RFR(S): JDK-8247938: Change various JVM enums like LinkInfo::AccessCheck and Klass::DefaultsLookupMode to enum class

[Kim Barrett]

> On Jul 31, 2020, at 1:55 PM, Lois Foltan <lois.foltan at oracle.com> wrote:
> 
> Please review the webrev to change the following unscoped enumeration declarations to scoped enumerations.
> 
> Klass::DefaultsLookupMode
> Klass::OverpassLookupMode
> Klass::StaticLookupMode
> Klass::PrivateLookupMode
> LinkInfo::AccessCheck
> 
> With C++11/14 enum class provides the added type safety to prevent 0 (integral) or false (boolean) to be implicitly converted to AccessCheck::needs_access_check for example.
> 
> open webrev at:http://cr.openjdk.java.net/~lfoltan/bug_jdk8247938.0/webrev/ <http://cr.openjdk.java.net/~lfoltan/bug_jdk8247938.0/webrev/index.html>
> bug link: https://bugs.openjdk.java.net/browse/JDK-8247938
> 
> Testing: hs-tier1 & 2 complete, hs-tier3-6 in progress
> 
> Thanks,
> Lois

Looks good.

For what it's worth, I didn't notice any cases here that seemed like they
would significantly benefit from C++20 "using enum":
http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2019/p1099r5.html
(Though it could have been used to signficantly reduce the size of the change.)

However, it does seem like some of the enumerators might benefit from a name
change, since they are now referred to by names that are qualified by the
enum type name.  For example, instead of this:

 199   enum class DefaultsLookupMode { find_defaults, skip_defaults };
 200   enum class OverpassLookupMode { find_overpass, skip_overpass };
 201   enum class StaticLookupMode   { find_static,   skip_static };
 202   enum class PrivateLookupMode  { find_private,  skip_private };

maybe use this:

 199   enum class DefaultsLookupMode { find, skip };
 200   enum class OverpassLookupMode { find, skip };
 201   enum class StaticLookupMode   { find, skip };
 202   enum class PrivateLookupMode  { find, skip };

since (for example) DefaultsLookupMode::find is obviously distinct from
StaticLookupMode::find, with the numerator suffixes being redundant.

Similarly, in class LinkInfo, perhaps:
  enum class AccessCheck { required, skip };

But that sort of thing can be done separately, assuming it's deemed
desirable.  Getting the benfit of the improved type safety is the important
part of this change.