Custom E0277 diagnostic for `Path`
r? @nikomatsakis we have a way to target `Path` exclusively, we need to identify the correct text to show to consider #23286 fixed.
This seemed like a good way to kick the tires on the
elided-lifetimes-in-paths lint (#52069)—seems to work! This was also
pretty tedious—it sure would be nice if `cargo fix` worked on this
codebase (#53896)!
rustc: future-proof error reporting for polymorphic constants in types.
Currently, we have 3 categories of positions where a constant can be used (`const` and associated `const` can be considered "aliases" for an expression):
* runtime - if the function is polymorphic, we could even just warn and emit a panic
* `static` - always monomorphic, so we can error at definition site
* type-system - **must** *enforce* evaluation success where it was written
That last one is the tricky one, because we can't easily turn *the presence* a type with an erroring const into a runtime panic, and we'd have to do post-monomorphization errors (which we'd rather avoid).
<hr/>
The solution we came up with, as part of the plans for const generics, is to require successful evaluation wherever a constant shows up in a type (currently in array lengths, and values for const parameters in the future), *through* the WF system, which means that in certain situations (e.g. function signatures) we can assume evaluation *will* succeed, and require it of users (e.g. callers) instead (we've been doing this for lifetime bounds, for a long time now, and it's pretty ergonomic).
So once we do sth about #43408, this example *should* work, by propagating the responsability, to callers of `foo::<X>`, of proving `std::mem::size_of::<X>()` succeeds (and those callers can do the same).
```rust
pub fn foo<T>(_: [u8; std::mem::size_of::<T>()]) {}
```
But this one *shouldn't*, as there is nothing in the signature/bounds to indicate it:
```rust
pub fn bar<T>() {
let _: [u8; std::mem::size_of::<T>()];
}
```
<hr/>
I've come across some bit of code in the compiler that ignores const-evaluation errors *even when* they come from a constant in a type, and I've added an ICE *only when* there are no other reported errors (e.g. it's fine to ignore evaluation errors if the constant doesn't even type-check).
r? @nikomatsakis cc @oli-obk @RalfJung @Centril
Implement Unsized Rvalues
This PR is the first step to implement RFC1909: unsized rvalues (#48055).
## Implemented
- `Sized` is removed for arguments and local bindings. (under `#![feature(unsized_locals)]`)
- Unsized locations are allowed in MIR
- Unsized places and operands are correctly translated at codegen
## Not implemented in this PR
- Additional `Sized` checks:
- tuple struct constructor (accidentally compiles now)
- closure arguments at closure generation (accidentally compiles now)
- upvars (ICEs now)
- Generating vtable for `fn method(self)` (ICEs now)
- VLAs: `[e; n]` where `n` isn't const
- Reduce unnecessary allocations
## Current status
- [x] Fix `__rust_probestack` (rust-lang-nursery/compiler-builtins#244)
- [x] Get the fix merged
- [x] `#![feature(unsized_locals)]`
- [x] Give it a tracking issue number
- [x] Lift sized checks in typeck and MIR-borrowck
- [ ] <del>Forbid `A(unsized-expr)`</del> will be another PR
- [x] Minimum working codegen
- [x] Add more examples and fill in unimplemented codegen paths
- [ ] <del>Loosen object-safety rules (will be another PR)</del>
- [ ] <del>Implement `Box<FnOnce>` (will be another PR)</del>
- [ ] <del>Reduce temporaries (will be another PR)</del>
add suggestion applicabilities to librustc and libsyntax
A down payment on #50723. Interested in feedback on whether my `MaybeIncorrect` vs. `MachineApplicable` judgement calls are well-calibrated (and that we have a consensus on what this means).
r? @Manishearth
cc @killercup @estebank
