Constant descriptor resolved too soon during constant resolution?

[Jorn Vernee]

Hello,

I think I have stumbled upon a bug in the condy-folding branch (tip).

This is the code to reproduce:

```
import java.lang.constant.*;
import static java.lang.constant.ConstantDescs.*;

public class Main {

     static final DirectMethodHandleDesc MHR_CONCAT = 
MethodHandleDesc.of(
         DirectMethodHandleDesc.Kind.VIRTUAL,
         CR_String,
         "concat",
         CR_String,
         CR_String
     );

     public static void main(String[] args) throws Throwable {
         ConstantDesc<String> d = 
DynamicConstantDesc.<String>of(BSM_INVOKE).withArgs(MHR_CONCAT, "Hello, 
", "world!");
         System.out.println(d); // <---- exception thrown here, on 
resolution of `d2`
     }

}
```

I'm wrapping a call to `ConstantBootstraps.invoke` together with a 
method handle for `String.concat` and 2 constant arguments (a toy 
example). The resolution should effectively call `"Hello, 
".concat("world!")`. Please note that I'm not resolving the result 
string here though, but I'm resolving the descriptor itself. While 
resolving the descriptor `d` an exception is thrown:

```
Exception in thread "main" java.lang.BootstrapMethodError: bootstrap 
method initialization exception
         at 
java.base/java.lang.invoke.BootstrapMethodInvoker.invoke(BootstrapMethodInvoker.java:253)
         at 
java.base/java.lang.invoke.ConstantBootstraps.makeConstant(ConstantBootstraps.java:71)
         at 
java.base/java.lang.invoke.MethodHandleNatives.linkDynamicConstantImpl(MethodHandleNatives.java:314)
         at 
java.base/java.lang.invoke.MethodHandleNatives.linkDynamicConstant(MethodHandleNatives.java:306)
         at Main.main(Main.java:18)
Caused by: java.lang.ClassCastException: Cannot cast 
java.lang.invoke.DirectMethodHandle to java.lang.constant.ConstantDesc
         at java.base/java.lang.Class.cast(Class.java:3613)
         at 
java.base/java.lang.invoke.BootstrapMethodInvoker.invokeWithManyArguments(BootstrapMethodInvoker.java:350)
         at 
java.base/java.lang.invoke.BootstrapMethodInvoker.invoke(BootstrapMethodInvoker.java:195)
         ... 4 more
```

This puzzled me for a while, but I _think_ the cause is that the 
`MHR_CONCAT` descriptor is being resolved into a `DirectMethodHandle` 
too early during resolution? Oddly enough, when using 
`Intrinsics.ldc(d)` to resolve the result string, the program completes 
successfully, and I can print the resulting string. The following 
version also works as expected:

```
     ConstantDesc<String> d = DynamicConstantDesc.of(
         BSM_INVOKE, DEFAULT_NAME, CR_Object, new 
ConstantDesc<?>[]{MHR_CONCAT, "Hello, ", "world!"}); // No folding here, 
because the array is not a constant (?)
     System.out.println(d); // This one is OK
```

And it prints: 
`DynamicConstantDesc[ConstantBootstraps::invoke(MethodHandleDesc[VIRTUAL/String::concat(String)String],Hello, 
,world!)Object]`. As far as I can tell these 2 snippets should behave 
the same (the generated bytecode is quite different though), so I think 
this is a bug?

Is there a flag to temporarily turn off folding? I'm not aware of any 
javac equivalent of `-XX:+PrintFlagsFinal`, so I don't have a way to 
find out about experimental flags.

Also, I hope this is the right place to post bug reports, JBS doesn't 
seem to cover amber, and I've seen a few people reporting bugs on other 
mailing lists, but I'd expect more people to be doing that, so maybe I'm 
in the wrong place?

Best regards,
Jorn Vernee