/**
  * @param Traversable|array[] $ASTs a series of AST roots
  *
  * @return string[] all the found symbols
  */
 public function __invoke(Traversable $ASTs) : array
 {
     // note: dependency injection is not really feasible for these two, as they need to co-exist in parallel
     $traverser = new NodeTraverser();
     $traverser->addVisitor(new NameResolver());
     $traverser->addVisitor($collector = new UsedSymbolCollector());
     $astSymbols = [];
     foreach ($ASTs as $astRoot) {
         $traverser->traverse($astRoot);
         $astSymbols[] = $collector->getCollectedSymbols();
     }
     return array_values(array_unique(array_merge([], ...$astSymbols)));
 }
 public function testWontCollectAnyUsageTypes()
 {
     $this->traverseStringAST('<?php function foo($bar) {}');
     self::assertSameCollectedSymbols([], $this->collector->getCollectedSymbols());
 }