repr(transparent): it's fine if the one non-1-ZST field is a ZST
This code currently gets rejected:
```rust
#[repr(transparent)]
struct MyType([u16; 0])
```
That clearly seems like a bug to me: `repr(transparent)` [got defined ](https://github.com/rust-lang/rust/issues/77841#issuecomment-716575747) as having any number of 1-ZST fields plus optionally one more field; `MyType` clearly satisfies that definition.
This PR changes the `repr(transparent)` logic to actually match that definition.
Improve invalid let expression handling
- Move all of the checks for valid let expression positions to parsing.
- Add a field to ExprKind::Let in AST/HIR to mark whether it's in a valid location.
- Suppress some later errors and MIR construction for invalid let expressions.
- Fix a (drop) scope issue that was also responsible for #104172.
Fixes#104172Fixes#104868
interpret: change ABI-compat test to be type-based
This makes the test consistent across targets. Otherwise the chances are very high that ABI mismatches get accepted on x86_64 but still fail on many other targets with more complicated ABIs.
This implements (most of) the rules described in https://github.com/rust-lang/rust/pull/115476.
There was an incomplete version of the check in parsing and a second
version in AST validation. This meant that some, but not all, invalid
uses were allowed inside macros/disabled cfgs. It also means that later
passes have a hard time knowing when the let expression is in a valid
location, sometimes causing ICEs.
- Add a field to ExprKind::Let in AST/HIR to mark whether it's in a
valid location.
- Suppress later errors and MIR construction for invalid let
expressions.
Add `FreezeLock` type and use it to store `Definitions`
This adds a `FreezeLock` type which allows mutation using a lock until the value is frozen where it can be accessed lock-free. It's used to store `Definitions` in `Untracked` instead of a `RwLock`. Unlike the current scheme of leaking read guards this doesn't deadlock if definitions is written to after no mutation are expected.
Permit recursive weak type aliases
I saw #63097 and thought "we can do ~~better~~ funnier". So here it is. It's not useful, but it's certainly something. This may actually become feasible with lazy norm (so in 5 years (constant, not reducing over time)).
r? `@estebank`
cc `@GuillaumeGomez`
Don't add associated type bound for non-types
We had this fix for equality constraints (#99890), but for some reason not trait constraints 😅Fixes#114744
fixed *const [type error] does not implement the Copy trait
Removes "error: arguments for inline assembly must be copyable" when moving an unknown type
Fixes: #113788
Select obligations before processing wf obligation in `compare_method_predicate_entailment`
We need to select obligations before processing the WF obligation for the `IMPLIED_BOUNDS_ENTAILMENT` lint, since it skips over type variables.
Fixes#114783
r? `@jackh726`
