c++: 'typename T::X' vs 'struct T::X' lookup [PR109420]

r13-6098-g46711ff8e60d64 made make_typename_type no longer ignore
non-types during the lookup, unless the TYPENAME_TYPE in question was
followed by the :: scope resolution operator.  But there is another
exception to this rule: we need to ignore non-types during the lookup
also if the TYPENAME_TYPE was named with a tag other than 'typename',
such as 'struct' or 'enum', since in that case we're dealing with an
elaborated-type-specifier and so [basic.lookup.elab] applies.  This
patch implements this additional exception.

	PR c++/109420

gcc/cp/ChangeLog:

	* decl.cc (make_typename_type): Also ignore non-types during the
	lookup if tag_type corresponds to an elaborated-type-specifier.
	* pt.cc (tsubst) <case TYPENAME_TYPE>: Pass class_type or
	enum_type as tag_type to make_typename_type accordingly instead
	of always passing typename_type.

gcc/testsuite/ChangeLog:

	* g++.dg/template/typename27.C: New test.

diff --git a/gcc/cp/decl.cc b/gcc/cp/decl.cc
index 5369714..772c059 100644 (file)
--- a/gcc/cp/decl.cc
+++ b/gcc/cp/decl.cc
@@ -4307,7 +4307,17 @@ make_typename_type (tree context, tree name, enum tag_types tag_type,
      lookup will stop when we hit a dependent base.  */
   if (!dependent_scope_p (context))
     {
-      bool want_type = (complain & tf_qualifying_scope);
+      /* We generally don't ignore non-types during TYPENAME_TYPE lookup
+        (as per [temp.res.general]/3), unless
+          - the tag corresponds to a class-key or 'enum' so
+            [basic.lookup.elab] applies, or
+          - the tag corresponds to scope_type or tf_qualifying_scope is
+            set so [basic.lookup.qual]/1 applies.
+        TODO: If we'd set/track the scope_type tag thoroughly on all
+        TYPENAME_TYPEs that are followed by :: then we wouldn't need the
+        tf_qualifying_scope flag.  */
+      bool want_type = (tag_type != none_type && tag_type != typename_type)
+       || (complain & tf_qualifying_scope);
       t = lookup_member (context, name, /*protect=*/2, want_type, complain);
     }
   else

diff --git a/gcc/cp/pt.cc b/gcc/cp/pt.cc
index 4429ae6..fcc8e0d 100644 (file)
--- a/gcc/cp/pt.cc
+++ b/gcc/cp/pt.cc
@@ -16580,9 +16580,16 @@ tsubst (tree t, tree args, tsubst_flags_t complain, tree in_decl)
              return error_mark_node;
          }
 
+       /* FIXME: TYPENAME_IS_CLASS_P conflates 'class' vs 'struct' vs 'union'
+          tags.  TYPENAME_TYPE should probably remember the exact tag that
+          was written.  */
+       enum tag_types tag_type
+         = TYPENAME_IS_CLASS_P (t) ? class_type
+         : TYPENAME_IS_ENUM_P (t) ? enum_type
+         : typename_type;
        tsubst_flags_t tcomplain = complain | tf_keep_type_decl;
        tcomplain |= tst_ok_flag | qualifying_scope_flag;
-       f = make_typename_type (ctx, f, typename_type, tcomplain);
+       f = make_typename_type (ctx, f, tag_type, tcomplain);
        if (f == error_mark_node)
          return f;
        if (TREE_CODE (f) == TYPE_DECL)

diff --git a/gcc/testsuite/g++.dg/template/typename27.C b/gcc/testsuite/g++.dg/template/typename27.C
new file mode 100644 (file)
index 0000000..61b3efd
--- /dev/null
+++ b/gcc/testsuite/g++.dg/template/typename27.C
@@ -0,0 +1,19 @@
+// PR c++/109420
+
+struct A {
+  struct X { };
+  int X;
+};
+
+struct B {
+  enum E { };
+  enum F { E };
+};
+
+template<class T, class U>
+void f() {
+  struct T::X x; // OK, lookup ignores the data member 'int A::X'
+  enum U::E e;   // OK, lookup ignores the enumerator 'B::F::E'
+}
+
+template void f<A, B>();