RemoveUnusedVariableAssignRector.php

<?php

declare(strict_types=1);

namespace Rector\DeadCode\Rector\Assign;

use PhpParser\Node;
use PhpParser\Node\Expr;
use PhpParser\Node\Expr\Assign;
use PhpParser\Node\Expr\AssignRef;
use PhpParser\Node\Expr\Cast;
use PhpParser\Node\Expr\Closure;
use PhpParser\Node\Expr\FuncCall;
use PhpParser\Node\Expr\Include_;
use PhpParser\Node\Expr\Variable;
use PhpParser\Node\Stmt;
use PhpParser\Node\Stmt\Class_;
use PhpParser\Node\Stmt\ClassMethod;
use PhpParser\Node\Stmt\Expression;
use PhpParser\Node\Stmt\Function_;
use PhpParser\NodeVisitor;
use PHPStan\Reflection\ClassReflection;
use PHPStan\Type\ObjectType;
use Rector\DeadCode\NodeAnalyzer\NoDiscardCallAnalyzer;
use Rector\DeadCode\SideEffect\SideEffectNodeDetector;
use Rector\NodeAnalyzer\VariableAnalyzer;
use Rector\NodeManipulator\StmtsManipulator;
use Rector\Php\ReservedKeywordAnalyzer;
use Rector\PhpParser\Enum\NodeGroup;
use Rector\PhpParser\Node\BetterNodeFinder;
use Rector\PhpParser\Node\Value\ValueResolver;
use Rector\Rector\AbstractRector;
use Rector\RuleDoc\CodeSample\CodeSample;
use Rector\RuleDoc\RuleDefinition;
use Rector\ValueObject\MethodName;

/**
 * @see \Rector\Tests\DeadCode\Rector\Assign\RemoveUnusedVariableAssignRector\RemoveUnusedVariableAssignRectorTest
 */
final class RemoveUnusedVariableAssignRector extends AbstractRector
{
    public function __construct(
        private readonly ReservedKeywordAnalyzer $reservedKeywordAnalyzer,
        private readonly SideEffectNodeDetector $sideEffectNodeDetector,
        private readonly VariableAnalyzer $variableAnalyzer,
        private readonly BetterNodeFinder $betterNodeFinder,
        private readonly StmtsManipulator $stmtsManipulator,
        private readonly NoDiscardCallAnalyzer $noDiscardCallAnalyzer,
        private readonly ValueResolver $valueResolver,
    ) {
    }

    public function getRuleDefinition(): RuleDefinition
    {
        return new RuleDefinition('Remove unused assigns to variables', [
            new CodeSample(
                <<<'CODE_SAMPLE'
class SomeClass
{
    public function run()
    {
        $value = 5;
    }
}
CODE_SAMPLE
                ,
                <<<'CODE_SAMPLE'
class SomeClass
{
    public function run()
    {
    }
}
CODE_SAMPLE
            ),
        ]);
    }

    /**
     * @return array<class-string<Node>>
     */
    public function getNodeTypes(): array
    {
        return [ClassMethod::class, Function_::class];
    }

    /**
     * @param ClassMethod|Function_ $node
     */
    public function refactor(Node $node): null|ClassMethod|Function_
    {
        $stmts = $node->stmts;
        if ($stmts === null || $stmts === []) {
            return null;
        }

        $assignedVariableNamesByStmtPosition = $this->resolvedAssignedVariablesByStmtPosition($stmts);
        if ($assignedVariableNamesByStmtPosition === []) {
            return null;
        }

        // we cannot be sure here, deep walk only when there is a candidate to remove
        if ($this->shouldSkip($stmts)) {
            return null;
        }

        $hasChanged = false;

        foreach ($assignedVariableNamesByStmtPosition as $stmtPosition => $variableName) {
            if ($this->stmtsManipulator->isVariableUsedInNextStmt($node, $stmtPosition + 1, $variableName)) {
                continue;
            }

            /** @var Expression<Assign> $currentStmt */
            $currentStmt = $stmts[$stmtPosition];

            /** @var Assign $assign */
            $assign = $currentStmt->expr;

            if ($this->isObjectWithDestructMethod($assign->expr)) {
                continue;
            }

            if ($this->isNullResetOfInternalObject($assign)) {
                continue;
            }

            if ($this->hasCallLikeInAssignExpr($assign)) {
                // clean safely
                $cleanAssignedExpr = $this->cleanCastedExpr($assign->expr);
                $newExpression = new Expression($cleanAssignedExpr);
                $this->mirrorComments($newExpression, $currentStmt);
                $node->stmts[$stmtPosition] = $newExpression;
            } else {
                unset($node->stmts[$stmtPosition]);
            }

            $hasChanged = true;
        }

        if ($hasChanged) {
            return $node;
        }

        return null;
    }

    private function isNullResetOfInternalObject(Assign $assign): bool
    {
        // resetting an internal PHP object to null releases the held resource/file handle,
        // e.g. $file = null on a SplFileObject/RecursiveDirectoryIterator/finfo
        if (! $this->valueResolver->isNull($assign->expr)) {
            return false;
        }

        $varType = $this->getType($assign->var);
        if (! $varType instanceof ObjectType) {
            return false;
        }

        $classReflection = $varType->getClassReflection();
        if (! $classReflection instanceof ClassReflection) {
            return false;
        }

        return $classReflection->isBuiltin();
    }

    private function isObjectWithDestructMethod(Expr $expr): bool
    {
        $exprType = $this->getType($expr);
        if (! $exprType instanceof ObjectType) {
            return false;
        }

        $classReflection = $exprType->getClassReflection();
        if (! $classReflection instanceof ClassReflection) {
            return false;
        }

        return $classReflection->hasNativeMethod(MethodName::DESTRUCT);
    }

    private function cleanCastedExpr(Expr $expr): Expr
    {
        if (! $expr instanceof Cast) {
            return $expr;
        }

        return $this->cleanCastedExpr($expr->expr);
    }

    private function hasCallLikeInAssignExpr(Expr $expr): bool
    {
        return (bool) $this->betterNodeFinder->findFirst($expr, $this->sideEffectNodeDetector->detectCallExpr(...));
    }

    /**
     * @param Stmt[] $stmts
     */
    private function shouldSkip(array $stmts): bool
    {
        return (bool) $this->betterNodeFinder->findFirst($stmts, function (Node $node): bool {
            if ($node instanceof Include_) {
                return true;
            }

            if (! $node instanceof FuncCall) {
                return false;
            }

            return $this->isNames($node, ['compact', 'get_defined_vars']);
        });
    }

    /**
     * @return string[]
     */
    private function collectAssignRefVariableNames(Stmt $stmt): array
    {
        if (! NodeGroup::isStmtAwareNode($stmt)) {
            return [];
        }

        $refVariableNames = [];
        $this->traverseNodesWithCallable($stmt, function (Node $subNode) use (&$refVariableNames): Node {
            if ($subNode instanceof AssignRef && $subNode->var instanceof Variable) {
                $refVariableNames[] = (string) $this->getName($subNode->var);
            }

            return $subNode;
        });

        return $refVariableNames;
    }

    /**
     * @param array<int, Stmt> $stmts
     * @return array<int, string>
     */
    private function resolvedAssignedVariablesByStmtPosition(array $stmts): array
    {
        $assignedVariableNamesByStmtPosition = [];
        $refVariableNames = [];

        foreach ($stmts as $key => $stmt) {
            if (! $stmt instanceof Expression) {
                $refVariableNames = array_merge($refVariableNames, $this->collectAssignRefVariableNames($stmt));
                continue;
            }

            if ($stmt->expr instanceof AssignRef && $stmt->expr->var instanceof Variable) {
                $refVariableNames[] = (string) $this->getName($stmt->expr->var);
            }

            if (! $stmt->expr instanceof Assign) {
                continue;
            }

            $this->traverseNodesWithCallable(
                $stmt->expr->expr,
                function (Node $subNode) use (&$refVariableNames) {
                    if ($subNode instanceof Class_ || $subNode instanceof Function_) {
                        return NodeVisitor::DONT_TRAVERSE_CURRENT_AND_CHILDREN;
                    }

                    if (! $subNode instanceof Closure) {
                        return null;
                    }

                    foreach ($subNode->uses as $closureUse) {
                        if (! $closureUse->var instanceof Variable) {
                            continue;
                        }

                        if (! $closureUse->byRef) {
                            continue;
                        }

                        $refVariableNames[] = (string) $this->getName($closureUse->var);
                    }
                }
            );

            $assign = $stmt->expr;
            if (! $assign->var instanceof Variable) {
                continue;
            }

            $variableName = $this->getName($assign->var);
            if (! is_string($variableName)) {
                continue;
            }

            if ($this->reservedKeywordAnalyzer->isNativeVariable($variableName)) {
                continue;
            }

            if ($this->shouldSkipVariable($assign->var, $variableName, $refVariableNames)) {
                continue;
            }

            if ($this->noDiscardCallAnalyzer->isNoDiscardCall($assign->expr)) {
                continue;
            }

            $assignedVariableNamesByStmtPosition[$key] = $variableName;
        }

        return $assignedVariableNamesByStmtPosition;
    }

    /**
     * @param string[] $refVariableNames
     */
    private function shouldSkipVariable(Variable $variable, string $variableName, array $refVariableNames): bool
    {
        if ($this->variableAnalyzer->isStaticOrGlobal($variable)) {
            return true;
        }

        if ($this->variableAnalyzer->isUsedByReference($variable)) {
            return true;
        }

        return in_array($variableName, $refVariableNames, true);
    }
}