Currently, javac allows a user to specify a file manager to the JavaCompiler API.

The current behavior is that specifying some options, like -classpath, -source, etc, have an unspecified permanent side effect on the user provided file manager.

In addition, as noted in JDK-8139607, options like -release only work in conjunction with a StandardJavaFileManager.

A different approach would be for javac to "wrap" any user provided file manager with an instance-specific file manager, such that any changes resulting from javac options are confined to that instance, and not propagated to the user-provided file manager.

Thus, the behavior of methods in such a wrapper would be:
    if this method is affected by local changes, impl the method locally; otherwise, delegate to the user provided file manager.

Note that (separately) the user file manager is already wrapped using ClientCodeWrapper, which exists to trap exceptions in a user provided file manager. The wrapping described here would be in addition to the use of ClientCodeWrapper.