Disallow URL in equals methods (or @Value.Immutable classes)

[iamdanfox]

What happened?

@jroitgrund and I just had a wild time with a debugger hooked up to a production service, where it seemed like an equals method was returning false when it should have been true!

@Value.Immutable
@ImmutablesStyle
@JsonSerialize(as = ImmutableDeploymentConfiguration.class)
@JsonDeserialize(as = ImmutableDeploymentConfiguration.class)
public interface DeploymentConfiguration {
	// ...
    @JsonProperty("public-url")
    URL publicUrl();

On the box, it seemed that the URL object constructed from the same string resulted in a DNS lookup which sometimes returned different IP addresses (because that service was deployed in multiple places).

this meant that occasionally, this would return false:

URL url1 = new URL("https://something.example.com");
// wait a bit because we tell Java to cache DNS for 20 seconds '-Dsun.net.inetaddr.ttl=20'
URL url2 = new URL("https://something.example.com");

url1.equals(url2); // 🌶🌶🌶 can return false! 

What did you want to happen?

We can't change the URL class itself, so I think we should write an errorprone check to prevent bugs like this.

We could ban comparisons of URL.equals URL and also @Value.Immutable fields which are URLs.

[carterkozak]

We may want to bump this to ERROR by default to catch subtler instances of this failure: http://errorprone.info/bugpattern/URLEqualsHashCode

[iamdanfox]

Closing out because promoting that to ERROR means it should catch stuff even inside generated immutables code!

[iamdanfox]

Re-opening because it seems like a dev team hit this exact case and error-prone didn't warn them :/

public interface KubernetesEnvironmentConfig {
    DockerConfig docker();

    SslConfiguration dispatcherSecurity();

    List<URL> ingressUris();  // <- 🌶🌶🌶