Spec: ACC_MANDATED

[Leonid Kuskov]

Hi all,

The draft JVM spec for JEP 359(Records)* states in chapter 4.7.8 that:

"The|Synthetic|attribute is a fixed-length attribute in 
the|attributes|table of a|ClassFile|,|field_info|, 
or|method_info|structure (4.1 
<https://docs.oracle.com/javase/specs/jvms/se12/html/jvms-4.html#jvms-4.1>,4.5 
<https://docs.oracle.com/javase/specs/jvms/se12/html/jvms-4.html#jvms-4.5>,4.6 
<https://docs.oracle.com/javase/specs/jvms/se12/html/jvms-4.html#jvms-4.6>). 
A class member that does not appear in the source code must be marked 
using a|Synthetic|attribute, or else it must have its|ACC_SYNTHETIC|flag 
set. The only exceptions to this requirement are compiler-generated 
methods which are not considered implementation artifacts, namely the 
instance initialization method representing a default constructor of the 
Java programming language (2.9.1 
<https://docs.oracle.com/javase/specs/jvms/se12/html/jvms-2.html#jvms-2.9.1>), 
the class or interface initialization method (2.9.2 
<https://docs.oracle.com/javase/specs/jvms/se12/html/jvms-2.html#jvms-2.9.2>), 
andthe|Enum.values()|and|Enum.valueOf()|methods*mandated members of 
enums and records*."

So specification allows RI  to mark final fields associated with 
components and some methods by ACC_MANDATED flag (0x8000). The latest 
JVMS specification 
(https://docs.oracle.com/javase/specs/jvms/se13/html/index.html) permits 
this flag only for 2 attributes: MethodParameters_attribute, 
Module_attribute . The flag is not mentioned in both tables: Table 
4.5-A. "Field access and property flags", Table 4.6-A. "Method access 
and property flags".
 From my point of view, usage of this flag with methods/fields 
contradicts the assertions:

>> All bits of the  access_flags item not assigned in Table 4.5-A are reserved for future 
use. *They should be* *set to zero* in generated class files and should 
be ignored by Java Virtual Machine implementations.
 >> All bits of the access_flags item not assigned in Table 4.6-A are 
reserved for future use. They should be set to zero in generated class 
files and should be ignored by Java Virtual Machine implementations.

Does it make sense to add a definition of ACC_MANDATED to the tables?

And:

Earlier the spec stated that the Enum.values() and Enum.valueOf() are 
exceptions to the requirement that a class member that does not appear 
in the source code must be marked using a Synthetic attribute, or have 
its ACC_SYNTHETIC flag set.
Now names of methods are removed and the more loose statement "mandated 
members of enums and records" is used. Does it mean that spec won't 
enumerate "mandated" methods anymore? And the setting of this flag will 
be implementation-specific? From my point of view, it might break the 
unambiguity of the signature tests.
Should the JCK signature test take into account the ACC_MANDATED flag?

Thanks,
Leonid

*) 
http://cr.openjdk.java.net/~gbierman/jep359/jep359-20191031/specs/records-jvms.html

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