Track where diagnostics were created.
This implements the `-Ztrack-diagnostics` flag, which uses `#[track_caller]` to track where diagnostics are created. It is meant as a debugging tool much like `-Ztreat-err-as-bug`.
For example, the following code...
```rust
struct A;
struct B;
fn main(){
let _: A = B;
}
```
...now emits the following error message:
```
error[E0308]: mismatched types
--> src\main.rs:5:16
|
5 | let _: A = B;
| - ^ expected struct `A`, found struct `B`
| |
| expected due to this
-Ztrack-diagnostics: created at compiler\rustc_infer\src\infer\error_reporting\mod.rs:2275:31
```
rustc_metadata: Encode even less doc comments
The fact that `def_id` is in the `tcx.privacy_access_levels(())` table is not very meaningful, especially after https://github.com/rust-lang/rust/pull/102026, `is_exported` (or `is_reachable` in the worst case) is what you need.
Follow up to https://github.com/rust-lang/rust/pull/98450.
r? `@GuillaumeGomez` `@lqd`
The new implementation doesn't use weak lang items and instead changes
`#[alloc_error_handler]` to an attribute macro just like
`#[global_allocator]`.
The attribute will generate the `__rg_oom` function which is called by
the compiler-generated `__rust_alloc_error_handler`. If no `__rg_oom`
function is defined in any crate then the compiler shim will call
`__rdl_oom` in the alloc crate which will simply panic.
This also fixes link errors with `-C link-dead-code` with
`default_alloc_error_handler`: `__rg_oom` was previously defined in the
alloc crate and would attempt to reference the `oom` lang item, even if
it didn't exist. This worked as long as `__rg_oom` was excluded from
linking since it was not called.
This is a prerequisite for the stabilization of
`default_alloc_error_handler` (#102318).
spastorino noticed some silly expressions like `item_id.def_id.def_id`.
This commit renames several `def_id: OwnerId` fields as `owner_id`, so
those expressions become `item_id.owner_id.def_id`.
`item_id.owner_id.local_def_id` would be even clearer, but the use of
`def_id` for values of type `LocalDefId` is *very* widespread, so I left
that alone.
privacy: Rename "accessibility levels" to "effective visibilities"
And a couple of other naming and comment tweaks.
Related to https://github.com/rust-lang/rust/issues/48054
For `enum Level` I initially used naming `enum EffectiveVisibilityLevel`, but it was too long and inconvenient because it's used pretty often.
So I shortened it to just `Level`, if it needs to be used from some context where this name would be ambiguous, then it can be imported with renaming like `use rustc_middle::privacy::Level as EffVisLevel` or something.
rustc_metadata: Add struct and variant constructors to module children at encoding time
instead of decoding time.
Continuation of https://github.com/rust-lang/rust/pull/95899.
The last time it caused some ICEs from generator use, but not everything seems ok.
Rollup of 6 pull requests
Successful merges:
- #101293 (Recover when unclosed char literal is parsed as a lifetime in some positions)
- #101908 (Suggest let for assignment, and some code refactor)
- #103192 (rustdoc: Eliminate uses of `EarlyDocLinkResolver::all_traits`)
- #103226 (Check `needs_infer` before `needs_drop` during HIR generator analysis)
- #103249 (resolve: Revert "Set effective visibilities for imports more precisely")
- #103305 (Move some tests to more reasonable places)
Failed merges:
r? `@ghost`
`@rustbot` modify labels: rollup
Get rid of native_library projection queries
They don't seem particularly useful as I don't expect native libraries to change frequently.
Maybe they do provide significant value of keeping incremental compilation green though, I'm not sure.
Introduce deduced parameter attributes, and use them for deducing `readonly` on indirect immutable freeze by-value function parameters.
Introduce deduced parameter attributes, and use them for deducing `readonly` on
indirect immutable freeze by-value function parameters.
Right now, `rustc` only examines function signatures and the platform ABI when
determining the LLVM attributes to apply to parameters. This results in missed
optimizations, because there are some attributes that can be determined via
analysis of the MIR making up the function body. In particular, `readonly`
could be applied to most indirectly-passed by-value function arguments
(specifically, those that are freeze and are observed not to be mutated), but
it currently is not.
This patch introduces the machinery that allows `rustc` to determine those
attributes. It consists of a query, `deduced_param_attrs`, that, when
evaluated, analyzes the MIR of the function to determine supplementary
attributes. The results of this query for each function are written into the
crate metadata so that the deduced parameter attributes can be applied to
cross-crate functions. In this patch, we simply check the parameter for
mutations to determine whether the `readonly` attribute should be applied to
parameters that are indirect immutable freeze by-value. More attributes could
conceivably be deduced in the future: `nocapture` and `noalias` come to mind.
Adding `readonly` to indirect function parameters where applicable enables some
potential optimizations in LLVM that are discussed in [issue 103103] and [PR
103070] around avoiding stack-to-stack memory copies that appear in functions
like `core::fmt::Write::write_fmt` and `core::panicking::assert_failed`. These
functions pass a large structure unchanged by value to a subfunction that also
doesn't mutate it. Since the structure in this case is passed as an indirect
parameter, it's a pointer from LLVM's perspective. As a result, the
intermediate copy of the structure that our codegen emits could be optimized
away by LLVM's MemCpyOptimizer if it knew that the pointer is `readonly
nocapture noalias` in both the caller and callee. We already pass `nocapture
noalias`, but we're missing `readonly`, as we can't determine whether a
by-value parameter is mutated by examining the signature in Rust. I didn't have
much success with having LLVM infer the `readonly` attribute, even with fat
LTO; it seems that deducing it at the MIR level is necessary.
No large benefits should be expected from this optimization *now*; LLVM needs
some changes (discussed in [PR 103070]) to more aggressively use the `noalias
nocapture readonly` combination in its alias analysis. I have some LLVM patches
for these optimizations and have had them looked over. With all the patches
applied locally, I enabled LLVM to remove all the `memcpy`s from the following
code:
```rust
fn main() {
println!("Hello {}", 3);
}
```
which is a significant codegen improvement over the status quo. I expect that if this optimization kicks in in multiple places even for such a simple program, then it will apply to Rust code all over the place.
[issue 103103]: https://github.com/rust-lang/rust/issues/103103
[PR 103070]: https://github.com/rust-lang/rust/pull/103070
indirect immutable freeze by-value function parameters.
Right now, `rustc` only examines function signatures and the platform ABI when
determining the LLVM attributes to apply to parameters. This results in missed
optimizations, because there are some attributes that can be determined via
analysis of the MIR making up the function body. In particular, `readonly`
could be applied to most indirectly-passed by-value function arguments
(specifically, those that are freeze and are observed not to be mutated), but
it currently is not.
This patch introduces the machinery that allows `rustc` to determine those
attributes. It consists of a query, `deduced_param_attrs`, that, when
evaluated, analyzes the MIR of the function to determine supplementary
attributes. The results of this query for each function are written into the
crate metadata so that the deduced parameter attributes can be applied to
cross-crate functions. In this patch, we simply check the parameter for
mutations to determine whether the `readonly` attribute should be applied to
parameters that are indirect immutable freeze by-value. More attributes could
conceivably be deduced in the future: `nocapture` and `noalias` come to mind.
Adding `readonly` to indirect function parameters where applicable enables some
potential optimizations in LLVM that are discussed in [issue 103103] and [PR
103070] around avoiding stack-to-stack memory copies that appear in functions
like `core::fmt::Write::write_fmt` and `core::panicking::assert_failed`. These
functions pass a large structure unchanged by value to a subfunction that also
doesn't mutate it. Since the structure in this case is passed as an indirect
parameter, it's a pointer from LLVM's perspective. As a result, the
intermediate copy of the structure that our codegen emits could be optimized
away by LLVM's MemCpyOptimizer if it knew that the pointer is `readonly
nocapture noalias` in both the caller and callee. We already pass `nocapture
noalias`, but we're missing `readonly`, as we can't determine whether a
by-value parameter is mutated by examining the signature in Rust. I didn't have
much success with having LLVM infer the `readonly` attribute, even with fat
LTO; it seems that deducing it at the MIR level is necessary.
No large benefits should be expected from this optimization *now*; LLVM needs
some changes (discussed in [PR 103070]) to more aggressively use the `noalias
nocapture readonly` combination in its alias analysis. I have some LLVM patches
for these optimizations and have had them looked over. With all the patches
applied locally, I enabled LLVM to remove all the `memcpy`s from the following
code:
```rust
fn main() {
println!("Hello {}", 3);
}
```
which is a significant codegen improvement over the status quo. I expect that
if this optimization kicks in in multiple places even for such a simple
program, then it will apply to Rust code all over the place.
[issue 103103]: https://github.com/rust-lang/rust/issues/103103
[PR 103070]: https://github.com/rust-lang/rust/pull/103070
If we fail to locate a native library that we are linking with, it could
be the case the user entered a complete file name like `foo.lib` or
`libfoo.a` when we expect them to simply provide `foo`.
In this situation, we now detect that case and suggest the user only
provide the library name itself.
fix a ui test
use `into`
fix clippy ui test
fix a run-make-fulldeps test
implement `IntoQueryParam<DefId>` for `OwnerId`
use `OwnerId` for more queries
change the type of `ParentOwnerIterator::Item` to `(OwnerId, OwnerNode)`
Move and rename `SessionDiagnostic` & `SessionSubdiagnostic` traits and macros
After PR #101434, we want to:
- [x] Move `SessionDiagnostic` to `rustc_errors`.
- [x] Add `emit_` methods that accept `impl SessionDiagnostic` to `Handler`.
- [x] _(optional)_ Rename trait `SessionDiagnostic` to `DiagnosticHandler`.
- [x] _(optional)_ Rename macro `SessionDiagnostic` to `DiagnosticHandler`.
- [x] Update Rustc Dev Guide and Docs to reflect these changes. https://github.com/rust-lang/rustc-dev-guide/pull/1460
Now I am having build issues getting the compiler to build when trying to rename the macro.
<details>
<summary>See diagnostics errors and context when building.</summary>
```
error: diagnostics should only be created in `SessionDiagnostic`/`AddSubdiagnostic` impls
--> compiler/rustc_attr/src/session_diagnostics.rs:13:10
|
13 | #[derive(DiagnosticHandler)]
| ^^^^^^^^^^^^^^^^^ in this derive macro expansion
|
::: /Users/jhonny/.cargo/registry/src/github.com-1ecc6299db9ec823/synstructure-0.12.6/src/macros.rs:94:9
|
94 | / pub fn $derives(
95 | | i: $crate::macros::TokenStream
96 | | ) -> $crate::macros::TokenStream {
| |________________________________________- in this expansion of `#[derive(DiagnosticHandler)]`
|
note: the lint level is defined here
--> compiler/rustc_attr/src/lib.rs:10:9
|
10 | #![deny(rustc::diagnostic_outside_of_impl)]
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
```
And also this one:
```
error: diagnostics should only be created in `SessionDiagnostic`/`AddSubdiagnostic` impls
--> compiler/rustc_attr/src/session_diagnostics.rs:213:32
|
213 | let mut diag = handler.struct_span_err_with_code(
| ^^^^^^^^^^^^^^^^^^^^^^^^^
```
> **Note**
> Can't find where this message is coming from, because you can see in [this experimental branch](https://github.com/JhonnyBillM/rust/tree/experimental/trying-to-rename-session-diagnostic-macro) that I updated all errors and diags to say:
> error: diagnostics should only be created in **`DiagnosticHandler`**/`AddSubdiagnostic` impls
> and not:
> error: diagnostics should only be created in **`SessionDiagnostic`**/`AddSubdiagnostic` impls
</details>
I tried building the compiler in different ways (playing with the stages etc), but nothing worked.
## Question
**Do we need to build or do something different when renaming a macro and identifiers?**
For context, see experimental commit f2193a98b4 where the macro and symbols are renamed, but it doesn't compile.
FIX - ambiguous Diagnostic link in docs
UPDATE - rename diagnostic_items to IntoDiagnostic and AddToDiagnostic
[Gardening] FIX - formatting via `x fmt`
FIX - rebase conflicts. NOTE: Confirm wheather or not we want to handle TargetDataLayoutErrorsWrapper this way
DELETE - unneeded allow attributes in Handler method
FIX - broken test
FIX - Rebase conflict
UPDATE - rename residual _SessionDiagnostic and fix LintDiag link
It's now much more like the `-Zhir-stats` output.
- Each line is preceded with `meta-stats`, which makes the provenance
clearer and allows filtering of the output.
- Sections are now sorted in reverse order of size.
- Column headings avoid the need to repeat the word "bytes" on every line.
- Long numbers now have `_` separators for easier reading.
- Consistent use of '-' within section labels, rather than a mix of '-',
'_', and ' '.
The code itself is shorter and easier to read thanks to:
- the `stat` macro, which encapsulates each section's encoding, avoids
some boilerplate, and removes the need for some low-value comments;
- the `stats` vector, which replaces dozens of local variables.
Fix `#[link kind="raw-dylib"]` to respect `#[link_name]`
Issue Details:
When using `#[link kind="raw-dylib"]` (#58713), the Rust compiler ignored any `#[link_name]` attributes when generating the import library and so the resulting binary would fail to link due to missing symbols.
Fix Details:
Use the name from `#[link_name]` if present when generating the `raw-dylib` import library, otherwise default back to the actual symbol name.
On later stages, the feature is already stable.
Result of running:
rg -l "feature.let_else" compiler/ src/librustdoc/ library/ | xargs sed -s -i "s#\\[feature.let_else#\\[cfg_attr\\(bootstrap, feature\\(let_else\\)#"
Stabilize generic associated types
Closes#44265
r? `@nikomatsakis`
# ⚡ Status of the discussion ⚡
* [x] There have been several serious concerns raised, [summarized here](https://github.com/rust-lang/rust/pull/96709#issuecomment-1129311660).
* [x] There has also been a [deep-dive comment](https://github.com/rust-lang/rust/pull/96709#issuecomment-1167220240) explaining some of the "patterns of code" that are enabled by GATs, based on use-cases posted to this thread or on the tracking issue.
* [x] We have modeled some aspects of GATs in [a-mir-formality](https://github.com/nikomatsakis/a-mir-formality) to give better confidence in how they will be resolved in the future. [You can read a write-up here](https://github.com/rust-lang/types-team/blob/master/minutes/2022-07-08-implied-bounds-and-wf-checking.md).
* [x] The major points of the discussion have been [summarized on the GAT initiative repository](https://rust-lang.github.io/generic-associated-types-initiative/mvp.html).
* [x] [FCP has been proposed](https://github.com/rust-lang/rust/pull/96709#issuecomment-1129311660) and we are awaiting final decisions and discussion amidst the relevant team members.
# Stabilization proposal
This PR proposes the stabilization of `#![feature(generic_associated_types)]`. While there a number of future additions to be made and bugs to be fixed (both discussed below), properly doing these will require significant language design and will ultimately likely be backwards-compatible. Given the overwhelming desire to have some form of generic associated types (GATs) available on stable and the stability of the "simple" uses, stabilizing the current subset of GAT features is almost certainly the correct next step.
Tracking issue: #44265
Initiative: https://rust-lang.github.io/generic-associated-types-initiative/
RFC: https://github.com/rust-lang/rfcs/blob/master/text/1598-generic_associated_types.md
Version: 1.65 (2022-08-22 => beta, 2022-11-03 => stable).
## Motivation
There are a myriad of potential use cases for GATs. Stabilization unblocks probable future language features (e.g. async functions in traits), potential future standard library features (e.g. a `LendingIterator` or some form of `Iterator` with a lifetime generic), and a plethora of user use cases (some of which can be seen just by scrolling through the tracking issue and looking at all the issues linking to it).
There are a myriad of potential use cases for GATs. First, there are many users that have chosen to not use GATs primarily because they are not stable (some of which can be seen just by scrolling through the tracking issue and looking at all the issues linking to it). Second, while language feature desugaring isn't *blocked* on stabilization, it gives more confidence on using the feature. Likewise, library features like `LendingIterator` are not necessarily blocked on stabilization to be implemented unstably; however few, if any, public-facing APIs actually use unstable features.
This feature has a long history of design, discussion, and developement - the RFC was first introduced roughly 6 years ago. While there are still a number of features left to implement and bugs left to fix, it's clear that it's unlikely those will have backwards-incompatibility concerns. Additionally, the bugs that do exist do not strongly impede the most-common use cases.
## What is stabilized
The primary language feature stabilized here is the ability to have generics on associated types, as so. Additionally, where clauses on associated types will now be accepted, regardless if the associated type is generic or not.
```rust
trait ATraitWithGATs {
type Assoc<'a, T> where T: 'a;
}
trait ATraitWithoutGATs<'a, T> {
type Assoc where T: 'a;
}
```
When adding an impl for a trait with generic associated types, the generics for the associated type are copied as well. Note that where clauses are allowed both after the specified type and before the equals sign; however, the latter is a warn-by-default deprecation.
```rust
struct X;
struct Y;
impl ATraitWithGATs for X {
type Assoc<'a, T> = &'a T
where T: 'a;
}
impl ATraitWithGATs for Y {
type Assoc<'a, T>
where T: 'a
= &'a T;
}
```
To use a GAT in a function, generics are specified on the associated type, as if it was a struct or enum. GATs can also be specified in trait bounds:
```rust
fn accepts_gat<'a, T>(t: &'a T) -> T::Assoc<'a, T>
where for<'x> T: ATraitWithGATs<Assoc<'a, T> = &'a T> {
...
}
```
GATs can also appear in trait methods. However, depending on how they are used, they may confer where clauses on the associated type definition. More information can be found [here](https://github.com/rust-lang/rust/issues/87479). Briefly, where clauses are required when those bounds can be proven in the methods that *construct* the GAT or other associated types that use the GAT in the trait. This allows impls to have maximum flexibility in the types defined for the associated type.
To take a relatively simple example:
```rust
trait Iterable {
type Item<'a>;
type Iterator<'a>: Iterator<Item = Self::Item<'a>>;
fn iter<'x>(&'x self) -> Self::Iterator<'x>;
//^ We know that `Self: 'a` for `Iterator<'a>`, so we require that bound on `Iterator`
// `Iterator` uses `Self::Item`, so we also require a `Self: 'a` on `Item` too
}
```
A couple well-explained examples are available in a previous [blog post](https://blog.rust-lang.org/2021/08/03/GATs-stabilization-push.html).
## What isn't stabilized/implemented
### Universal type/const quantification
Currently, you can write a bound like `X: for<'a> Trait<Assoc<'a> = &'a ()>`. However, you cannot currently write `for<T> X: Trait<Assoc<T> = T>` or `for<const N> X: Trait<Assoc<N> = [usize; N]>`.
Here is an example where this is needed:
```rust
trait Foo {}
trait Trait {
type Assoc<F: Foo>;
}
trait Trait2: Sized {
fn foo<F: Foo, T: Trait<Assoc<F> = F>>(_t: T);
}
```
In the above example, the *caller* must specify `F`, which is likely not what is desired.
### Object-safe GATs
Unlike non-generic associated types, traits with GATs are not currently object-safe. In other words the following are not allowed:
```rust
trait Trait {
type Assoc<'a>;
}
fn foo(t: &dyn for<'a> Trait<Assoc<'a> = &'a ()>) {}
//^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ not allowed
let ty: Box<dyn for<'a> Trait<Assoc<'a> = &'a ()>>;
//^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ not allowed
```
### Higher-kinded types
You cannot write currently (and there are no current plans to implement this):
```rust
struct Struct<'a> {}
fn foo(s: for<'a> Struct<'a>) {}
```
## Tests
There are many tests covering GATs that can be found in `src/test/ui/generic-associated-types`. Here, I'll list (in alphanumeric order) tests highlight some important behavior or contain important patterns.
- `./parse/*`: Parsing of GATs in traits and impls, and the trait path with GATs
- `./collections-project-default.rs`: Interaction with associated type defaults
- `./collections.rs`: The `Collection` pattern
- `./const-generics-gat-in-trait-return-type-*.rs`: Const parameters
- `./constraint-assoc-type-suggestion.rs`: Emit correct syntax in suggestion
- `./cross-crate-bounds.rs`: Ensure we handles bounds across crates the same
- `./elided-in-expr-position.rs`: Disallow lifetime elision in return position
- `./gat-in-trait-path-undeclared-lifetime.rs`: Ensure we error on undeclared lifetime in trait path
- `./gat-in-trait-path.rs`: Base trait path case
- `./gat-trait-path-generic-type-arg.rs`: Don't allow shadowing of parameters
- `./gat-trait-path-parenthesised-args.rs`: Don't allow paranthesized args in trait path
- `./generic-associated-types-where.rs`: Ensure that we require where clauses from trait to be met on impl
- `./impl_bounds.rs`: Check that the bounds on GATs in an impl are checked
- `./issue-76826.rs`: `Windows` pattern
- `./issue-78113-lifetime-mismatch-dyn-trait-box.rs`: Implicit 'static diagnostics
- `./issue-84931.rs`: Ensure that we have a where clause on GAT to ensure trait parameter lives long enough
- `./issue-87258_a.rs`: Unconstrained opaque type with TAITs
- `./issue-87429-2.rs`: Ensure we can use bound vars in the bounds
- `./issue-87429-associated-type-default.rs`: Ensure bounds hold with associated type defaults, for both trait and impl
- `./issue-87429-specialization.rs`: Check that bounds hold under specialization
- `./issue-88595.rs`: Under the outlives lint, we require a bound for both trait and GAT lifetime when trait lifetime is used in function
- `./issue-90014.rs`: Lifetime bounds are checked with TAITs
- `./issue-91139.rs`: Under migrate mode, but not NLL, we don't capture implied bounds from HRTB lifetimes used in a function and GATs
- `./issue-91762.rs`: We used to too eagerly pick param env candidates when normalizing with GATs. We now require explicit parameters specified.
- `./issue-95305.rs`: Disallow lifetime elision in trait paths
- `./iterable.rs`: `Iterable` pattern
- `./method-unsatified-assoc-type-predicate.rs`: Print predicates with GATs correctly in method resolve error
- `./missing_lifetime_const.rs`: Ensure we must specify lifetime args (not elidable)
- `./missing-where-clause-on-trait.rs`: Ensure we don't allow stricter bounds on impl than trait
- `./parameter_number_and_kind_impl.rs`: Ensure paramters on GAT in impl match GAT in trait
- `./pointer_family.rs`: `PointerFamily` pattern
- `./projection-bound-cycle.rs`: Don't allow invalid cycles to prove bounds
- `./self-outlives-lint.rs`: Ensures that an e.g. `Self: 'a` is written on the traits GAT if that bound can be implied from the GAT usage in the trait
- `./shadowing.rs`: Don't allow lifetime shadowing in params
- `./streaming_iterator.rs`: `StreamingIterator`(`LendingIterator`) pattern
- `./trait-objects.rs`: Disallow trait objects for traits with GATs
- `./variance_constraints.rs`: Require that GAT substs be invariant
## Remaining bugs and open issues
A full list of remaining open issues can be found at: https://github.com/rust-lang/rust/labels/F-generic_associated_types
There are some `known-bug` tests in-tree at `src/test/ui/generic-associated-types/bugs`.
Here I'll categorize most of those that GAT bugs (or involve a pattern found more with GATs), but not those that include GATs but not a GAT issue in and of itself. (I also won't include issues directly for things listed elsewhere here.)
Using the concrete type of a GAT instead of the projection type can give errors, since lifetimes are chosen to be early-bound vs late-bound.
- #85533
- #87803
In certain cases, we can run into cycle or overflow errors. This is more generally a problem with associated types.
- #87755
- #87758
Bounds on an associatd type need to be proven by an impl, but where clauses need to be proven by the usage. This can lead to confusion when users write one when they mean the other.
- #87831
- #90573
We sometimes can't normalize closure signatures fully. Really an asociated types issue, but might happen a bit more frequently with GATs, since more obvious place for HRTB lifetimes.
- #88382
When calling a function, we assign types to parameters "too late", after we already try (and fail) to normalize projections. Another associated types issue that might pop up more with GATs.
- #88460
- #96230
We don't fully have implied bounds for lifetimes appearing in GAT trait paths, which can lead to unconstrained type errors.
- #88526
Suggestion for adding lifetime bounds can suggest unhelpful fixes (`T: 'a` instead of `Self: 'a`), but the next compiler error after making the suggested change is helpful.
- #90816
- #92096
- #95268
We can end up requiring that `for<'a> I: 'a` when we really want `for<'a where I: 'a> I: 'a`. This can leave unhelpful errors than effectively can't be satisfied unless `I: 'static`. Requires bigger changes and not only GATs.
- #91693
Unlike with non-generic associated types, we don't eagerly normalize with param env candidates. This is intended behavior (for now), to avoid accidentaly stabilizing picking arbitrary impls.
- #91762
Some Iterator adapter patterns (namely `filter`) require Polonius or unsafe to work.
- #92985
## Potential Future work
### Universal type/const quantification
No work has been done to implement this. There are also some questions around implied bounds.
### Object-safe GATs
The intention is to make traits with GATs object-safe. There are some design work to be done around well-formedness rules and general implementation.
### GATified std lib types
It would be helpful to either introduce new std lib traits (like `LendingIterator`) or to modify existing ones (adding a `'a` generic to `Iterator::Item`). There also a number of other candidates, like `Index`/`IndexMut` and `Fn`/`FnMut`/`FnOnce`.
### Reduce the need for `for<'a>`
Seen [here](https://github.com/rust-lang/rfcs/pull/1598#issuecomment-2611378730). One possible syntax:
```rust
trait Iterable {
type Iter<'a>: Iterator<Item = Self::Item<'a>>;
}
fn foo<T>() where T: Iterable, T::Item<let 'a>: Display { } //note the `let`!
```
### Better implied bounds on higher-ranked things
Currently if we have a `type Item<'a> where self: 'a`, and a `for<'a> T: Iterator<Item<'a> = &'a ()`, this requires `for<'a> Self: 'a`. Really, we want `for<'a where T: 'a> ...`
There was some mentions of this all the back in the RFC thread [here](https://github.com/rust-lang/rfcs/pull/1598#issuecomment-264340514).
## Alternatives
### Make generics on associated type in bounds a binder
Imagine the bound `for<'a> T: Trait<Item<'a>= &'a ()>`. It might be that `for<'a>` is "too large" and it should instead be `T: Trait<for<'a> Item<'a>= &'a ()>`. Brought up in RFC thread [here](https://github.com/rust-lang/rfcs/pull/1598#issuecomment-229443863) and in a few places since.
Another related question: Is `for<'a>` the right syntax? Maybe `where<'a>`? Also originally found in RFC thread [here](https://github.com/rust-lang/rfcs/pull/1598#issuecomment-261639969).
### Stabilize lifetime GATs first
This has been brought up a few times. The idea is to only allow GATs with lifetime parameters to in initial stabilization. This was probably most useful prior to actual implementation. At this point, lifetimes, types, and consts are all implemented and work. It feels like an arbitrary split without strong reason.
## History
* On 2016-04-30, [RFC opened](https://github.com/rust-lang/rfcs/pull/1598)
* On 2017-09-02, RFC merged and [tracking issue opened](https://github.com/rust-lang/rust/issues/44265)
* On 2017-10-23, [Move Generics from MethodSig to TraitItem and ImplItem](https://github.com/rust-lang/rust/pull/44766)
* On 2017-12-01, [Generic Associated Types Parsing & Name Resolution](https://github.com/rust-lang/rust/pull/45904)
* On 2017-12-15, [https://github.com/rust-lang/rust/pull/46706](https://github.com/rust-lang/rust/pull/46706)
* On 2018-04-23, [Feature gate where clauses on associated types](https://github.com/rust-lang/rust/pull/49368)
* On 2018-05-10, [Extend tests for RFC1598 (GAT)](https://github.com/rust-lang/rust/pull/49423)
* On 2018-05-24, [Finish implementing GATs (Chalk)](https://github.com/rust-lang/chalk/pull/134)
* On 2019-12-21, [Make GATs less ICE-prone](https://github.com/rust-lang/rust/pull/67160)
* On 2020-02-13, [fix lifetime shadowing check in GATs](https://github.com/rust-lang/rust/pull/68938)
* On 2020-06-20, [Projection bound validation](https://github.com/rust-lang/rust/pull/72788)
* On 2020-10-06, [Separate projection bounds and predicates](https://github.com/rust-lang/rust/pull/73905)
* On 2021-02-05, [Generic associated types in trait paths](https://github.com/rust-lang/rust/pull/79554)
* On 2021-02-06, [Trait objects do not work with generic associated types](https://github.com/rust-lang/rust/issues/81823)
* On 2021-04-28, [Make traits with GATs not object safe](https://github.com/rust-lang/rust/pull/84622)
* On 2021-05-11, [Improve diagnostics for GATs](https://github.com/rust-lang/rust/pull/82272)
* On 2021-07-16, [Make GATs no longer an incomplete feature](https://github.com/rust-lang/rust/pull/84623)
* On 2021-07-16, [Replace associated item bound vars with placeholders when projecting](https://github.com/rust-lang/rust/pull/86993)
* On 2021-07-26, [GATs: Decide whether to have defaults for `where Self: 'a`](https://github.com/rust-lang/rust/issues/87479)
* On 2021-08-25, [Normalize projections under binders](https://github.com/rust-lang/rust/pull/85499)
* On 2021-08-03, [The push for GATs stabilization](https://blog.rust-lang.org/2021/08/03/GATs-stabilization-push.html)
* On 2021-08-12, [Detect stricter constraints on gats where clauses in impls vs trait](https://github.com/rust-lang/rust/pull/88336)
* On 2021-09-20, [Proposal: Change syntax of where clauses on type aliases](https://github.com/rust-lang/rust/issues/89122)
* On 2021-11-06, [Implementation of GATs outlives lint](https://github.com/rust-lang/rust/pull/89970)
* On 2021-12-29. [Parse and suggest moving where clauses after equals for type aliases](https://github.com/rust-lang/rust/pull/92118)
* On 2022-01-15, [Ignore static lifetimes for GATs outlives lint](https://github.com/rust-lang/rust/pull/92865)
* On 2022-02-08, [Don't constrain projection predicates with inference vars in GAT substs](https://github.com/rust-lang/rust/pull/92917)
* On 2022-02-15, [Rework GAT where clause check](https://github.com/rust-lang/rust/pull/93820)
* On 2022-02-19, [Only mark projection as ambiguous if GAT substs are constrained](https://github.com/rust-lang/rust/pull/93892)
* On 2022-03-03, [Support GATs in Rustdoc](https://github.com/rust-lang/rust/pull/94009)
* On 2022-03-06, [Change location of where clause on GATs](https://github.com/rust-lang/rust/pull/90076)
* On 2022-05-04, [A shiny future with GATs blog post](https://jackh726.github.io/rust/2022/05/04/a-shiny-future-with-gats.html)
* On 2022-05-04, [Stabilization PR](https://github.com/rust-lang/rust/pull/96709)
Add diagnostic arg 'current_crate'
With this fix, I get almost the same error message as on stable, again.
However, I expected to get the new error message `std is required by {$current_crate} because it does not declare #![no_std]`, but I didn't. Instead, I got a new line `help: consider building the standard library from source with cargo build -Zbuild-std`. So I obviously do not fully understand what is going on.
In any case, the bug itself seems to be fixed by this patch.
Closes#101640
Stabilize raw-dylib for non-x86
This stabilizes the `raw-dylib` and `link_ordinal` features (#58713) for non-x86 architectures (i.e., `x86_64`, `aarch64` and `thumbv7a`):
* Marked the `raw_dylib` feature as `active`.
* Marked the `link_ordinal` attribute as `ungated`.
* Added new errors if either feature is used on x86 targets without the `raw_dylib` feature being enabled.
* Updated tests to only set the `raw_dylib` feature when building for x86.
Update `SessionDiagnostic::into_diagnostic` to take `Handler` instead of `ParseSess`
Suggested by the team in [this Zulip Topic](https://rust-lang.zulipchat.com/#narrow/stream/336883-i18n/topic/.23100717.20SessionDiagnostic.20on.20Handler).
`Handler` already has almost all the capabilities of `ParseSess` when it comes to diagnostic emission, in this migration we only needed to add the ability to access `source_map` from the emitter in order to get a `Snippet` and the `start_point`. Not sure if adding these two methods [`span_to_snippet_from_emitter` and `span_start_point_from_emitter`] is the best way to address this gap.
P.S. If this goes in the right direction, then we probably may want to move `SessionDiagnostic` to `rustc_errors` and rename it to `DiagnosticHandler` or something similar.
r? `@davidtwco`
r? `@compiler-errors`
Suggested by the team in this Zulip Topic https://rust-lang.zulipchat.com/#narrow/stream/336883-i18n/topic/.23100717.20SessionDiagnostic.20on.20Handler
Handler already has almost all the capabilities of ParseSess when it comes to diagnostic emission, in this migration we only needed to add the ability to access source_map from the emitter in order to get a Snippet and the start_point. Not sure if this is the best way to address this gap
Remove EntryKind from metadata.
This PR continues the refactor of metadata emission to be more systematic, iterating on definitions and filtering based on each definition's `DefKind`. This allows to remove the large `EntryKind` enum, replaced by linear tables in metadata.
- ... when creating diagnostics in rustc_metadata
- use the error_code! macro
- pass macro output to diag.code()
- use fluent from within manual implementation of SessionDiagnostic
- emit the untested errors in case they occur in the wild
- stop panicking in the probably-not-dead code, add fixme to write test
Revert let_chains stabilization
This is the revert against master, the beta revert was already done in #100538.
Bumps the stage0 compiler which already has it reverted.
Remove separate indexing of early-bound regions
~Based on https://github.com/rust-lang/rust/pull/99728.~
This PR copies some modifications from https://github.com/rust-lang/rust/pull/97839 around object lifetime defaults.
These modifications allow to stop counting generic parameters during lifetime resolution, and rely on the indexing given by `rustc_typeck::collect`.
Lazily decode SourceFile from metadata
Currently, source files from foreign crates are decoded up-front from metadata.
Spans from those crates were matched with the corresponding source using binary search among those files.
This PR changes the strategy by matching spans to files during encoding. This allows to decode source files on-demand, instead of up-front. The on-disk format for spans becomes: `<tag> <position from start of file> <length> <file index> <crate (if foreign file)>`.
Implement `#[rustc_default_body_unstable]`
This PR implements a new stability attribute — `#[rustc_default_body_unstable]`.
`#[rustc_default_body_unstable]` controls the stability of default bodies in traits.
For example:
```rust
pub trait Trait {
#[rustc_default_body_unstable(feature = "feat", isssue = "none")]
fn item() {}
}
```
In order to implement `Trait` user needs to either
- implement `item` (even though it has a default implementation)
- enable `#![feature(feat)]`
This is useful in conjunction with [`#[rustc_must_implement_one_of]`](https://github.com/rust-lang/rust/pull/92164), we may want to relax requirements for a trait, for example allowing implementing either of `PartialEq::{eq, ne}`, but do so in a safe way — making implementation of only `PartialEq::ne` unstable.
r? `@Aaron1011`
cc `@nrc` (iirc you were interested in this wrt `read_buf`), `@danielhenrymantilla` (you were interested in the related `#[rustc_must_implement_one_of]`)
P.S. This is my first time working with stability attributes, so I'm not sure if I did everything right 😅
Thin `AssocItem`
This PR removes a few fields from `AssocItem` that should be easily computed using other queries.
This simplifies some of the metadata decoding.
Add tests for raw-dylib with vectorcall, and fix vectorcall code generation
* Adds tests for using `raw-dylib` (#58713) with `vectorcall`.
* Fixed code generation for `vectorcall` (parameters have to be marked with `InReg`, just like `fastcall`).
* Enabled running the `raw-dylib` `fastcall` tests when using MSVC (since I had to add support in the test for running MSVC-only tests since GCC doesn't support `vectorcall`).
Prefer visibility map parents that are not `doc(hidden)` first
Far simpler approach to #98876.
This only fixes the case where the parent is `doc(hidden)`, not where the child is `doc(hidden)` since I don't know how to get the attrs on the import statement given a `ModChild`... I'll try to follow up with that, but this is a good first step.
This attribute allows to mark default body of a trait function as
unstable. This means that implementing the trait without implementing
the function will require enabling unstable feature.
This is useful in conjunction with `#[rustc_must_implement_one_of]`,
we may want to relax requirements for a trait, for example allowing
implementing either of `PartialEq::{eq, ne}`, but do so in a safe way
-- making implementation of only `PartialEq::ne` unstable.
Improves the diagnostic when a feature attribute is specified
unnecessarily but the feature implies another (i.e. it was partially
stabilized) to refer to the implied feature.
Signed-off-by: David Wood <david.wood@huawei.com>
Stop keeping metadata in memory before writing it to disk
Fixes#96358
I created this PR according with the instruction given in the issue except for the following points:
- While the issue says "Write metadata into the temporary file in `encode_and_write_metadata` even if `!need_metadata_file`", I could not do that. That is because though I tried to do that and run `x.py test`, I got a lot of test failures as follows.
<details>
<summary>List of failed tests</summary>
<pre>
<code>
failures:
[ui] src/test/ui/json-multiple.rs
[ui] src/test/ui/json-options.rs
[ui] src/test/ui/rmeta/rmeta-rpass.rs
[ui] src/test/ui/save-analysis/emit-notifications.rs
[ui] src/test/ui/svh/changing-crates.rs
[ui] src/test/ui/svh/svh-change-lit.rs
[ui] src/test/ui/svh/svh-change-significant-cfg.rs
[ui] src/test/ui/svh/svh-change-trait-bound.rs
[ui] src/test/ui/svh/svh-change-type-arg.rs
[ui] src/test/ui/svh/svh-change-type-ret.rs
[ui] src/test/ui/svh/svh-change-type-static.rs
[ui] src/test/ui/svh/svh-use-trait.rs
test result: FAILED. 12915 passed; 12 failed; 100 ignored; 0 measured; 0 filtered out; finished in 71.41s
Some tests failed in compiletest suite=ui mode=ui host=x86_64-unknown-linux-gnu target=x86_64-unknown-linux-gnu
Build completed unsuccessfully in 0:01:58
</code>
</pre>
</details>
- I could not resolve the extra tasks about `create_rmeta_file` and `create_compressed_metadata_file` for my lack of ability.
Move abstract const to middle
Moves AbstractConst (and all associated methods) to rustc middle for use in `rustc_infer`.
This allows for const resolution in infer to use abstract consts to walk consts and check if
they are resolvable.
This attempts to resolve the issue where `Foo<{ concrete const }, generic T>` is incorrectly marked as conflicting, and is independent from the other issue where nested abstract consts must be resolved.
r? `@lcnr`
Rollup of 9 pull requests
Successful merges:
- #97917 (Implement ExitCodeExt for Windows)
- #98844 (Reword comments and rename HIR visiting methods.)
- #98979 (interpret: use AllocRange in UninitByteAccess)
- #98986 (Fix missing word in comment)
- #98994 (replace process exit with more detailed exit in src/bootstrap/*.rs)
- #98995 (Add a test for #80471)
- #99002 (suggest adding a derive for #[default] applied to variants)
- #99004 (Add a test for #70408)
- #99017 (Replace boolean argument for print_where_clause with an enum to make code more clear)
Failed merges:
r? `@ghost`
`@rustbot` modify labels: rollup
Fix FFI-unwind unsoundness with mixed panic mode
UB maybe introduced when an FFI exception happens in a `C-unwind` foreign function and it propagates through a crate compiled with `-C panic=unwind` into a crate compiled with `-C panic=abort` (#96926).
To prevent this unsoundness from happening, we will disallow a crate compiled with `-C panic=unwind` to be linked into `panic-abort` *if* it contains a call to `C-unwind` foreign function or function pointer. If no such call exists, then we continue to allow such mixed panic mode linking because it's sound (and stable). In fact we still need the ability to do mixed panic mode linking for std, because we only compile std once with `-C panic=unwind` and link it regardless panic strategy.
For libraries that wish to remain compile-once-and-linkable-to-both-panic-runtimes, a `ffi_unwind_calls` lint is added (gated under `c_unwind` feature gate) to flag any FFI unwind calls that will cause the linkable panic runtime be restricted.
In summary:
```rust
#![warn(ffi_unwind_calls)]
mod foo {
#[no_mangle]
pub extern "C-unwind" fn foo() {}
}
extern "C-unwind" {
fn foo();
}
fn main() {
// Call to Rust function is fine regardless ABI.
foo::foo();
// Call to foreign function, will cause the crate to be unlinkable to panic-abort if compiled with `-Cpanic=unwind`.
unsafe { foo(); }
//~^ WARNING call to foreign function with FFI-unwind ABI
let ptr: extern "C-unwind" fn() = foo::foo;
// Call to function pointer, will cause the crate to be unlinkable to panic-abort if compiled with `-Cpanic=unwind`.
ptr();
//~^ WARNING call to function pointer with FFI-unwind ABI
}
```
Fix#96926
`@rustbot` label: T-compiler F-c_unwind
Account for `-Z simulate-remapped-rust-src-base` when resolving remapped paths
Discovered in #97682, `-Z simulate-remapped-rust-src-base` only partially simulated the behavior of `remap-debuginfo = true`. While the flag successfully simulates the remapping when stdlib's `rmeta` file is loaded, the simulated prefix was not accounted for when the remapped path's local path was being discovered. This caused the flag to not fully simulate the behavior of `remap-debuginfo = true`, leading to inconsistent behaviors.
This PR fixes https://github.com/rust-lang/rust/issues/97682 by also accounting for the simulated path.
Rename `impl_constness` to `constness`
The current code is a basis for `is_const_fn_raw`, and `impl_constness`
is no longer a valid name, which is previously used for determining the
constness of impls, and not items in general.
r? `@oli-obk`
This simplifies things, but requires making `CacheEncoder` non-generic.
(This was previously merged as commit 4 in #94732 and then was reverted
in #97905 because it caused a perf regression.)
The current code is a basis for `is_const_fn_raw`, and `impl_constness`
is no longer a valid name, which is previously used for determining the
constness of impls, and not items in general.
Make `ExprKind::Closure` a struct variant.
Simple refactor since we both need it to introduce additional fields in `ExprKind::Closure`.
r? ``@Aaron1011``
This avoids the name clash with `rustc_serialize::Encoder` (a trait),
and allows lots qualifiers to be removed and imports to be simplified
(e.g. fewer `as` imports).
(This was previously merged as commit 5 in #94732 and then was reverted
in #97905 because of a perf regression caused by commit 4 in #94732.)
Handle `def_ident_span` like `def_span`.
`def_ident_span` had an ad-hoc status in the compiler.
This PR refactors it to be a first-class citizen like `def_span`:
- it gets encoded in the main metadata loop, instead of the visitor;
- its implementation is updated to mirror the one of `def_span`.
We do not remove the `Option` in the return type, since some items do not have an ident, AnonConsts for instance.
Fix#71363's test by adding `-Z translate-remapped-path-to-local-path=no`
The test relies on `library/std/src/error.rs` not corresponding to a local path, but remapping might still find the related local file of a remapped path. To fix the test, this PR adds a new `-Z` flag to disable finding the corresponding local path of a remapped path.
Revert part of #94372 to improve performance
#94732 was supposed to give small but widespread performance improvements, as judged from three per-merge performance runs. But the performance run that occurred after merging included a roughly equal number of improvements and regressions, for unclear reasons.
This PR is for a test run reverting those changes, to see what happens.
r? `@ghost`
This avoids the name clash with `rustc_serialize::Encoder` (a trait),
and allows lots qualifiers to be removed and imports to be simplified
(e.g. fewer `as` imports).
There are two impls of the `Encoder` trait: `opaque::Encoder` and
`opaque::FileEncoder`. The former encodes into memory and is infallible, the
latter writes to file and is fallible.
Currently, standard `Result`/`?`/`unwrap` error handling is used, but this is a
bit verbose and has non-trivial cost, which is annoying given how rare failures
are (especially in the infallible `opaque::Encoder` case).
This commit changes how `Encoder` fallibility is handled. All the `emit_*`
methods are now infallible. `opaque::Encoder` requires no great changes for
this. `opaque::FileEncoder` now implements a delayed error handling strategy.
If a failure occurs, it records this via the `res` field, and all subsequent
encoding operations are skipped if `res` indicates an error has occurred. Once
encoding is complete, the new `finish` method is called, which returns a
`Result`. In other words, there is now a single `Result`-producing method
instead of many of them.
This has very little effect on how any file errors are reported if
`opaque::FileEncoder` has any failures.
Much of this commit is boring mechanical changes, removing `Result` return
values and `?` or `unwrap` from expressions. The more interesting parts are as
follows.
- serialize.rs: The `Encoder` trait gains an `Ok` associated type. The
`into_inner` method is changed into `finish`, which returns
`Result<Vec<u8>, !>`.
- opaque.rs: The `FileEncoder` adopts the delayed error handling
strategy. Its `Ok` type is a `usize`, returning the number of bytes
written, replacing previous uses of `FileEncoder::position`.
- Various methods that take an encoder now consume it, rather than being
passed a mutable reference, e.g. `serialize_query_result_cache`.
The test relies on library/std/src/error.rs not corresponding to a local
path, but remapping might still find the related local file of a
remapped path. To fix the test, this adds a new -Z flag to disable
finding the corresponding local path of a remapped path.
Replace `#[default_method_body_is_const]` with `#[const_trait]`
pulled out of #96077
related issues: #67792 and #92158
cc `@fee1-dead`
This is groundwork to only allowing `impl const Trait` for traits that are marked with `#[const_trait]`. This is necessary to prevent adding a new default method from becoming a breaking change (as it could be a non-const fn).
libcore: Add `iter::from_generator` which is like `iter::from_fn`, but for coroutines instead of functions
An equally useful little helper.
I didn't follow any of the async-wg work, so I don't know why something like this wasn't added before.
`imported_source_files` adjusts lots of file positions, and then calls
`new_imported_source_file`, which then adjust them all again. This
commit combines the two adjustments into one, for a small perf win.
Remove `crate` visibility modifier
FCP to remove this syntax is just about complete in #53120. Once it completes, this should be merged ASAP to avoid merge conflicts.
The first two commits remove usage of the feature in this repository, while the last removes the feature itself.
Cache more queries on disk
One of the principles of incremental compilation is to allow saving results on disk to avoid recomputing them.
This PR investigates persisting a lot of queries whose result are to be saved into metadata.
Some of the queries are cheap reads from HIR, but we may also want to get rid of these reads for incremental lowering.
`simplify_type` improvements and cursed docs
the existing `TreatParams` enum pretty much mixes everything up. Not sure why this looked right to me in #94057
This also includes two changes which impact perf:
- `ty::Projection` with inference vars shouldn't be treated as a rigid type, even if fully normalized
- `ty::Placeholder` only unifies with itself, so actually return `Some` for them
r? `@nikomatsakis`
Add a query for checking whether a function is an intrinsic.
work towards #93145
This will reduce churn when we add more ways to declare intrinsics
r? `@scottmcm`
Cleanup `DebuggerVisualizerFile` type and other minor cleanup of queries.
Merge the queries for debugger visualizers into a single query.
Revert move of `resolve_path` to `rustc_builtin_macros`. Update dependencies in Cargo.toml for `rustc_passes`.
Respond to PR comments. Load visualizer files into opaque bytes `Vec<u8>`. Debugger visualizers for dynamically linked crates should not be embedded in the current crate.
Update the unstable book with the new feature. Add the tracking issue for the debugger_visualizer feature.
Respond to PR comments and minor cleanups.
Since Cargo wants to do its own fatal error handling for unused
dependencies, add the option `--json unused-externs-silent` which
has the original behaviour of not indicating non-zero exit status for
`deny`/`forbid`-level unused dependencies.
Generate synthetic object file to ensure all exported and used symbols participate in the linking
Fix#50007 and #47384
This is the synthetic object file approach that I described in https://github.com/rust-lang/rust/pull/95363#issuecomment-1079932354, allowing all exported and used symbols to be linked while still allowing them to be GCed.
Related #93791, #95363
r? `@petrochenkov`
cc `@carbotaniuman`
This adds `nounused` to the set of extern flags:
`--extern nounused:core=/path/to/core/libcore.rlib`.
The effect of this flag is to suppress `unused-crate-dependencies`
warnings relating to the crate.
Stop using CRATE_DEF_INDEX outside of metadata encoding.
`CRATE_DEF_ID` and `CrateNum::as_def_id` are almost always what we want. We should not manipulate raw `DefIndex` outside of metadata encoding.
Remove `--extern-location` and all associated code
`--extern-location` was an experiment to investigate the best way to
generate useful diagnostics for unused dependency warnings by enabling a
build system to identify the corresponding build config.
While I did successfully use this, I've since been convinced the
alternative `--json unused-externs` mechanism is the way to go, and
there's no point in having two mechanisms with basically the same
functionality.
This effectively reverts https://github.com/rust-lang/rust/pull/72603
Improved diagnostic on failure to meet send bound on future in a foreign crate
Provide a better diagnostic on failure to meet send bound on futures in a foreign crate.
fixes#78543
Refactor HIR item-like traversal (part 1)
Issue #95004
- Create hir_crate_items query which traverses tcx.hir_crate(()).owners to return a hir::ModuleItems
- use tcx.hir_crate_items in tcx.hir().items() to return an iterator of hir::ItemId
- use tcx.hir_crate_items to introduce a tcx.hir().par_items(impl Fn(hir::ItemId)) to traverse all items in parallel;
Signed-off-by: Miguel Guarniz <mi9uel9@gmail.com>
cc `@cjgillot`
