Fix array not narrowed to non-empty when count stored in variable

- When $count = count($a) and later $count > 1 or $count === 1,
  the array $a was not narrowed to non-empty-array
- Root cause: conditional expression matching required exact type
  equality, but count comparisons produce subtypes (e.g. int<2, max>
  is a subtype of int<1, max>)
- Added conditionalExpressionHolderMatches() that uses isSuperTypeOf
  for IntegerRangeType conditions, enabling count-based narrowing
- New regression test in tests/PHPStan/Analyser/nsrt/bug-4090.php

Closes phpstan/phpstan#4090

Author: VincentLanglet

src/Analyser/MutatingScope.php

@@ -2144,6 +2144,20 @@ public function enterAnonymousFunctionWithoutReflection(
 		);
 	}
 
+	private function conditionalExpressionHolderMatches(ExpressionTypeHolder $specified, ExpressionTypeHolder $condition): bool
+	{
+		if ($specified->equals($condition)) {
+			return true;
+		}
+
+		$conditionType = $condition->getType();
+		if (!$conditionType instanceof IntegerRangeType) {
+			return false;
+		}
+
+		return $conditionType->isSuperTypeOf($specified->getType())->yes();
+	}
+
 	private function expressionTypeIsUnchangeable(ExpressionTypeHolder $typeHolder): bool
 	{
 		$expr = $typeHolder->getExpr();
@@ -3218,7 +3232,7 @@ public function filterBySpecifiedTypes(SpecifiedTypes $specifiedTypes): self
 				}
 				foreach ($conditionalExpressions as $conditionalExpression) {
 					foreach ($conditionalExpression->getConditionExpressionTypeHolders() as $holderExprString => $conditionalTypeHolder) {
-						if (!array_key_exists($holderExprString, $specifiedExpressions) || !$specifiedExpressions[$holderExprString]->equals($conditionalTypeHolder)) {
+						if (!array_key_exists($holderExprString, $specifiedExpressions) || !$this->conditionalExpressionHolderMatches($specifiedExpressions[$holderExprString], $conditionalTypeHolder)) {
 							continue 2;
 						}
 					}

tests/PHPStan/Analyser/nsrt/bug-4090.php

@@ -0,0 +1,50 @@
+<?php declare(strict_types = 1);
+
+namespace Bug4090;
+
+use function PHPStan\Testing\assertType;
+
+/** @param string[] $a */
+function foo(array $a): void
+{
+	if (count($a) > 1) {
+		assertType('non-empty-array<string>', $a);
+		echo implode(',', $a);
+	} elseif (count($a) === 1) {
+		assertType('non-empty-array<string>', $a);
+		echo trim(current($a));
+	}
+}
+
+
+/** @param string[] $a */
+function bar(array $a): void
+{
+	$count = count($a);
+	if ($count > 1) {
+		assertType('non-empty-array<string>', $a);
+		echo implode(',', $a);
+	} elseif ($count === 1) {
+		assertType('non-empty-array<string>', $a);
+		echo trim(current($a));
+	}
+}
+
+
+/** @param string[] $a */
+function qux(array $a): void
+{
+	switch (count($a)) {
+		case 0:
+			assertType('array{}', $a);
+			break;
+		case 1:
+			assertType('non-empty-array<string>', $a);
+			echo trim(current($a));
+			break;
+		default:
+			assertType('non-empty-array<string>', $a);
+			echo implode(',', $a);
+			break;
+	}
+}