c++: outer 'this' leaking into local class [PR106969]

Here when resolving the implicit object for '&wrapped' within the
local class Foo, we expect to obtain a dummy object of type Foo& since
there's no 'this' available in this context.  And yet at this point
current_class_ref still corresponds to the outer class Context (and is
const), which confuses maybe_dummy_object into propagating the cv-quals
of current_class_ref and returning an object of type const Foo&.  Thus
decltype(&wrapped) wrongly yields const int* instead of int*.

The problem ultimately seems to be that the 'this' from the enclosing
class appears available for use when parsing the local class, but 'this'
shouldn't persist across classes like that.  This patch fixes this by
clearing current_class_ptr/ref before parsing a class definition.

After this change, for the test name-clash11.C in C++98 mode we would
now complain about an invalid use of 'this' in e.g.

  ASSERT (sizeof (this->A) == 16);

due to the way the test defines the ASSERT macro via a local class.
This patch redefines the macro using a local typedef instead.

	PR c++/106969

gcc/cp/ChangeLog:

	* parser.cc (cp_parser_class_specifier): Clear current_class_ptr
	and current_class_ref sooner, before parsing a class definition.

gcc/testsuite/ChangeLog:

	* g++.dg/lookup/name-clash11.C: Fix ASSERT macro definition in
	C++98 mode.
	* g++.dg/lookup/this2.C: New test.

diff --git a/gcc/cp/parser.cc b/gcc/cp/parser.cc
index a277003ea581e3996ce237eb52b77a3778cb4c43..c54972be85ae60735a7ccf652f20fea8c6235de1 100644 (file)
--- a/gcc/cp/parser.cc
+++ b/gcc/cp/parser.cc
@@ -26151,6 +26151,11 @@ cp_parser_class_specifier (cp_parser* parser)
   saved_in_unbraced_linkage_specification_p
     = parser->in_unbraced_linkage_specification_p;
   parser->in_unbraced_linkage_specification_p = false;
+  /* 'this' from an enclosing non-static member function is unavailable.  */
+  tree saved_ccp = current_class_ptr;
+  tree saved_ccr = current_class_ref;
+  current_class_ptr = NULL_TREE;
+  current_class_ref = NULL_TREE;
 
   /* Start the class.  */
   if (nested_name_specifier_p)
@@ -26369,8 +26374,6 @@ cp_parser_class_specifier (cp_parser* parser)
       /* If there are noexcept-specifiers that have not yet been processed,
         take care of them now.  Do this before processing NSDMIs as they
         may depend on noexcept-specifiers already having been processed.  */
-      tree save_ccp = current_class_ptr;
-      tree save_ccr = current_class_ref;
       FOR_EACH_VEC_SAFE_ELT (unparsed_noexcepts, ix, decl)
        {
          tree ctx = DECL_CONTEXT (decl);
@@ -26496,8 +26499,8 @@ cp_parser_class_specifier (cp_parser* parser)
        }
       vec_safe_truncate (unparsed_contracts, 0);
 
-      current_class_ptr = save_ccp;
-      current_class_ref = save_ccr;
+      current_class_ptr = NULL_TREE;
+      current_class_ref = NULL_TREE;
       if (pushed_scope)
        pop_scope (pushed_scope);
 
@@ -26529,6 +26532,8 @@ cp_parser_class_specifier (cp_parser* parser)
     = saved_num_template_parameter_lists;
   parser->in_unbraced_linkage_specification_p
     = saved_in_unbraced_linkage_specification_p;
+  current_class_ptr = saved_ccp;
+  current_class_ref = saved_ccr;
 
   return type;
 }

diff --git a/gcc/testsuite/g++.dg/lookup/name-clash11.C b/gcc/testsuite/g++.dg/lookup/name-clash11.C
index bc63645e8d3948b77c1b89e461ac90bb66281873..2ae9a65264d9927a771a1cb55ba8b1beb4d51db9 100644 (file)
--- a/gcc/testsuite/g++.dg/lookup/name-clash11.C
+++ b/gcc/testsuite/g++.dg/lookup/name-clash11.C
@@ -7,7 +7,7 @@
 #  define ASSERT(e) static_assert (e, #e)
 #else
 #  define ASSERT(e)                                             \
-  do { struct S { bool: !!(e); } asrt; (void)&asrt; } while (0)
+  do { typedef int asrt[bool(e) ? 1 : -1]; } while (0)
 #endif
 
 

diff --git a/gcc/testsuite/g++.dg/lookup/this2.C b/gcc/testsuite/g++.dg/lookup/this2.C
new file mode 100644 (file)
index 0000000..064c146
--- /dev/null
+++ b/gcc/testsuite/g++.dg/lookup/this2.C
@@ -0,0 +1,22 @@
+// PR c++/106969
+// { dg-do compile { target c++11 } }
+
+struct Context
+{
+    void
+    action() const
+    {
+        struct Foo
+        {
+            int wrapped;
+            decltype(&wrapped) get() { return &wrapped; }
+        } t;
+
+        *t.get()= 42; // OK, get() returns int* not const int*
+
+        struct Bar
+        {
+            using type = decltype(this); // { dg-error "invalid use of 'this'" }
+        };
+    }
+};