From 811ca69a1890477caa260b0353bb52bf36b886f8 Mon Sep 17 00:00:00 2001
From: ondrejmirtes <104888+ondrejmirtes@users.noreply.github.com>
Date: Mon, 9 Mar 2026 16:12:47 +0000
Subject: [PATCH] Fix union of constant string types lost when used with
 generics

- Changed TemplateTypeHelper::generalizeInferredTemplateType() to only
  generalize integer types (not strings) when template bound is array-key
- Previously, all scalar constant values were generalized when the bound
  was array-key, turning 'one'|'two' into string
- Updated test expectations in bug-13144.php and
  native-reflection-default-values.php to reflect the more precise types
- New regression test in tests/PHPStan/Analyser/nsrt/bug-8031.php

Closes https://github.com/phpstan/phpstan/issues/8031
---
 src/Type/Generic/TemplateTypeHelper.php       |  4 +--
 tests/PHPStan/Analyser/nsrt/bug-13144.php     |  2 +-
 tests/PHPStan/Analyser/nsrt/bug-8031.php      | 32 +++++++++++++++++++
 .../nsrt/native-reflection-default-values.php |  2 +-
 4 files changed, 36 insertions(+), 4 deletions(-)
 create mode 100644 tests/PHPStan/Analyser/nsrt/bug-8031.php

diff --git a/src/Type/Generic/TemplateTypeHelper.php b/src/Type/Generic/TemplateTypeHelper.php
index 6f09c29ccb..5933be8e5b 100644
--- a/src/Type/Generic/TemplateTypeHelper.php
+++ b/src/Type/Generic/TemplateTypeHelper.php
@@ -142,9 +142,9 @@ public static function generalizeInferredTemplateType(TemplateType $templateType
 	{
 		if (!$templateType->getVariance()->covariant()) {
 			$isArrayKey = $templateType->getBound()->describe(VerbosityLevel::precise()) === '(int|string)';
-			if ($type->isScalar()->yes() && $isArrayKey) {
+			if ($type->isInteger()->yes() && $isArrayKey) {
 				$type = $type->generalize(GeneralizePrecision::templateArgument());
-			} elseif ($type->isConstantValue()->yes() && (!$templateType->getBound()->isScalar()->yes() || $isArrayKey)) {
+			} elseif ($type->isConstantValue()->yes() && !$templateType->getBound()->isScalar()->yes()) {
 				$type = $type->generalize(GeneralizePrecision::templateArgument());
 			}
 		}
diff --git a/tests/PHPStan/Analyser/nsrt/bug-13144.php b/tests/PHPStan/Analyser/nsrt/bug-13144.php
index fb47f4d862..280c6fa07c 100644
--- a/tests/PHPStan/Analyser/nsrt/bug-13144.php
+++ b/tests/PHPStan/Analyser/nsrt/bug-13144.php
@@ -8,7 +8,7 @@
 
 $arr = new ArrayObject(['a' => 1, 'b' => 2]);
 
-assertType('ArrayObject<string, int>', $arr); // correctly inferred as `ArrayObject<string, int>`
+assertType("ArrayObject<'a'|'b', int>", $arr);
 
 $a = $arr['a']; // ok
 $b = $arr['b']; // ok
diff --git a/tests/PHPStan/Analyser/nsrt/bug-8031.php b/tests/PHPStan/Analyser/nsrt/bug-8031.php
new file mode 100644
index 0000000000..e07707109a
--- /dev/null
+++ b/tests/PHPStan/Analyser/nsrt/bug-8031.php
@@ -0,0 +1,32 @@
+<?php // lint >= 8.0
+
+declare(strict_types = 1);
+
+namespace Bug8031;
+
+use function PHPStan\Testing\assertType;
+
+/**
+ * @template TKey of array-key
+ * @template TValue of mixed
+ */
+class Collection
+{
+	/**
+	 * @param array<TKey, TValue> $val
+	 */
+	public function __construct(protected array $val) {}
+}
+
+/**
+ * @return Collection<'one'|'two', int>
+ */
+function test(): Collection
+{
+	$c = new Collection([
+		'one' => 1,
+		'two' => 2,
+	]);
+	assertType("Bug8031\Collection<'one'|'two', int>", $c);
+	return $c;
+}
diff --git a/tests/PHPStan/Analyser/nsrt/native-reflection-default-values.php b/tests/PHPStan/Analyser/nsrt/native-reflection-default-values.php
index 5d0b8cdeab..86bc65ddf4 100644
--- a/tests/PHPStan/Analyser/nsrt/native-reflection-default-values.php
+++ b/tests/PHPStan/Analyser/nsrt/native-reflection-default-values.php
@@ -7,5 +7,5 @@
 function () {
 	assertType('ArrayObject<*NEVER*, *NEVER*>', new \ArrayObject());
 	assertType('ArrayObject<*NEVER*, *NEVER*>', new \ArrayObject([]));
-	assertType('ArrayObject<string, int>', new \ArrayObject(['key' => 1]));
+	assertType("ArrayObject<'key', int>", new \ArrayObject(['key' => 1]));
 };