function () {
-    $a = true;
-    return $a;
+    return true;
 };

<?php

use Rector\CodeQuality\Rector\FunctionLike\SimplifyUselessVariableRector;
use Rector\Config\RectorConfig;

return RectorConfig::configure()
    ->withRules([
        SimplifyUselessVariableRector::class,
    ]);

Other rules in the Dead Code set

• RemoveFinalFromConstRector - Remove final from constants in classes defined as final
• NarrowWideUnionReturnTypeRector - Narrow overly wide union return type declaration if possible
• RemoveDeadReturnRector - Remove last return in the functions, since does not do anything
• RemoveNullNamedArgOnNullDefaultParamRector - Remove named null argument, where null is already a default param value
• RemoveNullArgOnNullDefaultParamRector - Remove default null argument, where null is already a default param value
• RemoveNonExistingVarAnnotationRector - Removes non-existing @var annotations above the code
• RemoveUnusedClosureVariableUseRector - Remove unused variable in use() of closure
• RemoveDeadZeroAndOneOperationRector - Remove operation with 1 and 0, that have no effect on the value
• RemoveFilterVarOnExactTypeRector - Removes filter_var() calls with exact type
• ReplaceBlockToItsStmtsRector - Replace Block Stmt with its stmts