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.

(cherry picked from commit bbf2424c57c2e13d1a972c4ef4e871c3119b9cb4)

3 files changed, 32 insertions, 5 deletions

diff --git a/gcc/cp/parser.cc b/gcc/cp/parser.cc
index e5211d8..d2c3fc1 100644
--- a/gcc/cp/parser.cc
+++ b/gcc/cp/parser.cc
@@ -25877,6 +25877,11 @@ cp_parser_class_specifier_1 (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)
@@ -26095,8 +26100,6 @@ cp_parser_class_specifier_1 (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);
@@ -26172,8 +26175,8 @@ cp_parser_class_specifier_1 (cp_parser* parser)
 	  cp_parser_late_parsing_nsdmi (parser, decl);
 	}
       vec_safe_truncate (unparsed_nsdmis, 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);
 
@@ -26205,6 +26208,8 @@ cp_parser_class_specifier_1 (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 bc63645..2ae9a65 100644
--- 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
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'" }
+        };
+    }
+};