Scalarize Lua tuples through ordered bundles

Author: Frotty

AGENTS.md

@@ -212,6 +212,20 @@ For config and run-pipeline changes, prefer these focused checks before broader
 
 Recent fixes established additional rules for backend work. Follow these for all future changes:
 
+### Compiler phase ownership and lowering invariants
+
+* Fix malformed or underspecified IR in the phase which creates it. Do not add downstream recovery,
+  name parsing, or backend-specific guessing for information an earlier phase discarded.
+* Semantic identity and specialization keys must use referenced AST/IM nodes plus structural type
+  arguments, never generated names or string comparison.
+* Each lowering phase has one explicit input/output contract. After an abstraction is lowered,
+  downstream phases consume the lowered representation and must not reconstruct its source meaning.
+* Prefer backend-appropriate, state-of-the-art lowering when semantics permit it. Jass limitations may
+  require compatibility compromises; do not carry those compromises into Lua without evidence.
+* Behavioral correctness is the primary requirement. Runtime and allocation performance are the next
+  requirement: common optimized paths must not retain avoidable compiler-introduced allocation,
+  dispatch, copying, or bookkeeping overhead.
+
 ### Jass/Lua feature parity
 
 * New language/compiler features must be validated for **both Jass and Lua** backends.

de.peeeq.wurstscript/src/main/java/de/peeeq/wurstio/WurstCompilerJassImpl.java

@@ -874,12 +874,11 @@ public LuaCompilationUnit transformProgToLua() {
 
         ImAttrType.setWurstClassType(null);
         int stage;
-        if (containsGenericNewCall() || containsTypeClassDispatch()) {
-            // Both operations need the concrete type argument, which erasure does not keep. Only
-            // the paths reaching them are specialised: the full elimination used for Jass is
-            // followed there by class elimination, and leaves state this backend cannot consume.
-            beginPhase(2, "Specialize generics for generic construction and type class dispatch");
-            new EliminateGenerics(getImTranslator(), getImProg()).transformGenericNewOnly();
+        boolean specializeTupleValueTypes = containsTupleTypeArgument();
+        if (containsGenericNewCall() || containsTypeClassDispatch() || specializeTupleValueTypes) {
+            beginPhase(2, "Specialize generics for Lua-only concrete operations");
+            new EliminateGenerics(getImTranslator(), getImProg())
+                .transformGenericNewOnly(specializeTupleValueTypes);
             timeTaker.endPhase();
         }
         if (runArgs.isNoDebugMessages()) {
@@ -919,6 +918,12 @@ public LuaCompilationUnit transformProgToLua() {
         getImProg().flatten(imTranslator2);
         EliminateLocalTypes.eliminateLocalTypesProg(getImProg(), imTranslator2);
 
+        timeTaker.beginPhase("eliminate tuples");
+        getImProg().flatten(imTranslator2);
+        EliminateTuples.eliminateTuplesProg(getImProg(), imTranslator2);
+        imTranslator2.assertProperties(AssertProperty.NOTUPLES);
+        timeTaker.endPhase();
+
         optimizer.removeGarbage();
         imProg.flatten(imTranslator);
         timeTaker.endPhase();
@@ -996,4 +1001,19 @@ public void visit(ImTypeVarDispatch dispatch) {
         });
         return found[0];
     }
+
+    /** Tuple type arguments need monomorphisation before tuples can become scalar storage. */
+    private boolean containsTupleTypeArgument() {
+        boolean[] found = {false};
+        getImProg().accept(new de.peeeq.wurstscript.jassIm.Element.DefaultVisitor() {
+            @Override
+            public void visit(ImTypeArgument argument) {
+                if (TypesHelper.typeContainsTuples(argument.getType())) {
+                    found[0] = true;
+                }
+                super.visit(argument);
+            }
+        });
+        return found[0];
+    }
 }