super: walk up inheritance chain past empty intermediates

doc/source/reference/language/classes.rst

@@ -146,6 +146,31 @@ Inside a derived class, ``super()`` calls the parent class constructor:
 Both forms are rewritten by the compiler into explicit calls to the parent class function:
 ``super()`` becomes ``Base`Base(self)`` and ``super.process(x)`` becomes ``Base`process(self, x)``.
 
+If the immediate parent does not define a matching constructor or method, ``super`` walks
+up the inheritance chain to the nearest ancestor that does:
+
+.. code-block:: das
+
+    class Base {
+        def process(x : int) { /* ... */ }
+    }
+
+    class Mid : Base {              // empty intermediate
+    }
+
+    class Leaf : Mid {
+        def Leaf {
+            super()                 // resolves to Base`Base(self) — Mid is skipped
+        }
+        def override process(x : int) {
+            super.process(x)        // resolves to Base`process(self, x) — Mid is skipped
+        }
+    }
+
+Walk-up matches by argument types, so overloaded ``super(args)`` calls pick the closest
+ancestor whose constructor or method accepts those arguments. If no ancestor matches, the
+call is rejected at compile time.
+
 Inside a derived class's finalizer (``operator delete``), ``delete super.self`` runs the
 parent's finalizer on the current object:
 
@@ -158,13 +183,19 @@ parent's finalizer on the current object:
         }
     }
 
-The compiler rewrites ``delete super.self`` into ``delete cast<Base>(self)``. It is only
-valid inside an ``operator delete`` (or equivalently ``def finalize``) of a class that has
-a base class; other uses are rejected at compile time. The same form also works for struct
-finalizers declared as free functions — see :ref:`Structs <structs>`.
+The compiler rewrites ``delete super.self`` into ``delete cast<T>(self)``, where ``T``
+is the closest ancestor whose ``finalize`` lookup resolves to a user-defined finalizer.
+For class hierarchies that means walking past intermediate classes that do not define
+their own ``def operator delete``. For struct hierarchies, ``finalize`` resolution honors
+inheritance substitution (a derived struct can be passed where its base is expected), so
+``T`` may be the immediate parent even when only an ancestor defines ``operator delete``.
+``delete super.self`` is only valid inside an ``operator delete`` (or equivalently
+``def finalize``) of a class that has a base with a finalizer; other uses are rejected
+at compile time. The same form also works for struct finalizers declared as free
+functions — see :ref:`Structs <structs>`.
 
 Base-class finalization is explicit, not automatic: a derived finalizer that omits
-``delete super.self`` will not run the base finalizer.
+``delete super.self`` will not run any ancestor finalizer.
 
 The option ``always_call_super`` can be enabled to require ``super()`` in every constructor
 (see :ref:`Options <options>`).

doc/source/reference/language/structs.rst

@@ -238,9 +238,14 @@ whose first argument is ``self``. Inside such a finalizer for a derived struct,
         // additional cleanup
     }
 
-The compiler rewrites ``delete super.self`` into ``delete cast<Foo>(self)``. See
-:ref:`Classes <classes>` for the full description of the ``super`` sugar — it applies
-identically to structs with inheritance.
+The compiler rewrites ``delete super.self`` into ``delete cast<T>(self)``, where ``T`` is
+the closest ancestor struct whose ``finalize`` lookup resolves to a user-defined finalizer.
+Because struct ``finalize`` resolution honors inheritance substitution (a derived struct
+can be passed where its base is expected), ``T`` is typically the immediate parent — even
+when only a more distant ancestor defines ``operator delete``. See :ref:`Classes <classes>`
+for the full description of the ``super`` sugar; the behavior is the same except that
+classes lack this substitution and instead skip past empty intermediate classes that
+don't define their own ``operator delete``.
 
 .. _structs_alignment:
 

src/ast/ast_infer_type.cpp

@@ -1400,15 +1400,46 @@ namespace das {
                     auto eVar = static_cast<ExprVar*>(eField->value);
                     if (eVar->name == "super") {
                         if (auto baseClass = func->classParent->parent) {
-                            reportAstChanged();
-                            auto callName = "_::" + baseClass->name + "`" + eField->name;
-                            auto newCall = new ExprCall(expr->at, callName);
-                            newCall->atEnclosure = expr->atEnclosure;
-                            newCall->arguments.push_back(new ExprVar(expr->at, "self"));
+                            // We're in argumentsFailedToInfer because `super` itself doesn't resolve.
+                            // The actual call args (i >= 2) may also still be uninferred — either
+                            // null type, or alias/expr placeholder waiting on a later pass. Defer
+                            // in either case (mirrors the allOtherInferred check below at line 1480
+                            // and the ExprLooksLikeCall contract that flags both as "not ready").
                             for (size_t i = 2; i != expr->arguments.size(); ++i) {
-                                newCall->arguments.push_back(expr->arguments[i]);
+                                if (!expr->arguments[i]->type || expr->arguments[i]->type->isAliasOrExpr()) {
+                                    return Visitor::visit(expr);
+                                }
+                            }
+                            vector<TypeDeclPtr> argTypes;
+                            auto selfType = new TypeDecl(Type::tStructure);
+                            selfType->structType = func->classParent;
+                            argTypes.push_back(selfType);
+                            for (size_t i = 2; i != expr->arguments.size(); ++i) {
+                                argTypes.push_back(expr->arguments[i]->type);
+                            }
+                            while (baseClass) {
+                                auto callName = "_::" + baseClass->name + "`" + eField->name;
+                                auto fnCandidates = findMatchingFunctions(callName, argTypes, false);
+                                if (fnCandidates.size() == 1) {
+                                    reportAstChanged();
+                                    auto newCall = new ExprCall(expr->at, callName);
+                                    newCall->atEnclosure = expr->atEnclosure;
+                                    newCall->arguments.push_back(new ExprVar(expr->at, "self"));
+                                    for (size_t i = 2; i != expr->arguments.size(); ++i) {
+                                        newCall->arguments.push_back(expr->arguments[i]);
+                                    }
+                                    return newCall;
+                                } else if ( fnCandidates.size() > 1 ) {
+                                    error("too many candidates for super call " + callName,
+                                        verbose ? program->describeCandidates(fnCandidates) : "", "",
+                                            expr->at, CompilationError::function_not_found);
+                                    return Visitor::visit(expr);
+                                }
+                                baseClass = baseClass->parent;
                             }
-                            return newCall;
+                            error("call to super in " + func->name + " is not allowed, no matching super method " + eField->name, "", "",
+                                    expr->at, CompilationError::function_not_found);
+                            return Visitor::visit(expr);
                         } else {
                             error("call to super in " + func->name + " is not allowed, no base class for " + func->classParent->name, "", "",
                                     expr->at, CompilationError::function_not_found);
@@ -2510,16 +2541,41 @@ namespace das {
                               "", "", expr->at, CompilationError::bad_delete);
                         return Visitor::visit(expr);
                     }
-                    reportAstChanged();
-                    auto selfVar = new ExprVar(expr->at, "self");
-                    auto castT = new TypeDecl(baseStruct);
-                    auto castExpr = new ExprCast(expr->at, selfVar, castT);
-                    auto newDel = new ExprDelete(expr->at, castExpr);
-                    newDel->alwaysSafe = true;
-                    newDel->native = expr->native;
-                    if (expr->sizeexpr)
-                        newDel->sizeexpr = expr->sizeexpr->clone();
-                    return newDel;
+                    // Walk up the inheritance chain to the nearest ancestor with a user-defined
+                    // finalizer (mirrors the super() / super.method() walk-ups). For structs, finalize
+                    // substitution via base type matches at the immediate parent even when only an
+                    // ancestor defines `def operator delete`. For classes there's no such substitution,
+                    // so we must skip empty intermediates and cast to the actual finalizer's class.
+                    while (baseStruct) {
+                        auto baseType = new TypeDecl(Type::tStructure);
+                        baseType->structType = baseStruct;
+                        vector<TypeDeclPtr> argTypes;
+                        argTypes.push_back(baseType);
+                        auto fnList = findMatchingFunctions("finalize", argTypes, false);
+                        // Skip auto-generated finalizers (generateStructureFinalizer / makeClassFinalize):
+                        // they don't chain to ancestors. Only stop at a user-defined finalizer (or one
+                        // that an ancestor's user finalizer matches via inheritance substitution).
+                        bool hasUserFinalize = false;
+                        for (auto &f : fnList) {
+                            if (!f->generated) { hasUserFinalize = true; break; }
+                        }
+                        if (hasUserFinalize) {
+                            reportAstChanged();
+                            auto selfVar = new ExprVar(expr->at, "self");
+                            auto castT = new TypeDecl(baseStruct);
+                            auto castExpr = new ExprCast(expr->at, selfVar, castT);
+                            auto newDel = new ExprDelete(expr->at, castExpr);
+                            newDel->alwaysSafe = true;
+                            newDel->native = expr->native;
+                            if (expr->sizeexpr)
+                                newDel->sizeexpr = expr->sizeexpr->clone();
+                            return newDel;
+                        }
+                        baseStruct = baseStruct->parent;
+                    }
+                    error("delete super.self in " + func->name + ": no ancestor of " + selfStruct->name + " defines a finalizer",
+                          "", "", expr->at, CompilationError::bad_delete);
+                    return Visitor::visit(expr);
                 }
             }
         }
@@ -5323,16 +5379,7 @@ namespace das {
                   "use let _ = " + call->name + "(...)", "",
                   call->at, CompilationError::result_discarded);
         }
-        if (func && func->isClassMethod && func->classParent && call->name == "super") {
-            if (auto baseClass = func->classParent->parent) {
-                call->name = baseClass->name + "`" + baseClass->name;
-                call->arguments.insert(call->arguments.begin(), new ExprVar(call->at, "self"));
-                reportAstChanged();
-            } else {
-                error("call to super in " + func->name + " is not allowed, no base class for " + func->classParent->name, "", "",
-                      call->at, CompilationError::function_not_found);
-            }
-        }
+        // super() constructor rewrite is done in visit(ExprCall*), once argument types are inferred
     }
     void InferTypes::preVisitCallArg(ExprCall *call, Expression *arg, bool last) {
         Visitor::preVisitCallArg(call, arg, last);
@@ -5361,6 +5408,45 @@ namespace das {
                 func->notInferred();
             return Visitor::visit(expr);
         }
+        // super(args) constructor rewrite — runs in post-visit so argument types are inferred.
+        // Walks up the inheritance chain looking for a parent class constructor that matches the
+        // argument types; this lets `super(...)` call the closest ancestor's constructor when an
+        // intermediate class doesn't define its own (mirrors super.method() / delete super.self).
+        if (func && func->isClassMethod && func->classParent && expr->name == "super") {
+            if (auto baseClass = func->classParent->parent) {
+                vector<TypeDeclPtr> argumentTypes;
+                auto selfType = new TypeDecl(Type::tStructure);
+                selfType->structType = func->classParent;
+                argumentTypes.reserve(1 + expr->arguments.size());
+                argumentTypes.push_back(selfType);
+                for (auto &arg : expr->arguments) {
+                    argumentTypes.push_back(arg->type);
+                }
+                while (baseClass) {
+                    auto candidateName = baseClass->name + "`" + baseClass->name;
+                    auto matching = findMatchingFunctions(candidateName, argumentTypes, false);
+                    if (matching.size() == 1) {
+                        expr->name = candidateName;
+                        expr->arguments.insert(expr->arguments.begin(), new ExprVar(expr->at, "self"));
+                        reportAstChanged();
+                        return Visitor::visit(expr);
+                    } else if (matching.size() > 1) {
+                        error("too many candidates for super constructor " + candidateName,
+                              verbose ? program->describeCandidates(matching) : "", "",
+                              expr->at, CompilationError::function_not_found);
+                        return Visitor::visit(expr);
+                    }
+                    baseClass = baseClass->parent;
+                }
+                error("call to super in " + func->name + ": no matching super constructor for " + func->classParent->name, "", "",
+                      expr->at, CompilationError::function_not_found);
+                return Visitor::visit(expr);
+            } else {
+                error("call to super in " + func->name + " is not allowed, no base class for " + func->classParent->name, "", "",
+                      expr->at, CompilationError::function_not_found);
+                return Visitor::visit(expr);
+            }
+        }
         if (forceInscopePod) {
             bool resolvedBefore = expr->genericFunction && expr->func;
             expr->func = inferFunctionCall(expr, InferCallError::functionOrGeneric, expr->genericFunction ? expr->func : nullptr);

tests/language/super.das

@@ -59,6 +59,32 @@ class Derived2 : Derived {
     }
 }
 
+// Skip-level inheritance: SkipMid is empty (inherits Base's constructor and methods).
+// SkipLeaf calls super() / super.method() — both must walk past SkipMid up to Base.
+class SkipMid : Base {
+}
+
+class SkipLeaf : SkipMid {
+    z : int = 0
+    def SkipLeaf {
+        super()
+        z = 100
+    }
+    def SkipLeaf(val : int) {
+        super(val)
+        z = val + 100
+    }
+    def override get_value() : int {
+        return x + z
+    }
+    def get_super_value() : int {
+        return super.get_value()
+    }
+    def override add(a, b : int) : int {
+        return super.add(a, b) + z
+    }
+}
+
 [test]
 def test_super(t : T?) {
     t |> run("super() calls parent default constructor") @(t : T?) {
@@ -130,4 +156,34 @@ def test_super(t : T?) {
             delete d
         }
     }
+    t |> run("super() walks past empty intermediate class") @(t : T?) {
+        unsafe {
+            // SkipMid has no constructor of its own; super() in SkipLeaf must reach Base.
+            var s = SkipLeaf()
+            t |> equal(s.x, 10)   // Base default ctor ran
+            t |> equal(s.z, 100)
+        }
+    }
+    t |> run("super(args) walks past empty intermediate class") @(t : T?) {
+        unsafe {
+            var s = SkipLeaf(7)
+            t |> equal(s.x, 7)
+            t |> equal(s.z, 107)
+        }
+    }
+    t |> run("super.method() walks past empty intermediate class") @(t : T?) {
+        unsafe {
+            var s = SkipLeaf()
+            // SkipLeaf.get_super_value calls super.get_value; SkipMid has no own override,
+            // so the call must resolve to Base.get_value (returns x).
+            t |> equal(s->get_super_value(), 10)
+        }
+    }
+    t |> run("super.method(args) walks past empty intermediate class") @(t : T?) {
+        unsafe {
+            var s = SkipLeaf()
+            // SkipLeaf.add calls super.add(a,b) + z; SkipMid has no add, walks to Base: a+b
+            t |> equal(s->add(3, 4), 107)
+        }
+    }
 }