Support for array access on objects with ArrayAccess interface

Author: pepakriz

src/Analyser/Scope.php

@@ -631,8 +631,11 @@ function (Expr\ArrayItem $item): Type {
 
 if ($node instanceof Expr\ArrayDimFetch && $node->dim !== null) {
 $arrayType = $this->getType($node->var);
-if ($arrayType instanceof ArrayType) {
-return $arrayType->getItemType();
+if (
+$arrayType->isIterable()->yes()
+&& ($arrayType instanceof ArrayType || $arrayType->hasMethod('offsetGet')
+)) {
+return $arrayType->getIterableValueType();
 }
 }
 

tests/PHPStan/Analyser/NodeScopeResolverTest.php

@@ -3285,6 +3285,46 @@ public function testIterable(
 );
 }
 
+public function dataArrayAccess(): array
+{
+return [
+[
+'string',
+'$this->returnArrayOfStrings()[0]',
+],
+[
+'string',
+'$this->returnArrayObjectOfStrings()[0]',
+],
+[
+'mixed',
+'$this->returnMixed()[0]',
+],
+[
+'mixed',
+'$this->returnTraversableOnlyStrings()[0]',
+],
+];
+}
+
+/**
+ * @requires PHP 7.1
+ * @dataProvider dataArrayAccess
+ * @param string $description
+ * @param string $expression
+ */
+public function testArrayAccess(
+string $description,
+string $expression
+)
+{
+$this->assertTypes(
+__DIR__ . '/data/array-accessable.php',
+$description,
+$expression
+);
+}
+
 public function dataVoid(): array
 {
 return [

tests/PHPStan/Analyser/data/array-accessable.php

@@ -0,0 +1,44 @@
+<?php // lint >= 7.1
+
+namespace ArrayAccesable;
+
+class Foo
+{
+
+public function __construct()
+{
+die;
+}
+
+/**
+ * @return string[]
+ */
+public function returnArrayOfStrings(): array
+{
+}
+
+/**
+ * @return \ArrayObject|string[]
+ */
+public function returnArrayObjectOfStrings(): \ArrayObject
+{
+
+}
+
+/**
+ * @return mixed
+ */
+public function returnMixed()
+{
+
+}
+
+/**
+ * @return \Traversable|string[]
+ */
+public function returnTraversableOnlyStrings(): \Traversable
+{
+
+}
+
+}