c++: ICE with TTP [PR96097]

We crash when dependent_type_p gets a TEMPLATE_TYPE_PARM outside
a template.  That happens here because in

  template <template <typename T, typename T::type TT> typename X>
  void func() {}
  template <typename U, int I>
  struct Y {};
  void g() { func<Y>(); }

when performing overload resolution for func<Y>() we have to check
if U matches T and I matches TT.  So we wind up in
coerce_template_template_parm/PARM_DECL.  TREE_TYPE (arg) is int
so we try to substitute TT's type, which is T::type.  But we have
nothing to substitute T with.  And we call make_typename_type where
ctx is still T, which checks dependent_scope_p and we trip the assert.

It should work to always perform the substitution in a template context.
If the result still contains template parameters, we cannot say if they
match.

	PR c++/96097

gcc/cp/ChangeLog:

	* pt.cc (coerce_template_template_parm): Increment
	processing_template_decl before calling tsubst.

gcc/testsuite/ChangeLog:

	* g++.dg/template/ttp44.C: New test.

diff --git a/gcc/cp/pt.cc b/gcc/cp/pt.cc
index cb3164d491473bd15802b646127476253369af6d..769e7999dac1132d0f382c493a42b3d0d75023f7 100644 (file)
--- a/gcc/cp/pt.cc
+++ b/gcc/cp/pt.cc
@@ -7951,7 +7951,9 @@ coerce_template_template_parm (tree parm, tree arg, tsubst_flags_t complain,
         i.e. the parameter list of TT depends on earlier parameters.  */
       if (!uses_template_parms (TREE_TYPE (arg)))
        {
+         ++processing_template_decl;
          tree t = tsubst (TREE_TYPE (parm), outer_args, complain, in_decl);
+         --processing_template_decl;
          if (!uses_template_parms (t)
              && !same_type_p (t, TREE_TYPE (arg)))
            return false;

diff --git a/gcc/testsuite/g++.dg/template/ttp44.C b/gcc/testsuite/g++.dg/template/ttp44.C
new file mode 100644 (file)
index 0000000..2a41297
--- /dev/null
+++ b/gcc/testsuite/g++.dg/template/ttp44.C
@@ -0,0 +1,13 @@
+// PR c++/96097
+// { dg-do compile }
+
+template <template <typename T, typename T::type TT> class X>
+void func() {}
+
+template <typename U, int I>
+struct Y {};
+
+void test()
+{
+  func<Y>();
+}