[DeadCode] Keep Assign expr on RemoveUnusedVariableAssignRector for i…

…mpure function (#282)

rules-tests/DeadCode/Rector/Assign/RemoveUnusedVariableAssignRector/Fixture/on_ob_get_clean.php.inc

@@ -0,0 +1,49 @@
+<?php
+
+namespace Rector\Tests\DeadCode\Rector\Assign\RemoveUnusedVariableAssignRector\Fixture;
+
+final class OnObGetClean
+{
+    public function run()
+    {
+        echo 'run';
+    }
+
+    public function execute()
+    {
+        ob_start();
+
+        $this->run();
+
+        $result = ob_get_clean();
+
+        echo 'done';
+    }
+}
+
+?>
+-----
+<?php
+
+namespace Rector\Tests\DeadCode\Rector\Assign\RemoveUnusedVariableAssignRector\Fixture;
+
+final class OnObGetClean
+{
+    public function run()
+    {
+        echo 'run';
+    }
+
+    public function execute()
+    {
+        ob_start();
+
+        $this->run();
+
+        ob_get_clean();
+
+        echo 'done';
+    }
+}
+
+?>

rules/DeadCode/Rector/Assign/RemoveUnusedVariableAssignRector.php

@@ -22,6 +22,7 @@
 use Rector\Core\PhpParser\Comparing\ConditionSearcher;
 use Rector\Core\Rector\AbstractRector;
 use Rector\DeadCode\NodeAnalyzer\UsedVariableNameAnalyzer;
+use Rector\DeadCode\SideEffect\PureFunctionDetector;
 use Rector\NodeTypeResolver\Node\AttributeKey;
 use Symplify\RuleDocGenerator\ValueObject\CodeSample\CodeSample;
 use Symplify\RuleDocGenerator\ValueObject\RuleDefinition;
@@ -35,7 +36,8 @@ public function __construct(
         private ReservedKeywordAnalyzer $reservedKeywordAnalyzer,
         private CompactFuncCallAnalyzer $compactFuncCallAnalyzer,
         private ConditionSearcher $conditionSearcher,
-        private UsedVariableNameAnalyzer $usedVariableNameAnalyzer
+        private UsedVariableNameAnalyzer $usedVariableNameAnalyzer,
+        private PureFunctionDetector $pureFunctionDetector
     ) {
     }
 
@@ -102,7 +104,9 @@ public function refactor(Node $node): ?Node
             return null;
         }
 
-        if ($node->expr instanceof MethodCall || $node->expr instanceof StaticCall) {
+        if ($node->expr instanceof MethodCall || $node->expr instanceof StaticCall || $this->isImpureFunction(
+            $node->expr
+        )) {
             // keep the expr, can have side effect
             return $node->expr;
         }
@@ -111,6 +115,15 @@ public function refactor(Node $node): ?Node
         return $node;
     }
 
+    private function isImpureFunction(Expr $expr): bool
+    {
+        if (! $expr instanceof FuncCall) {
+            return false;
+        }
+
+        return ! $this->pureFunctionDetector->detect($expr);
+    }
+
     private function shouldSkip(Assign $assign): bool
     {
         $classMethod = $assign->getAttribute(AttributeKey::METHOD_NODE);

rules/DeadCode/SideEffect/PureFunctionDetector.php

@@ -30,7 +30,7 @@ final class PureFunctionDetector
         'header', 'header_remove', 'http_response_code', 'setcookie',
 
         // output buffer
-        'ob_start', 'ob_end_clean', 'readfile', 'printf', 'var_dump', 'phpinfo',
+        'ob_start', 'ob_end_clean', 'ob_get_clean', 'readfile', 'printf', 'var_dump', 'phpinfo',
         'ob_implicit_flush', 'vprintf',
 
         // mcrypt