Fix multi-dimensional array shape wrongly inferred with hasOffsetValue

- When assigning to a nested array with a non-constant outer key like
  $matrix[$size - 1][8] = 3, the HasOffsetValueType(8, 3) from the inner
  dimension was incorrectly propagated to ALL entries of the outer array
- Added logic in AssignHandler::produceArrayDimFetchAssignValueToWrite()
  to strip HasOffsetValueType from the inner value when the outer offset
  is non-constant and the inner dimension was not a tracked expression
  (i.e., not from a foreach binding)
- New regression test in tests/PHPStan/Analyser/nsrt/bug-10089.php

Fixes phpstan/phpstan#10089

Author: staabm

src/Analyser/ExprHandler/AssignHandler.php

@@ -55,6 +55,7 @@
 use PHPStan\Type\ConstantTypeHelper;
 use PHPStan\Type\ErrorType;
 use PHPStan\Type\IntegerRangeType;
+use PHPStan\Type\IntersectionType;
 use PHPStan\Type\MixedType;
 use PHPStan\Type\ObjectType;
 use PHPStan\Type\StaticTypeFactory;
@@ -969,6 +970,7 @@ private function produceArrayDimFetchAssignValueToWrite(array $dimFetchStack, ar
 			$offsetValueTypeStack[] = $offsetValueType;
 		}
 
+		$previousIterationUsedExistingBranch = false;
 		foreach (array_reverse($offsetTypes) as $i => [$offsetType]) {
 			/** @var Type $offsetValueType */
 			$offsetValueType = array_pop($offsetValueTypeStack);
@@ -1009,8 +1011,31 @@ private function produceArrayDimFetchAssignValueToWrite(array $dimFetchStack, ar
 					}
 				}
 
+				$previousIterationUsedExistingBranch = true;
 			} else {
-				$valueToWrite = $offsetValueType->setOffsetValueType($offsetType, $valueToWrite, $i === 0);
+				$innerValueToWrite = $valueToWrite;
+				if (
+					$i > 0
+					&& !$previousIterationUsedExistingBranch
+					&& $offsetType !== null
+					&& $offsetType->getConstantScalarValues() === []
+					&& $innerValueToWrite instanceof IntersectionType // @phpstan-ignore phpstanApi.instanceofType
+				) {
+					$filteredTypes = [];
+					$hasRemovedOffsetValue = false;
+					foreach ($innerValueToWrite->getTypes() as $innerType) {
+						if ($innerType instanceof HasOffsetValueType) {
+							$hasRemovedOffsetValue = true;
+							continue;
+						}
+						$filteredTypes[] = $innerType;
+					}
+					if ($hasRemovedOffsetValue && $filteredTypes !== []) {
+						$innerValueToWrite = TypeCombinator::intersect(...$filteredTypes);
+					}
+				}
+				$valueToWrite = $offsetValueType->setOffsetValueType($offsetType, $innerValueToWrite, $i === 0);
+				$previousIterationUsedExistingBranch = false;
 			}
 
 			if ($arrayDimFetch === null || !$offsetValueType->isList()->yes()) {

tests/PHPStan/Analyser/nsrt/bug-10089.php

@@ -0,0 +1,31 @@
+<?php
+
+declare(strict_types = 1);
+
+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);
+		}
+
+		$matrix[$size - 1][8] = 3;
+
+		assertType('non-empty-list<non-empty-array<int<0, max>, 0|3>>', $matrix);
+
+		for ($i = 0; $i <= $size; $i++) {
+			assertType('0|3', $matrix[$i][8]);
+		}
+
+		return $matrix;
+	}
+
+}