RFR: 8246778: Compiler implementation for Sealed Classes (Second Preview) [v2]

[Mandy Chung]

On Mon, 30 Nov 2020 15:59:07 GMT, Jan Lahoda <jlahoda at openjdk.org> wrote:

>> This pull request replaces https://github.com/openjdk/jdk/pull/1227.
>> 
>> From the original PR:
>> 
>>> Please review the code for the second iteration of sealed classes. In this iteration we are:
>>> 
>>>     * Enhancing narrowing reference conversion to allow for stricter checking of cast conversions with respect to sealed type hierarchies
>>> 
>>>     * Also local classes are not considered when determining implicitly declared permitted direct subclasses of a sealed class or sealed interface
>>> 
>>>     * renaming Class::permittedSubclasses to Class::getPermittedSubclasses, still in the same method, the return type has been changed to Class<?>[] instead of the previous ClassDesc[]
>>> 
>>>     * adding code to make sure that annotations can't be sealed
>>> 
>>>     * improving some tests
>>> 
>>> 
>>> TIA
>>> 
>>> Related specs:
>>> [Sealed Classes JSL](http://cr.openjdk.java.net/~gbierman/jep397/jep397-20201104/specs/sealed-classes-jls.html)
>>> [Sealed Classes JVMS](http://cr.openjdk.java.net/~gbierman/jep397/jep397-20201104/specs/sealed-classes-jvms.html)
>>> [Additional: Contextual Keywords](http://cr.openjdk.java.net/~gbierman/jep397/jep397-20201104/specs/contextual-keywords-jls.html)
>> 
>> This PR strives to reflect the review comments from 1227:
>>  * adjustments to javadoc of j.l.Class methods
>>  * package access checks in Class.getPermittedSubclasses()
>>  * fixed to the narrowing conversion/castability as pointed out by Maurizio
>
> Jan Lahoda has updated the pull request with a new target base due to a merge or a rebase. The pull request now contains 12 commits:
> 
>  - Improving getPermittedSubclasses javadoc.
>  - Merge branch 'master' into JDK-8246778
>  - Moving checkPackageAccess from getPermittedSubclasses to a separate method.
>  - Improving getPermittedSubclasses() javadoc.
>  - Enhancing the Class.getPermittedSubclasses() test to verify behavior both for sealed classes in named and unnamed modules.
>  - Removing unnecessary file.
>  - Tweaking javadoc.
>  - Reflecting review comments w.r.t. narrowing conversion.
>  - Improving checks in getPermittedSubclasses()
>  - Merging master into JDK-8246778
>  - ... and 2 more: https://git.openjdk.java.net/jdk/compare/6e006223...4d484179

src/java.base/share/classes/java/lang/Class.java line 3042:

> 3040:             for (Class<?> c : classes) {
> 3041:                 // skip the package access check on a proxy class in default proxy package
> 3042:                 if (!Proxy.isProxyClass(c) || ReflectUtil.isNonPublicProxyClass(c)) {

If a sealed class is in a named module, the permitted subclasses/subinterfaces are in the same module as the sealed class.  If a sealed class is in an unnamed module, it will be in the same runtime package as the sealed class.   A proxy class is dynamically generated and not intended for statically named in `permits` clause of a sealed class`.  It can be in a different module or different package.  So a permitted subclass or interface should never be a proxy class. 

So the package access check for permitted subclasses/subinterfaces can be simplified.  I would suggest this check be inlined in `getPermittedSubclasses` as follows:

      SecurityManager sm = System.getSecurityManager();
        if (subclasses.length > 0 && sm != null) {
            ClassLoader ccl = ClassLoader.getClassLoader(Reflection.getCallerClass());
            ClassLoader cl = getClassLoader0();
            if (ReflectUtil.needsPackageAccessCheck(ccl, cl)) {
                Set<String> packages = new HashSet<>();
                for (Class<?> c : subclasses) {
                    if (Proxy.isProxyClass(c))
                        throw new InternalError("a permitted subclass should not be a proxy class: " + c);
                    String pkg = c.getPackageName();
                    if (!pkg.isEmpty())
                        packages.add(pkg);
                }
                for (String pkg : packages) {
                    sm.checkPackageAccess(pkg);
                }
            }
        }

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

PR: https://git.openjdk.java.net/jdk/pull/1483