PR c++/82565 - ICE with concepts and generic lambda.

	* pt.c (instantiate_decl): Clear fn_context for lambdas.

From-SVN: r258502

gcc/cp/ChangeLog

 2018-03-13  Jason Merrill  <jason@redhat.com>
 
+	PR c++/82565 - ICE with concepts and generic lambda.
+	* pt.c (instantiate_decl): Clear fn_context for lambdas.
+
+2018-03-13  Jason Merrill  <jason@redhat.com>
+
 	PR c++/84720 - ICE with rvalue ref non-type argument.
 	* pt.c (convert_nontype_argument): Handle rvalue references.
 

gcc/cp/pt.c

@@ -23460,6 +23460,9 @@ instantiate_decl (tree d, bool defer_ok, bool expl_inst_class_mem_p)
   bool push_to_top, nested;
   tree fn_context;
   fn_context = decl_function_context (d);
+  if (LAMBDA_FUNCTION_P (d))
+    /* tsubst_lambda_expr resolved any references to enclosing functions.  */
+    fn_context = NULL_TREE;
   nested = current_function_decl != NULL_TREE;
   push_to_top = !(nested && fn_context == current_function_decl);
 

gcc/testsuite/g++.dg/concepts/lambda1.C

+// PR c++/82565
+// { dg-do compile { target c++14 } }
+// { dg-additional-options -fconcepts }
+
+struct string
+{
+  string();
+  string(const char *);
+  bool empty() const;
+};
+
+template<typename T, typename ReturnType>
+concept bool Concept() {
+  return requires(T t, const string& s) {
+    { t(s) } -> ReturnType;
+  };
+}
+
+struct test {
+  string _str;
+
+  template<typename Visitor>
+    requires Concept<Visitor, bool>()
+  decltype(auto) visit(Visitor&& visitor) const {
+    return visitor(_str);
+  }
+
+};
+
+int main() {
+  test().visit([] (auto& x) { return x.empty(); });
+}