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.
Compute data layout of types
cc #4091
Things that aren't working:
* Closures
* Generators (so no support for `Future` I think)
* Opaque types
* Type alias and associated types which may need normalization
Things that show wrong result:
* ~Enums with explicit discriminant~
* SIMD types
* ~`NonZero*` and similar standard library items which control layout with special attributes~
At the user level, I didn't put much work, since I wasn't confident about what is the best way to present this information. Currently it shows size and align for ADTs, and size, align, offset for struct fields, in the hover, similar to clangd. I used it some days and I feel I liked it, but we may consider it too noisy and move it to an assist or command.
feat: type inference for generators
This PR implements basic type inference for generator and yield expressions.
Things not included in this PR:
- Generator upvars and generator witnesses are not implemented. They are only used to determine auto trait impls, so basic type inference should be fine without them, but method resolutions with auto trait bounds may not be resolved correctly.
Open questions:
- I haven't (yet) implemented `HirDisplay` for `TyKind::Generator`, so generator types are just shown as "{{generator}}" (in tests, inlay hints, hovers, etc.), which is not really nice. How should we show them?
- I added moderate amount of stuffs to minicore. I especially didn't want to add `impl<T> Deref for &T` and `impl<T> Deref for &mut T` exclusively for tests for generators; should I move them into the test fixtures or can they be placed in minicore?
cc #4309
feat: Display the value of enum variant on hover
fixes#12955
This PR adds const eval support for enums, as well as showing their value on hover, just as consts currently have.
I developed these two things at the same time, but I've realized now that they are separate. However since the hover is just a 10 line change (not including tests), I figured I may as well put them in the same PR. Though if you want them split up into "enum const eval support" and "show enum variant value on hover", I think that's reasonable too.
Since this adds const eval support for enums this also allows consts that reference enums to have their values computed now too.
The const evaluation itself is quite rudimentary, it doesn't keep track of the actual type of the enum, but it turns out that Rust doesn't actually either, and `E::A as u8` is valid regardless of the `repr` on `E`.
It also doesn't really care about what expression the enum variant contains, it could for example be a string, despite that not being allowed, but I guess it's up to the `cargo check` diagnostics to inform of such issues anyway?
