Fix: a TODO and some clippy fixes
- fix(todo): implement IntoIterator for ArenaMap<IDX, V>
- chore: remove unused method
- fix: remove useless `return`s
- fix: various clippy lints
- fix: simplify boolean test to a single negation
MIR episode 5
This PR inits drop support (it is very broken at this stage, some things are dropped multiple time, drop scopes are wrong, ...) and adds stdout support (`println!` doesn't work since its expansion is dummy, but `stdout().write(b"hello world\n")` works if you use `RA_SYSROOT_HACK`) for interpreting. There is no useful unit test that it can interpret yet, but it is a good sign that it didn't hit a major road block yet.
In MIR lowering, it adds support for slice pattern and anonymous const blocks, and some fixes so that we can evaluate `SmolStr::new_inline` in const eval. With these changes, 57 failed mir body remains.
Support `#[macro_use(name, ...)]`
This PR adds support for another form of the `macro_use` attribute: `#[macro_use(name, ...)]` ([reference]).
Note that this form of the attribute is only applicable to extern crate decls, not to mod decls.
[reference]: https://doc.rust-lang.org/reference/macros-by-example.html#the-macro_use-attribute
Parse associated return type bounds
This PR implements parser support for associated return type bounds: `T: Foo<bar(): Send>`. This PR does not implement associated return types (`T::bar(): Send`) because it's not implemented even in rustc, and also removes `(..)`-style return type notation because it has been removed in rust-lang/rust#110203 (effectively reverting #14465).
I don't plan to proactively follow this unstable feature unless an RFC is accepted and my main motivation here is to remove no-longer-valid syntax `(..)` from our parser, nevertheless adding minimal parser support so anyone interested (as can be seen in #14465) can experiment it without rust-analyzer's syntax errors.
