fix(cpp1): apply memberwise semantics to base assignment

regression-tests/pure2-bugfix-for-memberwise-base-assignment.cpp2

@@ -0,0 +1,18 @@
+Base: type = {
+  operator=: (out this) = { }
+  operator=: (out this, that)       = std::cout << "(out this, that)\n";
+  operator=: (implicit out this, x) = std::cout << "(implicit out this, x)\n";
+}
+
+Derived: type = {
+  this: Base            = ();
+  operator=: (out this) = { }
+  operator=: (out this, that)   = { }
+  operator=: (inout this, move that) = { }
+}
+
+main: () = {
+  d  := Derived();
+  d2 := d;
+  d2 = d;
+}

regression-tests/test-results/gcc-13/pure2-bugfix-for-memberwise-base-assignment.cpp.execution

@@ -0,0 +1,2 @@
+(out this, that)
+(out this, that)

regression-tests/test-results/pure2-bugfix-for-memberwise-base-assignment.cpp

@@ -0,0 +1,93 @@
+
+#define CPP2_USE_MODULES         Yes
+
+//=== Cpp2 type declarations ====================================================
+
+
+#include "cpp2util.h"
+
+#line 1 "pure2-bugfix-for-memberwise-base-assignment.cpp2"
+class Base;
+
+
+#line 7 "pure2-bugfix-for-memberwise-base-assignment.cpp2"
+class Derived;
+
+
+//=== Cpp2 type definitions and function declarations ===========================
+
+#line 1 "pure2-bugfix-for-memberwise-base-assignment.cpp2"
+class Base {
+  public: explicit Base();
+  public: Base(Base const& that);
+
+#line 3 "pure2-bugfix-for-memberwise-base-assignment.cpp2"
+  public: auto operator=(Base const& that) -> Base& ;
+
+#line 3 "pure2-bugfix-for-memberwise-base-assignment.cpp2"
+  public: Base(Base&& that) noexcept;
+
+#line 3 "pure2-bugfix-for-memberwise-base-assignment.cpp2"
+  public: auto operator=(Base&& that) noexcept -> Base& ;
+  public: Base(auto const& x);
+#line 4 "pure2-bugfix-for-memberwise-base-assignment.cpp2"
+  public: auto operator=(auto const& x) -> Base& ;
+};
+
+class Derived: public Base {
+
+  public: explicit Derived();
+  public: Derived(Derived const& that);
+  public: auto operator=(Derived&& that) noexcept -> Derived& ;
+};
+
+auto main() -> int;
+
+
+//=== Cpp2 function definitions =================================================
+
+
+#line 2 "pure2-bugfix-for-memberwise-base-assignment.cpp2"
+  Base::Base(){}
+  Base::Base (Base const& that) { std::cout << "(out this, that)\n"; }
+#line 3 "pure2-bugfix-for-memberwise-base-assignment.cpp2"
+  auto Base::operator=(Base const& that) -> Base&  { std::cout << "(out this, that)\n";
+                                      return *this;
+#line 3 "pure2-bugfix-for-memberwise-base-assignment.cpp2"
+                                     }
+#line 3 "pure2-bugfix-for-memberwise-base-assignment.cpp2"
+  Base::Base (Base&& that) noexcept { std::cout << "(out this, that)\n"; }
+#line 3 "pure2-bugfix-for-memberwise-base-assignment.cpp2"
+  auto Base::operator=(Base&& that) noexcept -> Base&  { std::cout << "(out this, that)\n";
+                                      return *this;
+#line 3 "pure2-bugfix-for-memberwise-base-assignment.cpp2"
+                                     }
+  Base::Base(auto const& x) { std::cout << "(implicit out this, x)\n";  }
+#line 4 "pure2-bugfix-for-memberwise-base-assignment.cpp2"
+  auto Base::operator=(auto const& x) -> Base&  { std::cout << "(implicit out this, x)\n";
+                                      return *this;
+#line 4 "pure2-bugfix-for-memberwise-base-assignment.cpp2"
+   }
+
+#line 9 "pure2-bugfix-for-memberwise-base-assignment.cpp2"
+  Derived::Derived()
+                            : Base{  }
+#line 9 "pure2-bugfix-for-memberwise-base-assignment.cpp2"
+  {}
+  Derived::Derived(Derived const& that)
+                                    : Base{ static_cast<Base const&>(that) }
+#line 10 "pure2-bugfix-for-memberwise-base-assignment.cpp2"
+                                {}
+  auto Derived::operator=(Derived&& that) noexcept -> Derived& {
+                                         Base::operator= ( static_cast<Base&&>(that) );
+                                         return *this;
+#line 11 "pure2-bugfix-for-memberwise-base-assignment.cpp2"
+  }
+
+#line 14 "pure2-bugfix-for-memberwise-base-assignment.cpp2"
+auto main() -> int{
+  auto d {Derived()}; 
+  auto d2 {d}; 
+  d2 = std::move(d);
+}
+

regression-tests/test-results/pure2-bugfix-for-memberwise-base-assignment.cpp2.output

@@ -0,0 +1,2 @@
+pure2-bugfix-for-memberwise-base-assignment.cpp2... ok (all Cpp2, passes safety checks)
+

source/cppfront.cpp

@@ -4584,23 +4584,34 @@ class cppfront
                 //  Otherwise, use a default... for a non-copy/move that's the member initializer
                 //  (for which we don't need to emit anything special because it will get used),
                 //  and for a copy/move function we default to "= that.same_member" (or, if this
-                //  is a base type, just "= that")
+                //  is a base type, to assigning from the lowered base subobject)
                 if (!found_explicit_init)
                 {
-                    if (emitting_move_that_function)
+                    if (emitting_that_function && (*object)->has_name("this"))
                     {
-                        initializer = "std::move(that)";
-                        if (!(*object)->has_name("this")) {
-                            initializer += "." + object_name;
+                        auto pass = std::string{" const&"};
+                        if (emitting_move_that_function) {
+                            pass = "&&";
                         }
+                        initializer =
+                            "static_cast<"
+                            + object_name
+                            + pass
+                            + ">(that)";
+                        found_default_init = true;
+                    }
+                    else if (emitting_move_that_function)
+                    {
+                        initializer =
+                            "std::move(that)."
+                            + object_name;
                         found_default_init = true;
                     }
                     else if (emitting_that_function)
                     {
-                        initializer = "that";
-                        if (!(*object)->has_name("this")) {
-                            initializer += "." + object_name;
-                        }
+                        initializer =
+                            "that."
+                            + object_name;
                         found_default_init = true;
                     }
                     else if ((*object)->initializer)