Do not narrow the falsey branch of a nested isset() at its intermediate offset

The falsey-branch dim-fetch narrowing in IssetHandler::specifyTypes() was
written for a single-level isset(), where the target's var is a plain variable
or property. For a nested isset() like isset($r['K']['Port']), the target's var
is itself an ArrayDimFetch ($r['K']) that may not exist, and narrowing that
intermediate offset in the falsey branch leaks its existence into the enclosing
scope, so $r['K'] ?? null lost its |null after the check.

Skip the block when the var is itself an offset access. Single-level isset()
keeps the narrowing #4983 added.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

Author: SanderMuller

src/Analyser/ExprHandler/IssetHandler.php

@@ -196,6 +196,10 @@ public function specifyTypes(TypeSpecifier $typeSpecifier, Scope $scope, Expr $e
 			if (
 				$issetExpr instanceof ArrayDimFetch
 				&& $issetExpr->dim !== null
+				// When the var is itself an offset access (a nested isset like
+				// $r['K']['Port']), narrowing it in the falsey branch leaks the
+				// intermediate offset's existence into the enclosing scope.
+				&& !($issetExpr->var instanceof ArrayDimFetch)
 			) {
 				$varType = $scope->getType($issetExpr->var);
 				if (!$varType instanceof MixedType) {

tests/PHPStan/Analyser/nsrt/bug-15005.php

@@ -0,0 +1,73 @@
+<?php declare(strict_types = 1);
+
+namespace Bug15005;
+
+use function PHPStan\Testing\assertType;
+
+/** @param array<string, array{Port: int, Secure: string|null}> $r */
+function nestedIssetLeak(array $r): void
+{
+	assertType('array{Port: int, Secure: string|null}|null', $r['K'] ?? null);
+
+	$port = isset($r['K']['Port']) ? $r['K']['Port'] : null;
+
+	assertType('array{Port: int, Secure: string|null}|null', $r['K'] ?? null);
+
+	$secure = $r['K']['Secure'] ?? null;
+
+	echo $port, $secure;
+}
+
+/** @param array<string, array{Port: int, Secure: string|null}> $r */
+function alsoAfterPlainIf(array $r): void
+{
+	if (isset($r['K']['Port'])) {
+		echo $r['K']['Port'];
+	}
+
+	assertType('array{Port: int, Secure: string|null}|null', $r['K'] ?? null);
+}
+
+/** @param array<string, array{Port: int, Secure: string|null}> $r */
+function notWithCoalesce(array $r): void
+{
+	$port = $r['K']['Port'] ?? null;
+	assertType('array{Port: int, Secure: string|null}|null', $r['K'] ?? null);
+	echo $port;
+}
+
+/** @param array<string, string|null> $r */
+function notWithSingleLevel(array $r): void
+{
+	$port = isset($r['K']) ? $r['K'] : null;
+	assertType('string|null', $r['K'] ?? null);
+	echo $port;
+}
+
+/** @param array<string, array<string, array{Port: int}>> $r */
+function threeLevels(array $r): void
+{
+	if (isset($r['A']['B']['Port'])) {
+		echo $r['A']['B']['Port'];
+	}
+
+	assertType('array{Port: int}|null', $r['A']['B'] ?? null);
+	assertType('array<string, array{Port: int}>|null', $r['A'] ?? null);
+}
+
+class Holder
+{
+
+	/** @var array<string, array{Port: int, Secure: string|null}> */
+	public array $arr = [];
+
+	public function doFoo(): void
+	{
+		if (isset($this->arr['K']['Port'])) {
+			echo $this->arr['K']['Port'];
+		}
+
+		assertType('array{Port: int, Secure: string|null}|null', $this->arr['K'] ?? null);
+	}
+
+}