Fix phpstan/phpstan#11565: False positive: Conditional return type takes the wrong branch (#5362)

Co-authored-by: github-actions[bot] <41898282+github-actions[bot]@users.noreply.github.com>
Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>
Co-authored-by: Markus Staab <markus.staab@redaxo.de>

Author: 4 people

src/Analyser/SpecifiedTypes.php

@@ -119,6 +119,21 @@ public function getRootExpr(): ?Expr
 		return $this->rootExpr;
 	}
 
+	public function removeExpr(string $exprString): self
+	{
+		$sureTypes = $this->sureTypes;
+		$sureNotTypes = $this->sureNotTypes;
+		unset($sureTypes[$exprString]);
+		unset($sureNotTypes[$exprString]);
+
+		$self = new self($sureTypes, $sureNotTypes);
+		$self->overwrite = $this->overwrite;
+		$self->newConditionalExpressionHolders = $this->newConditionalExpressionHolders;
+		$self->rootExpr = $this->rootExpr;
+
+		return $self;
+	}
+
 	/** @api */
 	public function intersectWith(SpecifiedTypes $other): self
 	{

src/Analyser/TypeSpecifier.php

@@ -814,6 +814,7 @@ public function specifyTypesInCondition(
 
 			if ($context->null()) {
 				$specifiedTypes = $this->specifyTypesInCondition($scope->exitFirstLevelStatements(), $expr->expr, $context)->setRootExpr($expr);
+				$specifiedTypes = $specifiedTypes->removeExpr($this->exprPrinter->printExpr($expr->var));
 			} else {
 				$specifiedTypes = $this->specifyTypesInCondition($scope->exitFirstLevelStatements(), $expr->var, $context)->setRootExpr($expr);
 			}

tests/PHPStan/Analyser/nsrt/bug-11565.php

@@ -0,0 +1,63 @@
+<?php declare(strict_types = 1);
+
+namespace Bug11565;
+
+use function PHPStan\Testing\assertType;
+
+/**
+ * @template T
+ * @param iterable<mixed, T> $iterable
+ * @return ($iterable is list ? never : list<T>)
+ */
+function iteratorToList(iterable $iterable): array {
+	$list = [];
+	foreach ($iterable as $item) {
+		$list[] = $item;
+	}
+	return $list;
+}
+
+/**
+ * @return iterable<string, string>
+ */
+function getItems(): iterable {
+	yield 'a' => 'foo';
+	yield 'b' => 'bar';
+}
+
+// Bug: when reassigning to the same variable, conditional return type resolves incorrectly
+$items = getItems();
+$items = iteratorToList($items);
+assertType('list<string>', $items);
+
+// Works fine when using a different variable
+$x = getItems();
+$items2 = iteratorToList($x);
+assertType('list<string>', $items2);
+
+// Same variable reassignment inside if condition (truthy context)
+// Non-null context recurses into $expr->var, not $expr->expr, so not affected
+$items3 = getItems();
+if ($items3 = iteratorToList($items3)) {
+	assertType('non-empty-list<string>', $items3);
+}
+
+// Property fetch as LHS - exercises removeExpr for non-Variable expressions
+class Holder {
+	/** @var iterable<string, string> */
+	public iterable $items;
+}
+
+function testPropertyFetch(Holder $holder): void {
+	$holder->items = iteratorToList($holder->items);
+	assertType('list<string>', $holder->items);
+}
+
+// Array dim fetch as LHS
+/**
+ * @param array{items: iterable<string, string>} $data
+ */
+function testArrayDimFetch(array $data): void {
+	$data['items'] = iteratorToList($data['items']);
+	assertType('list<string>', $data['items']);
+}