BuilderReturnThis
Builder instance method does not return 'this'

The problem

This check identifies instance methods in builder classes, and requires that they either return this;, or are explicitly annotated with @CheckReturnValue.

Instance methods in builders typically return this, to allow chaining. Ignoring this result does not indicate a https://errorprone.info/bugpattern/CheckReturnValue bug. For example, both of the following are fine:

Foo.Builder builder = Foo.builder();
builder.setBar("bar"); // return value is deliberately unused
return builder.build();

Foo.Builder builder =
    Foo.builder().setBar("bar").build();

Rarely, a builder method may return a new instance, which should not be ignored. This check requires these methods to be annotated with @CheckReturnValue:

class Builder {
  @CheckReturnValue
  Builder setFoo(String foo) {
    return new Builder(foo); // returns a new builder instead of this!
  }
}

This check allows the https://errorprone.info/bugpattern/CheckReturnValue enforcement to assume the return value of instance methods in builders can safely be ignored, unless the method is explicitly annotated with @CheckReturnValue.

Suppression

Suppress false positives by adding the suppression annotation @SuppressWarnings("BuilderReturnThis") to the enclosing element.