Turn ProjectionElem::Subtype into CastKind::Subtype
I noticed that drop elaboration can't, in general, handle `ProjectionElem::SubType`. It creates a disjoint move path that overlaps with other move paths. (`Subslice` does too, and I'm working on a different PR to make that special case less fragile.) If its skipped and treated as the same move path as its parent then `MovePath.place` has multiple possible projections. (It would probably make sense to remove all `Subtype` projections for the canonical place but it doesn't make sense to have this special case for a problem that doesn't actually occur in real MIR.)
The only reason this doesn't break is that `Subtype` is always the sole projection of the local its applied to. For the same reason, it works fine as a `CastKind` so I figured that makes more sense than documenting and validating this hidden invariant.
cc rust-lang/rust#112651, rust-lang/rust#133258
r? Icnr (bc you've been the main person dealing with `Subtype` it looks like)
Rename various "concrete opaque type" things to say "hidden type"
r? lcnr
I've found "concrete opaque type" terminology to be somewhat confusing as in conversation and when explaining opaque type stuff to people I always just talk about things in terms of hidden types. Also the hidden types of opaques are very much not *concrete* in the same sense that a type without any generic parameters is concrete which is an unfortunate overlap in terminology.
I've tried to update comments to also stop referring to things as concrete opaque types but this is mostly best effort as it difficult to find all such cases amongst the massive amounts of uses of "concrete" or "hidden" across the whole compiler.
```
error[E0716]: temporary value dropped while borrowed
--> $DIR/multiple-sources-for-outlives-requirement.rs:5:38
|
LL | fn foo<'b>() {
| -- lifetime `'b` defined here
LL | outlives_indir::<'_, 'b, _>(&mut 1u32);
| ---------------------------------^^^^-- temporary value is freed at the end of this statement
| | |
| | creates a temporary value which is freed while still in use
| argument requires that borrow lasts for `'b`
|
note: requirements that the value outlives `'b` introduced here
--> $DIR/multiple-sources-for-outlives-requirement.rs:1:23
|
LL | fn outlives_indir<'a: 'b, 'b, T: 'a>(_x: T) {}
| ^^ ^^
```
```
error[E0597]: `c` does not live long enough
--> $DIR/without-precise-captures-we-are-powerless.rs:19:20
|
LL | fn simple<'a>(x: &'a i32) {
| -- lifetime `'a` defined here
...
LL | let c = async move || { println!("{}", *x); };
| - binding `c` declared here
LL | outlives::<'a>(c());
| ---------------^---
| | |
| | borrowed value does not live long enough
| argument requires that `c` is borrowed for `'a`
LL | outlives::<'a>(call_once(c));
LL | }
| - `c` dropped here while still borrowed
|
note: requirement that `c` is borrowed for `'a` introduced here
--> $DIR/without-precise-captures-we-are-powerless.rs:7:33
|
LL | fn outlives<'a>(_: impl Sized + 'a) {}
| ^^
```
When encountering a `ConstraintCategory::Predicate` in a funtion call, point at the `Span` for that `Predicate` to explain where the lifetime obligation originates from.
fix 2 borrowck issues
fixes https://github.com/rust-lang/rust/issues/146467 cc ``@amandasystems``
our understanding here is as follows: region constraints from computing implied bounds gets `ConstraintCategory::Internal`. If there's a higher-ranked subtyping errors while computing implied bounds we then ended up with only `ConstraintCategory::Internal` and `ConstraintCategory::OutlivesUnnameablePlaceholder(_)` constraints.
The path was something like
- `'placeholderU2: 'placeholderU1` (`Internal`)
- `'placeholderU1: 'static` (`OutlivesUnnameablePlaceholder('placeholderU2)`)
It's generally somewhat subtle here as ideally relating placeholders doesn't introduce `'static` constraints. Relating the placeholders themselves will always error regardless, cc https://github.com/rust-lang/rust/pull/142623.
---
separately fixes https://github.com/rust-lang/rust/pull/145925#issuecomment-3303733357 by updating the location for deferred closure requirements inside of promoteds. I am not updating their category as doing so is 1) effort and 2) imo actually undesirable 🤔 see the comments in `TypeChecker::check_promoted` cc ``@lqd``
r? lqd
Clean up universe evaluation during type test evaluation
The logic was, as the removed comments suggest, hackish and meant to implement previous logic that was factored out. The new logic does exactly what the comments say, and is much less surprising.
I'm afraid we may want
r? `@lcnr`
for this one too.
I am sorry, but at least it should be easier to review.
The logic was, as the removed comments suggest, hackish
and meant to implement previous logic that was factored out.
The new logic does exactly what the comments say, and is much
less surprising.
Clean up `ty::Dynamic`
1. As a follow-up to PR rust-lang/rust#143036, remove `DynKind` entirely.
2. Inside HIR ty lowering, consolidate modules `dyn_compatibility` and `lint` into `dyn_trait`
* `dyn_compatibility` wasn't about dyn compatibility itself, it's about lowering trait object types
* `lint` contained dyn-Trait-specific diagnostics+lints only
This was done in #145740 and #145947. It is causing problems for people
using r-a on anything that uses the rustc-dev rustup package, e.g. Miri,
clippy.
This repository has lots of submodules and subtrees and various
different projects are carved out of pieces of it. It seems like
`[workspace.dependencies]` will just be more trouble than it's worth.
`-Znext-solver`: support non-defining uses in closures
Cleaned up version of rust-lang/rust#139587, finishing the implementation of https://github.com/rust-lang/types-team/issues/129. This does not affect stable. The reasoning for why this is the case is subtle however.
## What does it do
We split `do_mir_borrowck` into `borrowck_collect_region_constraints` and `borrowck_check_region_constraints`, where `borrowck_collect_region_constraints` returns an enormous `CollectRegionConstraintsResult` struct which contains all the relevant data to actually handle opaque type uses and to check the region constraints later on.
`query mir_borrowck` now simply calls `BorrowCheckRootCtxt::do_mir_borrowck` which starts by iterating over all nested bodies of the current function - visiting nested bodies before their parents - and computing their `CollectRegionConstraintsResult`.
After we've collected all constraints it's time to actually compute the concrete types for the opaques defined by this function. With this PR we now compute the concrete types of opaques for each body before using them to check the non-defining uses of any of them.
After we've computed the concrete types by using all bodies, we use `apply_computed_concrete_opaque_types` for each body to constrain non-defining uses, before finally finishing with `borrowck_check_region_constraints`. We always visit nested bodies before their parents when doing this.
## `ClosureRegionRequirements`
As we only call `borrowck_collect_region_constraints` for nested bodies before type checking the parent, we can't simply use the final `ClosureRegionRequirements` of the nested body during MIR type check. We instead track that we need to apply these requirements in `deferred_closure_requirements`.
We now manually apply the final closure requirements to each body after handling opaque types.
This works, except that we may need the region constraints of nested bodies to successfully define an opaque type in the parent. This is handled by using a new `fn compute_closure_requirements_modulo_opaques` which duplicates region checking - while ignoring any errors - before we've added the constraints from `apply_computed_concrete_opaque_types`. This is necessary for a lot of async tests, as pretty much the entire function is inside of an async block while the opaque type gets defined in the parent.
As an performance optimization we only use `fn compute_closure_requirements_modulo_opaques` in case the nested body actually depends on any opaque types. Otherwise we eagerly call `borrowck_check_region_constraints` and apply the final closure region requirements right away.
## Impact on stable code
Handling the opaque type uses in the parent function now only uses the closure requirements *modulo opaques*, while it previously also considered member constraints from nested bodies. `External` regions are never valid choice regions. Also, member constraints will never constrain a member region if it is required to be outlived by an external region, as that fails the upper-bound check. 564ee21912/compiler/rustc_borrowck/src/region_infer/opaque_types/member_constraints.rs (L90-L96)
Member constraints therefore never add constraints for external regions :>
r? `@BoxyUwU`
MIR dumping is a mess. There are lots of functions and entry points,
e.g. `dump_mir`, `dump_mir_with_options`, `dump_polonius_mir`,
`dump_mir_to_writer`. Also, it's crucial that `create_dump_file` is
never called without `dump_enabled` first being checked, but there is no
mechanism for ensuring this and it's hard to tell if it is satisfied on
all paths. (`dump_enabled` is checked twice on some paths, however!)
This commit introduces `MirWriter`, which controls the MIR writing, and
encapsulates the `extra_data` closure and `options`. Two existing
functions are now methods of this type. It sets reasonable defaults,
allowing the removal of many `|_, _| Ok(())` closures.
The commit also introduces `MirDumper`, which is layered on top of
`MirWriter`, and which manages the creation of the dump files,
encapsulating pass names, disambiguators, etc. Four existing functions
are now methods of this type.
- `MirDumper::new` will only succeed if dumps are enabled, and will
return `None` otherwise, which makes it impossible to dump when you
shouldn't.
- It also sets reasonable defaults for various things like
disambiguators, which means you no longer need to specify them in many
cases. When they do need to be specified, it's now done via setter
methods.
- It avoids some repetition. E.g. `dump_nll_mir` previously specifed the
pass name `"nll"` four times and the disambiguator `&0` three times;
now it specifies them just once, to put them in the `MirDumper`.
- For Polonius, the `extra_data` closure can now be specified earlier,
which avoids having to pass some arguments through some functions.
The dynamic dispatch cost doesn't matter for MIR dumping, which is
perf-insensitive. And it's necessary for the next commit, which will
store some `extra_data` closures in a struct.
Region inference: Use outlives-static constraints in constraint search
Revise the extra `r: 'static` constraints added upon universe issues to add an explanation, and use that explanation during constraint blame search. This greatly simplifies the region inference logic, which now does not need to reverse-engineer the event that caused a region to outlive `'static`.
This cosmetically changes the output of two UI tests. I blessed them i separate commits with separate motivations, but that can of course be squashed as desired. We probably want that.
The PR was extracted out of rust-lang/rust#130227 and consists of one-third of its functional payload.
r? lcnr
Support non-defining uses in HIR typeck
This changes the impl of `NormalizesTo` for opaque types to be structural during HIR typeck. The previous impl equated region variables of the opaque type key with existing entries which can result in spurious leak check errors and also results in mismatches with MIR borrowck, theoretically causing ICE.
The approach is very similar to rust-lang/rust#145244 in MIR typeck:
- we collect all uses of opaque types during HIR typeck
- before writeback, we search for *defining uses*
- the opaque type key has fully universal generic args modulo regions
- the hidden type has no infer vars
- we use these defining uses to compute the concrete type for the opaque and map it to the definition site
- we use this concrete type to check the type of all uses of opaques during HIR typeck. This also constrains infer vars in non-defining uses
Fixes https://github.com/rust-lang/trait-system-refactor-initiative/issues/135, fixes https://github.com/rust-lang/trait-system-refactor-initiative/issues/49.
r? `@BoxyUwU`
Account for impossible bounds making seemingly unsatisfyable dyn-to-dyn casts
Fixes https://github.com/rust-lang/rust/issues/141806
When we have an impossible where clause like `dyn Trait<u8>: Sized`, this may make a dyn-to-dyn cast like `dyn Trait<()> -> dyn trait<u8>` to successfully type check as if it were a wide-to-thin ptr cast (discarding metadata):
16ad385579/compiler/rustc_hir_typeck/src/cast.rs (L862-L865)
In borrowck, we are expecting that the only meaningful dyn-to-dyn cast to be a metadata-preserving wide-to-wide ptr cast, which requires that the principals of the dyn pointers are equal. Borrowck additionally assumes that these principals have already been proven equal *modulo regions*, and we thus ICE since `Trait<u8>` and `Trait<()>` do not unify:
16ad385579/compiler/rustc_borrowck/src/type_check/mod.rs (L1481-L1524)
This PR fixes this ICE by checking whether the RHS of the cast is considered to be Sized in the environment of the MIR typeck, and if so then skipping over this dyn->dyn principal compatibility check.
r? `@lcnr` perhaps?
Revise the extra `r: 'static` constraints added upon universe issues
to add an explanation, and use that explanation during constraint blame
search. This greatly simplifies the region inference logic, which
now does not need to reverse-engineer the event that caused a region
to outlive 'static.
