Fix array + array inference

Author: VincentLanglet

src/Reflection/InitializerExprTypeResolver.php

@@ -1499,18 +1499,45 @@ public function getPlusTypeFromTypes(Expr $left, Expr $right, Type $leftType, Ty
 				$keyType = TypeCombinator::union(...$keyTypes);
 			}
 
+			$leftIterableValueType = $leftType->getIterableValueType();
 			$arrayType = new ArrayType(
 				$keyType,
-				TypeCombinator::union($leftType->getIterableValueType(), $rightType->getIterableValueType()),
+				TypeCombinator::union($leftIterableValueType, $rightType->getIterableValueType()),
 			);
 
 			$accessories = [];
-			foreach ($leftType->getConstantArrays() as $type) {
-				foreach ($type->getKeyTypes() as $i => $offsetType) {
-					if ($type->isOptionalKey($i)) {
+			if ($leftCount > 0) {
+				// Use the first constant array as a reference to list potential offsets.
+				// We only need to check the first array because we're looking for offsets that exist in ALL arrays.
+				$constantArray = $leftConstantArrays[0];
+				foreach ($constantArray->getKeyTypes() as $i => $offsetType) {
+					if ($constantArray->isOptionalKey($i)) {
 						continue;
 					}
-					$valueType = $type->getValueTypes()[$i];
+
+					if (!$leftType->hasOffsetValueType($offsetType)->yes()) {
+						continue;
+					}
+
+					$valueType = $leftType->getOffsetValueType($offsetType);
+					$accessories[] = new HasOffsetValueType($offsetType, $valueType);
+				}
+			}
+
+			if ($rightCount > 0) {
+				// Use the first constant array as a reference to list potential offsets.
+				// We only need to check the first array because we're looking for offsets that exist in ALL arrays.
+				$constantArray = $rightConstantArrays[0];
+				foreach ($constantArray->getKeyTypes() as $i => $offsetType) {
+					if ($constantArray->isOptionalKey($i)) {
+						continue;
+					}
+
+					if (!$rightType->hasOffsetValueType($offsetType)->yes()) {
+						continue;
+					}
+
+					$valueType = TypeCombinator::union($leftIterableValueType, $rightType->getOffsetValueType($offsetType));
 					$accessories[] = new HasOffsetValueType($offsetType, $valueType);
 				}
 			}

tests/PHPStan/Analyser/nsrt/bug-13561.php

@@ -0,0 +1,37 @@
+<?php // lint >= 8.0
+
+namespace Bug13552;
+
+use function PHPStan\Testing\assertType;
+
+interface MyInterface {
+	public function doThing(): bool;
+
+	/**
+	 * @return array<string, string>
+	 */
+	public function getArray(): array;
+}
+
+function test_addition(MyInterface $i): void {
+	$x = $i->doThing() ? ['thing' => 'do'] : [];
+	assertType("array{}|array{thing: 'do'}", $x);
+
+	$x += $i->getArray();
+	assertType('array<string, string>', $x);
+
+	$x = $x ?: ['test' => 'string'];
+}
+
+function more_test(MyInterface $i): void {
+	$x = $i->doThing() ? ['thing' => 'do', 'always_here' => true] : ['always_here' => 42];
+	assertType("array{always_here: 42}|array{thing: 'do', always_here: true}", $x);
+
+	$a = $i->getArray() + $x;
+	assertType("non-empty-array<string, 42|string|true>&hasOffsetValue('always_here', 42|string|true)", $a);
+	assertType('true', isset($a['always_here']));
+
+	$b = $x + $i->getArray();
+	assertType("non-empty-array<string, 42|string|true>&hasOffsetValue('always_here', 42|true)", $b);
+	assertType('true', isset($b['always_here']));
+}