TreeUtils { public static Optional<Symbol> getSymbolFromTree(@Nullable Tree tree) { if (tree instanceof HasSymbol) { return Optional.ofNullable(((HasSymbol) tree).symbol()); } return Optional.empty(); } private  TreeUtils(); @CheckForNull static Tree firstAncestor(Tree tree, Predicate<Tree> predicate); @CheckForNull static Tree firstAncestorOfKind(Tree tree, Kind... kinds); static List<Token> tokens(Tree tree); static List<Token> nonWhitespaceTokens(Tree tree); static boolean hasDescendant(Tree tree, Predicate<Tree> predicate); static Stream<Expression> flattenTuples(Expression expression); static Optional<Symbol> getSymbolFromTree(@Nullable Tree tree); @CheckForNull static ClassSymbol getClassSymbolFromDef(@Nullable ClassDef classDef); @CheckForNull static FunctionSymbol getFunctionSymbolFromDef(@Nullable FunctionDef functionDef); static List<Parameter> nonTupleParameters(FunctionDef functionDef); static List<Parameter> positionalParameters(FunctionDef functionDef); static List<FunctionDef> topLevelFunctionDefs(ClassDef classDef); @CheckForNull static RegularArgument argumentByKeyword(String keyword, List<Argument> arguments); @CheckForNull static RegularArgument nthArgumentOrKeyword(int argPosition, String keyword, List<Argument> arguments); static boolean isBooleanLiteral(Tree tree); static String nameFromExpression(Expression expression); @CheckForNull static LocationInFile locationInFile(Tree tree, @Nullable String fileId);  }
@Test public void getSymbolFromTree() { assertThat(TreeUtils.getSymbolFromTree(null)).isEmpty(); Expression expression = lastExpression( "x = 42", "x"); assertThat(TreeUtils.getSymbolFromTree(expression)).contains(((HasSymbol) expression).symbol()); expression = lastExpression("foo()"); assertThat(TreeUtils.getSymbolFromTree(expression)).isEmpty(); }