled binary (__decls), so the reimporting module
+# treated M.Shape as concrete and synthesized a `.new` method for it - a vtable slot the exporting
+# module never created (mlirGenClassNew skips `.new` for abstract classes). Every base-class slot
+# after `.instanceOf` was thereby shifted by one in the importer's rebuilt vtable, and describe()'s
+# compiled-in slot-1 read for area() landed on `.new` instead - a pointer-returning function called
+# through a double-returning signature, so the "result" was whatever garbage was left in XMM0.
+# That garbage is why the symptom looked interface-specific: a preceding `assert(s.area() == 9)`
+# left 9.0 in XMM0, making the direct and base-class-cast calls "pass" by pure luck, while the
+# interface path (more string machinery in between) got 0. See the abstract-virtual-dispatch tests
+# below for the deterministic minimal regression pair.
+add_test(NAME test-compile-shared-export-import-class-implements-interface-abstract COMMAND test-runner -shared "${PROJECT_SOURCE_DIR}/test/tester/tests/import_class_implements_interface_abstract.ts" "${PROJECT_SOURCE_DIR}/test/tester/tests/export_class_implements_interface_abstract.ts")
+# minimal deterministic regression pair for the vtable-slot-shift bug above (single-level abstract,
+# describe() called twice before any area() call so XMM0 luck can't hide a regression)
+add_test(NAME test-compile-shared-export-import-class-abstract-virtual-dispatch COMMAND test-runner -shared "${PROJECT_SOURCE_DIR}/test/tester/tests/import_class_abstract_virtual_dispatch.ts" "${PROJECT_SOURCE_DIR}/test/tester/tests/export_class_abstract_virtual_dispatch.ts")
 # FIXED: see the matching test-compile-export-import-class-generic comment above (2026-07-22).
 add_test(NAME test-compile-shared-export-import-class-generic COMMAND test-runner -shared "${PROJECT_SOURCE_DIR}/test/tester/tests/import_class_generic.ts" "${PROJECT_SOURCE_DIR}/test/tester/tests/export_class_generic.ts")
 add_test(NAME test-compile-shared-export-import-function-generic COMMAND test-runner -shared "${PROJECT_SOURCE_DIR}/test/tester/tests/import_function_generic.ts" "${PROJECT_SOURCE_DIR}/test/tester/tests/export_function_generic.ts")
@@ -1007,8 +1009,9 @@ add_test(NAME test-jit-shared-export-import-class-static COMMAND test-runner -ji
 add_test(NAME test-jit-shared-export-import-class-implements-interface-multilevel COMMAND test-runner -jit -shared "${PROJECT_SOURCE_DIR}/test/tester/tests/import_class_implements_interface_multilevel.ts" "${PROJECT_SOURCE_DIR}/test/tester/tests/export_class_implements_interface_multilevel.ts")
 add_test(NAME test-jit-shared-export-import-class-implements-interface-optional COMMAND test-runner -jit -shared "${PROJECT_SOURCE_DIR}/test/tester/tests/import_class_implements_interface_optional.ts" "${PROJECT_SOURCE_DIR}/test/tester/tests/export_class_implements_interface_optional.ts")
 add_test(NAME test-jit-shared-export-import-class-structural-interface COMMAND test-runner -jit -shared "${PROJECT_SOURCE_DIR}/test/tester/tests/import_class_structural_interface.ts" "${PROJECT_SOURCE_DIR}/test/tester/tests/export_class_structural_interface.ts")
-# DISABLED: see the matching test-compile-shared-export-import-class-implements-interface-abstract comment above (known issue, 2026-07-22, NOT fixed) - the JIT tier of the abstract variant hits the same this.area()-returns-0-via-interface bug.
-# add_test(NAME test-jit-shared-export-import-class-implements-interface-abstract COMMAND test-runner -jit -shared "${PROJECT_SOURCE_DIR}/test/tester/tests/import_class_implements_interface_abstract.ts" "${PROJECT_SOURCE_DIR}/test/tester/tests/export_class_implements_interface_abstract.ts")
+# FIXED 2026-07-23 (was disabled): see the matching test-compile-shared-export-import-class-implements-interface-abstract comment above (DeclarationPrinter dropped `abstract`, shifting the reimported vtable's slots).
+add_test(NAME test-jit-shared-export-import-class-implements-interface-abstract COMMAND test-runner -jit -shared "${PROJECT_SOURCE_DIR}/test/tester/tests/import_class_implements_interface_abstract.ts" "${PROJECT_SOURCE_DIR}/test/tester/tests/export_class_implements_interface_abstract.ts")
+add_test(NAME test-jit-shared-export-import-class-abstract-virtual-dispatch COMMAND test-runner -jit -shared "${PROJECT_SOURCE_DIR}/test/tester/tests/import_class_abstract_virtual_dispatch.ts" "${PROJECT_SOURCE_DIR}/test/tester/tests/export_class_abstract_virtual_dispatch.ts")
 # FIXED: see the matching test-compile-export-import-class-generic comment above (2026-07-22).
 add_test(NAME test-jit-shared-export-import-class-generic COMMAND test-runner -jit -shared "${PROJECT_SOURCE_DIR}/test/tester/tests/import_class_generic.ts" "${PROJECT_SOURCE_DIR}/test/tester/tests/export_class_generic.ts")
 add_test(NAME test-jit-shared-export-import-function-generic COMMAND test-runner -jit -shared "${PROJECT_SOURCE_DIR}/test/tester/tests/import_function_generic.ts" "${PROJECT_SOURCE_DIR}/test/tester/tests/export_function_generic.ts")

tslang/test/tester/test-runner.cpp

@@ -270,7 +270,7 @@ std::string checkOutputAndCleanup(std::string tempOutputFileNameNoExt)
     auto output = readOutput(txtFile);
     auto errors = readOutput(errFile);
 
-    deleteFiles(tempOutputFileNameNoExt);    
+    if (!getenv("TSLANG_TEST_KEEP_TEMP")) deleteFiles(tempOutputFileNameNoExt);
 
     if (output.find("done.") != std::string::npos)
     {

tslang/test/tester/tests/export_class_abstract_virtual_dispatch.ts

@@ -0,0 +1,24 @@
+namespace M {
+
+    // Single-level abstract class whose CONCRETE method dispatches the
+    // still-abstract area() through `this` - the minimal shape of the
+    // cross-module vtable-slot-mismatch bug: DeclarationPrinter used to drop
+    // the `abstract` modifier when embedding this declaration into the
+    // compiled binary (__decls), so the reimporting module treated Shape as
+    // concrete and synthesized a `.new` vtable slot the exporting module
+    // never had (mlirGenClassNew skips it for abstract classes). That
+    // shifted every subsequent slot by one, and describe()'s baked-in
+    // slot-1 read for area() landed on `.new` instead - returning whatever
+    // garbage happened to sit in XMM0 (a pointer-returning function called
+    // through a double-returning signature).
+
+    export abstract class Shape {
+        color: string = "red";
+
+        abstract area(): number;
+
+        describe(): string {
+            return `${this.color} area=${this.area()}`;
+        }
+    }
+}

tslang/test/tester/tests/import_class_abstract_virtual_dispatch.ts

@@ -0,0 +1,29 @@
+import './export_class_abstract_virtual_dispatch'
+
+class Square extends M.Shape {
+    side: number = 3;
+
+    area(): number {
+        return this.side * this.side;
+    }
+}
+
+function main() {
+    const s = new Square();
+
+    // deliberately call describe() FIRST (no preceding area() call) and
+    // TWICE: with the vtable slots misaligned, describe() called `.new`
+    // through a double-returning signature, so the result was whatever was
+    // left in XMM0 - a preceding `assert(s.area() == 9)` could leave 9.0
+    // there and make a single assert pass by pure luck (this bug hid behind
+    // exactly that luck in import_class_abstract.ts for a while).
+    assert(s.describe() == "red area=9");
+    assert(s.describe() == "red area=9");
+    assert(s.area() == 9);
+
+    const asShape: M.Shape = s;
+    assert(asShape.describe() == "red area=9");
+    assert(asShape.area() == 9);
+
+    print("done.");
+}