Handle variable paths in a less naive fashion

Fixes #564

src/Psalm/Checker/AlgebraChecker.php

@@ -12,6 +12,9 @@ use Psalm\IssueBuffer;
 
 class AlgebraChecker
 {
+    /** @var array<string, array<int, string>> */
+    private static $broken_paths = [];
+
     /**
      * @param  PhpParser\Node\Expr      $conditional
      * @param  string|null              $this_class_name
@@ -88,7 +91,7 @@ class AlgebraChecker
 
             foreach ($assertions as $var => $type) {
                 if ($type === 'isset' || $type === '!empty') {
-                    $key_parts = preg_split('/(->|\[|\])/', $var, -1, PREG_SPLIT_DELIM_CAPTURE | PREG_SPLIT_NO_EMPTY);
+                    $key_parts = self::breakUpPathIntoParts($var);
 
                     $base_key = array_shift($key_parts);
 
@@ -144,6 +147,83 @@ class AlgebraChecker
         return [new Clause([], true)];
     }
 
+    /**
+     * @param  string $path
+     *
+     * @return array<int, string>
+     */
+    public static function breakUpPathIntoParts($path)
+    {
+        if (isset(self::$broken_paths[$path])) {
+            return self::$broken_paths[$path];
+        }
+
+        $chars = str_split($path);
+
+        $string_char = null;
+        $escape_char = false;
+
+        $parts = [''];
+        $parts_offset = 0;
+
+        for ($i = 0, $char_count = count($chars); $i < $char_count; ++$i) {
+            $char = $chars[$i];
+
+            if ($string_char) {
+                if ($char === $string_char && !$escape_char) {
+                    $string_char = null;
+                }
+
+                if ($char === '\\') {
+                    $escape_char = !$escape_char;
+                }
+
+                $parts[$parts_offset] .= $char;
+                continue;
+            }
+
+            switch ($char) {
+                case '[':
+                case ']':
+                    $parts_offset++;
+                    $parts[$parts_offset] = $char;
+                    $parts_offset++;
+                    continue;
+
+                case '\'':
+                case '"':
+                    if (!isset($parts[$parts_offset])) {
+                        $parts[$parts_offset] = '';
+                    }
+                    $parts[$parts_offset] .= $char;
+                    $string_char = $char;
+
+                    continue;
+
+                case '-':
+                    if ($i < $char_count - 1 && $chars[$i + 1] === '>') {
+                        ++$i;
+
+                        $parts_offset++;
+                        $parts[$parts_offset] = '->';
+                        $parts_offset++;
+                        continue;
+                    }
+                    // fall through
+
+                default:
+                    if (!isset($parts[$parts_offset])) {
+                        $parts[$parts_offset] = '';
+                    }
+                    $parts[$parts_offset] .= $char;
+            }
+        }
+
+        self::$broken_paths[$path] = $parts;
+
+        return $parts;
+    }
+
     /**
      * Negates a set of clauses
      * negateClauses([$a || $b]) => !$a && !$b

src/Psalm/Type/Reconciler.php

@@ -1,6 +1,7 @@
 <?php
 namespace Psalm\Type;
 
+use Psalm\Checker\AlgebraChecker;
 use Psalm\Checker\ProjectChecker;
 use Psalm\Checker\StatementsChecker;
 use Psalm\Checker\TraitChecker;
@@ -913,7 +914,7 @@ class Reconciler
      */
     private static function getValueForKey(ProjectChecker $project_checker, $key, array &$existing_keys)
     {
-        $key_parts = preg_split('/(->|\[|\])/', $key, -1, PREG_SPLIT_DELIM_CAPTURE | PREG_SPLIT_NO_EMPTY);
+        $key_parts = AlgebraChecker::breakUpPathIntoParts($key);
 
         if (count($key_parts) === 1) {
             return isset($existing_keys[$key_parts[0]]) ? clone $existing_keys[$key_parts[0]] : null;

tests/IssetTest.php

@@ -177,6 +177,10 @@ class IssetTest extends TestCase
                         return $arr[$b];
                     }',
             ],
+            'noExceptionOnBracketString' => [
+                '<?php
+                    if (isset($foo["bar[]"])) {}',
+            ],
         ];
     }