RFR: 8219810: javac throws NullPointerException [v4]

[Archie L. Cobbs]

> JVMS 4.5 states:
> 
>> Each field of a class may have at most one of its ACC_PUBLIC, ACC_PRIVATE, and ACC_PROTECTED flags set (JLS §8.3.1), and must not have both its ACC_FINAL and ACC_VOLATILE flags set (JLS §8.3.1.4).
> 
> and JVMS 4.6 states:
> 
>> Each method of a class may have at most one of its ACC_PUBLIC, ACC_PRIVATE, and ACC_PROTECTED flags set (JLS §8.4.3). 
> 
> However, when reading class files these illegal combinations are not actually checked, and this can lead to compiler crashes as in the bug example.
> 
> This patch adds checks for these illegal combinations.

Archie L. Cobbs has updated the pull request incrementally with one additional commit since the last revision:

  Use Flags.toString() to stringify flag bits.

-------------

Changes:
  - all: https://git.openjdk.org/jdk/pull/10826/files
  - new: https://git.openjdk.org/jdk/pull/10826/files/94cb9924..90aebcd5

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=10826&range=03
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=10826&range=02-03

  Stats: 4 lines in 3 files changed: 0 ins; 0 del; 4 mod
  Patch: https://git.openjdk.org/jdk/pull/10826.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/10826/head:pull/10826

PR: https://git.openjdk.org/jdk/pull/10826