bazelbuild/bazel · error · AssertionError

Failed to create converter

Error message

Failed to create converter

What it means

ConverterTester reflectively instantiates the Converter under test via getDeclaredConstructor().newInstance(); if that throws any ReflectiveOperationException it is wrapped in this AssertionError. In practice the converter class has no accessible no-arg constructor, or is abstract/interface/non-public, so the test harness cannot create an instance.

Source

Thrown at src/main/java/com/google/devtools/common/options/testing/ConverterTester.java:51

  private final Converter<?> converter;
  private final Class<? extends Converter<?>> converterClass;
  private final Object conversionContext;
  private final EqualsTester tester = new EqualsTester();
  private final LinkedHashSet<String> testedInputs = new LinkedHashSet<>();
  private final ArrayList<ImmutableList<String>> inputLists = new ArrayList<>();

  /** Creates a new ConverterTester which will test the given Converter class. */
  public ConverterTester(Class<? extends Converter<?>> converterClass, Object conversionContext) {
    this.converterClass = converterClass;
    this.converter = createConverter();
    this.conversionContext = conversionContext;
  }

  private Converter<?> createConverter() {
    try {
      return converterClass.getDeclaredConstructor().newInstance();
    } catch (ReflectiveOperationException ex) {
      throw new AssertionError("Failed to create converter", ex);
    }
  }

  /** Returns the class this ConverterTester is testing. */
  public Class<? extends Converter<?>> getConverterClass() {
    return converterClass;
  }

  /**
   * Returns whether this ConverterTester has a test for the given input, i.e., addEqualityGroup
   * was called with the given string.
   */
  public boolean hasTestForInput(String input) {
    return testedInputs.contains(input);
  }

  /**
   * Adds a set of valid inputs which are expected to convert to equal values.

View on GitHub (pinned to e6e199d060)

Solutions

  1. Add a public no-argument constructor to the converter class.
  2. Make the class concrete (not abstract/interface) and top-level or static-nested.
  3. Ensure the class is public and visible to the test.
  4. Ensure the no-arg constructor does not itself throw.

Example fix

// before
class MyConverter implements Converter<String> {
  private MyConverter(Config cfg) { ... }
}

// after
class MyConverter implements Converter<String> {
  public MyConverter() { this(DEFAULT_CONFIG); }
  private MyConverter(Config cfg) { ... }
}
Defensive patterns

Strategy: validation

Validate before calling

// Fail fast with a clear message before constructing the tester
static Class<? extends Converter<?>> checkInstantiable(Class<? extends Converter<?>> c) {
  int mods = c.getModifiers();
  if (Modifier.isAbstract(mods) || c.isInterface()) throw new IllegalArgumentException(c + " must be concrete");
  try { c.getDeclaredConstructor(); } catch (NoSuchMethodException e) {
    throw new IllegalArgumentException(c + " needs a public no-arg constructor", e);
  }
  return c;
}

Prevention

When it happens

Trigger: ConverterTester constructed with a Converter class that lacks a public no-arg constructor; converter declared abstract or as an interface; constructor package-private and the test runs in a different package; constructor exists but throws (newInstance wraps constructor exceptions in InvocationTargetException, a ReflectiveOperationException).

Common situations: Writing a new converter that takes constructor arguments or uses a private ctor with a static factory; converting an existing converter to a non-static inner class (implicit outer-class ctor parameter); JDK 9+ module access restrictions hiding the ctor.

Related errors

AI-assisted analysis of bazelbuild/bazel@e6e199d060 (2026-08-14). Data as JSON: /api/errors/25a6eded6bbd3077. Report an issue: GitHub.