RFR: 8294972: Convert jdk.jlink internal plugins to use the Classfile API [v8]

[Mandy Chung]

On Thu, 16 Mar 2023 16:06:15 GMT, Naoto Sato <naoto at openjdk.org> wrote:

>> This plugin does not fit to the Classfile API use cases portfolio at all. Here it is only needed to get interfaces list out of the constant pool and then the Utf8 CP entries are in-place modified. That is out of the Classfile API or ASM capabilities. Bad magic number is not the only difference, both libraries fail whenever touching even headers of any other standard classfile elements, only constant pool and interfaces seem to be "safe". 
>> I can prepare very simple standalone helper class dealing with this case to remove ASM dependency. 
>> However knowing more about the file format is always useful :)
>
> The file `LineBreakIteratorData_th` is not a class file, thus the exception is appropriate. This plugin test is trying to verify the integrity of the generated jimage, not only the required class files for the specified locale, but also the required resources as such. The file itself is a binary file that the BreakIterator uses internally.

@naotoj as these localedata resource files are not `.class`, the plugin should not use ASM (or Classfile API) to parse it but ASM ClassReader just happens to work.   Is the format documented anywhere?

@asotona  I agree that this ASM dependency should be replaced with a simple class to parse the localedata resources.   We can create a follow-up issue to document or validate the file format if appropriate.

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PR: https://git.openjdk.org/jdk/pull/12944