From 4457c55eda33ef04164f531e42f382c0a1a14f52 Mon Sep 17 00:00:00 2001
From: staabm <120441+staabm@users.noreply.github.com>
Date: Sat, 28 Feb 2026 10:13:27 +0000
Subject: [PATCH] Fix incorrect dependent type inference after repeated boolean
 checks

- Fixed conditional expression resolution in filterBySpecifiedTypes to intersect types
  instead of overwriting when multiple conditional expressions fire for the same target
- When two conditionals with the same guard produced different types (one more specific
  than the other), the less specific type could overwrite specifiedExpressions, causing
  cascading wrong matches that led to variables being incorrectly narrowed to *NEVER*
- New regression test in tests/PHPStan/Analyser/nsrt/bug-14211.php

Closes https://github.com/phpstan/phpstan/issues/14211
---
 src/Analyser/MutatingScope.php            | 10 ++++++++-
 tests/PHPStan/Analyser/nsrt/bug-14211.php | 25 +++++++++++++++++++++++
 2 files changed, 34 insertions(+), 1 deletion(-)
 create mode 100644 tests/PHPStan/Analyser/nsrt/bug-14211.php

diff --git a/src/Analyser/MutatingScope.php b/src/Analyser/MutatingScope.php
index a26a86a066..48f592e4c5 100644
--- a/src/Analyser/MutatingScope.php
+++ b/src/Analyser/MutatingScope.php
@@ -3833,7 +3833,15 @@ public function filterBySpecifiedTypes(SpecifiedTypes $specifiedTypes): self
 					}
 
 					$conditions[$conditionalExprString][] = $conditionalExpression;
-					$specifiedExpressions[$conditionalExprString] = $conditionalExpression->getTypeHolder();
+					$newTypeHolder = $conditionalExpression->getTypeHolder();
+					if (array_key_exists($conditionalExprString, $specifiedExpressions) && $specifiedExpressions[$conditionalExprString]->getCertainty()->yes() && $newTypeHolder->getCertainty()->yes()) {
+						$specifiedExpressions[$conditionalExprString] = ExpressionTypeHolder::createYes(
+							$newTypeHolder->getExpr(),
+							TypeCombinator::intersect($specifiedExpressions[$conditionalExprString]->getType(), $newTypeHolder->getType()),
+						);
+					} else {
+						$specifiedExpressions[$conditionalExprString] = $newTypeHolder;
+					}
 				}
 			}
 		}
diff --git a/tests/PHPStan/Analyser/nsrt/bug-14211.php b/tests/PHPStan/Analyser/nsrt/bug-14211.php
new file mode 100644
index 0000000000..8effe5a25a
--- /dev/null
+++ b/tests/PHPStan/Analyser/nsrt/bug-14211.php
@@ -0,0 +1,25 @@
+<?php declare(strict_types=1);
+
+namespace Bug14211;
+
+use function PHPStan\Testing\assertType;
+
+/** @param array<mixed> $data */
+function doSomething(array $data): bool {
+
+	if (!isset($data['x']))
+		return false;
+
+	$m = isset($data['y']);
+
+	if ($m) {
+		assertType('true', $m);
+	}
+	assertType('bool', $m);
+
+	if ($m) {
+		assertType('true', $m);
+	}
+
+	return true;
+}