From 56b1476d2976614110fe6cb0559040b2aa98d648 Mon Sep 17 00:00:00 2001
From: "github-actions[bot]"
 <41898282+github-actions[bot]@users.noreply.github.com>
Date: Mon, 30 Mar 2026 03:56:53 +0000
Subject: [PATCH] Fix phpstan/phpstan#10076: Union of string literal and
 class-string<T> loses literal members

- GenericClassStringType::isSuperTypeOf() returned Yes for non-class-string
  constants when the generic type was MixedType (including TemplateMixedType)
- This caused TypeCombinator::union to absorb string literals like 'object'
  and 'array' into class-string<T>, losing them from the union
- Added a check: when generic type is MixedType but the constant string is
  not a class-string, return Maybe instead of Yes
- New regression test in tests/PHPStan/Rules/Functions/data/bug-10076.php
---
 src/Type/Generic/GenericClassStringType.php   |  3 +++
 .../CallToFunctionParametersRuleTest.php      |  5 +++++
 .../Rules/Functions/data/bug-10076.php        | 20 +++++++++++++++++++
 3 files changed, 28 insertions(+)
 create mode 100644 tests/PHPStan/Rules/Functions/data/bug-10076.php

diff --git a/src/Type/Generic/GenericClassStringType.php b/src/Type/Generic/GenericClassStringType.php
index b4ac3eff88c..1d0cf1d5892 100644
--- a/src/Type/Generic/GenericClassStringType.php
+++ b/src/Type/Generic/GenericClassStringType.php
@@ -94,6 +94,9 @@ public function isSuperTypeOf(Type $type): IsSuperTypeOfResult
 		if ($type instanceof ConstantStringType) {
 			$genericType = $this->type;
 			if ($genericType instanceof MixedType) {
+				if (!$type->isClassString()->yes()) {
+					return IsSuperTypeOfResult::createMaybe();
+				}
 				return IsSuperTypeOfResult::createYes();
 			}
 
diff --git a/tests/PHPStan/Rules/Functions/CallToFunctionParametersRuleTest.php b/tests/PHPStan/Rules/Functions/CallToFunctionParametersRuleTest.php
index ee754a40d90..fb855592c83 100644
--- a/tests/PHPStan/Rules/Functions/CallToFunctionParametersRuleTest.php
+++ b/tests/PHPStan/Rules/Functions/CallToFunctionParametersRuleTest.php
@@ -2817,4 +2817,9 @@ public function testBug14312b(): void
 		$this->analyse([__DIR__ . '/data/bug-14312b.php'], []);
 	}
 
+	public function testBug10076(): void
+	{
+		$this->analyse([__DIR__ . '/data/bug-10076.php'], []);
+	}
+
 }
diff --git a/tests/PHPStan/Rules/Functions/data/bug-10076.php b/tests/PHPStan/Rules/Functions/data/bug-10076.php
new file mode 100644
index 00000000000..ca4a9b404b6
--- /dev/null
+++ b/tests/PHPStan/Rules/Functions/data/bug-10076.php
@@ -0,0 +1,20 @@
+<?php
+
+namespace Bug10076;
+
+/**
+ * @template T
+ *
+ * @param 'object'|'array'|class-string<T> $type
+ *
+ * @return list<mixed>
+ */
+function result($type = 'object'): array
+{
+	return [];
+}
+
+result();
+result('object');
+result('array');
+result(\DateTime::class);