RFR: JDK-8315458 Implementation of Implicitly Declared Classes and Instance Main Method (Second Preview) [v2]

[Maurizio Cimadamore]

On Thu, 2 Nov 2023 11:53:09 GMT, Jim Laskey <jlaskey at openjdk.org> wrote:

>> src/jdk.compiler/share/classes/com/sun/tools/javac/parser/JavacParser.java line 4057:
>> 
>>> 4055:         Name name = names.fromString(simplename);
>>> 4056:         JCModifiers implicitMods = F.at(Position.NOPOS)
>>> 4057:                 .Modifiers(Flags.FINAL|Flags.MANDATED|Flags.IMPLICIT_CLASS, List.nil());
>> 
>> I don't think the JVMS allows for a flag to have ACC_MANDATED flags?
>> 
>> 
>> It is a limitation of the class file format that only formal parameters and modules can be flagged as ACC_MANDATED ([§4.7.24](https://docs.oracle.com/javase/specs/jvms/se21/html/jvms-4.html#jvms-4.7.24), [§4.7.25](https://docs.oracle.com/javase/specs/jvms/se21/html/jvms-4.html#jvms-4.7.25)) to indicate that, despite being compiler-generated, they are not considered implementation artifacts. There is no way to flag other compiler-generated constructs so that they too are not considered implementation artifacts (JLS §13.1). This limitation means that reflective APIs of the Java SE Platform may not accurately indicate the "mandated" status of such constructs.
>
> The spec has been updated to include implicit classes.

Uhmm. In the spec I see implicit classes named here:


 For reference, the following constructs are declared implicitly in source code, but are not marked as mandated because only formal parameters and modules can be so marked in a class file (JVMS §4.7.24, JVMS §4.7.25):
 ```

Note the `but are not marked as mandated`.

I don't think javac sets the mandated flag for any of these. Note that ACC_MANDATED has the same value as the ACC_MODULE flag, so setting that flag on a class w/o at least filtering out when writing the classfile will be problematic.

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PR Review Comment: https://git.openjdk.org/jdk/pull/16461#discussion_r1380009418