Retain nominal metadata for tuple specializations

Author: Frotty

de.peeeq.wurstscript/src/main/java/de/peeeq/wurstscript/translation/lua/translation/LuaTranslator.java

@@ -1062,12 +1062,9 @@ private void initClassTables(ImClass c) {
         ));
 
         // set typeid metadata:
-        ImClass typeIdClass = c;
-        ImTranslator.Specialisation specialization = imTr.specialisationOf(c);
-        if (specialization != null && specialization.original() instanceof ImClass original) {
-            // Targeted Lua specialization preserves the nominal identity of the erased class.
-            typeIdClass = original;
-        }
+        // Targeted Lua specialization changes storage, not nominal identity. Garbage reachability
+        // retains this canonical metadata dependency before emission.
+        ImClass typeIdClass = imTr.canonical(c);
         deferMainInit(LuaAst.LuaAssignment(LuaAst.LuaExprFieldAccess(
             LuaAst.LuaExprVarAccess(classVar),
             ExprTranslation.TYPE_ID),
@@ -1486,11 +1483,11 @@ private void collectSuperClasses(LuaTableFields superClasses, ImClass c, Set<ImC
         }
         superClasses.add(LuaAst.LuaTableExprField(LuaAst.LuaExprVarAccess(luaClassVar.getFor(c)), LuaAst.LuaExprBoolVal(true)));
         visited.add(c);
-        ImTranslator.Specialisation specialization = imTr.specialisationOf(c);
-        if (specialization != null && specialization.original() instanceof ImClass original) {
+        ImClass nominalClass = imTr.canonical(c);
+        if (nominalClass != c) {
             // A targeted Lua specialization is a representation detail, not a new nominal type.
             // Keep erased-class runtime checks true without inheriting its fields a second time.
-            collectSuperClasses(superClasses, original, visited);
+            collectSuperClasses(superClasses, nominalClass, visited);
         }
         for (ImClassType sc : c.getSuperClasses()) {
             collectSuperClasses(superClasses, sc.getClassDef(), visited);

de.peeeq.wurstscript/src/main/java/de/peeeq/wurstscript/translation/lua/translation/RemoveGarbage.java

@@ -19,13 +19,18 @@
 public class RemoveGarbage {
 
     private static class Used {
+        private final ImTranslator translator;
         private final Set<ImFunction> functions = new HashSet<>();
         private final Set<ImMethod> methods = new HashSet<>();
         // methods that will be added once the class is used:
         private final Multimap<ImClass, ImMethod> waitingMethods = HashMultimap.create();
         private final Set<ImClass> classes = new HashSet<>();
         private final Set<ImVar> vars = new HashSet<>();
 
+        private Used(ImTranslator translator) {
+            this.translator = translator;
+        }
+
         public void addMethod(ImMethod m) {
             methods.add(m);
         }
@@ -65,6 +70,13 @@ public void addVar(ImVar var) {
 
         public void addClass(ImClass c) {
             classes.add(c);
+            ImClass nominalClass = translator.canonical(c);
+            if (nominalClass != c) {
+                // A targeted specialization has a distinct storage layout but keeps the source
+                // class's nominal type id and instanceof identity. The canonical class is therefore
+                // a real metadata dependency even when no source expression names it directly.
+                visitClass(nominalClass, this);
+            }
             Collection<ImMethod> imMethods = waitingMethods.get(c);
             Iterator<ImMethod> it = imMethods.iterator();
             while (it.hasNext()) {
@@ -76,7 +88,7 @@ public void addClass(ImClass c) {
     }
 
     public static void removeGarbage(ImProg prog, ImTranslator translator) {
-        Used used = new Used();
+        Used used = new Used(translator);
         for (ImFunction f : ImHelper.calculateFunctionsOfProg(prog)) {
             if (f.getName().equals("main")
                 || f.getName().equals("config")) {

de.peeeq.wurstscript/src/test/java/tests/wurstscript/tests/LuaBackendAuditTests.java

@@ -451,6 +451,29 @@ public void tupleSpecializedClassPreservesRuntimeTypeOperations() throws IOExcep
         assertFalse(compiled.contains("tupleCopy"));
     }
 
+    @Test
+    public void tupleSpecializedClassRetainsNominalMetadataWhenItIsTheOnlyReachableForm() throws IOException {
+        test().testLua(true).executeProg().lines(
+            "package Test",
+            "native testSuccess()",
+            "tuple pair(int x, int y)",
+            "interface Marker",
+            "class Box<T:> implements Marker",
+            "    T value",
+            "    construct(T initial)",
+            "        value = initial",
+            "init",
+            "    Marker box = new Box<pair>(pair(6, 7))",
+            "    if box != null",
+            "        testSuccess()"
+        );
+
+        String compiled = compiledLua(
+            "tupleSpecializedClassRetainsNominalMetadataWhenItIsTheOnlyReachableForm");
+        assertTrue(compiled.contains("Box_specialized"));
+        assertFalse(compiled.contains("tupleCopy"));
+    }
+
     @Test
     public void tupleReturningCallsAreCapturedBeforeComparison() throws IOException {
         test().testLua(true).executeProg().lines(