[code-reflection] RFR: Make Quotable a marker interface [v4]

[Maurizio Cimadamore]

On Wed, 8 Jan 2025 22:02:10 GMT, Paul Sandoz <psandoz at openjdk.org> wrote:

>> FI implementation can't access Quotable2 because it's not exported.
>
> Right, so i think we need to create an interface in `java.base` in a package exported to `jdk.incubator.code` e.g., create a package in `java.base` called `jdk.internal.code` and add:
> 
> // Implementations of this interface also implement jdk.incubator.code.Quotable
> interface QuotableWithQuotedAccess { // or whatever we call it
>     // Implementations return instances of jdk.incubator.code.Quoted
>     Object quoted();
> }
> 
> then modify `module-info.java` in `java.base` to export package `jdk.internal.code` to module `jdk.incubator.code`.
> 
> 
> More generally either this or the current approach will fail if the quotable functional interface is explicitly proxied via `Proxy.newProxyInstance` or `MethodHandleProxies.asInterfaceInstance`. And, regardless if we have `Quotable::quoted` proxying would fail for instances of the following:  
> 
> Runnable r = (Runnable & Quotable) () -> { ... };
> 
> 
> I think we have to specify that such proxying results in inaccessible models. Not great a great answer, but not terrible.

There's actually three modules:
1. the module in which capture occurs (e.g. where the quotable lambda is)
2. `java.base` which is where the lambda metafactory is
3. `jdk.incubator.code` which is where the code reflection code is

I'm not sure if the problem @mabbay is describing has to do with `Quotable2` not being accessible from (1) or (2). Putting the new interface in `java.base` will obviously address accessibility from (2). But I think there's still issues with respect to (1) ?

E.g. `InnerClassLambdaMetafactory`, at the end of the day, will call `defineClass` on the _caller_ lookup (e.g. the one in (1)). If the class being defined contains a symbolic reference to a non-exported interface, wouldn't that be an issue, regardless of whether the non-exported interface is in `java.base` or `jdk.incubator.code` ?

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PR Review Comment: https://git.openjdk.org/babylon/pull/302#discussion_r1907931025