add cfg_flags for boolean feature flags

[mobileink]

Add support for boolean config flags. --cfg 'feature="foo"' does not work; --cfg foo does. This change supports the latter.

Signed-off-by: Gregg Reynolds 601396+mobileink@users.noreply.github.com

[damienmg]

Thanks for the change, I was wondering if that needs an actual extra attribute. I haven't tested but it sounds like this could be done in rustc_flags, can't it? I could also make sense of going along as there is the crate_features next to it, but it feel kind of bloating the API to add more way to pass rustc flags.

[mobileink]

I tried to use rustc_flags but could not make it work. Maybe I'm doing something wrong?
If I had my druthers I would rename crate_features to cfg_options. I think it makes sense to partition rustc options into cfg_options (key-val pairs), cfg_flags (booleans), and everything else, since the cfg options indirectly configure the source code, and the rest configure the compiler. That way the user interface makes a conceptual distinction explicit.

[damienmg]

Would you be willing to go ahead and adapt this PR to actually add cfg_options and cfg_flags and emit a warning when using the old options (noting that they are marked for deprecation, and how to switch to new options)?

This is a way larger change so I would understand if you rather not dig into that rabbit hole.

[mobileink]

On Tue, Jun 2, 2020 at 3:53 AM Damien Martin-Guillerez < ***@***.***> wrote: Would you be willing to go ahead and adapt this PR to actually add cfg_options and cfg_flags and emit a warning when using the old options (noting that they are marked for deprecation, and how to switch to new options)?

Sure, I'd be happy to do that, but I might not be able to get to it this week.

…

This is a way larger change so I would understand if you rather not dig into that rabbit hole. — You are receiving this because you authored the thread. Reply to this email directly, view it on GitHub <#321 (comment)>, or unsubscribe <https://github.com/notifications/unsubscribe-auth/AAES2NHVYBJP4BLNR7HAFNLRUS4X3ANCNFSM4NNFA4FQ> .

[c0nk]

Would it make more sense to only add cfg_flags for both bools and key-values? This would make it similar to defines for C/C++ targets.

[UebelAndre]

Any updates here? In Damien's absence, I wonder if @illicitonion might have some thoughts here?

[illicitonion]

Sorry, I'm struggling a bit to understand the use-case here that isn't met by the existing rustc_flags - would it be possible to add a test or example, in either the test or examples directory, showing some code which uses this feature, but which doesn't compile without it?