[gcc r12-9493] c++: outer 'this' leaking into local class [PR106969]

[gcc r12-9493] c++: outer 'this' leaking into local class [PR106969]

[Patrick Palka]

https://gcc.gnu.org/g:458bda5432d352469e258f1c0e4c2a37c853575a

commit r12-9493-g458bda5432d352469e258f1c0e4c2a37c853575a
Author: Patrick Palka <ppalka@redhat.com>
Date:   Fri Mar 24 14:51:24 2023 -0400

    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)

Diff:
---
 gcc/cp/parser.cc                           | 13 +++++++++----
 gcc/testsuite/g++.dg/lookup/name-clash11.C |  2 +-
 gcc/testsuite/g++.dg/lookup/this2.C        | 22 ++++++++++++++++++++++
 3 files changed, 32 insertions(+), 5 deletions(-)

diff --git a/gcc/cp/parser.cc b/gcc/cp/parser.cc
index e5211d8075e..d2c3fc1d0b9 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 bc63645e8d3..2ae9a65264d 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 00000000000..064c146e937
--- /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'" }
+        };
+    }
+};