JDK 14 RFR of JDK-8202385: Annotation to mark serial-related fields and methods

Tue Aug 6 20:04:38 UTC 2019

Hi Roger,

Revised webev

     http://cr.openjdk.java.net/~darcy/8202385.5/

Diff of last two versions below. To ease review, I elected not to reflow 
the paragraphs at this time to reduce the number of lines of differences 
between the two versions.

Several platform annotation types start there javadoc with 
"Indicates..." so I kept that pattern.

It is true the serialization-defined fields and methods are accessed 
reflectively and may not be otherwise accessed. That seems more relevant 
to emphasize in the serialization spec itself, but it may be helpful to 
note here so I added one as requested.

Cheers,

-Joe

31c31
<  * Indicates that a field or method is related to the {@linkplain
---
 >  * Indicates that an annotated field or method is part of the {@linkplain
37c37,40
<  * validate method overriding.
---
 >  * validate method overriding. {@code Serializable} classes are 
encouraged to
 >  * use <code>@Serial</code> annotations to help a compiler catch
 >  * mis-declared serialization-related fields and methods,
 >  * mis-declarations that my otherwise be difficult to detect.
39c42
<  * <p>Specifically, annotations of this type are intended to be
---
 >  * <p>Specifically, annotations of this type should be
59c62
<  * A compiler can validate that a method or field marked with a
---
 >  * Compilers are encouraged to validate that a method or field marked 
with a
61c64,65
<  * methods or fields declared in a meaningful context.
---
 >  * methods or fields declared in a meaningful context and issue a warning
 >  * if that is not the case.
86a91,94
 >  *
 >  * Note that serialization mechanism accesses its designated fields
 >  * and methods reflectively and those fields and methods may appear
 >  * otherwise unused in a {@code Serializable} class.

On 8/1/2019 2:40 PM, Roger Riggs wrote:
> Hi Joe,
>
> It would be good to more closely define the semantics of the @Serial 
> annotation.
>
> Suggestion for the first sentence:
>
> "@Serial annotates each field or method specified by the <cite>Java 
> Object Serialization Specification</cite> of a {@linkplain 
> Serializable serializable} class."
>
> This annotation type is intended to allow compile-time checking of 
> serialization-related declarations, analogous to the checking enabled 
> by the {@link java.lang.Override} annotation type to validate method 
> overriding.
>
> It would be useful to describe that reflection is used to access and 
> use the fields and methods and they may  otherwise appear to be unused.
>
> A recommendation could be added in an @impleNote to apply @Serial to 
> each serialization defined method or field.
>
> $02, Roger
>
> On 7/13/19 1:16 PM, Joe Darcy wrote:
>> PS I've uploaded an updated an iteration of the webrev
>>
>> http://cr.openjdk.java.net/~darcy/8202385.4/
>>
>> to address. the syntactic concerns previously raised. I added
>>
>>     ...defined by the  <cite>Java Object Serialization 
>> Specification</cite>...
>>
>> which is the current name of the document and is similar to the style 
>> of reference made in java.io.Serializable. Offhand, I didn't know of 
>> the correct idiom to refer to the document as a working hyperlink, 
>> but would be switch to that idiom.
>>
>> Cheers,
>>
>> -Joe
>>
>> On 7/12/2019 8:19 PM, Joe Darcy wrote:
>>> Hi Roger,
>>>
>>> On 7/12/2019 1:31 PM, Roger Riggs wrote:
>>>> Hi Joe,
>>>>
>>>> As an annotation on a field or method, this is a use site annotation.
>>>
>>>
>>> It is an annotation intended for the declarations of fields and 
>>> methods of Serializable types.
>>>
>>>
>>>> From the description, the checks that could be added would only be 
>>>> done
>>>> if the annotation was present and the annotation is a tag for existing
>>>> fields and methods that are part of the serialization spec.
>>>
>>>
>>> Right; the annotation is semantically only applicable to the fields 
>>> and methods associated with the serialization system.
>>>
>>>
>>>>
>>>> The signatures of the fields and methods can be known to the 
>>>> compiler independent
>>>> of the annotation and produce the same warnings.
>>>> So this looks like a case of trying to have belt and suspenders.
>>>>
>>>> If the checks are not done when the annotation is not present, then 
>>>> it will still be
>>>> the case that incorrect or misused fields and methods will still 
>>>> escape detection.
>>>>
>>>> Though the details of the compiler check are outside of the scope 
>>>> of this annotation,
>>>> it seems unclear whether the annotation is necessary.
>>>
>>> I have a prototype annotation processor to implement checks for
>>>
>>>     JDK-8202056: Expand serial warning to check for bad overloads of 
>>> serial-related methods and ineffectual fields
>>>
>>> The current version of the processor does not assume the presence of 
>>> java.io.Serial. The summarize the existing checking methodology:
>>>
>>>     If a type is Serialiazable and a field or method has a name 
>>> matching the names of one of the special fields or methods to 
>>> serialization, check that the field or method has the required 
>>> modifiers, type, and, the the case of methods, parameter types and 
>>> exception types.
>>>
>>> That is all well and good and represents a large fraction of the 
>>> checking of interest. However, it does not catch a mis-declaration 
>>> like "readobject" instead of "readObject". One could argue that 
>>> sufficiently thorough testing should catch that kind of error; 
>>> however, my impression is that thoroughness of testing is rare in 
>>> practice. I don't think it would be reasonable for javac to have 
>>> some kind of Hamming distance 
>>> (https://en.wikipedia.org/wiki/Hamming_distance) check between the 
>>> name of fields/methods and the name of the serialization related 
>>> fields methods to try to catch such mis-declarations. An annotation 
>>> like java.io.Serial is intended to allow the programmer to indicate 
>>> "yes, this is supposed to be one of the serialization related fields 
>>> or methods" and enable the compile to perform checks against that 
>>> category of error.
>>>
>>>
>>>>
>>>> Can the name of the annotation be more descriptive?
>>>> Just "Serial" seems a bit too simple and does not have a strong 
>>>> binding to the Serialization classes and specification.
>>>> Alternatives:
>>>>    SerialMetadata
>>>>    SerialControl
>>>>    SerialFunction
>>>
>>> From the earlier design iterations "Serial" was chosen to be 
>>> evocative of the "@serial" javadoc tag.
>>>
>>> Thanks,
>>>
>>> -Joe
>>>
>>>>
>>>>
>>>> 39:  There should be a reference to the serialization specification 
>>>> for the definition
>>>> of the fields and methods to make it clear where the authoritative 
>>>> identification is spec'd.
>>>>
>>>> 73-75:  Please align the <ul> and </ul> tags on separate lines with 
>>>> matching indentation.
>>>>
>>>> 77: Extra leading space.
>>>>
>>>> Regards, Roger
>>>>
>>>> On 7/9/19 7:14 PM, Joe Darcy wrote:
>>>>> Hello,
>>>>>
>>>>> Returning to some old work [1], please review the addition of a 
>>>>> java.io.Serial annotation type for JDK 14 to mark serial-related 
>>>>> fields and methods:
>>>>>
>>>>>     webrev: http://cr.openjdk.java.net/~darcy/8202385.3/
>>>>>     CSR: https://bugs.openjdk.java.net/browse/JDK-8217698
>>>>>
>>>>> Thanks,
>>>>>
>>>>> -Joe
>>>>>
>>>>> [1] Previous review threads:
>>>>>
>>>>> http://mail.openjdk.java.net/pipermail/core-libs-dev/2018-May/053055.html 
>>>>>
>>>>>
>>>>> http://mail.openjdk.java.net/pipermail/core-libs-dev/2018-August/054801.html 
>>>>>
>>>>>
>>>>
>