[code-reflection] RFR: Cleanup JavaType factories [v3]

[Paul Sandoz]

On Fri, 3 May 2024 10:09:39 GMT, Maurizio Cimadamore <mcimadamore at openjdk.org> wrote:

>> This PR is a biggie cleanup of the various `JavaType` classes.
>> 
>> Perhaps the biggest contribution of this PR is to cleanup the factories in `JavaType`. The new factories are as follows:
>> * a factory to create a type from a `ClassDesc`
>> * a factory to create a type from a `j.l.r.Type`
>> * a couple of factories for creating parameterized types, which work on `JavaType` instances
>> * a couple of factories for array types
>> * a couple of factories for wildcard types
>> * a factory for type variables
>> 
>> This resolves the non-orthogonality found in the current set of factories, where one can take a `JavaType` and can, simultaneously, parameterize it, and turn it into an array type. Now the factories for these two operations are distinct.
>> 
>> The new factories also clarify the relationship between `JavaType`, `ClassDesc` and `j.l.Type` - that is:
>> 
>> * a type can be built from a nominal descriptor, using `type(ClassDesc)`
>> * a type can turned into a nominal descriptor, using `toNominalDescriptor()`
>> * a type can be built from a reflective type mirror, using `type(Type)`
>> * a type can turned into a nominal descriptor, using `resolve(Lookup)`
>> 
>> These operations are symmetric - that is, you can start from a reflective type mirror, build a `JavaType` form it, then resolve that into a `Type` and check that you get back where you started. I've enhanced `JavaTypeTest` to check round trip for both `ClassDesc` and `Type`.
>> 
>> Note that the `JavaType` can be associated with complex reflective mirrors, e.g. beyond just `Class<?>`. For this reason, existing uses of `JavaType::resolve` in `BytecodeGenerator` and `Interpreter` which were expecting to obtain a `Class` from a `resolve` call have been rewritten to use the idiom `type.erasure().resolve(...)`.
>> 
>> As part of this PR I've also added javadoc for all the methods/fields under the `JavaType` hierarchy that did not have one, and expanded existing docs.
>> 
>> I've added several tests to make sure that all the conversions work as expected, and I have verified the examples (by opening their files in the IDE and make sure there's no error, I did not build).
>
> Maurizio Cimadamore has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Address review comments
>   Move `TestErasure` under more apt `type` test folder

Marked as reviewed by psandoz (Lead).

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PR Review: https://git.openjdk.org/babylon/pull/71#pullrequestreview-2038208290