adopt "placeholders" to represent universally quantified regions
This does a few preliminary refactorings that lay some groundwork for moving towards universe integration. Two things, primarily:
- Rename from "skolemized" to "placeholder"
- When instantiating `for<'a, 'b, 'c>`, just create one universe for all 3 regions, and distinguish them from one another using the `BoundRegion`.
- This is more accurate, and I think that in general we'll be moving towards a model of separating "binder" (universe, debruijn index) from "index within binder" in a number of places.
- In principle, it feels the current setup of making lots of universes could lead to us doing the wrong thing, but I've actually not been able to come up with an example where this is so.
r? @scalexm
cc @arielb1
Give a special message when the later use is from a call. Use the span
of the callee instead of the whole expression. For conflicting borrow
messages say that the later use is of the first borrow.
use closure def-id in returns, but base def-id in locals
The refactorings to handle `let x: impl Trait` wound up breaking `impl Trait` in closure return types. I think there are some deeper problems with the code in question, but this a least should make @eddyb's example work.
Fixes#54593
r? @eddyb
Before this patch running the following command would generate the given output:
$ rustc +stage1 src/test/ui/liveness/liveness-move-in-while.rs -Zborrowck=mir -Ztwo-phase-borrows
error[E0382]: borrow of moved value: `y`
--> src/main.rs:8:24
|
8 | println!("{}", y); //~ ERROR use of moved value: `y`
| ^ value borrowed here after move
9 | while true { while true { while true { x = y; x.clone(); } } }
| - value moved here
|
= note: move occurs because `y` has type `std::boxed::Box<isize>`, which does not implement the `Copy` trait
We want to give the user more hint by telling them that the value was moved in the previous iteration of the
loop. After this patch, the error message adds the phrase "in previous iteration of loop" and in totality
looks like this:
$ rustc +stage1 src/test/ui/liveness/liveness-move-in-while.rs -Zborrowck=mir -Ztwo-phase-borrows
error[E0382]: borrow of moved value: `y`
--> src/test/ui/liveness/liveness-move-in-while.rs:17:24
|
17 | println!("{}", y); //~ ERROR use of moved value: `y`
| ^ value borrowed here after move
18 | while true { while true { while true { x = y; x.clone(); } } }
| - value moved here, in previous iteration of loop
|
= note: move occurs because `y` has type `std::boxed::Box<isize>`, which does not implement the `Copy` trait
[NLL] Get Polonius borrow check to work in simple cases
* Restores the generation of outlives facts from subtyping.
* Restore liveness facts.
* Generate invalidates facts at the start point of each location,
where we check for errors.
* Add a small test for simple cases (previously these cases have compiled, and more recently ICEd).
Closes#54212
cc #53142 (will need test)
### Known limitations
* Two phase borrows aren't implemented for Polonius yet
* Invalidation facts haven't been updated for some of the recent changes to make `Drop` terminators access fewer things.
* Fact generation is not as optimized as it could be.
* Around 30 tests fail in compare mode, often tests that are ignored in nll compare mode
r? @nikomatsakis
Using the `closure_base_def_id` indiscriminantely, as we were doing
before, winds up "going wrong" if the closure type includes the `impl
Trait` from the parent. The problem arises because the return value
for closures is inferred and meant to treat the return
type *opaquely*, so we don't want to be "desugaring" it into the
underlying type.
* Restores the generation of outlives facts from subtyping.
* Restore liveness facts.
* Generate invalidates facts at the start point of each location,
where we check for errors.
* Add a small test for simple cases.
`impl trait` in bindings (feature: impl-trait-existential-types)
This PR enables `impl Trait` syntax (opaque types) to be used in bindings, e.g.
* `let foo: impl Clone = 1;`
* `static foo: impl Clone = 2;`
* `const foo: impl Clone = 3;`
This is part of [RFC 2071](https://github.com/rust-lang/rfcs/blob/master/text/2071-impl-trait-existential-types.md) ([tracking issue](https://github.com/rust-lang/rust/issues/34511)), but exists behind the separate feature gate `impl_trait_in_bindings`.
CC @cramertj @oli-obk @eddyb @Centril @varkor
Previously, we would split the drop access into multiple checks for each
field of a struct/tuple/closure and through `Box` dereferences. This
changes this to check if the borrow is accessed by the drop in
places_conflict.
This also allows us to handle enums in a simpler way, since we don't
have to construct any new places.
When dropping a self-borrowing struct we shouldn't add a "values in a
scope are dropped in the opposite order they are defined" message,
since there is only one value being dropped.
For cases where there are references in the parameters and in the the
outputs that do not match, and where no closures are involved, this
commit introduces an improved error that mentions (or synthesizes)
a name for the regions involved to better illustrate why the borrow
does not live long enough.
Previously, region naming would always highlight the source of the
region name it found. Now, region naming returns the name as part
of a larger structure that encodes the source of the region naming
such that a region name can be optionally added to the diagnostic.
Previously, explain_borrow would emit an error with the explanation of
the a borrow. Now, it returns a enum with what the explanation for the
borrow is and any relevant spans or information such that the calling
code can choose to emit the same note/suggestion as before by calling
the emit method on the new enum.
Report when borrow could cause `&mut` aliasing during Drop
We were already issuing an error for the cases where this cropped up, so this is not fixing any soundness holes. The previous diagnostic just wasn't accurately describing the problem in the user's code.
Fix#52059
[NLL] Record more infomation on free region constraints in typeck
Changes:
* Makes the span of the MIR return place point to the return type
* Don't try to use a path to a type alias as a path to the adt it aliases (fixes an ICE)
* Don't claim that `self` is declared outside of the function. [see this test](f2995d5b1a (diff-0c9e6b1b204f42129b481df9ce459d44))
* Remove boring/interesting distinction and instead add a `ConstraintCategory` to the constraint.
* Add categories for implicit `Sized` and `Copy` requirements, for closure bounds, for user type annotations and `impl Trait`.
* Don't use the span of the first statement for Locations::All bounds (even if it happens to work on the tests we have)
Future work:
* Fine tuning the heuristic used to choose the place the report the error.
* Reporting multiple places (behind a flag)
* Better closure bounds reporting. This probably requires some discussion.
r? @nikomatsakis
NLL: disallow creation of immediately unusable variables
Fix#53695
Original description follows
----
This WIP PR is for discussing the impact of fixing #53695 by injecting a fake read in let patterns.
(Travis will fail, at least the `mir-opt` suite is failing in its current state)
The MIR/NLL type checker is in a much better position to classify
constraints and already has to classify into boring and interesting.
Adds spans to Locations::All for error reporting
Adds more constraint categories
Use `HybridBitSet` in `SparseBitMatrix`.
This fixes most of the remaining NLL memory regression.
r? @pnkfelix, because you reviewed #54286.
cc @nikomatsakis, because NLL
cc @Mark-Simulacrum, because this removes `array_vec.rs`
cc @lqd, because this massively improves `unic-ucd-name`, and probably other public crates
This requires adding a few extra methods to `HybridBitSet`. (These are
tested in a new unit test.)
This commit reduces the `max-rss` for `nll-check` builds of `html5ever`
by 46%, `ucd` by 45%, `clap-rs` by 23%, `inflate` by 14%. And the
results for the `unic-ucd-name` crate are even more impressive: a 21%
reduction in instructions, a 60% reduction in wall-time, a 96%
reduction in `max-rss`, and a 97% reduction in faults!
Fixes#52028.
