Fix null coalesce type inference for correlated int range variables

- Fixed getCoalesceType() in MutatingScope to avoid over-narrowing the right
  side of ?? when conditional expressions from scope merging make correlated
  variables all null together
- The fix uses the narrowed scope only when it successfully removes null from
  the right type (useful for `if ($a || $b) { $a ?? $b }` patterns), and
  falls back to the unfiltered type otherwise
- New regression test in tests/PHPStan/Analyser/nsrt/bug-14213.php

Closes phpstan/phpstan#14213

Author: phpstan-bot

src/Analyser/MutatingScope.php

@@ -6536,7 +6536,13 @@ private function getCoalesceType(BinaryOp\Coalesce $node): Type
 			return TypeCombinator::removeNull($this->filterByTruthyValue($issetLeftExpr)->getType($node->left));
 		}
 
-		$rightType = $this->filterByFalseyValue($issetLeftExpr)->getType($node->right);
+		$unfilteredRightType = $this->getType($node->right);
+		if (!$unfilteredRightType->isNull()->no()) {
+			$narrowedRightType = $this->filterByFalseyValue($issetLeftExpr)->getType($node->right);
+			$rightType = $narrowedRightType->isNull()->no() ? $narrowedRightType : $unfilteredRightType;
+		} else {
+			$rightType = $unfilteredRightType;
+		}
 
 		if ($result === null) {
 			return TypeCombinator::union(

tests/PHPStan/Analyser/nsrt/bug-14213.php

@@ -0,0 +1,27 @@
+<?php declare(strict_types = 1);
+
+namespace Bug14213;
+
+use function PHPStan\Testing\assertType;
+
+class HelloWorld
+{
+	public static function coalesce_int_range(): void
+	{
+		$x0 = $x1 = $x2 = null;
+
+		if (rand(0, 1)) {
+			$x0 = rand(0, 1);
+			$x1 = rand(2, 3);
+			$x2 = rand(4, 5);
+		}
+
+		$x = (
+			$x0 ??
+			$x1 ??
+			$x2
+		);
+
+		assertType('int<0, 5>|null', $x);
+	}
+}