RFR: 8219810: javac throws NullPointerException [v2]

[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 with a new target base due to a merge or a rebase. The incremental webrev excludes the unrelated changes brought in by the merge/rebase. The pull request contains three additional commits since the last revision:

 - Merge branch 'master' into JDK-8219810
 - Also disallow field access flags from having both FINAL and VOLATILE.
 - Detect invalid access flag combinations for fields and methods in classfiles.

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

Changes:
  - all: https://git.openjdk.org/jdk/pull/10826/files
  - new: https://git.openjdk.org/jdk/pull/10826/files/5d7fa500..b2667d90

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=10826&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=10826&range=00-01

  Stats: 218112 lines in 2202 files changed: 101760 ins; 81071 del; 35281 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