After this change, impl Trait existentials are
desugared to a new `abstract type` definition
paired with a set of lifetimes to apply.
In-scope generics are included as parents of the
`abstract type` generics. Parent regions are
replaced with static, and parent regions
referenced in the `impl Trait` type are duplicated
at the end of the `abstract type`'s generics.
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
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
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.
deduplicate projection error (E0271) messages
The `ErrorId` variant takes a u16 so that `DiagnosticMessageId` can retain
its `Copy` status (the present author's first choice having been the "EXXX"
code as a string).
The duplicated "type mismatch resolving `{}`" literal is unfortunate, but
the `struct_span_err!` macro (which we want to mark that error code as
used) is fussy about taking a literal, and the one-time-diagnostics set
needs an owned string.
This is concerning #33941 and probably #45805!
r? @estebank
MIR-borrowck: fix diagnostics for closures
Emit notes for captured variables in the same manner as AST borrowck.
```
error[E0499]: cannot borrow `x` as mutable more than once at a time (Ast)
--> $DIR/borrowck-closures-two-mut.rs:24:24
|
23 | let c1 = to_fn_mut(|| x = 4);
| -- - previous borrow occurs due to use of `x` in closure
| |
| first mutable borrow occurs here
24 | let c2 = to_fn_mut(|| x = 5); //~ ERROR cannot borrow `x` as mutable more than once
| ^^ - borrow occurs due to use of `x` in closure
| |
| second mutable borrow occurs here
25 | }
| - first borrow ends here
error[E0499]: cannot borrow `x` as mutable more than once at a time (Mir)
--> $DIR/borrowck-closures-two-mut.rs:24:24
|
23 | let c1 = to_fn_mut(|| x = 4);
| -- - previous borrow occurs due to use of `x` in closure
| |
| first mutable borrow occurs here
24 | let c2 = to_fn_mut(|| x = 5); //~ ERROR cannot borrow `x` as mutable more than once
| ^^ - borrow occurs due to use of `x` in closure
| |
| second mutable borrow occurs here
25 | }
| - first borrow ends here
```
Fixes#45362.
The `ErrorId` variant takes a u16 so that `DiagnosticMessageId` can retain
its `Copy` status (the present author's first choice having been the "EXXX"
code as a string).
The duplicated "type mismatch resolving `{}`" literal is unfortunate, but
the `struct_span_err!` macro (which we want to mark that error code as
used) is fussy about taking a literal, and the one-time-diagnostics set
needs an owned string.
This is concerning #33941 and probably #45805!
Implement arbitrary_self_types
r? @arielb1
cc @nikomatsakis
Partial implementation of #44874. Supports trait and struct methods with arbitrary self types, as long as the type derefs (transitively) to `Self`. Doesn't support raw-pointer `self` yet.
Methods with non-standard self types (i.e. anything other than `&self, &mut self, and Box<Self>`) are not object safe, because dynamic dispatch hasn't been implemented for them yet.
I believe this is also a (partial) fix for #27941.
Allow a trailling comma in assert_eq/ne macro
From Rust beginners IRC:
<???> It sure does annoy me that assert_eq!() does not accept a trailing comma after the last argument.
<???> ???: File an issue against https://github.com/rust-lang/rust and CC @rust-lang/libs
Figured that might as well submit it. Will become insta-stable after merging (danger zone).
cc @rust-lang/libs
Fix help for duplicated names: `extern crate (...) as (...)`
On the case of duplicated names caused by an `extern crate` statement
with a rename, don't include the inline suggestion, instead using a span
label with only the text to avoid incorrect rust code output.
Fix#45829.
Detect `=` -> `:` typo in let bindings
When encountering a let binding type error, attempt to parse as
initializer instead. If successful, it is likely just a typo:
```rust
fn main() {
let x: Vec::with_capacity(10);
}
```
```
error: expected type, found `10`
--> file.rs:3:31
|
3 | let x: Vec::with_capacity(10, 20);
| -- ^^
| ||
| |help: did you mean assign here?: `=`
| while parsing the type for `x`
```
Fix#43703.
On the case of duplicated names caused by an `extern crate` statement
with a rename, don't include the inline suggestion, instead using a span
label with only the text to avoid incorrect rust code output.
Only instantiate inline- and const-fns if they are referenced (again).
It seems that we have regressed on not translating `#[inline]` functions unless they are actually used. This should bring back this optimization. I also added a regression test this time so it doesn't happen again accidentally.
Fixes#40392.
r? @alexcrichton
UPDATE & PSA
---------------------
This patch **makes translation very lazy** -- in general this is a good thing (we don't want the compiler to do unnecessary work) but it has two consequences:
1. Some error messages are only generated when an item is actually translated. Consequently, this patch will lead to more cases where the compiler will only start emitting errors when the erroneous function is actually used. This has always been true to some extend (e.g. when passing generic values to an intrinsic) but since this is something user-facing it's worth mentioning.
2. When writing tests, one has to make sure that the functions in question are actually generated. In other words, it must not be dead code. This can usually be achieved by either
1. making sure the function is exported from the resulting binary or
2. by making sure the function is called from something that is exported (or `main()`).
Note that it depends on the crate type what functions are exported:
1. For rlibs and dylibs everything that is reachable from the outside is exported.
2. For executables, cdylibs, and staticlibs, items are only exported if they are additionally `#[no_mangle]` or have an `#[export_name]`.
The commits in this PR contain many examples of how tests can be updated to comply to the new requirements.
