C++ PATCH for c++/85866, error with .* in template arg

C++ PATCH for c++/85866, error with .* in template arg

[Jason Merrill]

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During function template argument deduction, when we encounter a
non-template parameter with a type that depends on other parameters,
we want to check whether substituting in the arguments we already have
causes a substitution failure.  Since we might not have all the
arguments yet, we need to do this with processing_template_decl set.
tsubst_copy_and_build wasn't dealing well with a call to a .*
expression in that context; outside of a template, that shows up as an
OFFSET_REF, but within a template it's DOTSTAR_EXPR.

Tested x86_64-pc-linux-gnu, applying to trunk and 8.

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commit 7704d0c55fb91ff619ff5487fec643490608d8d7
Author: Jason Merrill <jason@redhat.com>
Date:   Tue May 22 15:32:27 2018 -0400

            PR c++/85866 - error with .* in default template arg.
    
            * pt.c (tsubst_copy_and_build): Handle partial instantiation.

diff --git a/gcc/cp/pt.c b/gcc/cp/pt.c
index 81de633b1ee..0b04770e123 100644
--- a/gcc/cp/pt.c
+++ b/gcc/cp/pt.c
@@ -18433,7 +18433,9 @@ tsubst_copy_and_build (tree t,
 	      /* Unsupported internal function with arguments.  */
 	      gcc_unreachable ();
 	    }
-	else if (TREE_CODE (function) == OFFSET_REF)
+	else if (TREE_CODE (function) == OFFSET_REF
+		 || TREE_CODE (function) == DOTSTAR_EXPR
+		 || TREE_CODE (function) == MEMBER_REF)
 	  ret = build_offset_ref_call_from_tree (function, &call_args,
 						 complain);
 	else if (TREE_CODE (function) == COMPONENT_REF)
diff --git a/gcc/testsuite/g++.dg/cpp0x/fntmpdefarg9.C b/gcc/testsuite/g++.dg/cpp0x/fntmpdefarg9.C
new file mode 100644
index 00000000000..833049c6de3
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp0x/fntmpdefarg9.C
@@ -0,0 +1,29 @@
+// PR c++/85866
+// { dg-do compile { target c++11 } }
+
+template<typename _Tp, typename _Up = _Tp&&>
+_Up
+__declval(int);
+
+template<typename _Tp>
+_Tp
+__declval(long);
+
+template<typename _Tp>
+auto declval() noexcept -> decltype(__declval<_Tp>(0));
+
+template<typename...>
+using void_t = void;
+
+template<typename U, typename V,
+	 void_t<decltype ( (declval<U>().*declval<V>()) () )
+		>* = nullptr>
+void boom(){}
+
+struct Foo {
+  void bar(){}
+};
+
+int main() {
+  boom<Foo, decltype(&Foo::bar)>();
+}