ProtoAdapter and FieldBinding should use rawType's classloader.

[autonomousapps]

It is arguably a bug that ProtoAdapter implicitly uses the classLoader from itself when calling Class.forName(String). Instead, we should use Class.forName(String, boolean, ClassLoader), and the ClassLoader argument should be supplied by rawType.

Original description

This draft PR is intended first for discussion purposes, and to get feedback on what it would take to land something like this on trunk. We need this in our project because the wire-runtime library is loaded in a different classloader than the main app classes, leading to serialization errors when wire tries to instantiate a class instance via Class.forName(String). Arguably, best practice in cases like this indicates that an overload ought to be provided such that a library can use Class.forName(String, boolean, ClassLoader), because in general libraries cannot guarantee they'll be loaded in the same classloaders as application classes.

[autonomousapps]

@oldergod @bendotli I've updated this PR to use default arguments everywhere (I think), and also to use Optional<ClassLoader> = Optional.empty() in two places to handle the fact that a null classloader has a special value on the JVM. Let me know what you think.

[autonomousapps]

With a test failure like the following, is it literally saying that it doesn't like that I made the declaration take multiple lines?

 public final class Pizza extends Message<Pizza, Pizza.Builder> {
-  public static final ProtoAdapter<Pizza> ADAPTER = ProtoAdapter.newMessageAdapter(
-    Pizza.class,
-    "type.googleapis.com/squareup.proto3.Pizza",
-    Syntax.PROTO_3,
-    Pizza.class.getClassLoader()
-  );
+  public static final ProtoAdapter<Pizza> ADAPTER = ProtoAdapter.newMessageAdapter(Pizza.class, "type.googleapis.com/squareup.proto3.Pizza", Syntax.PROTO_3);

[oldergod]

@autonomousapps for the build fail, it says "Test files changed. Did you run ./gradlew generateTests?"

[autonomousapps]

for the build fail, it says "Test files changed. Did you run ./gradlew generateTests?"

a-ha, I did not! Thanks for the tip.

[autonomousapps]

Fixed the tests (./gradlew test succeeds), removed the injectable classLoader (we only need rawType's classLoader), and also changed all parameter names from loader to classLoader. @oldergod @swankjesse

[oldergod]

Let's go