RFR: 8344318: Enhance configure help for enabling/disabling single JVM features

[Erik Joelsson]

On Tue, 26 Nov 2024 18:08:24 GMT, Magnus Ihse Bursie <ihse at openjdk.org> wrote:

>> For any `--enable-<foo>` flag autoconf generates a corresponding `--disable-<foo>` flag. Using `--enable-<foo>` is equivalent to `--enable-<foo>=yes` and using `--disable-<foo>` is equivalent to `--enable-<foo>=no`. It's encouraged (from autoconf) to have "enable/disable" flags only take those values, but technically, you could supply any value to them. 
>> 
>> We try to use `--with-<foo>` for parameters that expect different arguments and those are usually possible to turn off as well using `--without-<foo>`, which is equivalent to `--with-<foo>=no`. I don't think we have properly implemented support for every `--without-<foo>` in our configure script however.
>
> Most --with flags actually check that we do *not* send in `no`; and those that don't probably should. :-) I can only think of a single case where we allow `--with-*=no`, and that is for gtest, where the way you disable it is to do `--without-gtest`.
> 
> Otherwise we really try to keep to the rule that `--enable/disable` are booleans that can be turned on or off, and `--with` are ways to send in an argument. But internally in autoconf, they are treated the same. And in GNU software, people do stuff like `--with-zlib` not to point to a library, but to enable linking with zlib, etc. So it's pretty messed up. I hope we can eventually ditch autoconf completely.

I disagree on the concept of `--without-<foo>` not being a valid usecase. It's very useful to be able to do for example `--without-devkit` to override a previous `--with-devkit=...` on the command line, when you are not in control of the full command line yourself. The typical usecase for me is when configuring using jib to get the Oracle official configuration, but wanting to override something specific.

-------------

PR Review Comment: https://git.openjdk.org/jdk/pull/22231#discussion_r1865998542