Improve ConstantArrayType inference

Author: staabm

src/Type/ArrayType.php

@@ -371,6 +371,22 @@ public function setOffsetValueType(?Type $offsetType, Type $valueType, bool $uni
 
 	public function setExistingOffsetValueType(Type $offsetType, Type $valueType): Type
 	{
+		if ($this->itemType->isConstantArray()->yes() && $valueType->isConstantArray()->yes()) {
+			$newItemType = $this->itemType;
+			foreach ($valueType->getConstantArrays() as $constArray) {
+				foreach ($constArray->getKeyTypes() as $keyType) {
+					$newItemType = $newItemType->setExistingOffsetValueType($keyType, $constArray->getOffsetValueType($keyType));
+				}
+			}
+
+			if ($newItemType !== $this->itemType) {
+				return new self(
+					$this->keyType,
+					$newItemType,
+				);
+			}
+		}
+
 		return new self(
 			$this->keyType,
 			TypeCombinator::union($this->itemType, $valueType),

tests/PHPStan/Analyser/nsrt/bug-11846.php

@@ -13,16 +13,16 @@ function demo(): void
 		$outerList[$id] = [];
 		array_push($outerList[$id], []);
 	}
-	assertType('non-empty-array<1|2, array{}|array{array{}}>', $outerList);
+	assertType('non-empty-array<1|2, array{array{}}>', $outerList);
 
 	foreach ($outerList as $key => $outerElement) {
 		$result = false;
 
-		assertType('array{}|array{array{}}', $outerElement);
+		assertType('array{array{}}', $outerElement);
 		foreach ($outerElement as $innerElement) {
 			$result = true;
 		}
-		assertType('bool', $result); // could be 'true'
+		assertType('true', $result);
 
 	}
 }