Unsetting optional offset might still give a list.

src/Type/Constant/ConstantArrayType.php

@@ -741,7 +741,12 @@ public function unsetOffset(Type $offsetType): Type
 					$k++;
 				}
 
-				return new self($newKeyTypes, $newValueTypes, $this->nextAutoIndexes, $newOptionalKeys, TrinaryLogic::createNo());
+				$newIsList = TrinaryLogic::createNo();
+				if (!$this->isList->no() && in_array($i, $this->optionalKeys, true)) {
+					$newIsList = TrinaryLogic::createMaybe();
+				}
+
+				return new self($newKeyTypes, $newValueTypes, $this->nextAutoIndexes, $newOptionalKeys, $newIsList);
 			}
 
 			return $this;

tests/PHPStan/Analyser/nsrt/bug-14177.php

@@ -0,0 +1,119 @@
+<?php declare(strict_types = 1);
+
+namespace Bug14177;
+
+use function PHPStan\Testing\assertType;
+
+class HelloWorld
+{
+	/**
+	 * @param list{0: string, 1: string, 2?: string, 3?: string} $b
+	 */
+	public function testList(array $b): void
+	{
+		if (array_key_exists(3, $b)) {
+			assertType('list{0: string, 1: string, 2?: string, 3: string}', $b);
+		} else {
+			assertType('list{0: string, 1: string, 2?: string}', $b);
+		}
+		assertType('list{0: string, 1: string, 2?: string, 3?: string}', $b);
+	}
+
+	/**
+	 * @param list{0: string, 1: string, 2?: string, 3?: string} $b
+	 */
+	public function testUnset0(array $b): void
+	{
+		assertType('true', array_is_list($b));
+		unset($b[0]);
+		assertType('false', array_is_list($b));
+		$b[] = 'foo';
+		assertType('false', array_is_list($b));
+	}
+
+	/**
+	 * @param list{0: string, 1: string, 2?: string, 3?: string} $b
+	 */
+	public function testUnset1(array $b): void
+	{
+		assertType('true', array_is_list($b));
+		unset($b[1]);
+		assertType('bool', array_is_list($b));
+		$b[] = 'foo';
+		assertType('false', array_is_list($b));
+	}
+
+	/**
+	 * @param list{0: string, 1: string, 2?: string, 3?: string} $b
+	 */
+	public function testUnset2(array $b): void
+	{
+		assertType('true', array_is_list($b));
+		unset($b[2]);
+		assertType('bool', array_is_list($b));
+		$b[] = 'foo';
+		assertType('false', array_is_list($b));
+	}
+
+	/**
+	 * @param list{0: string, 1: string, 2?: string, 3?: string} $b
+	 */
+	public function testUnset3(array $b): void
+	{
+		assertType('true', array_is_list($b));
+		unset($b[3]);
+		assertType('true', array_is_list($b));
+		$b[] = 'foo';
+		assertType('false', array_is_list($b));
+	}
+
+	public function placeholderToEditor(string $html): void
+	{
+		$result = preg_replace_callback(
+			'~\[image\\sid="(\\d+)"(?:\\shref="([^"]*)")?(?:\\sclass="([^"]*)")?\]~',
+			function (array $matches): string {
+				$id = (int) $matches[1];
+
+				assertType('list{0: non-falsy-string, 1: numeric-string, 2?: string, 3?: string}', $matches);
+
+				$replacement = sprintf(
+					'<img src="%s"%s/>',
+					$id,
+					array_key_exists(3, $matches) ? sprintf(' class="%s"', $matches[3]) : '',
+				);
+
+				assertType('list{0: non-falsy-string, 1: numeric-string, 2?: string, 3?: string}', $matches);
+
+				return array_key_exists(2, $matches) && $matches[2] !== ''
+					? sprintf('<a href="%s">%s</a>', $matches[2], $replacement)
+					: $replacement;
+			},
+			$html,
+		);
+	}
+
+	public function placeholderToEditor2(string $html): void
+	{
+		$result = preg_replace_callback(
+			'~\[image\\sid="(\\d+)?"(?:\\shref="([^"]*)")?(?:\\sclass="([^"]*)")?\]~',
+			function (array $matches): string {
+				$id = (int) $matches[0];
+
+				assertType('list{0: non-falsy-string, 1?: \'\'|numeric-string, 2?: string, 3?: string}', $matches);
+
+				$replacement = sprintf(
+					'<img src="%s"%s/>',
+					$id,
+					array_key_exists(2, $matches) ? sprintf(' class="%s"', $matches[2]) : '',
+				);
+
+				assertType('list{0: non-falsy-string, 1?: \'\'|numeric-string, 2?: string, 3?: string}', $matches);
+
+				return array_key_exists(1, $matches) && $matches[1] !== ''
+					? sprintf('<a href="%s">%s</a>', $matches[1], $replacement)
+					: $replacement;
+			},
+			$html,
+		);
+	}
+}

tests/PHPStan/Rules/Comparison/ImpossibleCheckTypeFunctionCallRuleTest.php

@@ -1145,4 +1145,10 @@ public function testPr4375(): void
 		$this->analyse([__DIR__ . '/data/pr-4375.php'], []);
 	}
 
+	public function testBug14177(): void
+	{
+		$this->treatPhpDocTypesAsCertain = true;
+		$this->analyse([__DIR__ . '/data/bug-14177.php'], []);
+	}
+
 }

tests/PHPStan/Rules/Comparison/data/bug-14177.php

@@ -0,0 +1,27 @@
+<?php declare(strict_types = 1);
+
+namespace Bug14177;
+
+class HelloWorld
+{
+	public function placeholderToEditor(string $html): void
+	{
+		$result = preg_replace_callback(
+			'~\[image\\sid="(\\d+)"(?:\\shref="([^"]*)")?(?:\\sclass="([^"]*)")?]~',
+			function (array $matches): string {
+				$id = (int) $matches[1];
+
+				$replacement = sprintf(
+					'<img src="%s"%s/>',
+					$id,
+					array_key_exists(3, $matches) ? sprintf(' class="%s"', $matches[3]) : '',
+				);
+
+				return array_key_exists(2, $matches) && $matches[2] !== ''
+					? sprintf('<a href="%s">%s</a>', $matches[2], $replacement)
+					: $replacement;
+			},
+			$html,
+		);
+	}
+}