[BUGFIX] Ensure valid position for first Rule added to RuleSet (#1262)

Part of #974.

Author: JakeQZ

CHANGELOG.md

@@ -105,6 +105,7 @@ Please also have a look at our
 
 ### Fixed
 
+- Ensure first rule added with `RuleSet::addRule()` has valid position (#1262)
 - Don't render `rgb` colors with percentage values using hex notation (#803)
 
 ### Documentation

src/RuleSet/RuleSet.php

@@ -117,6 +117,8 @@ public function addRule(Rule $ruleToAdd, ?Rule $sibling = null): void
             if ($rulesCount > 0) {
                 $last = $rules[$rulesCount - 1];
                 $ruleToAdd->setPosition($last->getLineNo() + 1, 0);
+            } else {
+                $ruleToAdd->setPosition(1, 0);
             }
         } elseif ($ruleToAdd->getColumnNumber() === null) {
             $ruleToAdd->setPosition($ruleToAdd->getLineNumber(), 0);

tests/Unit/RuleSet/RuleSetTest.php

@@ -95,10 +95,6 @@ public function addRuleWithoutSiblingAddsRuleAfterInitialRulesAndSetsValidLineAn
         array $initialPropertyNames,
         string $propertyNameToAdd
     ): void {
-        if ($initialPropertyNames === []) {
-            self::markTestSkipped('currently broken - first rule added does not have valid line number set');
-        }
-
         $ruleToAdd = new Rule($propertyNameToAdd);
         $this->setRulesFromPropertyNames($initialPropertyNames);