code: private void completeEnclosing(ClassSymbol c) {
          if (c.owner.kind == PCK) {
              Symbol owner = c.owner;
              for (Name name : Convert.enclosingCandidates(Convert.shortName(c.name))) {
                  Symbol encl = owner.members().findFirst(name);
                  if (encl == null)
                      encl = syms.getClass(c.packge().modle, TypeSymbol.formFlatName(name, owner));
                  if (encl != null)
                      encl.complete();
              }
          }
      }
docs: Tries to complete lexically enclosing classes if c looks like a
  nested class.  This is similar to completeOwners but handles
  the situation when a nested class is accessed directly as it is
  possible with the Tree API or javax.lang.model.*.