From dfdaf40fe7136e489559b1106d6421ce8c5d41a2 Mon Sep 17 00:00:00 2001
From: Markus Staab <maggus.staab@googlemail.com>
Date: Fri, 20 Mar 2026 11:52:47 +0100
Subject: [PATCH 01/13] Fix incorrect narrowing of nested array after
 assignment

---
 src/Analyser/ExprHandler/AssignHandler.php         | 14 ++++++++++++--
 .../PHPStan/Analyser/nsrt/assign-nested-arrays.php |  3 ++-
 tests/PHPStan/Rules/Arrays/data/bug-11679.php      |  3 ++-
 3 files changed, 16 insertions(+), 4 deletions(-)

diff --git a/src/Analyser/ExprHandler/AssignHandler.php b/src/Analyser/ExprHandler/AssignHandler.php
index 10b1f135eb4..f76020c2b5f 100644
--- a/src/Analyser/ExprHandler/AssignHandler.php
+++ b/src/Analyser/ExprHandler/AssignHandler.php
@@ -947,10 +947,11 @@ private function produceArrayDimFetchAssignValueToWrite(array $dimFetchStack, ar
 		$originalValueToWrite = $valueToWrite;
 
 		$offsetValueTypeStack = [$offsetValueType];
+		$overwrites = true;
 		foreach (array_slice($offsetTypes, 0, -1) as [$offsetType, $dimFetch]) {
 			if ($offsetType === null) {
 				$offsetValueType = new ConstantArrayType([], []);
-
+				$overwrites = false;
 			} else {
 				$has = $offsetValueType->hasOffsetValueType($offsetType);
 				if ($has->yes()) {
@@ -959,9 +960,11 @@ private function produceArrayDimFetchAssignValueToWrite(array $dimFetchStack, ar
 					if (!$scope->hasExpressionType($dimFetch)->yes()) {
 						$offsetValueType = TypeCombinator::union($offsetValueType->getOffsetValueType($offsetType), new ConstantArrayType([], []));
 					} else {
+						$overwrites = false;
 						$offsetValueType = $offsetValueType->getOffsetValueType($offsetType);
 					}
 				} else {
+					$overwrites = false;
 					$offsetValueType = new ConstantArrayType([], []);
 				}
 			}
@@ -1010,7 +1013,14 @@ private function produceArrayDimFetchAssignValueToWrite(array $dimFetchStack, ar
 				}
 
 			} else {
-				$valueToWrite = $offsetValueType->setOffsetValueType($offsetType, $valueToWrite, $i === 0);
+				$unionValues = false;
+				if ($i === 0) {
+					$unionValues = true;
+				} elseif ($overwrites === true && $i === count($offsetTypes) - 1) {
+					$unionValues = true;
+				}
+
+				$valueToWrite = $offsetValueType->setOffsetValueType($offsetType, $valueToWrite, $unionValues);
 			}
 
 			if ($arrayDimFetch === null || !$offsetValueType->isList()->yes()) {
diff --git a/tests/PHPStan/Analyser/nsrt/assign-nested-arrays.php b/tests/PHPStan/Analyser/nsrt/assign-nested-arrays.php
index 31cecaa4d1a..3de574894a4 100644
--- a/tests/PHPStan/Analyser/nsrt/assign-nested-arrays.php
+++ b/tests/PHPStan/Analyser/nsrt/assign-nested-arrays.php
@@ -12,8 +12,9 @@ public function doFoo(int $i)
 		$array = [];
 
 		$array[$i]['bar'] = 1;
-		$array[$i]['baz'] = 2;
+		assertType('non-empty-array<int, array{bar: 1}>', $array);
 
+		$array[$i]['baz'] = 2;
 		assertType('non-empty-array<int, array{bar: 1, baz: 2}>', $array);
 	}
 
diff --git a/tests/PHPStan/Rules/Arrays/data/bug-11679.php b/tests/PHPStan/Rules/Arrays/data/bug-11679.php
index 463362516aa..46374b8cb2f 100644
--- a/tests/PHPStan/Rules/Arrays/data/bug-11679.php
+++ b/tests/PHPStan/Rules/Arrays/data/bug-11679.php
@@ -31,7 +31,8 @@ public function sayHello(int $index): bool
 		assertType('array<int, array{foo?: bool}>', $this->arr);
 		if (!isset($this->arr[$index]['foo'])) {
 			$this->arr[$index]['foo'] = true;
-			assertType('non-empty-array<int, array{foo: true}>', $this->arr);
+			assertType('non-empty-array<int, array{foo?: bool}>', $this->arr);
+			assertType('true', $this->arr[$index]['foo']);
 		}
 		assertType('array<int, array{foo?: bool}>', $this->arr);
 		return $this->arr[$index]['foo']; // PHPStan does not realize 'foo' is set

From 7ffd3de459aae0cc6418ff2aab98bc411cdfa6a4 Mon Sep 17 00:00:00 2001
From: Markus Staab <maggus.staab@googlemail.com>
Date: Fri, 20 Mar 2026 11:54:14 +0100
Subject: [PATCH 02/13] Create bug-13857.php

---
 tests/PHPStan/Analyser/nsrt/bug-13857.php | 67 +++++++++++++++++++++++
 1 file changed, 67 insertions(+)
 create mode 100644 tests/PHPStan/Analyser/nsrt/bug-13857.php

diff --git a/tests/PHPStan/Analyser/nsrt/bug-13857.php b/tests/PHPStan/Analyser/nsrt/bug-13857.php
new file mode 100644
index 00000000000..737f17763e8
--- /dev/null
+++ b/tests/PHPStan/Analyser/nsrt/bug-13857.php
@@ -0,0 +1,67 @@
+<?php
+
+declare(strict_types = 1);
+
+namespace Bug13857;
+
+use function PHPStan\Testing\assertType;
+
+/**
+ * @param array<int, array{state: string}> $array
+ */
+function test(array $array, int $id): void {
+	$array[$id]['state'] = 'foo';
+	// only one element was set to 'foo', not all of them.
+	assertType("non-empty-array<int, array{state: string}>", $array);
+}
+
+/**
+ * @param array<int, array{state?: string}> $array
+ */
+function testMaybe(array $array, int $id): void {
+	$array[$id]['state'] = 'foo';
+	// only one element was set to 'foo', not all of them.
+	assertType("non-empty-array<int, array{state?: string}>", $array);
+}
+
+/**
+ * @param array<int, array{state: string|bool}> $array
+ */
+function testUnionValue(array $array, int $id): void {
+	$array[$id]['state'] = 'foo';
+	// only one element was set to 'foo', not all of them.
+	assertType("non-empty-array<int, array{state: bool|string}>", $array);
+}
+
+/**
+ * @param array<int, array{state: string}|array{foo: int}> $array
+ */
+function testUnionArray(array $array, int $id): void {
+	$array[$id]['state'] = 'foo';
+	// only one element was set to 'foo', not all of them.
+	assertType("non-empty-array<int, non-empty-array{foo?: int, state?: string}>", $array);
+}
+
+/**
+ * @param array<int, array{state: string}|array{foo: int}> $array
+ */
+function testUnionArrayDifferentType(array $array, int $id): void {
+	$array[$id]['state'] = true;
+	assertType("non-empty-array<int, array{state: string}|non-empty-array{foo?: int, state?: true}>", $array);
+}
+
+/**
+ * @param array<int, array{state: 'foo'}> $array
+ */
+function testConstantArray(array $array, int $id): void {
+	$array[$id]['state'] = 'bar';
+	assertType("non-empty-array<int, array{state: 'bar'}|array{state: 'foo'}>", $array);
+}
+
+/**
+ * @param array<int, array{state: 'foo'}> $array
+ */
+function testConstantArrayNonScalarAssign(array $array, int $id, bool $b): void {
+	$array[$id]['state'] = $b;
+	assertType("non-empty-array<int, array{state: 'foo'}|array{state: bool}>", $array);
+}

From 9311e604a30cfda91a17cb6bdd269c3e648595bf Mon Sep 17 00:00:00 2001
From: Markus Staab <maggus.staab@googlemail.com>
Date: Fri, 20 Mar 2026 12:13:18 +0100
Subject: [PATCH 03/13] Update AssignHandler.php

---
 src/Analyser/ExprHandler/AssignHandler.php | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/src/Analyser/ExprHandler/AssignHandler.php b/src/Analyser/ExprHandler/AssignHandler.php
index f76020c2b5f..977239cb1da 100644
--- a/src/Analyser/ExprHandler/AssignHandler.php
+++ b/src/Analyser/ExprHandler/AssignHandler.php
@@ -947,7 +947,7 @@ private function produceArrayDimFetchAssignValueToWrite(array $dimFetchStack, ar
 		$originalValueToWrite = $valueToWrite;
 
 		$offsetValueTypeStack = [$offsetValueType];
-		$overwrites = true;
+		$overwrites = $offsetTypes[array_key_last($offsetTypes)][0] !== null;
 		foreach (array_slice($offsetTypes, 0, -1) as [$offsetType, $dimFetch]) {
 			if ($offsetType === null) {
 				$offsetValueType = new ConstantArrayType([], []);

From c5ec96f432ba9c422f1610b1b267bda9f043b6b2 Mon Sep 17 00:00:00 2001
From: Markus Staab <maggus.staab@googlemail.com>
Date: Fri, 20 Mar 2026 12:17:51 +0100
Subject: [PATCH 04/13] Update AssignHandler.php

---
 src/Analyser/ExprHandler/AssignHandler.php | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/src/Analyser/ExprHandler/AssignHandler.php b/src/Analyser/ExprHandler/AssignHandler.php
index 977239cb1da..b5ac6667144 100644
--- a/src/Analyser/ExprHandler/AssignHandler.php
+++ b/src/Analyser/ExprHandler/AssignHandler.php
@@ -938,7 +938,7 @@ private function isImplicitArrayCreation(array $dimFetchStack, Scope $scope): Tr
 
 	/**
 	 * @param list<ArrayDimFetch> $dimFetchStack
-	 * @param list<array{Type|null, ArrayDimFetch}> $offsetTypes
+	 * @param non-empty-list<array{Type|null, ArrayDimFetch}> $offsetTypes
 	 *
 	 * @return array{Type, list<array{Expr, Type}>}
 	 */

From 44a4a9495f041463d2ba255c3c391adaa2f9d7cc Mon Sep 17 00:00:00 2001
From: Markus Staab <maggus.staab@googlemail.com>
Date: Fri, 20 Mar 2026 12:22:28 +0100
Subject: [PATCH 05/13] Update pr-4390.php

---
 tests/PHPStan/Analyser/nsrt/pr-4390.php | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/tests/PHPStan/Analyser/nsrt/pr-4390.php b/tests/PHPStan/Analyser/nsrt/pr-4390.php
index c318b9b6ee8..7a666f19c24 100644
--- a/tests/PHPStan/Analyser/nsrt/pr-4390.php
+++ b/tests/PHPStan/Analyser/nsrt/pr-4390.php
@@ -13,6 +13,6 @@ function (string $s): void {
 		}
 	}
 
-	assertType('non-empty-array<int<0, 9>, non-empty-array<int<0, 9>, string>>', $locations);
-	assertType('non-empty-array<int<0, 9>, string>', $locations[0]);
+	assertType('non-empty-array<int<0, 9>, array<int<0, 9>, string>>', $locations); // could be 'non-empty-array<int<0, 9>, non-empty-array<int<0, 9>, string>>'
+	assertType('array<int<0, 9>, string>', $locations[0]); // could be 'non-empty-array<int<0, 9>, string>'
 };

From fd70215da5dbfabc1d55da8eea69c58445eecb9d Mon Sep 17 00:00:00 2001
From: Markus Staab <maggus.staab@googlemail.com>
Date: Fri, 20 Mar 2026 14:50:49 +0100
Subject: [PATCH 06/13] Revert "Update pr-4390.php"

This reverts commit ab2ace493df7202cb58ce4f341e5761db7d3d946.
---
 tests/PHPStan/Analyser/nsrt/pr-4390.php | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/tests/PHPStan/Analyser/nsrt/pr-4390.php b/tests/PHPStan/Analyser/nsrt/pr-4390.php
index 7a666f19c24..c318b9b6ee8 100644
--- a/tests/PHPStan/Analyser/nsrt/pr-4390.php
+++ b/tests/PHPStan/Analyser/nsrt/pr-4390.php
@@ -13,6 +13,6 @@ function (string $s): void {
 		}
 	}
 
-	assertType('non-empty-array<int<0, 9>, array<int<0, 9>, string>>', $locations); // could be 'non-empty-array<int<0, 9>, non-empty-array<int<0, 9>, string>>'
-	assertType('array<int<0, 9>, string>', $locations[0]); // could be 'non-empty-array<int<0, 9>, string>'
+	assertType('non-empty-array<int<0, 9>, non-empty-array<int<0, 9>, string>>', $locations);
+	assertType('non-empty-array<int<0, 9>, string>', $locations[0]);
 };

From 9c7a3e43167cf46ebd57fa21c6449f8aa7b48f0a Mon Sep 17 00:00:00 2001
From: Markus Staab <maggus.staab@googlemail.com>
Date: Fri, 20 Mar 2026 16:37:32 +0100
Subject: [PATCH 07/13] fix

---
 src/Analyser/ExprHandler/AssignHandler.php | 10 +++++++++-
 1 file changed, 9 insertions(+), 1 deletion(-)

diff --git a/src/Analyser/ExprHandler/AssignHandler.php b/src/Analyser/ExprHandler/AssignHandler.php
index b5ac6667144..9cc5f98c0ce 100644
--- a/src/Analyser/ExprHandler/AssignHandler.php
+++ b/src/Analyser/ExprHandler/AssignHandler.php
@@ -1016,7 +1016,15 @@ private function produceArrayDimFetchAssignValueToWrite(array $dimFetchStack, ar
 				$unionValues = false;
 				if ($i === 0) {
 					$unionValues = true;
-				} elseif ($overwrites === true && $i === count($offsetTypes) - 1) {
+				} elseif (
+					$overwrites === true
+					&& $i === count($offsetTypes) - 1
+					&&
+						(
+							$originalValueToWrite->isConstantScalarValue()->yes()
+							|| !$offsetValueType->getIterableValueType()->isSuperTypeOf($valueToWrite)->yes()
+						)
+				) {
 					$unionValues = true;
 				}
 

From 674fdb8578e00dfc50a8e87107dc67e81f1d8551 Mon Sep 17 00:00:00 2001
From: Markus Staab <maggus.staab@googlemail.com>
Date: Fri, 20 Mar 2026 16:59:41 +0100
Subject: [PATCH 08/13] add regression test

---
 tests/PHPStan/Analyser/nsrt/bug-10089.php     | 44 +++++++++++++++++++
 ...rictComparisonOfDifferentTypesRuleTest.php |  5 +++
 2 files changed, 49 insertions(+)
 create mode 100644 tests/PHPStan/Analyser/nsrt/bug-10089.php

diff --git a/tests/PHPStan/Analyser/nsrt/bug-10089.php b/tests/PHPStan/Analyser/nsrt/bug-10089.php
new file mode 100644
index 00000000000..21122cdfc33
--- /dev/null
+++ b/tests/PHPStan/Analyser/nsrt/bug-10089.php
@@ -0,0 +1,44 @@
+<?php
+
+namespace Bug10089;
+
+
+use function PHPStan\Testing\assertType;
+
+class Test
+{
+
+	protected function create_matrix(int $size): array
+	{
+		$size = min(8, $size);
+		$matrix = [];
+		for ($i = 0; $i < $size; $i++) {
+			$matrix[] = array_fill(0, $size, 0);
+		}
+
+		// array<int<0, max>, non-empty-array<int, 0>>
+		assertType('list<non-empty-list<0>>', $matrix);
+
+		$matrix[$size - 1][8] = 3;
+
+		// non-empty-array<int, non-empty-array<int, 0|3>&hasOffsetValue(8, 3)>
+		assertType('non-empty-list<non-empty-array<int<0, max>, 0|3>>', $matrix);
+
+		for ($i = 0; $i <= $size; $i++) {
+			if ($matrix[$i][8] === 0) {
+				// ...
+			}
+			if ($matrix[8][$i] === 0) {
+				// ...
+			}
+			if ($matrix[$size - 1 - $i][8] === 0) {
+				// ...
+			}
+		}
+
+		return $matrix;
+	}
+
+}
+
+
diff --git a/tests/PHPStan/Rules/Comparison/StrictComparisonOfDifferentTypesRuleTest.php b/tests/PHPStan/Rules/Comparison/StrictComparisonOfDifferentTypesRuleTest.php
index 2450cb19b37..d5e7f59fd81 100644
--- a/tests/PHPStan/Rules/Comparison/StrictComparisonOfDifferentTypesRuleTest.php
+++ b/tests/PHPStan/Rules/Comparison/StrictComparisonOfDifferentTypesRuleTest.php
@@ -1046,6 +1046,11 @@ public function testBug13282(): void
 		$this->analyse([__DIR__ . '/../../Analyser/nsrt/bug-13282.php'], []);
 	}
 
+	public function testBug10089(): void
+	{
+		$this->analyse([__DIR__ . '/../../Analyser/nsrt/bug-10089.php'], []);
+	}
+
 	public function testBug11609(): void
 	{
 		$this->analyse([__DIR__ . '/data/bug-11609.php'], [

From 6a0b72a47a0464d6a21dc792e6d1d8867822f399 Mon Sep 17 00:00:00 2001
From: Markus Staab <maggus.staab@googlemail.com>
Date: Fri, 20 Mar 2026 17:14:38 +0100
Subject: [PATCH 09/13] Update AssignHandler.php

---
 src/Analyser/ExprHandler/AssignHandler.php | 10 +++++-----
 1 file changed, 5 insertions(+), 5 deletions(-)

diff --git a/src/Analyser/ExprHandler/AssignHandler.php b/src/Analyser/ExprHandler/AssignHandler.php
index 9cc5f98c0ce..24e2f6e29f0 100644
--- a/src/Analyser/ExprHandler/AssignHandler.php
+++ b/src/Analyser/ExprHandler/AssignHandler.php
@@ -947,11 +947,11 @@ private function produceArrayDimFetchAssignValueToWrite(array $dimFetchStack, ar
 		$originalValueToWrite = $valueToWrite;
 
 		$offsetValueTypeStack = [$offsetValueType];
-		$overwrites = $offsetTypes[array_key_last($offsetTypes)][0] !== null;
+		$overwritesExistingOffset = $offsetTypes[array_key_last($offsetTypes)][0] !== null;
 		foreach (array_slice($offsetTypes, 0, -1) as [$offsetType, $dimFetch]) {
 			if ($offsetType === null) {
 				$offsetValueType = new ConstantArrayType([], []);
-				$overwrites = false;
+				$overwritesExistingOffset = false;
 			} else {
 				$has = $offsetValueType->hasOffsetValueType($offsetType);
 				if ($has->yes()) {
@@ -960,11 +960,11 @@ private function produceArrayDimFetchAssignValueToWrite(array $dimFetchStack, ar
 					if (!$scope->hasExpressionType($dimFetch)->yes()) {
 						$offsetValueType = TypeCombinator::union($offsetValueType->getOffsetValueType($offsetType), new ConstantArrayType([], []));
 					} else {
-						$overwrites = false;
+						$overwritesExistingOffset = false;
 						$offsetValueType = $offsetValueType->getOffsetValueType($offsetType);
 					}
 				} else {
-					$overwrites = false;
+					$overwritesExistingOffset = false;
 					$offsetValueType = new ConstantArrayType([], []);
 				}
 			}
@@ -1017,7 +1017,7 @@ private function produceArrayDimFetchAssignValueToWrite(array $dimFetchStack, ar
 				if ($i === 0) {
 					$unionValues = true;
 				} elseif (
-					$overwrites === true
+					$overwritesExistingOffset === true
 					&& $i === count($offsetTypes) - 1
 					&&
 						(

From 1e002a79b7c99f8597a16e383e11d9a58c66eeda Mon Sep 17 00:00:00 2001
From: Markus Staab <maggus.staab@googlemail.com>
Date: Fri, 20 Mar 2026 17:55:01 +0100
Subject: [PATCH 10/13] Update AssignHandler.php

---
 src/Analyser/ExprHandler/AssignHandler.php | 10 +++++-----
 1 file changed, 5 insertions(+), 5 deletions(-)

diff --git a/src/Analyser/ExprHandler/AssignHandler.php b/src/Analyser/ExprHandler/AssignHandler.php
index 24e2f6e29f0..2f151eabb1b 100644
--- a/src/Analyser/ExprHandler/AssignHandler.php
+++ b/src/Analyser/ExprHandler/AssignHandler.php
@@ -947,11 +947,11 @@ private function produceArrayDimFetchAssignValueToWrite(array $dimFetchStack, ar
 		$originalValueToWrite = $valueToWrite;
 
 		$offsetValueTypeStack = [$offsetValueType];
-		$overwritesExistingOffset = $offsetTypes[array_key_last($offsetTypes)][0] !== null;
+		$generalizeOnWrite = $offsetTypes[array_key_last($offsetTypes)][0] !== null;
 		foreach (array_slice($offsetTypes, 0, -1) as [$offsetType, $dimFetch]) {
 			if ($offsetType === null) {
 				$offsetValueType = new ConstantArrayType([], []);
-				$overwritesExistingOffset = false;
+				$generalizeOnWrite = false;
 			} else {
 				$has = $offsetValueType->hasOffsetValueType($offsetType);
 				if ($has->yes()) {
@@ -960,11 +960,11 @@ private function produceArrayDimFetchAssignValueToWrite(array $dimFetchStack, ar
 					if (!$scope->hasExpressionType($dimFetch)->yes()) {
 						$offsetValueType = TypeCombinator::union($offsetValueType->getOffsetValueType($offsetType), new ConstantArrayType([], []));
 					} else {
-						$overwritesExistingOffset = false;
+						$generalizeOnWrite = false;
 						$offsetValueType = $offsetValueType->getOffsetValueType($offsetType);
 					}
 				} else {
-					$overwritesExistingOffset = false;
+					$generalizeOnWrite = false;
 					$offsetValueType = new ConstantArrayType([], []);
 				}
 			}
@@ -1017,7 +1017,7 @@ private function produceArrayDimFetchAssignValueToWrite(array $dimFetchStack, ar
 				if ($i === 0) {
 					$unionValues = true;
 				} elseif (
-					$overwritesExistingOffset === true
+					$generalizeOnWrite
 					&& $i === count($offsetTypes) - 1
 					&&
 						(

From 8aa457616cb80babebe33dab8eab716f384158ed Mon Sep 17 00:00:00 2001
From: Markus Staab <maggus.staab@googlemail.com>
Date: Fri, 20 Mar 2026 18:01:14 +0100
Subject: [PATCH 11/13] Update AssignHandler.php

---
 src/Analyser/ExprHandler/AssignHandler.php | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/src/Analyser/ExprHandler/AssignHandler.php b/src/Analyser/ExprHandler/AssignHandler.php
index 2f151eabb1b..fdd8e462b3b 100644
--- a/src/Analyser/ExprHandler/AssignHandler.php
+++ b/src/Analyser/ExprHandler/AssignHandler.php
@@ -1013,6 +1013,8 @@ private function produceArrayDimFetchAssignValueToWrite(array $dimFetchStack, ar
 				}
 
 			} else {
+				// when $unionValues=false the array-item type will be replaced with $valueToWrite
+				// when $unionValues=true the existing array item-type will be union with $valueToWrite
 				$unionValues = false;
 				if ($i === 0) {
 					$unionValues = true;

From 1af4f7847707ae7e52d5a199501e1558a58b2ded Mon Sep 17 00:00:00 2001
From: Markus Staab <maggus.staab@googlemail.com>
Date: Fri, 20 Mar 2026 18:02:33 +0100
Subject: [PATCH 12/13] Update AssignHandler.php

---
 src/Analyser/ExprHandler/AssignHandler.php | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/src/Analyser/ExprHandler/AssignHandler.php b/src/Analyser/ExprHandler/AssignHandler.php
index fdd8e462b3b..9d68c3a82dc 100644
--- a/src/Analyser/ExprHandler/AssignHandler.php
+++ b/src/Analyser/ExprHandler/AssignHandler.php
@@ -1013,7 +1013,7 @@ private function produceArrayDimFetchAssignValueToWrite(array $dimFetchStack, ar
 				}
 
 			} else {
-				// when $unionValues=false the array-item type will be replaced with $valueToWrite
+				// when $unionValues=false the array item-type will be replaced with $valueToWrite
 				// when $unionValues=true the existing array item-type will be union with $valueToWrite
 				$unionValues = false;
 				if ($i === 0) {

From d1ff83b8531bfdbf7106070430fd3dbbc266e88a Mon Sep 17 00:00:00 2001
From: Markus Staab <maggus.staab@googlemail.com>
Date: Fri, 20 Mar 2026 18:03:22 +0100
Subject: [PATCH 13/13] Update AssignHandler.php

---
 src/Analyser/ExprHandler/AssignHandler.php | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/src/Analyser/ExprHandler/AssignHandler.php b/src/Analyser/ExprHandler/AssignHandler.php
index 9d68c3a82dc..1baaa08905a 100644
--- a/src/Analyser/ExprHandler/AssignHandler.php
+++ b/src/Analyser/ExprHandler/AssignHandler.php
@@ -1014,7 +1014,7 @@ private function produceArrayDimFetchAssignValueToWrite(array $dimFetchStack, ar
 
 			} else {
 				// when $unionValues=false the array item-type will be replaced with $valueToWrite
-				// when $unionValues=true the existing array item-type will be union with $valueToWrite
+				// when $unionValues=true the existing array item-type will be union'ed with $valueToWrite -> type gets wider
 				$unionValues = false;
 				if ($i === 0) {
 					$unionValues = true;