Diagnostics: Be more careful when suggesting struct fields
Consolidate the various places which filter out struct fields that shouldn't be suggested into a single function.
Previously, each of those code paths had slightly different and incomplete metrics for no good reason. Now, there's only a single 'complete' metric (namely `is_field_suggestable`) which also filters out hygienic fields that come from different syntax contexts.
Fixes#116334.
More accurately point to where default return type should go
When getting the "default return type" span, instead of pointing to the low span of the next token, point to the high span of the previous token. This:
1. Makes forming return type suggestions more uniform, since we expect them all in the same place.
2. Arguably makes labels easier to understand, since we're pointing to where the implicit `-> ()` would've gone, rather than the starting brace or the semicolon.
r? ```@estebank```
rustdoc: fix & clean up handling of cross-crate higher-ranked parameters
Preparatory work for the refactoring planned in #113015 (for correctness & maintainability).
---
1. Render the higher-ranked parameters of cross-crate function pointer types **(*)**.
2. Replace occurrences of `collect_referenced_late_bound_regions()` (CRLBR) with `bound_vars()`.
The former is quite problematic and the use of the latter allows us to yank a lot of hacky code **(†)**
as you can tell from the diff! :)
3. Add support for cross-crate higher-ranked types (`#![feature(non_lifetime_binders)]`).
We were previously ICE'ing on them (see `inline_cross/non_lifetime_binders.rs`).
---
**(*)**: Extracted from test `inline_cross/fn-type.rs`:
```diff
- fn(_: &'z fn(_: &'b str), _: &'a ()) -> &'a ()
+ for<'z, 'a, '_unused> fn(_: &'z for<'b> fn(_: &'b str), _: &'a ()) -> &'a ()
```
**(†)**: It returns an `FxHashSet` which isn't *predictable* or *stable* wrt. source code (`.rmeta`) changes. To elaborate, the ordering of late-bound regions doesn't necessarily reflect the ordering found in the source code. It does seem to be stable across compilations but modifying the source code of the to-be-documented crates (like adding or renaming items) may result in a different order:
<details><summary>Example</summary>
Let's assume that we're documenting the cross-crate re-export of `produce` from the code below. On `master`, rustdoc would render the list of binders as `for<'x, 'y, 'z>`. However, once you add back the functions `a`–`l`, it would be rendered as `for<'z, 'y, 'x>` (reverse order)! Results may vary. `bound_vars()` fixes this as it returns them in source order.
```rs
// pub fn a() {}
// pub fn b() {}
// pub fn c() {}
// pub fn d() {}
// pub fn e() {}
// pub fn f() {}
// pub fn g() {}
// pub fn h() {}
// pub fn i() {}
// pub fn j() {}
// pub fn k() {}
// pub fn l() {}
pub fn produce() -> impl for<'x, 'y, 'z> Trait<'z, 'y, 'x> {}
pub trait Trait<'a, 'b, 'c> {}
impl Trait<'_, '_, '_> for () {}
```
</details>
Further, as the name suggests, CRLBR only collects *referenced* regions and thus we drop unused binders. `bound_vars()` contains unused binders on the other hand. Let's stay closer to the source where possible and keep unused binders.
Lastly, using `bound_vars()` allows us to get rid of
* the deduplication and alphabetical sorting hack in `simplify.rs`
* the weird field `bound_params` on `EqPredicate`
both of which were introduced by me in #102707 back when I didn't know better.
To illustrate, let's look at the cross-crate bound `T: for<'a, 'b> Trait<A<'a> = (), B<'b> = ()>`.
* With CRLBR + `EqPredicate.bound_params`, *before* bounds simplification we would have the bounds `T: Trait`, `for<'a> <T as Trait>::A<'a> == ()` and `for<'b> <T as Trait>::B<'b> == ()` which required us to merge `for<>`, `for<'a>` and `for<'b>` into `for<'a, 'b>` in a deterministic manner and without introducing duplicate binders.
* With `bound_vars()`, we now have the bounds `for<'a, b> T: Trait`, `<T as Trait>::A<'a> == ()` and `<T as Trait>::B<'b> == ()` before bound simplification similar to rustc itself. This obviously no longer requires any funny merging of `for<>`s. On top of that `for<'a, 'b>` is guaranteed to be in source order.
coverage: Allow each coverage statement to have multiple code regions
The original implementation of coverage instrumentation was built around the assumption that a coverage counter/expression would be associated with *up to one* code region. When it was discovered that *multiple* regions would sometimes need to share a counter, a workaround was found: for the remaining regions, the instrumentor would create a fresh expression that adds zero to the existing counter/expression.
That got the job done, but resulted in some awkward code, and produces unnecessarily complicated coverage maps in the final binary.
---
This PR removes that tension by changing `StatementKind::Coverage`'s code region field from `Option<CodeRegion>` to `Vec<CodeRegion>`.
The changes on the codegen side are fairly straightforward. As long as each `CoverageKind::Counter` only injects one `llvm.instrprof.increment`, the rest of coverage codegen is happy to handle multiple regions mapped to the same counter/expression, with only minor option-to-vec adjustments.
On the instrumentor/mir-transform side, we can get rid of the code that creates extra (x + 0) expressions. Instead we gather all of the code regions associated with a single BCB, and inject them all into one coverage statement.
---
There are several patches here but they can be divided in to three phases:
- Preparatory work
- Actually switching over to multiple regions per coverage statement
- Cleaning up
So viewing the patches individually may be easier.
non_lifetime_binders: fix ICE in lint opaque-hidden-inferred-bound
Opaque types like `impl for<T> Trait<T>` would previously lead to an ICE.
r? `@compiler-errors`
Suggest `pin!()` instead of `Pin::new()` when appropriate
When encountering a type that needs to be pinned but that is `!Unpin`, suggest using the `pin!()` macro.
Fix#57994.
Rollup of 5 pull requests
Successful merges:
- #115863 (Add check_unused_messages in tidy)
- #116210 (Ensure that `~const` trait bounds on associated functions are in const traits or impls)
- #116358 (Rename both of the `Match` relations)
- #116371 (Remove unused features from `rustc_llvm`.)
- #116374 (Print normalized ty)
r? `@ghost`
`@rustbot` modify labels: rollup
Don't suggest nonsense suggestions for unconstrained type vars in `note_source_of_type_mismatch_constraint`
The way we do type inference for suggestions in `note_source_of_type_mismatch_constraint` is a bit strange. We compute the "ideal" method signature, which takes the receiver that we *want* and uses it to compute the types of the arguments that would have given us that receiver via type inference, and use *that* to suggest how to change an argument to make sure our receiver type is inferred correctly.
The problem is that sometimes we have totally unconstrained arguments (well, they're constrained by things outside of the type checker per se, like associated types), and therefore type suggestions are happy to coerce anything to that unconstrained argument. This leads to bogus suggestions, like #116155. This is partly due to above, and partly due to the fact that `emit_type_mismatch_suggestions` doesn't double check that its suggestions are actually compatible with the program other than trying to satisfy the type mismatch.
This adds a hack to make sure that at least the types are fully constrained, but I guess I could also rip out this logic altogether. There would be some sad diagnostics regressions though, such as `tests/ui/type/type-check/point-at-inference-4.rs`.
Fixes#116155
For a single impl candidate, try to unify it with error trait ref
This allows us to point out an exact type mismatch when there's only one applicable impl.
cc `@asquared31415`
r? `@estebank`
If a BCB has more than one code region, those extra regions can now all be
stored in the same coverage statement, instead of being stored in additional
statements.
We're stabilizing `async fn` in trait (AFIT), but we have some
reservations about how people might use this in the definitions of
publicly-visible traits, so we're going to lint about that.
This is a bit of an odd lint for `rustc`. We normally don't lint just
to have people confirm that they understand how Rust works. But in
this one exceptional case, this seems like the right thing to do as
compared to the other plausible alternatives.
In this commit, we describe the nature of this odd lint.
