Fixing parser error when encountering complex variables.

#18

Author: floriankraemer

src/PhpParser/CognitiveMetricsVisitor.php

@@ -194,7 +194,7 @@ private function gatherMetrics(Node $node): void
     {
         match (true) {
             $node instanceof Node\Stmt\Return_ => $this->incrementReturnCount(),
-            $node instanceof Node\Expr\Variable => $this->trackVariable($node),
+            $node instanceof Node\Expr\Variable => $this->countVariablesNotAlreadyTrackedAsArguments($node),
             $node instanceof Node\Expr\PropertyFetch => $this->trackPropertyFetch($node),
             $node instanceof Node\Stmt\If_ => $this->trackIfStatement(),
             $node instanceof Node\Stmt\Else_,
@@ -208,10 +208,30 @@ private function incrementReturnCount(): void
         $this->currentReturnCount++;
     }
 
-    private function trackVariable(Node\Expr\Variable $node): void
+    /**
+     * Count variables that are not already tracked as method arguments.
+     *
+     * Important note about variable handling in this method:
+     *
+     * In PhpParser, the $node->name property of a Node\Expr\Variable can be either:
+     *
+     * - a string (for simple variables like $foo)
+     * - or an Expr node (usually another Variable or an expression, for complex variables like ${$bar} or variable
+     *   variables)
+     *
+     * This is because PHP allows variable variables and complex expressions as variable names, so the parser represents
+     * them as objects rather than plain strings. Always check the type before using it as an array key.
+     *
+     * When $node->name is an object (not a string), it represents complex or variable variables (like ${$foo})
+     * in PHP. These cases are rare in typical code and are challenging to statically analyze. For metrics like
+     * variable counting, they are usually not relevant or are intentionally skipped, since you cannot reliably
+     * determine the variable name at parse time.
+     *
+     * @link https://github.com/Phauthentic/cognitive-code-analysis/issues
+     */
+    private function countVariablesNotAlreadyTrackedAsArguments(Node\Expr\Variable $node): void
     {
-        // Only count variables not already tracked as arguments
-        if (!isset($this->methodArguments[$node->name])) {
+        if (is_string($node->name) && !isset($this->methodArguments[$node->name])) {
             $this->currentVariables[$node->name] = true;
         }
     }

tests/Unit/PhpParser/CognitiveMetricsVisitorTest.php

@@ -64,4 +64,33 @@ public function testMethodMetricsCalculation(): void
         $this->assertEquals(1, $metrics['ifNestingLevel']);
         $this->assertEquals(2, $metrics['elseCount']);
     }
+
+    public function testCountVariablesNotAlreadyTrackedAsArguments(): void
+    {
+        $code = <<<'CODE'
+        <?php
+        class Example {
+            public function foo($arg1) {
+                $a = 1;
+                $b = 2;
+                $arg1 = 3;
+                ${$dynamic} = 4;
+            }
+        }
+        CODE;
+
+        $parser = (new ParserFactory())->createForNewestSupportedVersion();
+        $ast = $parser->parse($code);
+
+        $visitor = new CognitiveMetricsVisitor();
+        $traverser = new NodeTraverser();
+        $traverser->addVisitor($visitor);
+        $traverser->traverse($ast);
+
+        $metrics = $visitor->getMethodMetrics();
+        $method = '\Example::foo';
+
+        $this->assertArrayHasKey($method, $metrics);
+        $this->assertEquals(3, $metrics[$method]['variableCount']);
+    }
 }