Class JavaScriptCodeGenerator

src/test/java/examples/JavaScriptCodeGenerator.java:11–300

/* Generates random strings that are syntactically valid JavaScript */
public class JavaScriptCodeGenerator extends Generator<String> {
    public JavaScriptCodeGenerator() {
        super(String.class); // Register type of generated object
    }

    private GenerationStatus status; // saved state object when generating
    private static final int MAX_IDENTIFIERS = 100;
    private static final int MAX_EXPRESSION_DEPTH = 10;
    private static final int MAX_STATEMENT_DEPTH = 6;
    private static Set<String> identifiers; // Stores generated IDs, to promote re-use
    private int statementDepth; // Keeps track of how deep the AST is at any point
    private int expressionDepth; // Keeps track of how nested an expression is at any point

    private static final String[] UNARY_TOKENS = {
            "!", "++", "--", "~",
            "delete", "new", "typeof"
    };

    private static final String[] BINARY_TOKENS = {
            "!=", "!==", "%", "%=", "&", "&&", "&=", "*", "*=", "+", "+=", ",",
            "-", "-=", "/", "/=", "<", "<<", ">>=", "<=", "=", "==", "===",
            ">", ">=", ">>", ">>=", ">>>", ">>>=", "^", "^=", "|", "|=", "||",
            "in", "instanceof"
    };

    /** Main entry point. Called once per test case. Returns a random JS program. */
    @Override
    public String generate(SourceOfRandomness random, GenerationStatus status) {
        this.status = status; // we save this so that we can pass it on to other generators
        this.identifiers = new HashSet<>();
        this.statementDepth = 0;
        this.expressionDepth = 0;
        return generateStatement(random).toString();
    }

    /** Utility method for generating a random list of items (e.g. statements, arguments, attributes) */
    private static List<String> generateItems(Function<SourceOfRandomness, String> genMethod, SourceOfRandomness random,
                                              int mean) {
        int len = random.nextInt(mean*2); // Generate random number in [0, mean*2)
        List<String> items = new ArrayList<>(len);
        for (int i = 0; i < len; i++) {
            items.add(genMethod.apply(random));
        }
        return items;
    }

    /** Generates a random JavaScript statement */
    private String generateStatement(SourceOfRandomness random) {
        statementDepth++;
        String result;
        // If depth is too high, then generate only simple statements to prevent infinite recursion
        // If not, generate simple statements after the flip of a coin
        if (statementDepth >= MAX_STATEMENT_DEPTH || random.nextBoolean()) {
            // Choose a random private method from this class, and then call it with `random`
            result = random.choose(Arrays.<Function<SourceOfRandomness, String>>asList(
                    this::generateExpressionStatement,
                    this::generateBreakNode,
                    this::generateContinueNode,