From 0ac8116e3c54f679392b57cdbbca134d19970d45 Mon Sep 17 00:00:00 2001
From: Ondrej Mirtes <ondrej@mirtes.cz>
Date: Tue, 28 Jul 2026 17:11:18 +0200
Subject: [PATCH 1/2] Treat a property with a default value as always set in
 isset resolution

issetCheck() treated every native non-virtual property without a tracked
expression type as possibly uninitialized. A property with a default
value cannot be uninitialized, so consult hasDefaultValue() in the
guard. This restores narrowing through ?? (the coalesce only builds the
left-is-null scope for its right side when the left is surely set) and
makes isset() on a defaulted non-nullable property infer true.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_019wqGgaD7iqL44t1KgpJS7b
---
 src/Analyser/MutatingScope.php                |  5 ++-
 .../nsrt/isset-coalesce-empty-type.php        |  2 +-
 .../nsrt/isset-property-default-value.php     | 32 +++++++++++++++++++
 3 files changed, 37 insertions(+), 2 deletions(-)
 create mode 100644 tests/PHPStan/Analyser/nsrt/isset-property-default-value.php

diff --git a/src/Analyser/MutatingScope.php b/src/Analyser/MutatingScope.php
index f8219658d15..8cc3329b835 100644
--- a/src/Analyser/MutatingScope.php
+++ b/src/Analyser/MutatingScope.php
@@ -1160,7 +1160,10 @@ public function issetCheck(Expr $expr, callable $typeCallback, ?bool $result = n
 			if ($propertyReflection->hasNativeType() && !$propertyReflection->isVirtual()->yes()) {
 				if (!$this->hasExpressionType($expr)->yes()) {
 					$nativeReflection = $propertyReflection->getNativeReflection();
-					if ($nativeReflection === null || !$nativeReflection->isPromoted() || (!$nativeReflection->isReadOnly() && !$nativeReflection->isHooked())) {
+					if (
+						($nativeReflection === null || !$nativeReflection->getNativeReflection()->hasDefaultValue())
+						&& ($nativeReflection === null || !$nativeReflection->isPromoted() || (!$nativeReflection->isReadOnly() && !$nativeReflection->isHooked()))
+					) {
 						if ($expr instanceof Node\Expr\PropertyFetch) {
 							return $this->issetCheckUndefined($expr->var);
 						}
diff --git a/tests/PHPStan/Analyser/nsrt/isset-coalesce-empty-type.php b/tests/PHPStan/Analyser/nsrt/isset-coalesce-empty-type.php
index ad81a1e6ac1..caa54683c96 100644
--- a/tests/PHPStan/Analyser/nsrt/isset-coalesce-empty-type.php
+++ b/tests/PHPStan/Analyser/nsrt/isset-coalesce-empty-type.php
@@ -246,7 +246,7 @@ class FooNativeProp
 	public int $canBeUninitialized;
 
 	function doFoo(FooNativeProp $foo): void {
-		assertType('bool', isset($foo->hasDefaultValue));
+		assertType('true', isset($foo->hasDefaultValue));
 
 		$foo->isAssignedBefore = 5;
 		assertType('true', isset($foo->isAssignedBefore));
diff --git a/tests/PHPStan/Analyser/nsrt/isset-property-default-value.php b/tests/PHPStan/Analyser/nsrt/isset-property-default-value.php
new file mode 100644
index 00000000000..0fc19bb8f6e
--- /dev/null
+++ b/tests/PHPStan/Analyser/nsrt/isset-property-default-value.php
@@ -0,0 +1,32 @@
+<?php declare(strict_types = 1);
+
+namespace IssetPropertyDefaultValue;
+
+use function PHPStan\Testing\assertType;
+
+class Holder
+{
+
+	public ?int $value = null;
+
+	public ?int $noDefault;
+
+}
+
+function coalesceWithDefault(Holder $a, Holder $b): void
+{
+	if ($a->value === null && $b->value === null) {
+		throw new \LogicException();
+	}
+
+	assertType('int', $a->value ?? $b->value);
+}
+
+function coalesceWithoutDefault(Holder $a, Holder $b): void
+{
+	if ($a->noDefault === null && $b->noDefault === null) {
+		throw new \LogicException();
+	}
+
+	assertType('int|null', $a->noDefault ?? $b->noDefault);
+}

From 96eb99e1e4cb45538f00551592466c13ed83294f Mon Sep 17 00:00:00 2001
From: Ondrej Mirtes <ondrej@mirtes.cz>
Date: Tue, 28 Jul 2026 17:19:04 +0200
Subject: [PATCH 2/2] Add regression test for #10786

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_019wqGgaD7iqL44t1KgpJS7b
---
 tests/PHPStan/Analyser/nsrt/bug-10786.php | 23 +++++++++++++++++++++++
 1 file changed, 23 insertions(+)
 create mode 100644 tests/PHPStan/Analyser/nsrt/bug-10786.php

diff --git a/tests/PHPStan/Analyser/nsrt/bug-10786.php b/tests/PHPStan/Analyser/nsrt/bug-10786.php
new file mode 100644
index 00000000000..4dc9333aba6
--- /dev/null
+++ b/tests/PHPStan/Analyser/nsrt/bug-10786.php
@@ -0,0 +1,23 @@
+<?php declare(strict_types = 1);
+
+namespace Bug10786;
+
+use function PHPStan\Testing\assertType;
+
+class Value {
+	public ?int	$value = null;
+}
+
+class HelloWorld
+{
+	public function sayHello(Value $a, Value $b): int
+	{
+		if (is_null($a->value) && is_null($b->value)) {
+			throw new \Exception();
+		}
+
+		assertType('int', $a->value ?? $b->value);
+
+		return $a->value ?? $b->value;
+	}
+}