RFR: 8332124: Jcmd processing should accept the "help" sub option as command argument [v2]

[Laurence Cable]

and jcmd already supports "help" w/o a target argument, so this pattern 
is a natural extension, and one which other toolsets have adopted!

On 6/25/24 1:28 PM, Laurence Cable wrote:
> what about '*jcmd <pid> help <cmd>*'
>
> not a great deal of additional code for the 'help' jcmd to delegate to 
> the target jcmd?
>
> - Larry
>
> On 6/25/24 10:15 AM, Kevin Walls wrote:
>> On Tue, 25 Jun 2024 13:55:32 GMT, Sonia Zaldana Calles<szaldana at openjdk.org>  wrote:
>>
>>>> Hi all,
>>>>
>>>> This PR addresses [8332124](https://bugs.openjdk.org/browse/JDK-8332124) enabling jcmd to accept "help" as an argument to subcommands.
>>>>
>>>> Testing:
>>>> - [x] Verified running `jcmd 4711 VM.metaspace help` works along with other subcommands.
>>>> - [x] Added test case passes.
>>>>
>>>> Thanks,
>>>> Sonia
>>> Sonia Zaldana Calles has updated the pull request with a new target base due to a merge or a rebase. The incremental webrev excludes the unrelated changes brought in by the merge/rebase. The pull request contains three additional commits since the last revision:
>>>
>>>   - Merge branch 'openjdk:master' into JDK-8332124
>>>   - Adding test case for suboptions with trailing spaces and adding null terminator to reordered command
>>>   - 8332124: Jcmd processing should accept the "help" sub option as command argument
>> I could benefit from this, I think it's natural to sometimes want to check the help after you've started typing, so I like the idea.  But can it actually clash with any other usage?
>>
>> e.g. "help" can be a filename.  We are making the filename "help" unusable.  Maybe not a big deal to most people, but we do need to make this clear.
>>
>>
>> jcmd PID Thread.dump_to_file help
>>
>> ...used to create a file "help", and now does not?
>>
>> Compiler.directives_add takes a filename and would accept "help".
>> GC.heap_dump used to create a dump file called "help".
>>
>> jcmd 7537 VM.set_flag help
>> ..could have been a clash if we had such a VM flag (not likely...).
>>
>>
>> I don't mean to labour artificial or uncommon cases, but we do want this to be clearly specified.  Maybe this is still OK with the right hints (somewhere?) about the filenames that are now not possible to read or create.
>>
>>
>> Any thoughts on if
>> jcmd PID command -help
>> or
>> jcmd PID command --help
>>
>> ..should work, or could work?  Additionally, or instead?  Maybe they are better, as users relying on files called "-help" would be really uncommon (and would be inviting problems!).
>>
>>
>> Good to ignore the trailing whitespace.
>> Not obvious whether trailing extra text should be ignored or cause an error.
>> e.g.
>> jcmd 7537 VM.stringtable help nonsense
>> 7537:
>> java.lang.IllegalArgumentException: Unknown argument 'help' in diagnostic command.
>>
>> ..where I guess it's not the "help" which is unknown.  Is the user better served by just giving the help and ignoring the additional "nonsense"?
>>
>> -------------
>>
>> PR Review:https://git.openjdk.org/jdk/pull/19776#pullrequestreview-2139311805
>
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