integrate MIR type-checker with NLL inference
This branch refactors NLL type inference so that it uses the MIR type-checker to gather constraints. Along the way, it also refactors how region constraints are gathered in the normal inference context mildly. The new setup is like this:
- What used to be `region_inference` is split into two parts:
- `region_constraints`, which just collects up sets of constraints
- `lexical_region_resolve`, which does the iterative, lexical region resolution
- When `resolve_regions_and_report_errors` is invoked, the inference engine converts the constraints into final values.
- In the MIR type checker, however, we do not invoke this method, but instead periodically take the region constraints and package them up for the NLL solver to use later.
- This allows us to track when and where those constraints were incurred.
- We also remove the central fulfillment context from the MIR type checker, instead instantiating new fulfillment contexts at each point. This allows us to capture the set of obligations that occurred at a particular point, and also to ensure that if the same obligation arises at two points, we will enforce the region constraints at both locations.
- The MIR type checker is also enhanced to instantiate late-bound-regions with fresh variables and handle a few other corner cases that arose.
- I also extracted some of the 'outlives' logic from the regionck, which will be needed later (see future work) to handle the type-outlives relationships.
One concern I have with this branch: since the MIR type checker is used even without the `-Znll` switch, I'm not sure if it will impact performance. One simple fix here would be to only enable the MIR type-checker if debug-assertions are enabled, since it just serves to validate the MIR. Longer term I hope to address this by improving the interface to the trait solver to be more query-based (ongoing work).
There is plenty of future work left. Here are two things that leap to mind:
- **Type-region outlives.** Currently, the NLL solver will ICE if it is required to handle a constraint like `T: 'a`. Fixing this will require a small amount of refactoring to extract the implied bounds code. I plan to follow a file-up bug on this (hopefully with mentoring instructions).
- **Testing.** It's a good idea to enumerate some of the tricky scenarios that need testing, but I think it'd be nice to try and parallelize some of the actual test writing (and resulting bug fixing):
- Same obligation occurring at two points.
- Well-formedness and trait obligations of various kinds (which are not all processed by the current MIR type-checker).
- More tests for how subtyping and region inferencing interact.
- More suggestions welcome!
r? @arielb1
This restores the behavior of regionck with respect to the
free-region-map: that is, it collects all the relations from the fn
and its closures. This feels a bit fishy but it's the behavior we've
had for some time, and it will go away with NLL, so seems best to just
keep it.
Add context to E0084, E0517, E0518
A small diagnostic enhancement to get my feet wet. Please scrutinize!
This modifies errors E0084, E0517, and E0518 to include both the annotation and the annotated item. All of these errors already had labels; I moved the label to the other span, and rephrased it as necessary.
Fixes#45886
check_unsafety: fix unused unsafe block duplication
The duplicate error message is later removed by error message
deduplication, but it still appears on beta and is still a bug.
r? @eddyb
Enable TrapUnreachable in LLVM.
This patch enables LLVM's TrapUnreachable flag, which tells it to translate `unreachable` instructions into hardware trap instructions, rather than allowing control flow to "fall through" into whatever code happens to follow it in memory.
This follows up on https://github.com/rust-lang/rust/issues/28728#issuecomment-332581533. For example, for @zackw's testcase [here](https://github.com/rust-lang/rust/issues/42009#issue-228745924), the output function contains a `ud2` instead of no code, so it won't "fall through" into whatever happens to be next in memory.
(I'm also working on the problem of LLVM optimizing away infinite loops, but the patch here is useful independently.)
I tested this patch on a few different codebases, and the code size increase ranged from 0.0% to 0.1%.
Implement `impl Trait` in argument position (RFC1951, Universal quantification)
Implements the remainder of #44721, part of #34511.
**Note**: This PR currently allows argument position `impl Trait` in trait functions. The machinery is there to prevent this if we want to, but it currently does not.
Rename `hir::TyImplTrait` to `hir::TyImplTraitExistential` and add `hir::TyImplTraitUniversal(DefId, TyParamBounds)`. The `DefId` is needed to extract the index of the parameter in `ast_ty_to_ty`.
Introduce an `ImplTraitContext` enum to lowering to keep track of the kind and allowedness of `impl Trait` in that position. This new argument is passed through many places, all ending up in `lower_ty`.
Modify `generics_of` and `explicit_predicates_of` to collect the `impl Trait` args into anonymous synthetic generic parameters and to extend the predicates with the appropriate bounds.
Add a comparison of the 'syntheticness' of type parameters, that is, prevent the following.
```rust
trait Foo {
fn foo(&self, &impl Debug);
}
impl Foo for Bar {
fn foo<U: Debug>(&self, x: &U) { ... }
}
```
And vice versa.
Incedentally, supress `unused type parameter` errors if the type being compared is already a `TyError`.
**TODO**: I have tried to annotate open questions with **FIXME**s. The most notable ones that haven't been resolved are the names of the `impl Trait` types and the questions surrounding the new `compare_synthetic_generics` method.
1. For now, the names used for `impl Trait` parameters are `keywords::Invalid.name()`. I would like them to be `impl ...` if possible, but I haven't figured out a way to do that yet.
2. For `compare_synthetic_generics` I have tried to outline the open questions in the [function itself](3fc9e3705f/src/librustc_typeck/check/compare_method.rs (L714-L725))
r? @nikomatsakis
We already disallowed them to be in the arg list, such as
Fn(impl Debug), but now we disallow Fn() -> impl Debug.
Also remove the ImplTraitContext argument from the function
lower_parenthesized_parameter_data as it is now unused.
Comment out part of test run-pass/impl-trait/xcrate.rs that now fails.
First some background:
To the compiler, the following two signatures in the trait vs the impl
are the same.
```rust
trait Foo {
fn foo(&self, &impl Debug);
}
impl Foo for () {
fn foo<U: Debug>(&self, x: &U) { ... }
}
```
We do not want to allow this, and so we add a new error and check.
The check just tests that all paramters 'syntheticness' match up. As
during collection, the impl Trait parameters are transformed into
anonymous synthetic generics.
Furthermore, causes a check for unused type parameters to be skipped in
check_bounds_are_used if there is already a TyError. Thus, an unused
input will not trigger `type parameter unused` errors.
Update the one test that checked for this error in the case of
a TyError.
always add an unreachable branch on matches to give more info to llvm
As part of https://github.com/djzin/rustc-optimization I discovered that some simple enum optimizations (src/unary/three_valued_enum.rs and src/unary/four_valued_enum.rs in the repo) are not applied - and the reason for this is that we erase the info that the discriminant of an enum is one of the options by putting the last one in an "otherwise" branch. This patch adds an extra branch so that LLVM can know what the possibilities are for the discriminant, which fixes the three- and four- valued cases.
Note that for whatever reason, this doesn't fix the case of 2 variants (most notably `Option` and `Result` have 2 variants) - a pass re-ordering might fix this or we may wish to add "assume" annotations on discriminants to force it to optimize.
MIR-borrowck: don't ICE for cannot move from array error
Closes#45694
compile-fail test E0508 now gives
```text
error[E0508]: cannot move out of type `[NonCopy; 1]`, a non-copy array (Ast)
--> .\src\test\compile-fail\E0508.rs:18:18
|
18 | let _value = array[0]; //[ast]~ ERROR E0508
| ^^^^^^^^
| |
| cannot move out of here
| help: consider using a reference instead: `&array[0]`
error[E0508]: cannot move out of type `[NonCopy; 1]`, a non-copy array (Mir)
--> .\src\test\compile-fail\E0508.rs:18:18
|
18 | let _value = array[0]; //[ast]~ ERROR E0508
| ^^^^^^^^ cannot move out of here
error: aborting due to 2 previous errors
```
update match-expressions.rs with DepNode labels
As a part of #44924, I have updated the match-expressions.rs. The PR has tests verified for the following dependency nodes for let-expressions
- MirValidated
- MirOptimized
- TypeCheckTables
- TypeOfItem
- GenericsOfItem
- PredicatesOfItem
- FnSignature
cc @michaelwoerister
r? @nikomatsakis
