[PATCH] c++: bogus warning w/ deduction guide in anon ns [PR106604]

[Patrick Palka via Gcc-patches]

Booststrapped and regtested on x86_64-pc-linux-gnu, does this look OK for
trunk and perhaps 13?

-- >8 --

We shouldn't issue a "declared static but never defined" warning
for a deduction guide (declared in an anonymous namespace).

        PR c++/106604

gcc/cp/ChangeLog:

        * decl.cc (wrapup_namespace_globals): Don't issue a
        -Wunused-function warning for a deduction guide.

gcc/testsuite/ChangeLog:

        * g++.dg/cpp1z/class-deduction116.C: New test.
---
 gcc/cp/decl.cc                                  | 1 +
 gcc/testsuite/g++.dg/cpp1z/class-deduction116.C | 8 ++++++++
 2 files changed, 9 insertions(+)
 create mode 100644 gcc/testsuite/g++.dg/cpp1z/class-deduction116.C

diff --git a/gcc/cp/decl.cc b/gcc/cp/decl.cc
index 792ab330dd0..9fe3a0b98fd 100644
--- a/gcc/cp/decl.cc
+++ b/gcc/cp/decl.cc
@@ -856,6 +856,7 @@ wrapup_namespace_globals ()
              && !TREE_PUBLIC (decl)
              && !DECL_ARTIFICIAL (decl)
              && !DECL_FRIEND_PSEUDO_TEMPLATE_INSTANTIATION (decl)
+             && !deduction_guide_p (decl)
              && !warning_suppressed_p (decl, OPT_Wunused_function))
            warning_at (DECL_SOURCE_LOCATION (decl),
                        OPT_Wunused_function,
diff --git a/gcc/testsuite/g++.dg/cpp1z/class-deduction116.C 
b/gcc/testsuite/g++.dg/cpp1z/class-deduction116.C
new file mode 100644
index 00000000000..00f6d5fef41
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp1z/class-deduction116.C
@@ -0,0 +1,8 @@
+// PR c++/106604
+// { dg-do compile { target c++17 } }
+// { dg-additional-options "-Wunused-function" }
+
+namespace {
+  template<class T> struct A { A(...); };
+  A(bool) -> A<bool>; // { dg-bogus "never defined" }
+}
-- 
2.42.0.rc0.25.ga82fb66fed