Fix #340 - give up with mixed type when accessing unknown key on objectlike

src/Psalm/Checker/Statements/Expression/FetchChecker.php

@@ -1005,6 +1005,8 @@ class FetchChecker
                         $has_valid_offset = true;
                     } else {
                         $invalid_offset_types[] = 'string';
+
+                        $array_access_type = Type::getMixed();
                     }
                 }
                 continue;

tests/ArrayAssignmentTest.php

@@ -703,6 +703,23 @@ class ArrayAssignmentTest extends TestCase
                     '$str' => 'string',
                 ],
             ],
+            'ignoreInvalidArrayOffset' => [
+                '<?php
+                    $a = [
+                        "b" => [],
+                    ];
+
+                    $a["b"]["c"] = 0;
+
+                    foreach ([1, 2, 3] as $i) {
+                        /**
+                         * @psalm-suppress InvalidArrayOffset
+                         * @psalm-suppress MixedOperand
+                         */
+                        $a["b"]["d"] += $a["b"][$i];
+                    }',
+                'assertions' => [],
+            ],
         ];
     }