Fix phpstan/phpstan#14314: strange behavior on regex capture groups

src/Analyser/TypeSpecifier.php

@@ -1294,6 +1294,27 @@ private function specifyTypesForCountFuncCall(
 					return $result;
 				}
 			}
+
+			// Fallback: directly filter constant arrays by their exact sizes.
+			// This avoids using TypeCombinator::remove() with falsey context,
+			// which can incorrectly remove arrays whose count doesn't match
+			// but whose shape is a subtype of the matched array.
+			$keptTypes = [];
+			foreach ($type->getConstantArrays() as $arrayType) {
+				if ($sizeType->isSuperTypeOf($arrayType->getArraySize())->yes()) {
+					continue;
+				}
+
+				$keptTypes[] = $arrayType;
+			}
+			if ($keptTypes !== []) {
+				return $this->create(
+					$countFuncCall->getArgs()[0]->value,
+					TypeCombinator::union(...$keptTypes),
+					$context->negate(),
+					$scope,
+				)->setRootExpr($rootExpr);
+			}
 		}
 
 		$resultTypes = [];

tests/PHPStan/Analyser/nsrt/bug-14314.php

@@ -0,0 +1,118 @@
+<?php
+
+declare(strict_types = 1);
+
+namespace Bug14314;
+
+use function PHPStan\Testing\assertType;
+
+function () {
+	preg_match('/^(.)$/', '', $matches) || preg_match('/^(.)(.)(.)$/', '', $matches);
+	assertType('array{}|array{non-falsy-string, non-empty-string, non-empty-string, non-empty-string}|array{non-falsy-string, non-empty-string}', $matches);
+	if (count($matches) === 2) {
+		assertType('array{non-falsy-string, non-empty-string}', $matches);
+		return;
+	}
+	assertType('array{}|array{non-falsy-string, non-empty-string, non-empty-string, non-empty-string}', $matches);
+	if (count($matches) === 4) {
+		assertType('array{non-falsy-string, non-empty-string, non-empty-string, non-empty-string}', $matches);
+	}
+};
+
+class Bug14314Test
+{
+	/**
+	 * Test: union with array{} and arrays with optional keys
+	 * @param array{}|array{0: string, 1: string, 2?: string} $arr
+	 */
+	public function testOptionalKeysWithEmpty(array $arr): void
+	{
+		assertType('array{}|array{0: string, 1: string, 2?: string}', $arr);
+		if (count($arr) === 3) {
+			assertType('array{string, string, string}', $arr);
+			return;
+		}
+		// Fallback keeps full array{0: string, 1: string, 2?: string} since its size
+		// range (2..3) is not fully contained in sizeType (3)
+		assertType('array{}|array{0: string, 1: string, 2?: string}', $arr);
+	}
+
+	/**
+	 * Test: IntegerRange sizeType fully covers optional key size range - array is correctly removed
+	 * @param array{}|array{0: string, 1: string, 2?: string} $arr
+	 * @param int<2, 3> $twoOrThree
+	 */
+	public function testIntRangeFullyCoveringOptionalKeys(array $arr, int $twoOrThree): void
+	{
+		if (count($arr) === $twoOrThree) {
+			assertType('array{0: string, 1: string, 2?: string}', $arr);
+			return;
+		}
+		// int<2,3> fully covers the optional-key array's size range (2..3),
+		// so the array is correctly removed in the falsey branch
+		assertType('array{}', $arr);
+	}
+
+	/**
+	 * Test: IntegerRange partially covers optional key size range - array is kept
+	 * @param array{}|array{0: string, 1: string, 2?: string, 3?: string} $arr
+	 * @param int<2, 3> $twoOrThree
+	 */
+	public function testIntRangePartiallyCoveringOptionalKeys(array $arr, int $twoOrThree): void
+	{
+		if (count($arr) === $twoOrThree) {
+			assertType('array{0: string, 1: string, 2?: string, 3?: string}', $arr);
+			return;
+		}
+		// int<2,3> does NOT fully cover size range (2..4), so the array is kept
+		assertType('array{}|array{0: string, 1: string, 2?: string, 3?: string}', $arr);
+	}
+
+	/**
+	 * Test: IntegerRange sizeType with union of constant arrays including array{}
+	 * @param array{}|array{string}|array{string, string, string, string} $arr
+	 * @param int<2, 4> $twoToFour
+	 */
+	public function testIntRangeWithUnionAndEmpty(array $arr, int $twoToFour): void
+	{
+		if (count($arr) === $twoToFour) {
+			assertType('array{string, string, string, string}', $arr);
+			return;
+		}
+		assertType('array{}|array{string, string, string, string}|array{string}', $arr);
+	}
+}
+
+// Test: sequential count checks preserve narrowing correctly
+function () {
+	preg_match('/^(.)$/', '', $m) || preg_match('/^(.)(.)(.)$/', '', $m) || preg_match('/^(.)(.)(.)(.)(.)(.)$/', '', $m);
+	assertType('array{}|array{non-falsy-string, non-empty-string, non-empty-string, non-empty-string, non-empty-string, non-empty-string, non-empty-string}|array{non-falsy-string, non-empty-string, non-empty-string, non-empty-string}|array{non-falsy-string, non-empty-string}', $m);
+	if (count($m) === 2) {
+		assertType('array{non-falsy-string, non-empty-string}', $m);
+		return;
+	}
+	assertType('array{}|array{non-falsy-string, non-empty-string, non-empty-string, non-empty-string, non-empty-string, non-empty-string, non-empty-string}|array{non-falsy-string, non-empty-string, non-empty-string, non-empty-string}', $m);
+	if (count($m) === 4) {
+		assertType('array{non-falsy-string, non-empty-string, non-empty-string, non-empty-string}', $m);
+		return;
+	}
+	assertType('array{}|array{non-falsy-string, non-empty-string, non-empty-string, non-empty-string, non-empty-string, non-empty-string, non-empty-string}', $m);
+	if (count($m) === 7) {
+		assertType('array{non-falsy-string, non-empty-string, non-empty-string, non-empty-string, non-empty-string, non-empty-string, non-empty-string}', $m);
+	}
+};
+
+// Test: count narrowing does not lose other variable types
+function (int $x) {
+	preg_match('/^(.)$/', '', $matches) || preg_match('/^(.)(.)(.)$/', '', $matches);
+	if ($x > 0) {
+		assertType('int<1, max>', $x);
+		if (count($matches) === 2) {
+			assertType('array{non-falsy-string, non-empty-string}', $matches);
+			assertType('int<1, max>', $x);
+			return;
+		}
+		assertType('array{}|array{non-falsy-string, non-empty-string, non-empty-string, non-empty-string}', $matches);
+		assertType('int<1, max>', $x);
+	}
+};