parser: fix ambiguous grammar rules

Author: yhabteab

lib/config/config_parser.yy

@@ -309,12 +309,12 @@ lterm_items: /* empty */
 	| lterm_items_inner sep
 	;
 
-lterm_items_inner: lterm %dprec 2
+lterm_items_inner: lterm %dprec 3
 	{
 		$$ = new std::vector<std::pair<std::unique_ptr<Expression>, EItemInfo> >();
 		$$->emplace_back(std::unique_ptr<Expression>($1), EItemInfo{true, @1});
 	}
-	| rterm_no_side_effect
+	| rterm_no_side_effect %dprec 4
 	{
 		$$ = new std::vector<std::pair<std::unique_ptr<Expression>, EItemInfo> >();
 		$$->emplace_back(std::unique_ptr<Expression>($1), EItemInfo{false, @1});
@@ -330,7 +330,7 @@ lterm_items_inner: lterm %dprec 2
 			$$->emplace_back(std::unique_ptr<Expression>($3), EItemInfo{true, @3});
 		}
 	}
-	| lterm_items_inner sep rterm_no_side_effect %dprec 1
+	| lterm_items_inner sep rterm_no_side_effect %dprec 2
 	{
 		if ($1)
 			$$ = $1;

test/config-ops.cpp

@@ -241,6 +241,18 @@ BOOST_AUTO_TEST_CASE(advanced)
 	expr = ConfigCompiler::CompileText("<test>", "{{ 3 }}");
 	func = expr->Evaluate(frame).GetValue();
 	BOOST_CHECK(func->Invoke() == 3);
+
+	expr = ConfigCompiler::CompileText("<test>", "var something; var different; () => { {{ {{{foo}}} }} }()");
+	auto assertExpectedErr = [](const std::exception& e) {
+		String message = e.what();
+		bool isExpectedError = message.Contains("Value computed is not used.");
+		BOOST_REQUIRE_MESSAGE(isExpectedError, "Unexpected error message: " << message);
+		return isExpectedError;
+	};
+	BOOST_CHECK_EXCEPTION(expr->Evaluate(frame), ScriptError, assertExpectedErr);
+
+	expr = ConfigCompiler::CompileText("<test>", "() => { {{ {{{foo}}} }} }()");
+	BOOST_CHECK_EXCEPTION(expr->Evaluate(frame), ScriptError, assertExpectedErr);
 }
 
 BOOST_AUTO_TEST_SUITE_END()