From c55c36a39dc7ff9eb1c93d4a90f53c84889d268d Mon Sep 17 00:00:00 2001
From: Richard van Velzen <richard@frank.nl>
Date: Mon, 25 Jul 2022 16:37:21 +0200
Subject: [PATCH] Fix incorrect mixed template type for impossible union
 template type intersection

---
 src/Type/TypeCombinator.php                   |  4 ++
 .../Analyser/NodeScopeResolverTest.php        |  1 +
 tests/PHPStan/Analyser/data/bug-7688.php      | 50 +++++++++++++++++++
 3 files changed, 55 insertions(+)
 create mode 100644 tests/PHPStan/Analyser/data/bug-7688.php

diff --git a/src/Type/TypeCombinator.php b/src/Type/TypeCombinator.php
index 8244bf601f..6cf51bc2f4 100644
--- a/src/Type/TypeCombinator.php
+++ b/src/Type/TypeCombinator.php
@@ -678,6 +678,10 @@ public static function intersect(Type ...$types): Type
 			}
 
 			$union = self::union(...$topLevelUnionSubTypes);
+			if ($union instanceof NeverType) {
+				return $union;
+			}
+
 			if ($type instanceof BenevolentUnionType) {
 				$union = TypeUtils::toBenevolentUnion($union);
 			}
diff --git a/tests/PHPStan/Analyser/NodeScopeResolverTest.php b/tests/PHPStan/Analyser/NodeScopeResolverTest.php
index e3bbf904f2..b28fd409ea 100644
--- a/tests/PHPStan/Analyser/NodeScopeResolverTest.php
+++ b/tests/PHPStan/Analyser/NodeScopeResolverTest.php
@@ -943,6 +943,7 @@ public function dataFileAsserts(): iterable
 			yield from $this->gatherAssertTypes(__DIR__ . '/data/bug-7663-php8.php');
 		}
 		yield from $this->gatherAssertTypes(__DIR__ . '/data/bug-7663.php');
+		yield from $this->gatherAssertTypes(__DIR__ . '/data/bug-7688.php');
 	}
 
 	/**
diff --git a/tests/PHPStan/Analyser/data/bug-7688.php b/tests/PHPStan/Analyser/data/bug-7688.php
new file mode 100644
index 0000000000..cc0f7818a8
--- /dev/null
+++ b/tests/PHPStan/Analyser/data/bug-7688.php
@@ -0,0 +1,50 @@
+<?php declare(strict_types = 1);
+
+namespace Bug7688;
+
+use function PHPStan\Testing\assertType;
+
+/**
+ * @template T of bool|null
+ * @param T|string $value
+ * @return T|non-empty-string
+ */
+function foo($value)
+{
+	if (is_string($value)) {
+		assertType('string', $value);
+		return $value === '' ? 'non-empty' : $value;
+	}
+
+	return $value;
+}
+
+/**
+ * @template T
+ * @param T|string $value
+ * @return T|non-empty-string
+ */
+function bar($value)
+{
+	if (is_string($value)) {
+		assertType('string', $value);
+		return $value === '' ? 'non-empty' : $value;
+	}
+
+	return $value;
+}
+
+/**
+ * @template T of bool|null
+ * @param T|int $value
+ * @return T|int<1,max>
+ */
+function baz($value)
+{
+	if (is_int($value)) {
+		assertType('int', $value);
+		return $value < 1 ? 1 : $value;
+	}
+
+	return $value;
+}