Array.length treated as @UnknownInitialization

[mernst]

Consider the following test case:

import org.checkerframework.framework.qual.AnnotatedFor;

@AnnotatedFor("nullness")
public class Issue3449 {

  int length;

  public Issue3449(Object... args) {
    length = args.length;
  }
}

Compiling it with

javac -g Issue3449.java -processor nullness -AuseConservativeDefaultsForUncheckedCode=source

yields this error:

Issue3449.java:9: error: [assignment.type.incompatible] incompatible types in assignment.
    length = args.length;
                 ^
  found   : @UnknownInitialization @NonNull int
  required: @Initialized @NonNull int
1 error

The file type-checks if I remove @AnnotatedFor or the -AuseConservativeDefaultsForUncheckedCode=source command-line option.

[smillst]

It's not the formal parameter that's @UnknownInitialization; it's the field access of length. I've got a fix in #3459.