c++: TYPENAME_TYPE lookup ignoring non-types [PR107773]

Currently when resolving a TYPENAME_TYPE for 'typename T::m' via
make_typename_type, we consider only type bindings of 'm' and ignore
non-type ones.  But [temp.res.general]/3 says, in a note, "the usual
qualified name lookup ([basic.lookup.qual]) applies even in the presence
of 'typename'", and qualified name lookup doesn't discriminate between
type and non-type bindings.  So when resolving such a TYPENAME_TYPE
we want the lookup to consider all bindings.

An exception is when we have a TYPENAME_TYPE corresponding to the
qualifying scope of the :: scope resolution operator, such as 'T::type'
in 'T::type::m'.  In that case, [basic.lookup.qual]/1 applies, and
lookup for such a TYPENAME_TYPE must ignore non-type bindings.  So in
order to correctly handle all cases, make_typename_type needs an
additional flag controlling whether to restrict the lookup.

To that end this patch adds a new tsubst flag tf_qualifying_scope
denoting whether we're substituting the LHS of the :: operator,
which make_typename_type will look for to conditionally restrict the
lookup to type bindings (by default we want to consider all bindings).
So in contexts such as substituting into the scope of TYPENAME_TYPE,
SCOPE_REF or USING_DECL we simply pass tf_qualifying_scope to the
relevant tsubst / tsubst_copy call, and if that scope is a TYPENAME_TYPE
then make_typename_type will restrict the lookup accordingly.  This flag
is intended to apply only to overall scope (TYPENAME_TYPE or not) so we
must be careful to clear the flag to avoid propagating it when recursing
into sub-trees of the scope.

	PR c++/107773

gcc/cp/ChangeLog:

	* cp-tree.h (enum tsubst_flags): New flag tf_qualifying_scope.
	* decl.cc (make_typename_type): Use lookup_member instead of
	lookup_field.  If tf_qualifying_scope is set, pass want_type=true
	instead of =false to lookup_member.  Generalize format specifier
	in diagnostic to handle both type and non-type bindings.
	* pt.cc (tsubst_aggr_type_1): Clear tf_qualifying_scope.  Tidy
	the function.
	(tsubst_decl) <case USING_DECL>: Set tf_qualifying_scope when
	substituting USING_DECL_SCOPE.
	(tsubst): Clear tf_qualifying_scope right away and remember if
	it was set.  Do the same for tf_tst_ok sooner.
	<case TYPENAME_TYPE>: Set tf_qualifying_scope when substituting
	TYPE_CONTEXT.  Pass tf_qualifying_scope to make_typename_type
	if it was set.
	(tsubst_qualified_id): Set tf_qualifying_scope when substituting
	the scope.
	(tsubst_copy): Clear tf_qualifying_scope and remember if it was
	set.
	<case SCOPE_REF>: Set tf_qualifying_scope when substituting the
	scope.
	<case *_TYPE>: Pass tf_qualifying_scope to tsubst if it was set.
	* search.cc (lookup_member): Document default argument.

gcc/testsuite/ChangeLog:

	* g++.dg/template/typename24.C: New test.
	* g++.dg/template/typename25.C: New test.
	* g++.dg/template/typename25a.C: New test.
	* g++.dg/template/typename26.C: New test.

8 files changed, 149 insertions, 30 deletions

diff --git a/gcc/cp/cp-tree.h b/gcc/cp/cp-tree.h
index be8775e..4ecd9c7 100644
--- a/gcc/cp/cp-tree.h
+++ b/gcc/cp/cp-tree.h
@@ -5597,6 +5597,9 @@ enum tsubst_flags {
   tf_tst_ok = 1 << 12,		 /* Allow a typename-specifier to name
 				    a template (C++17 or later).  */
   tf_dguide = 1 << 13,		/* Building a deduction guide from a ctor.  */
+  tf_qualifying_scope = 1 << 14, /* Substituting the LHS of the :: operator.
+				    Affects TYPENAME_TYPE resolution from
+				    make_typename_type.  */
   /* Convenient substitution flags combinations.  */
   tf_warning_or_error = tf_warning | tf_error
 };
diff --git a/gcc/cp/decl.cc b/gcc/cp/decl.cc
index d606b31..2f6412d 100644
--- a/gcc/cp/decl.cc
+++ b/gcc/cp/decl.cc
@@ -4305,9 +4305,10 @@ make_typename_type (tree context, tree name, enum tag_types tag_type,
      member of the current instantiation or a non-dependent base;
      lookup will stop when we hit a dependent base.  */
   if (!dependent_scope_p (context))
-    /* We should only set WANT_TYPE when we're a nested typename type.
-       Then we can give better diagnostics if we find a non-type.  */
-    t = lookup_field (context, name, 2, /*want_type=*/true);
+    {
+      bool want_type = (complain & tf_qualifying_scope);
+      t = lookup_member (context, name, /*protect=*/2, want_type, complain);
+    }
   else
     t = NULL_TREE;
 
@@ -4359,7 +4360,7 @@ make_typename_type (tree context, tree name, enum tag_types tag_type,
       else
 	{
 	  if (complain & tf_error)
-	    error ("%<typename %T::%D%> names %q#T, which is not a type",
+	    error ("%<typename %T::%D%> names %q#D, which is not a type",
 		   context, name, t);
 	  return error_mark_node;
 	}
diff --git a/gcc/cp/pt.cc b/gcc/cp/pt.cc
index e89dbf4..d11d540 100644
--- a/gcc/cp/pt.cc
+++ b/gcc/cp/pt.cc
@@ -13919,8 +13919,7 @@ tsubst_aggr_type_1 (tree t,
 {
   if (TYPE_TEMPLATE_INFO (t) && uses_template_parms (t))
     {
-      tree argvec;
-      tree r;
+      complain &= ~tf_qualifying_scope;
 
       /* Figure out what arguments are appropriate for the
 	 type we are trying to find.  For example, given:
@@ -13931,18 +13930,14 @@ tsubst_aggr_type_1 (tree t,
 	 and supposing that we are instantiating f<int, double>,
 	 then our ARGS will be {int, double}, but, when looking up
 	 S we only want {double}.  */
-      argvec = tsubst_template_args (TYPE_TI_ARGS (t), args,
-				     complain, in_decl);
+      tree argvec = tsubst_template_args (TYPE_TI_ARGS (t), args,
+					  complain, in_decl);
       if (argvec == error_mark_node)
-	r = error_mark_node;
-      else
-	{
-	  r = lookup_template_class (t, argvec, in_decl, NULL_TREE,
-				     entering_scope, complain);
-	  r = cp_build_qualified_type (r, cp_type_quals (t), complain);
-	}
+	return error_mark_node;
 
-      return r;
+      tree r = lookup_template_class (t, argvec, in_decl, NULL_TREE,
+				      entering_scope, complain);
+      return cp_build_qualified_type (r, cp_type_quals (t), complain);
     }
   else
     /* This is not a template type, so there's nothing to do.  */
@@ -15003,11 +14998,15 @@ tsubst_decl (tree t, tree args, tsubst_flags_t complain)
 	  tree scope = USING_DECL_SCOPE (t);
 	  if (PACK_EXPANSION_P (scope))
 	    {
-	      scope = tsubst_pack_expansion (scope, args, complain, in_decl);
+	      scope = tsubst_pack_expansion (scope, args,
+					     complain | tf_qualifying_scope,
+					     in_decl);
 	      variadic_p = true;
 	    }
 	  else
-	    scope = tsubst_copy (scope, args, complain, in_decl);
+	    scope = tsubst_copy (scope, args,
+				 complain | tf_qualifying_scope,
+				 in_decl);
 
 	  tree name = DECL_NAME (t);
 	  if (IDENTIFIER_CONV_OP_P (name)
@@ -15821,6 +15820,12 @@ tsubst (tree t, tree args, tsubst_flags_t complain, tree in_decl)
       || TREE_CODE (t) == TRANSLATION_UNIT_DECL)
     return t;
 
+  tsubst_flags_t tst_ok_flag = (complain & tf_tst_ok);
+  complain &= ~tf_tst_ok;
+
+  tsubst_flags_t qualifying_scope_flag = (complain & tf_qualifying_scope);
+  complain &= ~tf_qualifying_scope;
+
   if (DECL_P (t))
     return tsubst_decl (t, args, complain);
 
@@ -15889,9 +15894,6 @@ tsubst (tree t, tree args, tsubst_flags_t complain, tree in_decl)
   bool fndecl_type = (complain & tf_fndecl_type);
   complain &= ~tf_fndecl_type;
 
-  bool tst_ok = (complain & tf_tst_ok);
-  complain &= ~tf_tst_ok;
-
   if (type
       && code != TYPENAME_TYPE
       && code != TEMPLATE_TYPE_PARM
@@ -16428,7 +16430,9 @@ tsubst (tree t, tree args, tsubst_flags_t complain, tree in_decl)
 	tree ctx = TYPE_CONTEXT (t);
 	if (TREE_CODE (ctx) == TYPE_PACK_EXPANSION)
 	  {
-	    ctx = tsubst_pack_expansion (ctx, args, complain, in_decl);
+	    ctx = tsubst_pack_expansion (ctx, args,
+					 complain | tf_qualifying_scope,
+					 in_decl);
 	    if (ctx == error_mark_node
 		|| TREE_VEC_LENGTH (ctx) > 1)
 	      return error_mark_node;
@@ -16442,8 +16446,9 @@ tsubst (tree t, tree args, tsubst_flags_t complain, tree in_decl)
 	    ctx = TREE_VEC_ELT (ctx, 0);
 	  }
 	else
-	  ctx = tsubst_aggr_type (ctx, args, complain, in_decl,
-				  /*entering_scope=*/1);
+	  ctx = tsubst_aggr_type (ctx, args,
+				  complain | tf_qualifying_scope,
+				  in_decl, /*entering_scope=*/1);
 	if (ctx == error_mark_node)
 	  return error_mark_node;
 
@@ -16473,8 +16478,7 @@ tsubst (tree t, tree args, tsubst_flags_t complain, tree in_decl)
 	  }
 
 	tsubst_flags_t tcomplain = complain | tf_keep_type_decl;
-	if (tst_ok)
-	  tcomplain |= tf_tst_ok;
+	tcomplain |= tst_ok_flag | qualifying_scope_flag;
 	f = make_typename_type (ctx, f, typename_type, tcomplain);
 	if (f == error_mark_node)
 	  return f;
@@ -16879,7 +16883,7 @@ tsubst_qualified_id (tree qualified_id, tree args,
   scope = TREE_OPERAND (qualified_id, 0);
   if (args)
     {
-      scope = tsubst (scope, args, complain, in_decl);
+      scope = tsubst (scope, args, complain | tf_qualifying_scope, in_decl);
       expr = tsubst_copy (name, args, complain, in_decl);
     }
   else
@@ -17125,6 +17129,9 @@ tsubst_copy (tree t, tree args, tsubst_flags_t complain, tree in_decl)
   if (t == NULL_TREE || t == error_mark_node || args == NULL_TREE)
     return t;
 
+  tsubst_flags_t qualifying_scope_flag = (complain & tf_qualifying_scope);
+  complain &= ~tf_qualifying_scope;
+
   if (tree d = maybe_dependent_member_ref (t, args, complain, in_decl))
     return d;
 
@@ -17598,7 +17605,8 @@ tsubst_copy (tree t, tree args, tsubst_flags_t complain, tree in_decl)
 
     case SCOPE_REF:
       {
-	tree op0 = tsubst_copy (TREE_OPERAND (t, 0), args, complain, in_decl);
+	tree op0 = tsubst_copy (TREE_OPERAND (t, 0), args,
+				complain | tf_qualifying_scope, in_decl);
 	tree op1 = tsubst_copy (TREE_OPERAND (t, 1), args, complain, in_decl);
 	return build_qualified_name (/*type=*/NULL_TREE, op0, op1,
 				     QUALIFIED_NAME_IS_TEMPLATE (t));
@@ -17713,7 +17721,7 @@ tsubst_copy (tree t, tree args, tsubst_flags_t complain, tree in_decl)
     case TYPEOF_TYPE:
     case DECLTYPE_TYPE:
     case TYPE_DECL:
-      return tsubst (t, args, complain, in_decl);
+      return tsubst (t, args, complain | qualifying_scope_flag, in_decl);
 
     case USING_DECL:
       t = DECL_NAME (t);
diff --git a/gcc/cp/search.cc b/gcc/cp/search.cc
index f3f19caf..e472a97 100644
--- a/gcc/cp/search.cc
+++ b/gcc/cp/search.cc
@@ -1109,7 +1109,7 @@ build_baselink (tree binfo, tree access_binfo, tree functions, tree optype)
 
 tree
 lookup_member (tree xbasetype, tree name, int protect, bool want_type,
-	       tsubst_flags_t complain, access_failure_info *afi)
+	       tsubst_flags_t complain, access_failure_info *afi /* = NULL */)
 {
   tree rval, rval_binfo = NULL_TREE;
   tree type = NULL_TREE, basetype_path = NULL_TREE;
diff --git a/gcc/testsuite/g++.dg/template/typename24.C b/gcc/testsuite/g++.dg/template/typename24.C
new file mode 100644
index 0000000..8b2b371
--- /dev/null
+++ b/gcc/testsuite/g++.dg/template/typename24.C
@@ -0,0 +1,18 @@
+// PR c++/107773
+// Verify lookup for a non-neste TYPENAME_TYPE correctly considers
+// non-types.
+
+struct a {
+  typedef void get;
+};
+
+struct b : a {
+  int get(int i) const;
+};
+
+template<class T>
+void f() {
+  typedef typename T::get type; // { dg-error "'int b::get\\(int\\) const', which is not a type" }
+}
+
+template void f<b>();
diff --git a/gcc/testsuite/g++.dg/template/typename25.C b/gcc/testsuite/g++.dg/template/typename25.C
new file mode 100644
index 0000000..04e48e1
--- /dev/null
+++ b/gcc/testsuite/g++.dg/template/typename25.C
@@ -0,0 +1,33 @@
+// PR c++/107773
+// Verify lookup for TYPENAME_TYPE appearing to the left of the ::
+// scope resolution operator correctly ignores non-types.
+
+struct a {
+  typedef void type;
+};
+
+struct c {
+  struct b : a {
+    typedef b self;
+    static int m;
+  };
+  int b;
+};
+
+template<class T>
+void f() {
+  // A TYPENAME_TYPE whose TYPE_CONTEXT is a nested TYPENAME_TYPE.
+  typedef typename T::b::type type;
+  // A SCOPE_REF whose first operand is a TYPENAME_TYPE.
+  int m = T::b::m;
+}
+
+template void f<c>();
+
+template<class T>
+struct d : T::b::self {
+  // A USING_DECL whose USING_DECL_SCOPE is a TYPENAME_TYPE.
+  using typename T::b::type;
+};
+
+template struct d<c>;
diff --git a/gcc/testsuite/g++.dg/template/typename25a.C b/gcc/testsuite/g++.dg/template/typename25a.C
new file mode 100644
index 0000000..ecb34aa
--- /dev/null
+++ b/gcc/testsuite/g++.dg/template/typename25a.C
@@ -0,0 +1,37 @@
+// PR c++/107773
+// A variadic version of typename25.C
+// { dg-do compile { target c++11 } }
+
+struct a {
+  typedef void type;
+};
+
+struct c {
+  struct b : a {
+    typedef b self;
+    static int m;
+  };
+  int b;
+};
+
+template<class...> void sink(...);
+
+template<class... Ts>
+void f() {
+  // A TYPENAME_TYPE whose TYPE_CONTEXT is a nested TYPENAME_TYPE.
+  sink<typename Ts::b::type...>();
+  // A SCOPE_REF whose first operand is a TYPENAME_TYPE.
+  sink(Ts::b::m...);
+}
+
+template void f<c>();
+
+template<class... Ts>
+struct d : Ts::b::self... {
+#if __cpp_variadic_using
+  // A USING_DECL whose USING_DECL_SCOPE is a TYPENAME_TYPE.
+  using typename Ts::b::type...;
+#endif
+};
+
+template struct d<c>;
diff --git a/gcc/testsuite/g++.dg/template/typename26.C b/gcc/testsuite/g++.dg/template/typename26.C
new file mode 100644
index 0000000..f4b8bb2
--- /dev/null
+++ b/gcc/testsuite/g++.dg/template/typename26.C
@@ -0,0 +1,19 @@
+// Example 4 from [temp.res.general]/3.
+
+struct A {
+  struct X { };
+  int X;
+};
+struct B {
+  struct X { };
+};
+template<class T> void f(T t) {
+  typename T::X x; // { dg-error "'int A::X', which is not a type" }
+}
+void foo() {
+  A a;
+  B b;
+  f(b); // OK, T::X refers to B::X
+  f(a); // error: T::X refers to the data member A::X not the struct A::X
+  // { dg-message "required from here" "" { target *-*-* } .-1 }
+}