Introduce class adl_func_operation

This adds class adl_func_operation, which implements
argument-dependent lookup function calls.

Other function calls will be handled in a different way.  However,
because ADL calls were created in a single spot in the C++ parser, and
because they had different semantics from the other cases, it was
convenient to treat them specially.

gdb/ChangeLog
2021-03-08  Tom Tromey  <tom@tromey.com>

	* expop.h (class adl_func_operation): New.
	* eval.c (adl_func_operation::evaluate): New method.

gdb/expop.h

@@ -2030,6 +2030,25 @@ protected:
     override;
 };
 
+/* This class implements ADL (aka Koenig) function calls for C++.  It
+   holds the name of the function to call, the block in which the
+   lookup should be done, and a vector of arguments.  */
+class adl_func_operation
+  : public tuple_holding_operation<std::string, const block *,
+				   std::vector<operation_up>>
+{
+public:
+
+  using tuple_holding_operation::tuple_holding_operation;
+
+  value *evaluate (struct type *expect_type,
+		   struct expression *exp,
+		   enum noside noside) override;
+
+  enum exp_opcode opcode () const override
+  { return OP_ADL_FUNC; }
+};
+
 } /* namespace expr */
 
 #endif /* EXPOP_H */