Waffle Maybe

> Several adaptors say that they should be the outermost in the composition Is this true? Reading the docs I only see that `AutoSend` should be the outermost one. >...

I'll try to make docs clear & maybe add an example

I've updated the issue, so it's now clear what is and is not implemented.

This is still happening @fubaduba @derekbekoe can any progress be made here? This is v. annoying since I basically can't use any shortcuts when co-editing.

> If you feel it deserves to stay open, then clarify your use case and contact us to let us know how severe it’s for you. @derekbekoe I _do_ think...

@cuviper I think it could plausibly become stable, at least if/when `!` is stabilized

> it made me wonder whether it would be feasible to change return in general to be a free type variable instead of `!`? @scottmcm I'm not sure. I don't...

> I presume the next step is a crater run to evaluate the impact? @Amanieu yes.

@chorman0773 can you explain what you mean by "if this will cause issues in `if`/`else` blocks particularily"? This PR makes all `Err(..)?;` be compile time errors, the only way to...

@chorman0773 this exact case actually will still work: ```rust if some_error_case{ Err(/*error value*/)? } ``` else-less `if` requires the block to be of type `()`, so the type can be...