Implement reasons for leaving a room.

[Frinksy]

Resolves: #511

Also adds the reason field in the leave_room endpoint as defined in the unstable spec.

However there is a compilation error that I can't figure out with this part:

        /// Optional reason to be included as the `reason` on the subsequent membership event.
        #[cfg(feature = "unstable-pre-spec")]
        #[cfg_attr(docsrs, doc(cfg(feature = "unstable-pre-spec")))]
        #[serde(skip_serializing_if = "Option::is_none")]
        pub reason: Option<&'a str>,

Compilation succeeds with cargo check --all-features but the regular cargo check fails with:

error[E0392]: parameter `'a` is never used
  --> crates/ruma-client-api/src/r0/membership/leave_room.rs:25:29
   |
25 |         pub reason: Option<&'a str>,
   |                             ^^ unused parameter
   |
   = help: consider removing `'a`, referring to it in a field, or using a marker such as `PhantomData`

error: aborting due to previous error

I feel like there something obvious that I'm missing, but the same code snippet worked fine when adding blurhash support. (That is the only other Option<&str> field that is feature-gated that I could find.)

[DevinR528]

Is the gated field the only one with a lifetime? I bet the generated struct has a lifetime but without the field it has no need for it.

On my phone so I can't look into to deep.

[Frinksy]

Is the gated field the only one with a lifetime?

There is this one which isn't gated and also has a lifetime:

        /// The room to leave.
        #[ruma_api(path)]
        pub room_id: &'a RoomId,

[DevinR528]

Ok I think I see the problem, the RequestBody is getting a lifetime annotation and then no field with a lifetime hmm https://github.com/ruma/ruma/blob/main/crates/ruma-api-macros/src/api/request.rs#L152-L190. I'm not sure how to fix this @jplatte does the expanding macro have access to the feature list? Any ideas come to mind?

Oh wow, there's an ICE also it looks related to this rust-lang/rust#86438 maybe?

Something that helped me when I had macro issues is https://github.com/dtolnay/cargo-expand you have to be in one of the crates, sorry if you are aware of it

cd crates/ruma-client-api
cargo expand r0::membership::leave_room

[iinuwa]

Looks good, just needs a changelog. 😉

[jplatte]

Finally this works (through #664)! Squash-merged on the command line: 13af2e2