Does GWT remove unused classes during compilation?

Suppose I have a project structure that looks roughly like this:

{module-package}.webapp  
    module.gwt.xml
{module-package}.webapp.client
    Client.java
    UsedByClient.java
    NotUsedByClient.java

And the module.gwt.xml file has:

<source path='client'/>
<entry-point class='{module-package}.webapp.client.Client'/>

When I compile this project using GWT, how much of the Java code will be compiled into Javascript?

Is NotUsedByClient.java included, even though the entry point doesn't reference it?
Is UsedByClient.java fully or partially included? E.g. if it has method m() which isn't called by Client, will m be compiled or not?

The motivation is that unfortunately I'm working with a legacy codebase that has server-side code living alongside client-side code in the same package and it would be some work to separate them. The server-side code isn't used by the client, but I'm concerned that GWT might compile it to Javascript where someone might notice it and try to reverse engineer it.

Solution

All of the above and more happen:

unreferenced classes are removed
unreferenced methods and fields are removed
constants may be inlined
various operations on constants (like !, ==, +, &&, etc) may be simplified (based on some field always being null, or true, etc)
un-overridden methods may be made final...
...and final methods may be made static in certain situations (leading to smaller callsites, and no "this" reference inside that method)...
and small, frequently called static methods may be inlined

And this process repeats, with even more optimizations that I skipped, to further assist in removing code, both big and small. At the end, all classes, methods, fields, and local variables are renamed in a way to further reduce output size, including reordering methods in the output so that they are ordered by length, letting gzip more efficiently compress your content on the way to the client.

So while some aspects of your code could be reverse engineered (just like any machine code could be reverse engineered), code which isn't referenced won't be available, and code which is may not even be readable.