Fixing parser error when encountering complex variables. (#26)

Fixes #18

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.

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']);
+    }
 }