From 2716e226bbf11bdc39a2b8148ac7e292e9692e32 Mon Sep 17 00:00:00 2001
From: "github-actions[bot]"
 <41898282+github-actions[bot]@users.noreply.github.com>
Date: Tue, 10 Mar 2026 15:33:25 +0000
Subject: [PATCH] Fix phpstan/phpstan#11705: variable type forgotten for array
 dim fetch after narrowing

- In MutatingScope::resolveType(), when an ArrayDimFetch has a stored expression type
  and its dim has been narrowed to a constant scalar value, recompute the offset value
  type from the current array and dim types
- Only replace the stored type when the recomputed type is strictly more specific
- New regression test in tests/PHPStan/Analyser/nsrt/bug-11705.php
- Root cause: array_key_exists with non-constant key stored a broad type for the
  ArrayDimFetch expression, which was not updated when the key was later narrowed
  (e.g., in a switch case)
---
 src/Analyser/MutatingScope.php            | 19 +++++++++++++-
 tests/PHPStan/Analyser/nsrt/bug-11705.php | 31 +++++++++++++++++++++++
 2 files changed, 49 insertions(+), 1 deletion(-)
 create mode 100644 tests/PHPStan/Analyser/nsrt/bug-11705.php

diff --git a/src/Analyser/MutatingScope.php b/src/Analyser/MutatingScope.php
index f1dfb1f0da..d8b2f5524b 100644
--- a/src/Analyser/MutatingScope.php
+++ b/src/Analyser/MutatingScope.php
@@ -1043,7 +1043,24 @@ private function resolveType(string $exprString, Expr $node): Type
 			&& !$node instanceof Expr\ArrowFunction
 			&& $this->hasExpressionType($node)->yes()
 		) {
-			return $this->expressionTypes[$exprString]->getType();
+			$type = $this->expressionTypes[$exprString]->getType();
+
+			if ($node instanceof Expr\ArrayDimFetch && $node->dim !== null) {
+				$dimType = $this->getType($node->dim);
+				if ($dimType->isConstantScalarValue()->yes()) {
+					$arrayType = $this->getType($node->var);
+					$offsetValueType = $arrayType->getOffsetValueType($dimType);
+					if (
+						!$offsetValueType instanceof ErrorType
+						&& $type->isSuperTypeOf($offsetValueType)->yes()
+						&& !$offsetValueType->isSuperTypeOf($type)->yes()
+					) {
+						$type = $offsetValueType;
+					}
+				}
+			}
+
+			return $type;
 		}
 
 		/** @var ExprHandler<Expr> $exprHandler */
diff --git a/tests/PHPStan/Analyser/nsrt/bug-11705.php b/tests/PHPStan/Analyser/nsrt/bug-11705.php
new file mode 100644
index 0000000000..5e29e27fc0
--- /dev/null
+++ b/tests/PHPStan/Analyser/nsrt/bug-11705.php
@@ -0,0 +1,31 @@
+<?php declare(strict_types = 1);
+
+namespace Bug11705;
+
+use function PHPStan\Testing\assertType;
+
+/**
+ * @param array{'name':string,'owners':array<int,string>} $theInput
+ * @param array<int,string> $theTags
+ */
+function example(array $theInput, array $theTags): void
+{
+	foreach ($theTags as $tag) {
+		if (!array_key_exists($tag, $theInput)) {
+			continue;
+		}
+		switch ($tag) {
+			case 'name':
+				assertType("'name'", $tag);
+				assertType('string', $theInput[$tag]);
+				if ($tag === 'name') {
+					echo "Of course it is...";
+				}
+				assertType("'name'", $tag);
+				assertType('string', $theInput[$tag]);
+				break;
+			default:
+				// fall out
+		}
+	}
+}