Fix handling of built arrays

src/Psalm/Config/Creator.php

@@ -121,7 +121,6 @@ class Creator
                 $issues_at_level[$issue_level][$issue_type] = 0;
             }
 
-            /** @psalm-suppress MixedOperand */
             $issues_at_level[$issue_level][$issue_type] += 100/$counted_types;
         }
 

src/Psalm/Internal/Analyzer/Statements/Expression/Fetch/ArrayFetchAnalyzer.php

@@ -118,7 +118,7 @@ class ArrayFetchAnalyzer
         if ($keyed_array_var_id
             && $context->hasVariable($keyed_array_var_id)
             && !$context->vars_in_scope[$keyed_array_var_id]->possibly_undefined
-            && !$context->vars_in_scope[$keyed_array_var_id]->isVanillaMixed()
+            && !$context->vars_in_scope[$keyed_array_var_id]->hasVanillaMixed()
         ) {
             $statements_analyzer->node_data->setType(
                 $stmt,

src/Psalm/Type/Union.php

@@ -978,6 +978,19 @@ class Union implements TypeNode
             && count($this->types) === 1;
     }
 
+    /**
+     * @return bool
+     */
+    public function hasVanillaMixed()
+    {
+        /**
+         * @psalm-suppress UndefinedPropertyFetch
+         */
+        return isset($this->types['mixed'])
+            && !$this->types['mixed']->from_loop_isset
+            && get_class($this->types['mixed']) === Type\Atomic\TMixed::class;
+    }
+
     /**
      * @return bool
      */

tests/Loop/ForeachTest.php

@@ -985,6 +985,20 @@ class ForeachTest extends \Psalm\Tests\TestCase
                         $list = [4, 5, 6];
                     }',
             ],
+            'createNestedArrayInLoop' => [
+                '<?php
+                    function foo() : void {
+                        $arr = [];
+
+                        foreach ([1, 2, 3] as $i) {
+                            if (!isset($arr[$i]["a"])) {
+                                $arr[$i]["a"] = 0;
+                            }
+
+                            $arr[$i]["a"] += 5;
+                        }
+                    }'
+            ],
         ];
     }