feat: render docs from aliased type when type has no docs
Trying to close#18344
- [x] ~Find the docs by traversing upwards if the type itself has none but aliasing for another type that might have.~
- [x] Show docs from aliased type.
- [x] Showing description that we are displaying documentation for different definition in hover box.

terminology: #[feature] *enables* a feature (instead of "declaring" or "activating" it)
Mostly, we currently call a feature that has a corresponding `#[feature(name)]` attribute in the current crate a "declared" feature. I think that is confusing as it does not align with what "declaring" usually means. Furthermore, we *also* refer to `#[stable]`/`#[unstable]` as *declaring* a feature (e.g. in [these diagnostics](f25e5abea2/compiler/rustc_passes/messages.ftl (L297-L301))), which aligns better with what "declaring" usually means. To make things worse, the functions `tcx.features().active(...)` and `tcx.features().declared(...)` both exist and they are doing almost the same thing (testing whether a corresponding `#[feature(name)]` exists) except that `active` would ICE if the feature is not an unstable lang feature. On top of this, the callback when a feature is activated/declared is called `set_enabled`, and many comments also talk about "enabling" a feature.
So really, our terminology is just a mess.
I would suggest we use "declaring a feature" for saying that something is/was guarded by a feature (e.g. `#[stable]`/`#[unstable]`), and "enabling a feature" for `#[feature(name)]`. This PR implements that.
terminology: #[feature] *enables* a feature (instead of "declaring" or "activating" it)
Mostly, we currently call a feature that has a corresponding `#[feature(name)]` attribute in the current crate a "declared" feature. I think that is confusing as it does not align with what "declaring" usually means. Furthermore, we *also* refer to `#[stable]`/`#[unstable]` as *declaring* a feature (e.g. in [these diagnostics](f25e5abea2/compiler/rustc_passes/messages.ftl (L297-L301))), which aligns better with what "declaring" usually means. To make things worse, the functions `tcx.features().active(...)` and `tcx.features().declared(...)` both exist and they are doing almost the same thing (testing whether a corresponding `#[feature(name)]` exists) except that `active` would ICE if the feature is not an unstable lang feature. On top of this, the callback when a feature is activated/declared is called `set_enabled`, and many comments also talk about "enabling" a feature.
So really, our terminology is just a mess.
I would suggest we use "declaring a feature" for saying that something is/was guarded by a feature (e.g. `#[stable]`/`#[unstable]`), and "enabling a feature" for `#[feature(name)]`. This PR implements that.
Dominator-order information is only needed for coverage graphs, and is easy
enough to collect by just traversing the graph again.
This avoids wasted work when computing graph dominators for any other purpose.
epoll_ctl: throw unsupported error on unsupported opcode
`@tiif` this is a somewhat suspicious "return -1" without setting the `errno` -- what is the reasoning behind that?
Throwing a clear error seems better to me.
coverage: Make counter creation handle node/edge counters more uniformly
Similar to #130380, this is another round of small improvements informed by my ongoing attempts to overhaul coverage counter creation.
One of the big benefits is getting rid of the awkward special-case that would sometimes attach an edge counter to a node instead. That was needed by the code that chooses which out-edge should be given a counter expression, but we can avoid that by making the corresponding check a little smarter.
I've also renamed several things to be simpler and more consistent, which should help with future changes.