Go patch committed: reject invalid ... with call returning multiple results

[Ian Lance Taylor]

The Go frontend incorrectly accepted ... with a call returning
multiple results, as in
    f(g()...)
This is invalid and should not be accepted.  This patch from Chris
Manghane fixes the problem.  This is Go issue 9525.  Bootstrapped and
ran Go testsuite on x86_64-unknown-linux-gnu.  Committed to mainline.

Ian

diff -r 2ae1a676004b go/expressions.cc
--- a/go/expressions.cc Wed Jan 21 15:03:08 2015 -0800
+++ b/go/expressions.cc Wed Jan 21 20:05:37 2015 -0800
@@ -8580,6 +8580,17 @@
        {
          Call_expression* call = this->args_->front()->call_expression();
          call->set_is_multi_value_arg();
+         if (this->is_varargs_)
+           {
+             // It is not clear which result of a multiple result call
+             // the ellipsis operator should be applied to.  If we unpack the
+             // the call into its individual results here, the ellipsis will be
+             // applied to the last result.
+             error_at(call->location(),
+                      _("multiple-value argument in single-value context"));
+             return Expression::make_error(call->location());
+           }
+
          Expression_list* args = new Expression_list;
          for (size_t i = 0; i < rc; ++i)
            args->push_back(Expression::make_call_result(call, i));