On Wed, 11 Mar 2026 19:14:19 GMT, Chen Liang <[email protected]> wrote:
>> src/java.base/share/classes/java/lang/invoke/ConstantBootstrap.java line 46:
>>
>>> 44: * if the declaration is an instance method. The arguments can be
>>> 45: * variable-arity.
>>> 46: * <li>The first argument type is exactly {@link MethodHandles.Lookup}.
>>
>> Why is there a difference here with CallsiteBootrap for
>> MethodHandles.Lookup? It looks like the implementation checks assignability
>> for both.
>
> So indy bootstrap can have `(Object, Object...)` but that's illegal for
> condy. Condy's 1st arg must be declared exactly `MethodHandles.Lookup`.
That’s because we aspire (some day) to add new signatures for BSMs (maybe even
indy), where the Lookup is absent, and some other rule applies.
FTR: It could go either way, towards richer or poorer calling sequences.
Poorer — If a lookup and/or name and/or type are missing you just supply one
according to some rule. Richer (what I prefer) — Allow a single argument which
replaces all three required arguments; it handles most of the hardwired steps
in the JVM today — reflectively extracts name, type, and arguments, handles all
exceptions (for each extraction step). The reason I prefer this is we can then
remove the ad hoc rules from the JVMS, and just say, "If a Lookup/name/type are
supplied (the old way), then it as if the following standard BSM-handler object
were used instead." Less complexity in JVMS, more power to the end user. One
bit of new power: The end user can choose to reflectively query the
ConstantDesc for any or all BSM arguments, instead of today’s policy of forcing
a resolution of all arguments before BSM invocation (with catastrophic failure
if there’s an exception on any argument).
Anyway, if we do this stuff, there will be just one place to document it in the
JDK. And even today’s rules deserve a JDK javadoc block linked to all the
BSMs. So we are improving today, and leaving room for future improvement as
well.
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PR Review Comment: https://git.openjdk.org/jdk/pull/30125#discussion_r2920504553
