Fwd: Mandated/implicit parameters

[Hannes Greule]

 > Your patch looks nice. I suggest, in addition, to write the attribute
 > when any synthetic parameter is present as well (such as the first two
 > String and int of enum constructors).

Thank you. I'll look into synthetic parameters too.

 > In addition, I would recommend a
 > test for core reflection to ensure the newly emitted attributes allow
 > core reflection to correctly describe the parameterized types of inner
 > class constructors, etc.

I think I also need a test for the compiler output. I'll start working 
on that.

 > Once you can find a related issue on the bug tracker (or report one at
 > https://bugs.java.com/ if you can't find a fitting one), you can
 > submit this patch for that bug tracker issue.

I found JDK-8213329: Normalize inclusion of non-explicit parameters in 
JVM attributes[1] but that doesn't really fit the issue. I'll report a 
new one.

 > For the ClassReader, I think you may need a `index++;` before the
 > `continue;`, as that would better match the behavior of
 > LocalVariableTable register-based index assigning.

I looked into that a bit more. It seems more complicated as the 
ClassReader reads names from both the LocalVariableTable and the 
MethodParameters attribute if both are present. However, if the 
MethodParameters attribute is read after the LocalVariableTable, it will 
replace names from the LocalVariableTable. This causes issues if no 
names are written to the MethodParameters attribute.
I'm not sure what the best approach would be here, especially as 
indexing is different (due to the slot for `this` in non-static 
methods/ctors).

[1] https://bugs.openjdk.org/browse/JDK-8213329