RFR: 8294982: Implementation of Classfile API [v12]

[Adam Sotona]

On Wed, 8 Feb 2023 07:21:07 GMT, Adam Sotona <asotona at openjdk.org> wrote:

>>> Class `Signature` (aka `JavaTypeSignature`), all subclasses, `MethodSignature` and `ClassSignature` are designed according to [JVMS 4.7.9.1 Signatures](https://docs.oracle.com/javase/specs/jvms/se19/html/jvms-4.html#jvms-4.7.9.1)
>> 
>> The production is the same as the one I quoted, but thanks for pointing me at the correct one. So:
>> 
>> 
>> JavaTypeSignature:
>>    ReferenceTypeSignature
>>    BaseType 
>> 
>> 
>> and
>> 
>> 
>> ReferenceTypeSignature:
>>    ClassTypeSignature
>>    TypeVariableSignature
>>    ArrayTypeSignature
>> 
>> 
>> So, while I can expect that `ArrayTypeSignature` *is a* `Signature` (or `JavaTypeSignature`), I cannot explain why `ThrowsSignature` extends `Signature`. That doesn't seem to follow from the production. That is, if a client obtains a `Signature` and wanted to pattern match, what are the cases it should worry about? I believe the cases are the ones listed above.
>> 
>> One thing I missed is that e.g. `TypeParam` is *not* a signature (which is the only case among the nested classes in `Signature`). But `ThrowsSignature`, `TypeArg` and `TypeParam` are signatures even though that doesn't seem to be the case when looking at the production in the JVMS. If we want to keep these fine, but I don't think they should extend `Signature`, either directly or indirectly. That is, `Signature` should be a sealed type with 4 leaves (base-type/array/type var/class-type).
>
> **Specification:**
> 
> MethodSignature:
> [TypeParameters] ( {JavaTypeSignature} ) Result {ThrowsSignature}
> 
> Result:
> JavaTypeSignature 
> VoidDescriptor
> 
> ThrowsSignature:
> ^ ClassTypeSignature 
> ^ TypeVariableSignature
> 
> 
> 
> **Reflect in API mapping:**
> 
>     public sealed interface ClassTypeSig
>             extends RefTypeSig, ThrowableSig
> 
> and
> 
>     public sealed interface TypeVarSig
>             extends RefTypeSig, ThrowableSig
> 
> and
> 
>     /**
>      * @return method signature
>      * @param typeParameters signatures for the type parameters
>      * @param exceptions sigantures for the exceptions
>      * @param result signature for the return type
>      * @param arguments signatures for the method arguments
>      */
>     public static MethodSignature of(List<Signature.TypeParam> typeParameters,
>                                      List<Signature.ThrowableSig> exceptions,
>                                      Signature result,
>                                      Signature... arguments) {
> 
> 
> `Signature.ThrowableSig` is a `Signature` and it is a common super of `ClassTypeSig` and `ClassTypeSig`.

`TypeParam` is not a signature, because it simply is not a signature.
Per spec:

TypeParameter:
Identifier ClassBound {InterfaceBound}

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

PR: https://git.openjdk.org/jdk/pull/10982