classfile format for type annotations on instructions

[Eric Bruneton]

Hi,

For type annotations on class, fields and methods, it is clear how the 
annotations can be recovered from a class file, using both the 
target_type and target_info fields, and the Signature attribute of the 
corresponding class, field or method.

However, I don't see how this is possible for type annotations on 
instructions. The only generic type information that is available for 
instructions is about the local variables, in the LocalVariableTypeTable 
attribute 
(http://docs.oracle.com/javase/specs/jvms/se7/html/jvms-4.html#jvms-4.7.14). 
Even with some kind of type inference mechanism, I don't see how this is 
sufficient to know the generic types for any erased type on the stack or 
in the locals, at any point in the code (since an annotation can target 
any instruction). Can you explain how this works?

I also have a question about annotations for constructor calls (sections 
3.3.9 and 3.3.10). Why do they target the 'new' instruction instead of 
the 'invokespecial' that corresponds to the actual constructor call? At 
the 'new' instruction we don't even know which constructor will be 
called, how many arguments it takes and of which types, etc. On the 
contrary, this information is available at the 'invokespecial' 
instruction. Thus it seems more logical to target this instruction, to 
know the types targeted by 'target_info', to do consistency checks, etc.

Eric