Do not transform Mockito-generated classes

[nikita-tkachenko-datadog]

What Does This Do

Adds the common package for Mockito-generated classes to the list of global ignores.

Motivation

Whenever a class is mocked with Mockito, a new class is generated that replaces the original class' methods with the mocked ones.

If the tracer contains instrumentations that transform the original class, the same instrumentations will most likely be applied to the mocked class as it extends the original one.

Transforming the mocked class' code leads to errors: some instrumentations, when executed a transformed method, call another method of the same instance. Mockito does not handle this well: if a mocked method is called from inside another mocked method, Mockito's internal state gets corrupted.

The solution is to avoid transforming Mockito-generated classes, both because it fixes the errors and because tracing mock methods makes little sense.

Jira ticket: CIVIS-10060

[mcculls]

CombiningTransformerBuilder is not the place to add this kind of exclusion because it will degrade performance by adding an extra check on the name for everything - even when we already know the class doesn't start with that package.

Since you want to exclude everything under a package the simplest way is to add it to https://github.com/DataDog/dd-trace-java/blob/master/dd-java-agent/agent-tooling/src/main/resources/datadog/trace/agent/tooling/bytebuddy/matcher/ignored_class_name.trie where we maintain a list of packages and classes to ignore for performance reasons (because we know they are uninteresting) or they should never be instrumented because it would break things.

You should just need to add:

1 org.mockito.codegen.*

Note if you wanted to exclude generated/proxy classes which didn't have a common package, but had another recognizable token in their name then you can do that in https://github.com/DataDog/dd-trace-java/blob/master/dd-java-agent/agent-tooling/src/main/java/datadog/trace/agent/tooling/bytebuddy/matcher/ProxyClassIgnores.java

[mcculls]

LGTM, thanks!