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C++ PATCH for c++/91923 - failure-to-SFINAE with class type NTTP in C++17
- From: Marek Polacek <polacek at redhat dot com>
- To: GCC Patches <gcc-patches at gcc dot gnu dot org>, Jason Merrill <jason at redhat dot com>
- Date: Fri, 27 Sep 2019 12:03:45 -0400
- Subject: C++ PATCH for c++/91923 - failure-to-SFINAE with class type NTTP in C++17
We reject this well-formed test because the following error was triggering
even in a SFINAE context, while it should not:
https://en.cppreference.com/w/cpp/language/sfinae says that
"attempting to give an invalid type to a non-type template parameter" is
a SFINAE error.
I wonder if the tf_error check should be used more in that function. But
this is enough for this particular testcase.
Bootstrapped/regtested on x86_64-linux, ok for trunk?
2019-09-27 Marek Polacek <polacek@redhat.com>
PR c++/91923 - failure-to-SFINAE with class type NTTP in C++17.
* pt.c (invalid_nontype_parm_type_p): Only emit errors when
tf_error.
* g++.dg/cpp0x/nontype5.C: New test.
diff --git gcc/cp/pt.c gcc/cp/pt.c
index e5d64989b32..e71403460b0 100644
--- gcc/cp/pt.c
+++ gcc/cp/pt.c
@@ -25235,8 +25235,9 @@ invalid_nontype_parm_type_p (tree type, tsubst_flags_t complain)
{
if (cxx_dialect < cxx2a)
{
- error ("non-type template parameters of class type only available "
- "with %<-std=c++2a%> or %<-std=gnu++2a%>");
+ if (complain & tf_error)
+ error ("non-type template parameters of class type only available "
+ "with %<-std=c++2a%> or %<-std=gnu++2a%>");
return true;
}
if (dependent_type_p (type))
diff --git gcc/testsuite/g++.dg/cpp0x/nontype5.C gcc/testsuite/g++.dg/cpp0x/nontype5.C
new file mode 100644
index 00000000000..c31134581aa
--- /dev/null
+++ gcc/testsuite/g++.dg/cpp0x/nontype5.C
@@ -0,0 +1,17 @@
+// PR c++/91923 - failure-to-SFINAE with class type NTTP in C++17.
+// { dg-do compile { target c++11 } }
+
+template<typename T>
+constexpr bool is_integral_(...) {
+ return false;
+}
+template<typename T, T = 1>
+constexpr bool is_integral_(long) {
+ return true;
+}
+
+static_assert(is_integral_<int>(42), "");
+static_assert(!is_integral_<void>(42), "");
+
+struct S {};
+static_assert(!is_integral_<S>(42), "");