RFR: 8225003: NPE in Attr.attribIdentAsEnumType [v4]

[Guoxiong Li]

> Hi all,
> 
> `Attr.attribIdentAsEnumType` uses `enclClass` which would return null if some error types and/or error symbols exist.
> 
> And if we use annotation processor, some errors would be reported to `deferredDiagnosticHandler` and not immediately reported to the users. At this time, the `NullPointerException`(NPE) occurs and all the other work, including that the `deferredDiagnosticHandler` report the errors to users, would not be done. So the user would see the NPE and see that the compiler crashes.
> 
> In other words, the NPE also occurs without the annotation processor. But because the `deferredDiagnosticHandler` is not set without the annotation processor, some other errors would be shown immediately to users and the NPE is not shown when using [these catch code](https://github.com/openjdk/jdk/blob/0849117d5c3a9ae12231262fc0d3366a6e8a458d/src/jdk.compiler/share/classes/com/sun/tools/javac/main/Main.java#L349).
> 
> This patch fixes the NPE and reports the deferred diagnostics to users at the end of the compilation task. Maybe you can consider that this patch solves two bugs:
> 
> 1. [JDK-8225003 NPE in Attr.attribIdentAsEnumType](https://bugs.openjdk.java.net/browse/JDK-8225003)
> 2. Some deferred diagnostics would be not reported to user when the compiler crashes.
> 
> The test case needs to fix these two bugs to pass, so I put them together.
> 
> Thank you for taking the time to review.
> 
> Best Regards.

Guoxiong Li has updated the pull request incrementally with one additional commit since the last revision:

  Use meaningful name. Update copyright.

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

Changes:
  - all: https://git.openjdk.java.net/jdk/pull/1864/files
  - new: https://git.openjdk.java.net/jdk/pull/1864/files/33c67cee..e497ea12

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jdk&pr=1864&range=03
 - incr: https://webrevs.openjdk.java.net/?repo=jdk&pr=1864&range=02-03

  Stats: 5 lines in 1 file changed: 0 ins; 0 del; 5 mod
  Patch: https://git.openjdk.java.net/jdk/pull/1864.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/1864/head:pull/1864

PR: https://git.openjdk.java.net/jdk/pull/1864