David, I think that is a much better solution. Let the description of each Lookup mode be precise, and you have already updated PRIVATE mode to include nestmates.
I brought this concern up in the EG meeting yesterday and wanted to clarify the difference between handling of inner/outer classes for backward compatibility and general nestmate handling. Assumptions: 1. MethodHandle/VarHandle behavior is modeled on bytecode behavior. 2. Nestmates have the added capability of access to private members of their nestmates. Period. 3. In future we expect to use nestmates for more than inner/outer classes. 4. Inner/outer classes will continue to have the InnerClasses attribute, and starting in JDK11, javac will also generate NestHost and NestMember attributes. 5. With Nestmates, javac will not generate the default (package) trampolines to allow inner/outer classes to access each other’s private members. Note that today this is only done for members that have compile time accesses. (6. With Nestmates, bridges for protected members will still be generated unchanged.) For nestmates in general, the modifications you have made below allow a nestmate to access private members of their nestmates to match the bytecode behavior. Prior to nestmates, there is a special workaround in MethodHandles.Lookup.in() to allow inner/outer classes to access any member of any class that shares its top level class to emulate the generated trampolines. https://docs.oracle.com/javase/9/docs/api/java/lang/invoke/MethodHandles.Lookup.html#lookupModes-- In some cases, access between nested classes is obtained by the Java compiler by creating an wrapper method to access a private method of another class in the same top-level declaration. For example, a nested class C.D can access private members within other related classes such as C, C.D.E, or C.B, but the Java compiler may need to generate wrapper methods in those related classes. In such cases, a Lookup object on C.E would be unable to those private members. A workaround for this limitation is the Lookup.in <https://docs.oracle.com/javase/9/docs/api/java/lang/invoke/MethodHandles.Lookup.html#in-java.lang.Class-> method, which can transform a lookup on C.E into one on any of those other classes, without special elevation of privilege. This workaround will continue to be supported going forward explicitly for inner/outer classes. A side-effect of this workaround is the ability of the returned Lookup to access not only private methods in the “related” class, but also protected and inherited members of that class which are defined in other packages. So this workaround will continue to work for inner/outer classes that are also nestmates for backward compatibility. Going forward, for nestmates in general, the goal is to provide access to private members, which can be done via the access check to match bytecode behavior, and does not require special Lookup.in() workarounds. If at some point in the future we decide we want increased access for nestmates, we can widen this. Let’s just say that the complexity there is challenging and that it is better to err on the side of starting out more restrictive. Summary - I agree with David. We can leave the documentation as is, with the explicit changes to access checking modified below for private members accessible to nestmates. thanks David! Karen > On Feb 14, 2018, at 8:36 PM, David Holmes <david.hol...@oracle.com> wrote: > > Hi Karen, > > Thanks for looking at this. > > On 15/02/2018 1:16 AM, Karen Kinnear wrote: >> David, >> Re-reading these I had one suggestion: >>> - java/lang/invoke/MethodHandles.java >>> * <p> >>> - * In some cases, access between nested classes is obtained by the >>> Java compiler by creating >>> - * an wrapper method to access a private method of another class >>> - * in the same top-level declaration. >>> + * Since JDK 11 the relationship between nested types can be expressed >>> directly through the >>> + * {@code NestHost} and {@code NestMembers} attributes. >>> + * (See the Java Virtual Machine Specification, sections 4.7.28 and >>> 4.7.29.) >>> + * In that case, the lookup class has direct access to private members >>> of all its nestmates, and >>> + * that is true of the associated {@code Lookup} object as well. >>> + * Otherwise, access between nested classes is obtained by the Java >>> compiler creating >>> + * a wrapper method to access a private method of another class in the >>> same nest. >>> * For example, a nested class {@code C.D} >>> >>> Updated the nested classes description to cover legacy approach and new >>> nestmate approach. >>> >>> - * {@code C.E} would be unable to those private members. >>> + * {@code C.E} would be unable to access those private members. >>> >>> Fixed typo: "access" was missing. >>> >>> * <em>Discussion of private access:</em> >>> * We say that a lookup has <em>private access</em> >>> * if its {@linkplain #lookupModes lookup modes} >>> - * include the possibility of accessing {@code private} members. >>> + * include the possibility of accessing {@code private} members >>> + * (which includes the private members of nestmates). >>> * As documented in the relevant methods elsewhere, >>> * only lookups with private access possess the following capabilities: >>> * <ul style="font-size:smaller;"> >>> - * <li>access private fields, methods, and constructors of the lookup >>> class >>> + * <li>access private fields, methods, and constructors of the lookup >>> class and its nestmates >>> >>> Clarify that private access includes nestmate access. >>> >>> - * access all members of the caller's class, all public types in the >>> caller's module, >>> + * access all members of the caller's class and nestmates, all public >>> types in the caller's module, >> For the above, I would change this to >> * access all members of the caller’s class, all private members of >> nestmates, all types in the caller’s package, all public … >> Specifically, we are extended the PRIVATE mode as above to include access to >> all private members of nestmates >> and this description is trying to summarize access when all possible bits >> are set. >> None of the settings give you access to default (package-private) members >> that a nestmate inherits from a >> different package - since the Lookup model is based on the JVMS/bytecode >> behavior. > > True - you don't get access to a nestmates inherited protected members > declared in a different package. I certainly didn't intend to somehow imply > that. > >> I added the types in the caller’s package since PACKAGE gives you that but >> it was missing from the existing list. > > Backing up ... in 8 this method doc simply said: > > "A freshly-created lookup object on the caller's class has all possible bits > set, since the caller class can access all its own members." > > It doesn't try to say what a class can access, it just makes the obvious > statement that it can access all its own members. If that was the current > text I would not have needed to make any adjustment for nestmates. > > But for 9/10 it states: > > "A freshly-created lookup object on the caller's class has all possible bits > set, except UNCONDITIONAL. The lookup can be used to access all members of > the caller's class, all public types in the caller's module, and all public > types in packages exported by other modules to the caller's module." > > This is quite a different formulation as it now tries to enumerate the set of > accessible things - or at least gives that impression to me! But it is not > complete as it doesn't mention non-public types in the current package, nor > does it mention package-accessible members of types (whether public or not). > > With nestmates we have only expanded to include private member access, but > the original text doesn't touch on nestmates directly at all. If we were to > say only "all private members of nestmates" then we seem to suggest no access > to the all the other members (public, directly declared protected, package). > But if we say "nestmates" then that may imply more than intended as you point > out. If we say nothing then we again imply by omission that there is no > nestmate access. > > This seems to be a bit of an unwravelling thread started by the changes in 9. > I would suggest we simply delete this sentence altogether: > > "The lookup can be used to access all members of the caller's class, all > public types in the caller's module, and all public types in packages > exported by other modules to the caller's module." > > as each of the modes, together with the "Access Checking" section of the > class docs, define what is accessible under which mode. I don't think > lookupModes() needs to try and restate that. > > What do you think? > > Thanks, > David > >> thanks, >> Karen >>> >>> >>> Thanks, >>> >>> David
