RFR: 8350007: Add usage message to the javadoc executable [v3]

[Hannes Wallnöfer]

On Thu, 20 Feb 2025 16:25:33 GMT, Nizar Benalla <nbenalla at openjdk.org> wrote:

>> This patch adds a new message when you run the `javadoc` executable with any arguments.
>> Currently, unlike most other tools, running `javadoc` without any arguments does not show you how to use the tool or point you to use the `--help` option, this can be improved.
>> 
>> Before change:
>> 
>> W $ ./javadoc
>> error: No modules, packages or classes specified.
>> 1 error
>> 
>> 
>> After change:
>> 
>> W $ ./javadoc
>> Usage:
>>     javadoc [options] [packagenames] [sourcefiles] [@files]
>> For additional help on usage:           javadoc --help
>
> Nizar Benalla 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 four additional commits since the last revision:
> 
>  - respond to feedback
>  - Merge branch 'master' into javadoc-usage-message
>  - update test with new usage message
>  - improve javadoc executable message

src/jdk.javadoc/share/classes/jdk/javadoc/internal/tool/Start.java line 560:

> 558:                     showLinesUsingKey("main.usage.short");
> 559:                     showLinesUsingKey("main.for-more-details-see-usage");
> 560:                     return OK;

The currently used exit code is `2`, and the message is written to `stderr`, not `stdout`. I think these things should not be changed.

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PR Review Comment: https://git.openjdk.org/jdk/pull/23618#discussion_r1972045539